Research On Active Common-mode Suppression Strategy Based On Current-balance Mode For Five-phase Three-level Inverter System

As the traditional DC/AC power conversion equipment,voltage-source inverter using PWM technology has been widely used in electric energy conversion conditions such as motor drive.With the popularization of new wide-bandgap semiconductor devices such as Si C and Ga N and the wide application of high-voltage large-capacity devices,the conducted EMI caused by high-frequency switching of inverters becomes more serious,especially the common-mode leakage current caused by common-mode voltage(CMV).The security and stability of the inverter system will be seriously affected.The conventional method of suppressing the conducted EMI is to add EMI filters to the system to block the conducting path of EMI noise,but the extra filters will reduce the power density of the system.At present,the active common-mode suppression strategy optimized by inverter topology with high control degrees of freedom combined with advanced modulation strategy has high development potential in terms of common-mode suppression effect and inverter performance.Therefore,this paper takes NPC type threelevel five-phase PWM inverter as the research object to study the active common-mode suppression stategy of CMV elimination,and the main work is summarized as follows:Firstly,reducing the CMV amplitude through a suitable PWM strategy is the main means of active common-mode suppression strategy.The conventional active commonmode methods improve on two basic PWM strategies will still generate large commonmode leakage current on common-mode spurious loops with small capacitance.This paper proposes a zero-common-mode modulation strategy suitable for three-level fivephase inverters,which is based on the principle of PWM signal edge alignment to carry out carrier comparison modulation,avoid complex vector modulation calculation,and realize the CMV volt-second balance in the switching cycle by real-time phase shifting of PWM signals to ensure the elimination of CMV at any moment.In order to solve the problem of pulse delay caused by non-ideal factors such as inverter dead-band effect,the delay compensation scheme based on current ripple prediction is used to optimize the effect of zero-common-mode modulation strategy.The simulation results verify the effectiveness of the proposed zero-common-mode modulation strategy for three-level five-phase inverters.However,the common-mode methods of three-level five-phase inverter systems are mainly achieved under ideal conditions which the parameters at the load side are symmetrical and the phase voltage is balanced.Due to the problem of load asymmetry caused by non-ideal factors in five-phase motors,it will lead to unbalanced back EMF and affect the accuracy and stability of control system.Therefore,this paper introduces a resonant control strategy into the zero-common-mode modulation strategy and basic closed-loop control to optimize the phase current equalization problem of the system,which is simple algorithm and increases the robustness of the system.The simulation results verify the superiority of resonant control introduced in the paper.Finally,in order to verify the effectiveness of the above modulation strategy,an active common-mode suppression experimental platform for three-level five-phase inverters is built in the laboratory for further experimental verification.The experimental results show that the zero-common-mode modulation strategy of the three-level fivephase inverter has the ability to eliminate the common-mode voltage,suppress the common-mode leakage current,and ensure the differential mode performance of the system.The phase current equalization control scheme of resonant control is introduced to enhance the system’s resistance to load asymmetric disturbances.