A Soft Switching Technique For High-frequency ANPC Inverter

With the development of modern power electronics technology,the power level of inverter devices continues to increase,and the advantages of multi-level topology are more and more obvious,especially the three-level active neutral point clamp(ANPC)topology in medium and large power converters is becoming more and more widespread.With the background of power electronic converters towards miniaturization,high frequency,and high efficiency,traditional ANPC hard switching inverters face problems such as low switching frequency and large switching loss.A trend in industrial applications and research is the use of wide bandgap semiconductor devices such as silicon carbide(SiC)to alleviate these problems.Although the use of SiC devices can effectively reduce each switching loss,but with the practical application needs,when the switching frequency continues to increase to hundreds of kilohertz(k Hz),the hard switching loss of SiC devices is also very high,which limits the further improvement of inverter efficiency and power density.As a result,the soft switching inverter based on SiC devices is an important development direction of the converter,which is characterized by a significant increase in switching frequency and a significant decrease in switching loss.In order to further improve the high-frequency and high-power application of the three-level ANPC inverter,this paper proposes a soft switching technique based on a high-frequency ANPC inverter of SiC and silicon(Si)hybrid devices.On the basis of not changing the ANPC main circuit topology and modulation mode,this soft switching technique can realize all the high-frequency main switches zero voltage switching(ZVS)and all the auxiliary switches zero currnet switching(ZCS).It aims to further improve the efficiency of the ANPC inverter,give full play to the potential of SiC devices,and can be applied in practical engineering.Firstly,the commutation principle of the ANPC hard switching is briefly introduced,then the principle of single-phase ANPC inverter soft switching is described in detail,the resonant model is established,the main voltage and current formulas are deduced,and the design criterions of the soft switching are given.Then,the various losses of the hard and soft switching of the ANPC inverter are modeled and calculated,and make a comparison,the efficiency advantages of soft switching are obtained theoretically.In view of the large conduction loss caused by the auxiliary circuit,this paper proposes two improved methods of the soft switching,and compares the loss calculations to further improve the efficiency of soft switching.The improvement method of the external parallel diode is simple,but the extra hardware cost is increased.The improved method of synchronous rectification is used to improve the efficiency of the soft-switch without adding extra hardware.In order to verify the correct of the soft switching principle and the losses model,simulation verification was carried out,and a 1k W,200 k Hz experimental platform was built for experimental verification.Both the experimental waveforms and efficiencies verified the advantages of the soft switching implementation and efficiency improvement.