Pulse Nov2009

8/8/2019 Pulse Nov2009

1/16

HI G

H -P O W E R ED RESE

AR

CH

F

O

RT

H

ER

E

A

L

WO

RL

D

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

8/8/2019 Pulse Nov2009

2/16

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.

8/8/2019 Pulse Nov2009

3/16

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.

8/8/2019 Pulse Nov2009

4/16


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

8/8/2019 Pulse Nov2009

5/16

N O V E M B E R 2 0 0 9

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.

8/8/2019 Pulse Nov2009

6/16


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.

8/8/2019 Pulse Nov2009

7/16

N O V E M B E R 2 0 0 9

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

8/8/2019 Pulse Nov2009

8/16


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.

8/8/2019 Pulse Nov2009

9/16

N O V E M B E R 2 0 0 9

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

8/8/2019 Pulse Nov2009

10/16

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.

8/8/2019 Pulse Nov2009

11/16

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

8/8/2019 Pulse Nov2009

12/16

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

8/8/2019 Pulse Nov2009

13/16

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

8/8/2019 Pulse Nov2009

14/16

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

8/8/2019 Pulse Nov2009

15/16

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

[email protected]

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?

8/8/2019 Pulse Nov2009

16/16

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]

Documents

Pulse Nov2009