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The paper analyzes the theory of generating short circuit current during three-phase fault to research the low voltage ride through (LVRT) control of doubly fed induction generator (DFIG). The approximate analytical expressions of short circuit current are given in the condition of no load and synchronous speed to simplify the analysis. Based on this, the influences of different pre-fault conditions,...
This paper proposes controlled shunt capacitor called static Var compensation magnetic energy recovery switch (SVC MERS) for self-excited induction generator terminal voltage control. The proposed system consists of bi-directional switch, dc capacitor and inductor as a filter. Operation principle and characteristics are presented. A small scale experiment was conducted to verify the proposed system...
The comparison of inductive and capacitive filter for standalone variable speed operated doubly fed induction generator DFIG is presented in the paper. Simulation and experimental results of both methods of filtration are shown. The model equations with stator connected filtering capacitors are analyzed. Sensorless control of the stator voltage vector in the polar frame is described. PLL based frequency...
The importance of condition monitoring and fault detection increases. This paper presents a state-space observer based condition monitoring algorithm for the detection of rotor turn-to-turn faults in doubly-fed induction generators. A reduced order time invariant machine model for asymmetrical internal parameters will be derived. The model is used for simulation of rotor turn-to-turn faults, which...
In future grid codes wind farms will have to fulfill demanding fault ride through requirements. Among several grid faults the voltage swell is a critical event. Wind farms with doubly-fed induction generators will not be able to fulfill the new grid code requirements without additional fault mitigation equipment. In this publication the applicability of the dynamic voltage restorer and the static...
The present paper addresses the control of doubly fed induction generators under unbalanced voltage sags considering the converter limits. A control strategy is proposed by choosing certain current reference values in the positive and negative sequences so that the torque and the DC voltage are kept stable during such unbalanced sags considering the converter limits.
Doubly fed induction generators (DFIG) are more and more used in wind farms. Their reactive power generation capabilities are related to their operating points (wind speeds). This paper describes a hierarchical supervisory of the reactive power in a wind farm and focuses on the reactive power local supervisory unit of each DFIG based wind generator. In this context, a local supervisory algorithm is...
This paper presents the design and performance of a test bench to generate grid faults and disturbed grid voltage conditions to test grid connected devices. The test bench is applied to generate different reproducible types of disturbed grid voltages like symmetrical and unbalanced voltage dips, overvoltage, frequency variations and harmonic disturbances. By means of this grid emulator the behavior...
In this paper, the low voltage ride-through (LVRT) capabilities of an hybrid wind plant is studied. The hybrid wind plant considered combines fixed speed wind turbines (FSWTs) based on classical induction generator and full power converter variable speed wind turbines (VSWTs) with permanent magnet generator. However, it must be able to respect grid code requirements. A specific control of the variable...
This paper presents several shaft voltage reduction techniques for doubly-fed induction generators in wind turbine applications. These techniques includes: pulse width modulated voltage without zero vectors, multi-level inverters with proper PWM strategy, better generator design to minimize effective capacitive couplings in shaft voltage, active common-mode filter, reducing DC-link voltage and increasing...
This paper presents a high performance stationary frame non-linear controller for DFIG which improves the behavior of the grid connected wind turbines especially during asymmetric disturbances at the PCC. A controller design procedure that guarantees the DFIG stability under uncertainties and disturbances at grid side is presented in details. Furthermore, it is demonstrated in the paper that with...
This paper proposes an optimal energy recovery method in the case of a windmill, photovoltaic panels array and lead-acid batteries used for an islanded DC network. From renewable energy characteristics and especially power rates, we propose to drive the windmill and the PV array at optimal power by respectively a dichotomic algorithm and Fuzzy Logic Controller. The wind turbine drives an asynchronous...
Low voltage ride through (LVRT) of squirrel cage induction generators in wind farms is challenging due to the large required reactive power after low voltage period. Reactive power compensation with shunt compensation can improve the LVRT capability, but requires a large rating. The alternative use of series compensation is studied. Series compensation is based on increasing the reactive power transfer...
This paper describes the coordination in control systems between the DFIG and the firing delay angle control of the rectifier that comprises the HVDC-LCC link; as well as the Generator + Transmission topology formed by the DFIG and HVDC link to maintain the voltage and frequency output of offshore wind farms constant.
A new method for Grid connection of a Doubly Fed Induction Generator (DFIG) based wind power generation system relying on DPC principles is presented. This control method, called Direct Power Control for Grid Connection (DPCGC), is particularly very simple and gives fast response of the stator voltage to meet the synchronization conditions. Indeed the fact that the efficiency of the widely known control...
The present paper deals with the integration of electrical, control and mechanical models in a single platform to evaluate the response of wind turbines to different classes of voltages sags. Models of all the wind turbine parts are described and integrated in two different platforms. Mechanical and aerdynamics are modeled using GH Bladedcopy while electrical and control parts are modeled using Matlab...
Nowadays, the wind market is dominated by doubly fed induction generator (DFIG) based wind turbines. However, they are very sensitive to grid faults due to the small rated power converters and direct connection to the grid. In order to improve its Low Voltage Ride-Through (LVRT) capability, this paper proposes a modified vector control strategy of the DFIG by considering the dynamics of stator flux...
This paper shows a new induction generation system for wind power generation. This system has the voltage source converter exciting induction generator and the PFC converter to transfer the real power. This configuration enables asynchronous link and maximum power tracking for the cage rotor induction generator. Usually two full rating inverter sets are necessary to construct the asynchronous link...
Power relations of doubly fed induction generator (DFIG) wind power generation system are analyzed. Based on this, a method is proposed to calculate the reactive power limit. Furthermore, the reactive power control of DFIG wind farm is studied and the control scheme is provided to exert the reactive power dealing capability of wind power system. A reactive power compensation strategy for the local...
State-of-the-art doubly-fed induction generator drives avoid operation at synchronous speed. Engineers point out stability problems and unequal heating of semiconductors and windings as the main reasons. The latter problem is consequence of unequal losses distribution in the semiconductors and rotor windings. This work investigates the thermal behaviour of the inverter switches at this singular point...
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