SYNOPSIS OF THE THESIS. Enhanced Power Quality Management of Grid Connected Wind Farm

Transcription

1 SYNOPSIS OF THE THESIS Enhanced Power Quality Management of Grid Connected Wind Farm INTRODUCTION OF THE THESIS Faster depletion of fossil fuels and environmental damage has resulted into increased use of renewable energy sources as a sustainable option. Out of various renewable energy sources wind energy is one of the potential energy source. Grid embedded wind energy generation at large scale is increasing day by day and will become significant part of power system. Wind is a time dependent highly variable, unpredictable, fluctuating, difficult to control energy source. Integration of large scale wind farms comprising of squirrel cage, doubly fed induction and synchronous generator with grid imposes various challenges related with power quality, reliability and reactive power management. Utilities and transmission system operators have developed grid codes for wind farms. Considering increased integration of large scale wind farms in near future with different turbine technologies and topologies it becomes imperative to study power quality, reactive power, reliability and stability issues associated with integration of large scale wind farms to provide cost effective solutions. To cope up with grid codes wind turbine technology requires controlling of active as well as reactive power both in transient as well as steady state with enhanced fault ride through capabilities. International standards for assessment and quantification of power quality of grid connected wind farms are available and IEC is a commonly used standard for power quality assessment. Power quality issues related with integration of large scale wind farms are of two types: a) Wind turbine operation which affects power quality of grid. b) Grid side power quality issues which affects operation of Wind turbine. Grid side power quality issues are mainly related with short duration and long duration RMS voltage variations during steady state and transient grid conditions. Various parameters of grid side voltage quality are short and long duration RMS voltage magnitude variations, frequency variations, voltage unbalance and voltage harmonic distortion. Wind turbine related power quality issues are related with flicker, reactive power, current harmonic distortion, stability of wind turbine during grid faults etc. Power quality problems such as voltage sag, swell, under voltage, over voltage, voltage unbalance, harmonic distortion, voltage flicker, short and long duration interruptions along 1

2 with reactive power issues, low voltage ride through capability, fault ride through capability, voltage, power & rotor instability during fault, wind turbulence issues are major concern before researchers, utilities, system operators, and wind farm developers. Assessment of overall impact of integration of large scale wind farms to grid needs consideration of all factors which affects power quality of wind farms. Various factors which affect power quality of wind farms are 1) Wind turbine technology such as type of Electric generator, direct/controlled connection to grid, gear box or gearless transmission 2) Grid conditions at point of common coupling (PCC) such as short circuit power and X/R ratio, interconnection voltage level and regulation, type of interconnecting transformer, earthing system 3)Wind farm design and control such as number and nominal power of wind turbines, wind farm internal power system (X/R) ratio, added voltage /power control 4) Wind farm local characteristics such as turbulence intensity, operation of turbine during weak flow, spectrum of wind 3D component, spatial variability of wind. It is not only sufficient to estimate the power quality variation due to operation of large scale wind farms embedded in grid but optimization of its capacity and technical characteristics in order to avoid degradation in power quality. Grid codes mainly focus on 1) Identification of tolerable planning levels in receiving network 2) Allocation of the distortion limits to the generation facilities considering influence of adjacent network 3) Evaluation of tolerable limits for harmonic current injection and flicker. Voltage quality is governed by network impedance. Integration of large scale wind farms in weak power system imposes limitations. Wind energy in India has an extremely bright future and there is no doubt that, in the renewable energy sector, wind power would play a predominant role in adding clean and non polluting energy to the country s grids. India has a huge potential of wind generation and every year large number of wind farms are being added and interfaced to grid. As compared to developed countries, Indian power system is weak with poor infrastructure for power evacuation. The percentage of wind-based generation by use of large scale wind farms with synchronous and induction generator will increase at faster rate, which will result into power quality degradation and reactive power management issues. Literature review of various published literature reveals that many researchers have carried out research work in this area considering only single wind turbine connected to grid, small wind farms considering only few aspects, with single topology of wind park. Moreover available international standards are not addressing the impact of different wind farm topologies on power quality issues and impact on wind farm dynamic behavior. To provide 2

3 optimal solutions for integration of large scale wind farms it is necessary to carry out research related with integration of large scale wind farms considering all factors. Aim and scope of research work of thesis is to study all the issues related with integration of large scale wind farms to grid with different generators, wind farm topologies and all related factors which may govern power quality issues. Simulation of a large scale wind farm model includes a wind turbine and three different types of generators, which are three phase singly fed induction generator, three phase doubly-fed induction generator and three phase synchronous generator mainly used in large scale wind farms. All generators are connected in parallel at the point of common coupling (PCC) and connected to the utility grid through substation. Detailed simulation studies were carried out with following cases: 1) Wind farm with 75 MW capacity with sixty number of 1.25 MW singly fed induction generators connected to 132 kv grid by 150 MVA, 132/33 kv transformer. 2) Wind farm with 0.8 MW doubly fed induction generator connected to 132 kv grid by 150 MVA, 132/33 kv transformer. 3) Wind farm with 75 MW capacity with forty five number of 1.67 MW synchronous generators connected to 132 kv grid by 150 MVA, 132/33 kv transformer. 4) Wind farm with capacity MW with 75 MW with sixty number of 1.25 MW singly fed induction generators, 0.8 MW doubly fed induction generators, 75 MW capacity with forty five number of 1.67 MW synchronous generators connected to 132 kv grid by 150 MVA,132/33 kv transformer. Following studies were carried out on simulation model in PSCAD software for four above mentioned cases: 1) Evaluation of low voltage fault ride through capability of different types of generators for seven type of voltage sags A, B, C, D, E, F and G with different magnitude and duration, instantaneous, momentary and temporary voltage swell, under voltage and over voltages with different magnitude and duration. 2) Effect of operation of singly fed, doubly fed induction and synchronous generators on current harmonic distortion at PCC with different short circuit ratios with linear and non-linear load connected to grid and comparison of current harmonic limits at PCC as per IEEE Standard. 3) Effect of grid side voltage unbalance on operation of singly, doubly fed induction and synchronous generators. 3

4 4) Study of reactive power requirement in case of wind farm with singly fed induction generators, doubly fed induction generators, synchronous generators and Wind farm with all three types of generators. 5) Effect of symmetrical and unsymmetrical grid faults on low voltage ride through capability of three different types of wind generators connected in different configurations. 6) Effect of short circuit ratio on operational behavior of different generators. Different parameters of generator studied are active, reactive power, voltage profile and generator speed. 7) Effect of wind turbulence on wind speed with and without pitch angle control and its effect on power fluctuations. 8) Effect of symmetrical and unsymmetrical grid faults on voltage profile, active, reactive power, rotor instability on three types of wind generators connection in wind form in different configurations. 9) Effect of operation of three types of wind generators on voltage flicker. Based on the analysis of these studies, various issues related with interconnection of large scale wind turbines were identified and cost effective solution is provided for mitigation of power quality, reactive power, harmonic distortion, low voltage ride through capability by use of Static Synchronous Compensator (STATCOM). Simulation results were obtained with and without STATCOM. STATCOM is used as an active voltage and reactive power supporter to increase the power system stability. STATCOM unit is simulated to inject reactive power for mitigation of power quality problems and to get stable grid operation. STATCOM is used at the point of common coupling (PCC) to regulate terminal voltage of wind turbine system. Simulation results verify the effectiveness of the proposed system to mitigate the power quality issues, reactive power issues, low voltage ride through capability, voltage, power & rotor instability during fault, wind turbulence issues. This thesis investigates the use of a Static Synchronous Compensator (STATCOM) along with wind farms for the purpose of stabilizing the grid voltage after disturbances such as symmetrical and unsymmetrical fault. The study has demonstrated that an additional active voltage / Var support produced by a STATCOM at suitable location in case of multi machine power system with a large scale wind farm system can significantly improve the recovery of wind turbines from voltage collapse. This thesis 4

5 also investigates the application of STATCOM device to enhance the dynamic and transient performance of power systems with integration of a large scale wind farms with different types of generators and different wind farm topologies. CHAPTER WISE BRIEF ACCOUNT OF THE WORK DONE This thesis is organized into seven chapters. Chapter 1 covers introduction and classification of the wind turbine concepts & generator types. In this chapter various wind turbine concepts and different wind generators have been discussed. Three types of typical generator systems used in large scale wind farms are discussed. Different types of wind power control mechanisms are presented. Input wind power control ability divides wind energy conversion system (WECS) into four categories: pitch-controlled, stall-controlled, yaw control & power electronic controlled. Power control ability refers to the aerodynamic performance of wind turbines. There are different ways to control aerodynamic forces on the turbine rotor and thus to limit the power in very high winds in order to avoid the damage to the wind turbine. Control Strategy & technical challenges associated with wind farm, organization of thesis, contributions are covered. Chapter 2 provides a literature review for modeling and control of the induction and synchronous generator-based WECS connected to power grid, steady state reactive power capability of the generator, power quality issues, low voltage ride through capability and grid code requirements for connecting wind turbines to power grid. Moreover, chapter 2 also presents the literature review for necessity of additional reactive power source in the generator-based wind turbine system, modeling and control of the STATCOM, and control and operation of induction and synchronous generator -based wind turbine system. Chapter 3 provides problem identification and scope of work. Many researchers have focused on study of power quality, reactive power, stability, flicker, operation of wind energy generator under different grid conditions considering single type of generators. In large scale wind farms different types of generators are used with different wind farm topologies. More research was required to study all the issues mentioned and technical challenges of integration of large scale wind farms with different types of wind 5

6 energy generator technologies with different topologies to provide cost effective optimal solutions. Detailed scope of work covers study of power quality problems such as short duration RMS voltage variation (voltage sag & swell), long duration RMS voltage variation (under voltage & over voltage), voltage unbalance, flicker, harmonic distortion along with reactive power issues, low voltage ride through capability, fault ride through capability, effect of short circuit ratio, wind turbulence issues, & voltage, power & rotor instability during fault related with integration of large scale wind farm with different generator technologies, different wind farm topologies are covered. Impact of factors responsible for deterioration of power quality of grid due to operation of different wind turbine generator technologies and impact of poor power quality of grid on wind turbine operational behavior, stability during all conditions of grid, wind farm topologies are covered in scope of work. Providing optimal cost effective solution to resolve technical issues related with integration of large scale wind farms with different types of wind generators, topologies under different conditions of grid are covered. description. Chapter 4 describes the following four grid connected wind driven generator system 1) Grid Connected Wind Driven Squirrel Cage (Singly Fed) Induction Generator System: A wind farm typically consists of a large number of individual wind turbine generators (WTGs) with squirrel cage induction generators (SCIGs) connected by an internal electrical network. To study the impact of wind farms on the dynamics of the power system, an important issue is to develop appropriate wind farm models to represent the dynamics of many individual WTGs. The model is developed and compared by simulation & validation study in the PSCAD/EMTDC environment under different wind velocity and fluctuation conditions. Wind generators are primarily classified as fixed speed or variable speed. For the studies carried out in this chapter, it focuses on modeling the fixed speed unit. It consists of a 75 MW wind farm comprising 60 wind turbines, grouped into five clusters of similar properties. Each grouping contains 12 wind turbines of 1.25 MW unitary rating. The electric generators studied are squirrel cage machines of 1.6 MVA. The wind turbine designated has a stall regulated three-bladed horizontal axis rotor coupled to a squirrel cage induction generator. Each of these wind turbine units consists of rotor, gear box, squirrel cage induction 6

7 generator and a 0.69/33 kv transformer. The large scale wind farm is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system is modeled by using PSCAD simulation software. 2) Grid Connected Wind Driven Doubly Fed Induction Generator System: The DFIG is wound rotor induction generator with the stator windings directly connected to the constant-frequency three-phase grid and the rotor windings is fed by the rotor side converter (RSC) and the grid side converter (GSC) connected back-to-back. At steady state the RSC independently regulates stator active and reactive powers where as GSC keeps the DC link voltage constant independent of magnitude and direction of the rotor power. In this case the wind farm is represented using PSCAD library in PSCAD simulation software where one wind turbine and DFIG are represented as one equivalent DFIG driven by single equivalent wind turbine. The wind turbine having capacity 0.8 MW designated has a stall regulated three-bladed horizontal axis rotor coupled to a wound rotor induction generator having capacity 1 MVA. The large wind farm is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system is modeled by using PSCAD simulation. 3) Grid Connected Wind Driven Synchronous Generator System: A wind farm typically consists of a large number of individual wind turbine generators (WTGs) with electrically excited synchronous generators (EESGs) connected by an internal electrical network. To study the impact of wind farms on the dynamics of the power system, an important issue is to develop appropriate wind farm models to represent the dynamics of many individual WTGs. The model is developed and compared by simulation studies in the PSCAD/EMTDC environment under different wind velocity and fluctuation conditions. Modeling of variable speed unit is carried out. It consists of a 75 MW wind farm comprising 45 wind turbines, grouped into five clusters of similar properties. Each grouping contains 9 wind turbines of 1.67 MW unitary rating. The electric generators are synchronous machines of 2 MVA. The wind turbine designated has a stall regulated three-bladed horizontal axis rotor coupled to a synchronous generator. The connection to the grid is then performed through a full AC/DC/AC converter. The main advantage of this strategy is to allow removing the gear box in the wind turbine. Each of these wind turbine units consists of rotor, synchronous generator and a 0.69/33 kv transformer. The large wind farm is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system is modeled by using PSCAD simulation. 7

8 4) Large scale wind farm with Combination of Singly, Doubly Fed Induction Generator & Synchronous Generator System: A wind farm typically consists of a large number of individual wind turbine generators (WTGs) with squirrel cage induction generators (SCIGs), doubly fed induction generator and electrically excited synchronous generators connected by an internal electrical network. To study the impact of wind farms on the dynamics of the power system, an important issue is to develop appropriate wind farm models to represent the dynamics of many individual WTGs. The model is developed and compared by simulation studies in the PSCAD/EMTDC environment under different wind velocities and fluctuation conditions. Modeling of the fixed speed unit & variable speed is carried out. Large scale wind farm having capacity of MW consists of combination of all generators (squirrel cage induction generators (SCIGs), doubly fed induction generator (DFIG) and electrically excited synchronous generators (EESG). In a 75 MW squirrel cage induction generator wind farm consists of 60 wind turbines, grouped into five clusters of similar properties. Each grouping contains 12 wind turbines of 1.25 MW unitary rating. The electric generators are squirrel cage machines of 1.6 MVA. The wind turbine designated has a stall regulated three-bladed horizontal axis rotor coupled to a squirrel cage induction generator. In a 0.8 MW wound rotor induction generator wind farm consists of 0.8 MW wind turbine machine designated has a stall regulated three-bladed horizontal axis rotor coupled to a wound rotor induction generator having capacity 1 MVA. In a 75 MW synchronous generator wind farm comprising 45 wind turbines, grouped into five clusters of similar properties. Each grouping contains 9 wind turbines of 1.67 MW unitary rating. The electric generators are synchronous machines of 2 MVA. The wind turbine designated has a stall regulated three-bladed horizontal axis rotor coupled to a synchronous generator. The large wind farm is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system is modeled by using PSCAD simulation software. Chapter 5 In this chapter the comparison of SVC, STATCOM and UPFC is presented and based on technical merits, capabilities of various mentioned devices and requirements to resolve issues related with integration of large scale wind farms interface with grid, STATCOM device was considered for providing mitigation. Capacitor sizing criterion to provide reactive power by using STATCOM is discussed. Rating calculation and 8

9 location of STATCOM for active, reactive, apparent power, dc link voltage, V cmax, dc link capacitor rating is presented. Chapter 6 provides the effect & mitigation techniques for following generator system: 1) Grid Connected Wind Driven Squirrel Cage (Singly Fed) Induction Generator System: In this chapter a wind turbine fed squirrel cage induction generator is modeled using PSCAD and different power quality issues like short duration variations (voltage sag, swell), long duration variation (under voltage, over voltage) harmonics for linear load & nonlinear load, voltage unbalance, flicker, reactive power issues, LVRT, effect of short circuit ratio, effect of wind turbulence & effect of voltage, power & rotor instability are analyzed. In this case study, wind farm with squirrel cage induction generator having capacity 75 MW is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system & STATCOM connected at PCC is modeled using PSCAD/EMTDC software. The STATCOM used as a device to mitigate these problems and simulation results prove that STATCOM is an effective to mitigate these problems during continuous operation of grid connected wind turbines. Large scale wind farm consisting of squirrel cage induction generator connected by STATCOM is described in this chapter. 2) Grid Connected Wind Driven Doubly Fed Induction Generator System: Wind turbine fed doubly fed induction generator is modeled using PSCAD and different power quality issues like short duration variations (voltage sag, swell), long duration variation (under voltage, over voltage) harmonics for linear load & nonlinear load, voltage unbalance, flicker, reactive power issues, LVRT, effect of short circuit ratio, effect of turbulence & effect of voltage, power & rotor instability are analyzed. The STATCOM used as a device to mitigate these problems and simulation results prove that STATCOM is an effective to mitigate these problems during continuous operation of grid connected wind turbines. Analysis of large scale wind farm consisting of double fed induction generator with STATCOM is presented. In this case study, wind farm with doubly fed induction generator having capacity 0.8 MW is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system & STATCOM connected at PCC is modeled using PSCAD/EMTDC software. In this case the wind farm is represented using PSCAD library in PSCAD simulation software where one wind turbine and DFIG are represented as one equivalent DFIG driven by single equivalent wind turbine. The wind turbine having capacity 0.8 MW designated has a stall regulated three-bladed horizontal axis rotor coupled to a wound rotor induction generator 9

10 having capacity 1 MVA. Wind turbine units consists of rotor, gear box, wound rotor induction generator and a 0.69/33 kv transformer. The large wind farm is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system & STATCOM connected at PCC is modeled by using PSCAD simulation software. 3) Grid Connected Wind Driven Synchronous Generator System: In this chapter a wind turbine fed synchronous generator is modeled using PSCAD and different power quality issues like short duration variations (voltage sag, swell), long duration variation (under voltage, over voltage) harmonics for linear load & nonlinear load, voltage unbalance, flicker, reactive power issues, LVRT, effect of short circuit ratio, effect of turbulence & effect of voltage, power & rotor instability are analyzed. In this case study, wind farm with synchronous generator having capacity 75 MW is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system & STATCOM connected at PCC is modeled using PSCAD/EMTDC software. The STATCOM used as a device to mitigate these problems and simulation results prove that STATCOM is an effective means to mitigate these problems during continuous operation of grid connected wind turbines. Large scale wind farm consisting of synchronous generator connected by STATCOM is described in this chapter. 4) Large scale wind farm with Combination of Squirrel Cage, Doubly Fed Induction Generator & Synchronous Generator System: In this chapter large scale wind farm having capacity of MW consists of combination of all generators squirrel cage induction generators (SCIGs), doubly fed induction generator (DFIG) and electrically excited synchronous generators (EESG). In a 75 MW squirrel cage induction generator wind farm consists of 60 wind turbines, grouped into five clusters of similar properties. Each grouping contains 12 wind turbines of 1.25 MW unitary rating. The electric generators are squirrel cage machines of 1.6 MVA. The wind turbine designated has a stall regulated three-bladed horizontal axis rotor coupled to a squirrel cage induction generator. In a 0.8 MW wound rotor induction generator wind farm consists of 0.8 MW wind turbine machine designated has a stall regulated three-bladed horizontal axis rotor coupled to a wound rotor induction generator having capacity 1 MVA. In a 75 MW synchronous generator wind farm comprising 45 wind turbines, grouped into five clusters of similar properties. Each grouping contains 9 wind turbines of 1.67 MW unitary rating. The electric generators are synchronous machines of 2 MVA. The wind turbine designated has a stall regulated three-bladed horizontal axis rotor coupled to a synchronous generator. In this 10

11 case study, large scale wind farm having capacity MW is connected to 33/132 kv substation to 220 kv, 200 MVA electric grid system & STATCOM connected at PCC is modeled using PSCAD/EMTDC. Also power quality issues like short duration variations (voltage sag, swell), long duration variation (under voltage, over voltage) harmonics for linear load & nonlinear load, voltage unbalance, flicker, reactive power issues, LVRT, effect of short circuit ratio, effect of turbulence & effect of voltage, power & rotor instability are analyzed. The STATCOM is used to mitigate these issues and simulation results prove that STATCOM is an effective means to mitigate these problems. Chapter 6 also gives the cost analysis of all generating system. A simulation model of large scale wind farm consisting of squirrel cage, double fed induction generator & synchronous generator system is designed in PSCAD software without STACOM connected to the system having wind speed varying from 3 m/s to 30 m/s. Average power factor is calculated of the system by considering active power & apparent power. As induction generator requires reactive power for excitation purpose. Hence it lowers the power factor of the system. Status of power factor level & penalty (Monthly) without STATCOM connected to the system are evaluated. Chapter 7 covers results, discussion and conclusion on the basis of simulation results of all cases considered in scope of work of this thesis. Simulation studies were carried out on following configuration of wind farms. 1) Singly fed induction generator wind farm having capacity of 75 MW comprising of sixty number of wind turbines. 2) Doubly fed induction generator with 0.8 MW. 3) Synchronous generator having capacity of 75 MW comprising of forty five number of wind turbines. 4) Combination all three mentioned generator aggregated wind farm model with MW capacity. Different studies carried out to study impact of grid side power quality disturbances on operational behavior of three types of wind energy generators. a) Reactive power requirement, variations during different operating conditions of wind turbines and wind patterns, grid operating conditions under steady state and transient conditions. 11

12 b) Evaluation of low voltage fault ride through capability of three types of wind energy generators connected in different configuration for symmetrical and unsymmetrical power system faults. c) Effect of short circuit ratio on operational behavior of different wind generators. Different parameters of generator studied are active, reactive power, voltage profile and generator speed. d) Effect of various power system faults on voltage profile, active power, reactive power, rotor instability of three types of wind generators operating individually and in aggregated model. e) Evaluation of low voltage fault ride through capability of different types of generators for seven types of voltage sags with different magnitude and duration, instantaneous, momentary and temporary voltage swell, under and over voltages with different magnitude and duration, Voltage unbalance. Different studies are carried out to study impact of operation of wind turbine under different operating conditions on grid power quality as follows: a) Effect of wind turbulence on wind speed with and without pitch angle control and its impact on power fluctuations. b) Requirement of reactive power under different operating conditions of three types of generators. c) Voltage and current harmonic distortion issues related with operational three types of generators with linear and non-linear load. d) Cost benefit analysis of reactive power compensation. e) Effect of short circuit ratio on voltage harmonic distortion during operation of three types of wind energy generators used in aggregate model for linear and for different percentage of non linear as a part of total load. f) Evaluation of current harmonic emissions at PCC with different short circuit ratios for aggregate wind model comprising of three types of wind energy generators. Chapter 8 describes future scope work, bibliography & appendix 12

13 OVERALL CONCLUSIONS Based on analysis of large scale wind farm operation for mentioned combination various technical issues related with interfacing of large scale wind farms to grid with three types of generators are: Interfacing issues of large scale wind farms with singly fed induction generator: Meeting fast reactive power variation during different operating conditions of singly fed induction generator and response of reactive power generation system incorporated with generator. Reactive power support during grid fault to avoid voltage collapse and maintain stability of wind generator during different fault conditions at different locations such as near to generator, near to load & near PCC. Low voltage fault ride through capability under different power system faults. Self-excitation issues of singly fed generator with fixed capacitor banks during long duration interruption on grid. Voltage flicker due to wind fluctuations. Effect of short circuit ratio on voltage distortion, voltage profile, rotor instability, power profile was studied for weak grid with SCR less than 3, moderate grid 3 to 5, for strong grid more than 5.From simulation result voltage harmonic distortion, variation in voltage profile, power profile, rotor instability decreases from weak grid to strong grid. Effect of wind turbulence on wind speed fluctuations was studied without and with pitch angle control. Without pitch angle control, effect of wind turbulence results into variation in wind speed and power fluctuations. Effect of wind turbulence intensity and its effect on wind speed and power fluctuations are minimized using pitch angle control. Severity of voltage sag seen by wind generator for seven types of voltage sag is different and is more when fault is near generator. Severity of voltage sags goes on reducing with location of faults away from generators. Severity of voltage sag reduces in case of voltage sags of type A, type E, type C, type F &G, type D, type B. Less severe voltage sag is type B. To 13

14 minimize impact of power system fault on severity of voltage sag it is recommended to carry out regular maintenance of wind farm grid to reduce number of faults. Without using of STATCOM, low voltage fault ride through capability of singly fed induction generator is governed by type of fault as well as duration of fault. Ride through capability of SFIG is better for LL, LG, followed by LL-G and LLL fault. Low voltage fault ride through capability is lowest in case LLL-G fault. Hence while providing solutions to enhance ride through capability and sizing of power conditioning devices it is necessary to consider different types of fault. STATCOM was modeled and interfaced at PCC to mitigate the power quality, reactive power, stability, low fault ride though capability. Harmonic distortion was not an issue in case of large scale wind farm with singly fed induction generators hence STATCOM sizing was carried out without considering harmonic issues. Implementation of STATCOM provides reactive power requirement during steady state as well as transient operation resulting into better low voltage ride through capability for different fault conditions leading to better stability. Cost benefit analysis related with reactive power with STATCOM is presented. STATCOM system meets the rapid reactive power requirement during different operating conditions of wind turbine as well as steady state and transient conditions of grid. Interfacing issues of large scale wind farms with doubly fed induction generator: All issues related with singly fed induction generator are same in case of doubly fed induction generator, additional technical challenge is related to current harmonic distortion due to use of power converter used in doubly fed induction generator. Implementation of STATCOM near PCC helps to provide solutions to all problems related with interfacing of doubly fed induction generator under all operating conditions of wind generator and grid. Effect of short circuit ratio on voltage distortion, voltage profile, rotor instability, power profile was studied for weak grid with SCR less than 3, moderate grid 3 to 5, for strong grid more than 5.From simulation result voltage harmonic distortion, variation in voltage profile, power profile, rotor instability decreases from weak grid to strong grid. Effect of wind turbulence on wind speed fluctuations was studied without and with pitch angle control. Without pitch angle control, effect of wind turbulence results into variation in 14

15 wind speed and power fluctuations. Effect of wind turbulence intensity and its effect on wind speed and power fluctuations are minimized using pitch angle control. Severity of voltage sag seen by wind generator for seven types of voltage sag is different and is more when fault is near generator. Severity of voltage sags goes on reducing with location of faults away from generators. Severity of voltage sag reduces in case of type A, type E, type C, type F &G, type D, type B. Less severe voltage sag is type B. To minimize impact of power system fault on severity of voltage sag it is recommended to carry out regular maintenance of wind farm grid to reduce number of faults. Without using of STATCOM, low voltage fault ride through capability of doubly fed induction generator is governed by type of fault as well as duration of fault. Ride through capability of DFIG is better for LLL-G, LL, followed by LL-G and LG fault. Low voltage fault ride through capability is lowest in case LLL fault. Hence while providing solutions to enhance ride through capability and sizing of power conditioning devices it is necessary to consider type of fault. STATCOM was modeled and interfaced at PCC to mitigate the power quality, reactive power, stability, low fault ride though capability. Implementation of STATCOM provides reactive power requirement during steady state as well as transient operation resulting into better low voltage ride through capability for different fault conditions leading better stability. Cost benefit analysis related with reactive power with STATCOM is presented. STATCOM system meets the rapid reactive power requirement during different operating conditions of wind turbine as well as steady state and transient conditions of grid. Interfacing issues of large scale wind farms with synchronous generator: There are no issues of reactive power in case of synchronous generators for its operation as it has capability to generate, absorb reactive power based on various conditions of grid under steady state and transient conditions. However reactive power is required to be provided to meet reactive power requirement of un-compensated load and transformer which needs to be compensated by use of local reactive power generators. Severity of voltage sag seen by wind generator for seven types of voltage sag is different and is more when fault is near generator. Severity of voltage sags goes on reducing with location of faults away from generators. Severity of voltage sag reduces in case of type A, 15

16 type E, type C, type F &G, type D, type B. Less severe voltage sag is type B. Low voltage ride through capability of synchronous generator is lower as compared to singly and doubly fed induction generators due to use of power converters in addition to current and voltage harmonic distortion. Without use of STATCOM low voltage fault ride through capability of synchronous generator is governed by type of fault as well as duration of fault. Ride through capability of synchronous generator is better for LG, LL, followed by LL-G and LLL fault. Low voltage fault ride through capability is lowest in case LLL-G fault. Hence while providing solutions to enhance ride through capability and sizing of power conditioning devices it is necessary to consider type of fault. Effect of short circuit ratio on voltage distortion, voltage profile, rotor instability, power profile was studied for weak grid with SCR less than 3, moderate grid 3 to 5, for strong grid more than 5. From simulation result voltage harmonic distortion, variation in voltage profile, power profile, rotor instability decreases from weak grid to strong grid. Effect of wind turbulence on wind speed fluctuations was studied without and with pitch angle control. Without pitch angle control, affect of wind turbulence results into variation in wind speed and power fluctuations. Effect of wind turbulence intensity and its effect on wind speed and power fluctuations are minimized using pitch angle control. Implementation of STATCOM at PCC helps to resolve all technical issues related with interfacing of large scale wind farms using synchronous generators. Interfacing issues of large scale wind farms with three types of wind energy generator: Technical challenges are more in case on aggregated wind model with three different types of generator which covers reactive power issues, harmonic current and voltage distortion and stability issues. Low voltage ride through capability is low for different power system faults compared to large scale wind farm model with single type wind energy generator. Considering large scale integration of wind farms with different types of generators it is necessary to take into consideration all issues identified during course of this research work and is a major contribution of a researcher. All technical challenges identified during this research work are mitigated by using STATCOM placed at the location of PCC. Use of STATCOM at proper location helps to resolve all technical challenges related with 16

17 interfacing of large scale wind farms with aggregated wind model with three types of Wind energy generators. Outcome of research work will be useful to wind farm developers, R & D organization and standard bodies & various researchers working in this area. PUBLICATIONS ON RESEARCH WORK [1] Kadam D. P., Dr. Kushare B. E. Voltage Swell Mitigation in Wind Farm System International Journal of Engineering Sciences & Research Technology, ISSN , IJESRT/Volume 3, Issue 3, PP , March [2] Kadam D. P., Dr. Kushare B. E. Voltage & Rotor Stability in Wind farm under Power System Fault International Conference on Proceedings of Elsevier Track on Recent Trends in Engineering Sciences Published by Elsevier, A Division of Reed Elsevier India Private Ltd., ISBN , PP , March [3] Kadam D. P., Dr. Kushare B. E. Mitigation of Sag & Swell in Wind Farm System International Journal of Computing & Technology, IJCAT/Volume 1, Issue 1, PP.13-18, Feb [4] Kadam D. P., Dr. Kushare B. E. Stability and Reactive Power Compensation Techniques in Wind Farm International Journal of Engineering Sciences & Research Technology, ISSN , IJESRT/Volume 3, Issue 2,PP , Feb [5] Kadam D. P., Dr. Kushare B. E. LVRT Capability for Wind Farm System International Research Journal of Sustainable Science & Engineering, ISSN , IRJSSE/Volume 2, Issue 1,PP.1-4, Jan [6] Kadam D. P., Dr. Kushare B. E. Mitigation of Short Duration Variations in Grid Connected Large Scale Wind Farm Proceedings of Elsevier Track on Recent Trends in Power, Control & Instrumentation Engineering, Published by Elsevier, A Division of Reed Elsevier India Private Ltd. ISBN ,PP , Nov [7] Kadam D. P., Dr. Kushare B. E. Effects of STATCOM on a large Scale Wind Farm System International Journal of Research in Science & Advanced Technologies, ISSN , IJRSAT/Volume 4, Issue 2,PP , Aug-Sept