Analysis of star and delta connected modular multilevel cascaded converter-based STATCOM for load unbalanced compensation

Abstract This paper compares the operating capabilities of STATCOMs based on Modular Multilevel Cascaded Converters (MMCC) using star and delta connections, with special attention to unbalanced load compensation. Zero sequence voltage for star connection, and zero sequence current for delta, need to be applied to overcome the phase cluster DC-voltage unbalance. Expressions are derived for both zero sequence elements as functions of the degree of load unbalance defined as the ratio of negative to positive sequence load current. They show that the zero sequence voltage in star connection reaches a very high level as the degree of load unbalance increases, making the MMCC DC-link voltage too high for correct functioning. However the delta connected MMCC can cope with the high level of load current unbalance. Experimental results are presented to validate this analysis.

[1]  Jinjun Liu,et al.  A Study on DC Voltage Control for Chopper-Cell-Based Modular Multilevel Converters in D-STATCOM Application , 2013, IEEE Transactions on Power Delivery.

[2]  Makoto Hagiwara,et al.  Application of a modular multilevel cascade converter (MMCC-SDBC) to a STATCOM. Control of active power and negative-sequence reactive power , 2013 .

[3]  C. J. Nwobu,et al.  Control of a Single-Star Flying Capacitor Converter Modular Multi-level Cascaded Converter (SSFCC-MMCC) STATCOM for Unbalanced Load Compensation , 2016 .

[4]  Qunjing Wang,et al.  Implementation of a cascade D-STATCOM under unbalanced conditions , 2014, 2014 International Power Electronics and Application Conference and Exposition.

[5]  Xiao-Ping Zhang,et al.  Flexible AC Transmission Systems: Modelling and Control , 2006 .

[6]  P. Rodriguez,et al.  Enhanced control strategy for MMC-based STATCOM for unbalanced load compensation , 2014, 2014 16th European Conference on Power Electronics and Applications.

[7]  R.E. Betz,et al.  Symmetry Compensation using a H-Bridge Multilevel STATCOM with Zero Sequence Injection , 2006, Conference Record of the 2006 IEEE Industry Applications Conference Forty-First IAS Annual Meeting.

[8]  Chi-Jui Wu,et al.  Reactive power compensation and load balancing for unbalanced three-phase four-wire system by a combined system of an SVC and a series active filter , 2000 .

[9]  E. S. Ali,et al.  Optimal location of STATCOM in multimachine power system for increasing loadability by Cuckoo Search algorithm , 2016 .

[10]  G. Mirzaeva,et al.  Phase leg voltage balancing of a cascaded H-Bridge converter based STATCOM using zero sequence injection , 2009, 2009 13th European Conference on Power Electronics and Applications.

[11]  B. Blazic,et al.  Improved D-StatCom control for operation with unbalanced currents and voltages , 2006, IEEE Transactions on Power Delivery.

[12]  V Govindaraj.,et al.  Modular multilevel cascade converter based statcom for reactive power compensation , 2013, 2013 International Conference on Circuits, Power and Computing Technologies (ICCPCT).

[13]  Bangyin Liu,et al.  Individual Phase Current Control Based on Optimal Zero-Sequence Current Separation for a Star-Connected Cascade STATCOM Under Unbalanced Conditions , 2016, IEEE Transactions on Power Electronics.

[14]  I. B. Efika,et al.  Reactive Power Compensation by Modular Multilevel Flying Capacitor Converter-Based STATCOM Using PS-PWM , 2014 .

[15]  Luo An,et al.  Derivation of zero-sequence circulating current and the compensation of delta-connected static var generators for unbalanced load , 2016 .

[16]  Georgios Konstantinou,et al.  On extending the energy balancing limit of multilevel cascaded H-bridge converters for large-scale photovoltaic farms , 2013, 2013 Australasian Universities Power Engineering Conference (AUPEC).

[17]  Georgios Konstantinou,et al.  Power Balance Optimization of Cascaded H-Bridge Multilevel Converters for Large-Scale Photovoltaic Integration , 2016, IEEE Transactions on Power Electronics.

[18]  Qiang Song,et al.  Control of a Cascade STATCOM With Star Configuration Under Unbalanced Conditions , 2009, IEEE Transactions on Power Electronics.

[19]  I. B. Efika,et al.  A modular multilevel flying capacitor converter-based STATCOM for reactive power control in distribution systems , 2015, 2015 17th European Conference on Power Electronics and Applications (EPE'15 ECCE-Europe).

[20]  Trillion Q. Zheng,et al.  Research on modular multilevel converter based STATCOM , 2011, 2011 6th IEEE Conference on Industrial Electronics and Applications.

[21]  Hirofumi Akagi,et al.  Theoretical Comparison in Energy-Balancing Capability Between Star- and Delta-Configured Modular Multilevel Cascade Inverters for Utility-Scale Photovoltaic Systems , 2016, IEEE Transactions on Power Electronics.

[22]  E. S. Ali,et al.  Imperialist competitive algorithm for optimal STATCOM design in a multimachine power system , 2016 .

[23]  Leon M. Tolbert,et al.  Modular Cascaded H-Bridge Multilevel PV Inverter With Distributed MPPT for Grid-Connected Applications , 2015, IEEE Transactions on Industry Applications.

[24]  Wenhua Liu,et al.  Control of a Cascade STATCOM With Star Configuration Under Unbalanced Conditions , 2009 .

[25]  S. O. A. Elazim,et al.  Optimal SSSC design for damping power systems oscillations via Gravitational Search Algorithm , 2016 .

[26]  V. K. Sood,et al.  HVDC and FACTS Controllers: Applications of Static Converters in Power Systems , 2004 .

[27]  Laszlo Gyugyi,et al.  Understanding FACTS: Concepts and Technology of Flexible AC Transmission Systems , 1999 .

[28]  Alex Q. Huang,et al.  Fault-Tolerant Design and Control Strategy for Cascaded H-Bridge Multilevel Converter-Based STATCOM , 2010, IEEE Transactions on Industrial Electronics.

[29]  Georgios Konstantinou,et al.  Power Balance of Cascaded H-Bridge Multilevel Converters for Large-Scale Photovoltaic Integration , 2016, IEEE Transactions on Power Electronics.