Download VOLTAGE SOURCE INVERTER

INVERTERS
REFERENCE
1. Power Electronics-(CH-8)
M.S. Jamil Asghar
2. Power Electronics- Circuits,
Devices & Applications (CH-10)
(2nd edition)
M.H. Rashid
GENERAL CONCEPT
Converts DC to AC power by switching the DC
input voltage (or current)in a pre-determined
sequence so as to generate AC voltage (or
current) output.
APPLICATIONS




Un-interruptible power supply (UPS)
Industrial (induction motor) drives
Traction
HVDC
BLOCK DIAGRAM
Types of inverter


Voltage Source Inverter (VSI)-a) Square wave
b) PWM
Current Source Inverter (CSI)
What are the various types of Inverters?
Inverters can be broadly classified into two types. They are
Voltage Source Inverter (VSI)
Current Source Inverter (CSI)
When the DC voltage remains constant, then it is called voltage
inverter(VSI) or voltage fed inverter (VFI). When input current is
maintained constant, then it is called current source inverter (CSI) or
current fed inverter (CFI). Some times, the DC input voltage to the
inverter is controlled to adjust the output. Such inverters are called
variable DC link inverters. The inverters can have single phase or threephase output.
•A voltage source inverter is fed by a stiff dc voltage, whereas a current
source inverter is fed by a stiff current source.
•A voltage source can be converted to a current source by connecting a
series inductance and then varying the voltage to obtain the desired
current.
•A VSI can also be operated in current-controlled mode, and similarly a
CSI can also be operated in the voltage control mode.
•The inverters are used in variable frequency ac motor drives,
uninterrupted power supplies, induction heating, static VAR
compensators, etc.
VOLTAGE
VARIABLE




SOURCE INVERTER
DC
(VSI)
WITH
LINK
DC link voltage is varied by a DC-to DC converter
or controlled rectifier.
Generate “square wave” output voltage.
Output voltage amplitude is varied as DC link is
varied.
Frequency of output voltage is varied by changing
the frequency of the square wave pulses
The DC-link quantity is then impressed by an energy storage element
that is common to both stages, which is a capacitor C for the voltage DClink or an inductor L for the current DC-link.
VARIABLE DC

LINK INVERTER
(2)
Advantages
1.Simple waveform generation
2.Reliable

Disadvantages
1.Extra conversion stage
2.Poor harmonics
VSI



WITH FIXED
DC
LINK
DC voltage is held constant.
Output voltage amplitude and frequency are
varied simultaneously using PWM technique.
Good harmonic control, but at the expense of
complex waveform generation
OPERATION

OF SIMPLE SQUARE-WAVE INVERTER
To illustrate the concept of AC waveform generation
OPERATION OF SIMPLE SQUARE-WAVE INVERTER(2)
SINGLE PHASE HALF-BRIDGE




INVERTER
Also known as the “inverter leg”.
Basic building block for full bridge, three phase
and higher order inverters.
G is the “centre point”.
Both capacitors have the same value. Thus the DC
link is equally “spilt”into two.
SINGLE PHASE HALF-BRIDGE


INVERTER
(2)
The top and bottom switch has to be “complementary”,
i.e. If the top switch is closed (on), the bottom
must be off, and vice-versa.
•In practical, a dead time as shown below is
required to avoid “shoot-through” faults.
SINGLE PHASE HALF-BRIDGE INVERTER WITH R LOAD
SINGLE PHASE HALF-BRIDGE

Mode 1:

Mode 2:
INVERTER WITH
RL LOAD
SINGLE PHASE HALF-BRIDGE INVERTER WITH RL LOAD

Mode-3:

Mode-4:
SINGLE PHASE HALF-BRIDGE INVERTER WITH RL
LOAD
SINGLE PHASE HALF-BRIDGE INVERTER WITH RL LOAD
SINGLE PHASE HALF-BRIDGE
LOAD
INVERTER WITH
RC
SINGLE-PHASE,


FULL-BRIDGE
INVERTER (1)
Full bridge (single phase) is built from two
half-bridge leg.
The switching in the second leg is “delayed by
180 degrees” from the first leg.
SINGLE-PHASE,
FULL-BRIDGE
INVERTER (2)
SINGLE-PHASE,
FULL-BRIDGE
INVERTER (2)
PERFORMANCE PARAMETER
PERFORMANCE PARAMETER
PERFORMANCE

OF SQUARE-WAVE INVERTER
Study of harmonics requires understanding
of wave shapes. Fourier Series is a tool
to analysis wave shapes.
PERFORMANCE
OF SQUARE-WAVE INVERTER
SPECTRA
OF
SQUARE WAVE
SPECTRA
OF
SQUARE WAVE
DRAWBACKS


OF
SQUARE WAVE
For fixed voltage the output of the inverter
cannot be controlled.
The output voltage contains appreciable harmonics,
THD is also very high.
Pulse Width Modulation Technique
A better square wave notching is known as PWM
technique.
 Both amplitude and frequency can be controlled
independently. Very flexible
Modulation Techniques are:
1.SPWM
2.UPWM
3.SinPWM

SINGLE PULSE WIDTH MODULATION (SPWM)
UNIFORM /MULTIPLE

In a uniform PWM inverter, the output voltage has
several pulses of equal width in each half-cycle.

No of output pulses in each half-cycle, N =fc/2fref
=mf/2
SINUSOIDAL PULSE WIDTH MODULATION
 Bipolar
Switching Scheme :
1. VrefVc, S1 and S2 are on and Vo=V
2. VrefVc, S3 and S4 are one and Vo=-V
SINUSOIDAL PULSE WIDTH MODULATION
Unipolar Switching Scheme :
1. VrefVc, S1 is on and vref  Vc, S4 is on
2. -VrefVc, S3 is on and –Vref  Vc, S2 is on
UNIPOLAR SWITCHING SCHEME :