Optimal Energy Sharing in Hybrid Microgrid System Using Battery Energy Storage

A smart micro grid technology application facilitates the integration of renewable energy and increase its penetration. A smart grid is an electrical network which is built on advanced technology that uses dual-way digital communication to transmit electricity to buyers. The smart grid was created with the aim of using smart meters to overcome the problems faced by traditional grids. Microgrids allow for the integration of multiple renewable energy sources at different levels, improving the power system’s reliability, sustainability and efficiency. Remote places, spacecraft and maritime applications all use DC microgrids. Solar photovoltaic (PV) systems, wind energy, fuel cells, battery management systems, supercapacitors, and loads make up a DC microgrid. In this paper, some of the interesting approaches for optimal energy sharing in the hybrid microgrid are discussed.


1.
Introduction Electrical grid having low power production capacity and connected to the consumer load side is called microgrid.A smart grid is a digitally-based electrical network that uses dual-way digital communication to transmit electricity to buyers.The smart grid was created with the gain of using smart digital meters to overcome the problems faced by the traditional grids.The adoption of smart dc micro grid technology enables for easier renewable energy integration and penetration.Solar cells, wind turbines, and other renewable energy sources make up the majority of microgrids.Renewable energy resources are Solar, Wind, Biomass, Fuel cell etc.A microgrid is referred to as a hybrid microgrid system if it uses two or more different types of energy sources.Figure -1 shows complete microgrid systems.This microgrid system relates to different types of AC and DC load, battery energy storage, Electric vehicles, and utility grid.Microgrid systems are more reliable and efficient compared to the conventional grid systems.Microgrid systems are clean energy solutions and therefore they are environment friendly and pollution free which is need of the hour.Microgrids enable the distribution level integration of renewables, enhancing the dependability, sustainability, and effectiveness of the power system.Remote places, spacecraft, and maritime applications use DC microgrid.Solar photovoltaic systems, wind energy, fuel cell, battery and load make up a DC microgrid.Keeping all these advantages in perceptive, hybrid microgrid system is proposed in this paper.

2.
Literature Review This paper gives an idea about the optimal energy sharing of hybrid microgrid system.In literature different methods and techniques are available for the energy sharing.In paper [1] it is explained that a microgrid may be considered as an interconnection of loads and different active power or energy resources under specialized 1285 (2024) 012031 IOP Publishing doi:10.1088/1755-1315/1285/1/012031 2 supervision that boosts the dependability, sustainability, and efficiency of the current power system network.The suggested method strives to achieve a balance between generation and consumption in order to provide a dependable and stable functioning.[2] Proposes a fuel cell-based microgrid with energy management and a hybrid battery-fuel cell system for energy storage.

Figure-1: A Typical Microgrid system
[3] Proposes a centralized architecture-based control strategy for the best use of resources through data collection and management.The battery charge/discharge device circuit controls the DC link voltage while the most renewables are utilized [4].If solar irradiation or wind power is available, the suggested electrical Power Flow Management algorithm may choose the mode of operation, as well as battery voltage and demand, to guarantee that the load is provided with dependable and uninterrupted power [5].It is critical to constantly operate in MPPT mode to effectively use available renewable energy sources [6].An optimal positioning of energy storage device (ESD) improves the degree of quality of electrical power delivered by allowing for best control of frequency and voltage, in addition to lessening the effect of fluctuation by enhancing the current delivered, particularly during peak hours [7].ESD is made up of a battery, fuel cells and super capacitor which help to improve battery life while also providing a quick system reaction to compensate for transients [8].Different operating modes for a DC microgrid exist including islanded and integrated with an AC microgrid [9].Several control algorithmic programmes have been introduced in the literature to handle the DC-link voltage problems.It provides a survey of recent advanced techniques and developments in hybrid microgrid connection topology with energy resource management and control [10].An efficient control technique is necessary to ensure proper coordination between electricity generating resources, energy storage devices, and loads for the reliable and efficient functioning of standalone and connected microgrids.[11] describes control topologies such as centralised, decentralised, distributed, and hierarchical order.For microgrid administration, any of these control techniques can be employed.However, for optimal resource use, a hierarchical management structure with multiple control levels is recommended.[12] Outlines a control strategy based on centralised architecture for the efficient use of resources through the collection and management of data.This method's shortcoming is that it can't be applied to large systems since the central controller is overworked.[13] Suggests an alternative control methodology for the microgrid that is based on extremely minimum bandwidth communication and the droop control methods to reduce the trade-off between voltage regulation and current sharing.It has the benefits of a distributed and decentralized architecture without the need for separate communication links.However, expanding the method to many microgrid is problematic.[14] Describes an energy management strategy using total electricity generation, energy storage, and load demand data.For a reliable and stable operation, the strategy is to strike a balance between generation and consumption.[15] Describes the energy algorithmic management of a microgrid with a fuel cell and hybrid energy storage consisting of a battery and a super capacitor.[16] proposes an algorithm for managing the stored energy in Battery so as to increase life cycle of hybrid energy storage and to minimize the total cost of operation of microgrid.[17] gives optimal configuration of microgrid and energy dispatch management to minimize net present cost, fuel consumption and emissions using HOMAR software.[18] analyze and critically compare various control methods of energy storage in microgrid.[19] introduces a stochastic framework for optimal daily energy dispatch in standalone type of operation of microgrid to minimize running costs of grid and avoid nonavailability of electricity for customers.[20] proposes an energy management algorithm for controlling & regulating voltage to maintain balance in the DC microgrid.[21] presents a review to summarize energy management modelling and solution techniques such as mathematical programming, 3 adaptive dynamic programming etc. together with their implementation schemes.Figure -2 shows the contribution of the paper.Following contributions are made for the paper.

I.
Optimal energy sharing in Microgrid containing solar photovoltaic (SPV), dgset and battery Energy storage using MATLAB/Simulink.

II.
Optimal energy sharing in a solar photovoltaic by Maximum power point tracking (MPPT) technique using MATLAB/Simulink.

III.
Optimal energy sharing in Microgrid containing wind energy and battery energy storage using MATLAB/Simulink.

IV.
Optimal energy sharing in Hybrid microgrid system containing solar photovoltaic, wind energy, inverter and battery energy storage using MATLAB/Simulink.Simulation is carried out in the MATLB Simulink.Optimal energy sharing is done in microgrid containing solar photovoltaic (spv), dgset and battery using MATLAB/Simulink.Load is connected to the direct utility source as the energy provided by the solar photovoltaic is not sufficient for the uninterrupted power supply.Dgset is used here for providing the energy to the load when the energy provided by the solar is not sufficient.Battery source is connected for energy storage and for optimal energy sharing.We connect fixed load to the system for the constant supply and there is a variable load connected too, which varies during the peak and off hours.Island command is given to vary the load for 15 and 35 seconds.During the 15 sec a small load is introduced and at the 35 sec the large load is coupled to the system.Figure -5 shows the graph of microgrid frequency (Hz.),Power output (Kw), battery SoC and microgrid voltage Vs. time.Microgrid frequency graph shows the variation of the frequency at the 15 sec when a small amount of load and at the 35 sec the large amount of load is introduced in the system.In the distributed resource graph pv array yellow line shows that the extraction of energy is done.Battery soc (%) graph shows that the battery at the initial state is fully charged and after some time when load introduced battery starts getting discharged.In the voltage rms graph it is observed that voltage across the microgrid remains constant as the dgset is providing the energy and direct utility source is also connected for uninterrupted power supply.Battery, dgset is connected to maintain the constant voltage across the microgrid when the island command is given to the system, at 15 sec and 35 sec load varies and according to that the energy extraction from the battery and dgset changes.MPPT with solar PV array can be used for the extraction of maximum power output.Solar radiation is 1000 and cell temperature is taken as 25 degrees Celsius.Buck converter is basically used to make the voltage variable by stepping it down to the required magnitude so that the current gets high and the power gets maximum.Capacitor is used for removing the ripple in the voltage waveform to get smoother waveform and the proper voltage without ripples is obtained.Buck type power modulator is operated at a duty cycle of 0.4 and inductor and capacitor used in the buck converter is of certain predefined value.Solar mppt charge controller is used in the system for the introduction of the pwm method so that the low order harmonics gets eliminated and the high order harmonics gets increased.Battery is getting charged continuously and the productive ability of the solar pv is improved and maximum power is extracted.The pv power graph shows that there is variation in the waveform and when the buck converter gets operated at the duty cycle of 0.4 then the power curve starts getting constant value.Duty cycle graph shows that the 0.4 is the duty cycle of the buck converter.Maximum power point tracking charge controller efficiency graph shows that the after a duty cycle of 0.4 the pwm method is applied so that the lower harmonics get eliminated and the higher order harmonics get increased and the power curve gets constant value.

Simulation Graph
Voltage power graph shows that the power is maximum and the system is working more efficiently.The buck converter extracts the maximum amount of power from the solar panels at the duty cycle of 0.4.Solar pv efficiency at that point is also maximum.Continuous charging of battery is going on.

6.
Simple Wind energy farm model A wind farm with six wind turbines integrated to grid system exports electricity to a 120 kV grid via a 25 kV feeder.In wind turbines a doubly-fed type induction generator and an IGBT-switch operated PWM power modulator are used.The rotor is fed at a changeable frequency via an AC to DC digital modulator, while the stator is integrated to the 50 Hz grid.Active and reactive power is produced by the wind turbine-driven, doubly fed induction generator.The Doubly fed induction type technology minimises the mechanical stress on the turbine blades during high-speed wind gusts while optimising the turbine speed of the rotor to harvest the most energy from the wind at low wind speeds.The wind speed is kept constant at 15 meter per second.The control mechanism uses a torque limiter to maintain a steady speed.The wind turbine's true and apparent power output are set at 10MW and 0Mvar, respectively.

Figure-10: Active and reactive power of wind turbine
The first graph in figure-10, shows the active or true power given by the wind mill.There is a variation in the power as the wind velocity changes and the power extracted is maximum.The second graph in figure-10, represent the reactive power generated by the turbines of the wind mill.At the initial state the reactive power is 0 and as there is change in the speed of wind, the graph shows variation in reactive power output.The DFIG, which is propelled by the wind turbine, produces both the active and reactive powers.In the wind mill system, a doubly-fed type induction generator and an IGBT-switched PWM digital modulator are utilized.The rotor is given an adjustable frequency via an AC to DC digital modulator, while the stator is directly connected to the 50 Hz grid.

Grid connected hybrid solar PV, wind turbine with mppt and battery management system model
This model shows the hybrid smart microgrid consisting of solar photovoltaic, wind turbine with mppt controller, inverter, DFIG and a battery.The output of the wind turbine is connected with the DFIG and then the rectifier converts the output to dc.The signal next travels to the boost converter and PWM (pulse with modulation for maximum power extraction) and then it is coupled with the dc bus bar.The wind turbine's pitch angle is regarded as zero.Consider 12 m/s of wind speed.This wind setup can produce a maximum of about 2.8 KW.The wind mill is coupled with IGBT-switch operated PWM digital converter and DFIG.While the rotor is fed via an AC/DC digital converter with a variable frequency, the stator is coupled to the 50 Hz grid.
To achieve maximum possible electrical energy from the solar pv array, mppt algorithm is used.Solar radiation is 10 and cell temperature is taken as 25 degrees Celsius.Boost converter is basically utilized to make the voltage variable by stepping it up to the required magnitude so that the current gets low and the power gets maximum.Capacitor is used for removing the ripple in the voltage waveform and so that the wave gets smooth and the proper voltage without ripples is obtained.Boost converter is operated at a duty cycle of 0.4 and inductor and capacitor used in the boost converter is of certain predefined value.Solar mppt charge controller is used in the system for the introduction of the pwm method so that the low order harmonics get eliminated and the high order harmonic get increased.Battery is getting charged continuously and the efficiency of the solar PV is improved and maximum power of 3 KW is extracted.The battery is used for the storage of the energy produced by the solar photovoltaic cell and the wind turbine.Bidirectional dc/dc converter is used with pwm (pulse with modulation) to improve the higher order harmonics and reduce the lower order harmonics.Battery is assumed to be initially charged with 50%.Battery is then connected with the inverter module.For the dc to ac conversion in this case, a Ful bridge inverter is utilised.A bi-directional dc to dc power modulator is used as a crucial component for sustained power flow because the output of a renewable energy hybrid system changes due to variations in weather conditions.Direct utility is integrated to the grid for uninterrupted power supply.Inverter is connected to the load bus also.Simulation graphs are as follows The graph shows the battery voltage which is held constant so that the battery charging and its discharging takes place consciously with maximum extraction of power.Battery current is changing as the changes take place in the weather conditions like wind speed and solar irradiation.The graph shows the solar cell current vs voltage characteristics.In the second graph it shows the power extracted by the solar cell is maximum as maximum power point tracking algorithm is used.Power is extracted at maximum rate.The first graph shows PV converter current value which is changing initially as the battery is charging at the starting and wind system is also working for supplying the energy to the battery.Battery current and dc load current is also maintained constant for the maximum extraction of power.Inverter current is also constant.The first graph shows the dc bus voltage which is having some fluctuation but it is maintained constant.The second graph shows current of the dc bus which is having some fluctuation but it is also maintained constant for the maximum extraction of power.The power extracted is maximum which is shown in the fourth graph.

Figure-16: Waveform of Boost converter duty cycle
The duty cycle (D) of the boost converter used in photovoltaic solar cells and wind turbines is shown in the graph above.The duty cycle ratio is assumed to be 0.4.The graph depicts the voltage, current, and power of a PV solar cell.Fluctuations at starting is due to the variable load at the load bus.The graph shows the inverter voltage waveform, current waveform and the overall grid current wave 8. CONCLUSION MPPT is utilized to draw maximum power from the solar Photovoltaic module and a boost converter is integrated to alter the voltage, resulting in energy optimization in the grid.A wound type rotor induction generator system with an AC IGBT switch based PWM type modulator is used in wind power turbine with a dual-fed type induction generator with a boost converter connected at the end to optimise the power.The energy is stored in batteries and the voltage is kept constant to extract the maximum power.Energy supply to the load is carried out by the inverter module which converts DC to AC. Direct utility is given to the grid for the uninterrupted power supply.This paper presents a utilities interactive grid-connected wind-PV hybrid system with advanced storage batteries to accelerate the rate of renewable energy integration.When dealing with current electricity businesses, the hybrid system takes into account the dispatchability and quality of the power it injects into the grid.

Figure- 3 :
Figure-3: Grid connected hybrid solar pv and wind turbine with battery management system

8 Figure- 11 :
Figure-11: Hybrid microgrid model Electrical power is generated by the doubly fed induction generator, which is driven by the wind turbine.Boost converter is operated at a duty cycle of 0.4 and inductor and capacitor used in the boost converter is of certain predefined value:

7. 2
Figure-13: Solar PV cell current and power (W)The graph shows the solar cell current vs voltage characteristics.In the second graph it shows the power extracted by the solar cell is maximum as maximum power point tracking algorithm is used.Power is extracted at maximum rate.

Figure- 14 :
Figure-14: Wave form of PV, battery and inverter input current

7. 4
Figure-15: Waveform of DC Bus load Current, Voltage and Power

Figure- 17 :
Figure-17: Waveform of Generator voltage and current

7 . 11
Figure-22: Waveform of Inverter voltage, current and main grid current