采用新型评价表的三电平逆变器占空比调制直接转矩控制

Direct Torque Control Using New Evaluation Table of Three-Level Inverter Based on Duty Cycle Modulation

针对直接转矩控制系统稳态转矩波动较大的问题,提出一种采用新型评价表的三电平逆变器占空比调制算法。首先,为减小占空比调节过程对电机参数的依赖性,对三电平逆变器大、中和小矢量建立了转矩和磁链的矢量评价表,并针对反电动势建立了补偿评价表。其次,根据电机运行转速和矢量的转矩控制效果,分别给出低速和高速两种控制方案,在低速方案中采用小矢量和零矢量,在高速方案中采用大(中)矢量和小矢量来控制转矩,可更加合理地利用小矢量来保证输出转矩的平稳性。最后,在以上两种控制方案和评价表的基础上,利用预定价值函数可快速确定输出矢量及其占空比。在一台6k W永磁同步电机样机上对本文所提出算法进行了实验验证,实验结果表明所提算法可有效改善电机稳态转矩波动。

A direct torque control using new evaluation table of three-level inverter based on dutycycle modulation is proposed for neutral-point clamped three-level inverter-fed permanent magnetsynchronous motor drives in order to suppress the steady torque ripples. Firstly, the approachestablishes evaluation tables including three vector evaluation tables which evaluate torque and flux ofthe motor and a compensatory evaluation table which evaluate back electromotive force. The tables areindependent to motor parameters in the process of duty modulation adjustment. Secondly, the approachproposes two control schemes for low speed and high speed of the motor. Small vectors and zero vectorare employed in the scheme of low speed. Big/medium vectors and small vectors are employed in thescheme of high speed. In this way, the steady of torque is ensured by using the small vectors. Then thevector and duty selection scheme is established based on the cost functions. The proposed algorithm areverified by experiments of a 6kW permanent magnet synchronous motor (PMSM). And the experimentresults show that the steady torque ripples are suppressed effectively.