Three-phase PWM Rectifier Control And Harmonic Suppression Research

PWM rectifier solves serious harmonic pollution to grid perfectly due to its advangtages such as DC voltage controlled, low current harmonics of grid side, unity power factor, reversibility of energy, and so on, which has became a major research subject in power electronic technology. As the 15KW three-phase voltage source PWM rectifier is implemented basically in the thesis,a solution integrating two PWM rectifiers by parallel connection is presented to deal with the problem of AC current and DC voltage harmonics.After referring to the related literature at home and abroad, this thesis introduces the development status and basic operation principle of the three-phase voltage source PWM rectifier firstly. As three-phase PWM rectifier is a strong coupling, time-varying nonlinear system, so the mathematical models are established in the three-phase stationary coordinate and the synchronous rotating coordinate respectively. On top of this, the paper designs the double closed-loop control system and builds its Matlab simulation model of the three-phase voltage source PWM rectifier. The simulation results show that the proposed scheme is effective and practicable. According to the simulation, the selection of DC voltage’s low limit, the inductor on ac-side, the capacitor on dc-side and the current limiting resistance are analysed in detail.Aim at the problem of large error and difficult implementation in traditional Sinusoidal Pulse Width Modulation (SPWM), a stepping approaching SPWM method which is easier to realize with DSP is proposed. In order to reduce online computation of the algorithm and actual error, this method approachs the sinusoidal wave step by step by virtue of table lookup regularly in program. Simulation and experiment results show that the stepping approaching SPWM can satisfy the requirement of the real-time control and be implemented in engineering easier.In terms of rectifier harmonic suppression, the unbalance of three-phase voltage is the dominant factor to cause harmonics by theoretically analyzing. Therefore, a solution integrating two PWM rectifiers by parallel connection is adopted aimed at the unbalanced power supply. In this solution, one PWM rectifier acted as main one to produce positive sequence current and the other produces negative sequence part as assistant one to deal with the serious harmonics. The simulation results show that the proposed scheme is effective and practicable. In addition, a redundant high frequency mode is proposed with the three-phase voltage PWM rectifier in parallel in order to increase the fault tolerance and high-frequency effect.On the basis of previous work, three-phase voltage PWM rectifier is developed. In the 15KW rectifier experimental platform, experiments are carried out in the whole process of precharge, PWM control and stepping approaching SPWM algorithm.The experimental data and experimental waveforms show that PWM rectifier control system and its control strategy have achieved the expected goals.