Offshore Wind Energy Conversion System Connected to the Electric Grid: Modeling and Simulation

This paper is on modeling and simulation for an offshore wind system equipped with a semi-submersible floating platform, a wind turbine, a permanent magnet synchronous generator, a multiple point clamped four level or five level full-power converter, a submarine cable and a second order filter. The drive train is modeled by three mass model considering the resistant stiffness torque, structure and tower in deep water due to the moving surface elevation. The system control uses PWM by space vector modulation associated with sliding mode and proportional integral controllers. The electric energy is injected into the electric grid either by an alternated current link or by a direct current link. The model is intend to be a useful tool for unveil the behavior and performance of the offshore wind system, especially for the multiple point clamped full-power converter, under normal operation or under malfunctions

Constant frequency control of an Active Power Filter

Active Power Filters (APFs) improve the electricity supply by correcting harmonic distortions created by non-linear loads. It also corrects the poor power-factor resulting from inductive loads. Topologies and control techniques available for APFs are numerous. This paper considers a single phase APF. A scheme that requires minimum calculation burden has been selected. The system considered uses a unified constant frequency integration control that gives a minimum calculation burden and a faster response. The control method adapted requires sensing the load current and DC-link voltage only. However, it causes some problems at the integration level. The analog integrator gives some initial voltage when operated at high frequencies due to inability to reset the integrator fully. To avoid errors due to offset in the integrator, an offset feedback is proposed and tested in this study. The control is simulated and the results are validated with laboratory experimental waveforms

Frequency support from doubly fed induction generator wind turbines

An assessment on the capability of a doubly fed induction generator (DFIG) wind turbine for frequency regulation is presented. Detailed aerodynamic, structural and electrical dynamic models were used in this study. A control loop acting on the frequency deviation was added to the inertia contributing loop in order to enhance the inertia support from the DFIG wind turbine. The possibility of de-loading a wind turbine to provide primary and secondary frequency response was discussed. A frequency droop controller was examined where the droop is operating on the electronic torque set point below its maximum speed and is operating on the pitch demand at maximum speed. It is also shown that by reducing the generator torque set point the DFIG wind turbine can provide high frequency response

Influence of rotor structural dynamics representations on the electrical transient performance of FSIG and DFIG wind turbines

An assessment of the impact that the representation of rotor structural dynamics has on the electrical transient performance of fixed-speed induction generators (FSIGs) and doubly fed induction generators (DFIGs) wind turbines is presented. A three-mass model that takes into account not only the shaft flexibility but also the blade flexibility in the structural dynamics is developed and used to derive an effective two-mass model of the drive train dynamics, which represents the dominant natural frequency of vibration of the rotor structure. For the purposes of this investigation, the dynamic performance of both FSIG and DFIG wind turbines is evaluated during electrical transients such as a three-phase fault in the network. The studies are conducted in the software code Bladed, where a detailed representation of the structural dynamics is used to derive the three-mass model and the effective two-mass model. Simulation results which illustrate how these representations of the rotor dynamics affect the response of the wind turbine during the fault are presented and discussed

Influence of tower shadow and wind turbulence on the performance of power system stabilizers for DFIG-based wind farms

The aim of the paper is to demonstrate the way in which mechanical power variations, due to tower shadow and wind turbulence, influence control performance of power system stabilizer (PSS) loops for doubly-fed induction generators (DFIGs). The PSS auxiliary loops are applied on a specific DFIG control scheme, the flux magnitude and angle controller (FMAC). However, since the PSS signal is applied at the output of the basic controller, the PSS performance characteristics displayed are deemed typical for DFIG control schemes in general. The relative capabilities of PSS controllers based on stator power, rotor speed, and network frequency, when the DFIG turbine is subjected to aerodynamic torque variations, are investigated via simulation studies. A two-generator aggregate model of a wind farm is introduced, which enables the influence of tower shadow and wind turbulence on both an individual turbine and on the overall wind farm itself to be assessed