Parallel resonant inverter with a parallel resonant load. A current source is usually required to supply power. In induction heating, the current source is usually composed of a large inductance of the rectifier. Due to the large inductance value, it can be approximated that the current at the input of the inverter is fixed. By alternately turning on and off the controllable device on the inverter, an alternating square wave current can be obtained at the output of the inverter. The magnitude of the current depends on the current value of the input of the inverter, and the frequency depends on the device. On-off level. As shown in Fig. 2.4 , an inverter in which a compensation capacitor and a load coil (L and R) are connected in parallel as a load of an inverter bridge is called a parallel resonant inverter. The large inductance Ld is connected in series with the DC power supply in the parallel inverter , so the load current is constant and is not affected by the change of the load impedance. When the load power factor is not 1 , the reactive voltage component of the load is applied to the switching device. In order to prevent the IGBT from being damaged by the reverse voltage, a fast diode must be connected in series with the IGBT . Even with the IGBT module, the IGBT does not withstand the reverse voltage because it has an anti-parallel fast diode inside . The series fast diode cannot be cancelled, otherwise the device will be damaged by the circulating current caused by the reverse voltage. According to the load tank voltage and current phase relationship, the parallel inverter may work in three working states: resonant, inductive and capacitive states [22] due to the presence of large inductance Ld , in order to keep the current continuous, during the commutation process, Lower arm IGBT The principle of first turn-off and turn-off must be observed, that is, there should be an overlap time rt . The length of the commutation overlap time is closely related to the inverter output wiring inductance. The larger the inductance, the longer the time.