FPGA implementation of Unipolar SPWM for single phase inverter
Abstract—Nowadays, inverter which is also known as a DC-AC
converter is one of the most popular parts in electrical devices
that converts direct (DC) current to alternating current (AC) at
the desired output voltage and frequency. This project presents
development of a Unipolar Sinusoidal Pulse Width Modulation
(SPWM) for single phase full bridge inverter using Field
Programmable Logic Array (FPGA). The Unipolar SPWM is
employed to control the output voltage magnitude of the inverter.
Altera DE2-70 board with 16 bit serial configuration devices is
used as a controller for the implementation of the SPWM
inverter. Computation of the turn-on and turn-off times of the
SPWM is developed using Matlab. To verify the proposed FPGA
SPWM, voltage amplitude regulations are carried.
Keywords- Sinusoidal Pulse Width Modulation; Single Phase
Inverter; Field Programmable Logic Array
Inverters are commonly used to supply AC power fed from
DC sources such as solar panels or batteries. The most famous
technology that applies this electrical device is Uninterruptible
Power Supplies (UPS) . UPS electrical devices are used as
a battery back-up which provides emergency power when
utility power is unavailable. There are several types of
switching technique such as Single-Pulse Width Modulation,
Multiple-pulse Width Modulation (MPWM) and Sinusoidal
Pulse Width Modulation (SPWM).
In this project, Unipolar SPWM switching is used as a
switching technique. Circuitry of SPWM inverter is
constructed using IGBT (Integrated Gate Bipolar Transistor)
device that is commonly used due to several considerations
such as high power switching frequency and high power rating
This project presents the implementation of FPGA
technology in designing the SPWM switching signal through
Altera DE2-70 board. It provides a wide range of density,
memory, embedded multiplier, and packaging options in a
customer-defined FPGA feature set optimized for low-cost
applications. Besides that, it also supports a wide range of
common external memory interfaces and I/O protocols
common in low-cost applications. The use of FPGA will
produce better control signal phase of full bridge inverter .
The emergence of FPGA has drawn much attention due to its
shorter design cycle, lower cost and higher density .
Moreover, the use of FPGA can also solve several problem
that interface on source device such as less power
consumption, reduce size of circuit, easy to implement
because can easily changed using the program without any
changes in hardware, and flexibility of any changes on the
II. SINGLE PHASE SPWM-INVERTER
A. Inverter circuit operation.
An inverter operates the inverse process of a rectifier. The
input source of the inverters can be battery, fuel cell, solar cell
or other types of DC source. The output of the inverter has
square waveform due to the switching pattern. In order to
obtain a pure sine wave signal, the filter is used to reduce
harmonic content . The inverter is built from two half
bridge inverter which consists of four choppers . The
schematic diagram representation of a single phase full wave
inverter is shown in Fig. 1. The inverter consists of four
IGBT’s as switching devices connected in the form of a
Figure 1. Schematic diagram of single phase full-bridge inverter circuit.
B. Switching strategies.
There are various techniques to vary the inverter output
waveform. In SPWM method, the amplitude of the inverter
output voltage is determined by comparing a sinusoidal
reference (Vref) waveform with a triangular (Vtri) carrier
waveform, known as modulation index (ma). The amplitude of
the inverter output voltage proportion with ma, where the ma is
defined as (1),
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