A dual-current-loop control method based on system current detection for LCL-filter-based Active Power Filters

A dual-current-loop control method to solve the stability problem of LCL-filter-based shunt Active Power Filters (APF) with no need of additional sensors or damping resistors is proposed here. This method is based on system current detection, rather than load current detection. Making use of the inherent stability characteristic of converter-side current feedback control, the proportional (P) control of converter-side current, as inner loop, is adopted to guarantee the stability, which will not be affected by system parameter variations. The outer loop control of system current adopts the proportional resonant (PR) controller to improve steady-state accuracy. Discrete-time model of the proposed method is derived and analyzed, taking sampling, computation, and PWM output delay into consideration. Compared with the conventional method based on load current detection, the proposed one has no damping loss, higher steady-state accuracy and a much larger phase margin required for a better transient response. All these are verified by simulation results.