Variable parameter pulse width modulation-based current tracking technology applied to four-switch three-phase shunt active power filter

A novel configuration is proposed with a y/y step-up transformer adding to AC side of the four-switch three-phase (FSTP) active power filter (APF), so as to improve the utilisation of DC voltage and further widen the voltage range of FSTP APF. To ameliorate the current tracking performance of the FSTP inverter, a variable parameter pulse width modulation (VPPWM) approach is presented. In the proposed VPPWM method, the triangular wave is not fixed but derived by integration of reference current error signals. A pulse width coefficient T is also adopted in VPPWM together with the parameter k, so as to make the APF current tracking width adjustable and the resultant over-high switch frequency issue is effectively compromised. The principle and implementation of the VPPWM approach are elucidated in detail, and the validity is demonstrated by simulation studies. The simulation results are compared with that of the proportional-integral control triangular wave comparison approach and the current hysteresis tracking approach, which indicates that the VPPWM methodology shows superior performance in response speed and accuracy to the other ones.