Design of a Microcontroller-Based Automatic Voltage Regulator for Electrical Appliances in Nigerian Households

Voltage fluctuation from the Nigerian national grid causes significant damage to household electrical appliances, with overvoltage and undervoltage events particularly common in residential areas of states such as Kwara and Oyo. This project designed a microcontroller-based automatic voltage regulator for protecting household appliances rated up to 3 kVA. An ATmega328P microcontroller sampled mains voltage every 20 milliseconds using a precision voltage sensing circuit based on a step-down transformer and operational amplifier zero-crossing detector. Based on sampled voltage readings, the controller activated one of four relay-switched autotransformer boost or buck taps to bring the output voltage within the range of 210 to 230V. Time-delay relay logic prevented load connection until output voltage had stabilised for 3 seconds after mains power application. An LCD displayed input voltage, output voltage, and operating mode. The system was tested across 250 simulated voltage excursions ranging from 160V to 270V. Output regulation accuracy was within plus or minus 5V across all input conditions except for extreme spikes above 270V, where the system correctly isolated the load. Relay switching time averaged 42 milliseconds. No load voltage drop was 2.1V. Total component cost was 23,400 naira. The study recommends adding a built-in lightning surge arrester as a complementary protection measure and extending the input range handling to 150V to accommodate the more severe voltage sag conditions observed in rural supply networks in Kwara State.

Keywords: automatic voltage regulator, microcontroller, power quality, household protection, Nigerian grid