Introduction to the frequency converter
The frequency converter is mainly a power control device used to control the AC motor by changing the frequency of the motor’s operating power supply. It is mainly composed of rectifier, filter, inverter, braking unit, drive unit, detection unit and micro-processing unit. The inverter relies on the switching of the internal IGBT to adjust the voltage and frequency of the output power supply, and provides the required power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation. In addition, the inverter also has many protection functions. , such as overcurrent, overvoltage, overload protection, etc. With the continuous improvement of industrial automation, frequency converters have also been widely used.
Function of frequency converters
There are many ways to classify frequency converters. According to the working mode of the main circuit, they can be divided into voltage-type frequency converters and current-type frequency converters. Frequency converter; the voltage type is a frequency converter that converts the DC of the voltage source into AC, and the filter of the DC circuit is a capacitor. The current type is an inverter that converts DC from a current source into AC, and its DC loop filter is an inductor. The main circuit of the frequency converter is composed of three parts: a rectifier, a smoothing circuit and an inverter. The “rectifier” converts the industrial frequency power supply into DC power and absorbs the “smoothing” voltage pulsations generated by the converter and inverter. Loop.
1. Rectifier
Its function is to convert three-phase (or single-phase ) AC power is rectified into DC power. In SPWM inverters, full-wave rectification circuits are mostly used. In most medium and small-capacity inverters, the rectifier devices use uncontrollable rectifier diodes or diode modules.
2. Inverter
Its function is opposite to that of the rectifier. It is to invert DC power into AC power with variable voltage and frequency to achieve frequency conversion and speed regulation of AC motors. Inverter The transformer circuit is composed of switching devices, most of which use bridge circuits, often called inverter bridges. In SPWM inverters, the switching devices are controlled by the SPWM modulation signal in the control circuit and invert direct current into three-phase alternating current.
3. Control circuit
This part of the circuit consists of arithmetic circuits, detection circuits, drive circuits, protection circuits, etc., generally using large-scale integrated circuits.
The working principle of the frequency converter
We knowRoad, the synchronous speed expression of AC motor:
n=60 f (1-s)/p (1)
Where
n— ——The speed of the asynchronous motor;
f——The frequency of the asynchronous motor;
s——The slip rate of the motor;
p———— Number of motor pole pairs.
It can be seen from formula (1) that the rotation speed n is proportional to the frequency f. As long as the frequency f is changed, the rotation speed of the motor can be changed. When the frequency f changes in the range of 0 to 50Hz, the motor speed adjustment range Very wide. The frequency converter realizes speed regulation by changing the motor power frequency. It is an ideal high-efficiency and high-performance speed regulation method.
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