MPPT Solar Charge Controller using Buck Converter

Solar photovoltaic panels have a characteristic I-V curve with a single maximum power point (MPP) that shifts with irradiance and cell temperature. A panel connected directly to a battery is forced to operate at the battery voltage, which is rarely the MPP — on a cold bright morning the mismatch can waste a third or more of the available energy. Maximum power point tracking solves this with a DC-DC converter whose duty cycle is continuously adjusted to hold the panel at its MPP while delivering the right charging voltage to the battery. Commercial MPPT controllers do this with dedicated chips, but the algorithm is very teachable on a microcontroller. This project builds one from first principles: an Arduino measures panel voltage and current, runs the perturb-and-observe (P&O) algorithm, and drives a buck converter MOSFET stage, implementing a full 3-stage lead-acid charging profile with battery protection — a complete, demonstrable solar power-electronics build.

1. The solar panel feeds the buck converter input; voltage and current sensors (divider + Hall/ACS-type sensor) report panel V and I to the Arduino.
2. The firmware computes panel power (P = V × I) and runs the perturb-and-observe loop: it steps the PWM duty cycle, re-measures power, and keeps stepping in the direction that increases power.
3. The buck MOSFET, driven through a gate driver, converts the panel's MPP voltage down to the battery charging voltage at the commanded duty cycle.
4. A second voltage sense on the battery selects the charging stage: bulk delivers the full tracked current, absorption holds constant voltage, float maintains a trickle.
5. If the battery reaches full charge or the panel input disappears (night), charging stops and the blocking stage prevents reverse current.
6. The load output stays connected until battery voltage falls to the low-voltage cut-off, then disconnects and re-engages with hysteresis.
7. The LCD continuously shows panel V/I/P, battery voltage, active stage and duty cycle.

Tech stack:

• Arduino Uno/Nano (ATmega328P)
• Buck converter power stage (N-channel MOSFET, inductor, Schottky diode, capacitors)
• MOSFET gate driver
• Voltage dividers + Hall-effect current sensor (panel and battery sides)
• 16x2 character LCD
• Arduino IDE (C/C++ firmware)
• 12 V lead-acid battery and solar panel test rig

• [Perturb-and-observe MPPT] The firmware continuously nudges the buck duty cycle, compares panel power before and after, and climbs toward the maximum power point — the classic P&O algorithm, fully documented and tunable.
• [Buck converter power stage] A MOSFET buck stage with inductor, Schottky diode and output capacitors steps the panel voltage down to battery level at high switching frequency.
• [3-stage battery charging] Bulk (constant current), absorption (constant voltage) and float stages implement a proper lead-acid charging profile instead of crude on/off charging.
• [Live telemetry on LCD] Panel voltage, current and power plus battery voltage, charging stage and duty cycle are displayed on a 16x2 LCD, so the examiner can see tracking respond to shading the panel.
• [Load disconnect protection] The battery is disconnected from the load output at the low-voltage cut-off and reconnected with hysteresis, demonstrating deep-discharge protection.
• [Reverse and blocking protection] A blocking diode/MOSFET arrangement prevents night-time battery discharge back through the panel.
• [Adjustable setpoints] Absorption voltage, float voltage and cut-off thresholds are firmware constants, adjustable for different battery chemistries during the student's own setup.

• Working MPPT charge controller prototype (Arduino, buck stage, sensors, LCD, panel/battery test rig)
• Complete firmware source code (P&O tracking, 3-stage charging, protections, LCD)
• Circuit and wiring documentation with inductor/capacitor selection notes
• Component list with ratings
• Tuning procedure (buyer-run: set absorption/float voltages, verify tracking with shading tests)
• Project report PDF (PV characteristics, MPPT theory, buck design, methodology, test procedure)
• PPT presentation for final review
• Viva Q&A preparation document (MPP, P&O vs incremental conductance, buck operation, charging stages)
• Setup and demonstration guide

• This is an academic demonstration prototype sized for a small test panel and battery; it is not a substitute for a rated commercial charge controller.
• Converter efficiency and tracking accuracy are design targets verified by the buyer's own tests — the prototype ships untuned and final values depend on the panel, inductor and layout used.
• The P&O algorithm oscillates slightly around the MPP and can be confused by very fast irradiance changes; this behavior is documented as a teaching point, not a defect fix.
• Lead-acid profile by default; lithium charging needs different setpoints and a proper BMS, noted as an extension.
• High-current paths need adequately rated wiring and the MOSFET needs heatsinking — thermal notes are included.