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 user using DFIG wind farm and the distribution algorithms of reactive power demand are given. Simulation results are provided to verify the proposed theory.
"In this paper, the reference voltage value is set to the normal grid voltage. The distribution principle of the reactive power has been proposed in . In this paper, the reactive power is distributed among the different DFIG systems in a wind farm by the proportion principle referring to the power limit of each system. "
[Show abstract][Hide abstract] ABSTRACT: This paper presents an improved grid voltage control strategy for wind farms with doubly-fed induction generators (DFIGs) connected to distribution networks based on an analysis of the operation limits of DFIG systems. A modified reactive power limit calculation method in different operation states is proposed and a reactive power control strategy during grid voltage dips/rises is further discussed. A control strategy for compensating unbalanced grid voltage, based on DFIG systems, by injecting negative sequence current into the grid through the grid side converter (GSC) is proposed. In addition, the negative current limit of the GSC is discussed. The distribution principle of the negative sequence current among the different DFIG systems in a wind farm is also introduced. The validity of the proposed voltage control strategy is demonstrated by Matlab/Simulink simulations. It is shown that the stability of a wind farm and the power grid can be improved with the proposed strategy.
Journal of power electronics 05/2012; 12(3). DOI:10.6113/JPE.2012.12.3.495 · 0.78 Impact Factor
"While currently, little papers about reactive power control strategy in wind farm consisting of VSCF DFIG WTGS have compositely considered the reactive power compensation ability of both RPCD and wind generator (WG), and most of them focus on how to allocate the reactive power among all the WGs or how to take advantage of RPCD individually to compensate the reactive power in wind farm. According to the reactive power limit of DFIG,  proposed a reactive power nearby compensation strategy to the local consumers in wind farm, which mainly discussed the reactive power distribution rules between WGs in wind farm and between the stator-side and grid-side converters of a single WG, but the compensation ability of RPCD is ignored. Reference  presented a reactive power compensation method which includes local compensation on the WG terminal and centralized compensation on the substation of wind farm using shunt capacitors, while it didn't think over the reactive power output capability of WG. "
[Show abstract][Hide abstract] ABSTRACT: Doubly-fed Induction Generator (DFIG) is a kind of variable-speed constant-frequency (VSCF) wind generator (WG) which can output reactive power when not working in the constant power factor mode and be used as a reactive power supply for wind farm. In this paper, an optimal control strategy for reactive power in wind farms consisting of DFIG is proposed by combining the reactive power compensation ability of both DFIG and reactive power compensation device (RPCD). The control target is minimum power loss and optimal power flow (OPF) of wind farm. First, the reactive power characteristic of DFIG is detailed analyzed. Then the control strategy which includes three modules is presented based on the “Fix-place and Quantitative” thought, and the modules of which are Wind Farm Data Process Module (WFDPM), Wind Farm Data Acquisition Module (WFDAM) and Wind Farm Control Module (WFCM). As the core part of the strategy, WFDPM applies Sensitivity Analysis (SA) and improved genetic algorithm (IGA) to optimize the control strategy. At last, a wind farm consisting of twenty DFIGs of 1.5MW is built in DIgSILENT/PowerFactory, and the results data show that the optimal reactive power control strategy proposed in this paper can effectively achieve the minimum power loss and OPF.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a VAR regulation strategy when voltage of monitor bus fluctuates or drops severely. If voltage of monitor bus fluctuates and the CrowBar does not response, rotor side converter will change VAR output of DFIG by regulation strategy while the converter of grid side can only keep DC voltage stability. When severe grid fault occurs and CrowBar acts, rotor side converter is out of control. In this case grid side converter is forced to output VAR with set value. DFIG gives maximum VAR support to monitor bus. Simulation shows this strategy can restrain voltage fluctuates and can give VAR support to monitor bus when serious fault occurs.
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