Influence of the grid parameters during under voltage ride through (UVRT) testing

Abstract

Under-voltage ride through (UVRT) tests can be carried out on system test benches, most of them are equipped with a converter based grid simulator. This paper describes the control of the artificial grid impedance at the 4 MW test bench at CWD. Validation measurements with the commercial wind turbine E‑115 E2 show that the virtual impedance specification is sufficient to perform UVRT tests with different grid parameters. Comparative measurements between the voltage divider based FRT Container and the grid simulator with deliberately different grid parameters show a different behavior of the research wind turbine FVA nacelle. Therefore, it is recommended to perform UVRT tests on the test bench with predefined grid parameters.

Impact of Multi-Physics HiL Test Benches on Wind Turbine Certification

“…However, the analysis in this paper also illustrated in detail that a limited accuracy or errors of the HiL systems, their simulation models, and controls could easily compromise the quality of the certification result. In the previous analysis in Section 5, we showed, for instance, that the UVRT results are sensitive to the correct emulation of the impedance by the PHiL, which correlates with the findings in [35], and that, for example, frequency control and synthetic inertia tests can easily be jeopardized by a MHiL system whose bandwidth is limited due to test bench restrictions and poor feedback signals.…”

“…In a former publication, we have already shown that the impedance control provides precise results in steady state operation [35]. This work investigates to what extent the PHiL setup allows an impedance replication in case of faulty grids, e.g., in case of under-voltage events.…”

“…The voltage determined in the grid simulation (U PCC ) is the new set-point of the grid emulator, which now operates in an impedance-controlled manner. The corresponding structure of the grid emulator, consisting of the real-time measurement, the control, and the hardware components, is shown in Figure 3a [35].…”

A discussion on the characterization of grid emulators by apparent power rating and short-circuit power

“…Both UPCC and IPCC are control feedbacks to follow the setpoints for internal source voltage U0 and virtual impedance Zk. The effectiveness of virtual impedance control is verified by measurements and presented in [36].…”

“…Fig. 8 Virtual impedance control at the PCC [36]. a Control schematic, b Equivalent circuit vides a stiff grid with a natural SCR = 7.5.…”