Modelling and advanced controls of variable speed hydro-electric plants

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Modelling and advanced controls of variable speed

hydro-electric plants

Baoling Guo

To cite this version:

Baoling Guo. Modelling and advanced controls of variable speed hydro-electric plants. Electric power. Université Grenoble Alpes, 2019. English. �tel-02296865�

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THÈSE

pour obtenir le grade de

DOCTEUR DE LA COMMUNATUÉ UNIVERSITÉ DE GRENOBLE ALPES

Spécialité : Génie Électricque Arrêté ministériel : 25 mai 2016 Présentée par

Baoling GUO

Thèse dirigée par M. Seddik BACHA et codirigée par M. Mazen ALAMIR

préparée au sein du Laboratoire de Génie Électricque (G2Elab) et du Grenoble Images Parole Signal Automatique (Gipsa-lab) dans Ecole Doctorale d'Electronique, Electrotechnique,

Automatique, Traitement du Signal (EEATS)

Modélisation et commandes avancées de systèmes

hydro-électriques à vitesse variable

Modelling and advanced controls of variable speed

hydro-electric plants

Thèse soutenue publiquement le 18 mars 2019, devant le jury composé de:

Mme. Xuefang LIN-SHI

Professeur, INSA de Lyon, Présidente

M. Mohamed El Hachemi BENBOUZID

Professeur, Université Bretagne Occidentale, Rapporteur M. Hubert RAZIK

Professeur, Université Claude Bernard Lyon 1, Rapporteur M. Vladimir KATIC

Professeur, Université de Novi Sad, Examinateur M. Lambert PIERRAT

Consultant scientique avec LJ-Consulting, Invité M. Seddik BACHA

Professeur, Université Grenoble Aples, Directeur de thèse M. Mazen ALAMIR

Directeur de Recherche CNRS, Université Grenoble Aples, Co-directeur de thèse

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THÈSE

pour obtenir le grade de

DOCTEUR DE LA COMMUNATUÉ UNIVERSITÉ DE GRENOBLE ALPES

Spécialité : Génie Électricque Arrêté ministériel : 25 mai 2016 Présentée par

Baoling GUO

Thèse dirigée par M. Seddik BACHA et codirigée par M. Mazen ALAMIR

préparée au sein du Laboratoire de Génie Électricque (G2Elab) et du Grenoble Images Parole Signal Automatique (Gipsa-lab) dans Ecole Doctorale d'Electronique, Electrotechnique,

Automatique, Traitement du Signal (EEATS)

Modélisation et commandes avancées de systèmes

hydro-électriques à vitesse variable

Modelling and advanced controls of variable speed

hydro-electric plants

Thèse soutenue publiquement le 18 mars 2019, devant le jury composé de:

Mme. Xuefang LIN-SHI

Professeur, INSA de Lyon, Présidente

M. Mohamed El Hachemi BENBOUZID

Professeur, Université Bretagne Occidentale, Rapporteur M. Hubert RAZIK

Professeur, Université Claude Bernard Lyon 1, Rapporteur M. Vladimir KATIC

Professeur, Université de Novi Sad, Examinateur M. Lambert PIERRAT

Consultant scientique avec LJ-Consulting, Invité M. Seddik BACHA

Professeur, Université Grenoble Aples, Directeur de thèse M. Mazen ALAMIR

Directeur de Recherche CNRS, Université Grenoble Aples, Co-directeur de thèse

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Acknowledgement

Firstly, I would like to express my sincere gratitude to all the people who make eorts to the work presented in this thesis.

I want to express my deep and sincere gratitude to my supervisor, M. Seddik BACHA, for his support to work at G2ELab and providing valuable guidance and encouragement through-out this research. He always proposes the constructive ideas and points through-out the correct direc-tion in my research. His global vision and extensive knowledge background express me deeply. Great thanks for his kindness and encouragement no matter in my study or my life. Further, I am very grateful to my co-supervisor M. Mazen ALAMIR. I learn a lot from him, particularly his meticulous attitude on research. Thank you for his guidance, detailed corrections, and instructions on my thesis.

I would like to thank M. Mohamed El Hachemi BENBOUZID and M. Hubert RAZIK for accepting to be reviewers of my thesis, as well as to be members of the committee. I also would like to thank M. Vladimir KATIC and Mme. Xuefang LIN-SHI for accepting to take part in the committee. I would like thank M. Lambert PIERRAT for participating in my defence. I would thank all members of the committee for the eorts devoted to reading and correcting my thesis.

I would like thank to my colleague Amgad MOHMED who works at GIPSA lab. We work in the same project PSPC Innov'Hydro and cooperate to achieve the variable speed reduced-scale hydraulic model. Many thanks also go to M. Cédric BOUDINE and M. Hossein IMAN-EINI, they provide valuable assistances and advices on experimental setup issues as well as for instructions on dSPACE, RT-LAB, and hardware congurations.

I will thank M. Raphael CAIRE, my responsible of master program Smart Grids and Buildings. Great thanks for all his help and instructions during my master. I am grateful that he recommends me to my supervisor for continuing my PhD thesis. I also give my great thanks to Mme. Catherine CHIROUZE. She helped me a lot when I just arrived in France.

I would also devote my thanks to the nance support from the project PSPC Innov'Hydro that makes my thesis work possible.

I am very grateful for time spent with my friends, my room mates, and my colleagues during the past years in France. I give my great thanks to Mme. Malika Bacha, it is a so great experience to know her in Grenoble, she is like my family and gives me a lot of happiness. I would like to thank sta at G2Elab for their encouraging supports and help as well.

Finally, I will give my thankfulness and greatness to all my families. Without their en-couragements and supports, I can not overcome all diculties through my thesis.

Baoling GUO Grenoble, France i

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List of Figures

1.1 Global share of renewable energy (%), Source: world bank [OSHP16] . . . 10

1.2 Global potential and installed capacity, Source: world bank [OSHP16] . . . 11

1.3 Developed SHEP potential in western Europe, Source: world bank [OSHP16] . 12 1.4 Hydropower percent in the electricity production in France, Source: 2017 An-nual Electricity Report by French transmission system operator (RTE) [Fre17] . 13 1.5 Map of small hydro-electric plants in France, Source: http://www.france-hydro-electricite.fr . . . 13

1.6 Diagram of a typical run-of-river hydro-electric plant [KKN12] . . . 17

1.7 Diagram of a hydro-electric plant with reservoir [KKN12] . . . 17

1.8 Diagram of a pumped-storage hydropower system [KKN12] . . . 18

1.9 Example of a `Hill Chart' diagram and the variable speed operation, N11 and Q11 represent unitary values of the turbine rotation speed and ow rates, η is the hydraulic eciency. . . 19

1.10 Pressure pulsation and vibration of hydraulic turbines [VN16] . . . 20

1.11 Representative power topologies for VS-HEPs . . . 21

1.12 Representative laboratory-used model in the work of [Bor13]; [Bor17]; [BW13] . 23 1.13 Experimental facility layout in Spanish Hydraulics Laboratory [PDFA08] . . . . 24

1.14 Architecture of the autonomous variable speed micro hydro-electric plant [AR06] 24 1.15 A variable speed micro-hydro plant topology and its control design in [Bel13] . 25 1.16 Implemented topology of VS-HEP and the control design . . . 26

2.1 Global architecture of a variable speed hydro-electric plant . . . 30

2.2 Clark transformation and its inverse transformation . . . 31

2.3 Park transformation and its inverse transformation . . . 32

2.4 PMSG diagram: (a) Schematic under a rotating frame, (b) Equivalent circuit . 34 2.5 Schematic of the machine-side converter in rectier mode . . . 37

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viii List of Figures

2.6 Schematic of the three-phase grid-side converter . . . 40

2.7 DC-link model . . . 42

2.8 Hydro-electric plant connecting with the power grid . . . 43

2.9 Hydro-electric plant connecting with isolated loads . . . 43

3.1 Simulations categorises for dierent purposes . . . 46

3.2 Classication of hydraulic turbines . . . 48

3.3 Hydraulic turbines selection chart (http://www.energie.ch/wasserturbinen) . . . 48

3.4 Linear torque model [AR06] . . . 50

3.5 2-D eciency model [MMP10] . . . 50

3.6 Measurements of look-up tables [PDFA08] . . . 52

3.7 Look-up table based modelling [Bor+08], D the diameter of the turbine . . . . 52

3.8 Water ow measurements in a pipe [Bor17] . . . 53

3.9 Dynamic modelling approach classication of hydro-electric plants [KSS07] . . . 54

3.10 Dynamic model of micro-hydraulic turbine [MK92] . . . 54

3.11 Turbine torque vs speed [Bor13] . . . 55

3.12 Turbine ow vs speed [Bor13] . . . 55

3.13 Procedure of a `Hill Charts' based modelling . . . 57

3.14 ˜Q11 vs N11 for dierent values of γ . . . 59

3.15 ˜T11 vs N11 for dierent values of γ . . . 59

3.16 Relative error of Q11 regression (%) . . . 59

3.17 Relative error of T11 regression (%) . . . 59

3.18 η(γ, ω, H, D) where negative values are set to zero . . . 60

3.19 Pm(γ, ω, H, D)where negative values are set to zero . . . 60

3.20 Actuator's schematic, Ts and Td represent time constants of the actuator, γc is the reference guide vane opening, and γ the value of the opening ratio . . . 61

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List of Figures ix 3.21 Global schematic for a PHIL-based VS-HEP real-time simulation system, γ the

guide opening ratio, ω the rotational speed, Thdy the emulated hydraulic torque, Km the torque coecient, iDCM the current of DCM, Real-Time Physical

Em-ulator (RTPE). . . 64

3.22 Structure of the RT-LAB-based real-time faulty grid simulator . . . 66

3.23 PHIL-based real-time laboratory experimental benchmark . . . 67

3.24 Static characteristics of the simulated hydraulic model . . . 68

3.25 Dynamic performance of the torque tracking control . . . 70

3.26 Hydraulic dynamics of o-line simulation results . . . 70

3.27 Hydraulic dynamics of real-time simulation, Phdythe hydraulic power (200w/div), Thdy the hydraulic torque (2N · m/div), Q the water ow rate (0.2m3/s/div) . 70 3.28 Classication of voltage dips: (a) Three-phase fault, (b) Single-phase-to-ground fault, (c) Phase-to-phase fault, (d) Two-phase-to-ground fault . . . 71

3.29 Simulated three-phase voltages in cases of dierent voltages dips . . . 71

3.30 Simulated three-phase voltages polluted by harmonics disturbances . . . 72

4.1 Ideal closed-loop control diagram . . . 74

4.2 General closed-loop control diagram . . . 74

4.3 Possible disturbances of variable speed hydro-electric plant . . . 75

4.4 Global control design of a direct drive PMSG-based VS-HEP . . . 76

4.5 PMSG vector current control . . . 80

4.6 Direct torque control of PMSG . . . 81

4.7 Design relation between machine current control and grid current control . . . . 83

4.8 Structural schematic of ADRC . . . 85

4.9 Canonical form formulation procedures of ADRC controller . . . 87

4.10 Tracking performances of TP and TD under dierent parameters r0 . . . 88

4.11 Diagram of nonlinear feedback control . . . 89

4.12 Second-order nonlinear ADRC diagram . . . 90

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x List of Figures

4.14 Frequency domain analysis of LESO . . . 93

4.15 Performance of nonlinear ESO of a second-order system . . . 96

4.16 Performance of linear ESO of a second-order system . . . 96

4.17 Control performance comparison of a second-order system . . . 97

4.18 Performance of nonlinear ESO of a rst-order system . . . 98

4.19 Performance of linear ESO of a rst-order system . . . 98

4.20 Control performance comparison of a rst-order system . . . 98

5.1 Global control design of VS-HEP implemented in this thesis . . . 102

5.2 Machine-side converter control diagram, PS: Phase Sensor . . . 103

5.3 Block diagram of PI current correctors for machine-side converter . . . 105

5.4 Block diagram of the machine-side converter for q-axis current control . . . 105

5.5 Currents closed-loop control diagram with forward feedback . . . 107

5.6 Adaptive P&O MPPT technique [Bel+13b] . . . 108

5.7 ADRC-based speed control design diagram . . . 108

5.8 Schematic of the hydraulic torque observer . . . 112

5.9 Current control response to a step reference variation, the current reference i∗ mq (5A/div), the current measurement imq (5A/div), the current error errimq = imq− i∗mq (5A/div) . . . 113

5.10 Current control performance of varying guide vane opening, the current refer-ence i∗ mq (5A/div), the current measurement imq (5A/div), the current error errimq = imq− i ∗ mq (5A/div) . . . 113

5.11 Torque observer performance of a step hydraulic torque . . . 114

5.12 Torque observer performance of an oscillating hydraulic torque . . . 115

5.13 Rotational speed control performance of step reference, ω∗_{the rotational speed} reference (20 rad/s/div), ω the rotational speed measurement (20 rad/s/div), errω = ω − ω∗ the rotational speed error (20 rad/s/div) . . . 115 5.14 Rotational speed control performance when the guide vane opening changes,

ω∗ the rotational speed reference (20 rad/s/div), ω the rotational speed mea-surement (20 rad/s/div), errω= ω − ω∗ the rotational speed error (20 rad/s/div)116

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List of Figures xi 5.15 ESO performance in the starting process , with ω the rotational speed (20rad/s/div),

z1 the estimation of rotational speed (20rad/s/div), z2 the estimation of total

disturbances (200/div) . . . 116

5.16 ESO performance in the MPPT process, with ω the rotational speed (20rad/s/div), z1 the estimation of rotational speed (20rad/s/div), z2 the estimation of total disturbances (200/div) . . . 117

5.17 Robustness of the speed control loop under torque disturbances: (a) Step-up torque disturbance, (b) Step-down torque disturbance, (c) Oscillating torque disturbance. . . 118

5.18 Performance comparisons under dierent inertia values . . . 118

5.19 Control diagram of the grid-side converter . . . 119

5.20 General current control loop . . . 120

5.21 Bode diagram of closed-loop PI controllers with dierent parameters, where ki= 1 is xed for the bode diagram left and kp = 1 is chosen for the gure right.120 5.22 Bode characteristics of PR controllers, where kir = 1 and ωc = 1 are xed for the bode diagram left and kir = 1and kp = 1 are chosen for the bode diagram right. . . 121

5.23 Bode diagram of the closed-loop PR controller . . . 122

5.24 Bode diagram of open-loop PR transfer function and simplied transfer function123 5.25 Proposed enhanced ADRC-based DC-link control diagram . . . 124

5.26 Grid current control, iga the injected current of phase A (2A/div), i∗ga the injected current reference (2A/div), erriga = iga− i ∗ ga (2A/div) . . . 126

5.27 Three-phase injected currents, iga (2A/div), igb (2A/div), igc (2A/div) . . . 126

5.28 Grid-injected current synchronization control, iga the grid current of phase A (2A/div), vga the grid voltage of phase A (50V/div) . . . 127

5.29 Active and reactive current control, , iga the grid current of phase A (5A/div), vga the grid voltage of phase A (100V/div), igq the injected reactive current (2A/div), igd the injected active current (2A/div) . . . 127

5.30 Performances of extended state observer . . . 127

5.31 Comparative experimental results of PI controller and ADRC-based DC-link control under starting process and guide vane adjustment . . . 128

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xii List of Figures 5.32 Comparative experimental results of PI and ADRC-based DC-link control when

the step torque disturbance happens . . . 128

5.33 Comparative experimental results of PI controller and ADRC-based DC-link control when the cycle torque uctuations happen . . . 129

5.34 Global losses distribution of the hydraulic generation unit . . . 130

5.35 Power comparative curves . . . 131

5.36 Eciency comparative curves . . . 131

6.1 PLL schematic . . . 134

6.2 Proposed ESO-based SRF-PLL design diagram . . . 137

6.3 ESO-based SRF-PLL diagram in the frequency domain . . . 137

6.4 Estimated phase and frequency with a phase jump +20◦_{, ∆θ = ˆθ − θ the} estimated phase error (5◦_{/div), f the estimated frequency (1Hz/div) . . . 139}

6.5 Estimated phase and frequency with a frequency step change +2Hz, ∆θ = ˆθ−θ the estimated phase error (1◦_{/div), f the estimated frequency (0.5Hz/div) . . . 140}

6.6 Performance of the ESO in respect to disturbance estimation . . . 140

6.7 Grid-connected control performance under various disturbances regimes, the grid injected current of phase a ia (2A/div), the grid voltage of phase a va (50V/div) . . . 141

6.8 ESO-based DPLL diagram, with Low Pass Filter (LPF), Tdq+ and T_dq− the positive/negative sequences transforming matrices, index +/− represent the positive/negative sequences components, the upper index `-' indicates variables after lters . . . 142

6.9 ESO-based MAF-PLL diagram, the upper index `-' indicates variables after lters142 6.10 Performances of ESO-based controller its applications into DPLL and MAF-PLL143 6.11 Performance of the conventional ESO-based PLL, dw(2ω) the second-order har-monics disturbances (31.4/div), z2 the total estimated disturbances by ESO (31.4/div), δ the estimated phase error (2◦_{/div) . . . 146}

6.12 Proposed GI-ESO design diagram . . . 148 6.13 Bode diagram of the modied transfer function regarding the input error feu(s) 149

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List of Figures xiii

6.15 GI-ESO-based SRF-PLL schematic . . . 151

6.16 Performance of a GI-ESO-based PLL, dw(2ω) the second-order harmonic dis-turbances (31.4/div), z2(2ω)the estimated second-order harmonic disturbances (31.4/div), z2(0)the estimated DC or low-frequency disturbances (31.4/div), δ the phase error (2◦_{/div) . . . 152}

6.17 Voltage components in the dq synchronous frame, ∆vqe(2ω) the second-order harmonics in q-axis voltage (5V /div), R Z2(2ω)dt the integration of z2(2ω) (5V /div), vde the d-axis voltage (20V /div) . . . 152

6.18 Robustness test of a GI-ESO-based PLL, dw(2ω) the second-order grid fre-quency sinusoidal disturbances (50/div), z2(2ω)the estimated second-order grid frequency sinusoidal disturbance (50/div), z2(0) the estimated low-frequency disturbance (50/div), δ the phase error (5◦_{/div) . . . 153}

6.19 Phase estimation errors in presence of grid frequency deviation, δ1the phase er-ror with xed frequency (0.02◦_{/div), δ} 1the phase error with adaptive frequency (0.02◦_{/div) . . . 154}

6.20 Performance of GI-ESO-based PLL in presence of harmonics disturbances, dw(6ω) the 6th-order harmonic disturbances (50/div), z2(6ω) the estimated 6th-order harmonic disturbances (50/div), z2(0)the estimated DC-type or low-frequency disturbances (50/div), δ the phase error (2◦_{/div) . . . 154}

6.21 Performance of GI-ESO-based PLL in presence of harmonics disturbances, dw(ω) the 1st-order harmonic disturbances (31.4/div), z2(ω) the estimated 1st-order harmonic disturbances (31.4/div), z2(0) the estimated DC-type or low-frequency disturbances (31.4/div), δ the phase error (2◦_{/div) . . . 155}

7.1 Pumped-storage hydro-electric system under study . . . 159

7.2 Daily electricity tari . . . 159

7.3 Water consumption and inow [VR08] . . . 160

7.4 Typical wind power curves in winter and in summer (Source: www.rte-france.com)160 7.5 Multi-stage optimal path problem: (a) Multi-stage problem, (b) Forward dy-namic programming approach [OHB15]. . . 163

7.6 Pumped-storage management adapting to forward dynamic programming . . . 163

7.7 Flowchart for forward dynamic programming . . . 165

7.8 Water level of upper reservoir, (DP: Dynamic Programming, FS: Fixed Speed, VS: Variable Speed) . . . 168

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xiv List of Figures 7.9 Water ow rate Qp(t) in penstock, (DP: Dynamic Programming, FS: Fixed

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List of Tables

1.1 Classication of hydro-electric plants based on the installed capacity . . . 15

3.1 Comparisons of dierent hydraulic models for PHIL implementations . . . 62

3.2 Key parameters regarding dynamics . . . 69

4.1 Control parameters of second-order system . . . 95

4.2 Control parameters of rst-order system . . . 97

5.1 Denitions of the hydraulic dynamic variables . . . 114

7.1 Overall prots of dierent operation regimes . . . 169

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Table of Acronyms

PSPC Structuring Project of the Competitive Clusters VS-HEP Variable-Speed Hydro-Electric Plant

RoR Run of River

MPPT Maximum Power Point Tracking

PMSG Permanent Magnet Synchronous Generator

PI/PID Proportional-Integral/Proportional-Integral-Derivative

PR Proportional-Resonant

GI Generalized-Integrator

ADRC Active Disturbance Rejection Control

ESO Extended State Observer

PWM Pulse-Width Modulation

AC Alternating Current

DC Direct Current

PLL Phase-Locked-Loop

HIL/PHIL Hardware-In-the-Loop/Power Hardware-In-the-Loop

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General introduction

This PhD thesis is in the frame of project PSPC Innov'hydro1_{. It is a multi-disciplinary project} involving ve joint Grenoble INP laboratories with the CNRS and Grenoble Alpes University (LEGI2_{, 3SR}3_{, Gipsa-lab}4_{, LCIS}5_{, and G2Elab}6_{) and aims to review the association} turbine-generator-grid [IN'14]. Within this frame, LEGI will be responsible for developing digital simulation models of turbulence, cavitation phenomena, and breakaway which occur in ows based on various parameters. These established models are then validated by experiments on General Electric (GE) hydro test platforms. Based on the digital simulation results, the researchers at 3SR will also develop experimental protocols to study the fatigue of materials in the laboratory. The mechanical stresses will be reproduced in the laboratory on test benches in order to test the material composing the turbines with the same mechanical stresses as in real conditions. At the same time, GIPSA-lab will focus on the mechanical control part. New constraints are considered in the current machine. Advanced control algorithms are proposed to calculate and obtain the minimum response time that can be guaranteed for these machines without damaging the equipment. The turbines and actuators are taken into account in the model. This involves nely modelling the system in order to get close to the unstable zones without crossing them. Besides, the LCIS in Valence that specialises develop passive and identiable wireless sensors that will be used in the future for monitoring works among other things. Finally, G2Elab will be responsible for eciently converting the mechanical energy toward the electric power grid.

The hydro-electric plants can be found in dierent operating congurations [Bel13]; [SCA14]; [And09]. Two modes are mostly commonly used: the rst one is the grid following mode, which is also called `P Q mode' (Active and Reactive power controlled); the second one is the grid forming mode, also named as `V F mode' (Voltage and Frequency controlled). When the hydro-electric plant is connected with the grid as a supplier, it either delivers the exact amount of active and reactive power according to the actual demand or allows to exploit the maximum power of the available primary resource [Bel13]. This thesis focuses on the grid-connected case: the machine-side converter conrms the optimal rotational speed to nd the maximum power point; the grid-side converter keeps the DC-link voltage constant, and ensure a good quality grid-injected current.

In this thesis, the work is dedicated to advanced control techniques for eciently converting the hydraulic energy into electric power. Thus, we focus more on the control performance than on nding new conversion structures. This naturally brings us to a conventional conversion

1_{Innov'hydro: the Structuring Project of the Competitive Clusters (PSPC)} 2_{LEGI: Laboratoire des Écoulements Géophysiques et Industriels}

3_{3SR: Sols, Solides, Structures - Risques}

4_{Gipsa-lab: Grenoble Images Parole Signal Automatique laboratoire} 5_{LCIS: Laboratoire de Conception et d'Intégration des Systèmes} 6_{G2Elab: Grenoble Génie Electrique laboratoire}

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2 General introduction structure: the direct drive Permanent Magnet Synchronous Generator (PMSG) with two back-to-back voltage inverters. It is composed of a hydraulic turbine, a PMSG, double back-back-to-back voltage source converters interacting with the three-phase grid. Some ancillary devices such as the voltage, current, and position sensors are also required.

Further, the control design largely depends on the plants' behaviour and properties. Un-der ideal assumptions, neither external disturbances nor measurement noises are taken into account in the control process. If a controller is well designed, the plant would be perfectly controlled [Tia07]. However, a Variable-Speed Hydro-Electric Plant (VS-HEP) is a classical nonlinear time-varying system disturbed by various internal dynamics and external uncertain-ties as follows:

External disturbances mainly involve the following aspects: Firstly, `Run-of-river' based VS-HEP is required to keep a constant water head [Bor17]. Therefore, the generated hydraulic power would often change when the hydraulic conditions vary. Besides, the fast opening of the turbine's guide vane causes pressure uctuations which makes water ow rates to change, resulting in torque uctuations [Mes+15]. Also, there are cases where the turbine operates at unstable regions [LLW09]; [Mes+15]. In addition, the disturbances from the grid side such as voltage dips, harmonics injected, and short circuits cannot be neglected [EO+06].

Several internal dynamics need to be considered: A PMSG is faced with various un-certainties such as parameters variations caused by the aging factor, the non-constant friction, and the nonlinear magnetic eld eect [LL09]. Additionally, Power Electronics (PE) itself is also a sensitive system with disturbances including non-constant parame-ters caused by the aging factor, nonlinear variations due to heat eects [Guo+17]. The nonlinear features and large unpredictable disturbances in VS-HEPs would negatively aect the overall control performance. Consequently, considering the specicities of a VS-HEP, this thesis would devote more eorts for improving the control robustness and disturbance rejection ability. The global control design is studied from two perspectives as follows:

Machine-side converter control: The main objective is to achieve the optimal e-ciency point by controlling the turbine shaft to run at the optimal rotational speed. The speed is determined by the dynamic function of input hydraulic driven torque and the electromagnet torque of PMSG, which are achieved by current components control. In this thesis, an adaptive Maximum Power Point Tracking (MPPT) technique proposed in the work of [Bel+13b] is employed. The generator is vector-controlled upon the PMSG Park model. Double Proportional-Integral (PI) controllers are applied in the current control loops [BBR11]; [Guo+18b]. Besides, a rst-order Active Disturbance Rejection Control (ADRC)-based speed control is proposed in the outer speed control loop, which enables VS-HEP to be robust under various hydraulic conditions and disturbed regimes. Grid-side converter control: The voltage control loop ensures the stability of DC bus voltage. The current control loop achieves high-quality grid-injected current of fewer har-monics, no distortion, and small frequency disturbances (sub-harhar-monics, low-frequency

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General introduction 3 harmonics), as well as a controlled reactive power injection [BBR11]; [Guo+17]. In this thesis, the ADRC-based controller is used to maintain constant DC bus voltage, result-ing in higher disturbance rejection ability; the grid-injected current is controlled through three Proportional Resonant (PR) controllers upon the abc three phase frame [BBR11]. PR controller is ecient for the grid current control because its frequency uses to be kept around the nominal grid frequency (50Hz or 60Hz). These PR controllers also can be well adapted for multi-frequency applications, which can guarantee zero steady-state error for the considered harmonics [EO+06]. Due to the variable speed operation, a PI controller upon the dq frame is more appropriate for the machine current control.

Outline of the thesis

The manuscript is organised in seven chapters as follows:

Chapter 1, which is a global introduction, provides an expanded but not exhaustive view of the possibilities of developing variable speed hydraulics, particularly small hydro-electric plants. The potential development at international level, European level, and national level are respectively presented. The variable speed technologies are presented as well. Emphasis has been placed on the various variable speed topologies that can be used and the benets such technique brings. The chosen topology in this thesis is presented at the end of this chapter.

In Chapter 2, the elements of the hydraulic generation system have been modelled one by one, including the PMSG, power electronics interfaces, the DC-link, and the three-phase grid or isolated loads. Further, both the averaged model and the switched model are presented for the machine-side and the grid-side converter.

In Chapter 3, based on the exible real-time Power Hardware-In-the-Loop (PHIL) bench-mark in G2Elab, a variable speed hydraulic test rig is built, being adapted to the proposed reduced-scale hydraulic model. An improved modelling approach applied to a class of hy-draulic turbines with `Hill Charts' eciency characteristics is presented. The dynamic model of guide vane actuator is introduced in order to take into account the eects of the induced dynamics on the whole electric performance. Moreover, reduced-scale models can be exibly established for various laboratory operation conditions by using the similarity laws. In addi-tion, dierent types of disturbed power grid are digitally simulated by RT lab in real-time, and then physically reproduced by using a power amplier.

In Chapter 4, a partial review of advanced control techniques applied to variable speed hydro-electric plants is addressed. Besides, a partial model-based method ADRC is fully pre-sented before starting the control design of the VS-HEP. Simulation results of both nonlinear and linear ADRC schemes are provided to compare their performances.

In Chapter 5, the control strategies proposed in this thesis are fully presented. Firstly, the control system of the machine-side converter is designed, which includes PI regulators for the machine current over dq frame, the ADRC-based speed control, and the adaptive MPPT.

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4 General introduction Then, the control design of grid-side converter is presented, which mainly involves three-phase PR controllers for grid-injected currents and a robust ADRC-based DC-link voltage controller. Further, o-line simulation results in Matlab/Simulink and experimental results under real-time PHIL laboratory benchmark are respectively provided.

In Chapter 6, the synchronization techniques of three-phase grid-connected control system are discussed. An ESO-based controller is employed into the Synchronous Reference Frame-Phase-Locked Loop (SRF-PLL) to enhance the control robustness and disturbance rejection. Further, a Generalized Integrator (GI)-ESO is proposed for its applications of grid-connected control systems in presence of Fast-Varying Sinusoidal Disturbances (FVSD). A GI is inserted into the disturbance estimation loop to deal with FVSD. A frequency-adaptive mechanism is introduced in order to mitigate the eects from frequency deviations. Finally, a GI-ESO-based SRF-PLL is proposed for its applications under disturbed conditions (unbalanced grid voltage, harmonics disturbance, and voltage oset).

In Chapter 7, a forward Dynamic Programming (DP) approach is implemented to manage the operation of a pumped-storage hydro-electric system with water consumption. The hourly optimal operations for pump mode and turbine mode are dened for a period of one day. This chapter details a forward DP algorithm and describes its adaptation to the optimization problem with the constraints of limiting water ow rate, water consumption, minimal and maximal water level, desired water level, time period, electricity tari, etc. Two cases are discussed: pumped-storage hydro-electric system and hybrid pumped-storage wind-hydro-electric system. The forward DP optimization approach can provide a sequence of decisions to maximize the overall prots each day, meanwhile, the system could ensure the water supply for the local residents.

In the last chapter, conclusions and perspectives are provided.

Contributions of the thesis

This thesis is dealing with optimizing the control of a VS-HEP. The control design is rst tested by dynamic o-line simulations and then experimentally veried with a real-time hybrid physical PHIL benchmark. The main contributions of this work are as follow:

A. 3-D hydraulic model and its PHIL implementation

A 3-D reduced-scale hydraulic model is exibly established for various laboratory oper-ation conditions by using the similarity law.

The dynamic model of guide vane actuator is introduced in order to take into account the eects of the induced dynamics on the whole electric performance.

Based on the exible real-time PHIL benchmark in G2Elab, a variable speed hydraulic test rig is built, that is adapted to the proposed reduced-scale model. The adapted

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General introduction 5 real-time experimental benchmark allows the study of the variable seed hydro-electric plant under dierent scenarios and connection congurations.

B. Advanced controls of high robustness and disturbance rejection ability The nonlinear features and large unpredictable disturbances in VS-HEPs can negatively aect the overall control performance. Thus, ADRC-based controllers are implemented into the controls of VS-HEP, which achieves high robustness and fast control dynamics.

An ADRC-based speed controller is proposed to improve the speed tracking performance, thus enabling ecient MPPT operation. To mitigate the negative eects caused by hy-draulic torque variations, a torque observer is incorporated into the speed-control loop. Dierent operation schemes are experimentally validated: compared with PI-controllers, the proposed ADRC-based speed controller achieves higher robustness and faster dynam-ics in the presence of various uncertainties; further, the disturbance rejection ability of speed control is improved by introducing the torque observer.

An ADRC-based controller is designed for the DC-link voltage control loop. Experimen-tal results prove that the ADRC-based control achieves higher robustness and improve control dynamics, either in the starting process, or when the guide vane adjusts, or when the torque uctuation happens. Because the ESO can estimate both internal and external disturbances in real time, which then can mitigate the negative eects caused by unpredictable hydraulic conditions.

C. ESO-based synchronization technique

An enhanced ESO-based controller is designed for the application in the SRF-PLL. The internal uncertainties (variations of the amplitude, nonlinear features, etc.) and external disturbances (phase jumps, frequency variations, etc.) are lumped together as the generalized disturbances, which are dened as an extended state variable. The disturbances are then estimated via ESO and actively compensated into closed-loop dynamics in real-time, which achieves a great robustness. To highlight, the ESO can be incorporated into SRF-PLLs equipped with various lters.

Further, a GI-ESO is proposed for its applications of grid-connected control systems in presence of the FVSD. A GI is inserted into the disturbance estimation loop to deal with FVSD. A frequency-adaptive mechanism is introduced in order to mitigate the eects from frequency deviations. The proposed GI-ESO enables FVSD to be observed with a relatively low bandwidth, which resolves the trade-o between the bandwidth and the noise ltering.

Finally, a GI-ESO-based SRF-PLL is proposed for its applications under disturbed con-ditions (unbalanced grid voltage, harmonics disturbance, and voltage oset). The sinu-soidal harmonics disturbances caused by grid disturbances can be eciently observed by

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6 General introduction introducing the proposed GI-ESO. Then, the sinusoidal components are removed from the estimated phase angle by correctly compensating the disturbances.

D. Optimal Management of Pumped-Storage Hydro-Electric Plant

A forward DP approach is used to optimally manage the pumping and generating oper-ation time in a period of one day. Two cases are studied: pumped-storage hydro-electric system and hybrid pumped-storage wind-hydro-electric system.

The daily overall prots by introducing the DP optimization increase compared with the normal operation mode, meanwhile, it can maintain the hydraulic restrictions and water consumptions to local residents. Besides, the prots of variable speed operation and xed speed have been compared.

Scientic publications

Journal papers:

B. Guo, S. Bacha, M. Alamir, M. Amgad, and C. Boudinet, LADRC applied to variable speed micro-hydropower plants: experimental validation, Control Engineering Practice, Volume 85, 2019, pp. 290-298.

B. Guo, S. Bacha, M. Alamir, A. Mohamed, Variable speed micro-hydro power genera-tion system: Review and Experimental results, EPE journal, (under review).

B. Guo, S. Bacha, and M. Alamir, Generalized Integrator-Extended State Observer with Applications to Grid-connected Converters in Presence of Disturbances, IEEE Transac-tions on Control Systems Technology, (under review).

B. Guo, A. Mohamed, S. Bacha, and M. Alamir, Modelling of a class of variable-speed micro-hydraulic turbines with `Hill Chart' eciency Characteristics: Power Hardware-In-the-Loop Implementation, Mathematics and Computers in Simulation, Elsevier, (un-der submission).

International conference papers:

B. Guo, S. Bacha, M. Alamir and H. Iman-Eini, A Robust LESO-based DC-Link Voltage Controller for Variable Speed Hydro-Electric Plants, 2019 IEEE International Confer-ence on Industrial Technology (ICIT), Melbourne, Australia, 2019, pp. 361-366.

B. Guo, S. Bacha, M. Alamir, A. Ovalle Villamil, Optimal Management of Variable Speed Pumped-Storage Hydro-Electric Plant: Cases Study, 2019 IEEE International Conference on Industrial Technology (ICIT), Melbourne, Australia, 2019, pp. 1119-1125.

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General introduction 7 B. Guo, A. Mohamed, S. Bacha and M. Alamir, Variable speed micro-hydro power plant: Modelling, losses analysis, and experiment validation, 2018 IEEE International Conference on Industrial Technology (ICIT 2018), Lyon, 2018, pp. 1079-1084.

B. Guo, S. Bacha, M. Alamir and H. Imanein, An anti-disturbance ADRC based MPPT for variable speed micro-hydropower plant, IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, Beijing, 2017, pp. 1783-1789.

B. Guo, S. Bacha and M. Alamir, A review on ADRC based PMSM control designs, IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, Bei-jing, 2017, pp. 1747-1753.

National conference papers:

B. Guo, S. Bacha, M. Alamir, A. Mohamed, Variable speed micro-hydro power genera-tion system: Review and Experimental results, l3ème Édigenera-tion du Symposium de Génie Electrique (SGE 2018), Jul 2018, Nancy, France.

B. Guo, S. Bacha, M. Alamir, ADRC based speed control applied to a micro-hydropower plant, 14ème Conférence des Jeunes Chercheurs en Génie Électrique (JCGE 2017), May 2017, Arras, France.

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Chapter 1

Introduction

Contents

1.1 Context of small hydro-electric plants . . . 9 1.1.1 International context . . . 11 1.1.2 Context in Europe . . . 11 1.1.3 Context in France . . . 12 1.2 Advantages as the renewable energy . . . 14 1.2.1 Sustainability of resources . . . 14 1.2.2 Respect for the environment . . . 14 1.2.3 Possibility of distributed production . . . 14 1.2.4 Reliability of energy generation . . . 15 1.3 Types of hydro-electric plants . . . 15 1.3.1 Classication based on installed capacity . . . 15 1.3.2 Classication based on water head . . . 16 1.3.3 Classication based on levels of water impoundments . . . 16 1.4 Variable speed hydro-electric plants . . . 18 1.4.1 Benets of variable speed operation . . . 18 1.4.2 Representative power topologies . . . 21 1.4.3 Research on variable speed hydro-electric plants . . . 22 1.5 Architecture implemented in the thesis . . . 26 1.6 Chapter conclusions . . . 27

1.1 Context of small hydro-electric plants

Due to climate change and environmental issues, the demand for clean and sustainable sources of energy has been increasing in recent years. As a mature and cost-competitive renewable energy source, hydropower always plays an important role in electricity mix, representing more than 16% of the total electricity generation worldwide and about 85% of global renew-able electricity [OSHP16]. Furthermore, hydropower has been used to stabilise uctuations between demand and supply for many years. The grid has to face to rapid uctuations due to the penetration of large-scale intermittent renewable energy such as wind power and solar

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10 Chapter 1. Introduction photovoltaic. Hydropower, especially the pump-storage systems, contribute more to balance the intermittent electricity resources [Jea15]. Besides, other benets are brought in the hy-dropower development, which are water supply, ood and drought control, and irrigation management. In addition, Micro- and pico-hydro stations are used to serve people who live in rural and remote regions. For instance, in Nepal, more than 2,500 micro-hydro-based mini-grid systems have been built, achieved about 25 MW of installed capacity in early 2016 [REN17]. Hydropower can be classied into small-scale and large-scale systems, which is based on the size of the installed electricity capacity. However, there is no globally universal denition of the term `Small Hydro-Electric Plant' (SHEP). In fact, the classication diers from countries [KKN12]. In China, 50MW is dened as the limits for SHEPs, while the installed capacity of more than 30MW will be considered as large-scale one in United States. Many countries, especially in Europe, a threshold of 10 MW is usually used to classify small- versus large-scale hydropower [KKN12]. This thesis is dedicated to the small hydro-electric plants (<10MW) or even smaller. As reported in [OSHP16], the globally installed capacity of SHEP (<10 MW) is approximated at 78 GW in 2016. SHEP has a share of approximately 1.9% of the total power capacity in the world and represents 7% of the total renewable energy capacity. The large hydro-power still has the largest share in the renewable energy market, and SHEP comes to the fourth just after the wind and solar power (Figure 1.1).

Bioenergy 5% Solar power_11% Wind power 22% Small hydropower 7% Large hydropower 54% Geothermal power 1%

Bioenergy Solar power Wind power

Small hydropower Large hydropower Geothermal power

Figure 1.1: Global share of renewable energy (%), Source: world bank [OSHP16] As one of the most widely utilized form of renewable energy, SHEP becomes a more and more signicant share in the global energy market. In Europe, hydropower has been fully developed in a long history and achieved mature techniques. Hydroelectricity accounts for more than 10% of the total installed capacity in France, a percentage that is second only to its dominant nuclear power [Jea15]. The development of SHEP will be presented in the perspective of international context, European context, and national context.

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1.1. Context of small hydro-electric plants 11 1.1.1 International context

The globally installed SHEP capacity is estimated at 78 GW in 2016, an increase of approxi-mately 4% compared to data in 2013 [OSHP16]. The global estimated SHEP potential has also increased to 217 GW, an increase of over 24% since 2013. The global potential and installed capacity of SHEPs are presented in Figure 1.2. Due to the dominance of China in SHEP, Asia has the highest share of installed SHEP capacity, arriving nearly 65% of the total share. Europe has the highest development rate of SHEP, with approximately 48% of the overall potential already developed. The Americas and Africa come to the third- and fourth-highest installed capacity and potential of all ve regions, respectively. In 2016, a developed SHEP rate of 18% is reached in Americas. Obviously, Africa has a huge potential to develop its SHEP, having a development rate of less than 5%. Oceania, due to its special geographical conditions, shares the lowest proportion (1 %) of the total global installed SHEP capacity.

0 50000 100000 150000 200000 Asia Americas Europe Africa Oceanica 50729 7863 18684 580 447 120614 44162 38943 12197 1206

SHEP<10MW

Installed Capacity (MW) Potential Capacity (MW)

Figure 1.2: Global potential and installed capacity, Source: world bank [OSHP16]

1.1.2 Context in Europe

The development of SHEPs has come to a mature level in Europe. The overall SHEP installed capacity in the region arrives 18,684 MW, while the estimated potential has a capacity of 38,943 MW [OSHP16]. The SHEP potentials in Europe dier hugely from subregions, due to their various climates and landscapes. In particular, Western Europe has installed 85% of its estimated potential, being the highest SHEP developed rate worldwide. Signicant shares are contributed by the top three countries: Austria, France, and Germany, as given in Figure 1.3. Further, France has the largest share in regards to both estimated potential and the installed capacity in western Europe.

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12 Chapter 1. Introduction 0 1000 2000 3000 4000 5000 France Germany Austria Switzerland Belgium Luxembourg Netherlands 2021 1826 1368 859 72 34 3 2615 1830 1780 859 103 44 12

SHEP<10MW

Installed Capacity (MW) Potential Capacity (MW)

Figure 1.3: Developed SHEP potential in western Europe, Source: world bank [OSHP16] 1.1.3 Context in France

France is the second largest European producer of hydroelectricity just behind Norway. Hy-dropower in France plays an essential role in balancing the nation's nuclear base generation. In fact, more than 50% of the current hydropower supply in France is exible and allows for adjustment of production to meet uctuating demands [COU16]. Hydropower accounts for more than 10% of installed capacity in France, second only to its nuclear capacity. It is the leading source of renewable electricity in France as shown in Figure 1.4. In 2017, the hydro-electric reaches 25,519 MW of installed capacity, and a production of 53.6 TWh in one year. Further, the micro-hydro power represents a 1.5% of the total electricity production [Fre17].

The distribution map of SHEPs in France is presented in Figure 1.5. The three largest hydroelectric regions are: the Auvergne-Rhône-Alpes region, the Occitanie region, and the Provence-Alpes Côte d'Azur region.

Some key numbers of SHEPs in France are summarized as follow [Fra17]: - About 2500 small power plants on 250,000 km of rivers;

- About 2000 MW of installed capacity, annual production of 7 TWh;

- About 15% of total hydraulic production in France, and about 1.5% of total national electrical energy production;

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1.1. Context of small hydro-electric plants 13 Fossil fuels (10.3%) Bioenergy (1.7%) Solar (1.7%) Wind (4.5%) Hydropower (10.1%) Micro-hydropower (1.5%) Nuclear (71.6%) In France in 2017 529.4 TWh Electricity production 53.6 TWh Hydro-electricity

Figure 1.4: Hydropower percent in the electricity production in France, Source: 2017 Annual Electricity Report by French transmission system operator (RTE) [Fre17]

Figure 1.5: Map of small hydro-electric plants in France, Source: http://www.france-hydro-electricite.fr

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14 Chapter 1. Introduction

1.2 Advantages as the renewable energy

SHEP is a form of energy production that meets all criteria of the generally accepted denition for renewable energies: sustainability of resources, environmental friendly, and possibility of distributed production [Bel13]. In addition, SHEP achieves a highly reliable performance in the control of the power generation.

1.2.1 Sustainability of resources

Renewable energies are based on the exploitation of natural energy ows: solar radiation, cycle of water, wind and carbon in the biosphere, heat ux of the earth, eect of lunar, and solar attraction on the oceans. They are therefore renewable energies unlike fossil and mineral energies (coal, oil, natural gas, and uranium). Renewable energy is a resource that regenerates faster than it is exploited. Hydroelectric power is a ow energy that almost exclusively uses the "terrestrial" part of the water cycle, that is, the ow of water between the onshore arrival of precipitation (rain and snow) and the return of water in general to the sea. Indeed, the water used is always fully restored. The potential energy of water is rstly transformed into the mechanical form. Then, the mechanical energy is easy to be transformed into the electrical one, which constitutes the most exible utilized energy form. In all potential electricity resources, hydropower is no doubt the most important renewable resources [OSHP16].

1.2.2 Respect for the environment

Hydropower does not use any combustion in its whole generation process, it therefore releases no gas and in particular no carbon dioxide. During its operation, it emits no gas that can contribute to the greenhouse eect. However, certain environmental problems are raised in the development of large-scale hydro-electric plants: uncertain eects on the local ecosystem, landscape impacts, water ow and quality, etc [Bel13]; [C. 04]. However, small Run-of-River (RoR) projects are free from many of the environmental problems because they usually use the natural ow of the river, and thus produce relatively little change in the natural stream channel. The dams built for water storage in ROR projects are very small and impounds little water. In fact, most RoR schemes do not require having a dam. Thus, negative eects such as increased temperature, decreased water ow, and uncertain eects on creatures in the river are alleviated for many small-scale hydro-electric projects.

1.2.3 Possibility of distributed production

Hydropower is extendedly distributed all over the world. This energy therefore contributes to the energy independence. It also represents the decentralized energy, as the hydraulic station are mainly located in mountainous areas as well as in rural areas. Micro- and pico-hydro stations can work as distributed electricity generation in rural and remote regions [REN17].

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1.3. Types of hydro-electric plants 15 The micro-hydropower systems can be installed for o-grid applications, including irrigation, pumping, and other forms of mechanical power as well as supplemental power sources for grid-connected users [REN17]. Such locally distributed generation integrated to power system has several merits from the view point of environmental restrictions and location limitations, as well as transient and voltage stability in the power system [REN17].

1.2.4 Reliability of energy generation

Hydraulic production varies according to seasonal cycles. However, unlike solar energy and wind energy, the hydraulic conditions are relatively stable in a short time. Further, the water ow into the powerhouse can be regulated for SHEPs with small storage mechanism. The short-term intermittentence is hence mitigated for hydraulic schemes, meanwhile, the reliability of energy generation is further improved. Moreover, the hydraulic equipment itself is robust, operates simply, and has a long-life cycle.

1.3 Types of hydro-electric plants

Hydro-electric plants generally dier from its capacity, water heads, installation sites, tech-nologies, storage, and specic applications.

1.3.1 Classication based on installed capacity

Hydro-electric plants can be classied according to their size (the installed electricity capacity) as given in Table 1.1, however, which actually dier from countries [KKN12]. Many countries, especially in Europe, a limit of 10 MW is usually dened to classify the small- versus large-scale HEP. Further, the small HEP can be categorized into Pico, Micro, and Mini scheme. This thesis is dedicated to the small hydropower (<10MW) or even smaller one.

Table 1.1: Classication of hydro-electric plants based on the installed capacity

Category Power Range

Pico HEP 0 kW 5 kW Micro HEP 5 kW 100 kW Mini HEP 100 kW 1 MW Small HEP 1 MW 10 MW Medium HEP 10 MW 100 MW Large HEP 100 MW+

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16 Chapter 1. Introduction 1.3.2 Classication based on water head

Another classication of hydro-electric plants is based on the water level dierence between the inlet and the outlet, that is, water head [KKN12], and the denition is also not identical. In practice, the water head is a signicant factor to select the appropriate hydraulic turbine. Depending on the height of the water heads, hydro-electric plants can be classied into three categories according to the European Small Hydropower Association [C. 04] as follow:

- High head: 100m and more - Medium head: 30m to 100m - Low head: 2m to 30m

1.3.3 Classication based on levels of water impoundments

HEPs are usually categorized regarding the levels of water impoundments. Three mostly common types of projects are: run-of-river, reservoir-based, and pumped storage.

a. Run-of-River

Run-of-River (RoR) hydro-electric plants generate electricity from the river ow without sig-nicant storage. RoR scheme is more suitable for a river that has small ow variations or a river that is regulated by a large natural reservoir. It consists of these main components as schematically shown in Figure 1.6 [KKN12]:

- Water headrace, forebay, and penstock that delivers the water;

- Hydraulic turbines that transform the kinetic energy of owing water into the rotational mechanical energy;

- Alternator or generator driven by the the rotational mechanical torque, and converting the mechanical energy into the electricity;

- Regulators for adjusting the generator, such as AC-DC-AC power electronics converters; - Wiring or cable that delivers the electricity to the power grid or isolated loads.

RoR projects do not require large construction activities, which bring signicant economic benets. RoR projects impose less environmental problems because they use the natural ow of the river, and a relatively little change happens in the stream channel and ow. Because of their economic and environmental advantages, RoR schemes are commonly used in small-scale hydropower systems. A class of small-hydraulic turbines such as Semi-Kaplan [Bel+13b], Kaplan [AR06], Bulb [Mes+11], or Propeller [MMP10] turbines become the most attractive prime movers because of their high eciency under such conditions.

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1.3. Types of hydro-electric plants 17

Figure 1.6: Diagram of a typical run-of-river

hydro-electric plant [KKN12] Figure 1.7: Diagram of a hydro-electric plantwith reservoir [KKN12] b. Storage Hydropower

A storage hydropower project is schematically illustrated in Figure 1.7. A reservoir is usually installed behind a dam to store water for later power generation and other purposes (such as irrigation and water supply). Storage hydropower schemes are typically used for river systems of highly uctuated ows [KKN12].

The water ow can be regulated by the reservoir, therefore, more energy benets can be achieved compared with RoR-based hydro-electric plants. Firstly, the energy is stored in a form of potential energy in water behind a dam. This potential energy can be used to supply both base loads and peaking loads. Besides, storage hydropower projects have the ability to regulate ow in the river downstream of the dam. Further, because the ow into the powerhouse can be regulated, the performance of power control and the overall energy conversion eciency are thus enhanced for a storage hydropower system. Some ow-sensitive turbines like Kaplan and Francis are able to be operated at best eciency point.

c. Pumped Storage

Pumped-Storage Plant (PSP) have been the most important large-form storage mechanism in the power system. The water is pumped from a lower reservoir into an upper reservoir during o-peak hours, the extra electricity is transformed in the form of potential energy in water of the upper reservoir (see Figure 1.8); In contrary, a large amount of electricity is demanded during the peak-loads times, the reversible pumped-turbines work at the generation mode. The water stored in the upper reservoir is hence released back to the lower reservoir.

PSP as an important energy storage technology achieves highly power-adjusting functions [RKV11]; [CL04]; [Ma+15]; [Ngo+09]. Originally, in a hydrothermal system, the pumped-storage units are used to co-ordinate with thermal units to maximize the overall prots [Gua+94]; [Gua+97]. The PSP works at the generating mode during the peak load and the pumping mode is enabled when the electricity tari is low [Gua+94]; [Gua+97]; [Cha+01]; [LCD04]. Nowadays, the intermittent renewable energy are increasingly integrated into the

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18 Chapter 1. Introduction

Figure 1.8: Diagram of a pumped-storage hydropower system [KKN12]

grids, more large-form energy storage capacities are required in order to provide the consis-tent power [CL04]; [Ma+15]; [Ngo+09]. Besides, a pumped-storage is often designed to supply water for the local residents, as well as to regularize the irrigation ows [VR08]; [RKV11].

1.4 Variable speed hydro-electric plants

Hydropower is increasingly used in the renewable energy context [OSHP16]. Conventional topologies of hydro-electric plants operate in a stand-alone operation mode in remote areas [NMB12]; [SCA14]; [And+09b]. Recently, many of hydro-electric plants are integrated to the distribution network via Power Electronics (PE) interfaces. Generally, the hydraulic ef-ciency is sensitive to water ow rate variations and rotational speed changes, the variable speed operation can help nd the best eciency point when the hydraulic conditions change [NMB12]; [Guo+18a]. Besides, variable speed techniques can improve the operation process by mitigating the cavitation eects, alleviating water hammer disturbances, and optimiz-ing transient processes [Bel+13b]. Thus, a Variable Speed Hydro-Electric Plant (VS-HEP) equipped with PE units gives rise to advantages in small hydro-electric applications [NMB12]; [SCA14]; [And+09b]; [AR06]; [MMP10]; [Mes+11]; [PDFA08]; [Bor+08]; [Bor17]; [Guo+18b]; [Guo+18a]; [Tes+11a]. Limited to the capacity of the PE, variable speed technique is mainly implemented into small-/micro- hydro-electric plants [NMB12]; [SCA14]; [And+09b].

1.4.1 Benets of variable speed operation

Variable-speed operation achieves advantages in regards to increasing the conversion eciency, optimizing the operation of hydraulic turbines, and improving the overall performance of hydro-electric plants.

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1.4. Variable speed hydro-electric plants 19 1.4.1.1 Benets for the global eciency

SHEP is usually based on `Run-of-River', which has a low head and high water ow rates [Bel+13b]. A class of Micro-Hydraulic Turbines (MHTs) such as Semi-Kaplan [Bel+13b], Ka-plan [AR06], Bulb [Mes+11], or Propeller [MMP10] turbines become the most attractive prime movers because of their high eciency under such conditions. However, the VS-HEP is not dedicated to the low head conditions, it is also considerable for a small-scale mountain-based dam scheme of low discharge and high head [IEAbr]. The hydraulic turbines are usually opti-mized at rated operating point by manufacturers, which concerns the water head, discharge, and rotational speed. However, these parameters may have substantial daily, monthly, or seasonal variations. The eciency of such hydraulic turbines is sensitive to water ow rate variations and rotation speed changes, which is generally represented by the `Hill Chart' ex-pressed in the rotation speed vs the water ow rate unitary values (see Figure 1.9). This gure indicates the eciency will decrease when the water ow rates change.

11

Q

11

N

1



2



3 max



1 2 3

 





11 '

Q

11 ''

Q

11 '

N

11 ''

N

'' ' 2 1

 





 



Figure 1.9: Example of a `Hill Chart' diagram and the variable speed operation, N11 and Q11 represent unitary values of the turbine rotation speed and ow rates, η is the hydraulic eciency.

At a xed-speed case, only limited variations of head and discharge are allowed. The hydraulic eciency could fall rather sharply when the hydraulic conditions vary. In variable speed hydraulic turbines equipped with power electronics units [NMB12], the allowable op-eration range of variations is enlarged. Thus, the rotational speed can be adjusted in the presence of water head and discharge variations. The higher eciency is hence achieved by adjusting the rotational speed when the discharge changes (see Figure 1.9). Therefore, vari-able speed operation is more considervari-able in cases that the hydro schemes often meet large head variations and partial load operations.

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20 Chapter 1. Introduction 1.4.1.2 Benets for the hydraulic machine

In addition, vibration and cavitation problems of hydraulic machine can be greatly reduced. In xed-speed schemes, partial load operation and specic gate openings (normally around 40-60%) could cause pressure pulsations and result in considerable vibrations [VN16]. This can be considerably reduced by adjusting the speed to avoid hazardous operating zones. A comparative example between vibration signals of a reversible Francis turbine with xed-speed and variable-xed-speed operation is respectively presented in Figure 1.10. The vibrations of variable-speed operation are much less than the xed-speed case. It is known that vibration and cavitation problems could potentially lead to a higher maintenance and decreased lifetime. Therefore, a variable speed operation helps reduce the cost of the maintenance and civil works [VN16]. Besides, variable speed techniques can alleviate the water hammer disturbances and optimize transient processes [Bel+13b]

(a) Fixed-speed operation (b) Variable-speed operation Figure 1.10: Pressure pulsation and vibration of hydraulic turbines [VN16]

1.4.1.3 Benets for the pumped-storage system

In addition to the higher eciency and less vibration and cavitation problems, particular ad-vantages of variable-speed technology are brought in pumped-storage plants as the followings: - Pumped-storage is an important energy storage technology with highly power-adjusting functions. The dynamics of power adjustment can be improved by incorporating power electronics. This makes it achieve a faster response to stabilize the intermittence of renewable energies [Bel+13a].

- There is no need to use additional equipment for the pumping start-up. In conventional plants, frequency converters are needed for the pumping start-up and synchronization [VN16].

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1.4. Variable speed hydro-electric plants 21 1.4.2 Representative power topologies

Various energy conversion topologies based on PE units are proposed in order to achieve variable speed operation, thus enabling the ecient electricity generation [NMB12]; [BBC10]; [Che+12]. A classication of representative power topologies for VS-HEPs is shown in Figure 1.11. The topologies dier from three aspects: generators used, mechanical coupling, and power electronics connection.

AC DC AC

Excitation Converter

(a) DFIG configuration

(b) PMSG configuration (c) EESG configuration DFIG PMSG EESG Gearbox Gearbox Gearbox Grid Load Grid Load Grid Load

Figure 1.11: Representative power topologies for VS-HEPs

A. The generation units can be equipped with either Doubly Fed Induction Generator (DFIG) [NMB12]; [BBC10] or Permanent Magnet Synchronous Generator (PMSG) [BBR11]; [MMP10]. PMSG can be replaced by Electrically Excitation Synchronous Generator (EESG) [NMB12]; [SCA14].

B. Regarding the mechanical connection, a gearbox is essentially needed for DFIG [BBC10]. Both the systems equipped with gearbox and direct drive system can work with the PMSG and the EESG [NMB12].

C. Also, the PE connection has great dierences for various topologies. DFIG has a direct connection between the stator and the grid, and a back-to-back Voltage Source Converter (VSC) is connected to the rotor and the stator [BBR11]. This inverter carries only a fraction of the full-scale power by sacricing the control ability. PMSG has PE units connected to the stator and the grid, the converter decouples the generator from the grid [BBR11]. An excitation converter is needed for EESG [NMB12].

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22 Chapter 1. Introduction A PMSG has excellent electric driven capabilities due to its high eciency and the high power density [GBA17]. Besides, the converter decouples the generator from the grid, re-sulting in less eects of grid disturbances [Guo+18b]; [Guo+17]. Moreover, PMSGs with full power converters have an extended speed regulation range, which is preferable for the hydro-electric plants, often working at between 30%-120% of nominal state. In terms of their maintenance, a direct-drive PMSG without gearbox requires less maintenance compared with a DFIG equipped with gearbox and slip rings [BBC10]; [Che+12]. As for the costs, the costs of induction generator are normally lower than PMSG, especially for a large capacity [SCA14]; [NMB12], even though the cost of a PMSG is deceasing in recent years [MH13].

1.4.3 Research on variable speed hydro-electric plants

The hydropower technology has been relatively mature, but there is still research to be done in this area. On the one side, large eorts have been devoted to improving the plant performance such as improving the global eciency and optimizing the hydraulic behaviour. On the other side, it is important to better integrate within its environment so as to reduce the negative environmental impacts. The diculty lies in fact in the inter-disciplinary involved in the development of equipment, civil works, and environmental issues [KKN12]; [FA+06b]. To reduce the cost of investment, major eorts to simplify and standardize equipment are under way. To eliminate the damage to the sh fauna passing through the machines, new constructive provisions are considered [Boy+18]. To maintain the water quality, innovative devices are implemented to exclude the use of pollutant uid such as oil in machine parts, being in direct contact with water. Such improvements can help optimize the water quality [Bob15]; [WCW19].

To highlight, the issue of better integration into environment will not be extended in this work. This thesis is dedicated to optimizing the performance of energy generation. Regarding hydraulic turbines, the variable speed technology has recently aroused particular interests be-cause such technology has become mature and achieved reasonable prices [NMB12]; [BLM12]. The variable speed operation gives the system a considerable margin of adaptability for vary-ing hydraulic conditions. Moreover, the quality of energy produced and the management of hybrid energy systems are part of the objectives. All of these naturally lead to the develop-ment of advanced conversion and control structures. Some previous representative works are rst reviewed in this subsection.

1.4.3.1 Representative previous research

A representative model of the variable speed hydraulic energy conversion system is developed in the work of [Bor13]; [Bor17]; [BW13]; [Bor18a], which is presented in Figure 1.12. A propeller turbine is coupled with the permanent magnet synchronous generator. The power electronics interface is consisting of an uncontrolled rectier, the DC/DC boost converter, and the DC/AC converter. Based on the established benchmark, the Maximum Ecient Point Tracking (MEPT) is presented in [Bor17], and a neural-network-based measurement strategy

Modelling and advanced controls of variable speed hydro-electric plants

HAL Id: tel-02296865

https://hal.archives-ouvertes.fr/tel-02296865

Modelling and advanced controls of variable speed

hydro-electric plants

Baoling Guo

To cite this version:

THÈSE

Baoling GUO

Modélisation et commandes avancées de systèmes

hydro-électriques à vitesse variable

Modelling and advanced controls of variable speed

hydro-electric plants

THÈSE

Baoling GUO

Modélisation et commandes avancées de systèmes

hydro-électriques à vitesse variable

Modelling and advanced controls of variable speed

hydro-electric plants

Acknowledgement

Contents

List of Figures

List of Tables

Table of Acronyms

General introduction

Outline of the thesis

Contributions of the thesis

Scientic publications

Chapter 1

Introduction

1.1 Context of small hydro-electric plants

SHEP<10MW

SHEP<10MW

1.2 Advantages as the renewable energy

1.3 Types of hydro-electric plants

1.4 Variable speed hydro-electric plants

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Scientic publications