Exp 7 to Exp 10_power elctronics lab .pdf

Experiment-7
Analysis of Gate Driver Circuit for Power Electronics Converters
Objective of the Experiment:
To study the Gate driver circuit, both isolated & non-isolated, used in power electronics
converters. Observing the waveforms at different stages of the driver circuit through
simulation on multisim and then deduce some important conclusions from it.
Theory:
Gate driver circuit is an integral part of power electronics converters which is used to
drive power semiconductor devices like BJTs, IGBTs and MOSFETs. Output of DC-
DC converters mainly depend on behavior of gate driver circuits. It means if gate
-DC
converter output will not be working according to our requirement. Therefore, design
of gate driver circuit is critically important in designing of power electronics
converters.
Here we use an op-amp oscillator circuit to generate a triangular waveform. The op-
amp acts as an astable multivibrator, another op-amp is connected in cascade as a non-
inverting amplifier. The output of the first op-amp is a square wave that is clipped to
desire value ±10V by means of two zener diodes which are connected in back-to-back
fashion. A very small part of the output voltage across zener is fed to the non-inverting
pin to the op-
op-amp & ground, which is charged from the op-amp output through a charging
voltage range, the capacitor charges linearly. When
the voltage across the capacitor exceeds at the non-inverting input, the op-amp
changes polarity. Now the polarity of reverse voltage changes and op-amp becomes
inverting. Third op-amp is connected for voltage comparator, which compares
triangular waveform with control voltage and generates PWM waveform.
Gate driver circuits can be non-isolated or isolated. A non-isolated gate driver
requires a direct connection to the ground of the control logic and the power switching
device. In low power, low voltage designs provide a simple low-cost solution. But, if
the switching voltage is significantly higher than the logic voltage, or the current
levels is moderately high, or switching frequency is higher; then, using a driver is
needed to prevent coupling of energy via stray capacitance from damaging the logic
and ensuring the switching device is properly driven.

In case of switching high voltages, isolation of the control logic is important for safety
reason. Isolation when switching high current is useful in ensuring that ground bounce
does not damage logic circuits or result in output devices turning on or off
inappropriately. Another important feature of an isolated driver is the ability to
connect to a switching device that does not have a direct connect to a ground level.
Procedure:
1. All the required components are selected and placed in the design area.
2. Appropriate parameters for the components are set up.
3. Circuit connection was made as per the circuit diagram for Non-Isolated Gate Driver.
4. Running the Transient Analysis, the various waveforms were captured.
5. Changing the circuit connection for Isolated Gate Driver, Step 4 was repeated.
Simulation:
Non-Isolated Gate Driver
Circuit Connection:

Transient Analysis Configuration:

Waveforms:
Voltage at the ouput terminal of 1st
Op-amp:
Voltage at the Output of 2nd
Op-amp (Triangular):

Output Voltage (50% setting on R4 and 50% setting on R9):
We observe that the pulse width has been increased.
We observe that the frequency has been increased.

Isolated Gate Driver
Circuit Connection:

Waveforms:
Voltage at the ouput terminal of 1st
Op-amp:
Voltage at the Output of 2nd
Op-amp (Triangular):

Conclusion:
1. Simulations for Gate Driver circuit both non-isolated & isolated were done
successfully. Output waveforms in each case were analysed and verified.
2. Isolated gate driver required a power source on the output side to drive the control
devices. This can be provided from an external power source or some device
containing a DC to DC converter as part of the driver device.
3. Isolated gate drivers have a longer propagation delay than direct drivers but only by
a matter of 100 ns or less.
4. The frequency can be controlled by varying the resistor R4
References:
NPTEL Notes

Experiment-8
Simulation of Basic DC-DC Converters by using NI Multisim
To study DC-DC Converters: Buck, Boost, Asymmetrical Bridge and Full Bridge
Converters. Observing the waveforms in each of the converters through simulation on
multisim and then deduce some important conclusions from it.
Theory:
DC-DC converters are widely used to efficiently produce a regulated voltage from a
source that may or may not be well controlled to a load that may or may not be constant.
They are high-frequency power conversion circuits that use high-frequency switching
and inductors, and capacitors to smooth out switching noise into regulated DC voltages.
Closed feedback loops maintain constant voltage output even when changing input
voltages and output currents. At 90% efficiency, they are generally much more efficient
and smaller than linear regulators.
Buck Converter:
Buck converter is a step-down dc-dc converter where the output voltage is less than the
input voltage.
Circuit Diagram:
Formulae Used:

Boost Converter:
Boost converter is a step-up dc-dc converter where the output voltage is more than the
input voltage.
Procedure:
3. Circuit connection was made as per the circuit diagram.
4. Running the Interactive Simulation or Transient Analysis, the load voltage and load
current are captured.
5. Changing the circuit connection for different loads, Step 4 was repeated.

Simulation:
DC-DC Buck Converter:
Circuit Connection:
Pulse Voltage Source Configuration:

Waveforms:
Gate Pulse:
Dynamic Response of Output Voltage:
Dynamic Response of Inductor Current:

Discussion:
As per the pulse voltage configuration:
T=2*10-5
, D=25%= 0.25. Thus, Vo= D*Vin= 0.25* 30.5 =7.625V
Steady state output voltage obtained= 7.1 V. Thus, Error= 7%
Load current, Io= Vo/R = 0.265 A and avg. Inductor current theoretically, IL=Io
Steady state Inductor current obtained= 0.245 A. Thus, Error = 7.5%
DC-DC Boost Converter:
Circuit Connection:

Transient Analysis Configuration:

Discussion:
As per our pulse voltage configuration;
T=1*10-3
, D=50%= 0.5. Thus, Vo= Vin/(1-D) = 15/(1-0.5)=30 V
Steady state output voltage obtained= 25.7 V. Thus, Error= 14%
Load current, Io= Vo/R = 1.2 A and avg. Inductor current theoretically, IL=Io/(1-D)=
1.2/0.5 =2.4
Steady state Inductor current obtained= 2.2 A. Thus, Error = 8.3%

Asymmetrical Bridge Converter:
Circuit Connection:

Waveforms:
Gate Pulse:
Dynamic Response of Output Voltage and Inductor Current:

Full Bridge Converter:
Circuit Connection:
Pulse Voltage Source Configuration (V2): Pulse Voltage Source Configuration (V3):

Conclusion:
1. Simulations for DC-DC Converters were done successfully. Output waveforms in
each case were analysed and verified.
2. In case of Voltage source converter (Inverter), load voltage depends upon the source
voltage and load current depends upon the load parameter. While, in case of current
source converter (Inverter), load current depends upon the source current and load
voltage depends upon the load parameter.
3. The stepping up or stepping down of voltage of Buck-Boost converter depends
upon the duty cycle. When D<0.5, it behaves as buck converter and when D>0.5, it
behaves as boost converter.
4. In case of Full bridge converter having RLC load, we see overdamped response in
lagging power factor and underdamped response in leading power factor.
References:
NPTEL Notes

Experiment-9
Simulation of Closed Loop Control of DC-DC Converters
To study Closed Loop Control of DC-DC Converters mainly buck and boost converters.
Observing the waveforms in each of the converters through simulation on multisim and
then deduce some important conclusions from it.
Theory:
A DC-DC converter is a vital part of alternative and renewable energy conversion,
portable devices, and many industrial processes. It is essentially used to achieve a
regulated DC voltage from an unregulated DC source which may be the output of a
rectifier or a battery or a solar cell etc. Nevertheless, the variation in the source is
significant, mainly because of the variation in the line voltage, running out of a battery
etc., but within a specified limit. Taking all these into account, the objective is to
regulate the voltage at a desired value while delivering to a widely varying load.
A DC-DC switching regulator is known to be superior over a linear regulator mainly
because of its better efficiency and higher current-driving capability. The output voltage
of a DC-DC converter is controlled by operating it in the closed loop, and altering its
MOSFET (switch) gate signal accordingly. It is basically governed by a switching logic,
thus constituting a set of subsystems depending upon the status (on-off) of the switch.
In the well-known pulse width modulation (PWM) technique, the control is
accomplished by varying the duty ratio of an external fixed frequency clock through
one or more feedback loops, whenever any parameter varies.
PI controllers are the most widely-used type of controller for industrial applications.
They are structurally simple and exhibit robust performance over a wide range of
operating conditions. In the absence of the complete knowledge of the process, these
types of controllers are the most efficient choices.
DC-DC converters are widely used to efficiently produce a regulated voltage from a
source that may or may not be well controlled to a load that may or may not be constant.
They are high-frequency power conversion circuits that use high-frequency switching
and inductors, and capacitors to smooth out switching noise into regulated DC voltages.
Closed feedback loops maintain constant voltage output even when changing input
voltages and output currents. At 90% efficiency, they are generally much more efficient
and smaller than linear regulators.

Block Diagram of Closed Loop Control of Buck Converter:
Procedure:
3. Circuit connection for Closed Loop Control of Buck Converter was made as per the
circuit diagram.
4. Running the Interactive Simulation or Transient Analysis, the various waveforms are
captured.
5. Changing the circuit connection for Closed Loop Control of Boost Converter, Step 4
was repeated.
Simulation:
Closed Loop Control of DC-DC Buck Converter:
Circuit Connection:

Input Voltage Configuration:
Function Generator Configuration:

Waveforms:
Comparison between Control Signal and Triangular Wave of Boost Converter

Closed Loop Control of DC-DC Boost Converter:
Circuit Connection:
Input Voltage Configuration: Function Generator Configuration:

Conclusion:
1. Simulations for Closed Loop control of DC-DC Converters were done
successfully. Output waveforms in each case were analysed and verified.
2. In both cases the output voltage and inductor current settles to final values as
triangular pulse is provided in the function generator.
3. Buck converter steps down the voltage while boost converter steps up the voltage.
References:
NPTEL Notes

Experiment-10
Simulation of Three Phase Inverter
To study output waveform of three phase inverter. Observing the waveforms through
simulation on multisim and then deduce some important conclusions from it.
Theory:
A three-phase inverter converts a DC input into a three-phase AC output. Its three arms
are normally delayed by an angle of 120° so as to generate a three-phase AC supply.
There are basically 2 modes of conduction: - 180 and 120 degree. In 180-degree mode
of conduction, every device is in conduction state for 180° where they are switched ON
at 60° intervals. In 120-degree mode of conduction, each electronic device is in a
conduction state for 120°.
Procedure:
3. Circuit connection for Three Phase Inverter was made as per the circuit diagram.
4. Running the Interactive Simulation or Transient Analysis, the various waveforms are
captured.
Simulation:
Three Phase Inveter:
Circuit Connection:

PWM Configuration:
Waveform:
Output with Leg Voltage

Conclusion:
1. Simulations for three phase inverter were done successfully. Output waveforms in
each case were analysed and verified.
2. It is observed that we get three perfectly sinusoidal waveform phase shifted by 120
from each other as pwm pulses are applied to the switches.
References:
NPTEL Notes

Exp 7 to Exp 10_power elctronics lab .pdf

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