Improved Parallel Operation for Multi-modular Shunt APF Using Dual Harmonic Compensation Loop

Multi-modular shunt APF has been proved as the most effective device to compensate distorted current from large-scale nonlinear loads in power system. In this paper, an improved parallel operation for multiple APF units using dual harmonic compensation loop is proposed based on comparative analysis and summary of the existing controlling methods and connection topologies. Considering the main factors of dynamic response, compensation precision, expansibility, automatic redundancy and capacity utilization, several improvement measures that aims at obtaining optimized filtering performance are provided. Furthermore, this paper describes two types of typical harmonic compensation loops in feedback and feedforward topology. The proposed parallel operation has the following characteristics: 1) single CT; 2) centralized control; 3) combination of power and frequency splitting control; 4) feedback loop for suppressing lower order harmonics with lower switching frequency, and feedforward loop for suppressing higher order harmonics with higher switching frequency; 5) double grid-connected points. Finally, the reasonability and effectiveness of the proposed strategy are proven by the simulated and experimental results.