Research on 35kV Cascaded Statcom and ITS application

A Cascaded transformerless Static Synchronous Compensator (STATCOM) of 35kV/8Mvar has been successfully developed and putted into application. The STATCOM is self-excited and in star configuration, each phase consists of twenty-one units, which employees 3.3kV IGBTs. With power supply by itself and the adjacent one, each unit can be bypassed and thus implement N-1 redundant running. By optimized Carrier Phase-Shift PWM method, the frequency of STATCOM can be dropped as low as 275Hz with the efficiency as high as 99%. Based on high speed distributed digital processors and instant current control method, the device has realized synthesized voltage and reactive power regulation and VQC/AVC coordination. The response time of STATCOM is below 10ms when voltage sag detected, thus strongly sustain the power system voltage. The experimental data and the field operation results both show that the performances of the developed transformerless 35kV/8Mvar STATCOM are satisfied, which provides a new solution for voltage and reactive power control for electric power substation.