In off-grid areas, solar power systems must be cheap to assemble, highly efficient, and rugged enough to handle high temperatures and dust. This project covers the design of a synchronous buck Maximum Power Point Tracking (MPPT) controller designed to handle up to 800W of solar input, charging 12V or 24V battery banks.By pairing an ESP32 with synchronous rectification and a calibrated shunt-based current sensor, this design manages high-power conversion without the cost of premium Hall-effect sensors or dedicated power ICs.
Technical Implementation
Hardware & Topology
Synchronous Buck Converter: At 800W, a standard asynchronous buck converter (using a freewheeling diode) loses too much power to heat. Replacing the diode with a low R_DS(on) MOSFET (IRF3205, rated at 8 mΩ) reduced conduction loss significantly.
Microcontroller: An ESP32 serves as the central brain, handling analog-to-digital conversions, the tracking algorithm, safety checks, and remote telemetry.
Gate Drivers: I used the IR2104 half-bridge driver, which provides a hardware-enforced 520ns dead-time delay. This prevents shoot-through (both high-side and low-side MOSFETs turning on simultaneously), which would instantly destroy the power stage.
Low-Cost Current Sensing: Rather than using premium Hall-effect sensors, I used a low-resistance shunt resistor in the ground path.
Software & Firmware
Incremental Conductance (INC) Loop: The ESP32 processes high-frequency voltage and current samples. By comparing the incremental conductance (dI/dV) to the instantaneous conductance (I/V), the controller tracks the Maximum Power Point (MPP) during erratic weather.
ADC Calibration: The ESP32's built-in ADC is non-linear. To resolve this, I implemented 64x oversampling and a third-order polynomial correction curve to calibrate current and voltage readings against a bench multimeter.
Key Features
High-Current Synchronous Rectification: Reduces operating temperatures by over 25°C compared to diode-based buck converters.
Dynamic MPPT Tracking: Adapts to quick changes in irradiance caused by cloud cover.
Cost-Effective Design: Shunt-based sensing and an ESP32 keep the bill of materials low.
Reliable Safety Guards: Built-in over-voltage, over-current, and reverse polarity protection with hardware-enforced dead-time.
Challenges and Solutions
ESP32 ADC Non-linearity: The internal ADC is notoriously non-linear, especially near the rails. This was resolved by capturing data points across the operational spectrum and applying a custom polynomial correction in firmware.
Gate Timing: Early simulations showed potential shoot-through. Using the IR2104 gate driver solved this by enforcing a physical timing delay before switching states.
