studies on low inertia systems and application of ...€¦ · studies on low inertia systems and...

Studies on low inertia systems and application of synchronous condensersFrom Danish project SCAPP

Guangya Yang

Center for Electric Power and EnergyDepartment of Electrical EngineeringTechnical University of Denmark

2 DTU Electrical Engineering, Technical University of Denmark

Current system operation• Rotational mass from synchronous machines acting as the inertia of the system

for frequency regulation– Stabilize small imbalances in power generation and consumption;– In quasi-static operation the speed of the machine is a global measure of power balance;– Provide inertia to the system when subject to large power imbalances due to e.g. short circuit, which

limits the rate of change of frequency;

• Also acting as a strong voltage source– High short circuit power level that stabilizes the voltage fluctuations due to variation of loads and retain

power quality;– Overload capacity during faults that supplies short circuit current to the fault locations that retains the

reliability of the protection system operations.– Stiff grid enhances the commutation of HVDCs and connectivity of resources of different properties

such as power electronic devices, e.g. renewables, battery storage;


Converters vs synchronous machines• Converters are power electronics that have different nature as synchronous

machines– No rotational mass that supports frequency;– Significantly reduced short circuit current supply capability during severe voltage dips due to

limited overload capability of IGBTs;– Flexible in operation yet the response is dependent on the control systems;

• Response speed of the control system can differ due to different control parametersused;

• Different control strategies yield different outputs during faulty situations especially;– Lack of grid code that specifies the characteristics of the control to the extent that can be

useful for all operational situations;– Various grid connection conditions may yield control problems;– Testing methods are still under development for high power equipment;


A condenser


Future energy system

Inverter based generation

Inertia response

Frequency control

Short circuit power

Phase out synchronous generators

AC/DC mixed network

Volt/Var support

SCAPP OverviewSynchronous condensers may be a critical component for the transition.

The project will look at the following issues with a focus on the application of synchronous condensers (SC)

System frequency and inertia characterisation;

Short-circuit power and performance key protection relays;

Hardware-in-the-loop testing for validation;

Optimal properties of SC;

Use of RTDS at PowerlabDK; Intensive R&D project; Close DTU-Siemens collaboration;


Synchronous condensers in DK

Station Area kV Mvar YearBjæverskov DK2 400 270 2013Herslev DK2 400 200 2014Fraugde DK1 400 200 2014

• 7 synchronous condensers in DK • 3 recent synchronous condensers• Short circuit power

– BJS(2013) >800 MVA;– FGD/HKS (2014) > 1000 MVA;

• Reactive power compensation– -150/215 Mvar (BJS)– -120/180 Mvar (FGD/HKS)

• Installed at HVDC converter stations


Frequency and Inertia response

DK1 system

~

~

~

TJE

GER

NJVB2,3

NVV

~

Sweden

VHA

TRI

MKS SSVB3,4

~

~

~

ENVB3

EDR

ESVB3

FVO

~

FYVB7

FGDLAG

SHE

SVS

VKE

REV

KAS

~

~

~

FER

SKVB3

AHA

22/0.69 kV


Frequency response validation

110 115 120 125 130 135 140

Time (s)

49.995

50

50.005

50.01

50.015

50.02

50.025

50.03

50.035

50.04

50.045

f(Hz)

Frequency from PMU (Energinet.dk)

f-KASX: 115.1

Y: 50.04

X: 125.2

Y: 50

0 5 10 15 20 25 30

Time (s)

49.97

49.98

49.99

50

50.01

50.02

50.03

f (H

z)

Frequency from RTDS Simulation

f-KAS

X: 13.14

Y: 49.98

X: 3.058

Y: 50.02


Short circuit current validation


Hardware in the Loop testingHardware

Simulation

RTDS (Grid and synchronous

condenser models )

Communication Interface

Synchronous condenser automatic voltage regulator and

protection system

Communication and amplification Interface

Extract signals from simulation

to physical

Control and protection

signals


Frequency study results – base case


Frequency study results - – base case


Frequency study results - HWHL


Frequency study results – Short circuit + load trip


Converter control strategies during fault• Synchronous reference frame (SRF) vector control

– Positive sequence only with current limit;

• Flexible power control– Sequence power controlled separately – Considering both positive and negative sequence;

• both directions𝒊𝒊𝒓𝒓𝒓𝒓𝒓𝒓 = 𝒊𝒊𝒑𝒑

𝒓𝒓𝒓𝒓𝒓𝒓 + 𝒊𝒊𝒒𝒒𝒓𝒓𝒓𝒓𝒓𝒓

– Active power control

𝒊𝒊𝑝𝑝𝑟𝑟𝑟𝑟𝑟𝑟 =

𝑃𝑃𝑟𝑟𝑟𝑟𝑟𝑟

𝑽𝑽+ 2 + 𝑘𝑘𝑝𝑝 𝑽𝑽− 2 (𝑽𝑽+ + 𝑘𝑘𝑝𝑝𝑽𝑽−)

– Reactive power control

𝒊𝒊𝑞𝑞𝑟𝑟𝑟𝑟𝑟𝑟 =

𝑄𝑄𝑟𝑟𝑟𝑟𝑟𝑟

𝑽𝑽+ 2 + 𝑘𝑘𝑞𝑞 𝑽𝑽− 2 (𝑽𝑽⊥+ + 𝑘𝑘𝑞𝑞𝑽𝑽⊥−)


Control effects• Strategy 1: Constant active power control (𝒌𝒌𝒑𝒑=-1, 𝒌𝒌𝒒𝒒=1)

• Strategy 2: Balanced fault current control (𝒌𝒌𝒑𝒑=0, 𝒌𝒌𝒒𝒒=0)

• Strategy 3: Constant reactive power control (𝒌𝒌𝒑𝒑=1, 𝒌𝒌𝒒𝒒=-1)

-0.06504 -0.03333 0 0.03333 0.06667 0.1 0.13333-2

-1.33333

-0.66667

0

0.66667

1.33333

2

p.u.

IAH IBH ICH SL1

-0.06504 -0.03333 0 0.03333 0.06667 0.1 0.13333-100

16.667

133.333

250

366.667

483.333

600

MW

or M

var

P_HVDC Q_HVDC

-0.03333 0 0.03333 0.06667 0.1 0.13333-100

16.667

133.333

250

366.667

483.333

600

MW

or M

var

P_HVDC Q_HVDC

-0.03333 0 0.03333 0.06667 0.1 0.13333-2

-1.33333

-0.66667

0

0.66667

1.33333

2

p.u.

IAH IBH ICH SL1

-0.05615 -0.03333 0 0.03333 0.06667 0.1 0.13333-100

16.667

133.333

250

366.667

483.333

600

MW

or M

var

P_HVDC Q_HVDC

-0.05615 -0.03333 0 0.03333 0.06667 0.1 0.13333-2

-1.33333

-0.66667

0

0.66667

1.33333

2

p.u.

IAH IBH ICH SL1


Results - HiL• Real relay is used for test

• Relay performance is adversely affected by converters

• Generally more SC capacity, better relay performance


Short circuit power from converters• In general, all control strategies will not overcome the current limits given by the power electronic

elements. • Increasing the number of elements in the converter for higher current carrying capability will

increase the costs• Depending on the circuit parameters and the control system response time, the current phase can

differ from the ones provided by other elements;• The impact on the relays should be considered both on the current magnitude and phase;• Problems can occur either due to less fault current level, or relay cannot detect the fault;• Due to lack of requirements in general in this field (esp. unbalanced faults), there are needs for

more detailed specifications.


QUESTIONS?

Thank you for your attention!

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