Doubly Fed Induction Generator Reactive Power Research Articles

High proportion of new energy power system frequency and voltage support and regulation technology based on doubly fed induction generator

Abstract With the increasing proportion of new energy in power systems, issues regarding system voltage, inertia, and primary frequency regulation have become increasingly severe. In response to control and grid safety issues, a high proportion of new energy power system frequency and voltage support and regulation technology based on a doubly fed induction generator (DFIG) is proposed. The voltage-magnetic link equation of DFIG is theoretically derived, and the control principles of active and reactive power of DFIG are proposed. The support and regulation characteristics of improving the voltage of new energy substations are studied. Verification is conducted through large-scale grid simulation and on-site measurements.

High performance of variable-pitch wind system based on a direct matrix converter-fed DFIG using third order sliding mode control

In this paper, a full nonlinear control of a variable-pitch wind system (VPWS) based on the doubly fed induction generator (DFIG) fed by a direct matrix converter (DMC) has been presented. In this context, The MPPT has been implemented using the third order sliding mode control (TOSMC) in order to ensure maximum power provided by the wind turbine on the one side, on the other side the pitch control has been implemented in order to limit the power extracted to its nominal value. Moreover, a TOSMC has been incorporated into the direct flied-oriented control (DFOC) to ensure high-performance control of the active and reactive power of DFIG. To examine the performance of the TOSMC, a comparative study was performed between this last type and the first and second order sliding mode controllers. The obtained results affirmed the high performance provided by the TOSMC compared to lower order sliding mode controllers.

Limits of reactive power compensation of a doubly fed induction generator based wind turbine system

The doubly fed induction generator (DFIG) systems feature a significant amount of free power capacity that may be used for reactive power adjustment when they are put into practical use. This change, which is occasionally overlooked, is a significant one. Using DFIG systems for wind turbines (WT), this paper explored strategies for reducing and using reactive power. In order to investigate the power characteristic and how it is regulated in DFIG systems, a mathematical model for the steady-state performance of DFIG WT has been developed and presented. Here is a detailed derivation of the limiting range of DFIG's reactive power capacity as well as the physical constraints on reactive power output. The distribution of the DFIG WT at a distribution network's end is demonstrated by a simulation example. Within this simulation, reactive power management strategy, load fluctuation, and the change in wind speed are all taken into consideration. Due to the possibility of a rise in the voltage at the access point, can concluded that both acceptable and efficient to use DFIG WT's reactive power capabilities as an additional continuous reactive power source for effectiveness.

Simulation Studies of Control Systems for Doubly Fed Induction Generator Supplied by the Current Source Converter

The control system for a Doubly Fed Induction Generator (DFIG) supplied by a grid-connected Current Source Converter (CSC) is presented in this paper. Nonlinear transformation of DFIG model to the multi-scalar form is proposed. The nonlinear control strategy of active and reactive power of DFIG is realized by feedback linearization. In the proposed control scheme, the DFIG model and CSI parameters are included. Two Proportional-Integral (PI) controllers are dedicated for the control of the respective active and reactive powers. The control variables are the dc-link input voltage vector and the angular speed of the inverter output current. The proposed control approach is characterized by satisfactional dynamics and provides enhanced quality of the power transferred to the grid. In the simulation, evaluation of the characteristic operating states of the generator system, correctness of the feedback linearization and the dynamics of active and reactive power control loops are studied. Simulation results are adequately provided.

The voltage dip and doubly fed induction generator with considering uncertainty conditions

The paper presents the transient behavior of the doubly fed induction generator (DFIG) in the wind turbine (WT) in the normal and voltage dip condition. When voltage dip occurs in to the grid, the rotor current increases and the DC-link voltage increases too and start to oscilate. In this paper, the proportional integral (PI) controllers are used to control the DFIG-basedwind farms for regulating the electronic devices including rotor side converter (RSC) and grid side converter (GSC) to control the active and reactive power of DFIG. The PI parameters are tuned by imperialist competitive algorithm (ICA). So, the transient behavour of the DFIG-based WF is explors when the voltage dip occurs. Hence, the induced electric motive force in to the rotor is measured. Also, an existed uncertainty for mutual inductance is considered caused by saturated curve during three-phase fault conditions and the bahavour of DFIG-based WT is examined and analyzed. All of simulation is done by Matlab/Simulink®.

Optimal Power Tracking of DFIG-Based Wind Turbine Using MOGWO-Based Fractional-Order Sliding Mode Controller

AbstractThe doubly fed induction generator (DFIG)-based wind turbine as a nonlinear, compound, and multivariable time-varying system encompasses several uncertainties especially unfamiliar disturbances and unmodeled dynamics. The design of a high-performance and reliable controller for this system is regarded as a complex task. In this paper, an effective and roust fractional-order sliding mode controller (FOSMC) has been designed to accurately regulate the active and reactive power of DFIG. FOSMC has overcome the system uncertainties and abated the chattering amplitude. Since tuning the FOSMC is a challenging assignment, the application of a multi-objective optimization algorithm can efficiently and precisely solve the design problem. In this regard, non-dominated sorting multi-objective gray wolf optimizer (MOGWO) is taken into account to optimally adjust the FOSMC. In a word, the simulation results have definitively validated robustness of MOGWO-based FOSMC in order to accurately track DFIG's active and reactive power.

Designing a wide area damping controller to coordinate FACTS devices in the presence of wind turbines with regard to time delay

The main objective of this study is to increase the power system oscillation damping in the presence of wind farms using flexible alternating current transmission systems (FACTS) devices and predictive control. The desired design is conducted to coordinate static synchronous compensator-static synchronous series compensator and rotor side converter in doubly-fed induction generator (DFIG). This design is done to compensate for the DFIG reactive power and increase power system oscillation damping in the presence of uncertainties in the wind turbine. The method proposed for coordinated design was based on the network predictive control (NPC) so that it could improve damping, and compensate for the time delays in sending wide area signals. In fact, NPC is based on generalised predictive control (GPC) which has the ability to compensate for time delays using model identification method. Using MATLAB software, the simulation results were conducted on a 16-machine and 69-bus power system under different scenarios; and the ability of NPC is well proven compared with GPC and the classic method of wide area controller.

Second-Order Sliding Mode Based P-Q Coordinated Modulation of DFIGs Against Interarea Oscillations

This letter presents an active and reactive power coordinated damping controller for doubly fed induction generator (DFIG) using second-order sliding mode technique. Through simultaneously modulating active and reactive power of DFIG, the proposed controller has an enhanced damping performance. Its advantages include faster damping speed and robustness to modeling uncertainties and parameter variations. Simulation results have verified its superior performance over existing schemes.

Backstepping-Based DPC Strategy of a Wind Turbine-Driven DFIG Under Normal and Harmonic Grid Voltage

This paper presents a sort of nonlinear backstepping-based algorithm combining with direct power control (DPC) to a wind turbine-driven doubly fed induction generator (DFIG) under normal and especially harmonic grid voltage. First, the power control objectives are analyzed and designed under normal and harmonic grid voltage for the purpose of harmonic stator current suppression; second, a unified mathematic model of a DFIG under normal and harmonic grid voltage is founded, exploring its power model in detail; finally, the backstepping algorithm is introduced briefly and the backstepping-based DPC (BS-DPC) algorithm of the DFIG is developed under normal and harmonic grid voltage. The comparative simulation results between vector control (VC) with resonant controller, look-up table DPC (LUT-DPC) and BS-DPC under normal grid voltage verify that the proposed BS-DPC realizes the decoupling control of active and reactive power of DFIG, with better dynamic performance than VC, as well as with better steady performance than LUT-DPC. Under the harmonic grid voltage, further simulation results verify the effectiveness of BS-DPC for suppressing the harmonic stator current of the DFIG in contrast to VC with a resonant controller and LUT-DPC with improved control objectives proposed by this paper; meanwhile, the adaptability of BS-DPC to minute frequency derivation, harmonic component order and distorted degree of the grid voltage under harmonic conditions are verified as well.

Reactive power control strategy for a wind farm with DFIG

Reactive power control strategy for a wind farm with a doubly fed induction generator (DFIG) is investigated. Under stator flux-oriented (SFO) vector control, the real power of the DFIG is controlled by the q-axis rotor current Iqr and the reactive power is mainly affected by the d-axis rotor current Idr. To examine the effect of Idr on stator reactive power Qs and rotor reactive power Qr, the DFIG is operated under five different operating modes, i.e, the maximum Qs absorption mode, the rotor unity power factor mode, the minimum DFIG loss mode, the stator unity power factor mode, and the maximum Qs generation mode. In pervious works, stator resistance Rs was usually neglected in deriving the d-axis rotor currents Idr for different DFIG reactive power operating modes. In the present work, an iterative algorithm is presented to compute the d-axis rotor currents Idr for the five reactive power control modes. To demonstrate the effectiveness of the proposed iterative algorithm, the rotor current, rotor voltage, stator current, real power and reactive power of a 2.5 MW DFIG operated under the five different operating modes are computed.

Multi-objective Fuzzy-optimization of Crowbar Resistances for the Low-Voltage Ride-through of Doubly Fed Induction Wind Turbine Generation Systems

This study investigates the multi-objective fuzzy optimization of crowbar resistance for the doubly fed induction generator (DFIG) low-voltage ride-through (LVRT). By integrating the crowbar resistance of the crowbar circuit as a decision variable, a multi-objective model for crowbar resistance value optimization has been established to minimize rotor overcurrent and to simultaneously reduce the DFIG reactive power absorbed from the grid during the process of LVRT. A multi-objective genetic algorithm (MOGA) is applied to solve this optimization problem. In the proposed GA, the value of the crowbar resistance is represented by floating-point numbers in the GA population. The MOGA emphasizes the non-dominated solutions and simultaneously maintains diversity in the non-dominated solutions. A fuzzy-set-theory-based is employed to obtain the best solution. The proposed approach has been evaluated on a 3 MW DFIG LVRT. Simulation results show the effectiveness of the proposed approach for solving the crowbar resistance multi-objective optimization problem in the DFIG LVRT.

Direct Power Control of Doubly Fed Induction Generator Based on the Estimated Stator Flux

In order to improve the dynamic performance, based on the analysis of the dynamic model of doubly fed induction generator (DFIG), this paper presents an improved direct power control strategy which is based on the direct control of stator active and reactive power of DFIG. The proposed method only utilizes the estimated stator flux by the stator resistance which is the only machine parameter, so as to remove the power dithering resulting from the inaccuracy associated with rotor flux estimation. In the Matlab/Simulink, simulation results for a 15KW DFIG system demonstrate the high accuracy and excellent dynamic performance during variations of active and reactive power, and revolution.

Active Power Dispatch Plan among Units in DFIG Based Wind Farm

AbstractDuring normal operation, doubly-fed induction generator (DFIG) can generate certain range of reactive power according to the requirements of the power grid. According to the active power order from power dispatching center, a kind of wind turbines scheduling solution which also suits the actual operation situation of “three-north” area wind farms in China is proposed. This solution makes it possible for the wind farm to generate the maximum reactive power or the certain reactive power below the maximum reactive power which will meet the needs of the power grid by adjusting output active power and reactive power of each DFIG. Based on the DFIG reactive power limit, this paper proposes two theorems and an allocation algorithm to find out the active power dispatch plan. This plan avoids the grid side converter switch devices frequently action. The active power and reactive power generated by the wind farm can both satisfy the power grid's needs and provide a reference for the capacity of additional r...

Comparative study of voltage oriented and frequency coordinated control of grid connected doubly fed induction generator

In this paper, a comparative study between voltage oriented control (VOC) and frequency coordinated control (FCC) of grid connected doubly fed induction generator (DFIG) is presented. The two method controls are deeply done on DFIG converter sides, grid side converter (GSC), and rotor side converter (RSC). The VOC method permanently maintains the DFIG reactive power to zero values to achieve stable voltage. This control is implemented by regulating the rotor direct axis reference current in RSC using grid reactive power. On the other hand, the FCC has employed the active power obtaining from the system frequency deviation to control the rotor quadrature axis reference current in the RSC. The GSC is the same in two studies, and its applied vector controlled method. The comparison study between the two methods is conducted at a steady and dynamic state under constant and variable wind speeds. The simulation results are carried out by using PSCAD/EMTDC electromagnetic transient program to validate the comparison study between two methods control of DFIG. The outcomes of the simulation show that the VOC is very convenient when the DFIG operated at transient mode and variable wind speeds while the FCC is feasible and effective for steady-state mode applications. Furthermore, the FCC method has an ability to reduce the active and reactive powers ripples as well as decreasing torque harmonics. Both of two methods had fewer transient recovery values of output parameters, which ensure safety dynamic response of DFIG and power system. This study contributes significantly to choose the suitable control of the DFIG converters according to electrical grid operation conditions. In addition, if a joint control has been applied to these two methods, the wind power gained strong and flexible control of the frequency and voltage for different operating conditions.

A Comprehensive LVRT Control Strategy for DFIG Wind Turbines With Enhanced Reactive Power Support

<?Pub Dtl=""?> The paper presents a new control strategy to enhance the ability of reactive power support of a doubly fed induction generator (DFIG) based wind turbine during serious voltage dips. The proposed strategy is an advanced low voltage ride through (LVRT) control scheme, with which a part of the captured wind energy during grid faults is stored temporarily in the rotor's inertia energy and the remaining energy is available to the grid while the DC-link voltage and rotor current are kept below the dangerous levels. After grid fault clearance, the control strategy ensures smooth release of the rotor's excessive inertia energy into the grid. Based on these designs, the DFIG's reactive power capacity on the stator and the grid side converter is handled carefully to satisfy the new grid code requirements strictly. Simulation studies are presented and discussed.

Multi-objective reactive power support from wind farms for network performance enhancement

This paper examines the ability of the doubly fed induction generator (DFIG) to deliver multiple reactive power objectives during variable wind conditions. The reactive power requirement is decomposed based on various control objectives (e.g. power factor control, voltage control, loss minimisation, and flicker mitigation) defined around different time frames (i.e. seconds, minutes, and hourly), and the control reference is generated by aggregating the individual reactive power requirement for each control strategy. A novel coordinated controller is implemented for the rotor-side converter and the grid-side converter considering their capability curves and illustrating that it can effectively utilise the aggregated DFIG reactive power capability for system performance enhancement. The performance of the multi-objective strategy is examined for a range of wind and network conditions, and it is shown that for the majority of the scenarios, more than 92% of the main control objective can be achieved while introducing the integrated flicker control scheme with the main reactive power control scheme. Therefore, optimal control coordination across the different control strategies can maximise the availability of ancillary services from DFIG-based wind farms without additional dynamic reactive power devices being installed in power networks

Coordinated utilisation of wind farm reactive power capability for system loss optimisation

Most wind farms currently being installed are based upon doubly fed induction generator (DFIG) or direct-drive synchronous generator (DDSG) technology. Given that one of the impacts of introducing distributed generation is an alteration of steady-state power flows and voltages, both technologies are capable of providing local voltage support. Wind farms may, therefore, be included in optimal power flow (OPF) calculations to minimise fuel cost and/or network losses. The IEEE 30-bus system is considered as a case study, comparing fixed-speed induction generator (FSIG) requirements with DFIG capability. Results are presented for a range of DFIG capability modes, at varying system load and wind farm penetration levels. A significant reduction in losses can be achieved by suitable co-ordination of DFIG reactive power import/export, operating within typical grid code specifications. It is shown that the dynamic variability of reactive power requirements is readily accommodated by the power system. Finally, implementation options for the scheme and incentivising strategies are considered. Copyright © 2010 John Wiley & Sons, Ltd.