Research On Current Source Inverter With Hybrid Semiconductor Switches And Its Key Technologies

With the development of human society,the enery crisis and environmental pressures have gradually appeared in front of human beings.Developing the new green renewable energy such as the solar energy,wind energy and tidal energy,has become the energy-strategy consensus all around the world.Power converters are the key technology to cope with the future energy landscape and to achieve large-scale access to renewable energy.The power converter integrates components such as power semiconductor switches and high-frequency filters.The cost,reliability and working efficiency determine the economic benefits and availability of renewable energy generation systems.In the future of renewable energy,designing new power-electronic equipments,improving energy transmission capacity,increasing power supply security,improving power quality and the energy conversion efficiency,etc.,these aspects have become the quite important research topics in the field of electrical engineering.Current Source Inverter(CSI)has been regarded as a kind of power converter with great potential.Because of the inherent boosting capability and high reliability,CSI is an important energy converter in the fields of photovoltaic generation,wind plants,data centers and superconducting energy storage systems.And in recent years,it has received continuous attention from scholars.However,the current source inverter is usually equipped with a large inductor on the DC side.The bulky size and high cost of inductor adversely affect the application of CSI.At the same time,comparing to the same capacity Voltage Source Inverter(VSI),the power switching devices in CSI usually take more conduction losses,so that the efficiency is also relatively lower.Despite years of development,current source inverters still face a series issues such as cost,size and efficiency.How to overcome these traditional disadvantages are the quite challenging topics in the academic and industrial circles.On the other hand,the wide-bandgap semiconductor technology,which especially represented by Silicon Carbide(SiC),has developed rapidly in recent years.Compared to conventional silicon(Si)-based devices,the power devices constructed from silicon carbide materials are extremely resistant to voltage,temperature and switching frequency.SiC device has excellent high power density and high efficiency,making it an ideal choice for power converters.However,in the current research stage,although the SiC-based power switches have been gradually commercialized,the commercially available SiC-based power switches are still very rare,and the price is much higher than the Si-based power switches of the same level.Therefore,in the short term,it is difficult for SiC switches to completely replace all the Si-based power switches in power converters,and Si-based power switches are still the mainstream devices in power-electronic applications.In view of the development status of the power electronic technologies and the power semiconductors,scholars actively developed a variety of hybrid-switch type power converters,which are modified by configuring a small amount of high-performance advanced power switches.This technology significantly improves the performance of the converter,providing a cost-effective soultion for power-electronic equipment,and has become a new idea for the development of power converters.This paper focuses on the three-phase current source inverters.To improve the CSI performance and working efficiency,this paper begins with the CSI topologies and the employment of advanced wide-bandgap semiconductor power devices,combines the CSI circuitry with hybrid switching device technologies.A novel concept of CSI with hybrid silicon(Si)and silicon carbide(SiC)semiconductor switches has been proposed.A series of original works with insights have been carried out.The specific research contents are as follows:(1)Research on the configuration mechanism of current source inverter with hybrid semiconductor switches.In this paper,the traditional current source inverter and its variant topologies are studied.Based on the analysis of the advantages and limitations of each CSI structure,the common features and typical problems are summarized.The functions and tasks of silicon and silicon carbide semiconductor switches in CSI are clarified.Moreover,the optimization principles and specific steps of hybrid-switch CSI construction have been established.(2)Research on Hybrid-Switch H7 Current Source Inverter(HSH7-CSI).For the stand-alone three-phase CSI,based on the traditional H6 Current Source Inverter(H6-CSI),an HSH7-CSI solution with hybrid semiconductor switches is presented,which consists of a single shunt-connected silicon carbide switch and a traditional silicon H6-CSI circuitry.Two compatible modulation strategies are also proposed,which could employ the superior characteristics of SiC switch to significantly increase the whole switching frequency with expected low losses simultaneously.And the CSI circuitry is given the ability to reduce down the DC inductor.The proposed HSH7-CSI solves the inefficiency and bulcky inductor problems with low cost,making it a CSI solution with great protential.Finally,this paper uses MATLAB simulation and experimental platform to carry out a series of experimental tests,and the excellent performance of the HSH7-CSI has been verified.(3)Research on the Hybrid-Switch Five-level Current Source Inverter(HSF-CSI).For the multilevel CSI technology,a new hybrid-switch five-level current source inverter with eight power switches has been proposed in this paper.On this basis,the fundamental vectors as well as switching selections of HSF-CSI are illustrated,and a compatible high-efficiency modulation method is presented.HSF-CSI is able to obtain five-level output currents by employing a similar hardware cost and space occupation as the traditional H6-CSI.Furthermore,the filter configuration requirements have been reduced down,and at the same time the power density as well as the operational efficiency is increased significantly.HSF-CSI can be a cost-effective CSI solution with broad application prospects.Finally,the performance and superiority of the proposed HSF-CSI are verified by simulation and experimental tests.(4)Research on the Modular Cascaded Hybrid-Switch Current Source Inverter(MCHS-CSI).For the modular cascade CSI technology which is currently used in high-power applications such as the wind plants,a novel modular cascaded CSI with hybrid silicon and silicon carbide power switches is proposed in this paper.And the compatible modulation strategy with its operational principle is also presented,which makes MCHS-CSI work with all SiC-MOSFET switching losses to achieve the significant efficiency promotion,and meanwhile lower down the DC current ripple.Moreover,the fault tolerant mechanism is analyzed,and the energy-balance control scheme of each sub-module has been proposed.Finally,the proposed MCHS-CSI with its modulation method and the control strategy are verified by simulation and experiment.Compared with the traditional current source inverter solutions,the proposed current source inverter with silicon and silicon carbide semiconductor switches possesses a series notable features.It can significantly improve the performance(esp.efficiency and power density)of the CSI by configuring a small amount of SiC power semiconductor devices.The advantages such as low cost and easy to construct,make it a new cost-effective CSI solution with broad application prospects.It is of great significance for promoting the practical application of current source inverters and improving the efficiency of energy conversion.