Research On Digital Control Technique And EMC Charactristic For Three-phase Inverter

With the development of science and technology,the digital control scheme of Power Electronics equipment and EMI that caused by its'fast switching devices are hotspots in recent years. Because three inverter is used in many applications, realizing its'digital control and its'EMC is discussed. In most cases control design for the three-phase PWM inverters involves two steps: choice of the modulation strategy, which corresponds to open-loop inverter control, and design of closed-loop control. After review of the existing PWM schemes, it's concluded that space vector modulation schemes are the best choice for a high performance three-phase inverter. The space vector modulation scheme has the advantages of high DC link voltage utilization, low output distortion and harmonic contents, possibility to optimize for lower switching losses and/or distortion, and compatibility with digital controller. The mathematic model in abc and dq frame for three-phase inverter are established. Simulation-model is given, which makes clear the challenges the control design faces. Simulation results prove the validity of the space vector modulation scheme and the models. In order to realize digital control of three-phase, first, instantaneous feedback PI scheme is discussed, and the design of controller and flow chat are given. Repetitive control is suit for digital scheme,so instantaneous feedback controller paralleling with repetitive controller is presented. The repetitive of three-phase is different with single-phase's, the paper has detailed analysis. And more, the repetitive control with the state feedback pole assignment is presented, and the simulation and experiment's results show the strategy is feasible. In the paper, double loop control is also discussed simply. In the three-phase inverter-fed motor drives, the switching devices'PWM waves generate shaft voltage and bearing current, and these make the motor's life shorter. So the paper concentrate on the inverter itself,discuss how it generates differential mode noise and common mode noise. The EMI prediction and design of EMI filters are summarized, so it is also the emphases of future's job.