DESIGN AND CONSTRUCTION OF 1.5 KVA INVERTER

CHAPTER ONE

1.1. INTRODUCTION

Currently almost all the inverters available in the market use the PWM (Pulse Width Modulation) technology. PWM based inverters are superior in many ways compared to the inverters based on traditional technology. PWM based inverters use MOSFET devices in-its output section. So, these inverters are also known as PWM MOSFET inverter. These PWM MOSFET inverters contain many protection circuits to protect the inverter, inverter battery, load at the inverter output and the user from various fault conditions. Some of the special control/protection circuits used in the PWM MOSFET inverter are:

• Battery charging current sensing circuit

• Battery voltage sensing circuit

• AC mains sensing circuit

• Soft start circuit

• Low battery cut circuit.

·        Changeover circuit

• Overload protection circuit o Shutdown section

• PWM section to regulate output supply.

Other than these protection/control circuits, the PWM MOSFET inverters contain the following sections 

·        Oscillator Section

• Driver ‘Section  

• Output Section

• Battery Charging Section

1.2. BACKGROUNG OF STUDY

This is a fully automatic PWM technology based inverter, which provides very good performance. PWM or Pulse Width Modulationis mainly used to keep the AC supply output by the inverter to a constant 220V. In an ordinary inverter, the inverter output changes with any change in the value of the load connected at the inverter output. To solve this problem the PWM based inverter correct the output value based on the value of the load connected at the inverter output socket. In the PWM inverter this is done by changing the width of the switching frequency generated by the oscillator. In a PWM based inverter, the AC supply at the inverter output depends on the width of the oscillator frequency generated by the oscillator section.

In this inverter, a small part of the inverter output is given as reference voltage to the PWM controller 1C. Based on this reference voltage, the PWM section will increase “or reduce the width of the oscillation pulse generated by oscillator section. This change in the width will compensate any change in the inverter output, and the inverter output will always stay constant, even if there is any change in the load at the inverter output. When the inverter comes into AC mains mode, from the battery off mode, i.e. When the AC mains return after a power cut, the battery charging does not start immediately. It starts after a delay of about 8-10 seconds. – This is done to protect the MOSFET at the output section. If the charging is started immediacy, when the AC mains return, the MOSFET at the output section will receive high current and could get damaged.

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