pulse nov2009
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November 2009 Issue
1 Mapping of Equal Area Criterion
Conditions to the Time Domain
for Out-of-Step Protection
6 RTDS Simulator Technology Review
9 Design of a Bidirectional Buck-Boost
DC/DC Converter for a Series HybridElectric Vehicle Using PSCAD/EMTDC
14 Knowledge is Key
16 PSCAD 2009 Training Sessions
November 2009
A new procedure for out-of-step protection by
mapping the equal area criterion conditions
to the time domain was investigated by the
power system research group of the University
of Saskatchewan. The classification between stable
and out-of-step swings is done using the accelerating
and decelerating energies, which represents the area
under the power-time curve. The proposed approach
is based only on the local electrical quantities avail-able at the relay location, and does not depend on the
network configuration and parameters. The proposed
algorithm has been tested on a single machine infinite
bus and a three machine infinite bus system using
software simulations from PSCAD.
There are various techniques available in literature
and in practice to detect out-of-step conditions. Most
popular conventional out-of-step detection techniques
use a distance relay with blinders in the impedance
plane and a timer. The blinder and timer settings
require knowledge of the fastest power swing, the
normal operating region, and the possible swing
frequencies, and are therefore system specific [1].
Another technique monitors the rate of change of
swing centre voltage (SCV) and compares it with a
threshold value to discriminate between stable and
out-of-step swings. With some approximations,
the SCV is obtained locally from the voltage at the
relay location, which consequently makes the SCV
independent of power system parameters. However,
the approximation is true only if the total system
impedance is close to 90 [2]. For a multi-machine
system, the voltage measured at relay location
does not give an accurate approximation of SCV.
The technique also requires offline system stability
studies to set the threshold value (rate of change
of SCV), thereby making it system specific.
Other techniques, based on energy function criterionand classical equal area criterion are proposed in
references [3] and [4]. These methods also have
certain drawbacks which do not make them readily
applicable to implement in a protection algorithm.
These drawbacks are outlined in more detail in a
separate document by the authors which can be
made available for further reading.
Reference [4] proposed an out-of-step detection
technique based on the classical equal area criterion
(EAC) in the power angle ( ) domain. Pre and post-
disturbance power-angle (Pe- ) curves of the system
are to be known to the relay. As the Pe- curves
are dependent on the system configuration, many
measurement and communication devices at various
locations are required to gather the current system
information.
This project uses the above concept of EAC modified
to the time domain. An out-of-step protection
methodology is proposed using the concept of time
domain EAC. The time domain EAC is based on the
Mapping of Equal Area Criterion Conditions
to the Time Domain for Out-of-Step ProtectionSumit Paudyal, University of Waterloo, Canada
Gokaraju Ramakrishna & Mohindar S. Sachdev, University of Saskatchewan, Canada
Departments of Electrical and Computer Engineering
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2 P U L S E T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L
power-time (Pe-t) curve instead of the Pe- curves. The
proposed technique uses only local output power (Pe)information. The electrical output power, Pe, over time
is calculated from local voltage and current measure-
ments. The transient energy (area under the Pe-tcurve)
is computed, and the swing is classified as stable or
out-of-step based on the areas computed. The effec-
tiveness of the proposed algorithm has been studied
for a Single Machine Infinite Bus (SMIB) and a Three
Machine Infinite Bus System using the PSCAD
simulation software tool.
Proposed Algorithm Figure 1 shows an SMIB
configuration. A three phase fault is applied at the
middle of TL-II. The fault is cleared with some delay by
simultaneously opening the two breakers A and B.
The transient response following a disturbance in the
SMIB configuration is obtained if the swing equation
(1) is solved using numerical integration techniques,
where M is the generator inertia constant and is the
system frequency.
The advantage of EAC in domain is that it describes
the stability of the system without solving the swing
equation. The difficulties associated with EAC in
domain to detect an out-of-step condition were dis-
cussed in the previous section. The proposed algorithmis based on Pe-tcurve and this information can be
obtained directly from the measurements at relay
location. Thus, the proposed algorithm does not
require the solution of the swing equation to obtain
the Pe-tcurve.
Figure 2 shows the Pe- curves for stable system.
Figure 3 shows the Pe- curves for an unstablesystem. The corresponding Pe- curves are shown
in Figures 4 and 5.
In Figures 2 and 3, e represents the power angle
before the fault, c represents the power angle at
the instance of fault clearing and maxrepresents the
maximum swing of the power angle. The EAC in
domain shows that for a system to be stable, areaA1
is equal to areaA2, and areaA2 occurs before - 0.
The maximum swing of , max, for a stable swing is
less than - 0.
The mathematical expressions to evaluate areaA1
andA2 in time domain can be derived from the
swing equation (1). If the speed deviation of the
rotor is , then
where (t) is the speed of the rotor during transient.
Figure 1 A single machine infinite bus system.
Figure 2 Pe- curves illustrating a stable case.
Figure 3 Pe- curves illustrating an unstable case.
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N O V E M B E R 2 0 0 9
where tmaxis the time when = max. For a stable
system, at tmax, the speed of the rotor is synchronousspeed, so the speed deviation is zero. For an out-of-
step condition, the speed of the rotor at tmaxis greater
than the synchronous speed. Thus, the total area
for stable and out-of-step conditions from (5) and (6)
is given as follows:
For a stable condition,
For an out-of-step condition,
Equations (7) and (8) are the expressions for EAC in
time domain. The area under the Pe-tcurve represents
energy. Thus, this concept can be referred to as the
energy equilibrium criterion in the time domain.
A balance of transient energy results in a stable swing
whereas an unbalance of transient energy results in
an out-of-step swing.
Integrations in (7) and (8) are approximated by sum-
mation and Pm is set to Pe before the fault inception.
Thus, for a stable condition, the sum of two areasA1
andA2 becomes,
For an out-of-step condition,
wheret
0: Time when first occurs
tmax
: Time when (stable) or time when
From (1) and (2),
Integrating (3),
Areas are obtained from (4) by setting the limits of
integration accordingly.
Figure 4 Pe-t curve for a stable case.
Figure 5 Pe-t curve for an out-of-step case.
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4 P U L S E T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L
Equation (9) and the limit tmaxfor stable case do
not become exactly equal to zero because of the
approximation of integration by summation.
They are modified as:
tmax
: Time when and (Stable)
Equations (10) and (11) along with the conditions for
t0 and tmaxform the proposed algorithm for out-of-step
detection. Based on the proposed algorithm, a decision
regarding a stable or out-of-step condition is always
made at tmax(time corresponding to max) with an error
of tor less. Details, such as generator losses and
house loads, must be accounted for in the calculations.
SMIB Simulation A power system, as shown in
Figure 1, is used to test the proposed algorithm on an
SMIB configuration. An out-of-step relay is located at
R.At R.A discrete Fourier transform (DFT) technique
is used for estimating the values of voltage and current
phasors. The pre-fault power angle ( 0) is set at 30.
A three phase fault is applied at the middle of TL-II
and four different simulations are carried out with
fault duration times of 0.167, 0.20, 0.233 and 0.267 s.
Power system transient simulation tool PSCAD is
chosen for the simulation with a simulation time step
of 50s. The fault duration times of 0.167 and 0.20 s
make the system stable whereas the fault duration
times of 0.233 and 0.267 s result in an out-of-step
condition. The P-tcurves are shown in Figures 6 and 7
for two cases and the results are summarized in Table I.
The simulation results show that the proposed algo-rithm discriminates the stable and out-of-step swings
effectively. The cases 1 and2 are decided as stable
swing as the total areaA becomes zero. In cases 3 and
4; total area A becomes 0.034 and 0.051 pu-s respec-
tively. Thus, these cases are decided as out of step.
Figure 6 Pe-t curve for 0=30 and fault cleared after 0.20 s.
Figure 7 Pe-t curve for 0=30 and fault cleared after 0.233 s.
Table 1 Summary of stable and out-of-step swings on a SMIB system.
Case 1 2 3 4
Power Angle (0) 30 30 30 30
Fault Duration Time, s 0.167 0.20 0.233 0.267
Area (A1) pu-s 0.048 0.054 0.061 0.067
Area (A2) pu-s -0.048 -0.054 -0.027 -0.016
A=A1+A
20 0 0.034 0.051
Decision Time, s 0.640 0.850 0.598 0.504
Decision Stable Stable OS OS
OS: Out-of-step
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Acknowledgment The authors greatly appreciate
the help provided by Dr. Dharshana Muthumuni
and Mr. Juan Carlos Garcia Alonso (Manitoba HVDC
Research Centre) with PSCAD software.
References
[1] W. A. Elmore, Protective Relaying Theory and Applications,
2nd ed., rev. and expanded. ed.New York: Marcel Dekker, c2004.
[2] D. Tziouvaras and D. Hou, Out-Of-Step Protection Fundamentals
and Advancements, Proc. 30th Annual Western Protective Relay
Conference, Spokane, WA, October 21-23, 2003.
[3] R. Padiyar and S. Krishna, Online Detection of Loss of Synchronism
using Energy Function Criterion, Power Delivery, IEEE Transactions
on, vol. 21, pp. 46-55, 2006.
[4] V. Centeno, An Adaptive Out-of-Step Relay for Power
System Protection, Power Delivery, IEEE Transactions on,
vol. 12, pp. 61-71, 1997.
[5] M. A. Pai, Energy Function Analysis for Power System Stability,
Boston: Kluwer Academic Publishers, c1989.
Appendix
The system study parameters are outlined in a separate document by
the authors which can be made available for further reading. These
include:
SMIB Parameters
Three Machine Infinite Bus Parameters
Excitation System Parameters
Power System Stabilizer Parameters
Governor Parameters
Three Machine Infinite Bus Simulation A Three
Machine Infinite Bus system was considered to illustrate
the effectiveness of the proposed technique for a
multi-machine system. The parameters of the power
system are given in the full document. Results similar
to those described in section A above were observed.
To study the effect of pure local mode oscillations on
the proposed algorithm, a load increase of 0.15 pu was
applied at bus 3, and at the same instant, a decrease
in load by 0.15 pu was applied at bus 1. Results proved
that the proposed method is reliable under such condi-
tions as well (P-tcurves and summary tables are listed
in the full document).
The results showed that the proposed algorithm is
not only effective on a SMIB system, but it is equally
effective on an interconnected power system. The
application of this technique is straightforward even
for a large power system and avoids the need for any
cumbersome network reduction techniques, such as
center of inertia or center of angle technique [5].
To account for measurement inaccuracies and the
possibility of breaker re-closures, the decision times
could be delayed by a few sampling intervals
(i.e. 0.00104 s or more), so that inaccurate decisions
are avoided.
Conclusion A technique for out-of-step detection by
modifying the classical equal area criterion condition
to the time domain was proposed in this paper and
its effectiveness was tested on an SMIB and a Three
Machine Infinite Bus system. The proposed algorithm
perfectly discriminated between stable and out-of-
step swings based on the local voltage and currentinformation available at the relay location.
The proposed algorithm identifies stable and out-of-step
swings solely using the local voltage and current information
available at the relay location.
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6 P U L S E T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L
Some of the newer PSCAD users may not even
be aware, but there is a strong link between
the Manitoba HVDC Research Centre and the
RTDS Simulator. It was fundamental research
conducted at the Centre that resulted in the
development of RTDS, the worlds first fully digital
real time power system simulator. After the initial
development, it was soon evident that the simulator
should be promoted as a commercial product and
a license for the technology was granted to RTDS
Technologies Inc. The license covers the commerciali-
zation and further development of the simulator
and ensures the transfer of technology between
the two companies.
RTDS Technologies was formed in 1994 by research-
ers who participated in the development of the
simulator and now has approximately 30 employees.
The company will soon be moving into a new
20,000 sq.ft. facility in the technology park at the
University of Manitoba. RTDS Technologies develops
the simulation component models, the graphical
user interface RSCAD and the custom hardware
for the simulator, as well as providing sales and
support services.
With over 150 installations in 30 countries around
the world, the RTDS Simulator has become the
world standard for real time power system simula-
tors. Clients include practically all of the worlds
major manufacturers of power system components,
electrical utilities, universities and research institutes.
The wide range of clients has resulted in the simula-
tor being applied to many different applications.
The simulators initial application target, logicallysince it was developed at the Centre, was investiga-
tion of HVDC schemes and closed-loop testing of
controls. Even before the system was commercialized
though, other applications, such as protective relay
testing and high speed simulation studies, were
already identified.
In the early days, the available processing power
somewhat restricted the complexity of the compo-
nent models and required them to be written
in assembly language code and in some cases
demanded machine code optimization. However,
today a rack can deliver 12,000 MFLOPS with just
six Giga Processor Cards (GPC). The increase in
processing power compared to the earlier versions
has allowed the detail and flexibility of the models
to be improved. It also allows models to be created
by the user in C language. However, when ultimate
efficiency is required, RTDS Technologies write
and optimize assembly language code.
A good example of a model which has undergone
vast improvements over the years is the network
solution. The first version of the RTDS Simulator
relied on pre-calculating all possible switching states
and changing between them during the simulation.
However, since the number of matrices to be stored
is 2n, where n is the number of single-phase switches,
only 10 switches were allowed per subsystem. The
latest version of the network solution decomposes
the admittance matrix every timestep and allows
66 nodes and 56 single-phase switches per subsystem.
By decomposing the matrix every timestep, the new
network solution allows the inclusion of continually
varying conductance elements. Therefore, valve
groups and other components can be connected to
the network solution without using any of the 56
switches available. The ability to include continually
varying conductance components also improves the
numerical stability of some models, such as variable
loads, transformer saturation, etc.
The line commutated valve groups (HVDC, SVC and
TCSC) have also undergone very significant changes.
The first approach was to model these schemes asisolated subsystems and they suffered from the
effects of the turn-on resolution being restricted
to the size of the timestep. The new models are no
longer interfaced, but rather are connected into
the main network solution by variable conductances
and include advanced features, such as valve faults.
Improved firing was also added to the models to
provide continuous variation of the firing instant
with a resolution of approximately 1 s.
RTDS
Simulator Technology ReviewPaul A. Forsyth, P.Eng. RTDS Technologies Inc.
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Control system testing has not only been limited to
HVDC and FACTS schemes. It has also included testing
of Power System Stabilizers (PSS), Automatic Voltage
Controllers (AVR), excitation systems, governors, tap
changer control, etc.
Great strides have been made in the area of protective
relay development and application testing. Naturally
the increase in the number of nodes and switches
allowed in a subsystem has improved the capability
and flexibility of the simulator for this application.
However, many new models and features were also
added specifically to address the needs of the relay
engineer. Those include a powerful batch mode
facility to automate testing and reporting, detailed
instrument transformer models, fault models with
secondary arc representation, etc. One of the latest
developments for protection system testing is the
GTNET card which allows IEC 61850 GOOSE and
sampled value messaging between the simulator and
protection equipment. A new library was recently
released which includes distance, differential, over-
current and generator protection elements. Examples
are also available to guide users on implementing
their own protective relay models either using
C code or individual component blocks.
The increase in processing power mentioned above
could be applied in two main ways. The brute force
approach would have been to use the new processing
power to reduce the simulation timestep. The other
approach was to increase the size and detail of the
power systems being represented. Over the years,
clients have made it clear again and again that
the focus should be on the latterimplementing
larger and more detailed systems with less hardware.However, more recently Voltage Source Converter
(VSC) based schemes using high speed switching
have posed a conflict to this path.
A few years ago a novel technique was developed
for the RTDS Simulator to allow VSC based devices
to be represented using a timestep in the range
of 1-3 s while the main power system continues
to be represented with a timestep in the range 50 s.
The area of the simulation representing the VSC
components is referred to as a small timestep VSC
subnetwork. By using such a small timestep for the
VSC representation, the relevant dynamics and high
frequency switching can be properly represented.
The VSC elements within the subnetwork, including
the valve topology, are freely configurable.
Small timestep VSC subnetworks are being used,
among other things, for wind farm, STATCOM and
VSC based HVDC control system testing.
Although the subnetworks were intended to be
connected to areas of a network represented using
larger timesteps, there are also a number of cases
where the entire power system simulation is run using
several small timestep VSC subnetworks with timesteps
< 3 s. The different subnetworks each represent areas
of the network (i.e. subsystems) which are connected
via traveling wave transmission line or cable models.
The subnetworks include lines, transformers with
saturation, machines, filters, etc. so complex networks
can be built entirely based on this facility.
On the other end of the spectrum, there are clients
running large scale network simulations with as many
as 500 buses, 90 generators, HVDC, FACTS devices,
etc. The two largest RTDS Simulators are at CSG in
Guangdong China and KEPRI-KEPCO in South Korea.
These large scale simulators allow network stability
to be studied with physical control and protection
equipment connected to the system and at the same
time provide the full detail of an electromagnetic
transient simulation. More and more models for
protection, control and power system elements are
continually being developed for the RTDS
Simulatorto allow the actual operation of the power system to
be even better represented. New hardware is also
being developed to allow simulators with as many as
60 racks to be fully interconnected (i.e. each rack will
be able to communicate directly with any other rack).
With the wider variety of clients using the simulator,
it has also been applied to areas other than power
transmission systems. An excellent example of that is
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8 P U L S E T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L
some of the work done at the Center for Advanced
Power Systems (CAPS) at Florida State University. CAPS
has a fourteen rack simulator that is used for more
traditional power system applications, but is also
applied to naval systems and power hardware-in-the-
loop (HIL) simulations. CAPS has combined the RTDS
Simulator with a 5 MW dynamometer and a 5 MVA
amplifier for HIL simulations. The dynamometer is
controlled from the real time simulation and used as
a load for machines under test. The amplifier, which
consists of a controlled rectifier and a VSC inverter,
is capable of operation in all quadrants of the real
and imaginary power plain. It is part of the electrical
system interface between the RTDS Simulator and
the high power electrical system. The voltage fromthe simulation drives the amplifier in the high power
circuit while the current produced is measured and
fed back to the simulation. Once it is read into the
simulator, the current is injected into the digital
circuit to close the loop. CAPS has conducted ground
breaking research regarding the stability of these
HIL simulations and has the most advanced facility
of its kind in the world with the RTDS Simulator as
the heart of the system.
Huge changes have been made to both the simulator
hardware and software over the last fifteen years
changes which have been driven by customer feed-
back and a deep understanding of power system
simulation. The component models have been refined,
enhanced and tested over and over again. Several
new and exciting applications have been developed.
The simulator has been widely adopted by the power
engineering world. But most importantly, the focus
for the RTDS Simulator remains on continuing the
process of refining the system to better serve the
power systems and electrical industries.
Figure 1 Power hardware in the loop testing at FSU-CAPS of a 5 MW superconducting prototype marine propulsion motor.
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A hybrid gas-electric vehicle uses an energy stor-
age device in concert with an internal combus-
tion engine to provide propulsion to the vehicle;
thereby offering performance and operational
benefits not possible using only a single source
of energy [1], [2], [3]. Presented here are the
results of using PSCAD to develop a bidirectional
DC/DC converter to control power flow between the
engine and the DC bus of a series hybrid electric
vehicle. The converter allows a single permanent
magnet DC (PMDC) electric machine to be used for
both engine starting and generating modes as
shown in Figure 1.
PSCAD was used to study and refine the power
electronics and the control system methodology.
Several operation scenarios were studied using
parametric studies to aid in the selection of switch-
ing frequency and DC link capacitor values. A control
system was developed for which the control parametersare selected and optimized using nonlinear simplex
optimization. The converter and optimized control
system have been tested under a simulated scenario to
verify acceptable functionality and performance for the
hybrid vehicle architecture in which it will be utilized.
Design of a Bidirectional Buck-Boost
DC/DC Converter for a Series Hybrid
Electric Vehicle Using PSCAD/EMTDCD. R. Northcott, Westward Industries Ltd.
A. R. Chevrefils, Manitoba HVDC Research CentreS. Filizadeh, University of Manitoba
In this hybrid architecture the DC/DC converter plays
an important role in regulating the power flow in the
system. The battery bank voltage will vary with the
operating conditions of the vehicle. Since the battery
is directly connected to the main electrical node in the
system, it will make up the difference of the current
coming from the DC/DC converter going into the motor
drive as follows:
Although this arrangement saves the cost of a
converter at the battery terminals, the analysis of the
DC/DC converter operation becomes more complicated
and the performance of its control system becomes
more important. A design process that relies on accu-
rate simulations of the system and takes advantage
of design tools, such as simulation based optimization,
has been employed.
Design Specifications The DC/DC converter has been
designed to function within the system detailed in Fig-
ure 1. The required specifications are given in Table I.
Figure 1 Architecture of the series hybrid vehicle under study.
Table 1 DC/DC converter specifications
ParameterVoltage
Specification
Current
Specification
Engine starting mode
Motor-generated
output0 to 40V 0 to 50A
DC bus input 60 to 80V 0 to 50A
Engine generating mode
Motor-generated
input60 to 72V 0 to 150A
DC bus output 60 to 80V 0 to 100A
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10 P UL SE T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L
The Bidirectional Buck-Boost Converter
The bidirectional buck-boost DC/DC converter circuit
used is shown in Figure 2. The power electronic switch
S1 is used for boost converting while the switch S2 is
used for the buck conversion mode, where the two
modes control the power flowing in reverse directions.
In this design, the buck converter mode is used for
engine starting while the boost converter mode is
used to control the electric current from the generator
into the batteries and the motor drive. To reduce the
number of components, the PMDC machines induct-
ance is used as the filter inductance L, in Figure 2.
Converter Design and Simulation A simulation
case is developed using the PSCAD/EMTDC transient
simulator, which is capable of capturing transient
effects of the converter switching, as well as macro-
scopic effects from the vehicle drive train. Simula-
tions are run using a set of worst case conditions for
the boost mode of operation to select the switching
frequency and the DC-link capacitor sizing, after which
the more straight forward buck mode of operation
is confirmed using the values selected for switchingfrequency and DC-link filter capacitor. For details
please refer to [5].
To ensure expected operation of the vehicle, it is
important to accurately and responsively control the
power flowing from the engine through to the DC bus.
Thus, a closed-loop controller design is undertaken to
control the boost-mode operation of the converter, the
parameters of which are tuned using the integrated
non-linear simplex optimization methods of PSCAD.
Boost Mode Control System Development
The boost converter mode controls the power flow
from the engine to the main DC bus by varying its
duty cycle. The selected control topology is actually a
minimum selection of three individual control methods
as shown in Figure 3. Under normal conditions, power
flow control mode will be active. To protect the power
electronic switches and prevent over-currents, an over-
current limit is enforced using a current control loop.
As shown in Figure 1, the batteries are directly
connected to the DC bus. In order to protect the
batteries and other components on the bus, voltage
control is put in place as the final of the three control-
loops. The minimum block will automatically activate
the controller with the lowest output, thereby respect-
ing the upper limits of voltage, current and the existing
power set point.
Figure 2 The bidirectional buck-boost converter.
Figure 3 Boost converter control system block diagram.
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N O V E M B E R 2 0 0 9 1
It should be noted that the selected boost converter
topology exhibits a nonlinear voltage response. The
formula relating the voltage boost factor to the duty
cycle [4] is given as:
This can be linearized by first passing the PI output
through the following characteristic before sendingit on to the gate driver:
Where DNL is the non-linearized duty cycle from the PI
controller and DL is the duty cycle which will linearize
the response of the converter for the PI controllers
efforts. This is done to allow for simpler tuning of
the PI controller and allows for improved controller
performance.
Controller Implementation and Tuning Each of
the three control loops are connected and optimized
individually before being tested together as a complete
system. Initial PI control parameters are chosen
intuitively using a trial and error process until the
system begins to converge after a step-change in the
set point. The PSCAD test circuit is shown in Figure
4 and the optimization test cycle is shown in Table 2.
The test strategy is two different transients: (i) a step
change in the voltage followed by (ii) a step change
in the current.
The performance of the controller using initial param-eters is shown in Figure 5. The initial overshoot can be
ignored as it is mainly a consequence of the initializa-
tion of the simulation, a normal start-up would gently
ramp the set point from the existing DC bus conditions.
The objective function for the optimization will scale
and accumulate control loop error from 10ms to
50ms. Through multiple trials, the optimization will
successively and automatically (i.e. without designerintervention) improve the performance by adjusting
the Proportional Gain (P) and Integral Time (I) variables
until a chosen tolerance has been reached [6]. The
Simplex Optimum Run control block is configured
as shown in Figure 6.
Figure 4 Buck-boost DC/DC converter optimization circuit.
Table 2 Voltage controller optimization test cycle.
Figure 5 Voltage control results with initial parameters.
The optimization will successively and automatically
(i.e. without designer intervention) improve the
performance by adjusting the Proportional Gain (P)
and Integral Time (I) variables.
0
10
20
30
40
50
60
70
80
90
100
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
Time (s)
)V(egatloV
VoutSetpoint Vout
Time (ms) Voltage set point (V) Load current (A)
0 75 0
25 65 0
35 65 65
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1 2 P U LS E T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L
The objective function for this optimization is simplythe square of the controller error. Squaring the error
is done to make all errors positive for the accumulator
and can also be shown to speed the convergence of
the optimization.
As seen in Figure 7, the optimization converges toward
a better set of parameters for the system. Figure 8
shows the new tuning parameters in action. It is up
to the designer to decide if this result is acceptable,
or if modification should be undertake to the control
scheme or objective function to achieve better results.
This same optimization procedure is run for the current
and power controllers, each time producing a betterset of parameters than the initially determined values.
Full System Evaluation A full control system test
schedule is developed and shown in Table 3. It includes
the desired maximum voltage and current set points,
as well as varying the power set point.
As shown in Figure 9, the system initially operates in
power control mode, then enters current control mode
when the power set point is increased towards 8 kW.
Under this condition, 8 kW is not achievable without
violating the current limit. At approximately 0.35s,
the system enters voltage control mode when a large
current is injected into the battery from an external
source, to simulate a heavy regenerative braking
condition. The duty cycle is cut back dramatically to
keep the voltage at the 90V maximum.
Figure 7 Optimization progress for voltage controller.
Figure 8 Optimized voltage controller performance
Table 3 Control system test schedule.
Figure 6 Simplex Optimum run configuration.
0
20
40
60
80
100
120
0 10 20 30 40 50 60
Trial #
seulaVevitcejbO
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
seulaVI,P
Objective P I
0
10
20
30
40
50
60
70
80
90
100
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
Time (s)
)V(egatloV
VoutSetpoint Vout
TimeLoad
Current
Pout
set point
Iout
set point
Vout
set point
0 ms 40 A 5 kW 100 A 90 V
200 ms 40 A 8 kW 100 A 90 V
300 ms -100 A 8 kW 100 A 90 V
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N O V E M B E R 2 0 0 9 1
As can be seen from the data, controller overshoot
on the order of 10% for a short time can be expected
from this control scheme. This is because the PI con-
trollers do not have integrator ramp-up limiting, and
as a result there exists an adjustment period between
mode transitions. This can either be made acceptable
by ensuring a safety margin in the set point, or through
some additional modification and tuning of the controlscheme. A possible solution could involve back-calculat-
ing and setting the integrator PI controller upon transi-
tion between control modes.
Conclusion The results of the design and develop-
ment of a bidirectional DC/DC converter as a module
for a series hybrid vehicle were presented. PSCAD/
EMTDC was used to study several transient and
steady-state operation characteristics during the design
process. The effects of switching frequency and duty
cycle were studied, as well as different values of DC
link capacitor values were evaluated and several design
decisions were made on this information. Finally, a
closed loop control system was formulated and the
parameters were optimized to improve some system
performance metrics. The converter and control
system were simulated using a simple battery model
and current source to test the functionality of the
developed control scheme.
References
[1] M. Ehsani, Y. Gao, S. E. Gay, and A. Emadi, Modern Electric, Hybrid
Electric, and Fuel Cell Vehicles, Fundamentals, Theory, and Design,
New York: CRC Press, 2005.
[2] J. M. Miller, Propulsion Systems for Hybrid Vehicles, UK: IEE, 2004.
[3] Emadi, K. Rajashekara, S. S. Williamson, and S. M. Lukic,
Topological Overview of Hybrid Electric and Fuel Cell Vehicular
Power System Architectures and Configurations, IEEE Transactions
on Vehicular Technology, vol. 54, no. 3, pp. 763-770, May 2005.
[4] M. H. Rashid, Power Electronics, Circuits, Devices, and
Applications, 3rd ed. Upper Saddle River, NJ: Pearson Education, 2003.[5] D.N. Northcott, S. Filizadeh, A.R. Chevrefils,
Design of a Bidirectional Buck-Boost DC/DC Converter for a Series
Hybrid Electric Vehicle Using PSCAD/EMTDC, IEEE Conf. Proc.
Vehicle Power and Propulsion Conference, 2009, VPPC 2009
[6] M. Gole, S. Filizadeh, P. L. Wilson, R. W. Menzies,
Optimization-Enabled Electromagnetic Transient Simulation,
IEEE Tran. Power Delivery, vol. 20, no. 1, pp. 512-518, January 2005.
Figure 9 Results of full system test simulation.
0
20
40
60
80
100
120
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45
Time (s)
)A(tnerruC,)V(egatloV
0
1
2
3
4
5
6
7
8
9
10
)Wk(rewoP
Iout Vout Pout
Current ModePower Mode Voltage Mode
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J U N E 2 0 0 81 4 P U LS E T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L1 4 P U LS E T H E M A N I T O B A H V D C R E S E A R C H C E N T R E J O U R N A L
The Manitoba HVDC Research Centre is commit-
ted to providing effective training programs to
satisfy clients specific needs. From beginners
to experts, we have programs that will assist
all clients in obtaining their learning objectives.
The Centre offers a wide variety of PSCAD and
general power systems training courses to cover an
extensive range of learning needs. Some of our
standard courses include:
Introduction to PSCAD and Applications
HVDC Theory and Controls
AC Switching Study & Insulation Coordination Studies
Power Quality
Wind Power Modeling and Simulation
Modeling and Applications of FACTS Devices
Advanced Topics in PSCAD Simulation Training
o Machine Modeling including SSR Investigation
o Developing Custom Models for PSCAD
As an added benefit to these standard courses, our
instructors will discuss with the participants their
specific areas of interest and whenever possible,
tailor the course examples to be of most relevance.
This helps to ensure that individual learning objectives
will be met.
Some of these courses are designed to be a hands-
on learning environment where each participant is
provided with a temporary PSCAD license. This allows
individuals to experiment with the power system
phenomena being discussed and view the results.
Experimentation aids in learning the fundamentals
of a new topic.
We strive to keep classroom sizes small, providing
ample opportunity for questions and discussions.
Instructors are able to facilitate these extra discussions,
provide additional information, and elaborate on
study topics. Class members are also welcome to
share their experience and knowledge with the
group. The opportunities to hear others experiences
and network with them throughout the course is
valuable for all participants.
On-Site Training The Centre offers on-site training
sessions to its clients. There are a variety of reasons why
clients may choose to have an instructor travel to their
location. On-site training provides:
Custom courses arranged to meet your schedule.
Travel logistics: It is sometimes more convenient for
a company to have our instructor travel to their
location rather than sending a group to our location.
Large number of participants: In cases where a large
number of individuals are interested in receiving
training, it may be more feasible to have our
instructor travel to a clients location.
Necessity for a larger scope of study topics: On-site
training, dedicated to a group with similar learning
needs, can have a custom-made agenda. Our course
outlines can be modified to suit the specific
application needs of the group.
Company dedicated training: Clients who arrange
for our custom, on-site courses have the opportunity
to learn along side their fellow colleagues in an
environment that is familiar to them. Clients also
have the option of inviting individuals from outside
their organization to join their session.
In general, when people hear the word custom,
they think in terms of expensive and premium. This is
simply not the feedback we receive from our training
clients. Often the most effective and productive use of
time and money is receiving the training that meets
your needs content, schedule and location.
Dedicated course material can be provided through
our custom training programs, which can be delivered
to groups or individuals. Dedicated training for an
individual can be an effective way to have your specificquestions addressed in a timely fashion. These courses
range from one day to several weeks in duration, and
can be based on one or more of our standard courses
or be entirely customized to meet the clients needs.
Knowledge is KeyT. Stokotelny, Manitoba HVDC Research Centre
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PUBLICATION AGREEMENT # 41197
RETURN UNDELIVERABLE CANADIAN ADDRESSES
MANITOBA HVDC RESEARCH CENTRE I
244 CREE CRESCE
WINNIPEG MB R3J 3W1 CANA
T +1 204 989 1240 F +1 204 989 1
N O V E M B E R 2 0 0 9 1
Instructors Our skilled team of instructors are
not only proficient in PSCAD, they bring years of
experience in the power systems industry to the
classroom. In order to compliment our instruction
team, we often partner with internationally renowned
professionals from the University of Manitoba and
local industry. This combination of experience and
knowledge creates a highly productive and enjoyable
learning environment.
Schedule Courses are regularly offered at ouroffice in Winnipeg, Canada, and also are periodically
scheduled for various locations around the globe.
More Information Upcoming courses are always
listed on the back cover of our Pulse Newsletter.
Also be sure to regularly check the Training page
on our website at https://pscad.com/services/training/
for the most up-to-date training schedule.
For further information on our training programs,
please contact [email protected] .
Did you know that the ManitobaHVDC Research Centre provided
training courses and seminars to
611 people in 12 countries in 2008?
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Expanding KnowledgeThe following courses are available, as well
as custom training courses please contact
[email protected] for more information.
Introduction to PSCAD and Applications
Includes discussion of AC transients, fault and
protection, transformer saturation, wind energy,
FACTS, distributed generation, and power quality
with practical examples. Duration: 3 Days
Advanced Topics in
PSCAD Simulation Training
Includes custom component design, analysis of
specific simulation models, HVDC/FACTS, distributed
generation, machines, power quality, etc.
Duration: 24 Days
HVDC Theory & Controls
Fundamentals of HVDC Technology and
applications including controls, modeling
and advanced topics. Duration: 45 Days
AC Switching Study Applications in PSCAD
Fundamentals of switching transients,modeling issues of power system equipment,
stray capacitances/inductances, surge arrester
energy requirements, batch mode processing
and relevant standards, direct conversion of
PSS/E files to PSCAD. Duration: 23 Days
Distributed Generation & Power Quality
Includes wind energy system modeling, integration
to the grid, power quality issues, and other DG
methods such as solar PV, small diesel plants,
fuel cells. Duration: 3 Days
Wind Power Modeling and
Simulation using PSCAD
Includes wind models, aero-dynamic models,
machines, soft starting and doubly fed connections,
crowbar protection, low voltage ride through
capability. Duration: 3 Days
Industrial Systems Simulation & Modeling
Includes motor starting, power quality, capacitor
bank switching, harmonics, power electronic
converters, arc furnace, protection issues.
Duration: 12 Days
Lightning Coordination & Fast Front Studies
Substation modeling for a fast front study,
representing station equipment, stray capacitances,
relevant standards, transmission tower model for
flash-over studies, surge arrester representation
and data. Duration: 2 Days
Modeling and Application of FACTS Devices
Fundamentals of solid-state FACTS systems.
System modeling, control system modeling,
converter modeling, and system impact studies.Duration: 23 Days
Connect with Us!November 2225, 2009
SNPTEE Conference
www.xxsnptee.com.br
Recife, Brazil
January 2024, 2010
Elecrama 2010
www.elecrama.com
New Dehli, India
More events are planned! Please see
www.pscad.com for more information.
PSCAD Training Sessions
We regularly schedule training courses at the
Manitoba HVDC Research Centre, Winnipeg,
Manitoba, Canada, so please see www.pscad.com
for more information about course availability.
Please visit Nayak Corporation's websitewww.nayakcorp.com for courses in the USA.
For more information on dates,[email protected] today!
If you have interesting experiences and would
like to share with the PSCAD community in
future issues of the Pulse, please send in your
article to [email protected]