The Key Techniques Research On The Digital Controlled PWM Inverter

With the demands of important departments and electric equipments for higher quality power supply ascending,high performance PWM inverter are taken more and more attention. With its incomparable merits, digital control is gradually taking place of analog control. On the one hand, digital controlled PWM inverters gain more freedom for design, with which kinds of complicated and intelligent algorithms can be implemented easily; on the other hand, the traditional strategies are still playing an important pole in the digital control. The hybrid strategies of the advanced digital strategies and the traditional ones are now most accepted in the product application. But the reality the traditional ones implemented in digital method can't achieve the result as good as in analog, hinders the improvement of the digital controlled PWM inverters'performance. This dissertation is focused on the research of the causes which decrease the performance of the digital controlled PWM inverter induced by the process of zero hold and sample. There're two main causes. One is the change of the property arising from the process of the zero-order hold. The influence of the process of the zero-order hold on its frequency property is analyzes, also its influence on the system stability. Another one is the effect of the delay arising from the sample and calculation, which may result in the limitation of the maxium ratio of the inverter.To resolve this problem, one-step-delay control is usually adopted. The influence of this control method on the system stability is also analyzed. The analysis shows there're three key causes effecting the digital controlled PWM inverter's performance: (1) The process of the zero hold changes the open-loop frequency property of the inverter that is for under damp systems, the property varies periodically with sample time changing and for over damp systems, varies monotonously; (2) The process of the zero hold changes the system's stability and the stable zone lessens greatly; (3) The one-step-delay control method changes the system's stability too. The stability variation caused by zero hold process and one delay control method is the important reason influencing the digital PWM inverter. Based on the above analysis, the strategy that is one delay control and predictive control should be adopted under different sample time is proposed. The method to test the PWM inverter system's stability is also proposed. Simulations and experiments verify the rightness of the analysis and the feasibility of the proposed control strategy. To realize the predictive control, the accurate realization of the state observer should be promised. The kinds of the causes effecting the realization of the state observer have been analyzed in detail, which are parameters'error of the model, model construction error, the design method and the truncation error. Based on the above analysis, the right design procedure is proposed. To depress the effect of the model error more, the repetitive control compensate observer is proposed. The simulations verify its feasibility. Besides working as individual power supplies, inverters are also applied in the power system, where the phase-locked loop is the key part to connect inverters and net. While the digital phase-locked loop's parameter design of the loop filter is really a problem, we often get the parameters by try and try. This dissertation also tries to resolve this problem. The accurate model of the full digital phase-locked loop based on the TMS320F240 is proposed and also the parameter design method based on the equivalent model. The phenomenon of jump-period error, which may occur in the phase detection, is analyzed and the limitation of the parameters is provided. To resolve the detection fault which may occur in the multi-zero crossing in the zero crossing phase detection method, the phase-locked loop based on the discrete Fourier transform is proposed. Also the model and the parameter design method are proposed. The positive feedback phase detection fault, which may occur in the proposed method, is analyzed too.