Research On Soft-Switching PWM Inverters And Its Application In Electric Drive Control System

Based on the analysis and evaluation of current research status of soft-switching topology of three-phase inverter, the dissertation 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 dissertation is one part project of The Research of Energy Saving Technology of Electrical Driven and Control System (Project NO. is2006AA04Z183) that is supported by National High Technology Development Plan. The purpose of research on the main circuit topology and control strategy of soft-switching three-phase PWM inverter is to explore a soft-switching three-phase PWM inverter with high reliability and simple control, to study its working system and provide a feasible scheme of soft-switching three-phase PWM inverter for industry and apply it in electric drive control system.The main research work is as follows:1. A novel zero-voltage and zero-current soft-switching PWM inverter topology circuit with active auxiliary commutation is proposed, in which auxiliary switches are employed to control the resonant process. Because the voltage across main switches decreases to zero before main switches are turned on and the current decreases to zero before main switches are turned off in the novel topology, zero-voltage turn-on and zero-current turn-off can be realized. The problems of turn-on capacitive losses and the tail current are both solved. The equivalent circuits at different operation modes, the analysis of the circuit and parameter design method are presented. Simulation and experimental results are proposed to verify the validity.2. Six auxiliary switches are needed in the zero-voltage and zero-current three-phase soft-switching topology circuit which has been proposed in the dissertation. In order to reduce number of auxiliary switches, simplify the circuit structure and control strategy, improve reliability, author has improved the three-phase zero-voltage and zero-current soft-switching topology circuit and proposed a novel three-phase resonant DC link soft-switching PWM inverter topology circuit which only includes two auxiliary switches. The equivalent circuits at different operation modes, the analysis of the circuit, the control strategy and parameter design method are presented. Simulation and experimental results are proposed to verify the validity of the proposed three-phase resonant DC link soft-switching PWM inverter topology.3. Although two soft-switching PWM inverters which have been proposed in the paper can effectively realize soft-switching and reduce loss, active auxiliary switches are needed in the two topologies, which can lead to complicated control strategy, additional cost and relatively poor reliability. In order to simplify control strategy and improve reliability further, a novel three-phase passive soft-switching PWM inverter topology is proposed to reduce di/dt during turn-on transient and du/dt during turn-off transient to reduce switching loss of main switches. Zero-current turn-on and zero-voltage turn-off can be realized. There are no auxiliary switches in the auxiliary resonant circuit and control method is simple. In the novel topology, freewheeling of output current can be realized via energy storage components in the dead-time and the effect of dead-time is reduced. The distortion ratio of the output phase current in low frequency is also reduced. Three DC-bus electrolytic capacitors are placed for voltage sharing. The influence of voltage deviation of electrolytic capacitors on output voltage and soft-switching is analyzed. The working principles on how to realize soft-switching via the proposed topology are discussed. Besides, the realization conditions and control strategy are also studied. Furthermore, the topology is studied by simulation. Finally, a lkW experimental prototype is made to verify the validity of the proposed topology.4. The novel three-phase passive soft-switching topology is improved. There is only one common group of resonant inductors in three-phase resonant circuit of the original topology, which leads to mutual influence in resonant process and poor reliability; there are three groups of resonant inductors corresponding to three-phase resonant circuit of improved topology, so resonant process of every phase is independent, which enhances reliability. In addition, the realization condition of zero-voltage turn-off is also improved. By designing proper inductance parameters, loss during turn-off transient could also be reduced without the restriction of minimum width of trigger pulse. Simulation results verify the validity of the above improvement and establish foundation for application in electric drive control system.5. The improved three-phase passive soft-switching topology is applied in the10kW electric drive control system which is researched independently by project team. The composition and design of the system is described in brief. The improved three-phase passive soft-switching topology is experimentally studied. Experimental results show energy saving effectiveness of the improved three-phase passive soft-switching topology which is applied in electric drive control system.