Improving Power System Stability Through Integrated Power System StabilizersRudolf Wieser, Matthias Baechle, Valerijs Knazkins ATPE

OUTLINEControlled Generator on GridThe main functions of an Automatic Voltage Regulator (AVR)The main functions of a Power System Stabilizer (PSS)

How to test an AVR systemIntroduction to Real time Simulator

Grid Code compliance testingUNITROL built in compliance test functions

The main functions of an AVRAutomatic Voltage RegulatorState-of-the-art excitation systems are equipped with fast acting voltage regulators:Advantages:Fast acting voltage control and reactive power supportProviding synchronizing torque componentDisadvantage:Introducing negative damping torque component

Solution to the reduced damping torque problemPower System Stabilizers

Model of a single Generator connected to GridTurbine and Generator Mechanics Turbine driving torque TmGenerator braking torque TeMechanical rotational speed

Generator

Turbine

Tm

Te

Model of a single Generator connected to GridTurbine and Generator Connection to Grid Turbine + Generator Generator breaker Step-up transformerTransmission lineInfinite bus (constant voltage)

Generator

Turbine

Model of a single Generator connected to GridTurbine and Generator connected to Grid A single generator connected to a large grid can be represented by the Phillips-Heffron model (assuming constant field voltage and mechanical torque)

Generator

Turbine

K3s K3 Tdo + 1

K2

K2

K6

K5

K2

K4

K2

12H s

K2

K1

2pi*fNs

Kas Ka + 1

PSS

Tm

Te

Vg

Eq

Vfd

Vgref

0

Model of a single Generator connected to GridLinearized Model at certain Operating Point A single generator connected to a large grid can be represented by the Phillips-Heffron model (assuming constant field voltage and mechanical torque)

K3s K3 Tdo + 1

K2

K2

K6

K5

K2

K4

K2

12H s

K2

K1

2pi*fNs

Kas Ka + 1

PSS

Tm

Te

Vg

Eq

Vfd

Vgref

0

Model of a single Generator connected to GridTorque Disturbance Impact Harmonic Phasor RepresentationTorque equilibrium disturbanceElectric torque produces natural positive damping

K3s K3 Tdo + 1

K2

K2

K6

K5

K2

K4

K2

12H s

K2

K1

2pi*fNs

Kas Ka + 1

PSS

Tm

Te

Vg

Eq

Vfd

Vgref

0

Model of a single Generator connected to GridFast Voltage Control Impact Harmonic Phasor Representation Generator plus AVRElectric torque form AVR function produces negative damping torque

K3s K3 Tdo + 1

K2

K2

K6

K5

K2

K4

K2

12H s

K2

K1

2pi*fNs

Kas Ka + 1

PSS

Tm

Te

Vg

Eq

Vfd

Vgref

0

Model of a single Generator connected to GridPower System Stabilizer Function Power System Stabilizer (PSS)Band limited damping torque contributionSpeed estimator from electrical voltage and current signals

K3s K3 Tdo + 1

K2

K2

K6

K5

K2

K4

K2

12H s

K2

K1

2pi*fNs

Kas Ka + 1

PSS

Tm

Te

Vg

Eq

Vfd

Vgref

0

OUTLINEControlled Generator on GridThe main functions of an Automatic Voltage Regulator (AVR)The main functions of a Power System Stabilizer (PSS)

How to test an AVR systemIntroduction to Real Time Simulator

Grid Code compliance testingUNITROL built in compliance test functions

Synchronous Machine Transient Simulator Turbine, Generator, Transformer, Line to infinite Bus Typical turbine - generator arrangement in a power plantAutomatic Voltage Regulator (AVR)

Generator

Turbine

AVRExcitation

Governor

Synchronous Machine Transient Simulator Turbine, Generator, Transformer, Line to infinite Grid SMTS-RTReal Time Simulation of Turbine and governor (simplified)Generator Breaker and step-up transformerGrid representation with infinite Bus Voltage

Generator

Turbine

AVRExcitation

Governor

Synchronous Machine Transient Simulator Turbine, Generator, Transformer, Line to infinite Grid SMTS-RTAVR hardware in the loop Real Time Simulation

Generator

Turbine

AVRExcitation

Governor

Synchronous Machine Transient Simulator Turbine, Generator, Transformer, Line to infinite Grid SMTS-RT 6000UNITROL 6000

Synchronous Machine Transient Simulator SMTS-RT 6000; User Interface

OUTLINEControlled Generator on GridThe main functions of an Automatic Voltage Regulator (AVR)The main functions of a Power System Stabilizer (PSS)

How to test an AVR systemIntroduction to Real Time Simulator

Grid Code compliance testingUNITROL built in compliance test functions

AVR Grid Code ComplianceGrid Code ExampleExcerpt from of a local grid code:Overall Excitation System Control CharacteristicThe frequency domain tuning of the Power System Stabilizer shall also be demonstrated by injecting a 0.2Hz-2Hz band limited random noise signal into the Automatic Voltage Regulator reference while the Generating Unit is operating at a typical load level...The damping contribution of the Power System Stabilizer shall improve the system-stability within the frequency-band of interest (compared to the system response without a stabilizer): i.e., 0.2Hz - 2Hz

Grid Code Compliance TestingTest scheme for the measurement of the corresponding transfer function

Grid Code Compliance TestingTime domain-response of the system without the stabilizer, while injecting noise signals:

Grid Code Compliance TestingTime domain-response of the system with the stabilizer, while injecting noise signals:

Grid Code Compliance TestingTime domain-response of the system with the stabilizer, while injecting noise signals:

Grid Code Compliance TestingFrequency domain response of the system with (green line) and without (blue line) the stabilizer connected:

Grid Code Compliance TestingTime domain response of the system with (using different gains) and without (blue line) the stabilizer connected: