Modelling of an Interconnected Power System using Solar-Wind Energy Integration

This paper revolves around the modification and improvement required for increasing the efficiency of the power generation and distribution system. As the demand for electricity and power consumption is increasing day by day, more efficient and capable system is required to reduce the burden and complicatedness of the power grid. The transformation or conversion of conventional power grid to smart grid which contains number of actuators, sensors and transducers which provides ability to control, analyse and maintain the grid which provides support for various types of new loads that are introducing in current period. Along with that, the involvement and guidance of the human element is also increasing rapidly in the power generation and distribution station. This involvement allows the monitoring, analysing, and recording the information to be done more precisely with less factors of error. Based on this, the simulation and integration of renewable energy sources simulated through MATLAB/Simulink reduces the burden on non-renewable source of energies such as Coal, Fuel, etc. Although it will be impossible to replace these sources completely but integrating such sources along with smart grid will allow to monitor and share information regarding the grid and its performance much efficiently. The data shared from smart grid plays a valuable role in estimation energy consumption and what may the demand in the future.


Introduction
Electrical energy is the most important energy on which each economics of every nation heavily depends on.Electricity is a daily necessity for everyone day job whether domestic or commercial or industrial [1].Smart grid has evolved as newest form of energy management system.It has different types of efficiency and maintenance benefits.It consists of sensors and transducers for instant detection and update of faults.It can be easily paired up with conventional and non-conventional energy sources.As energy consumption is increasing day by day and availability of limited reliable source of clean and pure energy is making it necessary to combine various form of energy resources to contribute optimally in fulfilling the demand on one hand and reducing the adverse effects on the planet.Renewable resources can reduce the high dependency on non-renewable resources.It is the necessity of the time to use conventional energy sources wherever possible.Due to the generation of electrical power through conventional method, the efficiency of monitoring and analyzing the problem and solution becomes very difficult.This is because it needs the integration of information, telecommunications, and power technologies with the electricity generation and distribution systems IOP Publishing doi:10.1088/1755-1315/1285/1/012030 2 along with the power demands, especially peak demands [1,[2][3].The smart grids generally use smart energy meters and detectors to cover the power consumption structure of all consumers to enable the optimal way of delivering the power.It is advised to use two-way communication system wherein the data flows in both directions i.e. from source to consumers and as well from consumers to source.This is indeed veritably important when a consumer uses renewable energy like solar and wind.The power produced in similar ways can also be fed to the sources from consumer side during peak power demands.Renewable energy sources are experiencing significant growth to ensure normal operation of the system [4].HVAC, HVDC, VFT, and FASAL are amongst major technologies for grid interconnections with inclusion of clean energy initiatives and developments [5].Cross-region power exchange is significant in effective management of power demand with renewable energy integration [6].Maximum power tracking (MPT) algorithms are efficient in optimizing solar energy into the power system [7][8].Simple block representation of smart grid is given in Fig. 1.Considering a four-power source system with two as non-renewable electrical power sources (such as coal and fuel) and rest two as solar and wind energy source from renewable sources category.The smart sensors are used for the selection of optimal and appropriate source of power from the given number of sources.The distribution of energy from the power sources to the load (Houses/Industries) is done through Transmission Lines.The most widely used tool for the simulation of smart grid by integrating solar and wind energy along with conventional energy sources is Matlab and Simulink.For Wind energy conversion a turbine is connected to the shaft of the windmills which is further connected to asynchronous generator to convert the mechanical energy of the shaft to electrical energy to be transmitted to smart monitoring centers.Asynchronous generator is used for the conversion of wind energy to electrical energy because the rotational speed is higher than synchronous speed, generating AC electricity with the rotation of the rotor.The conversion of solar radiation to electricity is done through photovoltaic (PV) cells usually a PV Array [9].In PV cells, when light strikes on semiconductor material (like silicon) of the PV cell, electrical voltage is generated.Maximum Power Point Tracking (MPPT) controller is attached to measure the voltage and stored down to the battery or supplied directly to a grid.

Test System
Matlab Simulink provides virtual environment for modelling and simulation of dynamically changing systems.MATLAB and Simulink are also used for digital signal processing and automatic control for simulation and model-based design.Proper graphical interface is provided for the improvement and enhancement in the model with varieties of add on and features.Simulink is integrated with it for accessing algorithms and add on provided by the MATLAB and rendering systems with better understanding and practical knowledge.The programming environment has graphical modelling and is capable to analyze and simulate dynamic systems of multiple domains.Its main interface is a tool useful for graphical block diagramming and a set of block libraries which are customizable [10].Integration with the rest of the MATLAB environment is one of the main features of Simulink and we can either script MATLAB programmes or can examine using block diagrams.

Smart sensor for intelligent switching of optimal performance and monitoring Transmission line
House/ industry (load) Three Phase Pi-section line Three Phase source Three Phase Meter Power source2 Power source1 Discrete Ts=2.4s

Matlab Simulink diagram of the test system
The simulated model of smart grid power system with two renewable power source system is shown in Fig. 2. The detailed and exact circuit connection made for the simulation of the smart grid integrating solar and wind source of electricity.
Fig. 2: Simulated model of smart grid power system with two renewable power sources.
The system consists of two renewable sources of energy, Solar PV system and wind turbine.Other electrical systems used are step down transformer, three phase source, three phase measurement block, transmission lines, and subsystems, Houses are acting as load for the process.Two tapings are taken out from the three phase transmission lines for operating the subsystem.For observing and analyzing various waveform output instruments such as scope is used.Wind turbine is very prominent among the whole class of known renewable energy resources till date.It permutes to electrical energy once it is connected to Asynchronous Induction Generator (ASIG).The Output of ASIG is fed to a step-up transformer.Induction generator has advantages like lower cost, lower requirement of maintenance, variable speed, higher energy capture efficiency and better power quality [11].
The output of the ASIG is given to the AC/DC Thyristor Controlled Double-Bridge Rectifier because of its rectification efficiency, higher output voltage and power.The Thyristor Controlled Bridge Rectifier gives a fixed DC Voltage which is forwarded to the grid.A MPPT Controller is used to harness the maximum amount of energy from the PV Panel.It converts a High Voltage DC output from solar panels down to the lower voltage needed to charge batteries or to grid supply directly.For modelling and simulation sun power SRP-315E-WHT-D solar panel is used available in MATLAB.The dynamic model is designed and modelled on a photovoltaic production system.Improved system contains solar PV module, dc/dc converting a device with a transformer device designed for MPP made with reference control, produced with P&O algorithm, asynchronous generator, and double rectifier, and dc in ac thyristor [12].There is a contact between highly thick p-type semiconductor and relatively thin n-type semiconductor.Several electrodes which are conductive are integrated on top of the layer of the p-type semiconductors [9,13].There is a junction between the two types of semiconductors forming the depletion zone.For protection against the environmental and physical damage the entire system is enclosed into a glass sheet.The availability of sunlight or photons is not affected by the presence of the conductive electrodes.Fig. 3 presents the diagrammatic representation of the solar PV cell.In case of the generation of electricity through wind-turbine, wind becomes the carrier of the pressure causing the propeller of the wind mill to rotate.Due to application of wind pressure one side of the rotor experiences low pressure and other side experiences high pressure causing an imbalance.Rotor of the turbine rotates is connected to a turbine that converting mechanical energy into electrical energy.Fig. 4 shows diagrammatic representation of a wind turbine [14].The rotor of the turbine is connected to a drive shaft which is connected to a group of gears (collectively called Gearbox) which helps in increasing the speed according to the gear ratio present in the gear box.On the neck of the turbine a bearing is attached which helps the turbine to face perpendicular to the direction of the wind.Between the generator and gearbox, a high-speed shaft is linked which delivers mechanical energy to the rotor of the generator.

Connection diagram of PV and Wind Turbine system
The Fig. 5 and Fig. 6 presents internal of the solar and wind module respectively [13].Improved system contains solar PV module, dc / dc converting a device with a transformer device is designed for MPP made with reference control.They are produced with P&O algorithm, asynchronous generator, and double rectifier.The Irradiance is the number of photons or light energy from the sun falling on an area of unit m 2 each second.Its unit is Watt/meter 2 .Temperature of 25 o C is kept for the surrounding environment.For Wind module, the speed of wind is kept at 10 meter/second and rectifier is used for conversion of ac into dc.Turbine along with the asynchronous generator rated at 480V 275kVA and rest of the component is collectively named Wind module.

Simulation Cases and Results
The above system is tested on different cases.Following are the observations made for various cases:

Case 1: Conventional Energy Source Connected to the Simulation
The waveforms given in Fig. 7 are observed for the simulation when connected with the grid which operates using conventional energy resources such as coal for the generation of electricity.The fluctuation reduces the system reliability on the grid.The peak power in the house 1 is 3000 W or 3kW whereas in house 2 the peak power consumed is 4000W or 4kW.

Case 2: PV System Connected to the Simulation
When connected with PV or Solar power system which operates using non-conventional energy resources that is solar radiation of sun for the generation of electricity.House2 and Industry 2 are the one that experiences solar in their load curve.House2 peaks at around 7kW and Industry2 peaks at 7.5MW.Solar is reliable as well due to the condition that it gives best performance during the day in the availability of sun.The various results for this case are given in Fig. 8.

Case 3: Wind System Connected to the Simulation
The graph in Fig. 9 shows the performance of wind energy system as one of the prime sources of energy in the house 1 an industry 1.We can see that unlike solar power system; wind energy system is reliable as the wind blows entire day irrespective of the time of the day.House1 experiences constant power of 4kW and industry1 experiences that of 5MW.

Case 4: Resultant power consumption at load level
The graph in Fig. 10 represents the power consumption of the houses, industries taken over a time, we can observe the variation trends of the loads brought into effect in various time frames, it is a consolidated view to analyze the systems according to load curves.

Case 5: Combination of non-conventional energy resources
When the loads are connected in integration with the non-conventional sources, we can see the various trends of the houses and industries.It can be observed that a very systematic behaviour is presented by the loads when connected with wind and solar energy sources.The results are presented in Fig. 11.

Case 6: Comparison between model with conventional and non-conventional power output
The loads here are interconnected from the solar, wind, grid.A graph is plotted in terms of the power consumption when these loads are integrated with the whole combination of energy sources available in presented in Fig. 12.A significant observation can have inferred from these trends.

Case 7: Comparing load curves of different loads
In Fig. 13 graphs we have compared the individual Houses and the industries, a consequential observation can be made as to what trend is followed when seen in accordance with a similar system, this is very useful in designing systems and observing the reliability.

Conclusion
This research article confers observation made by simulating a model of Smart Grid using Simulink which consists of a photovoltaic and a wind energy sources as its main two sources.The developed system will be helpful for designers, engineers, and researchers to analyze the behaviour and performance of smart grid in a confined situation of real loads.The research findings also aim at providing a consolidated overview of mathematical modelling, designing techniques of the Wind Turbine simulation as well as PV Modules.It also gives us a broad insight of the energy exchange between the consumers and at the power generation.In conclusion the integration of renewable resources of energy into our grids is necessary to meet the growing demand of the power and to generate electricity from renewable sources especially during peak load hours.The adaption of

Fig. 4 :
Fig. 4: Diagrammatic Representation of Wind Turbine.The rotor of the turbine is connected to a drive shaft which is connected to a group of gears (collectively called Gearbox) which helps in increasing the speed according to the gear ratio present in the gear box.On the neck of the turbine a bearing is attached which helps the turbine to face perpendicular to the direction of the wind.Between the generator and gearbox, a high-speed shaft is linked which delivers mechanical energy to the rotor of the generator.