Palestine Polytechnic University
Workshop
Matlab/Simulink in Drives
and Power electronics
Lecture 4 : DC-Motor Chopper design
SimPowerSystems
Ghislain REMY
18-21 May 2009
Jean DEPREZ
Workshop Matlab/Simulink in Drives and Power electronics – Lecture 4
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Palestine Polytechnic University
Workshop Program
• 8 lectures will be presented based on Matlab/Simulink :
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1 Introduction to Matlab
2 Introduction to Simulink
3 DC-Motor Control design
4 DC-Motor Chopper design SimPowerSystems
5 Introduction to Stateflow/Statechart
6 Induction Motor Inverter Control
7 Synchronous Motor Modeling
8 Synchronous Motor Control
• Two system applications (four quadrants electric drives of
mechanical systems) will be used as "conducting lines" during
the workshop.
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Palestine Polytechnic University
SimPowerSystems Libraries
• SimPowerSystems software and other products of the Physical
Modeling product family work together with Simulink
software to model electrical, mechanical, and control systems.
• SimPowerSystems libraries contain models of:
– Power equipment such as transformers, lines, machines, and power
electronics.
• These models are proven ones coming from textbooks, and
their validity is based on the experience of :
– The Power Systems Testing and Simulation Laboratory of HydroQuébec, a large North American utility located in Canada,
– The École de Technologie Supérieure and Université Laval.
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SimPowerSystems main library
• The SimPowerSystems main library, powerlib, organizes its
blocks into libraries according to their behavior. The powerlib
library window displays the block library icons and names.
• The main powerlib library window also contains the Powergui
block that opens a graphical user interface for the steadystate analysis of electrical circuits.
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Building and Simulating a Simple Circuit
• SimPowerSystems software allows you to build and simulate
electrical circuits containing linear and nonlinear elements.
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Palestine Polytechnic University
Examples of SimPowerSystems Libraries
• Various Electrical Libraries are available:
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Electrical Sources
Elements (Inductance, Resistance…)
Power Electronics (Diode, MOSFET…)
Machines (DC-motor, PM Motor…)
Measurements (Voltage probe…)
Application Libraries
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Palestine Polytechnic University
Example: a Two-Quadrant 3ϕ Rectifier DC Drive
• Using SimPowerSystems:
– It is no more necessary to use Causal Approaches,
because it is Physical Connections.
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Palestine Polytechnic University
How SimPowerSystems Software Works
– Every time you start the simulation, a special initialization mechanism is
called. This initialization process computes the state-space model of your
electric circuit and builds the equivalent system that can be simulated by
Simulink software.
– This process performs the following steps:
• Sorts all SimPowerSystems blocks. The blocks are separated into linear and
nonlinear blocks, and all electrical nodes received a node number.
• Then, a state-space model (A, B, C, D matrices) of the linear part of the circuit is
computed. All steady-state calculations and initializations are performed at this
stage. Discrete state-space models are computed from the continuous state-space
model, using the Tustin method.
This matrix defines the network algebraic equations.
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Palestine Polytechnic University
Power Electronics Library: Diode
– The diode is a semiconductor device that is controlled by its own
voltage Vak and current Iak. When a diode is forward biased (Vak > 0),
it starts to conduct with a small forward voltage Vf across it. It turns
off when the current flow into the device becomes 0. When the diode
is reverse biased (Vak < 0), it stays in the off state.
– The Diode block is simulated by a resistor, an inductor, and a DC
voltage source connected in series with a switch. The switch operation
is controlled by the voltage Vak and the current Iak.
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Palestine Polytechnic University
Thyristor
– The thyristor is a semiconductor device that can be turned on via a
gate signal. The thyristor model is simulated as a resistor Ron, an
inductor Lon, and a DC voltage source representing the forward
voltage Vf, connected in series with a switch.
The switch is controlled by a logical signal depending on the voltage
Vak, the current Iak, and the gate signal g.
– The Thyristor block also contains a series Rs-Cs snubber circuit that
can be connected in parallel with the thyristor device.
– The static VI characteristic:
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Palestine Polytechnic University
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 (or line-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).
– The device numbering is different if the power electronic devices are
naturally commutated or forced-commutated.
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Palestine Polytechnic University
Diode and Thyristor Bridges
• For a naturally commutated three-phase converter (diode and
thyristor), numbering follows the natural order of
commutation:
• For the case of a two-phase diode or thyristor bridge, and for
any other bridge configuration, the order of commutation is
the following:
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Palestine Polytechnic University
GTO-Diode and IGBT-Diode bridges
• GTO-Diode bridge:
• IGBT-Diode bridge:
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Palestine Polytechnic University
MOSFET-Diode and Ideal Switch bridges
• MOSFET-Diode and Ideal Switch bridges
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Palestine Polytechnic University
Snubber resistance and capacitance
• Snubber resistance Rs, in ohms (Ω).
– Set the Snubber resistance Rs parameter to inf to eliminate the
snubbers from the model.
• Snubber capacitance Cs, in farads (F).
– Set the Snubber capacitance Cs parameter to 0 to eliminate the
snubbers, or to inf to get a resistive snubber.
– In order to avoid numerical oscillations when your system is
discretized, you need to specify Rs and Cs snubber values for diode
and thyristor bridges. For forced-commutated devices (GTO, IGBT, or
MOSFET), the bridge operates satisfactorily with purely resistive
snubbers as long as firing pulses are sent to switching devices.
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Palestine Polytechnic University
Tunning the snubbers
– If firing pulses to forced-commutated devices are blocked, only antiparallel
diodes operate, and the bridge operates as a diode rectifier. In this condition
appropriate values of Rs and Cs must also be used.
– When the system is discretized, use the following formulas to compute
approximate values of Rs and Cs,where
– These Rs and Cs values are derived from the following two criteria:
• The snubber leakage current at fundamental frequency is less than 0.1% of nominal
current when power electronic devices are not conducting.
• The RC time constant of snubbers is higher than two times the sample time Ts.
– These Rs and Cs values that guarantee numerical stability of the discretized
bridge can be different from values of a physical circuit.
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Palestine Polytechnic University
Interfacing SimPowerSystems with Simulink
1. The Voltage Measurement block acts as an interface
between the SimPowerSystems and the Simulink blocks, and
converts the measured voltages into Simulink signals.
2. Similarly, the Current Measurement block converts any
measured current into a Simulink signal.
3. The Controlled Voltage
Source block is use to
inject a voltage
in an electrical circuit
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Palestine Polytechnic University
Connecting Rules for Capacitors and Inductors
– You have to pay particular attention when you connect capacitor
elements together with voltage sources, or inductor elements in series
with current sources. When you start the simulation, the software
displays an error message if one of the following two connection
errors are present in your diagram: To fix this problem, you can add a
small resistance in series between the voltage source and the
capacitors.
– To fix this problem, you can add a large resistance in parallel with the
inductor and the capacitors.
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Palestine Polytechnic University
The Powergui Block to Simulate
• The Powergui block is necessary to simulate any Simulink
model containing SimPowerSystems blocks.
– It is used to store the equivalent Simulink circuit that represents the statespace equations of the SimPowerSystems blocks.
• You must follow these rules when using this block in a model:
– Place the Powergui block at the top level of diagram for optimal performance.
However, you can place it anywhere inside subsystems for your convenience;
its functionality will not be affected.
– Only one Powergui block per model
– You must name the block powergui
The Most used Simulation type are:
- Continous for Physical System
- Discrete for Commutating system
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Palestine Polytechnic University
SimPowerSystems Tools for Analysis
• Very useful analysis tools can be used:
– Use LTI Viewer (facilitate linear analysis
of SimPowerSystems Model with
Control System Toolbox)
– FFT Analysis (easy to plot FFT signal)
– Hysteresis Design Tool (to add hysteresis
and saturation to Transformer Model)
– Compute RLC Line Parameters (to identify
RLC value from characteristics of Grid Line)
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