Design and Simulation of Integral Cycle Control based Thyristor Controller for Power Quality Improvement

Natural uranium oxide fuel pellets are used for 220 MWe Pressurised Heavy Water Reactor. The virgin UO₂ powder is required to be converted into sintered pellets by processing through various operations. Sintering is the process by which a powder compact is heated below its melting point under suitable atmosphere for its densification. Sintering is carried out in multi zone electrically heated furnaces using resistance heating elements under reducing atmosphere of hydrogen/cracked ammonia. Presently, continuous pusher type furnaces are used for sintering of UO₂ fuel pellets. The capacity of furnaces are about 150-220 Metric Tonne with an electrical rating of 250 kW having sintering temperature of 1700° C. Prime criteria in operating furnace is to maintain specified temperature with bare minimum hysteresis which imposes requirement of precise current control. Hence furnace uses AC voltage controllers using phase angle control allowing the thyristors to conduct for part of the AC cycle drawing non-sinusoidal current from source deteriorating the power quality of mains. Considering the disadvantage of phase angle control technique, the paper proposes an integral cycle control topology for controlling the set temperature of sintering furnace. Integral cycle control considered in this paper is one of the able solutions to mitigate the harmonics in the power supply system to meet IEEE: 519-1992 standard. The paper presents the design and simulation of thyristor AC voltage controller based on integral cycle control technique for improving the power quality. The simulation results are also presented and discussed.