General-purpose inverters are power electronic devices that convert fixed-frequency AC power into variable-frequency AC power. They are widely used for speed regulation and control of various motors. Their operating principle is as follows:

Rectification Stage: General-purpose inverters first convert the input three-phase or single-phase AC power into DC power through a rectifier circuit. Common rectifier circuits include diode rectifier bridges and thyristor rectifier bridges. Diode rectifier bridges offer advantages such as simple structure, low cost, and high reliability, making them suitable for applications with low power factor requirements. Thyristor rectifier bridges allow adjustment of DC output voltage by controlling the firing angle of the thyristors and are suitable for applications requiring variable DC voltage.

DC Link Stage: The rectified DC power then passes through a DC link for filtering and energy storage. The purpose of filtering is to smooth the DC voltage and reduce voltage ripple and fluctuations, providing a stable DC source for the subsequent inverter stage. Common filtering methods include capacitor filtering and inductor filtering. Capacitor filtering is suitable for low-power inverters, while inductor filtering is used for high-power inverters.

Inversion Stage: The inverter stage is the core part of a general-purpose inverter. It converts the DC voltage into variable-frequency and variable-voltage AC power to control motor speed and torque. The inverter circuit usually consists of bridge circuits using power semiconductor devices such as IGBTs. By controlling the switching on and off of the IGBTs, the frequency and voltage of the output AC power can be adjusted.