High-frequency AC Pulse Density Modulation Theory And Its Application In Electric Vehicle

High-frequency link power converters are receiving increasing attention. When the input frequency of AC-AC converter is quite high, such as 20KHz or above, in order to make sure the converter switching action is restricted to the zero crossing point of the link voltage, the switching cycle becomes discrete pulse spectrums, however, the conventional PWM converters are ruled out because they would fail either to the efficiency or the low-distortion criteria. The three-phase high-frequency AC pulse density modulation (PDM) converter, which is proposed in this paper, can efficiently synthesize low-distortion variable frequency variable amplitude low frequency voltage signals from the fixed-frequency voltage of the high frequency link. The main advantage of this PDM converter is that one half-cycle of the high-frequency voltage becomes the basic unit of synthesis of the low-frequency signals. The area difference under the reference signal and synthesized signal and the next pulse with the polarity will reduce this difference. With this feedback, the density of the half-cycle pulses in the synthesized output is modulated by the amplitude of the reference signal. According to the mechanism characteristics of the AC motor, with zero-voltage switching technology, the PDM converter mathematical models both the PWM and rectangular wave control mode are given in this paper. And the voltage and current harmonic analysis and the simulation waveforms of the output voltage, current and power are also described respectively. The simulation results prove that the PDM control theory can be fit for the high frequency AC link power conversion distribution system, especially be suitable for the electric driver system of the electric vehicle in the future.