Inverters are classified into AC-AC inverters and AC-DC-AC inverters according to the frequency conversion method. AC-AC inverters can directly convert industrial frequency AC power into AC power with controllable frequency and voltage, hence the name direct inverter. Today we will talk about AC-AC inverters.
Working principle of AC inverter
The working principle of an AC-AC frequency converter is to directly generate the required voltage and frequency power from a three-phase mains frequency power supply through several sets of phase-controlled switches. Its advantages are high efficiency and easy energy return to the grid. Its biggest drawback is that the highest output frequency must be less than 1/3 or 1/2 of the input power frequency; otherwise, the output waveform will be too poor, causing motor vibration and preventing operation. Therefore, AC-AC frequency converters are currently limited to low-speed speed control applications, thus greatly restricting their application range.
Features of AC-AC inverters
An AC-AC inverter is a converter that directly transforms a higher, fixed-frequency voltage into a lower, variable-frequency voltage without a DC intermediate link. The characteristics of this type of inverter include:
First, because it is a direct conversion, it has higher efficiency than a regular frequency converter;
Secondly, since its AC output voltage is directly composed of a portion of the envelope of the AC input voltage wave, the output waveform is better when the output frequency is much lower than the frequency of the input AC power supply.
Third, the frequency converter uses ordinary thyristors for natural commutation based on the grid voltage zero crossing;
Fourth, due to the characteristics of the circuit configuration, a large number of thyristor components are used; fifth, the power factor is low, especially at low speeds, requiring appropriate compensation.
Given the above characteristics, AC-AC frequency converters are particularly suitable for large-capacity low-speed transmissions and have broad application prospects in steel rolling, cement, traction and other fields.
