Adjustment of induction heating circuit and matching of loads

The total efficiency of the induction heating system, that is, the ratio of the power obtained on the workpiece to the total efficiency of the power input, is related to the following two factors: ⑴ The conversion efficiency of the power supply; ⑵ The tuning state of the induction heating circuit; ⑶ The effect of the heating load and coil on the power supply Matching state; (4) Coupling state between coil and workpiece. Among the above four related factors, the conversion efficiency of the power supply is closely related to the type of current converter. Generally speaking, solid-state oscillators have higher conversion efficiency, while vacuum tube RF oscillators have the lowest conversion efficiency.

Energy conversion between induction heating coil and power supply. The highest conversion efficiency can only be obtained when the heating load and heating coil are matched to the power supply, and the circuit containing such components is properly tuned. Load matching allows the induction generator to produce full rated power; circuit tuning ensures that this power is used for actual heating. In practical applications, it is better to tune the circuit first so that the power factor is equal to 1. Then, match the impedance of the coil to the work piece and the source impedance.

1. Adjustment of induction heating circuit

Most induction heating devices use an AC circuit called a "tank circuit." This tank circuit includes a capacitor and an inductor. Because both inductors and capacitors can store energy - just like troughs that store things, "trough circuits" get their name. Here, capacitors store electrical energy and inductors store magnetic energy. The oscillation tank circuit can be composed of a parallel circuit or a series circuit.

Tuning of the induction heating circuit usually refers to adjusting the capacitance and inductance in the oscillation tank circuit including the induction coil and the workpiece, so that the "resonant" frequency of the circuit is equal to or close to the frequency of the induction heating power supply.

2. Adjust the capacitor

In practical applications, capacitor banks are often used to adjust induction heating circuits so that the resonant frequency of the parallel circuit is close to the power frequency. There are two types of capacitor banks commonly used: one is oil-filled multi-connector capacitors, which are mainly used in situations where the frequency is lower than or equal to 1000hz; the other is ceramic capacitors or insulating solid capacitors. Try this kind of capacitor. Used in new devices with frequencies above 5000hz.

In inductive adiabatic heating, the role of the capacitor is to store energy. Therefore, its reactive power should be considered. In the induction heating furnace of the third frequency or medium frequency, it is often necessary to adjust the tap and select to use or connect a composite capacitor bank step by step to achieve a certain predetermined kva value. In high-frequency induction heating circuits, there is generally a fixed number of rated capacitors, and the capacity can be adjusted to reach a predetermined value by connecting or removing the capacitors during use.

Increasing the capacitance value of the resonant circuit will cause the resonant frequency to decrease, the capacitive reactance of the circuit and the total impedance of the circuit to decrease, and the current of the circuit to increase. Therefore, when adjusting the circuit and reducing the rating, it must be considered that the capacitor's current carrying capacity should be increased accordingly. Be sure to use the appropriate non-power rating at 1000hz frequency.