Download integration of multiple renewable energy sources for dc microgrid

Rajnish Kumar* et al. /International Journal of Pharmacy & Technology
ISSN: 0975-766X
CODEN: IJPTFI
Research Article
Available Online through
www.ijptonline.com
INTEGRATION OF MULTIPLE RENEWABLE ENERGY SOURCES FOR DC
MICROGRID
1
Rajnish Kumar, 2Sam Daniel
Student - Saveetha School of Engineering, Chennai.
2
Assistant professor - Saveetha School of Engineering, Chennai.
Email: [email protected]
1
Received on: 15.08.2016
Accepted on: 20.09.2016
Abstract
A new topology of a hybrid distributed generator based on photovoltaic and wind-driven permanent magnet
synchronous generator is proposed. In this generator, the sources are together connected to the grid with the help of
only a single boost converter followed by an inverter. Thus, compared to earlier schemes, the proposed scheme has
fewer power converters. Model of the proposed scheme in d-q axes reference frame is developed. Two low cost
controllers are also proposed for the new hybrid scheme to separately trigger the DC-DC converter and the inverter
for tracking the maximum power from both the sources.
The integrated operations of both the proposed controllers for different conditions are demonstrated through
simulation and experimentation. Steady-state performance of the system and transient response of the controllers are
also presented to demonstrate the successful operation of the new hybrid system. Comparison of experimental and
simulation results are given to validate the simulation model.
1. Introduction:
A new topology of a hybrid distributed generator based on photovoltaic and wind-driven permanent magnet
synchronous generator is proposed. In this generator, the sources are together connected to the grid with the help of
only a single boost converter followed by an inverter. Thus, compared to earlier schemes, the proposed scheme has
fewer power converters.
Model of the proposed scheme in d-q axes reference frame is developed. Two low cost controllers are also proposed
for the new hybrid scheme to separately trigger the DC-DC converter and the inverter for tracking the maximum
power from both the sources. The integrated operations of both the proposed controllers for different conditions are
demonstrated through simulation and experimentation. Steady-state performance of the system and transient response
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of the controllers are also presented to demonstrate the successful operation of the new hybrid system. Comparison of
experimental and simulation results are given to validate the simulation model.
2. Objective:

To extract maximum power at high efficiency from the integrated energy source.

Renewable sources of energy such as wind,battery and solar panels have attracted much attention because they
are environmentally friendly, do not consume fossil fuels.
3. The following are the issues addressed by several authors:

Voltage regulation of DC bus. Circulating current due to difference in Instantaneous values of voltages Load
sharing among sources.

Power balance between source and load.

Maximum power extraction from the DGs.
In this paper, a DC micro-grid with multiple energy sources is considered which addresses maximum power
extraction from the sources with reduced circulating current. System configuration and different operating modes are
discussed in the following sections. The effectiveness of the proposed
Fig. 2: PV characteristic block diagram.
Fig. 3: Single diode equivalent circuit of a PV cell.
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4. System Description:
The block diagram of proposed DG scheme is given in where a direct driven PMSG and a PV array are the sources.
The PMSG output is rectified and fed into a DC-DC boost converter. The rectifier output voltage varies with the
wind-speed. The PV array terminals are connected to the output of the DC-DC converter to form a common DC link
for the proposed system. The inverter input terminals are tied to this common DC link. The PV array voltage (VPV)
is fixed to the output voltage of the DC-DC converter (VDC) since the output terminals of both the PV array and the
DC – DC converter are tied together. The output voltage of the DC-DC converter is automatically varied by a PV
MPPT controller (Controller 1) to PV array’s maximum power point voltage. Under this condition, the maximum
current for the given irradiation is drawn from the PV array by the action of current controller (controller 2) of the
inverter. The basic Perturb &Observe (P&O) algorithm is employed albeit with an inverted duty-cycle adjustment in
controller 1. This revised adjustment in the proposed scheme is because of the DC-DC boost converter being fed by a
stiff DC source (rectifier output) instead of the PV array.
Energy Sources:
Distributed generations typically use renewable energy sources, including solar power wind power, small hydro,
biomass, biogas and geothermal power. In this paper solar energy systems are considered as the DGs. Different
models of solar panel have already been developed. Most commonly used one is the single diode equivalent circuit,
which is shown in Fig.3.
The circuit consists of a current source, a diode in parallel with the current source, and series resistance. The current
(I) - voltage (V) characteristics of a typical solar cell is shown in Fig.3. This equivalent circuit is considered in this
paper for simulation studies.
Fig. 4: V-I characteristic of typical solar cell.
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5. Residential Microgrid System:
This section presents the residential microgrid system under study. The next subsections describe the system (DG
sources, storage devices, types of load and types of buses), operation modes (including the operation flowchart),
converters topology, converters specifications and bus voltages levels.
A. System Design:
The proposed residential microgrid is composed of two DG sources (photovoltaic panels and biofuel generator) and
one battery bank, and is able of supplying both AC and DC loads, including a PHEV. The microgrid has two buses:
one main DC bus in which the DG sources, storage device and DC loads are connected, and one AC bus in which AC
loads are connected and the point of common coupling (PCC) with the utility grid is located. Illustrates the microgrid
system. The arrows beside each converter indicate the possible power flow directions.
B. Operation Modes:
This subsection presents considerations to define the system operation modes and operation flowchart. This is a very
important stage, because it describes in which manner the microgrid will operate in each possible situation, depending
on some input variables.
It is important to highlight that the microgrid can operate in both grid connected and island modes. The
considerationsare listed next.
1) The photovoltaic (PV) panels rated power is lower than the microgrid total installed load.
2) The generator presents a starting time until begin the energy generation.
3) The battery bank can be charged through the main grid or photovoltaic panels.
4) The battery bank only discharges to supply loads or to maintain the buses voltages, never to export energy to the
main grid.
5) In grid connected mode, the battery bank is always fully charged or being charged.
C. Converters Topologies: The converter used to connect the energy storage device to the DC link presents a wide
range of possibilities, according to a bibliographic review. As an example, the interleaved half-bridge converter is
used. The traditional half-bridge converter is used. Some papers, a comparison among severaltopologies, in order to
highlight their advantages and limitations.
Regarding these analysis, the half-bridge converter is chosen to connect the battery bank to the DC bus, due to
advantages like requirement of only one inductor, lower current and voltage semiconductor stress levels, and higher
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efficiency in consequence of lower switching and conduction semiconductor losses and lower inductor losses. A
detailed analysis on the energy storage system converter focusing the proposed residential microgrid in under analysis
and will generate content for next publications. A single phase unidirectional rectifier is used to connect
the biofuel generator to the DC link due to its simplicity. A boost converter is used to connect the PV panels to the
DC link due to its simplicity, high efficiency and possibility of voltage boost required to this situation.Finally, a
single phase full-bridge inverter/rectifier is used to connect the DC bus to the AC bus. It is rated to the total DGs and
battery bank power, resulting in 7.24 kW.
6. Block Diagram:
7. Modules Description: Circuit Diagram:
8. Simulation Design:
The complete schematic of controller 2 is given in Fig. 6. High frequency op-amps (LM-318) are used to construct
the hysteresis-current-controller. IPV and Ib are sensed by the current transducers and digitized by the internal ADC
module of the microcontroller. Based on (15), Iref is determined and available as digital output from the
microcontroller. This digital value is subsequently processed by a Digital to Analog Conversion (DAC) IC to obtain a
DC value whichCorresponds to the peak value of Iref. This DC value is multiplied with the sine wave reference
extracted from the grid voltage, by a multiplier IC and fed to the hysteresis current- controller as the reference current
signal. When PV array (or PMSG) alone generates power, Ib (or IPV) will be zero and Iref is perturbed and adjusted
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automatically to extract the maximum power from PV array (or PMSG). When both the sources are generating, Iref
will be perturbed based on (15) and adjusted to maximize the DC link current IDC for the corresponding irradiation
and wind-speed conditions. As the sine wave reference is taken from the grid, the inverter output current will have
grid frequency and will be in phase with the grid voltage.
6. Conclusion:
This paper presented a DC micro-grid based power generation system with multiple energy sources. A new control
method is proposed to extract maximum power from the sources and to suppress the circulating current
simultaneously. The simulated results have been verified. Different cases considered in this paper have proven that
the system performance is fast and accurate. The transient time for the system when a sudden variation has been
applied is less than 0.1s.The results clarified that each source worked according to the control, and maximum power
has been extracted from the sources with reduced circulating current.
9. Output Voltage Waveform:
References
1.
J.Byun, S.Park, B.Kang, I.Hong, S.Park, "Design and implementation of an intelligent energy saving system
based on standby power reduction for a future zero-energy home environment”, IEEE Trans. Consum. Electron.,
vol.59, no. 3, pp.507-514, Oct. 2013.
IJPT| Dec-2016 | Vol. 8 | Issue No.4 | 20568-20575
Page 20573
2.
Rajnish Kumar* et al. /International Journal of Pharmacy & Technology
Jinwei He, Yun Wei Li, Blaabjerg, F., "Flexible Microgrid Power Quality Enhancement Using Adaptive Hybrid
Voltage and Current Controller," IEEE Trans. Ind. Electron., vol.61, no.6, pp.2784-2794, June 2014
3.
Weiwei Li, XinboRuan, ChenleiBao, Donghua Pan, Xuehua Wang, "Grid Synchronization Systems of ThreePhase Grid-Connected Power Converters: A Complex-Vector-Filter Perspective," IEEE Trans. Ind. Electron.,
vol.61, no.4, pp.1855-1870, April 2014.
4.
C. Liu, K.T. Chau, X. Zhang, “An Efficient Wind-Photovoltaic Hybrid Generation System Using Doubly
Excited Permanent-Magnet Brushless Machine”, IEEE Trans.Ind.Electron,vol.57, no.3, pp.831-839,Mar.2010.
5.
L. Xu and D. Chen, “Control and operation of a dc microgrid with variable generation and energy storage,”
Power Delivery, IEEE Transactions on, vol. 26, no. 4, pp. 2513–2522, 2011.
6.
S. Anand, B. G. Fernandes, and M. Guerrero, “Distributed control to ensure proportional load sharing and
improve voltage regulation in low-voltage dc microgrids,” Power Electronics, IEEE Transactions on, vol. 28, no.
4, pp. 1900–1913, 2013.
7.
X. Jianfang and W. Peng, “Multiple modes control of household dc microgrid with integration of various
renewable energy sources,” in Industrial Electronics Society, IECON 2013-39th Annual Conference of the IEEE.
IEEE, 2013, pp. 1773–1778.
8.
S. Anand and B. Fernandes, “Steady state performance analysis for load sharing in dc distributed generation
system,” in Environment and Electrical Engineering (EEEIC), 2011 10th International Conference on. IEEE,
2011, pp.1–4.
9.
Y. Ito, Y. Zhongqing, and H. Akagi, “Dc microgrid based distribution power generation system,” in Power
Electronics and Motion Control Conference, 2004.IPEMC 2004.The 4th International, vol. 3. IEEE, 2004, pp.
1740–1745.
10. C. Li, S. K. Chaudhary, T. Dragicevic, J. C. Vasquez, and J. M. Guerrero, “Power flow analysis for dc voltage
droop controlled dc microgrids,” in Multi-Conference on Systems, Signals & Devices (SSD), 2014 11th
International. IEEE, 2014, pp. 1–5.
11. M. Martino, Y. F. Qui˜nones, P. Raboni, and Z. Chen, “Intelligent control for a dc micro-grid system,” in
Universities Power Engineering Conference (UPEC), 2012 47th International. IEEE, 2012, pp. 1–5.
12. N. Eghtedarpour and E. Farjah, “Control strategy for distributed integration of photovoltaic and energy storage
systems in dc micro-grids,” Renewable energy, vol. 45, pp. 96–110, 2012.
IJPT| Dec-2016 | Vol. 8 | Issue No.4 | 20568-20575
Page 20574
Rajnish Kumar* et al. /International Journal of Pharmacy & Technology
13. Mummadi, Veerachary, and B. S. Singamaneni, “Stability analysis of cascaded dc–dc power electronic system,”
IEEJ Transactions on Electrical and Electronic Engineering, vol. 4, no. 6, pp. 763–770, 2009.
14. R. W. Erickson and D. Maksimovic, Fundamentals of power electronics.Springer Science & Business Media,
2001.
15. N. Mohan and T. M. Undeland, Power electronics: converters, applications, and design. John Wiley & Sons,
2007.
16. H. Nagayoshi, S. Orio, Y. Kono, and H. Nakajima, “Novel pv array/module iv curve simulator circuit,” in
Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE. IEEE, 2002, pp.
1535–1538.
17. J. Ollila, “A medium power pv-array simulator with a robust control strategy,” in Control Applications, 1995.,
Proceedings of the 4th IEEE Conference on. IEEE, 1995, pp. 40–45.
18. E. Koutroulis, K. Kalaitzakis, and V. Tzitzilonis, “Development of an fpga-based system for real-time simulation
of photovoltaic modules,” Microelectronics journal, vol. 40, no. 7, pp. 1094–1102, 2009.
19. Y. Li, T. Lee, F. Z. Peng, and D. Liu, “A hybrid control strategy for photovoltaic simulator,” in Applied Power
Electronics Conference and Exposition, 2009. APEC 2009.Twenty-Fourth Annual IEEE. IEEE, 2009, pp. 899–
903.
20. A. Vijayakumari, A. T. Devarajan, and N. Devarajan, “Design and development of a model-based hardware
simulator for photovoltaic array,” Electrical Power and Energy Systems, vol. 43, pp. 40–46, April 2012.
IJPT| Dec-2016 | Vol. 8 | Issue No.4 | 20568-20575
Page 20575