Multilevel Optimal Modulation and Dynamic Control Strategies for STATCOMs Using Cascaded Multilevel Inverters

A multilevel optimal modulation strategy was developed for static synchronous compensators (STATCOMs) using cascaded multilevel inverters. In this strategy, besides the minimized harmonic distortion level, the inverter units' fundamental output voltages are also equalized. Therefore, all the inverter units in each phase leg can equally share the exchanged active and reactive power with the utility grid. This greatly helps the DC-link voltages balancing control. A special gating-pattern swapping scheme was developed to further maintain the DC capacitors' charge balance and equalize the current stress of the switching devices. The modulation strategy also includes a redundant operation scheme and a transformer DC magnetization prevention scheme. The performance of the proposed strategy was compared with the conventional fundamental frequency modulation strategy. To implement a fast and robust control of reactive power, a nonlinear feedback linearization controller with a direct voltage control capability was employed. The scheme of modulation index controlling and the operating modulation index range are presented. The effects of the system uncertainties on the closed loop dynamic performance are also discussed. A plusmn30 kVAr 21-level STATCOM prototype was developed. All the modulation and dynamic control strategies were verified using the experimental results from the scaled prototype.

[1]  Leon M. Tolbert,et al.  Charge balance control schemes for cascade multilevel converter in hybrid electric vehicles , 2002, IEEE Trans. Ind. Electron..

[2]  Abdelkrim Benchaib,et al.  Analysis of a robust DC-bus voltage control system for a VSC transmission scheme , 2001 .

[3]  T. Nakajima.  Operating experiences of STATCOMs and a three-terminal HVDC system using voltage sourced converters in Japan , 2002, IEEE/PES Transmission and Distribution Conference and Exhibition.

[4]  D. Soto,et al.  Nonlinear control strategies for cascaded multilevel STATCOMs , 2004, IEEE Transactions on Power Delivery.

[5]  Fang Zheng Peng,et al.  A multilevel voltage-source inverter with separate DC sources for static VAr generation , 1995, IAS '95. Conference Record of the 1995 IEEE Industry Applications Conference Thirtieth IAS Annual Meeting.

[7]  Fang Zheng Peng,et al.  Dynamic performance and control of a static VAr generator using cascade multilevel inverters , 1996, IAS '96. Conference Record of the 1996 IEEE Industry Applications Conference Thirty-First IAS Annual Meeting.

[8]  Seddik Bacha,et al.  Optimized linearization via feedback control law for a STATCOM , 1997, IAS '97. Conference Record of the 1997 IEEE Industry Applications Conference Thirty-Second IAS Annual Meeting.

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

[10]  M. B. Brennen,et al.  Vector analysis and control of advanced static VAr compensators , 1991 .

[11]  P. Pillay,et al.  Multilevel selective harmonic elimination PWM technique in series-connected voltage inverters , 1998, Conference Record of 1998 IEEE Industry Applications Conference. Thirty-Third IAS Annual Meeting (Cat. No.98CH36242).

[12]  Peter W. Lehn,et al.  Experimental evaluation of STATCOM closed loop dynamics , 1998 .

[13]  T. W. Cease,et al.  Operation of /spl plusmn/100 MVAr TVA STATCON , 1997 .

[14]  P.K. Steimer,et al.  IGCT-a new emerging technology for high power, low cost inverters , 1997, IAS '97. Conference Record of the 1997 IEEE Industry Applications Conference Thirty-Second IAS Annual Meeting.

[15]  M. L. Woodhouse,et al.  Type testing of the GTO valves for a novel STATCOM convertor , 2001 .

[16]  Kenichi Suzuki,et al.  A new control method preventing transformer DC magnetization for voltage source self-commutated converters , 1996 .

[17]  Fang Zheng Peng,et al.  Multilevel converters-a new breed of power converters , 1995, IAS '95. Conference Record of the 1995 IEEE Industry Applications Conference Thirtieth IAS Annual Meeting.

[18]  D. J. Hanson.  A transmission SVC for National Grid Company plc incorporating a ±75 MVAr STATCOM , 1998 .

[19]  A. Isidori.  Nonlinear Control Systems , 1985 .

[20]  Qiu Xiao-gang,et al.  BASIC CONTROL OF UNIFIED POWER FLOW CONTROLLER , 2003 .