Control of voltage source converters with an unbalanced supply system

Voltage source converters (VSCs) are becoming more common in electric power system transmission and distribution systems, due to their good controllability, useful electrical characteristics, and falling cost. They are often connected to a slightly unbalanced AC network, which results in harmonics being generated and propagated through the network. This paper presents a linearised frequency coupling matrix (FCM) approach to the analysis of harmonic generation under unbalanced AC conditions, and uses it to determine the best control response under these conditions. Both PWM and six pulse converters are analysed and compared.