Laboratory work 3
Smart Grid Systems
Title: Study of Voltage Source Converters and PWM in MATLAB SimPowerSystem
Objective of this lab: This laboratory work aims to study the operation of PWM based
voltage source converter using SimPowerSystem Toolbox.
Study System: The following system is required to be simulated using SimPowerSystem
Toolbox to understand the VSC operation.
Figure 1: VSC interfaced power system
Universal Bridge: The Universal Bridge block implements a universal three-phase
power converter that consists of up to six power switches connected in a bridge
configuration. The type of power switch and converter configuration are selectable
from the dialog box. The Universal Bridge block allows simulation of converters using
both naturally commutated power electronic devices (diodes or thyristors) and forced-
commutated devices (GTO, IGBT, MOSFET). The Universal Bridge block is the basic
block for building two-level voltage-sourced converters (VSC). Details of universal
bridge can be found in the MATLAB help file.
Data: DC voltage:
dc =V V1000 . Filter data: R = 1m , LΩ = . 0 4mH . Load data: 3
phase, ∆ type, nominal phase – phase voltage 600 V, Apparent Power 510 kVA, 0.98
leading power factor. PWM Data: Amplitude modulation ratio 0.95 and
frequency modulation ratio 33.
m = While running the simulation choose discrete
simulation type with sampling frequency 2 micro second.
1. Develop the above system shown in Figure 1 in Simpower system toolbox.
2. Carry out the simulation of the system using (i) detailed model using 6 IGBTs
and 6 anti-parallel diodes, (ii) Switching-Function type equivalent model, and
(iii) average-model of VSC.
3. Measure the output line-line AC voltage of the VSC using voltage measurement
device, volt meter. Calculate RMS value of the fundamental frequency (50 Hz)
component voltage using RMS block.
4. Measure the load line-line voltage using voltage measurement device, volt meter.
5. Study the effect of amplitude and frequency modulation ratio.
6. Write discussion on the study of the system.
Required Simulink Blocks:
a. Universal Bridge.
b. PWM Generator (2-Level).
c. Series RL branch.
d. Sine Wave Generator.
f. RMS Block.
1. Universal bridge using 6 IGBTs and 6 anti-parallel diodes provides detail model
of the VSC.
2. In Switching-Function type equivalent model switches of the universal bridge
are replaced by two voltage sources on AC side and a current source on DC
side. As for detailed model, this model uses the 6 IGBT pulses as control input
(g). This model correctly represents harmonics generated by the VSC.
3. Average model uses the three reference signals (uref) representing the three
average voltages generated at ABC terminals. The model does not represent
harmonics. It can be used with larger sample times (typically 10 times larger
than required by detailed model) while preserving the average voltage dynamics.
In both Switching-Function type equivalent model and average model, the VSC
is assumed to be ideal (AC instantaneous power= DC instantaneous power).