Design of a Microcontroller-Based Automatic Power Factor Correction Unit for Small Manufacturing Firms in Anambra State

Small manufacturing firms in Anambra State, South East Nigeria, incur heavy electricity billing penalties due to low power factor caused by inductive motor loads, yet they lack affordable automatic power factor correction infrastructure. This project designed a microcontroller-based automatic power factor correction unit for deployment at small industrial facilities. A voltage and current zero-crossing detection circuit was built around an ATmega2560 microcontroller to calculate real-time power factor from phase angle measurement. Based on the computed power factor, the system automatically switched capacitor banks (five stages of 5 kVAR each) via thyristors to compensate for lagging reactive power and improve the load power factor toward a target of 0.95 lagging. A 16x2 LCD displayed live power factor, reactive power, and active power readings. An RS-485 interface allowed Modbus-based monitoring integration with a supervisory PC. The system was tested on a resistive-inductive load bench simulating a 15 kVA inductive load. Pre-correction power factor measured 0.68 lagging; post-correction power factor reached 0.96 lagging. Reactive power reduction was 67.4 percent. Switching transient overvoltage was within safe limits at 1.15 times rated voltage. The correction unit achieved stable operation within 3 cycles after load change. The estimated monthly electricity bill reduction for a firm consuming 800 kWh at 0.68 power factor was 22.4 percent. The study recommends independent calibration of the zero-crossing detector to improve accuracy at low load conditions.

Keywords: power factor correction, microcontroller, reactive power, manufacturing, Anambra State