Research on parallel operation of active power filters applied to high-voltage high-power system

Due to the limitation of voltage level and current capability of power devices, it is very difficult to handle nonlinear loads for the traditional active power filter (APF) in high-voltage high- power grid. In this paper, an active power filter is presented, which is composed of APF modules with a multi-level NPC inverter. This module is very suitable for high voltage system. Moreover, this module has the capacity limitation function of compensating load harmonics, when the demand current exceeds the limit current of the module. The proposed APF fully compensates load harmonics by connecting some modules in parallel such that the PWM converter of each module needs not to handle high power. It operates independently and has expansion flexibility. In addition to describe the theoretic bases of the proposed APF, this paper also researches the close loop control algorithm of the APF. Theory analysis and simulation results illustrate that the performance of the proposed APF is suitable for harmonic loads with high voltage and large capacity.