Research On Three-phase Resonant DC Link Soft-switching Inverter

In pursuit of high frequency,high efficiency and high power,modern power electronic inverter device also hopes to have smaller volume and lower cost.The auxiliary circuit of the three-phase resonant DC link inverter is located in the DC side of the inverter,which has the advantages of simple structure,less auxiliary devices and low hardware cost,and has attracted extensive attention of experts and scholars.In this paper,the high efficiency of three-phase resonant DC link soft switching inverter is studied.The second chapter of this paper proposes an energy-saving resonant DC link inverter.there is no large-volume transformer and voltage-dividing capacitor in the auxiliary circuit,and there is no problem of magnetic flux reset and neutral point potential drift,which is also conducive to the miniaturization and weight reduction of the inverter.At the same time,the steady-state voltage of DC link is not higher than that of DC power supply,which does not increase the voltage value borne by the switching device,avoiding the use of switching devices with higher voltage withstand and higher price,which is conducive to reducing the hardware cost.When the main switch needs to be switched,the auxiliary circuit is brought into the resonant state in advance,and the DC link voltage is changed to zero to ensure that the main switch completes the zero voltage soft switching,which improves the conversion efficiency of the inverter.In the second chapter,there are many auxiliary switches in the DC link of the inverter,which leads to the increase of power loss and the complexity of control,and correspondingly affects the improvement of inverter efficiency.In order to further optimize the auxiliary circuit structure,a three-phase resonant DC link inverter with soft switching function is proposed in Chapterthree.There are only two auxiliary switches in the auxiliary resonant circuit,which correspondingly reduces the power loss of the circuit,and the duty cycle of the trigger pulse of one auxiliary switch can be designed as a fixed value,simplifying the control of the auxiliary circuit.At the same time,the bridge arm does not need to be directly connected during the operation of the inverter,and the mature SVPWM method can be used directly,which simplifies the control of the main switch of the inverter.The inverters proposed in the second and third chapters,the main switches cannot perform zero-current soft-off,and the IGBT tail current cannot be completely eliminated.There will be a certain power loss when the main switch is turned off.Therefore,Chapter four proposes a new three-phase low-energy resonant DC link inverter.The main switch of the inverter does not have a buffer capacitor in parallel.The main switch can not only perform zero-voltage soft turn-on,but also complete zero-current soft turn-off.IGBT and MOSFET can be used as the switching devices of the inverter,which widens the selection range of switching devices.At the same time,in the control process of the auxiliary circuit,the resonance is directly triggered after the auxiliary switch on the parallel branch is opened.When controlling the switching of the auxiliary switch,it is not necessary to monitor the change of the resonance current in real time,and the trigger pulse duty cycle of the auxiliary switch can be designed to a fixed value,Simplifying the control of the auxiliary circuit.In this paper,the working forms of the circuits in different processes is analyzed in detail.At the same time,the parameter design rules,the design process and the expression of the auxiliary circuit loss are given.Finally,wave forms simulation model is by simulink module.The simulation results show that the main switch and the auxiliary switch of the proposed three-phase resonant DC link soft switch inverter can achieve soft switching,which improves the inverter performance Efficiency.