Grid-connected Wind Turbine Generator Research Articles

An Approach to Improve Power System Resiliency in Grid-Connected Wind Turbine Generator Power System

An Approach to Improve Power System Resiliency in Grid-Connected Wind Turbine Generator Power System

Detailed and Average Models of a Grid-Connected MMC-Controlled Permanent Magnet Wind Turbine Generator

In this paper, a detailed model and an average model of an MMC (Modular Multilevel Converter)-controlled Permanent Magnet Synchronous Generator (PMSG)-based direct drive wind turbine are proposed. The models are used to analyze the steady-state and transient characteristics of the grid connectivity study of the wind turbine generator. Configuration of the electrical topology and the control scheme of the wind turbine generator for both models are comprehensively presented. In the detailed model, the MMC circuit is represented by power electronic IGBTs, with switching phenomena considered. Meanwhile, in the average model, the MMC circuit is simplified by using voltage source representation, hence the complexity of the MMC circuit and the simulation duration of the analysis can be reduced. Comparative analysis between the detailed and the simplified models is also investigated through simulation performed using PSCAD/EMTDC. The simulation results show that both models have a good controllability and dynamic stability under steady-state and transient conditions. The simulation results also confirm that the average model has adequate accuracy, and simulation time can be reduced significantly.

Performance Evaluation of Grid-Connected Wind Turbine Generators

The risk of oscillation of grid-connected wind turbine generators (WTGs) is well known, making it all the more important to understand the characteristics of different WTGs and analyze their performance so that the problems’ causes are identified and resolved. While many studies have evaluated the performance of grid-connected WTGs, most lack clarity and precision in the modeling and simulation techniques used. Moreover, most of the literature focuses on a single mode of operation of WTGs to analyze their performances. Therefore, this paper updates the literature by considering the different operating conditions for WTGs. Using MATLAB/SIMULINK it expands the evaluation to the full range of vulnerabilities of WTGs: from the wind turbine to grid connection. A network representing grid-connected squirrel-cage induction generator (SCIG) and doubly-fed induction generator (DFIG) wind turbines are selected for simulation. The performances of SCIG and DFIG wind turbines are evaluated in terms of their energy generation capacity during constant rated wind speed, variable wind speed, and ability of fault-ride through during dynamic system transient operating conditions. The simulation results show the performance of DFIG is better than SCIG in terms of its energy generation capacity during variable wind speed conditions and active and reactive power control capability during steady-state and transient operating conditions. As a result, DFIG wind turbine is more suitable for large-scale wind power plants connected to weak utility grid applications than SCIG.

Comparison of Methods to Examine Sub-Synchronous Oscillations Caused by Grid-Connected Wind Turbine Generators

This paper compares three methods, the impedance model based analysis, the positive net damping analysis, and the open-loop modal resonance analysis. The differences and connections among these three methods are revealed, which helps to gain better understanding on the limitations of the methods for studying the mechanism of sub-synchronous oscillations (SSOs) caused by grid-connected wind turbine generators (WTGs) in a power system. Following useful conclusions are obtained, which are evaluated and demonstrated by study cases: First, both the negative resistance and negative net damping are highly related with strong dynamic interactions between the WTGs and ac grid under the condition of modal resonance. This explains why resistance and net damping may become negative from the standpoint of system modal condition. Second, it is possible that results of impendence model based analysis (IMA) and positive net damping analysis (PDA) may not reflect correctly the system SSO instability risk brought about by the WTGs. The reason is that the IMA and PDA are based on the sufficient condition of system stability. Assessment made by the IMA or PDA may be very conservative. In study cases, three methods are compared in the parameter space of converter controllers of the WTGs such that all the parameter conditions are covered in comparison.

Improvements in primary frequency regulation of the grid‐connected variable speed wind turbine

Primary frequency regulation capability of the wind turbine generators is an appealing topic in order to consider safe increasing of the wind power integration into power grids. This study introduces improvements in the primary frequency contribution of the grid-connected variable speed wind turbine generators, which operate under de-loaded conditions. A new dynamic droop control approach based on the fuzzy logic system is proposed. In this control approach, the droop setting is continuously adjusted in response to the de-loaded rotor speed, the frequency deviation, and the rate of change of frequency. In addition, a new dynamic de-loading technique based on the Sugeno-Fuzzy inference system is proposed where the de-loading percentage of the wind turbine generator is decided continuously according to the frequency deviation. The effectiveness of the proposed dynamic de-loading and dynamic droop control approaches is verified through extensive comparative studies. The simulation results confirmed that the proposed control approaches have the ability to provide transient and steady-state power-sharing and improve effectively the frequency stabilisation of the power system within the stable and secure limits of the wind turbine.

Open-loop modal analysis to identify the SSO instability risk caused by grid-connected wind farms

We proposed and applied the method of open-loop modal analysis previously for examining power system sub-synchronous oscillations (SSOs). However, the method was only applicable to grid-connected wind turbine generators, because we only theoretically proved the applicability of open-loop modal analysis for a single-input single-output (SISO) closed-loop interconnected model. In this study, we present the theoretical proof that in a multi-input multi-output closed-loop (MIMO) interconnected model, open-loop modal analysis is still applicable for examining power system SSOs by using the open-loop modal information. Hence, we propose to apply the open-loop modal analysis to detect the risk of growing SSOs caused by grid-connected wind farms, rather than wind turbine generators, in the power system. This is because in practice, dynamic interactions introduced by a grid-connected wind farm, in fact, constitute MIMO closed-loop interconnected model. Thus, the study has extended and enhanced the applicability of method of open-loop modal analysis. In the paper, the applicability is demonstrated and evaluated by example power systems with grid-connected wind farms. The SSO instability dangers brought about by the wind farms to the example power system were detected by the proposed method of open-loop modal analysis.

PMSG based wind system for real-time maximum power generation and low voltage ride through

This work presents an efficient control strategy for low voltage ride through (LVRT) and maximum power tracking of a permanent magnet synchronous generator (PMSG) based variable speed grid connected wind turbine generator. Three-level Neutral Point Clamped converters are connected back to back to perform the power conversion. A controller is proposed and implemented for the machine side converter to maximize the power generation and loss minimization under varying wind speed. A controller is also proposed and implemented for the grid side converter to transfer the generated power to a local load and grid by keeping the DC link voltage constant. To test the LVRT capability, a three phase short circuit fault is applied on the grid side. The real time digital simulator results on a 2 MW/4 kV PMSG verify the effectiveness and superiority of the proposed control scheme under different loading and fault conditions.

Supervisory control of a grid-connected wind turbine generator

In this article, the supervisory controller is proposed to manage a hybrid wind turbine generator and a grid supplying a village load. The main problem is the compatibility of coupling of different sources. To avoid this problem, the grid supplies a motor to supplement the torque of the wind turbine when the wind speed is low, and the village demand is higher than the wind turbine generator power. On the other hand, the excess power from the wind turbine generator can be absorbed by a dynamic power load that is connected to the grid. The fuzzy proportional–integral/proportional–integral–derivative supervisory controller objectives are to stabilize the frequency and voltage of the system and satisfy the village power demand. This is achieved by balancing the active and reactive powers of the wind turbine generator and village load through a grid contribution. The whole system has been simulated using SIMPOWER in MATLAB/SIMUILINK software. The efficiency of the proposed controller has been proved by the obtained results.

Wind time series modeling and stochastic optimal control for a grid-connected permanent magnet wind turbine generator

Summary In this paper, the control system of a permanent-magnet synchronous machine wind turbine generator connected to the grid is studied. A set of wind speed time series is used to model the rapidly changing wind speed component as a stochastic process. Several control laws, including the nonlinear stochastic optimal controller, are developed, and their efficiency is examined comparatively and under various conditions. Also, the effect of parameter uncertainty to the system efficiency is shown through simulations. The results show that the system efficiency increase obtained by the use of sophisticated control techniques, although not dramatic, is not negligible. Copyright © 2015 John Wiley & Sons, Ltd.

Adaptive Type-2 Fuzzy Sliding Mode Control for Grid-Connected Wind Turbine Generator Using Very Sparse Matrix Converter

The strategy to improve both efficiency and power quality of grid-connected wind turbine generator systems (WTGs) are presented. WTGs efficiency is improved by developing a variable speed control to obtain maximum power at all wind speeds. Variable speed control based on Adaptive Type-2 Fuzzy Sliding Mode Control (AFSMOC) is proposed by employing Very Sparse Matrix Converter (VSMC). Type-2 fuzzy system is used to improve the robustness of sliding mode control. VSMC can provide low harmonics in line current, so the power quality problems can be minimized. The simulation results shows that the AFSMOC can regulate the generator speed at optimum Tip Speed Ratio (TSR) with maximum error 2.5 rpm, so that the maximum power can be obtained at all wind speeds. VSMC also provide good performance with Total Harmonic Distortion (THD) of voltage 0.35% and THD of current 6,82%

Improving Low Voltage Ride-through Capabilities for Grid Connected Wind Turbine Generator

Low Voltage Ride-Through (LVRT) is one of the most dominant grid connection requirements to be met by Wind Energy Conversion Systems (WECS). In presence of grid voltage dips, a mismatch is produced between the generated active power and the active power delivered to the grid. Low voltage ride through requirement demands management of this mismatch, which is a challenge for the WECS. In this paper, LVRT requirements provided by Wind Grid Codes have been reviewed. This paper discusses the standards for interconnection of wind generators to local grid during healthy and fault conditions. As per LVRT requirement, during dip occurrence, the wind power generation plant must remain connected to the grid and in addition, it has to deliver reactive power into the grid to aid the utility to hold the grid voltage. Voltage sag proves to be the most prominent power quality issue and the effect of voltage sag on different wind generator topologies has been investigated. Several methods for LVRT fulfillment have been explored and the LVRT scheme has been validated based on MATLAB-SIMULINK simulation.

An improved fuzzy synthetic condition assessment of a wind turbine generator system

This paper presents an improved fuzzy synthetic model that is based on a real-time condition assessment method of a grid-connected wind turbine generator system (WTGS) to improve the operational reliability and optimize the maintenance strategy. First, a condition assessment framework is proposed by analyzing the monitored physical quantities of an actual WTGS with an electrically excited synchronous generator (EESG) and a full-scale converter. To examine the variable speed operational performances, the dynamic limits and the deterioration degree functions of the characteristic variables are determined by analyzing the monitoring data of the WTGS. An improved fuzzy synthetic condition assessment method is then proposed that utilizes the concepts of deterioration degree, dynamic limited values and variable weight calculations of the assessment indices. Finally, by using on-line monitoring data of an actual 850kW WTGS, real-time condition assessments are performed that utilize the proposed fuzzy synthetic method; the model’s effectiveness is also compared to a traditional fuzzy assessment method in which constant limited values and constant weights are adopted. The results show that the condition assessment that utilizes the improved method can predict the change of operating conditions and has a better coherence with real operating conditions than that of a traditional fuzzy assessment method.

Control and Interfacing of a Grid-Connected Small-Scale Wind Turbine Generator

An ac/dc/ac power converter is an important device used to extract power from variable speed permanent magnet wind generators and feed it into the grid. This paper describes how these converters incorporate maximum power point tracking based on its power feed to the grid at different wind speeds. Using the permanent magnet generator voltage, grid current, and grid voltage samples, the proposed system achieves an enhanced dynamic behavior. This feature effectively prevents the grid from “boost” charging the dc side of the H-bridge inverter at the start of operation. Since small wind turbines normally do not have expensive pitch control mechanisms, a thyristor-based “dump-load circuit” is employed to protect the turbine from high wind speed operation when disconnected from the grid. The thyristor controller also protects the inverter from high dc voltage input from the wind generator at high wind speed. Preliminary results are included using a laboratory 2-kW prototype converter.

연계선로의 조건 변화에 따른 DFIG와 FSIG 풍력발전시스템의 운전특성 비교

This paper analyzes the steady-state output characteristics of variable-speed wind turbine systems using doubly-fed induction generators(DFIG) compared with fixed-speed induction generator(FSIG) wind turbine systems. It also presents simulations of a grid-connected wind turbine generation system for dynamics analysis on MATLAB/Simulink and compares the responses between DFIG and FSIG wind turbine systems with respect to wind speed variation, impedance changes and X/R ratio changes of interconnecting circuits. Simulation results show the variation of generator's active output, terminal voltage and fault currents at the interconnecting point. Case studies demonstrate that DFIG wind turbine systems illustrate better performance to 3-phase fault than FSIG's.

Real-Time Simulation of a Wind Energy System Based on the Doubly-Fed Induction Generator

This paper presents the real-time digital simulation of a grid-connected wind turbine generator system (WTGS) based on a doubly-fed induction generator (DFIG). A 1.5-MW WTGS is the basis for model development. First a detailed electromagnetic transient model for the WTGS is developed in the MATLAB/SIMULINK environment. This model includes the complete aerodynamic, mechanical and electrical components of the wind turbine, the back-to-back voltage source converter (VSC)-based power electronic interface, as well as the mechanical and electrical controllers of the WTGS. The overall grid-connected WTGS model was then order-reduced and implemented on a PC-cluster-based real-time digital simulator. The maximum execution time of the DFIG model and control was 5.53 mus, while that of the grid-connected WTGS was 15.375 mus. Real-time oscilloscope results are presented to illustrate the WTGS controller performance, the variable wind speed dynamics, and interaction of the WTGS with grid faults. The real-time WTGS model can be readily used for hardware-in-the-loop testing.

MATLAB/Simulink에서 계통연계 풍력발전시스템의 특성해석에 대한 시뮬레이션

The paper presents a modeling of the grid-connected wind turbine generation system on MATLAB/Simulink and aims to perform simulations for analysis of the system`s characteristics. It performs a pitch regulation for control of the wind generator`s output with respect to wind speed variation, and presents a relationship between interconnecting transformer`s connections and fault current by reviewing the variations of fault current according to transformer connections in a grid-connected wind power generation system. It also investigates the effect of grounding methods of the interconnecting transformer`s neutral point on fault current variations. The simulation results show the differences of fault currents, voltages and generator`s characteristics for a line-to-ground fault according to interconnecting transformer`s four different connections, and the differences of fault currents of the system according to grounding methods of the transformer neutral point. Therefore, the case studies demonstrate the effectiveness of the proposed simulation model on Simulink.

Simulating dynamic interactions of grid-linked wind turbines

Models for dynamic interaction of wind turbine generators (WTGs) on electric utility networks have been suggested, but only a few publications have addressed the aggregation of hundreds of turbine generators. This topic has a significant impact on studies related to power system dynamics, because it helps reduce system complexity and computation cost. This article features a study that set out to: simulate the electromechanical dynamics of a typical grid-connected wind turbine generator, test an aggregation technique for representing a group of WTGs by a single unit, and demonstrate how such a complicated analysis of interconnected systems can be performed using state-of-the art software that performs both numerical simulation and linearized eigenstructure studies. The SIMULINK software simplifies the analysis of the interconnected power systems, performing both numerical simulation and linearized eigenstructure studies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>