A static synchronous compensator using series-connected hybrid multiinverters

This paper gives an analysis and design of a static synchronous compensator (STATCOM) using a hybrid multi-inverter system. The hybrid system consists of two GTO inverters and a single IGBT inverter connected in series by three transformers. The hybrid configuration STATCOM has the potential that the harmonic components of the output voltages/currents would be less than conventional configuration STATCOM, and the total switching losses would be smaller than PWM STATCOM. However, the hybrid STATCOM has a problem that it tends to operate in an overmodulation range if a considerable change in reactive currents occurs. To solve the problem this paper proposes a variable DC voltage control strategy, where the DC voltage is adaptively adjusted in accordance with the amount of required reactive current. The proposed STATCOM can operate in a power factor correction mode or a point of common coupling (PCC) voltage stabilization mode. The validity of the proposed STATCOM and the control strategy were verified by experimental results.