Power regulator for direct heating of material with inverse resistance-temperature properties
K. Rush, J.M. Rochelle, M.J. Kelly · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1981
An ac power regulator was designed for loads with inverse resistance-temperature properties. It is equipped with an integrated-circuit, analog multiplier for power computation. Its output power accuracy, achieved by automatic zero correction of the multiplier drift, is +-1% full scale over a range from 0 to 4 kW. Power is controlled by symmetrical phase firing of inverse-parallel SCRs; series inductance maintains loop stability when the load resistance is very low, reduces the current waveform crest factor, lowers the harmonic power content, inherently limits the load current, reduces the di/dt, and practically eliminates the rf noise often generated by phase-fired equipment. This report describes the design details for the current feedback, multiplier, error integrator, conduction angle control, and SCR firing circuits.