AN ADVANCED REACTIVE OWER MANAGEMENT SYSTEM FOR …

AN ADVANCED REACTIVE POWER

MANAGEMENT SYSTEM FOR THE

SEOUL METROPOLITAN POWER

SYSTEM

Scott G. Ghiocel1, Sangwook Han2, Byung-Hoon Chang3,

Yong-gu Ha3, Byong-Jun Lee2, Joe H. Chow1, and

Robert Entriken4

1Rensselaer Polytechnic Institute (RPI) 2Korea University (KU) 3Korea Electric Power Company (KEPCO) 4Electric Power Research Institute (EPRI)

AGENDA

• Overview

• Features

• Stability margin calculation

• Optimization

• Real-time dispatch

• Operator training

• Architecture

• Components

• Software

5/19/2011

2

SGG - EPRI Advanced Voltage Control Workshop

OVERVIEW

• Korean power system

• The Seoul metropolitan area is supplied by distant coastal

generation, which creates potential voltage stability issues.

• Over the last few years, KEPCO has installed 2 SVCs and

a STATCOM in the Seoul metropolitan area.

• Goals

• Coordinate the three FACTS controllers with local

switched shunt capacitors and reactors

• Maintain adequate voltage stability margin

• Reduce shunt switching

• Maintain steady-state voltages

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KOREAN POWER SYSTEM

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Seoul metropolitan area

MULTIPLE FACTS CONTROL SYSTEM

(MFCS) COMPONENTS

• Multiple FACTS Controller (MFC) – calculates

FACTS controller settings for voltage stability.

• Reactive Power Manager – coordinates FACTS

controllers and other reactive power resources.

Implements settings from the MFC algorithm.

Minimizes shunt switching through optimization.

• Background daemon program – monitors EMS output

for new state estimator solution

• MySQL database – data storage

• InTouch HMI – user interface

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5/19/2011 SGG - EPRI Advanced Voltage Control Workshop

SYSTEM ARCHITECTURE

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ALGORITHM

1. New state estimator solution arrives.

2. Reactive power manager starts the MFC algorithm.

3. While the MFC algorithm is working, the manager

calculates the VQ sensitivities and loads the SE data

into the database.

4. After the MFC is complete, the manager retrieves

the MFC results and loads them into the database.

5. The manager uses the MFC results to calculate the

reactive power dispatch, and loads the results into

the database.

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COMPONENT: MFC ALGORITHM

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MFC ALGORITHM – I

• PURPOSE: Determine the necessary dynamic Q

reserve to withstand major contingencies.

• INPUTS:

• State estimator solution (RAW file)

• FACTS controller parameters

• Contingencies

• Algorithm parameters

• OUTPUTS:

• FACTS controller settings: V references, Q reserves

• FV and YV curve data

• Uses continuation methods to evaluate stability

margins.

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Control the operating point

Secured margin

Capacitive Inductive 0

MFC ALGORITHM – II


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YV Analysis FV Analysis

1: Pre-Contingency

Flows (MW)

Bus

Voltage

[pu]

0

1 2

2: Post-Contingency

Pre-Contingency Operating Point

Post-Contingency Operating Point

Flow Margin

Parameter λ

Bus

Voltage

[pu]

1.0 0

λ max

1 2 3

1: Stable 2: Marginal 3: Unstable

MFC ALGORITHM – III

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YV Analysis

Individual FACTS controllers

State estimator data

No Yes

Yes

Emergency Check Alarm Check Normal conditions

Calculate Q reserves according to sensitivity analysis result

Stable? No

Yes

YV Analysis after adjusting Q reserves

Stable? FV Analysis

Stable?

No

Calculate Q reserves according to sensitivity analysis result

Stable? No

Yes

FV Analysis after Adjusting Q reserves

OPF module

Objective function : P Loss minimization NIPM algorithm

Determine the Q reserves and Vref of each substation

for stability Determine the Q reserves and

Vref of each substation for stability

Determine Vrefs of each substation

for Loss minimazation (need not Q reserves)

Stable? Stable?

COMPONENT: REACTIVE POWER MANAGER

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REACTIVE POWER MANAGER – I

• PURPOSE: Coordinate dispatch of FACTS

controllers and other reactive power resources

(optimization).

• INPUTS:

• State Estimator solution (PSS/e RAW file)

• FACTS controller setpoints (V references, Q reserves)

• System forecast data


• OUTPUTS:

• New dispatch for FACTS controllers and switched shunts

• VQ sensitivities

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SENSITIVITY-BASED REACTIVE POWER

DISPATCH – I

• The system VQ sensitivities (load lines) can be found from

the load flow Jacobian by setting ∆P = 0

from which we obtain the reduced Jacobian (JR)

• The reduced Jacobian matrix provides a linearized

relationship between V and Q

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DISPATCH – II

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-Q

capacitive

Q

inductive

Voltage

Vop 2

Vop 1

After insertion

Before insertion

ΔVcap

ΔQcap

sensitivity of voltage magnitude at

bus i due to reactive power insertion at bus k

i

k

V

Q

cap cap

sh

VV Q

Q

i

k

V

Q


DISPATCH – III

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-Q

capacitive

Q

inductive

Voltage

Vref

Vunc 1

Vunc 2

Vop 2

Vop 1

Droop LineAfter shunt

capacitor

Before shunt

capacitorΔVcap


DISPATCH – IV

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0 200 400 600 800 1000 12000

0.002

0.004

0.006

0.008

0.01

0.012

0.014

Bus #

V

(p.u

.)

Comparison of Loadflow Results and Prediction using VQ Sens.

dVLF

dV

REACTIVE POWER MANAGER – II

• Optimization:

• Maintain voltage stability (contingency survival)

• Implemented as constraints on the optimization

• Constraints on FACTS devices provided by the MFC algorithm

• Minimizing shunt switching action and device parameter

changes

• Incorporated into the objective function as a cost per switching

event

• Maintaining the desired voltage profile

• Incorporated into the objective function for specified pilot buses

• Voltage deviation from desired reference value

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REACTIVE POWER MANAGER – III

• Formulation:

• Linear program with continuous and discrete values (mixed–integer linear program)

• Continuous values: FACTS Q setpoints and/or V references

• Discrete values: Shunt switching logic

• Constraints:

• Device limits

• Bus voltage limits

• Voltage stability limits (on FACTS controllers)

• Objective function:

• Number of switchings

• Voltage deviation at pilot buses

• FACTS deviation from setpoints

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REACTIVE POWER MANAGER – IV

• VQ sensitivities are used to predict the voltage effects

due to reactive power injection, i.e.,

where is the inverse of the reduced load flow

Jacobian.

• Bus voltage constraints

i.e., the new dispatch must adjust the new voltage to be

within the specified bus voltage limits.

• Voltage stability constraints

• Ensure adequate FACTS dynamic reserve:

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1

RJ Q V

1

RJ

0 0

1

LOW HIGHRV V J Q V V V

FACTS setQ Q

REACTIVE POWER MANAGER – V

• OBJECTIVE FUNCTION:

• Terms

1. Number of shunt switchings

2. Number of FACTS Vref changes

3. Voltage deviation at pilot nodes

4. FACTS Q output deviation from setpoint values

• Ratio of weights in the objective determines priorities

in the optimization.

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1 2 3 4set pilot set FACTSc c c V V c Q Q

REACTIVE POWER MANAGER – VI

• System forecast:

• To optimize the shunt switching over longer periods of

time (several hours ~ few days), past and future data are

very useful.

• Future data (load forecasts) allows us to make smart

decisions about switching shunts.

• Example: Keep a capacitor on in the morning instead of turning

it off, in anticipation of a future load increase.

• Past data allows us to keep track of switching events, and

can be used as an alternative for prediction if forecast data

is not available.

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DATABASE (MYSQL)

• PURPOSE: Stores network and dispatch data for MFCS. Enables communication between HMI and other components.

• STORED DATA:

• State Estimator solutions (new and old)

• MFC results

• FACTS setpoints

• FV/YV curve data

• MFCS dispatch results (new and old)

• Input from InTouch HMI


• Contingencies

• Note: Database should be implemented on a separate server from the rest of the system.

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COMPONENT: MFCS HMI

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MFCS HMI – I

• PURPOSE: Displays MFCS data and allows the

operator to change contingencies and algorithm

parameters.

• DISPLAY SCREENS:

• One-line diagrams (present, past and future values)

• FACTS operator screens (including droop and load line)

• Device status (switched shunts, tap changers, etc.)

• Contingency analysis results

• MFC results

• MFCS configuration

• Contingencies

• Algorithm parameters (MFC and dispatch settings)

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MFCS HMI – III

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MFCS HMI – IV

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MFCS HMI – V

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MFCS HMI – VI

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MFCS HMI – VII

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MFCS HMI – VIII

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OPERATOR TRAINING SIMULATOR – I

• The MFCS can also be used in offline mode for

operator training.

• Operators select from a list of cases (RAW files), and

apply a contingency if desired.

• The MFCS runs the selected case, applying a

contingency directly to the RAW file (if requested),

and outputs the results to the InTouch HMI.

• MFCS can use any RAW file and contingency

combination for offline simulation and training.

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OPERATOR TRAINING SIMULATOR – II


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• Cases to consider:

• Line outages

• Daily variation

• Seasonal variation

• Contingencies:

• Single-line

• Double-line

• Interface line outages

• Metro area generator outages

IMPLEMENTATION

• Communication Links:

• SE data to MFCS: PSS/e version 30 RAW file

• Manager to/from MFC algorithm: ASCII text files

• Manager to/from database:

• MySQL client over TCP/IP

• MATLAB MySQL client over TCP/IP

• HMI to/from database: ODBC over TCP/IP (within control center firewall)

• MFCS to remote substations: TCP/IP over secured lines

• Software:

• MFC Algorithm: C++, FORTRAN

• Reactive Power Manager: MATLAB, Perl, MySQL, C++, C

• Database: MySQL

• HMI: WonderWare InTouch

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THANK YOU FOR YOUR ATTENTION!

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