Theory & Background

Solar panel I-V curve: at short circuit → max current (Isc), at open circuit → max voltage (Voc). Maximum Power Point (MPP): point on curve where P = V × I is maximum. MPP changes with irradiance and temperature. MPPT algorithm continuously finds and tracks MPP. Perturb & Observe (P&O): perturb panel voltage by ΔV, observe power change. If P increased → continue perturbation direction. If P decreased → reverse direction. Simple, effective, widely used. Incremental Conductance (INC): uses dP/dV = 0 condition directly. More complex but faster tracking. Both achieve 99%+ MPPT efficiency in steady-state.

Components & Requirements

10 components required for this project.

#	Component	Purpose	Qty
1	STM32F3 MCU (ADC + op-amps)	MPPT algorithm and control	x1
2	SiC MOSFET (C2M0040120D, 1200V, 40A)	Synchronous buck switch	x2
3	Large ferrite inductor (100µH, 40A)	Buck converter energy storage	x1
4	INA228 (voltage + current monitor, 85V)	PV input and battery output measurement	x2
5	High-voltage gate driver (UCC27531)	MOSFET gate drive	x2
6	Solar panel (18V, 150W)	PV input source for testing	x1
7	Lead-acid or LiFePO4 battery (12V, 100Ah)	Energy storage target	x1
8	Temperature sensor (NTC, battery)	Temperature-compensated charging	x2
9	Hall effect current sensor (ACS758, 50A)	Battery charge current monitoring	x1
10	LCD 20×4 + RS485 Modbus	Display and remote monitoring	x1

Step-by-Step Implementation

Follow these 4 steps carefully.

1

MPPT Theory and Algorithms

Solar panel I-V curve: at short circuit → max current (Isc), at open circuit → max voltage (Voc). Maximum Power Point (MPP): point on curve where P = V × I is maximum. MPP changes with irradiance and temperature. MPPT algorithm continuously finds and tracks MPP. Perturb & Observe (P&O): perturb panel voltage by ΔV, observe power change. If P increased → continue perturbation direction. If P decreased → reverse direction. Simple, effective, widely used. Incremental Conductance (INC): uses dP/dV = 0 condition directly. More complex but faster tracking. Both achieve 99%+ MPPT efficiency in steady-state.

2

Buck Converter Design

Synchronous buck: high-side MOSFET switches solar panel voltage. Low-side MOSFET conducts when high-side is OFF (replaces diode, higher efficiency). Duty cycle D = V_bat / V_pv. At 18V PV, 14.4V battery: D = 14.4/18 = 80%. Inductor selection: ΔiL = V_pv × D × (1-D) / (Fsw × L). Target ΔiL = 10% of I_avg (ripple current). At 40A × 10% = 4A ripple. L = 18 × 0.8 × 0.2 / (100kHz × 4A) = 7.2µH. Use larger value (100µH) for better current ripple. Switching frequency 100 kHz: SiC MOSFET enables high frequency with low switching losses.

3

Multi-Stage Battery Charging (CC/CV/Float)

Stage 1 — Bulk (CC mode): charge at maximum current (limited by converter rating). Battery voltage rises. Duration: 70–80% of capacity. Stage 2 — Absorption (CV mode): when battery reaches absorb voltage (14.4V for 12V lead-acid, 54.6V for 48V), hold voltage constant. Current tapers as battery charges. Duration: 1–3 hours. Stage 3 — Float: reduce to float voltage (13.6V, 54.4V for LFP). Maintains full charge without overcharging. Temperature compensation: reduce absorb voltage by 3–5mV per cell per °C above 25°C (lead-acid). LiFePO4: CC to 14.6V (3.65V/cell × 4), then CV until current < 1%C.

4

Efficiency Optimization

Loss components: MOSFET conduction loss (I²×Rds_on), switching loss (½×C_oss×V²×Fsw × I × tr,tf), inductor core loss, inductor copper loss (I²×R_winding). Target: >97% peak efficiency. Optimize: SiC MOSFETs have lower switching losses vs Si at high frequency. Synchronous rectification: replace diode with low-Rds MOSFET (SiC, Rds=3mΩ vs diode 0.6V drop). Snubber: RC snubber absorbs switching spikes. Dead time: optimize dead time to minimize body diode conduction (diode has higher forward voltage than MOSFET). Measure: efficiency = P_out / P_in = (V_bat × I_bat) / (V_pv × I_pv).

Code & Implementation

Core code for mppt_algorithm.c:

mppt_algorithm.c
  C

// MPPT Perturb & Observe Algorithm // Runs every 100ms on STM32F3  #include "ina228.h"  typedef struct {     float V_pv, I_pv, P_pv;  // PV measurements     float V_bat, I_bat;        // Battery measurements     float V_ref;               // Duty cycle voltage reference     float dV;                  // Perturbation step     float P_prev;              // Previous power } MPPT_State;  MPPT_State mppt = {.V_ref = 15.0f, .dV = 0.2f};  void mppt_update(void) {     // Read PV input measurements     INA228_ReadAll(PV_SENSOR, &mppt.V_pv, &mppt.I_pv);     mppt.P_pv = mppt.V_pv * mppt.I_pv;      // P&O Algorithm     float dP = mppt.P_pv - mppt.P_prev;      if(dP > 0.5f) {           // Power increased: continue perturbing         mppt.V_ref += mppt.dV;     } else if(dP < -0.5f) {   // Power decreased: reverse direction         mppt.V_ref -= mppt.dV;     }     // If |dP| < 0.5W: near MPP, no action (reduces oscillation)      // Battery voltage limits     float V_charge_limit = get_charge_voltage_setpoint(); // Stage-dependent     INA228_ReadAll(BAT_SENSOR, &mppt.V_bat, &mppt.I_bat);      if(mppt.V_bat >= V_charge_limit) {         // CV mode: hold battery voltage, let current taper         mppt.V_ref = mppt.V_bat;     }      // Clamp reference within physical limits     mppt.V_ref = fmaxf(mppt.V_bat + 1.0f,           // Must be above battery                        fminf(mppt.V_pv * 0.95f, mppt.V_ref)); // Below PV Voc      // Update duty cycle: D = V_bat / V_ref_pv     float D = mppt.V_bat / mppt.V_ref;     D = fmaxf(0.1f, fminf(0.95f, D));     set_pwm_duty(D);      mppt.P_prev = mppt.P_pv; }

Testing & Troubleshooting

Test MPPT Solar Charge Controller by verifying each subsystem individually before full integration.

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Troubleshooting Tips

Verify power voltages, check ground connections, use serial monitor for debug.

Real-World Applications

*Off-grid solar power system

*Solar-powered remote IoT station

*RV and marine solar charging

*Solar street light system

*Agricultural solar pumping system

*Emergency power backup with solar

*Telecoms tower solar power

*Electric vehicle solar range extension

Extensions & Next Steps

Add grid-tie inverter for net metering (requires MPPT → inverter integration)
Implement EIS (Electrochemical Impedance Spectroscopy) for battery health
Add weather prediction for predictive load management
Build a remote monitoring dashboard via GPRS/4G
Implement multiple PV string optimization with per-string MPPT

Interactive Playground

Coming Soon

An interactive simulator will be available here — simulate circuits and run code in-browser without hardware.

Frequently Asked Questions

What is MPPT efficiency and how much energy does it save over PWM controllers?

PWM solar charge controller: simple on/off switching, directly connects panel to battery at battery voltage. Panel operates at battery voltage (not optimal MPP). In cool morning conditions with 21V panel and 12.5V battery: panel operates at 12.5V instead of 17V MPP → only 60–70% of available power extracted. MPPT controller: DC-DC converter allows panel to operate at MPP voltage (17V) while charging 12V battery. MPPT efficiency: typically 93–98%. Energy gain: MPPT vs PWM: 10–30% more energy daily depending on conditions. Greatest difference: in low irradiance conditions (morning/evening/cloudy) when MPP voltage differs most from battery voltage.

Introduction