The basic working principle of the thyristor intermediate frequency power supply is to rectify the 50 Hz industrial frequency AC current into DC through a three-phase bridge rectifier circuit. Circuit diagra:

1. Rectifier circuit. From the circuit diagram, we can see that it is composed of six thyristors. This circuit is called a three-phase fully controlled rectifier bridge, commonly known as six-pulse rectifier. The working principle is to arrange the corresponding thyristors to turn on and off at the appropriate time according to certain rules, and ultimately convert three-phase alternating current into direct current.
2. Filtering. Since the rectified voltage fluctuates greatly, a larger inductor needs to be connected in series in the circuit to make the current flow more smoothly, which can make the voltage with larger fluctuations more smoothly. This is called filtering. This inductor is usually called a reactor. The characteristic of a reactor is to keep the current from changing suddenly. The smoother DC power after filtering is provided to the inverter circuit.
3. Conversion. The inverter circuit converts DC power into higher frequency AC power to supply the load, so this inverter is actually an AC-DC-AC converter. Its basic circuit is as shown in Figure 2
4. Series resonance It can be seen from the figure that there are two circuits. The simple way of saying that the compensation capacitor and the induction coil are connected in series is series resonance. This is what is usually referred to as a series furnace.
5. Parallel resonance. When the compensation capacitor and the induction coil are connected in parallel, it is called parallel resonance. Normally, Shennai furnaces are connected in parallel by default.
6. Working principle: How does the inverter circuit convert DC power into AC power? Assume that Q1Q4 is first allowed to conduct DC current through the induction coil and charge the capacitor at the same time. In the next cycle, Q2Q3 is turned on, which has two effects. The first is to cause the capacitor to discharge the induction coil in the reverse direction, and the second is to cause Q1Q4 to be charged in the reverse direction. Its shutdown is called forced shutdown. In this way, the induction coil is energized twice in a forward and reverse cycle, so the direct current is changed into alternating current.
7. Frequency. The natural frequency is determined by the capacitance of the capacitor and the inductance of the induction coil.