Fault analysis addressing the combined influence of high penetration of DFIG, SCIG, PMSG wind farms, and PV farms in power grid integration

This chapter presents modeling of generators that are used in wind farms such as squirrel cage induction generators (SCIG), doubly fed induction generators (DFIG) and, permanent magnet synchronous generator (PMSG). Installing wind farms must fulfill some rules or requirements. These requirements are developed by transmission system operator in order to guarantee the continuity and stability of the interconnected grid. This chapter presents the stability of two different types of combined wind farms. The first type is based on a combination of SCIG and DFIG wind turbines and known as combined wind farm (CWF). CWF collects the benefits of SCIG and DFIG where SCIG is cheaper compared with DFIG and PMSG. Despite DFIG is expensive, DFIG is more stable than SCIG. CWF is more suitable for developing countries. The second type is based on a combination of modern generators DFIG and PMSG and known as modern combined wind farm (MCWF). MCWF collects the benefits of DFIG and PMSG where DFIG features by its ability to control the active power independently of reactive power while PMSG can operate used for small and medium powers. This chapter discusses the impact of CWF and MCWF on the stability of interconnected electric distribution networks during single line to ground and double lines fault as examples of unsymmetrical and during three phase fault and three phase open circuit fault as examples for symmetrical. Also, this chapter discusses the impact of CWF and MCWF on the stability of interconnected electric distribution networks during different types of operation conditions of electric distribution networks such as voltage sage and over voltage.

Recently, sub-synchronous interactions (SSIs) between wind turbine generators and weak AC networks have generated great concerns. Traditional SSIs happened between doubly-fed induction generators (DFIGs) and AC grids with series-compensation. A new type of SSI incident has occurred recently in the AC network connected to a permanent magnet synchronous generator (PMSG) based wind farm, without series compensation. This incident has reignited the research interest in SSIs, especially those associated with PMSG and weak AC grids. Therefore, in order to analyze the characteristics of this new type of SSI, a simplified system model with multiple PMSGs connected with a weak AC grid is established in this paper. In addition, an eigenvalue analysis of the established small-signal model is conducted to investigate the SSI modes of the system. The small-signal stability study is validated by time-domain simulations. The results indicated that the stability of the PMSG based wind farms connected to a weak AC grid is mainly affected by the short-circuit ratio (SCR) and control parameters of the grid-side converter (GSC). A low SCR and inappropriate control parameters of GSC will cause the unstable oscillations in the power system.

To utilize the renewable energy resources, wind energy conversion systems (WECS) are a popular choice. In WECS, generators such as, Squirrel Cage Induction Generator (SCIG), Permanent Magnet Synchronous Generator (PMSG), Wound Field Synchronous Generator (WFSG), and Doubly Fed Induction Generator (DFIG), are used. Recently PMSG is gaining popularity over conventional generators, due to benefits such as no gearbox, high power density, and high precision and easy to control. Since, these generators are located very near to the load, power quality (PQ) disturbance, due to non-linear loads, mostly affects them. Thus, analysis of wind generator performance with harmonics injected by non-linear loads becomes necessary. This effect of harmonics injected by non-linear loads has been analyzed for PMSG in off-grid mode. The analysis has been performed for different ratings of the PMSG operating with variable wind speed using Mat lab/Simulink. Further, the effects of variation of ratings of PMSG on the total harmonic distortion (THD) of generator voltage and current with variation of wind speed has been analyzed. The results show that higher rating generators are more affected by harmonics in off-grid mode.

In this paper the dynamic behavior of different wind turbine generator configurations including doubly fed induction generators (DFIG), squirrel cage induction generator (SCIG), wound rotor induction generator (WRIG), and permanent magnet synchronous generator (PMSG) under ferroresonant conditions of energization and de-energization was investigated using Simulink/MATLAB (version 2017B, MathWorks, Natick, MA, USA). The result showed that SCIG had the highest overvoltage of 10.1 PU during energization, followed by WRIG and PMSG, while the least was DFIG. During de-energization, PMSG had the highest overvoltage of 9.58 PU while WRIG had the least. Characterization of the ferroresonance was done using a phase plane diagram to identify the harmfulness of the ferroresonance existing in the system. It was observed that for most of the wind turbine configurations, a chaotic mode of ferroresonance exists for both energization and de-energization scenarios. Although overvoltage during energization for wind turbine generator configurations was higher than in the de-energization with an exception of PMSG, their phase plane diagrams showed that de-energization scenarios were more chaotic than energization scenarios. The study showed that WRIG was the least susceptible to ferroresonance while PMSG was the most susceptible to ferroresonance.

The recently stipulated grid codes require wind generators to re-initiate normal power production after grid voltage sag. This paper presents a comparative performance of two commonly employed variable speed wind turbines in today’s electricity market, the doubly fed induction generator (DFIG) and the permanent magnet synchronous generator (PMSG) wind turbines. The evaluation of both wind turbines was performed for weak, normal and strong grids, considering the same machine ratings of the wind turbines. Because of the critical situations of the wind turbines during faulty conditions in the weak grids, an analysis was done considering the use of effective series dynamic braking resistor (SDBR) for both wind turbines. The grid voltage variable was employed as the signal for switching the SDBR in both wind turbines during transient state. Additionally, an overvoltage protection system was considered for both wind turbines using the DC chopper in the DC-link excitation circuitry of both wind turbines. Furthermore, a combination of the SDBR over-voltage protection scheme (OVPS) was employed in both wind turbines at weak grid condition in order to improve the performance of the variable speed wind turbines and keep the operation of the power converters within their permissible limits. Furthermore, the performance of the DFIG and PMSG wind turbines in weak grids were further investigated, considering the combination of 75% and 50% effectively sized SDBR and OVPS. It was observed that, even with a 50% reduction in SDBR or OVPS, the performance of both wind turbines is still satisfactory with faulty conditions. Therefore, it is recommended to use a combination of the SDBR and OVPS with DFIG- or PMSG-based variable speed wind turbines to achieve a superior fault ride through performance, especially in weak grids. The system performance was evaluated using the power system computer design and electromagnetic transient including DC (PSCAD/EMTDC) platform.

In this paper, system level design of an oscillating wave energy conversion system (WECS) using doubly-fed induction generator (DFIG) is compared with systems using squirrel-cage induction generator (SCIG) and permanent magnet synchronous generator (PMSG). The comparative study is carried out considering major hardware components and their rating requirements for each system. Although, SCIG and PMSG based systems are more simple and reliable, DFIG can enable compact and cost effective systems especially for high power WECS design. DFIG can generate power above its nominal rating at super-synchronous rotor speed and hence can offer an attractive solution for the oscillating power pattern of WECS. Moreover, rotor side control of the DFIG enables one to work with lower voltage and power level which effectively reduces the ratings of the power converters and other passive elements in the system. The system design comparison is performed with a wave energy converter (WEC) modeled for maximum power output around 500 kW. System operation with singly-fed generator (SCIG) and doubly-fed generator (DFIG) have been studied through simulation in real time simulator (OPAL-RT). The results of the comparison are shown with details of the major component rating of each system.

To study the on grid wind turbine generator made in china, three types of horizontal axis three-blade wind turbine generator were researched. The design of wind turbine and the factors which influence the property of the wind wheel were studied. The mathematical model and operation principle of wind turbine with squirrel cage induction generator, doubly-fed induction generator and permanent magnet synchronous generator were studied. The operation conditions of the wind turbine generators in Dabancheng wind farm were investigated. The conclusion is that all the three types of wind turbine generators can be used well according the wind condition of the wind farm. The variable speed wind turbine with doubly-fed induction generator and with permanent megnet synchronous generator have less influence to the power system and they can recover the power generation easier while grid fault is cleared compared with the wind turbine with squrrel-cage induction generator.

In power systems voltage stability is a key issue which attracts worldwide attention. This research presents an implementation of a modified IEEE 14 bus system model in Power System Analysis Toolbox (PSAT) — free and open source software. A newly developed Squirrel Cage induction generator (SCIG) and Doubly Fed Induction Generator (DFIG) wind turbine model are modeled and connected to a modified IEEE 14 bus system. This paper investigates the impact of Squirrel Cage induction generator (SCIG) and Doubly Fed Induction Generator (DFIG) on the power system stability. Here considered wind generators are SCIG which is fixed speed and DFIG is variable speed. Small signal stability study has been conducted on a modified IEEE 14 bus system with SCIG, DFIG wind turbine systems and their simulation results have been analyzed in this paper.

In this paper, a comparative analysis based performance study of Squirrel Cage Induction Generator (SCIG) and Doubly Fed Induction Generator (DFIG) wind turbine consisting wind energy conversion system (WECS) has been conducted for a renewable energy oriented microgrid for a sample population at St. Martin's Island in Bangladesh on MATLAB/Simulink environment. The designed microgrid system consists of wind turbine farms — along with solar PV farm and AC loads. Based on simulation results as per varying natural conditions encountered by both type of wind turbine based farms, the opted type of wind turbine farm is included in microgrid along with PV farm to cater for maximum load demand of the community over the entire year. Finally, simulation study of the microgrid consisting the chosen type of wind turbine based farm and solar PV farm is performed for varying realistic circumstances and designed microgrid's desired functionality is examined.

Wind energy conversion systems are becoming popular in the research areas of renewable energy resources. The commonly used generators with wind energy conversion system (WECS) are Squirrel Cage Induction Generator (SCIG), Doubly Fed Induction Generator (DFIG), Wound Field Synchronous Generator (WFSG) and Permanent Magnet Synchronous Generator (PMSG). Recently PMSG is gaining popularity as it has many advantages over conventional generators. Due to the variable nature of wind, PMSG cannot be directly coupled with the grid. An intermediate power electronic link needs to be provided between the generator and the grid. Many power electronic converter topologies are being used with PMSG. In this paper a review of recent and past grid connected converter topologies, used with PMSG for wind power generation, has been presented.

This paper presents the modeling and analysis of grid-connected wind turbine systems using real time digital simulator (RTDS). The different modeled systems of wind turbine generator systems (WTGS) such as permanent magnet synchronous generator (PMSG), induction generator (IG), synchronous generator (SG) and doubly fed induction generator (DFIG) are simulated. Three control schemes for 3 MW WTGSs of squirrel cage induction generator (SCIG), DFIG with back-to-back converter and PMSG with back-to-back converter are designed for the modeled systems. The simulation results show the performances of each type of WTGS under the same wind speed pattern. It has been verified that the RTDS based realtime simulations of grid-connected wind turbine generator systems to be effectively employed to evaluate the control schemes and output performances of different types of WTGSs.

Grid integration of Renewable Energy Systems (RES) involves various types of power electronics-based converters and inverters. The use of these electronic-based devices results in inducing both current and voltage harmonics to the grid. In order to reduce harmonics, especially for large-scale integration of RES, harmonic forecasting is one of many techniques used to design harmonic mitigation devices. The core objective of this work is to develop a novel forecasting model for accurate and reliable harmonic estimation for RES. To achieve this two hybrid generator models are used. First model consists of wind turbine coupled with Doubly Fed Induction Generator (DFIG) combined with Solar Photo Voltaic (PV) based power generator which are connected to common grid. The second model uses Permanent Magnet Synchronous Generator (PMSG) with wind turbine in conjunction with Solar-PV generator. With real world meteorological data (wind speed and solar irradiation) as inputs, these generators simulate and produce output power with current and voltage waveforms. Harmonics are extracted from these waveforms to record, analyze, arrange and forecast future harmonics. Three parameters namely, Total Harmonics Distortion (THD) and the dominant individual harmonic contents, 11 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic (h11) and 13 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic (h13) are forecasted for both voltage and current waveforms. Artificial Neural Networks (ANN) and Adaptive Neuro Fuzzy Inference Systems (ANFIS) are the prominent methods used for forecasting. Three types of three-layered ANN structures namely Cascaded Neural Network with Recurrent Local feedback (3LCRNNL), Cascaded Neural Network with Recurrent Global feedback (3LCRNNG) and Cascaded Neural Network with Local and Global feedback (CRNNGL) have been proposed and utilized in this work with hyperbolic tangent as transfer function to adjust weights and scaled conjugate gradient method as optimizer to reduce training error. ANFIS is also employed with subtractive clustering method to improve adaptability and accuracy of forecasts. The results are compared and presented which shows that ANFIS recorded the best performance for THDV and h13 and 3LCRNNGL for h11 for the Wind DFIG-PV model voltage harmonics forecast. For forecasts of the current harmonics, 3LCRNNGL performed best for THDI and h11, whereas ANFIS performed best for h13. For Wind PMSG-PV generator model, ANFIS yields the best results in every scenario involving voltage and current harmonics.

In order to verify the short-circuit current characteristics of wind farms and the effects on power grids due to the large scale wind farms integration at Rongcheng substation, Shandong Electric Power Company organized the three phase and single phase short circuit tests on Jun 12th, 2014. By using the field tests data got from the digital fault recorder, the short-circuit current characteristics of different types of wind turbines are compared. The wind turbine's contributions of the Squirrel Cage Induction Generator (SCIG), Doubly Fed Induction Generator (DFIG) and Permanent Magnet Synchronous Generator (PMSG) to the system short-circuit current are analyzed in detail. In addition, the short-circuit current characteristics of wind farms are summarized and deeply understood from the field tests data. With the analysis results, the Shandong Rongcheng wind farms short-circuit field tests will have a very good reference and directive significance to the large scale wind power centralized integration of the actual power grids.

The risk of oscillation of grid-connected wind turbine generators (WTGs) is well known, making it all the more important to understand the characteristics of different WTGs and analyze their performance so that the problems’ causes are identified and resolved. While many studies have evaluated the performance of grid-connected WTGs, most lack clarity and precision in the modeling and simulation techniques used. Moreover, most of the literature focuses on a single mode of operation of WTGs to analyze their performances. Therefore, this paper updates the literature by considering the different operating conditions for WTGs. Using MATLAB/SIMULINK it expands the evaluation to the full range of vulnerabilities of WTGs: from the wind turbine to grid connection. A network representing grid-connected squirrel-cage induction generator (SCIG) and doubly-fed induction generator (DFIG) wind turbines are selected for simulation. The performances of SCIG and DFIG wind turbines are evaluated in terms of their energy generation capacity during constant rated wind speed, variable wind speed, and ability of fault-ride through during dynamic system transient operating conditions. The simulation results show the performance of DFIG is better than SCIG in terms of its energy generation capacity during variable wind speed conditions and active and reactive power control capability during steady-state and transient operating conditions. As a result, DFIG wind turbine is more suitable for large-scale wind power plants connected to weak utility grid applications than SCIG.

In recent times, various types of wind generators have been linked to the power grids globally and the focus has been to control them to be more efficient and reliable. This study concisely discusses performance analysis, modeling, and assessment of different wind generators (permanent magnet synchronous generator, doubly-fed induction generator, squirrel cage induction generator), covering their benefits, drawbacks, and impact on the electric power systems. This comparison aims to guarantee that their technical and economic evaluations are comparable, allowing engineers to make a more informed decision about which generator is best suitable for their installation. Findings for the investigated wind generators lead to significant observations about their application fields, such as permanent magnet synchronous generator outperforms doubly-fed induction generator and squirrel cage induction generator, especially during grid disruptions; on the other hand, squirrel cage induction generator is simple and inexpensive.