MARS is an integrated concept PV and ESS to ac grid and HVdc links. This system is modular and can autonomously reconfigure. It can provide inertial and primary frequency response support and reject disturbances. Also incorporates an energy balancing control to manage the PV, ESS, and HVdc system

1. RENEWABLE INTEGRATION IN HYBRID AC/DC
SYSTEMS USING A MULTIPORT AUTONOMOUS
RECONFIGURABLE SOLAR POWER PLANT(MARS)
ASWATHY S ANAND
05 PSC
GOVERNMENT ENGINEERING COLLEGE BARTON HILL
TRIVANDRUM
February 16, 2021
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 1 / 26

2. Overview
1 Introduction
2 MARS System
3 PV Submodule
4 ESS Submodule
5 Control of MARS
6 Simulation Results
7 MARS Performance
8 MARS Performance
9 Conclusion
10 Reference
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 2 / 26

3. Abbreviations
MARS - Multi Port Autonomous Re-configurable Solar Power Plant
AC - Alternating Current
DC - Direct Current
PV - Photo Voltaic
ESS - Energy Storage System
HVdc - High Voltage Direct Current
SM - Sub Module
VSG - Virtual Synchronous Generator
DAB - Dual Active Bridge
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 3 / 26

4. Introduction
Introduction
As penetration of solar PV increases, inertia is reduced and increased
primary frequency response requirements
Grid forming inverters connecting PV to grid and ESS play an
important role
Due to this grid capability to recover from frequency or voltage
disturbances are reduced
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 4 / 26

5. MARS System
MARS System
MARS is an integrated concept PV and ESS to ac grid and HVdc links
This system is modular and can autonomously reconfigure
It can provide inertial and primary frequency response support and
reject disturbances
Also incorporates an energy balancing control to manage the PV,
ESS, and HVdc system
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 5 / 26

6. MARS System
MARS System
Figure 1: MARS Circuit Architecture
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 6 / 26

7. MARS System
MARS System
The circuit of MARS consists of 3 phase-legs connecting to HVdc and
transmission ac grids
The SMs in each arm can be of three types:
1 PV-SM that connects to string PV panels
2 ESS-SM that connects to energy storage
3 Normal SM
The SMs in each arm are divided into Nnorm normal SMs, Npv
PV-SMs, and Ness number of ESS-SMs
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 7 / 26

8. MARS System
PV Submodule
Figure 2: Grid interface PV connected Modular Multilevel Converter
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 8 / 26

9. PV Submodule
PV Submodule
The two possible structures for the converter are:
1 direct passive interface
2 indirect active interface
The isolated boost converetr is based on a standard DAB
PV input capacitor vcpv,y,l,j is given by
Cpv
dvcpv,y,l,j
dt
= ipv,y,l,j − iLpv,y,l,j (1)
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 9 / 26

10. ESS Submodule
ESS Submodule
The ESS system is integrated into the SM using a bidirectional dc-dc
converter
Figure 3: Structure of a sub-module with integrated ESS
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 10 / 26

11. ESS Submodule
ESS Submodule
Uxyz - Average terminal module voltage
ixy - Phase arm current
PCxyz - Average instantaneous module capacitor power
axyz - Duty cycle
The amount of birectional energy flow shall be emulated by adjusting
the battery current
The battery current iBatxyz is regulated by controller of dc - dc
converter
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 11 / 26

12. Control of MARS
Control of MARS
Figure 4: Control System of MARS
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 12 / 26

13. Control of MARS
Control of MARS
L1 controller provides voltage and frequency support and maintains
power dispatch
Also controls dc link voltages, ac/dc currents, and provides energy
balancing
It is based on virtual synchronous generator (VSG)
The L-1 controller sends the modulation indices of each arm,
reference PV power, and reference ESS power to the L-2 controller
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 13 / 26

14. Control of MARS
Control of MARS
Figure 5: L-1 Control of MARS
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 14 / 26

15. Control of MARS
Control of MARS
Receives power dispatch commands from the system operator that
include Pac,ref , Pdc,ref and Qac,ref
The voltage and frequency support in L-1 controller is based on
virtual synchronous generator
L-1 controller also determines the reference power commands of PV
and ESS in MARS (Ppv,ref and Pess,ref )
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 15 / 26

16. Control of MARS
Control of MARS
(a) L-3 PV Control (b) L-3 ESS Control
The L-3 controller is present only in PV and ESS SMs.
In PV SMs, the L-3 controller identifies maximum power that can be
generated by PV, and controls voltage and current based on reference
from L-2
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 16 / 26

17. Control of MARS
Virtual Synchronous Generator
The L-1 controller uses a VSG-based control method to determine the
active and reactive power
The ac-side voltages of MARS are processed by a phase-lock loop to
determine the peak value and frequency of the voltages
Figure 7: VSG Control in MARS
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 17 / 26

18. Control of MARS
Energy Balancing Control
Figure 8: Energy Balancing Control in MARS
The main challenge of MARS is balancing voltage in different SM
The harmonic circulating current reference is
icirc,1,q =
2vpk
3
(Pda,ref + Pdb,ref + Pdc,ref ) (2)
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 18 / 26

19. Control of MARS
Energy Balancing Control
icirc,1,d = −
2Vpk
3
(Qd,ref ) (3)
Balancing of voltage is important to avoid instability from low voltage
or over voltage
Vcap
P
,j,p - Upper arm summation of SM Capacitor voltages
Vcao
P
,j,n - Lower arm summation of SM Capacitor voltages
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 19 / 26

20. Simulation Results
Simulation Results
A case study of MARS connecting PV and ESS to HVdc and
transmission ac system at Pittsburg Substation
(a) Voltage during line-to-line fault
(b) Frequency during generator
loss event
Figure 9: Comparison of developed grid model with reference grid model
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 20 / 26

21. MARS Performance
MARS Performance
(a) Arm Current (b) SM Capacitor Voltage
(c) PV and ESS Inductor current
Figure 10: Steady state and step change case study of MARS at Pittsburg
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 21 / 26

22. MARS Performance
MARS Performance
(a) SM Capacitor voltages (b) SM Inductor current
(c) Power exchanged in ac side by
MARS
Figure 11: Transmission line fault case study of MARS at Pittsburg
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 22 / 26

23. MARS Performance
MARS Performance
(a) SM Capacitor voltages (b) SM Inductor current
(c) Power exchanged in ac side by
MARS
(d) Frequency with and without
support from MARS
Figure 12: Generator loss case study of MARS at Pittsburg
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 23 / 26

24. Conclusion
Conclusion
An integrated system of PV, ESS, and HVdc system connecting to
transmission ac system is proposed
The circuit topology and control system of MARS are presented and
analyzed
Performance of MARS is studied under different operating conditions.
Stable operation of MARS is observed under different steady-state
and dynamic operating conditions.
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 24 / 26

25. Reference
Reference
T. Soong and P. W. Lehn, “Internal Power Flow of a Modular
Multilevel Converter With Distributed Energy Resources,” IEEE Trans.
Emerg. Sel. Topics Power Electron., vol. 2, no. 4, pp. 1127–1138, Dec
2014.
M. Schroeder and J. Jaeger, “Advanced Energy Flow Control Concept
of an MMC for Unrestricted Operation as a Multiport Device,” IEEE
Trans. Power Electron., vol. 34, no. 11, pp. 11 496–11 512, Nov 2019
F. Briz, M. Lpez, A. Zapico, A. Rodrguez, and D. Daz-Reigosa,
“Operation and control of MMCs using cells with power transfer
capability,” in IEEE Applied Power Electronics Conference and
Exposition (APEC), March 2015, pp. 980–987
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 25 / 26

26. Reference
ASWATHY S ANAND 05 PSC (GEC-BH) SEMINAR February 16, 2021 26 / 26