Andreas Petersson

Modeling and experimental verification of grid interaction of a DFIG wind turbine

The response of the doubly fed induction generator (DFIG) wind turbine system to grid disturbances is simulated and verified experimentally. The results are compared to the response that a fixed-speed wind turbine would have given. A voltage sag to 80% (80% remaining voltage) is handled very well, which is not the case for a fixed-speed wind turbine. A second-order model for prediction of the response of DFIG wind turbines is derived, and its simulated performance is successfully verified experimentally. The power quality impact by the DFIG wind turbine system is measured and evaluated. Steady-state impact, such as flicker emission, reactive power, and harmonic emission, is measured and analyzed. It is found that the flicker emission is very low, the reactive power is close to zero in the whole operating range, and the current THD is always lower than 5%.

Comparison between stator-flux and grid-flux-oriented rotor current control of doubly-fed induction generators

Grid-flux (or grid-voltage)-oriented rotor current control of the doubly-fed induction generator is investigated in this paper. It is shown that by using a grid-flux-oriented system, the stability and damping of the system is independent of the d component of the rotor current, in contrast to a stator-flux-oriented system. Also for the stator-flux-oriented system, a certain value of the d component of the rotor current causes the system to become unstable. Hence, with a grid-flux-oriented system it is possible to produce as much reactive power as desired from a stability point of view. The theoretical results are verified experimentally with good result.

DC-Link Stabilization and Voltage Sag Ride-Through of Inverter Drives

Previous results concerning instability of the dc link in inverter drives fed from a dc grid or via a rectifier are extended. It is shown that rectifier-inverter drives equipped with small (film) dc-link capacitors may need active stabilization. The impact of limited bandwidth and switching frequency in the inverter-motor current control loop is considered, and recommendations for selection of the dc-link capacitor, the switching frequency, and the dc-link stabilization control law in relation to each other are given. This control law is incorporated in a field-weakening (to enhance voltage sag ride-through) current controller for which design recommendations are presented

Grid disturbance response of wind turbines equipped with induction generator and doubly-fed induction generator

This panel paper presents measured and simulated grid disturbance responses of fixed-speed wind turbines equipped with induction generator and variable-speed wind turbines equipped with double-fed induction generator. The measured response of the fixed-speed turbine agrees very well with simulations, while the response of a double-fed induction generator cannot be assessed without detailed knowledge of the control system.

Kriegers Flak 640 MW Off-Shore Wind Power Grid Connection—A Real Project Case Study

This paper reports on the feasibility study performed to investigate the possibilities of connecting the 640-MW off-shore wind power farm, planned for Kriegers Flak 30 km south of Trelleborg, to the E.ON 130-kV subtransmission system. The Kriegers Flak commissioning is planned for 2010. The aim of this study is to answer the question if such a connection is possible, and under what conditions; it is not meant as a design project. Following a general connection design discussion, the study comprises of three major parts: fault current calculations, load flow calculations, and dynamic simulations. The study shows that it is possible to connect such a large off-shore wind power farm to the 130-kV subtransmission system, but reinforcement concerning load currents during normal operation and fault currents have to be made

Voltage Sag Response of PWM Inverters for Variable-Speed Wind Turbines

Abstract The voltage sag response of PWM inverters is analyzed for a candidate dc-link voltage control system. It is shown that the voltage sag response is mainly determined by the dynamics of the dc-link voltage and the control system PWM inverters are found to be robust against voltage sags, but the remaining grid voltage limits the maximum active power that can be delivered to the utility grid.

Detailed modeling for large scale wind power installations - a real project case study

This paper reports on the modeling issues performed related to a feasibility study to investigate the possibilities to connect the 640 MW off-shore wind power farm, planned for Kriegers Flak 30 km south of Trelleborg (Sweden), to the E.ON 130 kV subtransmission system. The aim of the entire study is to answer the question if such a connection is possible, and under what conditions; it is not meant as a design project. Following a general connection design discussion, the study comprises three major parts, fault current calculations, load flow calculations, and dynamic simulations. Concerning the modeling aspects, much effort has been put on details and scalability for the dynamic simulations.

Monte Carlo versus multilevel Monte Carlo in weak error simulations of SPDE approximations

The simulation of the expectation of a stochastic quantity E[Y] by Monte Carlo methods is known to be computationally expensive especially if the stochastic quantity or its approximation Y-n is expensive to simulate, e.g., the solution of a stochastic partial differential equation. If the convergence of Y-n to Y in terms of the error |E[Y - Y-n]| is to be simulated, this will typically be done by a Monte Carlo method, i.e., |E[Y] - E-N [Y-n]| is computed. In this article upper and lower bounds for the additional error caused by this are determined and compared to those of |E-N [Y - Y-n]|, which are found to be smaller. Furthermore, the corresponding results for multilevel Monte Carlo estimators, for which the additional sampling error converges with the same rate as |E[Y - Y-n]|, are presented. Simulations of a stochastic heat equation driven by multiplicative Wiener noise and a geometric Brownian motion are performed which confirm the theoretical results and show the consequences of the presented theory for weak error simulations.