B. Silva, Senior Researcher, INESC TEC

Contribution of variable-speed pump hydro storage for power system dynamic performance

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Framework

The work presented was developed within the framework of FP7- HyperboleProject.The Hyperbole project intend to study the flexibility of hydro technology from

a mechanical an electrical perspective.

From the electrical perspective, variable speed pump storage powerplants

(var-speed PSP) were detailed studied.

HYPERBOLE

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Objective

• Develop a var-speed PSP reduced-order model in PSS/E to assess the impact overcoming from the progressive integration of such units in the Portuguese Power System dynamic performance

HOW?

1. Develop a PSS/E model which describes the main dynamics of frequency responsive PSP

2. Integrate the model in the Portuguese Power system PSS/E model

3. Play major disturbances leading to generation/load mismatch frequency deviation

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Development of frequency-responsive PSP model

• Based on the research developed within the Hyperbole Project, a PSP was to be developed in PSS/E in order to be further integrated with Portuguese grid Model;

• Initial approach:

• Graphical Model Builder (GMB) PSS/E toolbox

Several difficulties regarding severe limitations disabling its adoption;

• Alternative approach:

• Design a frequency responsive power injector associated with PSP control schemes, representing its main dynamics.

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Development of frequency-responsive PSP model

Key assumptions:• Generators are electronically interfaced (focus on deriving a model representing the

operation of a full size frequency converter - FSFC);

• Generators (FSFC) are represented by a controllable load (approach adopted for modelling electronic interface units such as Wind and PV farms);

• The load model (power injector) reacts to grid disturbances by setting an active power variation proportionally to the frequency deviation Fortran user-written model

• Pinj<0 Pump mode;• Pinj>0 Turbine mode;

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Integrate the model in the Portuguese Power system PSS/E model

• REN provided representative grid scenarios Valley hours was adopted to take advantage of having PSP operating in pump mode.

• Spanish-grid side was not represented due to confidentiality aspects dynamic equivalents were developed and included in each PT-ES interconnection.

• The aforementioned grid was considered to be the “BASE CASE” scenario;

• Progressive integration of frequency-responsive variable-speed PSP model in the study case;

• Python script to monitor the amount of non-Fault ride-through compliant WF.

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Scenario #1: Fault at Lavos substation

Variable-speed Units

CASE A None BASE CASE

CASE B Venda Nova III 1 x 360 MW

CASE CVenda Nova III 1 x 360 MW

Aguieira 3 x 91 MW

CASE D

Venda Nova III 1 x 360 MW

Aguieira 3 x 91 MW

Alqueva 4 x 110 MW

Venda Nova II

Aguieira

Alqueva

Disturbance: • 3-phase short-circuit at Lavos 400 kV busbar• The disturbance led to the sudden

disconnection of 1130 MW of non-Fault Ride-Through compliant wind farms

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Results – Fault at Lavos Busbar

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Results – Fault at Lavos Busbar

• Variable-speed PSP are able to respond by providing active power support (reduction of absorbed power) and thus helping the system frequency support;

• The presence of variable-speed PSP helps on damping resulting oscillations.

• The increase of frequency-responsive variable-speed PSP helps on the achievement of faster frequency recovery and reduction on the minimum frequency excursion, enhancing the power system dynamic performance.

• The observed Active power oscillations for the cases where var-speed PSP are set to respond to primary frequency control are related with voltage oscillations and the modelling of electronic units as constant admittance.

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Scenario #1: Generation trip at Pêgo powerplant

Variable-speed Units

CASE A None BASE CASE

CASE B Venda Nova III 1 x 360 MW

CASE CVenda Nova III 1 x 360 MW

Aguieira 3 x 91 MW

CASE D

Venda Nova III 1 x 360 MW

Aguieira 3 x 91 MW

Alqueva 4 x 110 MW

Venda Nova II

Aguieira

Alqueva

Disturbance:

Sudden disconnection of Pêgo thermal powerplantthat was generating 220 MW

Pêgo thermal powerplant

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Results – Generation trip at Pêgo thermal Powerplant

• Hydro pumping units are able to respond by providing active power (absorption reduction) and thus helping the system frequency support;

• The presence of variable-speed units helps on damping aftermath oscillations.

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Results – Generation trip at Pêgo thermal Powerplant

A slight power increase can beobserved for the base casefollowing the disturbance since itis related with the powercalculation methods that aredependent of voltage variations.

The variable-speed PSP is able to respond by decreasing the active power absorbed

Venda Nova III- Trip of Pêgo powerplant

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Main Conclusions

• A reduced order model has been developed and tested in PSS/E;

• The model allowed to assess the impact of having frequency responsive var-speed hydro pumping units in the Portuguese power system modelled in PSS/E;

• The results showed that the var-speed PSP can play an important role on providing primary frequency support in scenarios of large-scale renewable integration where reduced amount of synchronous generation units are connected to the system

• This model can be used by TSO for assessing the impact of variable-speed frequency-responsive PSP in power systems planning and operational perspectives;

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Thank you!!bsilva@inesctec.pt