Energy feedback unit suppliers remind you that with the advancement of the industrial era, variable frequency speed regulation technology has become an important development direction of modern power transmission technology. As the core of the variable frequency speed regulation system, the performance of the frequency converter is increasingly becoming the determining factor of the speed regulation performance. In addition to the "innate" conditions of the manufacturing process of the frequency converter itself, the control method adopted for the frequency converter is also very important.
Classification of frequency converters
1. Classified by the nature of DC power supply:
a. Current type frequency converter The characteristic of current type frequency converter is that a large inductor is used as the energy storage link in the middle DC link to buffer reactive power, that is, to suppress the change of current and make the voltage close to a sine wave. Due to the high internal resistance of this DC link, it is called current source type frequency converter (current type). The characteristic (advantage) of current type frequency converter is that it can suppress frequent and rapid changes in load current. Often used in situations where the load current changes significantly;
b. Voltage type frequency converter The characteristic of a voltage type frequency converter is that the energy storage element in the middle DC link uses a large capacitor, which buffers the reactive power of the load. The DC voltage is relatively stable, and the internal resistance of the DC power supply is small, equivalent to a voltage source. Therefore, it is called a voltage type frequency converter and is often used in situations where the load voltage changes greatly.
2. Classified by the working mode of the main circuit:
a. Voltage type frequency converter. In a voltage type frequency converter, the rectifier circuit or chopper circuit generates the DC voltage required by the inverter circuit, and outputs it after smoothing through the capacitor of the DC intermediate circuit; The rectifier circuit and the DC intermediate circuit serve as DC voltage sources. The DC voltage output by the voltage source is converted into an AC voltage with the required frequency in the inverter circuit;
b. Current type frequency converter. In a current type frequency converter, the rectifier circuit provides direct current and smooths the current through the reactance of the intermediate circuit before outputting it. The rectifier circuit and the DC intermediate circuit act as current sources, and the DC current output by the current source is converted into AC current with the required frequency in the inverter circuit, and distributed to each output phase as AC current to be provided to the motor.
3. Classified by switching force:
a. PAM control. PAM control, short for Pulse Amplitude Modulation control, is a control method that controls the amplitude of the output voltage (current) in the rectifier circuit and the output frequency in the inverter circuit;
b. PWM control. PWM control, short for Pulse Width Modulation, is a control method that simultaneously controls the amplitude and frequency of the output voltage (current) in the inverter circuit;
c. High carrier frequency PWM control. This control method is actually an improvement on the PWM control method in principle, and is a control method adopted to reduce the operating noise of the motor. In this control method, the carrier frequency is increased to a frequency that can be heard by the human ear (10-20kHz) or higher, thereby achieving the goal of reducing motor noise.
4. Classify by the stages of transformation:
a. It can be divided into AC-AC frequency converters. Directly converting power frequency AC into AC with adjustable frequency and voltage, also known as direct frequency converter;
b. AC-DC-AC frequency converter. It is a widely used universal frequency converter that first converts AC power frequency into DC through a rectifier, and then converts DC power into AC power with adjustable frequency and voltage. It is also known as an indirect frequency converter.