Control Strategy Of Cascaded STATCOM And The Design Of Power Cell

As one of the important reactive power compensators in Flexible AC Transmission Systems, STATCOM has gain world-wide application not only in the transmission system, but also in the chemical, coal and other industrial applications, for it can provide fast dynamic voltage support, maintain bus-voltage stability, provide reactive power, inhibition voltage fluctuation and flicker effectively, change unbalance of the system,and so on. Cascade structure is considered to be cost-effective topology of high pressure STATCOM .Therefore,it make great senses to develop the STATCOM device and make it more popular.This paper derived from the basic principle of STATCOM based on cascaded H-bridges, of which modulation strategies and control algorithm were mathematical analyzed and simulated. The unipolar dual-frequency carrier phase-shifted PWM with inverting modulation wave were choosen as the modulation strategy,which can double the equivalent switching frequency. When came to control algorithm,state feedback decoupled control algorithm ,which realizing the full decoupling of active and reactive power, were applied to AC side, while DC voltage balancing were layered controlled, in the upper it was fixed with a constant value, and in the lower it was controlled with active voltage vector superposition. Modulation strategy and control algorithm were simulated in Matlab environment, in order to verify the response speed, effect of reactive power compensation, the DC bus voltage balance.Secondly, accomplished the design of power cell in cascaded STATCOM. Combined with the specific functions of the hardware circuit, the circuit that can finish driving and protecting IGBT, three-phase input missing detection, and the multi-output switching power supply with high input-voltage were designed. Communication between PC and the drive circuit should be fast, achieve good electromagnetic isolation, therefore, optical fiber were choosen, and the relative software program were finished.At last, all the functions of the drive circuit are debugged in the hardware debugging environment. Applications environment were simulated to verify the correctness of the power cell design. Also a preliminary calculation of the main parameters are given, and the model parameters were selected.