Analysis, design, and implementation of a fast on-load tap changing regulator

The on-load tap changing (OLTC) regulators have been widely used since the introduction of electric energy. They ensure a good regulation of the output voltage in presence of large variations of the input voltage with typical response time from 100 ms to several seconds. The continuous growth of power semiconductor devices, such as the insulated gate bipolar transistor, allows the development of fast OLTC regulators being able to fix other problems in the ac mains, like sags and flicker. This paper reports the analysis, design, and experimental implementation of a fast OLTC regulator, using a two-step commutation strategy and a demagnetizing auxiliary circuit. The control stage is DSP-based, ensuring flexibility in programming the control algorithms. The experimental results demonstrate that the fast OLTC is able to correct several disturbances of the ac mains besides the long duration variation in a time much lower than the one corresponding to the traditional regulators.