Zero-cross switch control of AC resistive load with multi-cycle period delta-sigma modulator

An approach to adjust the feeding power to resistive electric heaters using zero-cross switching of the power line with 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. To manage this constraint of the switching sequence, the pulse sequence for the switch is determined with a period of several cycles of the line voltage with a criterion of the noise-shaping filter in the delta-sigma modulator. As a result, the quantization noise in the lower frequency region becomes lower than the case the switch is controlled with a unit of the line cycle.