Inverter Introduction and Principle

The inverter converts DC power (battery, storage bottle) into AC power (usually 220v50HZ sine or square wave). Emergency power supply generally converts DC battery into 220V AC. In layman's terms, the inverter is a device that converts direct current (DC) into alternating current (AC). It consists of an inverter bridge, control logic and filter circuit. It is widely used in air conditioners, home theaters, electric grinding wheels, power tools, sewing machines, DVDs, VCDs, computers, televisions, washing machines, range hoods, refrigerators, video recorders, massagers, fans, lighting, etc.

The reverse process of converting direct current into alternating current using a thyristor circuit is defined as inversion. For example, when an electric locomotive using thyristors is running downhill, the DC motor is used as a generator for braking, and the potential energy of the locomotive is converted into electrical energy and sent back to the AC power grid. Another example is that if a running DC motor is to be braked quickly, the motor can also be operated as a generator, converting the kinetic energy of the motor into electrical energy and sending it back to the power grid.

The circuit that converts direct current into alternating current is called an inverter circuit. In certain situations, the same set of thyristor converter circuits can be used for both rectification and inversion. When the converter is working in the inverter state, it is simple to connect the AC side of the converter to the AC circuit, but the harmonic content of the output voltage waveform is too large, that is, the THD (current harmonic distortion rate) is too large; the harmonic content of the output voltage waveform of the phase-shifted multiple superposition inverter power supply is small, that is, the THD is small, but the circuit is more complicated. The PWM pulse width modulation inverter power supply has both computer circuits and output voltage waveforms, so it has been widely used.

The so-called PWM (Pulse Width Modulation) technology uses a reference wave (usually a sine wave, sometimes a trapezoidal wave or a sine wave or square wave injected with zero-sequence harmonics, etc.) as the modulating wave, and a triangular wave (sometimes a sawtooth wave) with N times the frequency of the modulating wave as the carrier wave for waveform comparison. A set of rectangular pulse sequences with equal amplitude and width proportional to the modulating wave are generated in the part where the modulating wave is larger than the carrier wave to equal the modulating wave, replacing the analog quantity with the switching quantity, and converting direct current into alternating current by controlling the on/off of the inverter power switch tube. This technology is called pulse width controlled inverter technology.

Since the up and down width of the carrier triangle wave (or sawtooth wave) changes linearly, this technology is called pulse width control inverter technology. Since the up and down width of the carrier triangle wave (or sawtooth wave) changes linearly, this modulation method is also linear. When the modulating wave is a sine wave, the pulse width of the output rectangular pulse sequence changes according to the sine law. This modulation technology is usually called sinusoidal pulse width modulation (Sinusoida PWM) technology.