低载波比下三电平中点钳位变流器改进型同步载波脉宽调制策略研究

Research on Improved Synchronized Carrier Based PWM for Three-Level Neutral Point Clamped Converter under Low Carrier Ratio

当三电平变流器应用于大功率电机的牵引传动系统时,为优化谐波性能,通常在低载波比段使用同步调制。传统同步载波脉宽调制(SCBPWM)计算简单,但其只能在3的奇数倍载波比下使得输出电压波形满足三相对称和半波对称,且其无法进入方波。针对SCBPWM存在的缺陷,该文首先研究两类SVPWM开关序列在不同载波比下的相电压波形,并根据不同的波形特性基于调制波等效提出改进型SCBPWM(ISCBPWM),其可分别在3的奇数倍和偶数倍载波比下实现同步调制。通过在线计算功率器件动作的开关角,使得ISCBPWM可进入方波。在此基础上分析ISCBPWM的性能并设计基于ISCBPWM的全速度范围调制策略。最后仿真和实验结果表明,ISCBPWM相比传统SCBPWM,适用的载波比段更多、直流电压利用率更高。其可以在3的任意整数倍载波比下实现同步调制并可进入方波,其计算简单、实现方便。

When the three-level converter is applied to traction drive system of high power motor,synchronized modulation is usually used under low carrier ratio to optimize harmonic performance.Synchronized carrier based PWM(SCBPWM)is simple to calculate,but the carrier ratio must be an odd integer multiple of 3 to ensure synchronization,three-phase symmetry and half-wave symmetry,and it cannot enter the square wave modulation.In order to overcome the shortcomings of SCBPWM,this paper firstly studies the phase voltage waveforms of two SVPWM switching sequences under different carrier ratios,and then proposes an improved SCBPWM(ISCBPWM)based on modulation wave equivalence,which can realize synchronized modulation when the carrier ratio is an odd and an even integer multiples of 3,respectively.By calculating the switching angle online,the ISCBPWM can enter the square wave modulation.On this basis,the performance of ISCBPWM is analyzed and the modulation strategy based on ISCBPWM in full speed range is designed.Finally,the simulation and experimental results show that compared with the traditional SCBPWM,ISCBPWM has more suitable synchronous segments and higher DC voltage utilization.It can realize synchronous modulation at any integer multiple carrier ratio of 3 and enter the square wave modulation,and its implementation is very convenient.