Trapezoidal-wave power distribution system specialized for diode rectifier loads

This paper proposes a novel three-phase power distribution system specialized for diode rectifier loads with filter capacitors. The voltage waveforms of the system are trapezoidal, which are formed by synchronously superposing wave-shaping voltages onto sinusoidal voltages available from a utility power source. The system can naturally reduce harmonics of the line currents without electronically controlled switching devices because of a spontaneously widened conduction period of the currents. The reduction of the harmonic currents also contributes to improve total power factor at the load input terminals and efficiency of transmission lines. Since the diodes of the rectifiers successively commutate the trapezoidal voltages during periods of their flat parts, not only total harmonic distortion of the currents is improved, but also voltage ripples across the dc-buses of the rectifiers can effectively be reduced with less filter capacitors. In addition, the system offers an uninterruptible power supply function by immediately changing its outputs from the wave-shaping voltages to the trapezoidal voltages when interruption occurs in the power grid. In this paper, a prototype of the system is experimentally examined from various angles of operating characteristics and test results are presented to prove feasibility of the proposed strategy.