Development of active filter with series resonant circuit

An active AC harmonic filter, composed of high-frequency inverters and a series-resonant LC circuit turned to the fundamental frequency, is proposed to solve harmonic distortion problems on distribution systems at lower cost and with higher efficiency. The design includes a voltage-source inverter for further decrease of the loss, a static-induction thyristor for instantaneous current response, control logic that takes into account the coupling circuit characteristics, and high-speed harmonic voltage detection to suppress overloading of the customer's LC filter. Operational experience with a prototype filter on a 6.6 kV system is presented, verifying reduction of the operating and improvement of the transient response. In particular, there is a sharp reduction of inverter rating and operating loss about one-third to one-fourth, compared to results for an active filter without a coupling circuit.<>