Impact of control algorithm solutions on Modular Multilevel Converters electrical waveforms and losses

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To cite this version :

François GRUSON, Julian FREYTES, Shabab SAMIMI, Philippe DELARUE, Xavier GUILLAUD, Frédéric COLAS, Mohamed Moez BELHAOUANE - Impact of control algorithm solutions on Modular Multilevel Converters electrical waveforms and losses - In: EPE ECCE europe 2014, Suisse, 2015-09-07 - EPE ECCE europe 2015 - 2015

Any correspondence concerning this service should be sent to the repository Administrator : archiveouverte@ensam.eu

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• Context :

control of the stored energy of the MMC (Modular Multilevel Converter)

• Objectives :

Study the impact of two control variants (compensation of the average or the instantaneous AC grid power) :

differential and AC grid currents, capacitor voltages ripple, losses.

F. Gruson

1 , J. Freytes

2 , S. Samimi

2 , P. Delarue

3 , X. Guillaud

2 , F. Colas

1 , M.M. Belhaouane

2

1_{L2EP, Arts et Métiers ParisTech, 8Bd Louis XIV, 59046 Lille, France;}2L2EP, Ecole Centrale de Lille, 59650 Villeneuve d’Ascq, France ; 3_{L2EP, Université Lille 1, 59655 Villeneuve d’Ascq, France}

• The impact of two control variants (compensation of the average or the instantaneous AC grid power) : differential and AC grid currents, capacitor voltages ripple, losses.

Conclusion

Simulation Results

Impact of control algorithm solutions on Modular Multilevel

Converters electrical waveforms and losses

If capacitor voltage balancing is achieved:

Simplified model of MMC

ua m m_ub m_uc la m m_lb m_lc ga v gb v gc v ga

i

gb

i

gc

i

ua i i_ub i_uc lb i i_lb i_lc _ cua tot

v v_{cub tot}_{_} v_{cuc tot}_{_}

_ cla tot v v_{clb tot}_{_} v_{clc tot}_{_} dc

i

dc

v

C N C N C N C N C N C N mua v mla v mub v mlb v muc v mlc v

Current Control of the MMC Converter

Modeling of the MMC converter

_ _

;

ml i l i cl i tot mu i l i clui tot

cl i tot clui tot

l i l i u i u i v m v v m v dv dv C C m i m i N dt N dt          ; ; 2 2 2 mu i ml i ml i mu i ui li diff i diff i v i v v v v i i i   v   v   ( ) ( ) ( ) 2 2 2 gd

arm arm arm

vd gd gd gq di L R L v v L R i L i dt         ( ) ( ) ( ) 2 2 2 gq

arm arm arm

vq gq v q gd di L R L v v L R i L i dt          + - i_{diff i}_{_ref}

 

i diff C s       i pu C s s  gd ref i gq ref i   gq i gd i  

 

1 s P  s  _{ } R s P  ++ gi

v

  ' pu pu L  _ cui tot v _ cli tot v diff i i li m gi i / 2 dc v ' pu pu L    i pu C s     + + ui m



, ,



with i a b c



, ,



with i a b c

This converter has 11 independent state variables

Requires 11 control loops to achieve the global control Current control  5 control loops



Stored Energy Control  6 other control loops (3*sum+3*difference)

Stored Energy Control of the MMC Converter





_

(

)

.

, ,

(

)

_ˆ

ˆ

cl i cu i dc diff i DC AC i T cl i cu i v i diff i AC T

d W

W

V i

p

dt

with

i

a b c

d W

W

v i

dt

 



_



_















_











_











0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 2 4 6 8 10x 10 8 time (s) A c ti ve P ow e r (W ) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 2 4 6 8 10 12x 10 7 time (s) R é a c ti ve P ow e r (V A R ) Qmes Qref Pac Pdc Pref 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 6 6.5 7 x 105 Time (s) E qui va le nt C apa ci tor V ol ta ge s (V ) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -2000 0 2000 Time (s) A C G ri d C ur re nt s (A ) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -500 0 500 1000 Time (s) di ff er ent ia l C ur re nt s (A ) Δ = 104kV Δ = 100kV

At t=0.1s : a slope is done in the AC power references (Pac) equal to 0.8 GW and the reactive reference (Qac) to 100MVAR. Before 0.55s, the Stored Energy control compensate the average power (Pac/3)

After 0.55s, the Stored Energy control compensate the instantaneous one for each phase (p_aci).

L 50 mH C 10 mF R 50 mΩ N 400 L_arm 50 mH V_dc 640 kV R_arm 50 mΩ ω 314 rad.s-1 S_N 1100MVA _Vg _{192 kV} Tr__igdq 5ms Tr _{∑Vci_tot} 50ms Tr__idiffi 10ms Tr _{ΔVci_tot} 100ms Conduction losses:

Simulation Losses Comparison Results

Switching losses: Passive elements losses:

+

=

Total MMC losses: + +

 

vDC

C

s



dc

v

_p

_ACi diff i DC ref

i

_

 

vAC

C

s



dc

v

diff i AC ref

p

_ diff i AC ref

i

_ diff i DC ref

p

_ - + 2 _ cli tot

v

Filter - + 2 _ cui tot

v

Filter 2 _ _ref cli tot

v

2 _ _ref cui tot

v

+ + +

-+ + +

-

, ,



3

AC AC i

P

p



with

i



a b c

 introducing the AC fluctuating power term

-Reduce the ripples in the v_{c_tot} since p_AC= p_DC

The choice of introducing or not the fluctuating part of the AC power modifies the control  - different quantity of activated sub-modules

- current passes through a different number of IGBT and diodes.

it may have sense to use a control inducing a slightly larger current if this current passes through more diodes.

- IGBT conduction losses>diode conduction losses

the hypothesis of limiting the RMS current can be questionable.

521 A_RMS 581 A_RMS

• compensation of the average AC grid power:

• differential currents are constant

• V_{ci_tot}ripple are 4% higher

• compensation of the instantaneous AC grid power:

• differential currents have DC and AC components at 2ω • RMS differential currents is 11% higher

• Losses

Usual assumption is not every time validate

the MMC converter using considerable number of semiconductor; the losses are not only related to the RMS current value but also to the way of this current (diode or IGBT)  therefore to the control Usual assumption:

To Limit the losses, the I_diff-i value is limited by considering only the average power of the AC grid (P_ac) in the stored energy control (p_AC≠ p_DC)