power electronics in power systems - controllers …sasidharan.webs.com/documents/jec final.pdf ·...

1

POWER ELECTRONICS IN POWER SYSTEMS

- CONTROLLERS

By

JEC - STTP

Sasidharan Sreedharan

www.sasidharan.webs.com

2

Executive Summary

The work presents the application of power electronics in power system with special emphasis on artificial intelligence based controllers for renewable integration

JEC - STTP

Power Electronics in Power System

“POWER ELECTRONICS IN POWER SYSTEM – CONTROLLER”

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Electric power systems are comprised of components that produce electrical energy and

transmit this energy to consumers.

A modern electric power system has mainly six main components:

• Power plants which generate electric power,

• Transformers which raise or lower the voltages as needed

• Transmission lines to carry power

• Substations at which the voltage is stepped down

for carrying power over the distribution lines

• Distribution lines

• Distribution transformers which lower the voltage

to the level needed for the consumer equipment.

Problem • We need to supply good quality power (possibly pure sinusoidal supply at rated voltage

and frequency) at minimum cost to consumers.

• But it is very difficult and challenging and duty of Power Electronics too.

• Power Electronics: is the electronics applied to conversion and control of electric

power

• Often Power Electronics applications in renewable integration of power system is by

embedding algorithm to an intelligent controller and hence the title

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POWER ELECTRONICS

IN POWER SYSTEM

- KEY DIAGRAM

Contents

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Part Topic

1 Challenges faced by the power sector

2 High Voltage Direct Current Transmission System (HVDC)

3 Flexible AC Transmission Systems (FACTS)

4 Custom Power Devices

5 Controllers for the grid integration of renewables

Conclusion Power Electronics in Smart Grid

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6

Presentation Objective &

Approach

• Identify the problems and challenges

faced by the power sector.

• Explore the possible power electronic

solutions to solve those problems.

7

PART- I

CHALLENGES FACED BY THE

ELECTRICAL POWER SECTOR

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Major Challenges faced by Electrical Power Sector

1. High reactive power losses & its management

2.Grid stability at large scale integration of renewables.

3. Limited transmission capacity

4. Power quality issues

5. Control of power flow

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INDIAN POWER GRID AT A GLANCE

http://www.srldc.org

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HIGH VOLTAGE DC CURRENT

TRANSMISSION (HVDC)

PART- II

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SOLUTION

HVDC is the only practical solution

to the above stated problems

HVDC Links In India

Asynchronous Connection and Bulk Power Transfer

1.Interconnection of non-

synchronous AC power systems, even at different frequencies.

2.Power transmission over long

undersea cable links.

3.Point-to-point, long-distance

transmission of large blocks of power.

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Advantages

• Voltage transformation

• Asynchronous Tie /Link

• Frequency as system-wide control signal

• Low losses (direct current)

• No limitations in length (Cables can be used over long

distances as there is no reactive power consumption)

Limitations

• Base costs for converter stations economically interesting only at

longer distances

• Point-to-point connection (multi-terminal possible with VSC -

HVDC)

Salient Features of HVDC Transmission

System

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HVDC Transmission System Model

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Source: http://www.ptd.siemens.de/artikel0506.html

HVDC EAST- SOUTH INTERCONNECTION IN INDIA

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Source: http://www.ptd.siemens.de/artikel0506.html

HVDC INSTALLATIONS

EAST- SOUTH INTERCONNECTION IN INDIA

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HVDC Topologies

Source: http://www.abb.com/hvdc

http://www.abb.com/hvdc



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HVDC Classic

• Mostly used for long distance point-to-point transmission

• Requires fast communication channels between two stations

• Large reactive power support at both stations

• Thyristor valves are commonly used.

• Line or phase commutated converters are used.

HVDC Light

Power transmission through HVDC utilizing voltage source converters

with insulated gate bipolar transistors (IGBT) which extinguishes the

current more faster and with less energy loss than GTOs.

• It is economical even in low power range.

• Real and reactive power is controlled independently in two HVDC

light converters.

• Controls AC voltage rapidly.

• No contribution to short circuit current.

• No need to have fast communication between two converter stations.

• Operates in all four quadrants.

• PWM scheme is used.

HVDC Technologies

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MATLAB MODEL OF 1000MW HVDC TRANSMISSION SYSTEM

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HVDC PLACEMENT ANALYSIS IN POWER SYSTEM

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HVDC PLACEMENT IN POWER SYSTEM

(Power Flow Analysis)

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(Voltage Profile)

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(Power Flow Profile)

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HVDC WORLD WIDE INSTALLATIONS

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• The power system can be stabilized and the

transmission limitations on the AC line can be

increased by using HVDC .

• A HVDC transmission line costs less than an AC line

for the same transmission capacity.

• However, the terminal stations are more expensive in

the HVDC case due to the fact that they must

perform the conversion from AC to DC and vice

versa.

• The "break-even distance“ for long overhead lines

is > 700 km

CONCLUSION - HVDC

• HVDC can control/ transmit contracted amounts of power and alleviate unwanted

loop flows.

• An HVDC link can alternatively be controlled to minimize total network losses

• An HVDC link can never be overloaded

• The HVDC damping controller is a standard feature in many HVDC projects in

operation. It normally takes its input from the phase angle difference in the two

converter stations. (see fig.)

27

PART- III

FLEXIBLE AC TRANSMISSION SYSTEMS

(FACTS)

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Flexible AC Transmission System

Alternating current

transmission systems

incorporating power

electronics-based and

other static controllers to

enhance controllability

and increase power

transfer capability

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Sub-synchronous resonance

• Resonant frequencies below the

fundamental.

• Occurs due to interaction between

series capacitors and nearby

turbine‐generators

Role of FACTS

• Dynamic: – Transient and

dynamic stability

– Sub synchronous oscillations

– Dynamic overvoltage and under voltages

– Voltage collapse

– Frequency collapse

• Steady-State:

– Uneven power flow

– Excess reactive power flows

– Voltage capability

– Thermal capability

30 JEC - STTP

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Benefits of FACTS Control of power flow

– Contractual Power Flow

– Increase the loading capability of lines to their

thermal capabilities.

– Increase the system security through raising the

transient stability limit, limiting short-circuit currents and

overloads, managing cascading blackouts and damping

electromechanical oscillations of power systems and

machines.

Provide secure tie line connections to neighboring utilities

and regions thereby decreasing overall generation

reserve requirements on both sides.

– Provide greater flexibility in new generation.

– Reduce reactive power flows, thus allowing the lines to

carry more active power. JEC - STTP

FACTS Devices

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• Static VAR Compensator - SVC

• Thyristor Controlled Series Compensator - TCSC

• Thyristor Controlled Phase Angle Regulator - TCPAR

• Static Synchronous Compensator - StatCom

• Solid State Series Compensator - SSSC

• Unified Power Flow Controller - UPFC

Shunt connected controllers

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Series connected controllers

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Combined shunt and series connected controllers

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Other controllers

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FACTS devices are solid-state converter that have the capability of control of various electrical parameters in transmission circuit Thyristor Controlled Series

Compensator (TCSC)

Static VAR Compensator (SVC)

Unified Power Flow Controller (UPFC)

Static Compensator (STATCOM)

Static Synchronous Series Compensator (SSSC), etc

37

etc etc

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FLEXIBLE AC TRANSMISSION SYSTEM

38 JEC - STTP

•(TG- Turbine Governor; AVR-Automatic Voltage regulator; C-Synchronous Compensator)

CASE STUDY: SVC PLACEMENT IN KERALA GRID

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SVC

SVC

SVC

SVC


40

0.00

1.00

2.00

3.00

4.00

5.00

6.00

1 3 5 7 9 11 13 15 17 19 21 23 25

Rea

l pow

er l

oad

(pu

)

Bus no.

Base case (with out wind)

Base case (with wind)

Maximum penetration (with controller)

0.95

0.97

0.99

1.01

1.03

1.05

1.07

1.09

1.11

1 2 3 4 5 6 7 8 9 10111213141516171819202122232425

Bu

s volt

age

(pu

)

Bus no.

Base Case (with out wind)Base case (with wind)Maximum penetration (with controller)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

1 3 5 7 9 11 13 15 17 19 21 23 25

Rea

l pow

er g

ener

atio

n (

pu

)

Bus no.



Maximum penetration (with controller)

-15

-10

-5

0

5

10

15

-6 -5 -4 -3 -2 -1 0

Eigen value(0 to-5)

Eigenvalue (Real part)

Eig

enval

ue

(Im

agin

ary p

art)

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Wind Farm Bus : 1,21

Slack Bus : 5


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PART- IV

CUSTOM POWER DEVICES

(Power Quality Solutions)

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Custom Power & FACTS

• Similar to FACTS for the transmission systems, the term custom power (CP)

means the use of power electronic controllers for distribution systems.

• Custom power devices enhances the quality and reliability of power that are

delivered to customers.

• There is also a concept called “Custom Power Park” that can serve customers

who demand a high quality of power and ready to pay a premium price for the

service.

• Custom power assures the pre-specified quality/ specifications:

– Reduce the Frequency of rare power interruptions.

– Magnitude and duration of over and under voltages within specified

limits.

– Low harmonic distortion in the supply voltage.

– Low phase unbalance.

– Low flicker in the supply voltage.

– Frequency of specified voltage with specified limits

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Custom Power Devices

• Customer power devices can be classified in to two main types.

– Reconfiguring type

– Compensating type

• Reconfiguring type - Changes the network topology or re-configure the next

work by altering the network.

– Solid State Current Limiter (SSCL)

– Solid State Circuit Breaker (SSCB)

– Solid State Transfer Switch (SSTS)

• Compensating devices - Compensate a load, by correcting power factor,

balancing an unbalanced load or improve the quality of the supply voltage

– Distribution STATCOM (D-STATCOM)

– Dynamic Voltage Restorer (DVR)

– Unified Power Quality Conditioner (UPQC)

(D-STATCOM is a shunt device used for load compensation, dynamic and static voltage control. DVR is a series connected

device used for voltage compensation. UPQC is a combination of D-STATCOM and DVR.)

.

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Solid State Current Limiter

• The major components are an inductor, pair of opposite poled switches (GTOs or IGBTs) and a snubber circuit.

• Snubber circuit is a series RC circuit which prevents a huge sudden voltage rise across the inductor.

• Current limiter is connected in series with the feeder such that it can restrict the fault current in case of a fault downstream.

• During the normal operation the opposite poled switches remained closed. JEC - STTP 44

Solid State Circuit Breaker

• Same topology as that of SSCL, except the current limiting

inductor is connected in series with the thyristor pair.

• These thyristor pair is switched on simultaneously with the

bidirectional switch and switch off upon detection of fault.

• This will force the current to flow through the thyristors and

current limiting inductors.

• The thyristor pair is blocked after few cycles if the fault still

persists.

• In this case, the current through the thyristor will cease to flow in

the next available zero crossing.

• There still might be a small amount of current flow through the

snubber circuit which can be easily interrupted by a mechanical

switch.

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Solid State Transfer Switch

• Used to transfer power from the preferred to alternative sources in case of a

problem in the preferred feeder (e.g. voltage sag or swell, fault on the

feeder).

• This switch could be used to protect sensitive loads.

• The main component of SSTS is two pair of opposite poled switch

(thyristors).

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Compensating Custom Device -

DSTATCOM

• Distribution Static Compensator (DSTATCOM) is basically

the same as STATCOM used in the transmission system,

except the switches used here are high speed medium power.

Load compensating DSTATCOM

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DSTATCOM

• Distribution STATCOM (DSTATCOM) exhibits high speed

control of reactive power to provide voltage stabilization,

flicker suppression, and other types of system control.

• The compensator must inject current such that Is becomes

fundamental and positive sequence.

• In addition to those the compensator can also make the

current Is to be in phase with bus voltage at Bus-2.

• DSTATCOM is compensating load current.

• As far as the utility is concerned Load along with the

DSTACOM is drawing a unity power factor and balanced

current at fundamental frequency.

• The desired performance of the DSATCOM is that it

generates a current If such that it cancels the reactive,

harmonic components and balanced the load current. JEC - STTP 48

DSTATCOM - Analysis

Example: Consider the following circuit in which

the voltage sources is considered to be stiff.

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DSTATCOM operating in the

current control mode

DSTATCOM

• The DSTACOM injects

currents that cancel

harmonics from load current

and also balance the load.

• It also forces the current draws

from the source to be in phase

with the voltage at PCC, i.e.

draws current at unity power

factor (only real current).

• Power supplied by the sources

is constant, the power supplied

by the DSTATCOM has zero

mean.

• DSTATCOM neither absorbs or

injects real power to the load. JEC - STTP 50

Voltage Regulating DSTATCOM

• The basic idea in this kind of schemes is to inject the current id in such a

way that the voltage vt follows a specified reference.

• The DSTACOM should operate in such a manner that it does not inject or

absorb any real power in the steady state.

• The magnitude of the terminal voltage can be arbitrarily chosen.

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52

Matlab Model of DSTATCOM

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Case Study-Arc Furnace

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For weak distribution systems where the operation of arc furnaces causes

significant power quality problems, a high performance flicker compensation

device is necessary.

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• The flicker caused by the arc furnace operation was measured by use of

a flicker meter.

In this application, the flicker suppression realized was 58% on

average with utilization of the DSTATCOM. http://www.donsion.org

Dynamic Voltage Regulator (DVR)

• A Dynamic Voltage Regulator is used to protect sensitive loads from sag/swell or disturbances in the supply voltage.

Vl=Vt+Vf

• Where Vl is the load bus voltage, Vt is the terminal voltage and Vf is the DVR

voltage.

• DVR can regulate the bus voltage to any arbitrary value by measuring terminal

voltage and supplying the balance voltage Vf.

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Dynamic Voltage Regulator (DVR)

Unified Power Quality Conditioner (UPQC)

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• A device that is similar in construction to a Unified Power flow

Conditioner (UPFC).

• The UPQC, just as in a UPFC, employs two voltage source inverters

(VSIs) that are connected to a d.c. energy storage capacitor.

• One of these two VSIs is connected in series with a.c. line while the

other is connected in shunt with the a.c. system.

• A UPQC that combines the operations of a Distribution Static

Compensator (DSTATCOM) and Dynamic Voltage Regulator (DVR)

together

Unified Power Quality Conditioner (UPQC)

• One of the serious problems in electrical systems is the increasing number of

electronic components that injects harmonics in the distribution system.

• The device that can be used for this purpose is unified power quality conditioner

(UPQC)

• If the source voltage is unbalanced and distorted, the terminal voltage will also be

unbalanced and distorted and all the customers connected to the feeder will be

affected.

• All the loads connected to the feeder, including unbalanced and nonlinear loads,

will have a balanced sinusoidal voltage.

• It will not be possible to correct the unbalance and distortion produced by source using this device.

• There are two ways of connecting a UPQC. – The series device is placed before the shunt

– The shunt device is placed before the series device.

• Usually, the inverter realizing the series device is supplied with a dc capacitor. Similarly, the shunt inverter is also supplied with a capacitor.

• In UPQC, these inverters are supplied by a common capacitor

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Custom Power Park (CPP)

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• A custom power park control center is fully loaded with a DSTACOM, a DVR and a stand by generator.

• The DSATCOM eliminates harmonics and/or unbalance, while the DVR eliminates any sag or distortion.

• Here the electrical power to the park is supplied through two feeders that are joined together via a SSTS.

• The SSTS ensures that the feeder with higher voltage selected in less than half a cycle in the case of a voltage dip or (sag).

• The SSTS can also be used to protect the loads in the park from dynamic over

voltage.

• DSTACOM when operated in voltage control mode and can provide reactive

power support to the park and maintain voltage.

• There are three different grades of power can be supplied to the park’s

customers.

– Grade A

– Grade AA

– Grade AAA

JEC - STTP 60


• Grade A: The basic quality power in the park.

– Since the SSTS protect the incoming feeders, the quality of power is usually better than the one from normal utility supply.

– In addition this grade has the benefit of low harmonic power due to the presence of DSTATCOM.

• Grade AA: This includes all the features of Grade A + – It also receives the benefits of standby generator which can be brought into

service with in 10-20 seconds (e.g. serious emergency such as power failure in both feeders).

• Grade AAA: This includes all the features of Grade AA+ It enjoys the benefits of receiving distortion and dip free voltage due to the presence of DVR.

– Semiconductor plant AAA

– Hospital both AA and AAA

– Shopping malls and office buildings AA

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PART- V

CONTROLLER FOR THE GRID INTEGRATION OF

RENEWABLES

The Work Presents the development of particle swarm optimization

based controller for maximizing the wind energy penetration in power

system.

63

(Controller/Algorithm)

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Controller Schematic

1. Consumer loads are changing instantaneously.

2. The nature of grid hence is very dynamic.

3. We have to supply power at the minimal cost to the consumers.

4. Wind is abundantly available and cost/unit is very less; and is also green.

5. Wind power has to be increased in the grid.

6. But as the wind share increases, there arise lots of instability problems in grid (Voltage and frequency).

7. So the question finally arises

HOW MUCH MAXIMUM WIND SHARE WE CAN ALLOW AT ANY TIME?

WHAT ARE THE METHEDOLOGIES AND TECHNIQUES FOR MAXIMIZING WIND PENETRATION

64

The Wind Penetration Controller Problem

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Control bus

Wind Farm Control

Pw Nf

1-Xn

1-X3

GN

1-X2

1-X1

G3 G2 G1

Market Analyzer and Planner

1+Y1 1+Y2

L1

1+Y3

1+Yn

L2 L3 LN

OPF

FACTS Controller Optimizer

Storage requirement

calculator

Contingency analysis

Combined load increase and generation

displacement method

Load increase method

Generation displacement

method

Voltage SSSA

Single

Objective

Multi

Objective

TSA

Optimization

Stability

Data bus Implemented Yet to implement

Grid Control

65 JEC - STTP

The Complete Wind Penetration Controller

Maximize

Pw; Real power output of all the wind farms to the grid by adjusting the grid parameters

Subject to

1. Power flow constraints Nodal power balance constraints

Active power generation limit constraints

Reactive power generation limit constraints

Voltage limit constraints

Line limit constraints

2. Wind generation constraints

3. Grid Stability Constraints Voltage stability constraints

Angle stability constraints

4. FACTS Controller Constraints

66 JEC - STTP

Controller Problem Description

67

It was developed in 1995 by J. Kennedy and R. Eberhart

PSO is a robust stochastic optimization technique base on the movement and intelligence of swarms.

PSO applies the concept of social interaction to problem solving.

It uses a number of agents (particle) than constitute a swarm moving around the search space looking for the best solution.

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Particle Swarm Optimization

68

IEEE 14-bus Test System

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•(TG- Turbine Governor; AVR-Automatic Voltage regulator; C-Synchronous Compensator)

WFPI Rank-1 for Bus No: 3

Case Study- IEEE 14 bus System

Problems in Wind

Farm Integration

Small Scale Impacts

• Branch flows and node voltages

• Protection schemes and fault

currents

• Power Quality

Large Scale Impacts

Power system dynamic

stability

Frequency control and load

following

Reactive power and voltage

control

Wind speed

Interconnection

bus strength

Interconnection

cable length

Wind farm

size

69 JEC - STTP

70

GRID

STABILITY

Angle Voltage

Fast voltage

stability Index

Line stability

factor

Small signal

stability analysis

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71 JEC - STTP

Methodology

Connect Wind

Farm at the

best suitable

bus.

Formulate

DFIG based

Wind Farm

model.

Using PSO,

calculate the

optimal grid

and FACTS

controller

settings

Obtain

maximum

wind

penetration

limit

Methodology

72

Objective Function

Constraints

GRID STABILITY CONSTRAINTS

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Detailed Problem Formulation

73 JEC - STTP

SVC is used for wind penetration maximization.

The location of the SVC is judged by conducting the static voltage

stability analysis and the setting is done by using PSO

Bus number Normalized tangent vector near collapse

point

14 0.015802

10 0.01404

13 0.013938

9 0.013764

FACTS Controller Placement

74

0.00

0.50

1.00

1.50

2.00

2.50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Rea

l pow

er l

oad (

pu

)

Bus no.



Maximum penetration (with

controller)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Rea

l p

ow

er g

ener

atio

n (p

u)

Bus no.



Maximum penetration (with

controller)

-15

-10

-5

0

5

10

15

-6 -5 -4 -3 -2 -1 0

eigen…

Eigen value (Real

part)

Eig

en v

alu

e (I

mag

inar

y p

art)

0.95

0.97

0.99

1.01

1.03

1.05

1.07

1.09

1.11

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Bu

s volt

age

(pu

)

Bus no.

Base case (with out wind)Base case (with wind)Maximum penetration (with controller)

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SVC

Bus:10,14

Analysis Results

Power Electronics in Smart Grid

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Smart Grid

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• The Smart Grid is a combination of hardware, management and reporting software, built atop an intelligent communications infrastructure.

• In the world of the Smart Grid, consumers and utility companies alike have tools to manage, monitor and respond to energy issues.

• The flow of electricity from utility to consumer becomes a two-way conversation, saving consumers money, energy, delivering more transparency in terms of end-user use, and reducing carbon emissions.

• The Smart Grid in large, sits at the intersection of Energy, IT and Telecommunication Technologies.

• Smart Grid Consists of the following

– Transmission Optimization

– Demand Side Management

– Distribution Optimization

– Asset Optimization

What is Smart Grid ? What is Smart Grid

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Demand Optimization Smart Metering –

Automatic, Time of Use, Consumer Communication & Load Control

Communications : Automated Metering Infrastructure (AMI) – LAN, WAN etc.

DRMS (Demand Response Management Sytem)

Elements of Smart Grid

It is having the following GIS (geo-spatial Information Systems),

AMI,

SAP (ERP),

OMS (Outage management System),

DMS (Distribution Management System),

EMS (Energy Management System),

DRMS (Demand Response management

System).

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80

Regards

Sasidharan Sreedharan

www.sasidharan.webs.com

JEC - STTP

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