OBJECTIVE:
Practice single-phase full bridge inverter circuit and duplicate the text book concepts related to
the performance of bridge inverter circuit.
Components Required:
• 555 Timer IC (1)
• 741 IC (1)
• Diode (2) – 1N4001--7
• Potentiometer – 100 k Ω
• Resistor (1) – 10 k Ω, 1 k Ω,
• Capacitor (2) –0.01µF
• Capacitor (1) – 1µF
• BJT (4) – 2N2222A
• Breadboard
INTRODUCTION:
The inverter is an electrical device that converts DC input supply to symmetric AC voltage of
standard magnitude and frequency at the output side. It is also named as DC to AC converter.
An ideal inverter input and output can be represented either in a sinusoidal and non-sinusoidal
waveform. Inverters are classified into 2 types according to the type of load being used i.e.
single-phase inverters, and three-phase inverters. Single-phase inverters are further classified
into 2 types of half-bridge inverter and full-bridge inverter.
SINGLE-PHASE BRIDGE INVERTER:
A single-phase full bridge inverter is a switching device that generates a square wave AC voltage
in the output on the application of DC voltage in the input by adjusting the switch ON and OFF.
The voltage in the output of a full bridge inverter is either -VDC, +VDC or 0.
Classification of Inverters
Inverters are classified into
➢ According to the output characteristics
• Square wave inverter
• Sine wave inverter
• Modified sine wave inverter.
➢ According to the source of the inverter
• Current source inverter
• Voltage source inverter
➢ According to the type of load
Single-phase inverter
• Half-bridge inverter
• Full bridge inverter
Three-phase inverters
• 180-degree mode
• 120-degree mode
Construction:
The single-phase full bridge inverter is built using a 555 timer, a gate driver circuit, and four
MOSFETs or BJTs in an H-bridge configuration. The 555 timer, configured in astable mode,
generates a continuous square wave signal. This signal is fed into the gate driver circuit, which
amplifies it to drive the MOSFETs/BJTs. The H-bridge consists of four switches (T1, T2, T3, T4)
connected to a DC power source. The load is connected across the bridge's midpoints.
In the first half-cycle, T1 and T4 are turned on, allowing current to flow in one direction through
the load, generating a positive AC half-cycle. In the second half-cycle, T2 and T3 are turned on,
reversing the current flow, producing a negative AC half-cycle. This alternating switching
produces an AC output from the DC input. Filtering circuits can be added to smooth the output
waveform.
Figure 1: Single Phase Full bridge inverter with R Load
Working of Single-Phase Full Bridge Inverter:
The "H-bridge" arrangement of four switching devices (transistors, IGBTs, MOSFETs, or
thyristors) and four feedback diodes used in a full-bridge inverter topology. In comparison to
the half-bridge architecture, this topology provides a larger output voltage capability. Full-
bridge inverters offer improved performance and are often used in many single-phase inverter
applications, including motor drives, solar inverters, and UPS systems, despite having a larger
component count and complexity.
The load in a full-bridge inverter may be resistive (R) or resistive and inductive (RL). An R load's
current waveform and output voltage waveform are the same. However, due to the inductive
nature of load, the current waveform for an RL load is phase-shifted to the voltage waveform.
The power factor of the load affects the phase shift's magnitude.
Operation with R Load:
Full Bridge Inverter Gate Signals and Output Voltage for R Load
The output voltage as well as the inverter gating signals are displayed. It may be readily shown
that the fundamental component of the output has an RMS value.
For a Single Phase Full-bridge inverter with R load, the two primary modes of operation are:
Mode 1 of Full Bridge Inverter with R Load
Mode 1 for R load in a full bridge inverter. The output voltage is equal to the DC source voltage
when the upper-left switch (T1) and lower-right switch (T2) are turned ON, and the upper-right
switch (T3) and lower-left switch (T4) are turned OFF. Current flows through the load, the
upper-left switch (T1), and the lower-right switch (T2).
Across the load, the output voltage is
Vo=Vdc
Similarly, the output current is
Vo/RL
Mode 2 of Full Bridge Inverter with R Load
Mode 2 for R load in a full bridge inverter. The output voltage is equal to the negative DC
source voltage when the upper-right switch (T3) and the lower-left switch (T4) are turned ON
and the upper-left switch (T1) and lower-right switch (T2) are turned OFF. In this case, the
current flows through the load, the upper-right switch (T3), and the lower-left switch (T4).
Across the load, the output voltage is
Vo = -Vdc
Similarly, the output current is
Vo/RL
CALCULATION:
1. frequency =
2. Output voltage =
Advantages of Single-Phase Full Bridge Inverter
The following are the advantages
• Absence of voltage fluctuation in the circuit
• Suitable for high input voltage
• Energy efficient
• The current rating of the power devices is equal to the load current.
Disadvantages of Single-Phase Full Bridge Inverter
The following are the disadvantages
• The efficiency of the full-bridge inverter (95%) is less than half the bridge inverter (99%).
• Losses are high
• High noise.
Applications of Single-Phase Full Bridge Inverter
The following are the applications
• Applicable in applications like low and medium power example square wave.
• A sinusoidal wave which is distorted is used as input in high power applications.
• Applications like AC variable motor, heating induction device, standby power supply
• Solar Inverters
• Compressors
