Single Phase Inverter

Overview

Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

DC power is unidirectional and flows in one direction, whereas, AC current alternates directions at a frequency of 50-60 Hz. Most common electronic devices are designed to run off of AC power; therefore an input DC source must be inverted to AC. Inverters convert DC voltage to AC through switching action that repeatedly flips the polarity of the input DC source at the output or load side for part of a switching period. A typical power inverter requires a stable DC power input, which is then switched repeatedly using mechanical or electromagnetic switches. The output can be a square-wave, sine-wave or a variation of a sine-wave, depending on circuit design and the user needs.

The objective of this experiment is to build and analyze the operation of DC/AC half-bridge inverters. Half-bridge inverters are the simplest form of DC/AC inverters, but are the building blocks for H-bridge, three-phase, and multi-level inverters. Square-wave switching is studied here for simplicity, but sinusoidal pulse width modulation (SPWM) and other modulation and switching schemes are typically used in DC/AC inverters.

Procedure

1. Switching Source Setup

Set two function generators with outputs as square-waves at 10 kHz frequency and 48% duty ratio.
1. The function generators should be synchronized so that their output signals are 180° out of phase.
2. The 2% dead time is used as 1% on each side of the square-wave output. Dead time prevents a shoot-through condition where both the upper and lower switches are conducting thus shorting the input DC supply.
Test that the function generators&

Results

It is expected from building this half-bridge inverter that the output voltage waveform is a square-wave with a maximum of V_dc/2 and a minimum of -V_dc/2 with some dead-time causing the output voltage to be zero for around 4% of the switching period.

Square-wave inverters have high total harmonic distortion (THD) and are rarely used in real applications, however, they are the building block

Application and Summary

Inverters are very common in interfacing clean energy sources, e,g, solar photovoltaics, fuel cells, wind turbines, as well as with energy storage systems, e.g. batteries, with the grid. They are essential in uninterruptable power supplies (UPS systems), in micro-grids with clean energy penetration, and in hybrid and electric transportation systems. Among the main applications of inverters is in motor drives where motor control can be provided by adjusting the inverter switching patterns to achieve desired speed and/or t