Two-transformer-series approach in developing a transistor based-AC voltage regulator for consumer-end applications

AC voltage regulators, an important family of power conditioners, are intended to reduce line-voltage fluctuations of AC mains at customer premises. Typical designs are based on automatic tap changers, motor-driven variacs, thyristor-based systems, ferro-resonant systems and solid-state versions. Solid-state regulators typically rely on high frequency switching, so have significant RFI/EMI problems, while ferro-resonant regulators are bulky, have high no-load power consumption and waveform defects. Thyristor-driven designs are light in weight, but also have waveform defects. Motor-driven variacs are slow-responding, while automatic tap changers create spikes. A linear design using an array of serially connected transistors was developed in late 1980's to address these issues, and to achieve rapid output response without requiring thyristors, high-frequency switching or mechanical systems [1], [2]. We have built on these ideas to develop an AC voltage regulator for consumer use, with a power output ranging from 500 to 3000 W. A multi-primary-winding transformer design was originally proposed, but was found to be uneconomical due to manufacturing costs. The simple approach is to combine two standard step-down transformers. The viability of this approach demonstrated with practical results for a scaled down prototype which can be scaled up to a full 230 V, 2 kVA commercial product. Energy efficiency is optimized by minimizing the losses in the transistor array.