Reactive power control of DFIG wind turbines for power oscillation damping under a wide range of operating conditions

This study analyses the effect of replacing existing synchronous generators (SGs) equipped with power system stabilisers (PSS) by doubly fed induction generator (DFIG) based wind farms on the damping of power system oscillations in a multi-machine power system. A power system stabiliser was designed to enhance the capability of DFIG to damp power systems oscillations. The validity and effectiveness of the proposed controller are demonstrated on the widely used New England 10-machine 39-bus test system that combines conventional SGs and DFIG based wind farms using eigenvalue analysis and non-linear simulation. The non-linear simulation is used to demonstrate how the damping contribution of DFIG based wind farms is affected by different operating conditions within the same wind farm and stochastic wind speed behaviour. The results show that installing conventional fixed parameters PSS within reactive power control loop of DFIG rotor side converter has a positive damping contribution for a wide range of operating conditions. Furthermore, the results clearly show that DFIG based wind farms equipped with the proposed farm level PSS can damp power system oscillations more effectively than SGs PSS

Effects of POD control on a DFIG wind turbine structural system

This paper investigates the effects power oscillation damping (POD) controller could have on a wind turbine structural system. Most of the published work in this area has been done using relatively simple aerodynamic and structural models of a wind turbine which cannot be used to investigate the detailed interactions between electrical and mechanical components of the wind turbine. Therefore, a detailed model that combines electrical, structural and aerodynamic characteristics of a grid-connected Doubly Fed Induction Generator (DFIG) based wind turbine has been developed by adapting the NREL (National Renewable Energy Laboratory) 5MW wind turbine model within FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. This detailed model is used to evaluate the effects of POD controller on the wind turbine system. The results appear to indicate that the effects of POD control on the WT structural system are comparable or less significant as those caused by wind speed variations. Furthermore, the results also reveal that the effects of a transient three-phase short circuit fault on the WT structural system are much larger than those caused by the POD controller

Impacts of high penetration of DFIG wind turbines on rotor angle stability of power systems

With the integration of wind power into power systems continues to increase, the impact of high penetration of wind power on power system stability becomes a very important issue. This paper investigates the impact of doubly fed induction generator (DFIG) control and operation on rotor angle stability. Acontrol strategy for both the rotor-side converter (RSC) and grid-side converter (GSC) of the DFIG is proposed to mitigate DFIGs impacts on the system stability. DFIG-GSC is utilized to be controlled as static synchronous compensator (STATCOM) to provide reactive power support during grid faults. In addition, a power system stabilizer (PSS) is implemented in the reactive power control loop of DFIG-RSC. The proposed approaches are validated on a realistic Western System Coordinating Council (WSCC) power system under both small and large disturbances. The simulation results show the effectiveness and robustness of both DFIG-GSC control strategy and PSS to enhance rotor angle stability of power system

Power oscillation damping capabilities of doubly fed wind generators

With the increased levels of wind power penetration into power systems, the influence of wind power on stability of power systems requires more investigation. Conventional synchronous generators are increasingly replaced by wind turbines and thus wind turbines have to contribute to power system stability. In this paper, the effects of double fed induction generator (DFIG) based wind farms and their controllers on small signal stability are investigated. Moreover, since wind turbines have to contribute to power system oscillation damping, a power oscillation damping controller within DFIG rotor side converter is developed in this study. The proposed damping control is validated on realistic Western System Coordinating Council (WSCC) power system consisting of DFIG based wind farm and synchronous generators. The simulation results show the effectiveness of the proposed power oscillation damping controller. With the proposed controller, DFIG based wind farm improves the system small signal stability dramatically by damping the system oscillations effectively

Impact of DFIG based offshore wind farms connected through VSC-HVDC link on power system stability

With the increased levels of offshore wind power penetration into power systems, the impact of offshore wind power on stability of power systems require more investigation. In this paper, the effects of a large scale doubly fed induction generator (DFIG) based offshore wind farm (OWF) on power system stability are examined. The OWF is connected to the main onshore grid through a voltage source converter (VSC) based high voltage direct current (HVDC) link. A large scale DFIG based OWF is connected to the New England 10-machine 39-bus test system through a VSC-HVDC. One of the synchronous generators in the test system is replaced by an OWF with an equivalent generated power. As the voltage source converter can control the active and reactive power independently, the use of the onshore side converter to control its terminal voltage is investigated. The behaviour of the test system is evaluated under both small and large grid disturbances in both cases with and without the offshore wind farm

Impact of Electrolysers on the Network

The “Impact of Electrolysers on the Distribution Network” project was commissioned to establish if it is possible to manage the production of hydrogen by electrolysis such that the need for network reinforcement is reduced, delayed or removed, and also to investigate the impact on renewable generation output where electrolysers are integrated with renewable technologies. Scottish and Southern Electricity Networks (SSEN) operated as a partner in the Aberdeen Hydrogen Bus Project which included the design, construction and operation of a Hydrogen Refuelling Station (HRS) located in the Kittybrewster area of Aberdeen.SSEN developed a control system to run trials on the Kittybrewster HRS. Through the trials a series of network scenarios were simulated including demand‐constrained and generation constrained networks. The capacity of the electrolysers to operate flexibly in response to network, generation, and economic signals was also investigated and the outcomes of these trials are contained in this report. Through the development and implementation of these trials it was important to recognise that as the HRS is a fully operational site, the key and overriding requirement was to ensure that enough hydrogen was available to meet the refuelling needs of the ten hydrogen fuel cell buses that were operating across Aberdeen as part of the Aberdeen Hydrogen Bus Project

Model-free semi-active structural control of floating wind turbines

This paper addresses the load/vibration reduction problem of offshore floating wind turbines (FWTs). Based on the tuned mass damper (TMD), a novel semi-active control method is designed to mitigate the floating platform’s structural vibration. Different from existing results, the proposed control method is model-free and insensitive to system uncertainties and unmodelled dynamics. We base our design on the model-free adaptive control (MFAC) method. A data-based surrogate model is developed to approximate the unknown FWT dynamical system through the dynamic linearization technique. In addition, a quadratic programming (QP) module is embedded in our MFAC-based semi-active structural controller for constraint handling and control allocation purposes. High-fidelity simulations of FWTs show that our model-free semi-active structural controller can address the limitations of existing results and significantly reduce the platform’s vibration

New complex dyes for wool

The set of mono azo dyes having in ortho position to tje azo group thiol, methylthio or methoxy group was prepared in the present work. The structure of these dyes was confirmed by MS and NMR spectra.Katedra technologie organických látekDokončená práce s úspěšnou obhajobo

Impacts of high penetration of DFIG wind turbines on rotor angle stability of power systems

This thesis investigates the effects of increased penetration levels of DFIG based wind turbines on rotor angle stability of power systems and how these impacts could be mitigated. The main outcome of this research is the comprehensive assessment of the stability improvements that can be achieved through a novel cost-effective control approach using existing DFIG equipments. A control strategy for both the rotor-side converter (RSC) and grid-side converter (GSC) of the DFIG is proposed to mitigate DFIGs impacts on the system stability. DFIG-GSC is utilised as a static synchronous compensator (STATCOM) to provide reactive power support during the active crowbar time when controlling of both reactive and active power is lost and a large amount of reactive power is absorbed. In addition, a supplementary power system stabiliser (PSS) is designed taking into account the influence of the crowbar system. To overcome the effects of PSS active power modulation, the PSS is designed to be implemented in the reactive power control loop of DFIG-RSC.The proposed approaches are examined on IEEE 9-bus and IEEE 39-bus systems under both small and large disturbances. The simulation results show the effectiveness and robustness of both approaches to enhance rotor angle stability. As the levels of wind penetration are increased, the benefit of such a control scheme is that the DFIG-based wind farms are able to take over the synchronous generators responsibility to support power system stability.As wind power is stochastic and fluctuates with the variation of wind speed, the proposed DFIG PSS should have the capability to damp power system oscillations effectively under non-uniform variable wind speeds across the wind farm. Therefore, the feasibility of the proposed fixed parameters PSS is evaluated using the IEEE 39-bus test system taking into account the non-uniform and variable wind speed profiles. The results confirm the robustness and stabilising effect against various operating modes and under various wind speeds.This thesis investigates the effects of increased penetration levels of DFIG based wind turbines on rotor angle stability of power systems and how these impacts could be mitigated. The main outcome of this research is the comprehensive assessment of the stability improvements that can be achieved through a novel cost-effective control approach using existing DFIG equipments. A control strategy for both the rotor-side converter (RSC) and grid-side converter (GSC) of the DFIG is proposed to mitigate DFIGs impacts on the system stability. DFIG-GSC is utilised as a static synchronous compensator (STATCOM) to provide reactive power support during the active crowbar time when controlling of both reactive and active power is lost and a large amount of reactive power is absorbed. In addition, a supplementary power system stabiliser (PSS) is designed taking into account the influence of the crowbar system. To overcome the effects of PSS active power modulation, the PSS is designed to be implemented in the reactive power control loop of DFIG-RSC.The proposed approaches are examined on IEEE 9-bus and IEEE 39-bus systems under both small and large disturbances. The simulation results show the effectiveness and robustness of both approaches to enhance rotor angle stability. As the levels of wind penetration are increased, the benefit of such a control scheme is that the DFIG-based wind farms are able to take over the synchronous generators responsibility to support power system stability.As wind power is stochastic and fluctuates with the variation of wind speed, the proposed DFIG PSS should have the capability to damp power system oscillations effectively under non-uniform variable wind speeds across the wind farm. Therefore, the feasibility of the proposed fixed parameters PSS is evaluated using the IEEE 39-bus test system taking into account the non-uniform and variable wind speed profiles. The results confirm the robustness and stabilising effect against various operating modes and under various wind speeds

Stability and dynamic analysis of the PMSG-based WECS with torsional oscillation and power oscillation damping capabilities

The direct-drive permanent-magnet synchronous generator (PMSG) based wind energy conversion system (WECS) with a soft drivetrain shaft is vulnerable to torsional oscillation when it participates in power oscillation damping (POD) services for the AC grid. This paper investigates three possible scenarios of incorporating both torsional oscillation damping (TOD) and POD controllers into PMSG-based WECS. A model of a PMSG-based offshore wind farm (OWF) connected to the IEEE 39-bus AC grid is developed and utilized to analyze the stability and dynamic performances of the WECS within these three scenarios. Comprehensive modal analysis is carried out to analyze the interaction between the torsional and power oscillations, and to tune the TOD and POD controllers to damp these oscillations simultaneously in each scenario. Furthermore, the dynamic performances of the PMSG-based WECS within these scenarios are evaluated through time-domain simulations. Then an optimal scenario for PMSG-based WECS to damp both oscillation types with close frequencies is identified, which is modulating the DC-link voltage for the TOD and the grid-side active power for the POD. This result can provide useful guidance for the future industrial application of the TOD and POD control in the PMSG-based WECS