Sameer Tembhekar et al. 2017, Volume 5 Issue 3 ISSN (Online): 2348-4098 ISSN (Print): 2395-4752

 

International Journal of Science,Engineering and Technology

An Open Access Journal

© 2017 Sameer Tembhekar et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

Grid Integration of Hybrid Electrical Energy 1Sameer Tembhekar, 2Prabodh Khampriya

Introduction

Microgrid or distributed energy resource system is an electrical power system that have DER and load, have the ability to disconnect from and parallel with area EPS, include local EPS or may include area EPS and are intentionally planned[1]. A typical microgrid configuration combines several renewable energy sources, such as Wind Turbine (WT) and Photo-Voltaic (PV) panels, with energy storage system. The renewable sources are used as primary energy sources, which are generating whenever there is availability of wind or solar irradiation. However, because the sun irradiance and the wind speed are uncontrollable parameters, a support energy source is needed to increase the degree of controllability and operability of the microgrid. Traditionally, this function is performed by an energy storage system such as battery.

The energy storage system is considered to be an effective solution to balance the Generation and demand supporting the renewable energy deficit when necessary, and storing the primary energy excess when possible. All renewable sources and energy storage are connected together to a central dc bus by means of power converters such as choppers. These converters are designed to deliver energy from the energy sources, ensuring stable, sustainable and reliable operation. The effective utilization between various distributed energy sources and fulfil the load requirement,energy

management system plays an important role. An energy management system is a system of computer-aided tools used by operators of electrical utility grids to monitor, control and optimize the performance of generation system. EMS plays vital role in microgrids due to presence of intermittent sources of energy. Relevant literature on microgrid is increasing day by day [2-14]. Reference [2] introduces the concept, benefits and features of microgrid and gives a review of researchers and activities of microgrid technologies. Operation and control of a dc microgrid in both grid connected and isolated modes are explained in [3]. A generalized formulation is presented in [4], [5] to determine the optimal operating strategy and cost optimization scheme for microgrid. At present, there are some literatures that describe the energy management research [15-17].

One research based on the central controller and hierarchical control of energy management strategy and analysis two kinds of market policy in operation was proposed in literature [15]. One research based on the photovoltaic, wind power and battery singlephase AC of energy management strategy and the cost of optimize the system operation and service life of battery was proposed in literature [16]. A distributed power supply side model was proposed in literature [17]. There is a comparison between the installation and running costs of distributed generation and supply of the electricity sector cost in the model and a discussion of the optimal

Abstract

Day by day the electricity demand is increasing exponentially. To fulfill this increasing demand of electricity more and more utilization of non-conventional energy sources are required as conventional sources are reduces. The best way to utilize the different renewable energy sources (RES) together is by using application of Microgrid. This paper illustrates the simple model of DC Microgrid with energy management system (EMS) which schedules the generation and load. The simulation model is developed in MATLAB/Simulink software containing photovoltaic array, wind turbine generator system (PMDC generator), battery storage system, grid and energy management controller. The simulation results are presented with variable load and variable generation conditions.

Keywords— Distributed energy sources, energy storage

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Sameer Tembhekar et al. International Journal of Science, Engineering and Technology, 2017, Volume 5 Issue 3 ISSN (Online): 2348-4098 , ISSN (Print): 2395-4752

investment problem. In [18], a new hysteresis-based EMS for a HRES composed of renewable energies, hydrogen and battery, and a hysteresisbased control for the three-phase inverter, which connects the HRES to grid is proposed.

Fig: 1 Block diagram of DC microgrid with EMS

Fig. 1 shows the developed block diagram of dc microgrid with energy management system, which consists of various renewable energy sources like photovoltaic arrays (PV), wind turbine generator system (WTGS), battery storage (BS), utility grid (UG) and load. All energy sources and load are connected to the 48V dc bus. PV is connected to the bus through closed loop boost converter, which gives 48V constant outputs. WTGS is also connected with the same closed loop boost converter. Battery system of 180Ah is taken to supply energy for back up and resistive load is considered.

Developed Energy Management System

A. Microgrid model

Fig. 2 shows the developed simulation model of dc microgrid consists of a string of photovoltaic array, wind turbine generator (PM DC generator), battery storage system, grid and load. PV array and wind turbine generator system each of 1 kW with constant voltage closed loop boost converter that step up the PV array voltage from 36V to 48V are connected to the dc bus of 48V. Lithium ion battery of 180 Ah, 48V is used for energy storage system with charging and discharging controller.

The rectified voltage of grid is connected to the dc bus through static switch to supply power when renewable energy sources and battery do not have sufficient energy to supply load. Resistive load of 1.5kW is supplied from dc bus out of which 500W of critical load. The mathematical model of Energy Management System based on optimal scheduling of generation and load is developed. The input signals are generated power of PV array, wind turbine generated power, SOC of battery and load. The output signals are g1 for battery charging, g2 for battery discharging, g3 for grid on/off and g4 for load on/off.

B. Energy management System formulation

The total energy generated from renewables is,

PP + PW = PE (1)

where, PP is power generated by PV and PW is power generated by WTGS and total load,

PL1 + PL2 = PL (2)

where, PL1 is critical load and PL2 is manageable load. After comparing PR and PL,

if PE > PL

then charge battery through renewable energy sources by triggering charging controller, that is giving signal g1 = 1, otherwise g1 = 0,

if PE < PL

then discharge battery to supply extra load which is not available to renewables, by triggering discharging controller that is giving signal g2 = 1 if SOC of battery is greater than

0.6, otherwise g2 = 0,

If SOC < 0.6

Then check PG to supply extra load if PG > 0

Then give signal g3 = 1 otherwise g3 = 0, when PG do not have an extra power to supply, in this

condition switch off some manageable load by giving g4 = 0 otherwise g4 = 1.

The flowchart of the system is illustrated in Fig.3.

Fig :2.Simulation model of microgrid

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Sameer Tembhekar et al. International Journal of Science, Engineering and Technology, 2017, Volume 5 Issue 3 ISSN (Online): 2348-4098 , ISSN (Print): 2395-4752

Fig :3 Flowchart of EMS

Simulation Result with Comparison

Simulation results are illustrated for variable generation andload, in which the data of solar irradiation and wind are assumed to be variable for the day and taken equivalent 0.1 seconds for simulation. The generated power from PV and WTGS are plotted on the same axis, with solar radiation variable from 500 to 1000W/m2 and wind speed varies between 25 to 60 rad/sec. The simulation is run for 0.1 s. Different cases are considered for illustration as shown in table I, case 1, is the condition where PV generation is considered maximum and WTGS generation is at minimum. PV output is considered to be variable from 700 watts to 800 watts and wind turbine generation is from 250 watts to 450 watts. Load is also variable from 500 watts to 1700 watts as shown in fig. 4. It can be seen from the graph that, whenever generated power from renewable is more than connected load, battery charges otherewise discharges whenever it lacks. The SOC, battery voltage and battery current is shown in fig. 5. At simulation time 0.03 to 0.068 battery discharges becouse load exceeds generation and from 0.068 second it starts charging as load decrese to below generation.

TABLE I: DIFFERENT CASES OF SCHEDULING GENERATION AND LOAD

Case

Generated Power

(PV+WTG )

CONNECTED LOAD BATTERY STATE

Case

1 PV Maximum

500-1700 W Charging Charging/Discharging

WTGS Minimum

Case

2

PV Minimum

WTGS Maximum

500-1700 W Charging Charging/Discharging

Case

3 Both Minimum 400-800 W No Action

Fig: 4total power generated and connected load while PV at maximum and WTGS at minimum

Fig: 5 Battery parameters while PV at maximum and WTGS at minium

Case 2, in which WTGS generation is maximum and PV generation is at minimum. WTGS output is considered to be variable from 500 watts to 800 watts and PV is from 400 watts to 500 watts. load is variable from 500 watts to 1700 watts as shown in fig. 6. As like previous condition where battery charges and discharges acconrding to the generated

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Sameer Tembhekar et al. International Journal of Science, Engineering and Technology, 2017, Volume 5 Issue 3 ISSN (Online): 2348-4098 , ISSN (Print): 2395-4752

power and load requirement. The SOC, battery voltage and battery current is shown in fig.7.

Fig: 6 total power ganerated and connetced load while pv atminimum and wtgs at maximum

Fig: 7 battery parameters while PV at minimum and WTGS at minium

In case 3, the renewables are at lower to supply and batteryalso having less state of charge, therefore this is considered thecondition of grid insufficient to supply load or load scheduling in the grid, the power required by the load in this condition isnot available at renewable, battery and grid, therefore it isneeded to shut down some load of microgrid. Only fixed (critical) load will be supplied by the battery and rewable energy sources as available. Fig. 8 shows the generated power and load for case 3, at 0.04 second load exceeds generation by renewable and battery state of charge is also at minimum, grid is having

load scheduling, therefore it is needed to shut down some load.

Fig.8 Case 3 total power generated and connected load

Conclusion

The generation and load scheduling is done with proposed energy management system. Generation among various renewable sources and load are considered to be variable. For every source or load, static switches are used which are controlled by the gate signals generated by the energy management system. Further scope of work is incorporating bidirectional power flow with utility grid. References [1] IEEE Standards Coordinating Committee 21, “IEEE Std.1547.4-2011:IEEE Guide for Design, Operation, and Integration of Distributed Resource Island Systems with Electric Power Systems”, Jul. 2011

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Author’s details 1,2Department of Electrical Engineering, Sri Satya Sai Institute of Science and Technology Sehore, Bhopal, Email: sameer.tembhekar80@gmail.com khampriya5@gmail.com

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