The PWM circuit modulation method involves modulating the width of the pulse waveform. It primarily relies on the switching characteristics of the inverter to chop and modulate the DC power source, achieving a constant U/t control as required. Compared to PAM circuit modulation, PWM circuit modulation has higher power efficiency, hence both yield an average voltage output in the form of a square wave.
The PAM circuit modulation method involves modulating the pulse amplitude of the output waveform. Its application is less frequent compared to PWM. Compared to PWM circuit modulation, PAM modulation drives have less noise and a smaller noise level, but they have a lower power factor and a more complex circuit.
The SPWM modulation method was developed because both PWM and PAM modulation outputs are square waves. To achieve a better waveform, sine waves are used as outputs. The SPWM method, which employs high-frequency pulse width modulation to generate higher-order harmonics that are easily filtered out, is a reasonable modulation method and is commonly used in variable-frequency power supplies.
