Voltage Regulation Innovation for Photovoltaic DC Bus Using RLS-PZC-Based Autotuning PID with Output Scaler and Discharge Path

Output voltage of photovoltaic DC bus tends to fluctuate with environment and load dynamics. To prevent undervoltage or overvoltage that may disrupt load operation, a voltage regulator is required. This article proposes a new voltage regulator using a buck converter and RLS-PZC-based autotuning PID with output scaler and discharge path. The research contribution includes minimizing voltage fluctuation and maintaining the transient response characteristic. Periodically, RLS (Recursive Least Squares) identifies the buck converter's transfer function by processing its input-output signals, and then PZC (Pole Zero Cancellation) uses the RLS result to update PID parameters in producing an overshoot-free DC bus voltage that settles in a specified duration. To prevent the output from fluctuating due to input voltage variation, the input voltage is read by a sensor, and the output scaler uses the reading to adjust the PID output in keeping forward path gain at a particular value. A discharge path is activated during negative PID output to further reduce spikes caused by load shedding. The proposed method is simpler and deterministic, unlike metaheuristic approaches. It is implemented in a Matlab script and C program code running on an 8-bit 16-MHz microcontroller in a Proteus simulation. Results show that RLS-PZC can identify load changes and retune PID parameters in 40.2 ms. The output fluctuation due to input voltage variation can be significantly reduced by the output scaler, where its ITAE (Integral of Time-weighted Absolute Error) is only 9.27% of regular PID. Employing a discharge path can improve voltage regulation by reducing the regular PID spikes up to 73.6% when a 5-ohm load is shed from a 50-ohm default load.