The structure of thyristor intermediate frequency circuit

Medium frequency power supply is a device that converts three-phase power frequency (50Hz) AC power into single-phase medium frequency AC power. Frequency conversion circuits can be divided into two categories: AC-AC frequency conversion circuits and AC-DC-AC frequency conversion circuits. The former is characterized by directly converting 50Hz AC power into intermediate frequency AC power with frequency f, without any DC intermediate links. The advantages of this frequency conversion circuit are high efficiency and complex circuitry, and it is currently rarely used. The characteristic of AC-DC-AC frequency conversion circuit is that it consists of an intermediate DC link, which is converted into DC electricity through a rectifier circuit, and then converted into AC electricity through an inverter circuit. It has a simple circuit, easy debugging, and high efficiency, and is currently widely used in China.

According to different combinations of inverter circuits and loads, induction heating can be divided into parallel variable frequency circuits, series variable frequency circuits, and series parallel variable frequency circuits. Now introduce the parallel variable frequency circuit

The three-phase bridge full wave rectification circuit rectifies the 50HZ power frequency into pulsating DC power, and the adjustable DC voltage Ud is used to regulate the load current. LD is a filtering reactance that separates the power frequency and intermediate frequency networks and filters the DC current into a flattened waveform. The inverter circuit is a single-phase bridge inverter circuit composed of 8 thyristors, which converts DC current into AC square wave intermediate frequency current and sends it to the load. The load circuit is composed of a furnace coil and an electric heating capacitor in parallel resonance. The output frequency of the inverter circuit is controlled by the oscillation frequency of the load circuit and operates slightly higher than the oscillation frequency of the load.

Parallel variable frequency circuits have particularly strong adaptability to loads and are currently the most widely used circuit, mainly used as power sources for intermediate frequency melting and heat transfer.