Grid-connected Wind Power Generation System Research Articles

Backstepping Control of an AC/DC/AC Converter in a Grid Connected Wind Power System

The contribution of this paper is to study a nonlinear control approach known as the backstepping control method to manage reactive and active power using new parametric values for the grid connected wind power generation system. Specifically, the research focuses on a system containing a wind turbine system, a permanent magnet synchronous generator (PMSG), and a grid connected via AC/DC/AC converter. A comprehensive mathematical model for both the wind turbine system, PMSG, and the grid connected via AC/DC/AC converter was developed for this purpose. The Simulation results of the grid-connected wind power generation system are presented and analyzed to show the performance of the nonlinear backstepping control method. The characteristics of the response to variations in generator speed and the power injected into the grid show the highlight of the performance of the backstepping method, under varying wind conditions.

Stability Modeling and Analysis of Grid Connected Doubly Fed Wind Energy Generation Based on Small Signal Model

Stable wind power generation can ensure the quality of power transmitted by the grid. The application of large-scale grid-connected wind power systems will induce problems such as grid oscillation and frequency instability. In order to solve the problem of abnormal power system interaction caused by large-scale wind power access and improve the stability of grid-connected doubly-fed wind power generation, this paper proposes a stability modeling analysis of grid-connected doubly-fed wind power generation based on small signal model. First, the operating conditions of the grid-connected DFIG are analyzed, and the vector diagrams of the three operating conditions are given. When the grid-connected DFIG is in the super-synchronous working state, the sub-synchronous working state and the synchronous working state. According to the operating conditions of the grid-connected doubly-fed generators, the grid-connected doubly-fed wind power generation system is linearized. According to the relationship between the actual speed and the synchronous speed of the doubly-fed generator, the operating conditions of the doubly-fed generator are analyzed. By introducing the small-signal model, we analyze the small-signal of the grid-connected doubly-fed wind power generation system. The indirect current control circuit is used to perform reactive power compensation for grid-connected doubly-fed wind turbines. By calculating the reactive power loss of the grid-connected DFIG and the reactive power loss of the transmission line, the compensation capacity of the grid-connected DFIG is calculated. The transient voltage of the wind turbine is controlled by the rotor-side frequency converter, combined with the pitch angle control model. So far, this paper has realized the modeling analysis of grid-connected doubly-fed wind power generation stability. The simulation results show that the modeling analysis in this paper is reasonable for the small-signal analysis results of the stability of grid-connected doubly-fed wind power generation. In the rotor voltage simulation test, after the oscillation occurs for 1 s, the model starts to simulate and eliminate the fault. During the simulation period of 0.7 s∼1.0 s, the output voltage of the converter decreased to 168 V, and the voltage waveform did not fluctuate greatly after 1.0 s. The experimental results show that this method can improve the stability of grid-connected doubly-fed wind power generation.

Stability Enhancement of Grid-Connected Wind Power Generation System Using PSS, SFCL and STATCOM

The stability related issues may occur in a power system due to disturbances in generating or loading conditions, especially in the presence of distributed generation (DG) based on renewable energy resources (RERs). This paper proposes a novel strategy for the stability enhancement of a wind power generation system (WPGS) by using a combination of three devices, namely, a power system stabilizer (PSS), resistive superconductor fault current limiter (R-SFCL) and static synchronous compensator (STATCOM). The small signal (SS) stability of the test system is enhanced by selecting the best PSS type from the different types of PSS. An R-SFCL is used for improving the rotor angle and the frequency stability of the test system. Two indices, namely, transient stability index and sum of maximum deviations (SMD) index are introduced for determining the optimal locations of different sized R-SFCLs for increasing the rotor angle stability. The sensitivity index (SI) based on the power change between areas is applied for determining the optimal locations of different sized R-SFCLs for enhancing the frequency stability. Along with rotor angle and frequency stability, LVRT capability improvement of the wind farm using STATCOM is also considered. Finally, the combined effect of R-SFCL and STATCOM on the rotor angle and the frequency stability, for different fault locations, is also investigated for determining the optimal location of an R-SFCL in the presence of STATCOM. The results presented in the paper show that STATCOM affects both the number of feasible locations and the optimal locations that can be selected for different sized R-SFCLs for augmenting the rotor angle and the frequency stability of the system during faults. Moreover, it is pointed out that an optimal combination between the different sizes and the locations of R-SFCLs and STATCOM exists to enhance the overall stability of the test system under fault conditions.

Research on Power Quality Based on Doubly-Fed Induction Wind Generator

The influence of grid-connected wind power generation system on power quality has always been a focus of researchers. Doubly-fed induction generators are the most widely used wind turbine generators in the wind power industry, and their impact on the power grid during power generation and grid connection has also received widespread attention. In this paper, based on the power quality problem of double-fed induction generators connected to the grid, three aspects of voltage fluctuation, flicker and harmonics are analyzed respectively, and the influence of this model on grid power quality is analyzed.

Real-Time Multiple Open-Switch Fault Diagnosis in Three-phase AC/DC PWM Converter for PMSG Based Grid-Connected Wind Power Generation System

This paper proposes a new multiple open-switch fault diagnosis method and faulty switch localization algorithm in three-phase AC/DC PWM converter for permanent magnet synchronous generator (PMSG) based grid-connected wind power generation system. In the proposed scheme, the open-switch fault is detected by using normalized three-phase RMS currents and faulty switch location is identified by using normalized three-phase RMS currents as well as average phase currents. Various kinds of fault may occur in AC/DC PWM converter, which decreases the generator output power and degrades the stability in wind power generation system. In this paper, multiple as well as single open-switch fault conditions are investigated. The proposed fault detection and faulty switch localization algorithms do not require additional sensors or hardware since they use only the information on measured phase currents. In addition, they are quite simple, cost-effective and easy to use. To verify that the proposed methods are effective to detect faults and to identify the faulty switches position, the simulation results under twenty-one cases of open-switch faults are presented on different operating conditions.

Application of Advanced MPPT Control for Grid-Connected Wind Power Generation System

The wind speed is varying with fluctuations and random feature, as for conventional HCS algorithm, the oscillation around maximum power point (MPP) was serious, which can cause vibrations of crankshaft and mechanical parts wear, also the misleading decision of conventional HCS method causes the failure in keeping maximum power. A new HCS method for MPPT control was proposed, the principle of MPPT was analyzed and new algorithm was programmed, the new method inherits the advantages of variable step HCS, so that the MPP reached rapidly. Also the detection and halt mechanism was introduced, which can reduce searching direction misleading and rotor speed oscillations at MPP, the feasibility and effectiveness of the proposed MPPT strategy have been verified through simulations and experimental results.

Short-Term Wind Speed Forecasting Based on Optimizated Support Vector Machine

To avoid the impact which is caused by the characteristics of the random fluctuations of the wind speed to grid-connected wind power generation system, accurately prediction of short-term wind speed is needed. This paper designed a combination prediction model which used the theories of wavelet transformation and support vector machine (SVM). This improved the model’s prediction accuracy through the method of achiving change character in wind speed sequences in different scales by wavelet transform and optimizing the parameters of support vector machines through the improved particle swarm algorithm. The model showed great generalization ability and high prediction accuracy through the experiment. The lowest root-mean-square error of 200 samples was up to 0.0932 and the model’s effect was much stronger than the BP neural network prediction model. It provided an effective method for predicting wind speed.

HTS SMES Application for the Frequency Stabilization of Grid-Connected Wind Power Generation System

Output power of the wind power generation system (WPGS) fluctuates due to wind speed variation and affects the frequency and voltage fluctuations of the utility. Superconducting Magnetic Energy Storage (SMES) can overcome these fluctuations because of fast response time for energy charging and discharging. To stabilize the frequency fluctuation, HTS SMES should be connected to the terminal of the WPGS. Ulleung island power network in Korea was modeled to demonstrate the effectiveness of SMES for frequency stabilization. Based on the simulation results using EMTDC, a toroidal-type HTS SMES cooled by conduction cooling method and a DC/DC chopper for current charging and discharging were fabricated for experiment. Power network including WPGS was implemented through a Real Time Digital Simulator (RTDS). The simulation and experimental results for frequency stabilization using real HTS SMES and RTDS are discussed in detail.

Direct Rotor Current-Mode Control Improves the Transient Response of Doubly Fed Induction Generator-Based Wind Turbines

The transient response is actually a critical dynamic characteristic of doubly fed induction generator-based wind turbines, especially in the presence of fast transient events, such as, for example, faults in the power system. This paper presents a direct rotor current-mode control (CMC) for the rotor-side converter of these induction generators, which is aimed to improve the transient response in relation to the dynamic performance achieved with the conventional (indirect) CMC. The theoretical study considers two grid fault scenarios, with balanced and unbalanced voltages, and presents a direct rotor CMC scheme for each situation. These control schemes are compared in terms of performance and cost with the indirect CMC schemes. The theoretical contribution of this paper is validated by means of selected simulation results from a 9-MW grid-connected wind power generation system.

Simplified Maximum Power Point Tracking Method for the Grid-connected Wind Power Generation System

A novel maximum power point tracking (MPPT) method for the grid-connected wind power generation system is proposed in this article. The main feature of the proposed method is that the MPPT of the wind power generation system can be obtained via only adjusting the amplitude of the DC/AC inverter's output current and observing the output DC voltage of an AC/DC power converter connected with a permanent magnet synchronous wind generator (PMSWG). Thus, no practical calculation of generated power of the PMSWG is required. Experimental results of the developed prototype show that the performance of the proposed method is as expected.

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.