Solar Power Inverter design - Quick Reference guide

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Introduction

The aim of this article is to provide a quick reference guide to make a Solar Inverter for Residential use.

The Solar Inverter converts the Solar energy to Electrical energy which can be used to supply power to the Consumer Electronics.

It is an attractive alternative to conventional sources of energy for many reasons : it is safe, silent, non-polluting, renewable and highly modular.

Hardware Modules

The Solar Inverter includes the following hardware modules :

Solar Panels
DC to DC Converter
DC to AC Inverter
Microcontroller
Charge Controller
Batteries

Solar Inverter Block diagram

The Solar Panels are connected as Inputs to the System, they provide 36 Volts DC.

The DC-DC Converter is used to step up the DC voltage from 36 Volts to 400 Volts DC. The MPPT feature is used to extract maximum power under all environment conditions.

The DC-AC Inverter Converts the 400 Volts DC to 230 Volts AC to be used for home appliances.

The Battery Charger controller is used to charge the batteries for standby operation, the controller prevents the reverse current and protects the batteries.

Push Pull DC-DC Converter

Function : The Q1 and Q2 Transistors are switched alternatively using the PWM duty cycle and the transformer is used to step up the Voltage. V out = 2 x Vin x (N2/N1) x d.

N2/N1 is the secondary to primary windings ratio.

d is the duty cycle of the transformers.

Input : +36 Volts DC from the Solar panels, PWM control from the Microcontroller.

Output : +400 Volts DC.

DC-AC Inverter : Full bridge

Function : The full bridge inverter converts the 400 Volts DC input from the DC converter to 230 Volts AC output. It can be controlled by only 2 PWM channels from the Microcontroller which are used to control the switching MOSFET’s through the high voltage half bridge drivers. The Resistor R is used to sense overcurrent overvoltage conditions.

Inputs : +400 Volts DC, 2 x PWM channels

Output : 230 Volts AC

Battery Charge Controller

Function : A switch mode charger can be used for battery charge controller. It consists of a Rectifier, step down transformer and output filter. It can be controlled by an ASIC or a Microcontroller.

Inputs : 230 Volts AC, Logic Control

Output : DC Output to the Battery

Microcontroller Module

Function : The function of the MCU is to control all the modules by providing PWM function, Analog to Digital Conversion, Switching logic, MPPT function, fault sensing and prevention and user interface functions.