Structure of Thyristor Intermediate Frequency Circuit
Structure of Thyristor Intermediate Frequency Circuit
An intermediate frequency power supply is a device that converts three-phase power frequency (50Hz) AC power into single-phase intermediate frequency AC power. Frequency converter circuits can be divided into two main categories: AC-AC converter circuits and AC-DC-AC converter circuits. The former directly converts 50Hz power frequency AC power into intermediate frequency AC power at frequency f, without a DC intermediate link. This type of converter circuit has the advantages of high efficiency but is complex and is rarely used currently. The AC-DC-AC converter circuit uses an intermediate DC link, rectifies it into DC power, and then converts it back to AC power through an inverter circuit. It has the advantages of simple circuit, convenient 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 converter circuits, series converter circuits, and series-parallel converter circuits. Parallel converter circuits are introduced below.
A three-phase bridge full-wave rectifier circuit rectifies the 50Hz power frequency into pulsating DC power. The adjustable DC voltage Ud can be used to regulate the load current. The LD (Low-Inductance Filter) is a filter reactance that separates the power frequency and intermediate frequency networks and flattens the DC current waveform. The inverter circuit is a single-phase bridge inverter circuit composed of eight thyristors, which converts the DC current into an AC square wave intermediate frequency current and supplies it to the load. The load circuit consists of a furnace coil and a heating capacitor forming a parallel resonant circuit. The output frequency of the inverter circuit is controlled by the oscillation frequency of the load circuit and operates slightly higher than the load oscillation frequency.
Parallel frequency converter circuits have particularly strong load adaptability and are currently the most widely used type of circuit, mainly used as power supplies for intermediate frequency melting and through-heating.
