Research On Resonant DC Link Zero-voltage Switching Inverter

Modern inverter uses soft switching technology,which can not only improve the switching frequency and efficiency of inverter,but also reduce the electromagnetic interference and noise pollution caused by its operation.The resonant DC link inverter only needs one set of auxiliary circuits in the DC link,which greatly reduces the hardware cost of the inverter.The resonance generated by the auxiliary circuit makes the switch tube in zero voltage or zero current state in the switching process,thus reducing energy consumption and noise pollution,and greatly improving the switching frequency of the switching device.In order to further improved the inverter performance,three topologies were proposed in this thesis.In the second chapter of this paper,a new resonant DC link inverter with zero-voltage soft switching function was proposed.Its innovation was that when the DC bus voltage drops to zero,the DC bus voltage rises immediately by switching the auxiliary switch,and the DC bus voltage did not need to be kept in zero state for a certain time,which was beneficial to improve the DC voltage utilization rate of resonant DC link inverter and promote its popularization and application.And the auxiliary circuit did not contain a voltage dividing capacitor,so that the structure was relatively simple,the neutral point potential was stable,and the stability of the inverter was enhanced.The disadvantage was that the voltage stress on the auxiliary switches S_a2and S_a3was large,which increased the switching loss.And three auxiliary switches were needed,so the hardware cost was high.In chapter 3,a new resonant DC link inverter with low auxiliary circuit loss was proposed.Compared with other resonant DC link inverters,the outstanding advantage was that the auxiliary circuit was not in resonance during the voltage drop of DC bus,and when the instantaneous value of load current was small,the auxiliary circuit did not participate in commutation,which was beneficial to realize low power consumption of auxiliary circuit.The disadvantage was that the auxiliary switch S_a2between DC buses did not realize soft turn-off.The reason why it failed to realize soft turn-off was that when the auxiliary circuit was in resonance,the current flowing through the resonant inductor needs to flow through the auxiliary switch to freewheel.After resonance,the current flowing through the auxiliary switch still exists.At this time,the auxiliary switch needs to be turned off immediately to feed back the electric energy in the resonant inductor to the DC power supply,so the auxiliary switch cannot realize zero-current soft turn-off.In chapter 4,a resonant DC link inverter with a single auxiliary switch was proposed,which not only provided the inverter with zero voltage off and zero current on conditions,but also reduced the number of auxiliary switches,further reduced the hardware cost and improved the inverter efficiency.In this thesis,the main circuit and equivalent circuit of three topologies were given first,and then the working flow of each circuit in a switching cycle was analyzed in detail,and the expressions of auxiliary circuit loss and efficiency improvement are calculated and derived.Finally,the simulation platform was built by Simulink,and the correctness of inverter topology was verified by analyzing the output waveform.