Three-phase Passive Soft-switching Inverter And Its Performance Evaluation

In recent years, with the development of PWM inverter, there have been radical changes on the design of power converter. It has been changed from heavy and enormous power frequency transformer to light and small density power converter, and the whole efficiency of converter has been greatly improved too. These changes will benefit the design and application of PWM inverter. Traditional inverter technology is mature, reliable, widely applied, but there are some disadvantages such as large on size, big audio noise, poor system dynamic characteristics, large loss, etc. Soft switching circuits solved these problems about the hard-switching inverter.Based on the analysis and evaluation of current research status of soft-switching topology of three phase inverter, the thesis focused on the topic of soft-switching three phase PWM inverter, and made further research on circuit topology of soft-switching three phase PWM inverter. The research topic of the thesis which is soft-switching three phase PWM inverter is one part project of The Research of Energy Saving Technology of Electrical Driven and Control System (Project NO. is2006AA04Z183) that is economic supported by National High Technology Development Plan (Strategy863). The purpose of researching on the main circuit topology and control strategy of soft-switching three-phase PWM inverter is to explore a practical soft-switching three-phase PWM inverter, to study its working system and to provide for industry a feasible scheme of soft-switching three-phase PWM inverter.Firstly, the thesis introduced the purpose and current research status of soft-switching inverter. Generally, accessorial switcher is used to help control the resonance process in the structure topology of current resonant soft-switching inverter, and its control method is more complex than original ones of hard-switching converter, so it is harder to realize. Based on this situation, this thesis proposes a easy controlled three-phase soft-switching inverter. This kind of devices are easily controlled, and do not need to change the original hard-switching inverter. Also, topology auxiliary circuit does not increase the power switching device but only increase the resonant capacitor, fast recovery diode, coupled inductors and other passive auxiliary devices to the hard-switching added inverter resonant inductor. The devices have the characters like simple structure, easy controlled, low cost, small power consumption and so on. Besides, through the topology of the energy storage components, continued flow can be achieve in the dead time, and reduce the impact of the dead-zone to output current and voltage.Secondly, the thesis introduced the main circuit topology of this three-phase passive soft-switching inverter, then analyzed the soft-switching working principle and soft-switching operation mechanism. Equivalent circuit figures of different working modes were given in the thesis. It gave out the equivalent circuit plots of different operation modes, proposed mathematically the dynamic process of each mode in the operation timing of soft-switching action schedulingof inverter, and established SPWM control strategy for realization of inverter’s soft-switching operation. And the thesis introduced the design method of loop parameter. Then, the thesis introduced the design of drive circuit, control circuit and the parts selection in this three-phase passive soft-switching inverter. A testing device with1KW power was made to do experiments. On the basis of theoretical analysis, we have simulations and experiments. Through the comparison simulations and experiments, we prove that the loop control method is simple, the output current is low at low-frequency and switching loss is low, etc.At last, some exsiting issues in the theory and application of soft-switching three phase PWM inverter are pointed out and the prospect of research work of next step is presented in the thesis.