Power supply for induction heating

The induction heating process is put into effect through an inductor with high current flowing in its winding. The part to be heated is placed in the inductor magnetic field and can be represented by an equivalent transformer secondary shorted one-turn winding, the inductor being the primary winding of this transformer. The inductor is often powered by a resonance converter fed from the mains through a rectifier. The rectifier (e.g. six-pulse diode bridge), and the smoothing capacitor at its output results in a distortion of the current consumed from the mains(that is its non-linear harmonic distortion coefficient increase) and in the reduction of the induction heating converter power factor. To reduce non-linear harmonic distortion coefficient of the input current, power supplies are used in conjunction with passive harmonic filters or with parallel active power filters. Due to the introduction of the standards normalizing the emission of high-order harmonic currents by technical means, the task of creating power supplies with high power factor and with minimal distortion of input currents is becoming relevant. The article proposes a circuit solution of power supply for induction heating. The de-signed power supply is powered from a three-phase mains and has a small distortion of the input current wave shape. A characteristic feature of the power supply is the use of direct conversion of a three-phase mains voltage into a high frequency voltage, which is then used for «pumping» the output resonant circuit with the inductor. The power part of the proposed converter consists of six identical semiconductor diode-transistor switches – two per a phase. Converter control system ensures the formation of the mains currents so that they are proportional to the corresponding instantaneous phase voltages. Thus, the designed power supply presents a symmetrical and purely active load in relation to the mains