High‐power active filter using <i>LC</i>‐tuned filter

AbstractUsually, to eliminate the harmonics of transmission lines, LC tuned filters are employed to bypass these harmonic components. However, the elimination ability is limited by its damping resistance. Therefore, active filters composed of high‐frequency PWM converters are desirable. In comparison with the LC tuned filters, the cost would be very high even in high‐power systems.In this paper, a low‐cost and high‐power active filters for a dc transmission system is proposed. It has active filter ability as well as low cost for high‐power uses. Its main circuit is composed of conventional LC filters in series with square‐wave voltage inverters. The voltage of the inverter is controlled to cancel the voltage drop of the internal resistance of the LC filter. Thus the Q‐factor of the filter can appear at infinity. Calculation of the harmonic and the control are done by DSP (TMS 32010). In the experimental system and simulations, two three‐phase tuned filters, 5th and 7th, are employed. Excellent results under 1 percent distortion voltage are obtained.