Parallel converter scheme for high-power active power filters

A new topology for efficient utilisation of parallel converters as VAR compensators and active power filters (APF) for high power loads is proposed. Because of limited power handling capacity of individual devices, paralleling is the choice to increase rating of equipment, while keeping the THD of the current at the PCC within the agency specified standards. It has been reported in the literature that paralleling several converters, rather than switches, is more reliable in sharing of load. From this perspective, multilevel converters carry lot of weight, as their typical power circuit configuration limits the stress on individual devices to an appreciable extent. Also, they have the advantage of low switching frequency and full utilisation of switching devices, which is essential in high-power applications. These advantages have been utilised in parallel combination with a low-power high-frequency current-controlled APF, such that the higher order harmonics can be eliminated. A new parallel converter topology with a three-level neutral point clamped (NPC) converter and an auxiliary current-controlled VSI has been proposed and control techniques have been developed. Extensive simulation study have been carried out in a SABER simulator for linear and non-linear loads.