International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017
p-ISSN: 2395-0072
www.irjet.net
DIGITAL AVERAGE CURRENT SHARING CONTROL FOR LOW VOLTAGE DC MICROGRIDS Anuja Ann Mathews1, Veena Mathew2, Geethu James3 1PG
Scholar, Dept. of EEE, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India Professor, Dept. of EEE, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India 3Assistant Professor, Dept. of EEE, Mar Athanasius College of Engineering, Kothamangalam, Kerala, India 2Assistant
---------------------------------------------------------------------***--------------------------------------------------------------------these objectives, it requires high speed Abstract - As compared to AC system, DC microgrids communication and offers less reliability due to have high efficiency, high reliability, and easy interconnection of renewable sources. DC microgrid should single point of failure. In this paper a comparison of be controlled in such a way so as to ensure proportional droop controllers and Digital average current sharing load sharing among sources and also to maintain low control schemes are explained. voltage regulation of the system. Conventional droop controllers are not effective in achieving both the above mentioned objectives simultaneously. Even though centralized controller satisfies these objectives, it requires high speed communication and offers less reliability because of single point of failure. In this paper a decentralized controller for dc microgrid is explained. Key advantages are high reliability, low voltage regulation, and proportional load sharing. Simulation of both decentralized controller and droop controller is carried out in MATLAB.
2. DROOP CONTROLLER Figure 1 shows the block diagram of droop controller. Each source is represented using a power electronic converter (PEC).For each source there is a droop control and an inner voltage and current control loop.
Key Words: DC microgrid, Droop controller, ACS control, DACS control, Decentralized controller .
1. INTRODUCTION Distributed power generation systems are gaining popularity due to increasing energy demand. High reliability, remote electrification, low distribution losses, reduced chances of blackout and easy scalability are the key advantages of the distributed systems[1]. Microgrid includes the control and coordination of distributed generation and storage units to maintain power balance between sources and loads. The control objectives of DC microgrid are to ensure equal load sharing in per unit among sources and also to maintain low voltage regulation of the system[4]. There are different control strategies for DC microgrid. Droop controller, Average current sharing (ACS)control etc are some of the controllers for DC microgrid. Conventional droop controllers are not effective in achieving both the control objectives of DC microgrid simultaneously[5]. Reasons for this are identified to be the error in nominal voltages and load distribution. Though centralized controller achieves © 2017, IRJET
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Figure1.Block diagram of droop controller
There is no secondary control. For dc systems, droop between voltage and current is given by
vjref = vj0- djij
…………………….(1)
where dj, ij and vj0 are the droop gain, source current, reference voltage and nominal voltage of source j respectively. As there is no secondary control, parameters of the droop control are set such that system voltage is maintained within the specified value. Inorder to ensure low-voltage regulation, low value of droop gain dj should be used. Figure 2 shows the steady state equivalent circuit of DC microgrid. For two parallel connected DC sources, unequal load sharing due to small error in nominal voltages is shown in figure 3. In case of small droop gain, the deviation in source current, i.e., ( i1- i2 ), is large. As the droop gain is increased, ( i1- i2 ) reduces. ISO 9001:2008 Certified Journal
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