Research And Design Of Three-phase PV Grid-Connected Inverter Using SiC MOSFET

With the development social science and technology,people's demand for energy is increasing day by day.However,fossil energy resources are limited and faced with the thread of resource depletion.Therefore,renewable energy represented by solar photovoltaic has attracted widespread attention.Grid-connected inverters,as the interface between PV system and power grid,are a key link in PV system which has a significant impact on the performance of the whole system.IGBT are widely used in traditional grid-connected PV inverters.However,the switching speed of IGBT is limited by the current trailing effect,which lead to a large switching loss.Besides,the switching frequency of the IGBT inverter is difficult to improve,which limits the improvement of the inverter efficiency and power density.Because of the higher insulating breakdown field strength,The silicon carbide MOSFET has lower on-resistance,smaller junction capacitance and gate charge,faster switching speed as well as better temperature resistance compared with traditional silicon-based devices.Using SiC MOSFET instead of IGBT can improve the inverter efficiency,power density as well as reliability.The purpose of this paper is to develop a three-phase PV grid-connected inverter based on SiC MOSFET,which has certain theoretical significance and engineering practical value for improving the efficiency and power density of the three-phase PV inverter.Compared with Si IGBT,the most important feature of SiC MOSFET is its fast switching speed and increased sensitivity of parasitic parameters.Switching oscillation and mistriggering caused by parasitic circuit parameters are more serious in SiC MOSFET based PV inverters.Besides,SiC MOSFET also has special requirements for the driving circuit because of the fast switching speed.In this paper,the characteristics of SiC MOSFET are discussed,and the requirements of driving circuit for SiC MOSFET are summarized.Then,using the parasitic parameter model of SiC MOSFET provided by Cree Company,a double-impulse test circuit is built in LTSpice software for simulation.The switching oscillation,mistriggering and driving oscillation of SiC MOSFET are analyzed with the result of simulation.Usually,the switching frequency of IGBT based PV inverters is 10-20 kHz.This paper designs a hardware circuit for 10 kW SiC MOSFET three-phase PV inverters with a switching frequency of 40 kHz,which can reduce the size of the filter and improve the power density of the inverter.In order to reduce stray inductance of main power circuit and drive circuit,this paper optimizes the circuit design and hardware layout.Because the switching speed of SiC MOSFET is faster,the electromagnetic interference in the inverters is more severe than that in the IGBT inverters.In order to improve the reliability of the circuit,appropriate anti-interference measures are considered in the design of the control circuit.The grid-connected control algorithm of PV grid-connected inverters is usually implemented by digital processor DSP.With the increase of the switching frequency,the requirement for the computing power of DSP is higher.In this paper,TI company's TMS320F28377 S is used as the core of inverter control system.In the software program,the CLA coprocessor of DSP is used to complete the closed-loop control algorithm,and the main CPU completes the logical control and communication functions of system.The parallel operation of CLA and main CPU further improves the calculation and processing performance of the inverters.In addition,the problem of EMI is more serious and the DSP simulator is very sensitive to circuit interference,which often leads to simulator disconnection.Therefore,a host computer debugging software is developed in the design,which simplifies the debugging process.Relevant debugging and experimental tests are carried out on the SiC MOSFET inverter prototype,which verifies the feasibility of the design.