A Transformerless Medium-Voltage STATCOM Topology Based on Extended Modular Multilevel Converters

A new transformerless four-leg topology is suggested for shunt compensation, the modular multilevel converters (MMC) based on the half-bridge converters, to achieve higher performance as a STATCOM in a distorted and unbalanced medium-voltage large-current (MV-LC) system. Further, an extended MMC (EMMC) is proposed in order to manage more accurate compensation for high-power applications. Both proposals can be controlled for various purposes such as reactive power and unbalance compensation, voltage regulation, and harmonic cancellation. Moreover, related control strategies are also suggested for both the MMC and the EMMC to ensure that the source-end three-phase currents are sinusoidal and balanced. Also, the dc-link capacitors of the half-bridge converters are regulated. One interesting application for the EMMC-based STATCOM could be the improvement in power quality and performance of the electrified railway traction power supply system. Both the MMC- and the EMMC-based STATCOM along with their proposed control strategies were simulated; further, to verify the suggestions, these proposals were also implemented on a 30-kVA modular laboratory prototype. Experiments and simulations confirm the predefined objectives.

[1]  Donald Grahame Holmes,et al.  Voltage form factor control and reactive power compensation in a 25 kV electrified railway system using a shunt active filter based on voltage detection , 2001, 4th IEEE International Conference on Power Electronics and Drive Systems. IEEE PEDS 2001 - Indonesia. Proceedings (Cat. No.01TH8594).

[2]  A.K.S. Bhat,et al.  Averaging Technique for the Modeling of STATCOM and Active Filters , 2008, IEEE Transactions on Power Electronics.

[3]  H. Mohammadi Pirouz,et al.  New transformerless STATCOM topology for compensating unbalanced medium-voltage loads , 2009, 2009 13th European Conference on Power Electronics and Applications.

[4]  Hirofumi Akagi,et al.  Instantaneous power theory and applications to power conditioning , 2007 .

[5]  Bin Wu,et al.  Multilevel Voltage-Source-Converter Topologies for Industrial Medium-Voltage Drives , 2007, IEEE Transactions on Industrial Electronics.

[6]  H. Akagi,et al.  Control and Performance of a Transformerless Cascade PWM STATCOM With Star Configuration , 2007, IEEE Transactions on Industry Applications.

[7]  Fang Zheng Peng,et al.  Multilevel inverters: a survey of topologies, controls, and applications , 2002, IEEE Trans. Ind. Electron..

[8]  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.

[9]  Marc Hiller,et al.  Modulation, Losses, and Semiconductor Requirements of Modular Multilevel Converters , 2010, IEEE Transactions on Industrial Electronics.

[10]  Henry Shu-Hung Chung,et al.  Circuit-level comparison of STATCOM technologies , 2003, IEEE 34th Annual Conference on Power Electronics Specialist, 2003. PESC '03..

[11]  R.E. Betz,et al.  Using a cascaded H-bridge STATCOM for rebalancing unbalanced voltages , 2007, 2007 7th Internatonal Conference on Power Electronics.

[12]  H. Akagi,et al.  Control and Experiment of Pulsewidth-Modulated Modular Multilevel Converters , 2009, IEEE Transactions on Power Electronics.

[13]  R. Naderi,et al.  Phase-Shifted Carrier PWM Technique for General Cascaded Inverters , 2008, IEEE Transactions on Power Electronics.

[14]  Frede Blaabjerg,et al.  Shunt Active-Power-Filter Topology Based on Parallel Interleaved Inverters , 2008, IEEE Transactions on Industrial Electronics.

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

[16]  F.Z. Peng,et al.  A universal STATCOM with delta-connected cascade multilevel inverter , 2004, 2004 IEEE 35th Annual Power Electronics Specialists Conference (IEEE Cat. No.04CH37551).

[17]  M. Tavakoli Bina,et al.  Design and installation of a ±250 kVAr D-STATCOM for a distribution substation , 2005 .