A three order harmonic injection method to reduce current harmonics for high speed PM generator

Recently more attention has been paid to the distributed power systems due to their high flexibility and reliability. The high speed permanent magnet (PM) generator driven by micro-turbine has been widely investigated since it has small size, high efficiency and power density. The output high frequency AC power of the high speed PM generator needs to be converted into the AC power with constant frequency and voltage using AC/DC/AC converter. The normal AC/DC conversion through diode rectifier will generate harmonic currents in the generator winding which will cause additional losses and increase temperature rise of the generator. This paper utilizes a three-order harmonic injection passive method to eliminate the harmonic components in polyphase rectifying system. Three-order harmonic source can be obtained through the midpoint voltage of split capacitive in DC side and could inject into supply side input circuit. It is not necessary for an additional external harmonic source, thus could simplify the circuit structure, cost savings and improve the reliability of the circuit. The principle of three-order harmonic injection method and structure of circuit are analyzed in detail. The feasibility of control strategy and system topology is verified by the simulation results.