Steinmetz theory applied to fundamental phase reference current calculation for a STATCOM with delta configuration

This paper proposes a fundamental phase reference current calculation method for a static synchronous compensator (STATCOM) with delta-connected cascade multilevel converter. This STATCOM is applied to compensate reactive current, unbalance current and harmonics in a three-phase three-wire system. In previous work, instantaneous power theory was used to calculate the phase reference current. Zero-sequence injection method was adopted to modify the reference current, so that active power was redistributed among delta-connected clusters for balancing dc voltages. Steinmetz theory is applied to calculate fundamental phase reference current in this paper. The obtained reference current has a 90 degree phase difference with the line voltage. There is no active power exchange between the inverter and grid even unbalance currents are compensated. As a result, the dc voltage of the cascade multilevel converter can be easily balanced. Simulation results are provided to show the effectiveness of the proposed method.