Lag compensation errors in active power filters based on DSP controllers

The growing problems of harmonic pollution on coal mine power lines caused by high-power DC drive systems has increased the use of active power filters. We analyzed compensation errors caused by the time lag in the detecting circuits of an active power filter based on DSP control. We derived a mathematical model for the compensation error starting from the error estimation when a single distortion frequency is present. This model was then extended to the case where multiple frequencies are present in the distortion. A formula for a general theory of compensation error with fixed load and fixed lag time is presented. The theoretical analysis and experimental results show that the delay time of an active power filter mainly arises from the sampling time. Lower sampling frequencies introduce larger compensation errors in the active power filter reference current.