Experimental verification of dominant harmonic active filter (DHAF) for high power applications

A synchronous reference frame (SRF) based controller for a dominant harmonic active filter (DHAF) system has been proposed previously by the authors (1996, 1998). The SRF controller is designed to achieve harmonic isolation at the dominant harmonic frequencies (such as the 5/sup th/ or the 7/sup th/) between supply and load. Such design allows implementation of the DHAF system by square-wave inverters switching at the 5/sup th/ and 7/sup th/ harmonic frequencies. Compared to the conventional active filter systems which require high switching frequency PWM inverters for implementation, the square-wave inverter based DHAF system is more viable and cost-effective for high power nonlinear load (10 MW and above) or cluster of nonlinear loads to meet the IEEE 519 harmonic standard. In this paper, a new feedforward command of the SRF controller is proposed to provide better dynamic performance. If the resonance of source impedance and passive filter bank occurs near the dominant 5/sup th/ or 7/sup th/ harmonic frequency, the amplification effect at the harmonic frequencies will cause severe distortion in the supply current. The improved feedforward command of the SRF controller is able to suppress the resonance and meet the requirement of IEEE 519 harmonic standard. Experimental results are also presented in this paper to validate the effectiveness of the SRF controller and the square-wave inverter based DHAF system.