Frequency converters adjust the voltage and frequency of the output power supply by switching their internal IGBTs, providing the required power voltage according to the actual needs of the motor, thereby achieving energy saving and speed regulation. In addition, frequency converters have many protection functions, such as overcurrent, overvoltage, and overload protection. With the continuous improvement of industrial automation, frequency converters have been widely used.
In AC-DC-AC inverters, based on the nature of the DC power supply during the process of converting the main circuit power supply into DC power supply, inverters are classified into voltage-source inverters and current-source inverters.
Working principle of AC-DC-AC frequency converter
The working principle of an AC-DC-AC inverter is to use microelectronic devices, power electronic devices and control technology to first rectify the power frequency power into DC power through diodes, and then use power electronic devices to invert the DC power into AC power with adjustable frequency.
An AC-DC-AC frequency converter consists of a main circuit (including a rectifier, an intermediate DC link, and an inverter) and a control circuit. The functions of each part are as follows:
1. A rectifier's function is to rectify three-phase (or single-phase) AC power into DC power. In SPWM frequency converters, full-wave rectifier circuits are mostly used. In most medium and small capacity frequency converters, uncontrolled rectifier diodes or diode modules are used as rectifier devices.
2. An inverter functions oppositely to a rectifier, converting direct current (DC) into alternating current (AC) with variable voltage and frequency to achieve variable frequency speed control for AC motors. Inverter circuits consist of switching devices, mostly employing a bridge circuit, often called an inverter bridge. In an SPWM inverter, the switching devices are controlled by the SPWM modulation signal in the control circuit, converting DC into three-phase AC.
3. Control Circuit This part of the circuit consists of arithmetic circuits, detection circuits, drive circuits, protection circuits, etc., and generally uses large-scale integrated circuits.
Currently, the vast majority of general-purpose frequency converters are AC-DC-AC type frequency converters, especially voltage converters, which are the core circuits of the frequency converter. They consist of a rectifier circuit (AC-DC switching), a DC filter circuit (energy consumption circuit), and an inverter circuit (DC-AC conversion). Of course, they also include current limiting circuits, braking circuits, control circuits, and other components.
