Nayeem Rahmat Ullah

Temporary Primary Frequency Control Support by Variable Speed Wind Turbines— Potential and Applications

This paper quantifies the capability of providing a short-term excess active power support of a commercial multi-megawatt variable speed wind turbine (VSWT) and generalizes the findings by considering different wind turbine (WT) physical parameters in a wider range from the example case. The paper also identifies some possible applications of it, in particular, in a hydro dominated system. To be able to quantify the system characteristic, a delay model of the studied hydro system is developed. Due to the fact that the initial power surge of a hydro turbine is opposite to that desired, the short-term extra active power support from a wind farm (WF) could be beneficial for a hydro dominated system in arresting the initial frequency fall, which corresponds to an improvement in the system temporary minimum frequency (TMF). The improvements in the TMF are calculated by using both the developed delay model and a detailed model, and the results show good agreement. It is shown that the WT under consideration can provide a 0.1 pu extra active power support for 10 s quite easily which is twice the Hydro-Quebec requirement.

Wind Farms as Reactive Power Ancillary Service Providers—Technical and Economic Issues

This paper examines the possibility of providing reactive power support to the grid from wind farms (WFs) as a part of the ancillary service provisions. Detailed analysis of the WF capability curve is carried out considering maximum hourly variation of wind power from the forecasted value. Different cost components are identified, and subsequently, a generalized reactive power cost model is developed for wind turbine generators that can help the independent system operator (ISO) in managing the system and the grid efficiently. Apart from the fixed cost and the cost of loss components, a new method is proposed to calculate the opportunity cost component for a WF considering hourly wind variations. The Cigre 32-bus test system is used to demonstrate a case study showing the implementation of the developed model in short-term system operations. A finding is that higher wind speed prediction errors (a site with high degree of wind fluctuations) may lead to increased payments to the WFs for this service, mainly due to the increased lost opportunity cost (LOC) component. In a demonstrated case, it is found that 2340

Voltage and Transient Stability Support by Wind Farms Complying With the E.ON Netz Grid Code

/h is paid to the WF as the LOC payment only, when the wind prediction error is 0.5 per unit (p.u.), whereas 54

Variable Speed Wind Turbines for Power System Stability Enhancement

/h is the expected total payment to the WF when the prediction error is 0.2 p.u. for its reactive power service.

Operation of Wind Energy Installations During Power Network Disturbances

In this paper, the impact of the response of a wind farm (WF) on the operation of a nearby grid is investigated during network disturbances. Only modern variable speed wind turbines are treated in this work. The new E.ON Netz fault response code for WF is taken as the base case for the study. The results found in this paper are that the performance of the used Cigre 32-bus test system during disturbances is improved when the WF is complying with the E.ON code compared to the traditional unity power factor operation. Further improvements are found when the slope of the reactive current support line is increased from the E.ON specified value. In addition, a larger converter of a variable speed wind turbine is exploited that is to be used in order to improve the stability of a nearby grid by extending the reactive current support. By doing so, it is shown in this paper that the voltage profile at the point of common coupling (pcc) as well as the transient stability of the grid are improved compared to the original E.ON code, in addition to the improvements already achieved by using the E.ON code in its original form. Finally, regarding the utilization of a larger converter, it is important to point out that the possible reactive power in-feed into the pcc from an offshore WF decreases with increasing cable length during network faults, making it difficult to support the grid with extra reactive power during disturbances.

Reactive Power Ancillary Service from Wind Farms

This paper investigates possible improvements in grid voltage stability and transient stability with wind energy converter units using modified P/Q control. The voltage source converter (VSC) in modern variable speed wind turbines is utilized to achieve this enhancement. The findings show that using only available hardware for variable-speed turbines improvements could be obtained in all cases. Moreover, it was found that power system stability improvement is often larger when the control is modified for a given variable speed wind turbine rather than when standard variable speed turbines are used instead of fixed speed turbines. To demonstrate that the suggested modifications can be incorporated in real installations, a real situation is presented where short-term voltage stability is improved as an additional feature of an existing VSC high voltage direct current (HVDC) installation

Small scale integration of variable speed wind turbines into the local grid and its voltage stability aspects

The response of wind energy installations to grid disturbances is studied in this panel session contribution. In particular, the transient stability influence of a wind energy installation on a nearby grid with a synchronous generator unit is studied. Both fixed-speed as well as variable speed turbine installations are treated. For the variable-speed turbine installations, the influence of using various levels of reactive power infeed from the wind energy installation is investigated. The idea is to use the power electronic hardware that anyway is available in modern wind turbines to make the turbines to, in addition to the normal active power production, also work as STATCOM units. The Cigre 32-bus test system is used to form a case study. The results found were that improvements can be obtained by using variable speed turbines instead of fixed-speed turbines, and further improvements could be obtained by using reactive power infeed from the wind energy installation instead of constant power factor operation.

Detailed modeling for large scale wind power installations - a real project case study

Reactive power/voltage control support, temporary primary frequency control support, power oscillation damping support are some of the functions that can be provided by modern wind farms (WFs) equipped with variable speed wind turbines (VSWT) with power electronic converters. This paper examines the possibility of WFs providing reactive power support to the grid system as part of ancillary service provisions. Detailed analysis of the WF capability curve is carried out, and a reactive power cost model is developed for wind turbine generators that can help the market operator or the independent system operator (ISO) in managing the system and the grid efficiently. The Cigre-32 bus test system is used to demonstrate a case study showing a 24-hour calculation of 10-minute average system operation cost considering the incoming wind energy.

Effect of operational modes of a wind farm on the transient stability of nearby generators and on power oscillations: a Nordic grid study

The effect of small scale variable speed (VS) wind energy integration into the local grid is investigated in this paper. In particular, the effect of reactive power control from wind turbines on the local voltage stability considering different types of load is analyzed here. Both steady-state and dynamic analysis have been done. It is found that integration of wind power in several feeders of a sub station could influence the operation of the tap changing transformer at the substation. With the high level of integration of wind turbines at the local grid, mixed with different critical loads, high load-low wind condition is the most critical situation from a load power quality point of view when lost voltage-time area at the load bus will be higher for a given disturbance at the grid. To overcome a relatively low voltage disturbance (grid voltage dip higher than 85%) by utilizing the fast power electronic converter of the nearby wind turbine, keeping the active power production from the wind turbine at the pre-disturbance value, it is the high wind-low load situation which is the difficult case to handle from the wind turbine side. Mitigation of a larger voltage disturbance in this way requires a larger grid side converter. Instead, injecting reactive current into the grid keeping the active current injection from the wind turbine at the pre-fault level, gives satisfactory contingency performance of the wind turbine from the grid point of view

Wind Power - Added Value for Network Operation

This paper reports on the modeling issues performed related to a feasibility study to investigate the possibilities to connect the 640 MW off-shore wind power farm, planned for Kriegers Flak 30 km south of Trelleborg (Sweden), to the E.ON 130 kV subtransmission system. The aim of the entire study is to answer the question if such a connection is possible, and under what conditions; it is not meant as a design project. Following a general connection design discussion, the study comprises three major parts, fault current calculations, load flow calculations, and dynamic simulations. Concerning the modeling aspects, much effort has been put on details and scalability for the dynamic simulations.