Modular Solar Grid Tie Inverter - MPPT Module

This is an analog solar MPPT function module meant for use in a modular solar grid-tie/on-grid inverter main board.

Eg. 1000W Main Board

Module implements analog perturb and observe method to find and track maximum power point of the connected solar array.

It uses a simplified analog multiplier to create a wattmeter. Wattmeter uses input voltage ripple created by the DC-DC or DC-AC power stages to scan the PV characteristic of the connected solar panels in real time. By sensing the phase of power change and the phase of the voltage change a simple XOR comparator can detect, if the power rises with voltage, falls with voltage or is optimal (maximum power point reached). XOR comparator switches a 250 uA CV signal sink on and off depeding on the phase difference.

CV signal is meant to be connected to the FB signal in the power inverter control module, and with its internal 150 uA pullup creates a +150 uA and -100 uA current source to charge or discharge the power integration capacitor on the FB network and increase or decrease the inverter output power to achieve optimal power extraction from the connected solar array.

Trimmer TR1 adjusts the Q3 mosfet threshold voltage compensation, and should be adjusted for maximum inverter output power. With proper adjustment the inverter then tracks the solar array MPP automatically even with changing conditions. Combination of Q4 and D4 and the resistor value ratios set the temperature compensation, which should be roughly correct for the 2N7000/2N7002 MOSFET at around -600 uV/°C.

Module is meant to be powered by fairly accurate 5V on the VCC input.

Module is designed for 150 V to 300 V solar array voltage range. Current sensing resistor is connected externally between GND and Isen signal. Voltage drop across the current sensing resistor at the nominal maximum solar array power, so the Impp current, should be roughly 500 mV. Eg. for Impp = 5 A, Rsen = 100 mOhms.