Frequency converters can be divided into AC-AC type and AC-DC-AC type according to frequency conversion methods. AC-AC type frequency converters can directly convert power frequency AC power into AC that can be controlled by both frequency and voltage, so they are called direct frequency converters. Today, we will talk about AC-AC frequency converters.
Working principle of AC frequency converter
The working principle of AC frequency converter is to directly generate the required variable voltage and frequency power supply through several sets of phase controlled switches to control the three-phase power supply. Its advantages are high efficiency, and energy can be easily returned to the grid. Its biggest disadvantage is that the maximum output frequency must be less than 1/3 or 1/2 of the input power frequency, otherwise the output waveform is too poor, the motor will shake, and it cannot work. The traditional AC frequency converter is still limited to low speed speed regulation applications, which greatly limits its range of use.
Characteristics of AC frequency converters
AC-AC frequency converter refers to a converter without a DC intermediate link, which directly converts a higher fixed frequency voltage into a lower frequency and is a variable output voltage. The characteristics of this type of frequency converter include:
Firstly, because it is a direct conversion, it has higher efficiency than ordinary frequency converters;
Secondly, due to the fact that its AC output voltage is directly composed of certain parts 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;
Thirdly, the frequency converter can naturally commutation according to the zero crossing voltage of the power grid, and ordinary thyristors can be used;
Fourthly, due to the characteristics of the circuit composition, a large number of thyristor components are used; Fifth, the power factor is relatively low, especially during low-speed operation, and requires appropriate compensation.
Given the above characteristics, AC-AC frequency converters are particularly suitable for high-capacity low-speed transmission and have broad application prospects in steel rolling, cement, traction, and other fields.