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Tests on the POD-P controller of INELFE Spain-France VSC-HVDC interconnector
Javier Renedo, Agustín Diaz-García, Gilles Torresan, Eduardo Lorenzo Cabrera, Antonio Cordón, Silvia Sanz Verdugo, Juan Peiró, Javier Pérez Castro, Gorka Calvo, Aitor Hernández Sautua, Ambroise Petit, Hamza Oukhayi, Samy Akkari, Hani Saad
TL;DR
Inter-area oscillations challenge the Continental Europe power system, motivating validation of higher-gain POD-P control and its operation with angle difference control on the INELFE interconnector. Simulations, hardware-in-the-loop, and field tests confirmed correct behavior and increased inter-area damping across operating modes, with larger improvements when line Vic-Baixas was open.
Problem
Inter-area oscillations in the Continental Europe power system require validation of more effective damping control for the INELFE interconnector.
Method
The study used simulations, hardware-in-the-loop, and field tests to validate higher-gain POD-P control with operation in both CPC and ADC modes.
Results
Tests confirmed correct POD-P behavior and increased inter-area damping in CPC and ADC modes, with greater improvements when line Vic-Baixas 400 kV was open.
Takeaways & Limitations
The modified POD-P controller was validated and used in normal operation for both CPC and ADC modes from 5 January 2023.
Takeaways & Limitations
The exact improvement produced by POD-P is difficult to quantify because multiple factors affect the inter-area damping ratio.
Abstract
from arXiv · showhide
INELFE interconnector consists of a 2x1000 MW high voltage direct current system based on voltage source converters (VSC-HVDC) interconnecting France and Spain. INELFE VSC-HVDC link is embedded into the high voltage alternating current (HVAC) system. Electromechanical oscillations, also known as power oscillations, are a major concern worldwide. INELFE VSC-HVDC link has specific controllers to damp power oscillations by modulating active (P)- and reactive (Q)-power injections of the VSC converters (POD-P and POD-Q controllers, respectively). The Spanish and French Transmission System Operators (TSOs) carried out a join task force to - Increase the gain of POD-P controller of INELFE VSC-HVDC link. - Make it possible to use the POD-P controller together with angle difference control (ADC) of INELFE VSC-HVDC interconnector. The objective of these modifications is to improve the effectiveness of POD-P controller and, therefore, to increase its contribution to the damping of inter-area oscillations in the Continental Europe (CE) power system. Such changes require (a) extensive simulation studies and (b) extensive tests in different operation modes, in order to ensure the correct behavior of the system. This paper presents simulation studies and field tests on the POD-P controller of INELFE VSC-HVDC interconnector in different modes of operation.
1 INTRODUCTION,
The paper addresses inter-area oscillations in the Continental Europe power system by modifying INELFE’s POD-P controller to improve damping effectiveness. It evaluates these changes through simulations, implementation studies, and field tests across operating modes, confirming correct controller behavior.
- Inter-area oscillations are a major concern in the large synchronous Continental Europe power system.
- The modifications increase the POD-P controller gain to improve effectiveness and permit its activation alongside angle difference control.
- These changes aim to increase POD-P’s contribution to damping inter-area oscillations in the Continental Europe power system.
- Extensive simulations and tests in different operating modes assess implementation and ensure correct POD-P controller behavior.The paper presents simulation studies, implementation aspects, and field tests on the INELFE VSC-HVDC interconnector.
2 DESCRIPTION OF THE SYSTEM
INELFE is a 2×1000 MW, 320 kV symmetrical-monopole VSC-HVDC interconnector embedded in the France–Spain AC network. Its active-power control combines constant-power or angle-difference operation with a frequency-difference-based POD-P controller, whose gain and ADC logic were modified for improved use.
- System configuration: INELFE comprises two 1000 MW symmetrical monopoles at 320 kV DC and operates in parallel with the Vic-Baixas 400 kV line.Each converter has a reactive-power capability of [-600 Mvar, +400 Mvar].
- Active-power control: The HVDC system supports constant-power control (CPC/Pmode1) and angle-difference control (ADC/Pmode3).ADC uses the angle difference between the AC terminals and is more practical than CPC when the HVDC link is embedded in an AC network.
- POD-P controller: POD-P measures the frequency difference between the two AC terminals and produces a supplementary active-power setpoint through gain, low-pass, wash-out, and saturation elements.Under ADC, its supplementary setpoint is combined with the constant and ADC setpoints.
- Controller modifications: POD-P gain increased from 500 MW/Hz to 2500 MW/Hz per link, while logic changes enabled operation in ADC mode after ADC was slowed to τ = 50 s [12].The modifications were supported by power-system studies, replica hardware-in-the-loop studies, and field tests.
3 POWER SYSTEM STUDIES ON POD-P CONTROLLER
The dynamic studies used tuned DSM and DRM models that accurately reproduced the East-Center-West inter-area oscillation, enabling assessment of INELFE HVDC control effects.
- Dynamic study models: Tuned DSM and DRM models reproduced the East-Center-West inter-area oscillation in frequency, damping ratio, and mode shape, supporting studies of INELFE HVDC control impact.Red Eléctrica used PowerFactory for small-signal stability studies and PSS/E for transient studies.
Eigenvalue analysis
Small-signal eigenvalue analysis shows that POD-P increases inter-area-mode damping, with a stronger effect when the Vic-Baixas 400 kV line is open. Extensive time-domain simulations then evaluated the modified controller across network conditions and operating modes to verify these results and detect adverse effects.
- Eigenvalue analysis: POD-P increased the inter-area-mode damping ratio, with substantially greater effectiveness when the Vic-Baixas 400 kV line was open.The analysis considered France importing 2000 MW from Spain in CPC mode using SMAS3 small-signal analysis.
- Eigenvalue analysis: With POD-P ON at a gain of 2500 MW/Hz/link, the reported inter-area mode had 0.20 Hz frequency and 5.9% damping.
- Time domain simulations: Extensive time-domain simulations covered full-network conditions, short circuits, outages, exchange levels, and HVDC angle-difference and constant-power modes.They were intended to verify the eigenvalue-analysis results and ensure that the controller changes created no adverse effects.
Discussion
The discussion identifies K_P=2500 MW/Hz/link as a conservative compromise for POD-P, balancing stability margins, saturation behavior, and increased inter-area damping. Simulations found gains from 2500–5000 MW/Hz/link effective, while the selected value is consistent with typical frequency-error-based POD-P settings,,.
- Discussion: A gain of 2500 MW/Hz/link appears to be a good compromise because the system remains stable and POD-P saturates only at the beginning of severe events.Saturation requires Δω=ω_A−ω_B=40 mHz, a deviation expected only during very severe events.
- Discussion: Opening the Vic-Baixas 400 kV line can significantly increase the inter-area mode damping ratio with the selected POD-P gain.This conclusion is based on the frequency amplitudes observed during historical system events.
- Discussion: K_P=2500 MW/Hz/link was selected conservatively because simulations found gains of 2500–5000 MW/Hz/link effective, while accounting for dynamic-model inaccuracies.The selected value preserves stability margins and is consistent with typical POD-P controllers using frequency-error input signals,,.
4 PRACTICAL IMPLEMENTATION OF THE CHANGES MADE ON POD-P CONTROLLER
The POD-P modifications were validated before onsite updates using an HIL setup with physical INELFE control and protection replicas. Tests showed that POD-P activation with ADC was feasible and that a gain of K_P=2500 MW/Hz/link increased inter-area-mode damping.
- 4 PRACTICAL IMPLEMENTATION OF THE CHANGES MADE ON POD-P CONTROLLER: The controller modifications were tested before onsite updates in an HIL setup connecting physical INELFE C&P replicas to a real-time simulator.The installation had been validated several years earlier.
- 4 PRACTICAL IMPLEMENTATION OF THE CHANGES MADE ON POD-P CONTROLLER: K_P=2500 MW/Hz/link with constant-power control or ADC increases the damping ratio of the inter-area mode.Simulations tested multiple operating conditions, including inverter and rectifier modes, 0 MW crossing, active-power and AC-voltage/reactive-power control, and different POD-P gains.
- 4 PRACTICAL IMPLEMENTATION OF THE CHANGES MADE ON POD-P CONTROLLER: POD-P activation with ADC and τ=50 s was possible in the tested simulations.
5 TESTS ON POD-P CONTROLLER
Field tests conducted from September to December 2022 assessed the modified POD-P controller’s behavior across CPC and ADC modes and varied INELFE operating conditions. The tests included small-disturbance evaluation and a line-outage scenario, with PMU data from Spain and France used for analysis.
- Operating conditions: The test campaign covered single- and multi-link operation, CPC and ADC, either PCONMASTER converter station, both power-flow directions, and Vic-Baixas line disconnection.These conditions were used to check correct controller behavior after implementing the POD-P changes.
- Test campaign: Two field tests were performed: CPC and ADC tests on 5 October 2022, and an INELFE-1 test during Vic-Baixas 400 kV line disconnection on 9 December 2022.Phasor Measurement Unit data from Spain and France were exported for result analysis.
- Test 1: Tests of POD-P control in CPC and ADC: Tests assessed POD-P behavior in constant active power control and angle difference control during small system disturbances, verifying correct operation.The CPC and ADC tests were conducted during a planned Vic-Baixas 400 kV outage, identified as a suitable scenario for evaluating POD-P performance.
- Test 1: Tests of POD-P control in CPC and ADC: Before Test 1, HVDC-1 and HVDC-2 were in service in multi-link mode, France was PCONMASTER, power flowed from Spain to France, and Vic-Baixas was disconnected for a planned outage.These operating conditions defined the CPC and ADC test setup.
Test 1-a: CPC with POD-P
Test 1-a evaluated INELFE POD-P in CPC mode using frequency differences and HVDC active-power responses, while WAMS measurements assessed inter-area-mode damping. Activating POD-P increased the average damping ratio by around 10% in CPC operation.
- Test 1-a: CPC with POD-P: During the transient, higher Llogaia frequency than Baixas frequency increased active power from Spain to France through both INELFE HVDC links, while lower frequency decreased it.The terminal-frequency difference was non-negligible because the Vic-Baixas 400 kV line was open.
- Damping ratio of the inter-area mode: WAMS PMU data monitored the critical East-Center-West inter-area mode during the tests, whose frequency was around 0.15 Hz.The mode’s stated oscillation-frequency range was 0.15–0.25 Hz.
- Damping ratio of the inter-area mode: Activating POD-P increased the average damping ratio of the Continental Europe inter-area mode by around 10% in CPC operation.The critical East-Center-West mode oscillated at approximately 0.15 Hz, and damping was averaged over each test-case time window.
6 CONCLUSIONS
Simulation, hardware-in-the-loop, and field tests validated the INELFE POD-P controller modifications, including increased gain and operation during angle difference control. The modified controller behaved correctly across scenarios, increased inter-area-mode damping, and entered normal operation.
- 6 CONCLUSIONS: POD-P modifications were implemented successfully and validated through simulation, hardware-in-the-loop, and field tests.The changes increased controller gain and enabled POD-P activation during angle difference control.
- 6 CONCLUSIONS: Tests confirmed correct POD-P behavior across different scenarios under constant active power control and angle difference control.
- 6 CONCLUSIONS: POD-P increased the inter-area-mode damping ratio, with larger improvements when the Vic-Baixas 400 kV line was open.The modified controller was validated and is being used in normal operation.