Nurhan Rizqy Averous

Grid emulator requirements for a multi-megawatt wind turbine test-bench

Full-scale nacelle test-benches accelerate the development process of new multi-megawatt wind turbines. The device-under-test (DUT) is connected to an artificial grid that is emulated by a power-electronic converter system. Since the desired sinusoidal waveform of the voltage can only be approximated, filters have to be applied to suppress voltage harmonics sufficiently. But still, the output voltage is not purely sinusoidal due to a remaining share of harmonics. For the verification of the total harmonic distortion (THD) caused by the DUT, the influence of the grid emulator on the measurements of voltage and current has to be known. Otherwise the source of the harmonics cannot be identified clearly and the DUT might be characterized incorrectly. Within this work the requirements for grid emulators to allow the sufficiently high measurement of the THD caused by the DUT are derived analytically and validated with simulation models. Furthermore, the dynamic of voltage dips that have to be emulated to test the low-voltage ride-through (LVRT) capability of the DUT has to fulfill the established standards (IEC 61400-21) for emulating a faulty grid realistically. The consequently derived requirements for the power electronic converters are presented within this paper.

Analysis of wind turbines connected to medium-voltage DC grids

The transmission and distribution of electrical energy with direct current (dc) is a promising alternative to established alternating-current (ac) systems. Higher efficiencies, fewer lossy pulse-width modulated converters and smaller transformers reduce operation and investment costs. Moreover, dc collector grids within wind parks leads to benefits for harvesting electrical energy. In this paper, a modular dual-active bridge (DAB) dc-dc converter system for integrating renewable energy sources, especially wind turbines (WT), into medium-voltage dc (MVDC) grids is presented and analyzed. Also, the design and efficiency of the machine-side power converter of the WT for dc grids are discussed.

Optimum design of medium-voltage DC collector grids depending on the offshore-wind-park power

DC collector grids within offshore wind park offer advantages regarding efficiency and investment costs. Dual-active bridge (DAB) dc-dc converter systems can be applied for stepping-up the dc output-voltage of wind turbines (WT). The increase of the voltage level reduces the effort for cabling and increases the system efficiency. Within this paper, the advantage of DAB converter systems used in offshore medium-voltage dc (MVDC) grids is presented. Also, the optimum design of wind park clusters regarding the wake effect and grid losses is investigated to maximize the energy yield.

Development of a 4 MW full-size wind-turbine test bench

The in-field validation of wind turbines behavior is very time consuming and cost intensive, especially when fault ride-through (FRT) tests are conducted. Full-size wind-turbine test benches allow a realistic operation of wind turbines in an artificial environment. Due to the independency of wind and grid conditions, the cost and duration of the test program and certification can be reduced. This paper presents the development of 4 MW full-size wind-turbine test bench following a multi-physics hardware in-the-loop (HiL) concept. With the currently installed test bench setup, a synchronization of the device-under-test converters is possible. Through the measurement results of the test programs conducted on the test bench, the capability of the test bench in replicating the field conditions is demonstrated. In addition, a time consuming efficiency measurement can be performed with the reduced duration on the test bench. This shows another main benefit of the test bench compared to the conventional test method for wind turbines.

Performance characteristics of a doubly-fed generator on a test-rig with full-scale converter-based grid emulator

One key factor for a successfull penetration of wind turbine (WT) products into the market is certification. For the development and certification purpose, a 1 MW test-rig for WT nacelles has been developed at RWTH Aachen University which offers the possibility of WT testing with emulated environmental conditions. In this paper, the performance characteristics of a doubly-fed-generator (DFG) on the developed test-rig is discussed. Firstly, the effect of filter impedance of the grid emulator on the controller performance is analyzed under normal grid conditions. Secondly, the transient characteristic of a DFG WT considering the grid emulator setup is identified. A simulation is performed to verify the analysis. Under normal grid condition, the impedance of the grid emulator does not influence the controller of the DFG WT significantly. For fault-ride-through (FRT) tests with a grid emulator, only the series inductive elements of the grid emulators filter influence the transient characteristic of the DFG WT. The developed 1-MW test-rig fulfills the technical requirement for FRT test in terms of the grid impedance.

Performance tests of a power-electronics converter for multi-megawatt wind turbines using a grid emulator

A vast increase of wind turbines (WT) contribution in the modern electrical grids have led to the development of grid connection requirements. In contrast to the conventional test method, testing power-electronics converters for WT using a grid emulator at Center for Wind Power Drives (CWD) RWTH Aachen University offers more flexibility for conducting test scenarios. Further analysis on the performance of the device under test (DUT) is however required when testing with grid emulator since the characteristic of the grid emulator might influence the performance of the DUT. This paper focuses on the performance analysis of the DUT when tested using grid emulator. Beside the issue regarding the current harmonics, the performance during Fault Ride-Through (FRT) is discussed in detail. A power hardware in the loop setup is an attractive solution to conduct a comprehensive study on the interaction between the power-electronics converters and the electrical grids.