International Journal of Modern Research in Engineering & Management (IJMREM) ||Volume|| 1||Issue|| 6 ||Pages|| 09-14 || June 2018|| ISSN: 2581-4540
Performance Analysis of DC Micro Grid with PV-Fuel Cell Hybrid Generation 1,
Noor – ul -Ain, 2, Shafi M. Jiskani, 3, Dr. Anwar A. Sahito 1,
Student M.E. (Electrical Power) IICT, Mehran UET Jamshoro; 2, Assistant Prof. Electrical Engg. Mehran UET, Jamshoro 3, Associate Professor, Electrical Engg., Mehran UET, Jamshoro
------------------------------------------------------ABSTRACT---------------------------------------------------Conventional energy resources are being replaced by Renewable energy sources mainly due to increasing environmental concerns. Photovoltaic (PV) and Fuel cell (FC) are suitable to be used in modern DC microgrids due to their DC output. In this research work, a DC microgrid structure is proposed for small residential areas using hybrid PV and FC generation. Power Electronic converters are used to regulate generated voltage of the two sources for integration to a common DC bus. Proposed system is simulated using MATLAB SIMULINK to observe its performance. Simulation results show that output voltage is properly maintained at different DC buses of the microgrid. FC is suitable to cope up the variation in PV output and maintain load requirements. INDEX TERMS: DC microgrid, DC-DC Converters, Renewable Energy interconnection ----------------------------------------------------------------------------------------------------------------------------- --------Date of Submission: Date, 30 May 2018 Date of Accepted: 04 June 2018 ----------------------------------------------------------------------------------------------------------------------------- --------I. INTRODUCTION Renewable energy sources like solar, wind, fuel cells are increasing rapidly as electricity generation source around the world. Renewable energy resources being eco-friendly are being promoted by various world health and environment organizations. On the other hand, renewables also provide diversity in generation resources. Availability and almost zero fuel cost makes renewables the only choice for power generation [1]. Solar Photovoltaic (PV) cells are considered as most commonly used renewable energy source. It offers simple installation and low cost for small power applications. PV power generation is dependent upon weather condition and solar irradiance therefore nonlinear PV output needs to be controlled to be supplied to loads [2]. Fuel Cell (FC) is electrochemical device which produce electric current through chemical reaction of hydrogen and oxygen using electrolyte. Like PV they are intermittent source of generation, because of fast load response, modularity and high efficiency. Unlike battery they are not rechargeable. Fuel for FC is hydrogen and other hydrogen containing compounds, which on reprocessing produce hydrogen [3]. Because of intermittent nature of many renewable energy sources (solar, wind etc) hybrid combination of two or more renewable source along with alternative energy sources and storage can improve system performance. These hybridized systems also called micro grids. These microgrids may work independently as isolated systems and may be connected with larger grid to supply loads located at different locations [4]. Nonlinear PV output is overcome by integrating another renewable source like Wind, Storage (i.e battery) and Fuel Cell that ensure uninterruptible high-quality power to load and also a maximum Power Tracking Point (MPPT) controller has been associated with each PV generator in order to obtain an optimal power output under changing climatic condition [5]. A Suitable control strategy is required to maintain balanced power and voltages at different buses in hybrid generation fed microgrids. [6] proposed neural network-based controllers for controlling output of hybrid generation and storage used in grid connected microgrid. Additionally, local controllers are used to regulate output of the power electronic converters. [7] proposed reactive power compensation for grid connected hybrid PV and FC generation. Voltage source converter guarantees the maximum utilization of PV array the optimal use of FC. [8] proposed a hybrid energy system with wind turbine, PV and Fuel Cell to supply standalone loads. They used three individual boost converters to control power flow to load. DC-DC converter is simple and cost-effective method for maximum power tracking from wind and PV system. [9] employed the information gap decision gap theory (IGDT) technique to model the uncertainty of electrical load. The uncertainty modeling o load enables operator to make decision to optimize the systems operation against possible changes in load. In this research work, a PV and FC based hybrid generation system is proposed. Output of the two generations are regulated using DC-DC converters to integrate at a common DC bus of an isolated DC microgrid. Proposed DC microgrid is suitable for rural electrification in Asian countries.
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Performance Analysis of DC Micro Grid with PV-Fuel‌ II.
SYSTEM DESCRIPTION
Proposed system consists of hybrid generation using PV and FC. Block diagram of the system is shown in Fig. 1. Outputs of the generation resources are regulated through DC-DC boost converters and connected to a common DC bus of 100V. Heavy load is connected to this common bus. A section of distribution line is added before another 100V DC bus. Another load is connected to that bus. For the loads operating at 12V, 100V DC voltage is stepped down to 12V using DC-DC Buck converter. Small loads are connected to this bus.
Fig: 1 Block diagram of DC Micro grid with hybrid PV-FC generation
III.
RESEARCH METHODOLOGY
Microgrid system is developed in MATLAB/Simulink@ 2017(b) as shown in Fig: 2. Simulation of microgrid is performed to analyze performance of the proposed microgrid. PV model was developed in matlab/Simulink while developing a hybrid power generating system. Input parameters of PV are temperature and irradiance and model generate output voltage and output current of PV module according to these input parameters. According to Standard Test Condition (STC) normal temperature is 25 oC and PV normal irradiance per square meter is 1000W/m2. FC is used for simulation analysis SOFC type having power rating of 5KW. The operating temperature of SOFC is 650oC-1000oC and the electrical efficiency is 55-60%. Their durability is about 4x104 hour. Mostly used for large scale power generation of about 50MW. Constant parameters of SOFC are used as inputs in proposed model and output voltage, current and power of model are determined. As the output of PV is variable in terms of voltage and current hence DC-DC Boost converter is used at the output terminals of PV to increase its voltage to 100V. Boost converter performs function of voltage regulator. Also, voltage is increased to desired level for utilization of heavy loads and better transfer of power over distribution line reducing its voltage drop and power losses. Output of DC is also stepped up to 100V using another Boost converter so that both outputs are connected to one common bus. Further another DC bus 2 is taken out from bus 1 (100V) with line resistance R to supply a 4kw/100V load. For low voltage applications at the DC bus 3, the voltages of DC bus 2 are step down by a dc-dc buck converter. Resistive line model is used to represent a section of the distribution line between two 100V DC buses. Buck converter model is connected between buses 2 and 3 to step down DC voltage to 12V to be utilized by consumer appliances. DC-DC converters are controlled though PI controllers. Block diagram for the control scheme implementation for Boost converter is shown in Fig. 3. The error signal between output voltage and reference voltage is proceed through PI controller so to control PWM pulse is generated. Thus, generating a pulse sequence with appropriate duty ratios. Similarly, Buck converter and its implemented control strategy is shown in Fig. 4. An appropriate response of controller is required because of the nonlinear behavior of Buck converter.
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Performance Analysis of DC Micro Grid with PV-Fuel…
Fig. 2: Proposed DC micro grid with hybrid Fuel Cell (FC) and PV power generation system
Fig. 3: Boost converter with control loop
Fig. 4: Buck converter with its control loop
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Performance Analysis of DC Micro Grid with PV-Fuel‌ In order to operate the proposed hybrid PV-FC system following conditions are required [1] The system should transfer energy from dc link to load with controlled output power without injecting any harmonic current. [2] A DC power is supplied to load even though output of PV is changed or FC stop/start supplying to load. [3] The control strategy employed must take care different time constants of PV and FC. The controlled dc output power of PV is given as: đ?‘ƒđ?‘ƒđ?‘‰ = đ??źđ?‘ƒđ?‘‰ đ?‘‰đ?‘ƒđ?‘‰ (1) đ?‘ƒđ?‘ƒđ?‘‰ = đ??źđ?‘ƒđ?‘‰ đ?‘‰đ?‘ƒđ?‘‰ (1 − đ??ˇđ?‘ƒđ?‘‰ ) (2) Where đ??źđ?‘ƒđ?‘‰ đ?‘Žđ?‘›đ?‘‘ đ?‘‰đ?‘ƒđ?‘‰ are respectively current and voltage of PV array and đ??ˇđ?‘ƒđ?‘‰ is the duty ratio of the Boost converter connected to PV array. Similarly, controlled output of the FC is given in Eq. (3) đ?‘ƒđ??šđ??ś = đ??źđ??šđ??ś đ?‘‰đ??šđ??ś (1 − đ??ˇđ??šđ??ś ) (3) đ??źđ??šđ??ś đ?‘Žđ?‘›đ?‘‘ đ?‘‰đ??šđ?‘? are respectively current and voltage of FC stack and đ??ˇđ??šđ??ś is the duty ratio of the Boost converter connected to output of FC stack. Any deficit of power supplied to load by PV will be fulfilled by FC stack through control of duty cycle of FC.
IV.
RESULTS AND DISCUSSIONS
In this paper performance of DC micro grid with hybrid PV-FC generation system under normal steady state operation is analyzed. Proposed system with its individual controllers is simulated using Matlab/Simulink. Fig. 5 shows waveform for PV voltage and current and stepped down voltage and current. Output voltage of PV is 48V and current of 167A. Voltage and current after Boost converter are 100V and 80A. Fig. 6 shows current and voltage of the FC generation along with the voltage and current after Boost converter. The output voltage of FC is 48V and current of 104A. Whereas after Boost converter voltage is 100V and current is 50A.
Fig. 5: Waveforms (a) output voltage of PV b) output current of PV (c) PV boost voltage (d) PV boost current
Fig. 6: Waveforms (a) output voltage of PV b) output current of PV (c) PV boost voltage (d) PV boost current
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Performance Analysis of DC Micro Grid with PV-Fuel‌ Fig. 7 shows voltage, current and power at bus 1 where outputs of PV and DC are combined. Similarly Fig.8 shows current. Voltage and power at 100V Bus 2. Step down Buck converter is connected between Buses 2 and 3. Current, voltage and power at Bus 3 are shown in Fig. 9.
Fig. 7: (a) current (b) voltage (c) Power ay Bus 1
Fig. 8: (a) current (b) voltage (c) Power ay Bus 2
Fig. 9: (a) current (b) voltage (c) Power ay Bus 3
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Performance Analysis of DC Micro Grid with PV-Fuel… V.
CONCLUSIONS
DC microgrid is an efficient and economical power supply system for small area. Isolated microgrid is a suitable operation for rural electrification. Renewable energy based microgrid is economical and reduce carbon emissions. Hybrid combination of generation will increase reliability of the microgrid. In this paper, PV-FC hybrid generation-based DC microgrid is analyzed through simulation using MATLAB/Simulink@ 2017(b). Steady state analysis shows that voltage at different buses is maintained to rated voltage through DC-DC converters controlled through PI controllers.
VI. ACKNOWLEDGEMNTS Authors are thankful to Mehran University of Engineering & Technology Jamshoro for providing necessary resources for carrying this research work.
[1] [2] [3] [4]
[5] [6] [7] [8]
[9]
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Noor – ul -Ain, et al. “Performance Analysis of DC Micro Grid with PV-Fuel Cell Hybrid Generation.” International Journal of Modern Research In Engineering & Management (IJMREM), vol. 1, no. 6, 11 June 2018, pp. 09–14., www.ijmrem.com.
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