基于SHEPWM的多模式调制切换算法

为了抑制切换过程电流和转矩冲击，提出了一种基于特定次谐波消除脉宽调制（SHEPWM）的多模式调制平滑切换算法. 根据SHEPWM算法的基本原理分析了相电压波形谐波分布情况；基于异步电机等效电路模型得到不同开关角个数下各次电流谐波幅值和调制度的关系；将切换过程抽象为电流基波及各次谐波的一阶暂态响应过程，建立了切换过程的数学模型，从电路原理的角度分析了切换冲击的产生机理；基于RT-LAB半实物实验平台对两种切换算法进行了硬件在环半实物试验对比. 研究结果表明:谐波幅值突变是造成转矩冲击的原因，在相电压基波相位π/2和3π/2处切换谐波电流幅值不发生变化，相电流可以平滑过渡；三相无法同时满足相位为π/2或3π/2的条件，因此分别在相电压基波相位π/2和3π/2处切换，切换过程电流和转矩冲击得到有效抑制. 

Switching Scheme of Multi-mode Modulation Based on Selected Harmonic Elimination Pulse Width Modulation

In order to suppress the current and torque shock, a switching scheme of multi-mode modulation based on selected harmonic elimination pulse width modulation (SHEPWM) was proposed. Based on the basic principle of SHEPWM, the spectrum of phase voltage was analyzed. The relationship between current harmonics and modulation index was acquired with different switching angle numbers. Then, the switching process was abstracted as the first-order transient response of the fundamental circuit and harmonics circuits, and the mathematic model of the switching process was built. The mechanism of current shock during switching process was analyzed. Hardware-in-loop (HIL) experiments of two switching schemes were carried out on the RT-LAB HIL experimental platform. The results indicate that the main cause of the torque shock is the harmonic current amplitude step change during the switching process, and the harmonic currents amplitude keeps constant when switching at π/2 or 3π/2, so the phase current switches smoothly. The three phase currents can’t satisfy the phase requirement at the same time, so each phase switching at π/2 or 3π/2 separately can suppress the current and torque shock effectively.