Minimizing neutral current of two parallel STATCOMs

This paper proposes control augmentations to allow two Static Synchronous Compensators (STATCOMs) devices to operate in parallel from a shared DC bus. Two parallel connected four-wire STATCOMs will be shown to be highly susceptible to an uncontrolled circulating current in the neutrals when operating with a three degree of freedom current control scheme. The circulating current can be calculated from the local inverter phase currents and neutral current. This paper shows the circulating component is readily suppressed by a neutral voltage offset that is determined by a proportional controller (P). The controller is validated by both simulation and experimental results.