| Dual PWM converter consists of PWM rectifier and PWM inverter, which is becoming to a hot topic for its sinusoidal current of grid side, unity power factor and bi-directional energy flow. This thesis take dual PWM control system as research object, and in view of the existing problems of it under independent control method, adopts coordinated control of load current feed forward strategy and coordinated control of load power feed-forward strategy, The control target is to minimized the DC voltage fluctuation, the capacitance and unity power factor as,and the theoretical research and simulation experimental research have been done.Firstly, analyze and study the working principle and mathematic modules of PWM rectifier which is a key part of dual PWM converter, then instantaneous power theory was introduced and power mathematical model of PWM rectifier was constructed in order to analyze the power flow character of dual PWM.Secondly, the existing problems of dual PWM converter under independent control strategy were anaylazed. And througuh the analysis of the output voltage of PWM rectifier under double closed loop, point out that the double closed loop control doesn’t consider the effect of the load current fluctuations on the DC voltage. Coordinated control of load current feed-forward is researched based on the structure of double closed loop control, including the calculation of the load current and the principle of load current feed forward compensation. Then take a simulation, and the simulation results show that integrated control of load current can achieve the goal to control objectives well.Thirdly, the integrated control strategy of load power feed-forward was researched. The switching singal was outputed from hysteresis comparator in traditional direct power control system.. Due to the hysteresis comparator’s own characteristics, it’s easy to cause the circuit switching frequency unfixed and voltage fluctuation. Therefore, the thesis adopt direct power control based on fixed switching frequency. On that basis, take load power feed-forward as the control strategy. Study the principle of load power feed-forward, while the dynamic response of load power feed-forward and independent control are analyzed.Point out that the DC voltage is immune from load change through the rational controller parameters. Furthermore, introduce several common load power estimation methods and analyze their defects. The load power was estimated accurately by the command values of rectifier output voltage and current.Finally, this thesis take TMS320LF2812DSP chip as control core, and then design dual PWM inverter system has been designed.Some experimental results have been obtained, which lays a foundation for the further subject research. |
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