Fine power control by discontinuous phase-controlled switching

Different voltage control techniques are commonly used for heating power control. In the proposed method, the drawbacks of integral-cycle control and phase-controlled switching techniques are removed by combining them together. Step and fine voltage variations are achieved by the former and latter methods, respectively. Load resistance is replaced by several equivalent parallel resistances to eliminate subsynchronous harmonics completely, to reduce higher order harmonics significantly, and to bring power factor close to unity.