说明：  SPWM法就是以该结论为理论基础，用脉冲宽度按正弦规律变化而和正弦波等效的PWM波形即SPWM波形控制逆变电路中开关器件的通断，使其输出的脉冲电压的面积与所希望输出的正弦波在相应区间内的面积相等，通过改变调制波的频率和幅值则可调节逆变电路输出电压的频率和幅值
(SPWM method is based on this conclusion. The PWM waveform, which is equivalent to sine wave when the pulse width changes according to the sine law, is used to control the on-off of the switch device in the inverter circuit, so that the area of the output pulse voltage is equal to the area of the desired output sine wave in the corresponding interval. By changing the frequency and amplitude of the modulation wave, the output voltage of the inverter circuit can be adjusted Frequency and amplitude of)