Principle of PWM and generation of PWM wave

1. Definition

Pulse width modulation （Pulse width modulation,PWM）, Simply put, it can replace other waveforms by adjusting the duty cycle of square wave . Because it's a digital signal , Not susceptible to interference .

2. Circuit implementation

Pictured , A sine wave is an input signal , Triangular wave is a carrier signal , Output high level between the intersection of the two , Because the period of triangular wave must , So the output period is certain , The duty cycle changes PWM wave , The realization of the circuit requires a triangular wave generator , A voltage comparator can achieve .
The picture below is TI From the official website PWM Generator circuit .

3.SPWM

SPWM： Sine wave pulse width modulation .
SPWM The definition of waveform is to divide sine half wave into N Equal division , The area enclosed by each bisection and abscissa is replaced by an equal height rectangle equal to its area , available N Rectangular pulses , as follows ：

stay SPWM Legal cross - straight - AC variable frequency speed regulation ,SPWM Compared with the six beat step wave, the method can output a voltage closer to the sine wave , Reduce high-order harmonic components , And the power factor of the power grid is close to 1, Greatly improve system performance .