A Novel Control of Self-Commutated Converters for Large Power Applications

Abstract

Self-commutated converters are intensively studied to realize high performance power equipment for electric power systems. The converters have attractive features such as independent control of active and reactive power and reliable operations in power line faults. The switching losses of the converters with gate turn-off thyristors are, however, rather larger than those of conventional line commutated converters. To reduce the losses, a conventional PWM scheme such as subharmonic modulation requires low switching frequencies and causes inferior control performance especially in power line faults.
This paper proposes a novel PWM method for series connected multiple self-commutated converters. The method employs the space vector representation of the multiple converters and the switching actions are determined through comparing the vectors with voltage command vectors. The scheme realizes a low switching number in steady state as well as fast response to ensure reliable operations even in the power line faults. The validity of the control is examined by a computer simulation and experiments with a static var compensator.