Which is better at a high power reactive power compensation system, high PWM frequency or multiple connection?

In general, higher PWM frequency gives better performance at small or medium capacity inverters. This paper deals with the comparisons between two systems, SB and MB at a multi-10 MVA GTO power converter for reactive power compensation from the viewpoints of desired switching frequency and converter connections. SB is a single bridge system consisting of a three-phase bridge power converter unit and a transformer and its PWM frequency varies from 450 Hz to 1800 Hz. The line frequency is 50 Hz. 1 MB or 3 MB is a multiple bridge system consisting of plural single- or three-phase power converter units and transformers. Two kinds of systems using different transformer windings are considered. Type A uses conventional but complicated zigzag windings and type B simple star and delta windings. The switching frequencies are chosen the lowest, 50 Hz for 1 MB and 150 Hz for 3 MB. The evaluated items are harmonic distortion, power loss, GTO utilization factor and control response. A simulation study shows that MB is superior to SB in any case, even in the case of severe line faults where very quick response is requested. A new control strategy is adopted for obtaining quick response. Type B system has almost the same characteristics as type A system and can easily conquer the DC magnetization of the power converter transformers that may be encountered at a line voltage disturbance.>