Development of models and performance simulation of a Doubly Fed Induction Generator for standalone

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Development of models and performance simulation of a Doubly Fed Induction Generator for standalone EV Charging Applications Nikhil Kumar Chaubey1, Shradha Gupta2 1,2Masters of Technology Student 1Department of Electrical department, Indian Institute of Technology, Delhi, New Delhi, India 2Department of Electrical department, National Institute of Technology, Delhi, New Delhi, India

-------------------------------------------------------------------------***-----------------------------------------------------------------------properties and performance indicators under varied Abstract: This paper reports on the development of models

operating circumstances would probably be part of the simulation. Analyzing variables including power production, efficiency, and reaction to load variations throughout the EV charging process may fall under this category. Evaluating the viability and efficiency of employing DFIG technology for environmentally friendly EV charging solutions is the aim of this kind of simulation. To improve the charging system's sustainability, the simulation might also investigate integrating renewable energy sources like solar or wind. All things considered; this study may help develop new uses for renewable energy in electric vehicles.

and performance simulation of a doubly fed induction generator for standalone electric vehicle charging applications. Standalone electric vehicle charging systems that do not require the availability of the electrical grid for their operation have gained acceptance lately as convenient and environmentally friendly alternatives for areas without easy access or with less reliable electrical power supply. The DFIG has been chosen as a generator for this application in light of its inherent benefits. Some of these inherent advantages include variable speed operation, which provides improved efficiency in power generation. Thus, the paper is essentially a mathematical model development based on the DFIG with components such as an electric vehicle, power electronics, and energy storage system. Simulation studies are performed in order to analyze the performance of the DFIG for standalone EV charging applications. It would be perfect enough to charge electric vehicles reliably as well as efficiently, especially working even in standalone mode. Thus, this work advances the understanding and optimizes DFIG-based standalone EV charging systems. The models and simulation results that have been developed can then serve as a guide for further research and development into the most efficient and sustainable charging of electric vehicles in areas not directly connected to the existing grid.

2. Literature review The Doubly Fed Induction Generator (DFIG) has emerged as a pivotal technology in the realm of renewable energy, particularly for standalone electric vehicle (EV) charging applications. Its ability to operate efficiently across a wide range of speeds makes it an attractive option for harnessing variable renewable energy sources, such as wind and hydropower. The DFIG's architecture, which includes both stator and rotor windings connected to a power converter, allows for effective control of active and reactive power, thus enhancing its performance in fluctuating operational conditions [2] Recent advancements in control strategies for DFIGs have significantly improved their operational efficiency and reliability. For instance, feedback linearization control techniques have been developed to accommodate the nonlinear characteristics of DFIGs, particularly under magnetic saturation conditions [8]. This approach enhances the generator's responsiveness to changes in load and generation conditions, which is critical for standalone applications where stability and power quality are paramount. Additionally, the implementation of direct power control strategies has been shown to reduce power ripple during grid synchronization, further stabilizing the output of DFIGs in EV charging scenarios [5].

Keywords: DFIG, Battery, wind turbine, Power Electronic Converter.

1. Introduction Wind energy which generates electricity is becoming one of the fastest growing environmental friendly energy sector now a days, wind energy is one of the most ecofriendly energy used by nations to reduce the consumption of fossil fuel and carbon emission, so one of the application of this energy is to charge EV through it. In the context of standalone electric vehicle (EV) charging systems, the input pertains to a performance simulation of a Doubly Fed Induction Generator (DFIG). Because DFIGs can function effectively at different speeds, they are frequently utilized in wind energy applications. The main goal of this scenario is to demonstrate how a DFIG may be used to independently supply electricity for electric vehicle charging without depending on the grid. Modelling the DFIG's electrical

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The modelling and simulation of DFIGs are essential for optimizing their performance in standalone applications.

Various studies have utilized simulation tools such as MATLAB/Simulink to develop comprehensive models that account for different operational scenarios, including fault conditions and transient stability [9]. These models facilitate

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the analysis of the DFIG's behaviour under various load conditions and help in designing control strategies that ensure stable operation during disturbances, which is particularly important for EV charging stations that may experience variable demand [11].

Also when isolated induction generator or alternator is used which is powered with mechanical energy by wind turbine through gear box so this system will allow speed to vary so we will get output of varying voltage and varying frequency but this variable voltage can be converted to dc by rectifier and ripple harmonic can be removed from dc link capacitor voltage further it can be converted into 3 phase ac supply by inverter of constant voltage and constant frequency and further sent it to grid by the help of suitable step up transformer but in this case entire electricity generated through wind turbine and generator has to pass 2 stages of electronic converter so the size, cost and losses increases so the overall system becomes highly expensive, less reliable and in efficient in small system of low power rating we use that type of system but in high power rating it is not suitable.

The integration of wind turbines with electric vehicle (EV) charging systems has gained traction as a sustainable solution for energy generation and consumption. The Doubly Fed Induction Generator (DFIG) is particularly well-suited for this application due to its ability to operate efficiently across a wide range of wind speeds, thus maximizing energy capture. The DFIG's architecture, which includes a rotor connected to a power converter, allows for variable speed operation while maintaining grid compatibility, making it an ideal candidate for renewable energy systems aimed at EV charging [13].

4. Modelling

Recent studies have highlighted the advantages of using DFIGs in wind energy conversion systems (WECS). The DFIG can provide both active and reactive power control, which is essential for maintaining grid stability during fluctuations in wind energy production [14]. This capability is particularly beneficial for EV charging stations, where demand can vary significantly. By employing advanced control strategies, such as sliding mode control, the performance of DFIGs can be optimized to ensure reliable power delivery to EV chargers.

These control methods enhance the DFIG's ability to track maximum power points and manage reactive power, which is crucial for maintaining the quality of the power supplied to EVs [16].

4.1. Wind turbines Wind turbines capture power from the wind.

Aerodynamically designed blades generate rotating mechanical power. The number of blades is normally three and rotational speed decreases as radius of the blade increases. For megawatt range wind turbines, the rotational speed will be 10-15 rpm. The efficient way to convert lowspeed, high torque wind power to generate electrical power is to use a gearbox and a generator with standard speed, else to operate generator at low speed of wind turbine we have to use machine of high number of poles which make performance rating very poor. Robust size gear box also acts as mechanical shock absorber.

In addition to DFIGs, alternative technologies such as Brushless Doubly Fed Induction Machines (BDFIM) are being explored for wind energy applications. BDFIMs eliminate the need for slip rings, reducing maintenance costs and improving reliability (Afshar et al., 2021; Strous et al., 2017).

These machines also retain the benefits of variable speed operation and can be integrated into wind turbine systems for EV charging, offering a potential pathway for enhancing the efficiency and reliability of renewable energy sources [21].

3. Problem Identification If we use synchronous alternator instead of DFIG, in case of variation in wind velocity will change the speed of windmill and hence the drive shaft of windmill changes, in case of strong air blast of wind the windmill will accelerate the drive shaft and in case of light wind condition the retarding electromagnetic forces will slow down the drive shaft so this drive shaft will have the varying velocity condition but the stator-rotor shaft will have fixed speed due to fix frequency of grid in this case this variation will produce damaging forces in drive shaft, gear box and stator rotor shaft also in huge power levels the stable operation is not possible.

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Fig. 1 Wind turbine Block properties 4.2. Power electronic converter The most significant part of operation is electronic converter functioning connected between generator and battery electronic system consists of two back-to-back converters.

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During all major grid problems, converter control keeps the torque-producing part of the rotor current in line with the air gap flux. When input power will vary torque and rpm of rotor shaft of generator will vary the converter will change voltage and frequency accordingly for smoothing operation.

4.3. DFIG

Rectifiers are devices that convert alternating current (AC) from the power grid into direct current (DC), which is necessary for charging the batteries of electric vehicles. This conversion is crucial because EV batteries operate on DC power. Choppers, on the other hand, are used to control the voltage and current supplied to the battery during the charging process. They can adjust the power levels to optimize charging efficiency by reducing ripple and protect the battery from overcharging. Together, rectifiers and choppers ensure that the charging process is safe, efficient, and compatible with the battery's requirements.

Understanding these components is essential for designing effective EV charging infrastructure, as they directly impact charging speed and battery longevity.

Double-fed induction generator (DFIG) is an electrical machine widely used in wind turbines and other renewable energy systems and works on the principle of an induction machine having rotor and stator both connected to the electrical grid. Most prominent feature of a DFIG is its ability to enable variable speed wind turbine operation which is helpful in optimally harnessing wind energy. In a DFIG wind turbine, the rotor current is fed by a variable frequency converter which allows controlling the output power or current of the generator. Thus, any given model does not work on a specific wind speed, and is designed to be more effective at a range of wind speeds leading to enhancing energy output. Furthermore, DFIGs can also help in enhancing stability of the grid since they can assist in providing reactive power requirements of the grid. Using a DFIG may also reduce mechanical stress on the turbine components and be less expensive than conventional generators running at fixed speeds.

Selection of L and C in DC-DC converter is very crucial for model to work smoothly in continuous conduction mode:

These are the mathematical equations needed to formulate the DFIG Model:

(i)

Selection of L:

= Peak to Peak Inductor ripple current, …………(1) At boundary condition

On solving the equations, we get; is the minimum value the value of inductor selected must be greater than this value for continuous conduction mode. (ii)

Fig.2 Equivalent circuit of DFIG

Selection of C:

Steady state voltage:

Peak to peak ripple voltage is area under the capacitor current;

( + )

………… (2)

=

Sensitive electronics usually require lower ripple, around 1% or less because High ripple can cause uneven charging and lead to excessive heating, reducing battery lifespan. So, the value of C must be chosen accordingly.

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(

=

+

………… (3) +

+

( + ) ………… (4)

Flux: ( (stator flux)

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) +

=

+

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…… (5)

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= ( (rotor flux)

)

+

= …… (6)

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=

+

…… (15)

=

+

…… (16)

Power flow operation: +

=

+

The rotor and grid voltage are seen from phasor:

+

… (16)

Efficiency of machine: =

..(17)

if

Slip of machine:

…. (18)

S=

…… (19)

Power:

4.4. Battery

Active power +3

.…… (7)

– 3s

….…… (8)

The heart of an EV is known as battery, The batteries form part of EV technology that would give the energy required for electric motors conventionally lead acid battery was used in EV which was low range, High maintenance and to be changed in every 3 years, to overcome this we replaced the battery with lithium-ion. Other reasons for choosing Lithium-Ion battery are due to the high energy density, which makes them have more extended ranges than other ty pes of batteries. They also tend to have a relatively low selfdischarge rate, hence the charge for extended periods in case they are not used. One benefit is that batteries have light weight and reduced volumetric dimensions.

Reactive power +3

…… (9)

+3

…… (10)

Electromagnetic torque in shaft:

Some important parameters of EV battery are: 1.

DQ- MODELLEING: The 3-phase rotating machine is always rotating and hence 2. it’s parameters always changes with respect to time, this cannot be used for modelling and control purpose, as we cannot estimate every instantaneous value, so we have to convert rotating reference from to synchronously rotating reference frame to make it easier to observe and control 3.

The rotor voltages in synchronously rotating D-Q reference frame can

Rated Capacity of Battery: EV batteries usually have rated capacities ranging from about 20 kWh to over 100 kWh, depending on the vehicle's range and size.

State of Charge: SOC represents the battery's current charge level as a percentage of its total capacity.

SOC is generally managed within a safe range for EVs, usually between 10% and 90%.

Nominal Voltage (Battery): EV batteries typically have nominal voltages around 350–400 V for standard EVs. Parameters used for battery simulation:

…… (11) …… (12) Flux induces in d-q axis =

+

=

+

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…… (13) …… (14)

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The power drawn from the grid feeds the stator windings, which are in fact the stationary parts of the generator. Stator windings create a rotating magnetic field. This induces the electric current in the rotor windings.

The rotor windings, in fact, the rotating part of the generator, is connected to the power electronic converter. This converter allows the rotor to have variable speed control that is required in the case of applications for the charging of an EV. This makes it efficient power conversion and synchronization with the grid.

The rotor windings rotation creates a rotating magnetic field, inducing voltage and current in the stator windings, and it is channelled to the EV battery via power electronics to charge the same.

The DFIG is provided with sensors and control algorithms to monitor and regulate the speed, phase, and voltage of the generator to synchronize with the power grid. Such synchronization prevents various power quality issues and allows efficient power transmission from the generator to the grid.

Fig. 3 Block Properties of Battery

5. Future scope However, there are also some problems with technology.

Under serious system faults, the grid voltage would be close to collapse. The turbine can attain uncontrolled operational speed. Attempts of meeting a target voltage or even power factor will drive quite high currents into the rotor and hence through the converters.

The converters would face thermal damage from these kinds of high currents. One additional factor is the quality of input data and assumptions considered during modeling, which makes the simulation less accurate.

The other disadvantage involved includes significant initial costs for establishing a simulation environment and hardware. Further, reliance on simulation might not allow for real variables like interactions with the grid or issues of maintenance that would impact the reliability of the charging system.

Scalability might be limited since the simulation may not represent larger systems or even charging stations properly and thus less applicable for massive deployment.

6. Working A doubly fed induction generator is essentially a kind of electric generator that is mainly used in wind power generation systems, though it can also be used for charging electric vehicles. In an electric vehicle charging application, the DFIG is employed to convert energy from the power grid into mechanical energy aimed at charging the battery of the electric vehicle.

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Fig.4 Flowchart of working

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7. Result The development of models and performance simulation of a Doubly Fed Induction Generator (DFIG) for standalone Electric Vehicle (EV) Charging Applications has shown promising results. The entire mathematical model of the DFIG system has been developed, including its rotor, stator, power converters, and control system. This will then be able to accurately simulate the detailed behavior and performance of the generator. Simulated results show that DFIG can charge the EV efficiently in standalone operations.

The generator supplies sufficient power for charging the EV with stable operation and good voltage level. The capacity to regulate both active and reactive powers of the DFIG provides optimal charging conditions of the EVs under various conditions of available power and the grid.

Simulation results have also proven that the DFIG is robust for changes in load and input power conditions. The generator's control system adapts and responds to changes in real time, ensuring the stable and reliable operation of the charging system.

MATLAB GRAPHS RESULT:

Fig.6 Stator phase currents of different Phases of DFIG. 2.

Rotor different phase current:

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Fig.5 Wind Turbine Power Characteristics Doubly Fed Induction Generator parameters are as follows: 1.

Stator different phases currents:

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Fig.7 rotor different phase current.

3.

Fig.9 rotor different D and Q axis voltage.

Rotor D and Q phase current in rotor reference frame:

Battery 1.

SOC (State of Charge):

Fig.10 SOC of Battery The SOC finally settles at 100% means the battery is fully charged.

2.

Voltage:

Fig.8 rotor different D and Q axis current.

4.

Rotor D and Q voltage: Fig.11 Nominal voltage of Battery

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The voltage at which charging starts is equal to nominal voltage of battery.

Conference on Electrical Machines and Systems (ICEMS), pp.1-5, 2019.

3.

2. Muhammad Taha Ali, Dao Zhou, Yipeng Song, Mehrdad Ghandhari, Lennart Harnefors, Frede Blaabjerg, "Analysis and Mitigation of SSCI in DFIG Systems with Experimental Validation", IEEE Transactions on Energy Conversion, vol.35, no.2, pp.714-723, 2020.

Current:

3. F. Bizzarri, A. Brambilla, F. Milano, "Simplified Model to Study the Induction Generator Effect of the Sub synchronous Resonance Phenomenon", IEEE Transactions on Energy Conversion, vol.33, no.2, pp.889-892, 2018.

Fig.12 Current in Battery

4. O. Veneri, L. Ferraro, C. Capasso, D. Iannuzzi “Charging infrastructures for EV: Overview of technologies and issues”.

2019 EPES

Some graphs of mechanical parameters of DFIG are shown:

5. Ghazaleh Sarfi Mohsen Kalantar “Predictive Direct Power Control of Doubly Fed Induction Generators to Reduce the Power Ripple During the Grid Synchronization” 2020 EPES 6. Mohammed Wadi, Wisam Elmasry, Mohammed Jouda, Hossein Shahinzadeh, Gevork B. Gharehpetian, "Overview of Electric Vehicles Charging Stations in Smart Grids", 2023 13th International Conference on Computer and Knowledge Engineering (ICCKE), pp.540-546, 2023.

7. M. Anders 2012 “Speed Software for Electric Machine Design and Analysis”.

Fig. 13 rotor speed

8. Gayatri Rajput, Gaurav B. Patil, Bhagyashree Patil, Dhiraj Sonawane, Sahil Pendharkar, Yash Patil, "Bidirectional Charger System Design Enabling V2G and G2V Energy Transfer", 2024 Second International Conference on Inventive Computing and Informatics (ICICI), pp.720-725, 2024.

9. System A. Rahab, F. Senani, H. Benalla. “Direct Power Control of Brushless Doubly-fed Induction Generator Used in Wind Energy Conversion”. 2017 IJPEDS

Fig.14 rotor angle

8. Conclusion

10. Thomas Logan R.A. McMahon Keith A. Seffen . “Noise and vibration in brushless doubly fed machine and brushless doubly fed reluctance machine”, 2014, IET Electric Power Applications

The development of a model and performance simulation for standalone EV Charging Applications holds enormous promise toward addressing the growing requirements placed on the charging infrastructure on electric vehicles.

The capability to handle power is well-controlled, which means adaptation by DFIG to both a change in load and any alteration in input conditions is ideal for standalone charging purposes. Further research in more testing by experimental validation through simulation results may be important.

11. Seyed Behzad Naderi Dao Zhou Michael Negnevitsky et al. “A Review on Fault Current Limiting Devices to Enhance the Fault Ride-Through Capability of the Doubly-Fed Induction Generator Based Wind Turbine” 2018 Applied Sciences 12. D. Harkat, A. Bouchemha, L. Yousfi and S. Kahla, "Optimal DFIG-Based Wind Turbine Speed and Reactive Power Control Using Particle Swarm Optimization Algorithm," 2024 2nd International Conference on Electrical Engineering and Automatic Control (ICEEAC), Setif, Algeria, 2024, pp. 1-6, doi: 10.1109/ICEEAC61226.2024.10576409.

9. References 1. GUOQING TAO, YUN WANG, YANPING WU, YU CHEN, "Subsynchronous Interaction Analysis of PMSG Based Wind Farm with AC Networks", 2019 22nd International

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13. Thomas Logan R.A. McMahon Keith A. Seffen 3 2014, IET Electric Power Applications. “Noise and vibration in brushless doubly fed machine and brushless doubly fed reluctance machine” 14. A. P. Sidharthan and S. A. Arefi, "Optimization of Charging in a Multi-Port EV Charging Station for Emergency Vehicle Priority Fast Charging," 2021 IEEE International Women in Engineering (WIE) Conference on Electrical and Computer Engineering (WIECON-ECE), Dhaka, Bangladesh, 2021, pp.

192-195, doi: 10.1109/WIECON-ECE54711.2021.9829632.

15. Mateusz Szypulski Grzegorz Iwański “Bulletin of the Polish Academy of Sciences: Technical Sciences” 2018 IET Electric Power Applications.

16. A. Rahab F. Senani H. Benalla3. “Direct Power Control of Brushless Doubly-fed Induction Generator Used in Wind Energy Conversion System” 2017 IJPEDS 17. Mohsen Rahimi Mostafa Parniani “Grid-fault ridethrough analysis and control of wind turbines with doubly fed induction generators”. 2010 Electric Power Systems Research.

18. X. Zhu and Z. Pan, "Study on the influencing factors and mechanism of SSR due to DFIG-based wind turbines to a series compensated transmission system," 2017 IEEE 26th International Symposium on Industrial Electronics (ISIE), Edinburgh, UK, 2017, pp.

1029-1034, doi: 10.1109/ISIE.2017.8001387.

19. H. Hoimoja, A. Rufer, G. Dziechciaruk, A. Vezzini “An ultrafast EV charging station demonstrator” 2018, IET Electric Power Applications.

20. Tim D. Strous H. Polinder J.A. Ferreira3. “Brushless doubly-fed induction machines for wind turbines: developments and research challenges” 2017, IET Electric Power Applications.

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