Under voltage ride through tests on nacelle test benches equipped with a power hardware in the loop setup

• Spannungseinbruchstests auf Gondelprüfständen unter Berücksichtigung eines Power-Hardware-in-the-Loop-Aufbaus

Frehn, Anica Renate; Monti, Antonello (Thesis advisor); Andresen, Björn (Thesis advisor)

1. Auflage. - Aachen : E.ON Energy Research Center, RWTH Aachen University (2023)
Book, Dissertation / PhD Thesis

In: E.On Energy Research Center : ACS, Automation of Complex Power Systems 112
Page(s)/Article-Nr.: 1 Online-Ressource : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2022

Abstract

Wind energy is the leading energy source in Germany and therefore significant for a safe and reliable grid operation. To ensure supply stability, proof of grid compliance of the Wind Power Plant (WPP) is required. This includes measuring the electrical characteristics and creating and validating a Wind Turbine Generator System (WT) model. IEC 61400-21-1 defines the testing requirements, supplemented in Germany by FGW TG3, to demonstrate compliance with grid connection rules. The measurement of the electrical characteristics is currently performed on the installed turbine in the field. Due to dependence on weather and grid conditions, this approach can be very time consuming and costly. In addition, individual measurements are not reproducible due to fluctuating external conditions. Nacelle test benches offer the possibility to measure the electrical characteristics under laboratory conditions and are suitable to replace the field measurement or parts of it. Grid emulators, usually installed on test benches, represent an artificial grid as a fully controllable voltage source. They offer a variety of new setting options and defined input parameters that are not available with the previous test methods based on voltage dividers in the field. Thus, even today’s commercially available grid emulators offer test possibilities that go beyond the requirements defined in the standards. As a further component of the certification, grid emulators enable the validation of the WT models under known, predefined input parameters. This increases the accuracy of the model validation by eliminating previous uncertainties, such as the grid condition, which are not precisely known during field measurements. At the same time, grid emulators have an increased modelling effort as they are an actively controlled system. However, detailed analyses of the required model depth indicate that it is sufficient to embed the impedance replication in the simulation. The main scientific contribution of this work is to define the necessary extensions of the technical guidelines to take into account the extended setting possibilities that are already provided by today’s grid emulators. The aim is to maintain the high quality of the UVRT tests and the comparability of the individual measurements. Some of the proposed extensions have already been included in current technical guidelines such as FGW TG3 Rev.26 and IEC 61400-21-4. In addition, this work identifies potential additions to the existing test procedures as well as new test possibilities. This is mainly done by experimental investigations at the 4 MW test bench at Center for Wind Power Drives (CWD), supplemented by individual simulations. In addition to a freely adjustable voltage and frequency, grid emulators enable the controllability of the grid parameters at the connection point. This allows for the first time the investigation of the UVRT behaviour at different grid conditions. The WT behaves differently depending on the set grid parameters, which not only affects the reproducibility of the field measurement on the test bench. Rather, it complicates the comparability of individual UVRT measurements. The comparison of a test bench measurement and a field measurement with an identical turbine proves the reproducibility of the field measurement on the test bench under the assumption of identical grid parameters. A further test series shows that the transferability of the results is not guaranteed in the case of strongly deviating impedance values between the test voltage divider based test method and the grid emulator. The WT behaves differently depending on the test method used. In addition to the impedance emulation, grid emulators allow a controllable voltage transition during the voltage dip. To ensure conclusions about the parameters to be set for the instantaneous voltages, the previous description of the voltage profile based on effective values is not unambiguous. A variant using dq0 components developed and recommended by the author accounts for the variability during the voltage transients and thus allows a clearer definition of the expected voltage profile. This further ensures the comparability of individual tests. As renewable energy sources become more significant, the requirements for these energy sources themselves are changing. As experiments demonstrate, a preferential active power injection can be beneficial in fault case, in contrast to the current requirements in the grid codes. It provides greater voltage support in grids with high resistive loads and ensures stable frequency in grids driven by renewable energy sources. It is therefore advisable to test the capability of active power injection in the future, even in the fault condition. To this purpose, grid emulators provide a unique test environment due to the impedance emulation. The adjustable transient voltage transition additionally allows tests with different envelopes during the fault occurrence. This allows the WT’s response to near and far faults to be investigated to ensure the correct response of the WT to stabilize the disturbed power system. The results of this work consequently demonstrate that test benches equipped with grid emulators not only reproduce previous field measurements. Rather, due to the adjustable input parameters, new test procedures arise that reflect the characteristics of a power grid increasingly based on renewable energies.

Institutions

• E.ON Energy Research Center [080052]
• Institute for Automation of Complex Power Systems [616310]