The basic principle of PWM controller is based on: narrow pulses with the same impulse but different shapes have the same effect when applied to the link with inertia. According to the controller principle, the waveform is divided into 6 equal parts, which can be replaced by 6 square waves equivalently.

There are many classification methods of pulse width modulation, such as unipolar and bipolar, synchronous and asynchronous, rectangular wave modulation and sine wave modulation. The unipolar PWM controller means that the carrier only changes in one direction in a half cycle, and the resulting PWM waveform only changes in one direction, while the bipolar PWM control method changes the carrier in two directions in a half cycle, and the resulting PWM The waveform also changes in both directions.
According to whether the carrier signal is synchronized with the modulation signal, the PWM controller can be divided into synchronous modulation and asynchronous modulation. The characteristic of rectangular wave pulse width modulation is that the output pulse width column is of equal width, and only a certain number of harmonics can be controlled; the characteristic of sine wave pulse width modulation is that the output pulse width column is of unequal width, and the width changes according to the sine law, The output waveform is close to a sine wave. Sine wave pulse width modulation is also called SPWM. The key to this technology is to generate the pulse width according to the control signal. Commonly used triangular wave comparison method, hysteresis comparison method and space voltage vector method.