In our daily lives, most electronic products use switching power supplies or other rectifier circuits to convert 110V or 220V AC power to DC. Inverting is the process of converting DC to AC, a process that is the inverse of the rectifier's conversion, hence the name "inverter."

Inverters bring many conveniences to our lives. For example, outdoor barbecues, outdoor lighting, and car refrigerators all use inverters to convert DC power from batteries into AC power. Let's learn about the basic working principles of an inverter.

How does an inverter work?

Working Principle

The four switches S1 through S4 form two bridge arms, with S1 and S2 sharing one arm and S3 and S4 sharing the other. When S1 and S4 are connected and S2 and S3 are disconnected, Uo = Ud across their load resistors. Conversely, when S2 and S3 are connected and S1 and S4 are disconnected, Uo = -Ud across the load resistors. By continuously operating the switches like this, an AC waveform is generated at the load, thus completing the DC to AC conversion process.

It is important to note that switches in the same bridge arm cannot be connected simultaneously to prevent a power short circuit. The frequency of the AC power can be varied by varying the switching frequency. In fact, the four switches in the diagram above are ideal models of various semiconductor switching devices. Common semiconductor switching devices used in inverters include thyristors, field-effect transistors, and insulated-gate bipolar transistors (IGBTs).

The circuit's switching devices consist of N-channel field-effect transistors and P-channel enhancement-mode field-effect transistors, forming a push-pull output. The P-channel field-effect transistor operates when the drive signal is low (L), and the N-channel field-effect transistor operates when the input signal is high (H). This alternating conduction pattern avoids the risk of short circuits caused by simultaneous conduction of two switches in the same bridge arm.

The operating process is as follows: FETs TR3 and TR4 are connected to one bridge arm, while TR5 and TR6 are connected to another. The four switches, controlled by pulse signals, conduct and close, generating an alternating signal that is applied to the transformer's low-voltage winding.

Conclusion

The above is just the basic operating principle of an inverter. In practice, inverter applications are far more complex. An inverter consists entirely of a main circuit, a control circuit, a drive circuit, and an auxiliary power supply.

Main Circuit

The main circuit includes the various switching circuits that perform inversion. It primarily consists of a DC power supply (capacitor), a buffer, a switching bridge circuit, a filter, and a transformer, which handles energy level processing.

Drive Circuit

According to the switching signals from the control board, it drives and ensures the reliable switching of switching devices such as field-effect transistors.

Control Circuit

Collects feedback from the main circuit, implements control algorithms and protection strategies, and generates switching signals.

Auxiliary Circuit

Auxiliary power supplies and circuits for the control and driver chips.

In short, an inverter is a device that converts DC power into AC power.