| With the advancement of technology and the complexity of motor control modes,there are increasingly higher requirements for the safety and reliability of MCU(Motor Control Unit).The EME(E-motor Emulation)tests the motor controller by simulating the characteristics of the real motor load port.Compared with the traditional mechanical bench,it has the advantages of convenient testing,flexible operation,and reduced development cycle and cost.Parallel multi-level has the advantages of low output harmonics,high efficiency,high redundancy and high reliability,and is very suitable as the topology of EME.However,parallel multi-levels will cause current imbalance problems,and the circulating current will increase the total harmonic distortion of the three-phase current,reduce the current stress of the switching device and the system efficiency,and even damage the power device.The current balance problem has become a key issue of parallel multi-level,so the study of parallel multi-level circulating current suppression has significant value for the stability,reliability and high efficiency of EME.This paper analyzes the factors that affect the circulating current in the parallel multi-level power topology,including CPS-SPWM(Carrier Phase-Shifted Sinusoidal Pulse Width Modulation),inverter dispersion,inconsistent driving signals,and inconsistent line parameters,etc.,and studies its mathematics law.According to Kirchhoff’s voltage law,the mechanism of circulating current generation is deduced from the perspective of theory and mathematical model,and the relationship between circulating current and EME bus voltage,target current,control period,and electrical time constant is obtained.Analyze and derive the impedance of different output coupling network structures,combined with the actual engineering application of the motor simulator,determine the output coupling network structure suitable for the motor simulator,and design and build it.Based on the parallel multi-level power topology structure of the motor simulator built,the mathematical model of the output coupling network is established,the state equation of the output coupling network is analyzed,and a current sharing control scheme suitable for it is proposed.Based on the discrete system eigenvalue analysis method,the stability of the proposed current sharing control algorithm is analyzed to improve the overall robustness of the motor simulator system.Combining software and hardware to suppress high-frequency circulation and eliminate low-frequency circulation.This paper designs and builds the output topology of EME based on the cascade coupling structure,including device selection and structural layout.Based on CPS-SPWM,a parallel multi-level driver is built in LABVIEW to achieve multi-level phase voltage output.And according to the basic idea of the proposed current balance control algorithm,the current balance control algorithm is built and implemented in LABVIEW.Finally,the experimental results show that after the current balance control algorithm is turned on,the circulating current amplitude of all parallel branches is suppressed to about 0.2A and the total harmonic distortion is significantly reduced.The experiment verifies the effectiveness of the c current balance control algorithm. |
