Wind Generator Output Power Research Articles

Stabilization of Power System Including Wind Farm by PWM Voltage Source Converter and Chopper Controlled SMES

This paper presents a dynamic model of Superconducting Magnetic Energy Storage (SMES) device developed, which can significantly decrease the voltage and power fluctuations of grid connected fixed speed wind generators. The SMES system with a voltage–source IGBT converter and two–quadrant DC–DC chopper is analyzed as a controllable energy source. The objective of the proposed SMES control strategy is to smooth the wind farm output by absorbing or providing real power. Moreover, its reactive power output can also be controlled to keep the wind farm terminal voltage constant. The control methodology of SMES system is suitable for the two objectives stated above. The performance of the proposed system is evaluated by dynamic simulations using a test power system. Real wind speed data is used in the simulation analyses, which validates the effectiveness of the proposed control strategy. Simulation results clearly show that the proposed control strategy can smooth well the wind generator output power and also maintain the terminal voltage at rated level. Key words: Minimization of fluctuations; superconducting magnetic energy storage (SMES); wind generator stabilization; voltage source converter (VSC); DC–DC chopper

Design and Implementation of Flexible Control Strategy for Stand Alone Wind Generator System

This paper presents the design and implementation of the flexible control strategy for stand alone wind generator system controlled by a digital signal processor. The system is composed of a wind generator, a step-up dc/dc converter and battery energy storage system (BESS). The wind generator is the main power source of the system, and the BESS is used for energy storage and power compensation for the lack of stability of the wind power. Since the output power of wind generator varies with the change of wind speed, a flexible control strategy is used to determine the system working state and the operating mode of BESS. In charging mode, the battery is charged by multi-stage current charging method with maximum power point tracking (MPPT) algorithm to raise the charging efficiency and completely employ the finite power. Fuzzy logic control algorithm is used to improve the transient response when the battery discharges in discharging mode. Finally, a 100 W power converter system is constructed and the performance is verified.

Reactive power compensation and stability analysis of fixed speed wind generators using STATCOM integrated with energy storage devices

In this paper, the interaction of the wind farm, energy storage, reactive power compensation and the power system network is analysed. This article discusses the performance of a STATCOM/superconducting magnetic energy storage topology to provide both the active and reactive power, which can significantly decrease the voltage and power fluctuations of grid-connected fixed speed wind generators. One major problem in wind generator output power smoothing is the setting of the reference output power. A simple moving average technique is used to generate the reference output power which corresponds to the energy storage capacity and thus the energy capacity of an energy storage system unit can be small. Moreover, a simulation model has been tested in MATLAB, and the simulation results are compared.

Performance of Governor System on Minimizing Frequency Fluctuations with Wind Power Generation

As wind turbine output is proportional to the cube of wind speed, the wind turbine generator output fluctuates due to wind speed variations. Hence, if the power capacity of wind power generators becomes large, wind power generator output can have an influence on the power system frequency. Therefore, this study investigates the influence of governor control systems of synchronous generators (SGs) for minimizing frequency fluctuations with high wind power penetration level, when a total capacity of SGs is considered as 100 MVA. It is seen that when both SGs operate as governor free (GF) operation, system perform better frequency control. But it can not be maintained to the acceptable level when SGs operate at GF-LFC or LFC-GF operation with wind power capacity about 5% of total capacity. Finally, it is seen that when several interconnected SGs are operated with different control modes, system frequency become more severe for 10% capacity of wind power. DOI: http://dx.doi.org/10.11591/ijece.v2i1.180 Full Text: PDF

Smoothing Control of Wind Farm Output Fluctuations by Fuzzy Logic Controlled SMES

Due to random variations of wind speed, the output power and terminal voltage of a fixed speed wind generator fluctuate continuously. These irregularities in power output are affecting both the power quality and reliability. It is reported that STATCOM/SMES (Superconducting Magnetic Energy Storage) system can significantly decrease voltage and output power fluctuations of grid connected fixed speed wind generator. But the main problem in wind generator output power smoothing is the choice of the reference output power, because it corresponds to energy storage capacity. The storage capacity of SMES that is sufficient for the smoothing control but as small as possible is very important, considering cost effectiveness. In this paper, a fuzzy logic controlled STATCOM/SMES system is proposed, in which both SMA (Simple Moving Average) and EMA (Exponential Moving Average) are used to generate output power reference. Real wind speed data are used in the simulation analyses, which validate the effectiveness of the proposed control strategy. Simulation results clearly show that the proposed STATCOM/SMES system can smooth well the wind generator output power and also maintain the terminal voltage at rated level in both cases when SMA or EMA is used to generate output reference power. Finally, it is shown that reference output power generated by EMA provides better performance with reduced SMES storage capacity than that of output power generated by SMA. Keywords: Minimization of fluctuations, fixed speed wind generator, STATCOM/SMES, simple moving average (SMA) and exponential moving average (EMA), and wind farm (WF). DOI: http://dx.doi.org/10.11591/ijece.v1i2.181

Wind power and hydrogen generation system with cooperatively controlled three‐level NPC‐VSC based energy capacitor

AbstractOne of the recent challenges for transmission system operators (TSO) or power grid companies is to smoothen the output power fluctuation of wind generator due to the random variation of wind speed. In addition to the output power fluctuation of fixed‐speed wind turbine generator system (WTGS), it suffers greatly from terminal voltage fluctuation. The fixed capacitor bank connected to its terminal cannot maintain constant terminal voltage under randomly varying wind speed. On the other hand, besides the continuous growth of wind power, hydrogen generation system is also becoming very popular nowadays using the electrical energy from wind power plants. This study proposes a three‐level neutral point clamped voltage source converter (NPC‐VSC) based energy capacitor system (ECS), composed of electric double layer capacitor (EDLC) and power electronic converters, to smoothen output power and terminal voltage fluctuations of grid connected fixed speed wind farm. A simple low pass filter (LPF) is adopted in this study to generate the power reference of ECS. Another salient feature of this study is the generation of hydrogen by using wind generator output power. Effective topology of wind power and hydrogen generation system with cooperatively controlled NPC‐VSC based ECS is proposed from the cost and performance points of view. Copyright © 2009 John Wiley & Sons, Ltd.

Stabilization of Wind Power Generation Output Fluctuation by Cooperative Control of Controllable Distributed Generator and Battery System

Wind power generation is expected as one of countermeasures for the environmental issues and energy security crisis. However, uncertain and volatile fluctuations in wind power generation output may disturb the system frequency control. This paper proposes a fluctuation stabilization method utilizing a controllable distributed generator (CDG) and a battery system considering the actual technical requirement for a wind power generation system set by the Tohoku Electric Power Co. In the proposed method, the CDG plays a role of main compensator and the battery is used to support the slow dynamic response of CDG. In this paper, the validity of proposed method is ascertained and the necessary capacity of battery system is evaluated through some computational simulations.

Stabilization of Wind Generator by Using STATCOM/SMES

In this work, the STATCOM/SMES system with a voltage-source IGBT converter is modeled as a controllable energy source. The objective of the proposed STATCOM/SMES topology is to provide both active and reactive power, which can significantly decrease the voltage and power fluctuations of grid connected fixed speed wind generators. One major problem in wind generator output power smoothing is setting of the reference output power. Constant output power reference is not a good choice because there can be some cases where wind speed is very low and then sufficient power cannot be obtained. In that case, energy storage device can solve the problem but large energy capacity may be needed. To generate output power reference, a Simple Moving Average (SMA) technique is used which corresponds to the energy storage capacity. Thus the capacity of SMES can be small (50% of wind farm capacity). Real wind speed data is used in the simulation analyses, which validates the effectiveness of the proposed control strategy. Keywords: STATCOM/SMES; Energy storage system (ESS); Simple moving average (SMA); Fixed speed wind generator; Voltage source converter (VSC).© 2009 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved.DOI: 10.3329/jsr.v1i3.2605 J. Sci. Res. 1 (3), 528-538 (2009)

Calculation of economic transmission connection capacity for wind power generation

Applications for the connection of large-scale wind power generation to transmission networks are presenting new issues both for transmission system planners and generation developers. One of the major problems faced is the assessment of transmission system capacity requirements for the export of power from areas with high penetration of variable and intermittent sources of generation such as wind power. A method for evaluating the required transmission connection capacity from an area dominated by wind generation to the main interconnected system is presented, based on historical time series data for both wind power generation output and the demand in the group. The operational implications for the transmission system and generation owners are evaluated using a cost-benefit approach. The method is demonstrated for a number of network situations. Conclusions are drawn about the value of the method and, more generally, about the trade-off between investment in transmission capacity and curtailment of wind generation under favourable wind conditions.

Analysis of a fuel cell micro-grid with a small-scale wind turbine generator

If electric power is supplied using an independent micro-grid connected to renewable energy, it can flexibly match the energy demand characteristics of a local area. And an independent micro-grid is expected to be effective in cutting greenhouse gas discharge and energy costs, as well as in eliminating the need for an emergency power supply system. Since the output of renewable energy is unstable, other energy equipment needs to cover the stability of output. Thus, the operating conditions of an independent micro-grid that supplies power with natural power sources and fuel cells are investigated. The operation conditions of a fuel-cell independent micro-grid with wind power generation were investigated by numerical analysis. Step loads and an apartment house power load model were analyzed using the dynamic characteristics of a fuel cell obtained from experiments. The output of wind power generation and fuel cells is controlled by proportional-integral control of an independent micro-grid for rapid power demand change.

Transient Stability Enhancement of Wind Generator by a New Logical Pitch Controller

In order to investigate the impacts of the integration of wind farms into utilities networks, transient stability should be analyzed before connecting wind turbine generator system (WTGS) to the power system. In this paper, a new logical pitch controller equipped with fuzzy logic controller (FLC) has been proposed, which can enhance the transient performance of WTGS during severe network disturbances. Moreover, it can maintain the output power at rated level when wind speed is over the rated speed. Before transient stability analysis, it is necessary to determine initial values of WTGS connected to the external network. In this paper, the initial value calculation method of WTGS is discussed at different wind conditions. Finally, in order to evaluate the effectiveness of the proposed controller in improving the transient stability, simulations have been carried out for severe network disturbances and windy conditions, considering mechanical dead zone of the pitch actuation system. Simulation results clearly indicate that the proposed controller can enhance the transient stability of wind generator at any network, fault or windy condition, and maintain output power of wind generator at rated level when wind speed is over the rated speed.