Rapid zero-cross switch control of AC resistive load with deep delta-sigma modulator

An improved approach to adjust the feeding power to resistive electric heaters using zero-cross switching of the power line with a delta-sigma modulator is proposed. The switch is on or off with a unit of a half cycle of the power line suppressing low frequency components of the load voltage to prevent the transformer saturation. The delta-sigma modulator operates at a control period equal to the half cycle for rapid control allowing deep modulation. To realize these features, the pulse sequence for the switch is calculated over several cycles of the line voltage with a criterion of the noise-shaping filter in the delta-sigma modulator but the first element of the sequence is used at each half cycle.