Wind and solar integrated to smart grid using islanding operation

INTERNATIONAL Electrical EngineeringELECTRICAL ENGINEERING
International Journal of JOURNAL OF and Technology (IJEET), ISSN 0976 –
6545(Print), ISSN 0976 – 6553(Online) Volume 4, Issue 1, January- February (2013), © IAEME
& TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 4, Issue 1, January- February (2013), pp. 27-35
IJEET
© IAEME: www.iaeme.com/ijeet.asp
Journal Impact Factor (2012): 3.2031 (Calculated by GISI) ©IAEME
www.jifactor.com

WIND AND SOLAR INTEGRATED TO SMART GRID USING
ISLANDING OPERATION

K.Raja1, I.Syed Meer Kulam Ali2, P.Tamilvani3, K.Selvakumar4
1
(Assistant Professor, Dept of EEE, Knowledge Institute of Technology, Salem
Email: smartraja13@gmail.com)
2
(Assistant Professor, Dept of EEE, EBET Group of Institutions, Tirupur
Email: syed24may@gmail.com)
3
(Assistant Professor, Dept of EEE, EBET Group of Institutions, Tirupur
Email: tamilvani.eee@gmail.com)
4
(Assistant Professor, Dept of EEE, Muthayammal Engineering College, Rasipuram
Email: selvakse@gmail.com)

ABSTRACT

Utility grid is disconnected for any reason; the distributed generation still supplies the
required power to that section of local loads. This Phenomenon is called islanding operation.
When an islanding occurs, the voltages and frequencies in the islanded area cannot be
controlled by the grid system. This may lead to damage of electrical equipments and pose a
danger to the working personnel. To avoid the occurrence of islanding phenomena, many
control schemes have been proposed and devised to sense the islanding. A basic distribution
system consists of Distributed Generators such as Photovoltaic panels, Wind turbines and
other forms of renewable energy. As these renewable sources produce a Direct current, a DC
to AC inverter is needed to convert the Direct current to an Alternating current with the right
frequency and harmonics in relative to the AC coming out of the utility grid. A battery
storage system can be inculcated into the system to store the excess energy. Due to big
disturbance in a micro grid, voltage and frequency fluctuation occurs during transition from
emergency mode to islanding mode. However, due to the power fluctuation from renewable
energy sources, voltage and frequency deviations occur in islanded power systems. This work
presents an islanding operation method of AC smart grid. The power system consists of
photovoltaic, wind generators and controllable loads. In this work, the bus voltage and
frequency fluctuations of AC grid are reduced by the photovoltaic, the wind generators and
the controllable loads. Therefore, the AC bus voltage is maintained within the acceptable
range by applying the power control of the photovoltaic and pitch angle control of wind
turbine.

27

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 –

Keywords - Wind Turbine Generator, Photovoltaic, Maximum Power Point Tracker,
Permanent Magnet Synchronous Generator, Smart Grid.

1. INTRODUCTION

This paper presents about renewable energies such as photovoltaic’s and wind energy
is important for greenhouse gas reduction and oil substitution. Renewable power resources
are safe, clean, and abundant in nature. However, due to the power fluctuation of renewable
energy sources, voltage and frequency deviations are occurred in island power systems whose
ability to maintain stable supply-demand balance is low. Therefore, it is necessary to control
the system frequency and voltage at the supply-side. At supply-side, installation of storage
equipment and pitch angle control of wind generator has been proposed for control of
distribution power system. However, the installation of storage equipment that needs large
storage capacity and the cost of maintenance for battery degradation are not expected. Hence,
in case of using the renewable energy plants connected to power system, the supply-side
control has limitations. Therefore, the mutual cooperation control with the demand-side is
required because it is difficult to maintain the power quality by only the supply-side control.
Therefore, the study on the islanding operation of AC smart grid is important. In this paper,
an islanding operation of AC smart grid is presented. The proposed AC smart grid consists of
PVs, a wind turbine generator (WTG), a generator-side converter, and controllable loads. The
AC bus voltage and frequency fluctuation due to the renewable power plants (WTG and PV)
and loads is suppressed by the consumed power control of controllable loads based on droop
characteristics and the power control of the renewable power plants. The renewable power
plants are operated to suppress the AC bus voltage fluctuation by reducing the output power
when the controllable loads reach at the rated power. By using the proposed method, stable
power supply can be achieved even in the islanding operation. Besides, power companies can
expect high quality power supply and can reduce the cost by cooperative control between
supply side and demand side.

2. AC SMART GRID CONFIGURATION AND CONTROL SYSTEM

2.1 System Configuration
The configuration of the AC smart grid is shown in Fig. (1). The WTG is a gearless
2MW permanent magnet synchronous Generator (PMSG). PMSG has a simple structure and
high efficiency and is expected to be installed in next generation WTG systems. The AC
smart grid also consists of PV generators, a generator-side converter, a grid-side inverter,
controllable loads (Batteries and EWHs) and variable load. The system is connected to a
10MVA diesel generator and variable AC load through the grid side inverter and the
transformer. Wind power energy obtained from the windmill is sent to the PMSG. In order to
generate maximum power, the rotational speed of the PMSG is controlled by the PWM
converter. PMSG’s output power and PV’s output power are supplied to the AC load through
the AC distribution line. And, the remaining power of the PMSG is supplied to the AC load
through the grid-side inverter.

28


Fig 1 Block Diagram
ଵ
ܲఠ = ଶ ‫ܥ‬௣ (ߣ, ߚ)ߩΠܴ ଶ ܸ ଷ
ఠ (1)
ଵ
ܶఠ = ଶఒ ‫ܥ‬௣ (ߣ, ߚ)ߩΠܴ ଷ ܸ ଶ
ఠ (2)

Fig 2 Generator-Side Converter Control System

2.2 PMSG Model
The windmill output power Pw and the windmill torque ܶఠ are given by the following
equations:
షభమ.ఱ
ଵଵ଺
‫ܥ‬௣ = 0.22( Γ
− 4ߚ − 5)݁‫݌ݔ‬ Γ (3)
ଵ
Γ= భ బ.బయఱ (4)
ି
ഊశబ.బఴഁ ഁయ శభ
where, Vw is the wind speed, ρ is the air density, R is the radius of the windmill, Cp is the
windmill power coefficient, λ = ωwR/Vw is the tip speed ratio, ωw is the angular rotor speed
for the windmill and β is the pitch.
The Fig (2) shows the generator side converter controls the rotational speed of the
PMSG in order to achieve variable speed operation with maximum power
The Fig (3) shows the pitch angle control system of wind turbine.

Fig 3 Pitch angle control system

29


Where, φf is the permanent magnetic flux, Ld and Lq are the dq-axis inductance, and i1q is
the q-axis current. The error between the dq-axis current commands, i1d and i 1q, and the
actual dq-axis currents is used as the input of the current controller. The current controller
produces the dq axis voltage commands v 1d and v 1q after decoupling. The rotor position θe
used for the transformation between abc and dq variables is calculated from the rotational
speed of PMSG. MPPT control is applied when the wind speed Vw is less than the rated wind
speed Vwref=12m/s. When the wind speed Vw is greater than the rated wind speed Vwref,
then the output power of the PMSG is controlled by the pitch angle control system. For the
wind speed range between 5m/s and the rated wind speed, the pitch angle is selected to be
β=2◦ because the energy of the windmill is largest at β=2◦. When the wind speed is between
the rated wind speed and 24m/s, Pw is 1 pu so that pitch angle β is selected to keep the
windmill output Pw=1 pu. For the other wind speed range, Pw is 0 pu and the pitch angle is
fixed at β=90◦. Fig. 3 shows the pitch angle control system that determines the pitch angle β,
where the output power error e is used as the input of the PI controller. The pitch angle
control system includes a hydraulic servo system. The system has nonlinear characteristics
and can
3. AC DISTRIBUTION VOLTAGE AND FREQUENCY CONTROL BY DROOP
CHARACTERISTICS
This section describes the control of decentralized controllable loads according to
droop characteristic. By using the droop control, the AC network needs no central control and
no communication between the different elements of the network. In the AC grid, AC bus
voltage fluctuations occur due to the output fluctuation produced by WTG, PV and loads. The
suppression of this fluctuation is achieved by controllable loads connected to the AC grid.
Determination of the power consumption command is needed for each controllable load
which has different capacity. Therefore, the controllable loads are controlled according to the
droop characteristics and load is shared according to the capacities of controllable loads.
The droop characteristics of EWHs for AC bus voltage are shown in Fig (4). When
the AC bus voltage rises, the droop characteristics are configured such that the bigger the
capacity. When the DC bus voltage rises, the droop characteristics of batteries are configured
such that the bigger the capacity of battery is, the more the charging power of battery are.
Additionally, when the DC bus voltage falls, the droop characteristics are also configured
such that the bigger the capacity of battery is, the more the discharging power of battery are.
The droop characteristics of EWH and battery are presented by the following equations:
∗
ܸா = ܸௗ௖ − ܴா ‫ܫ‬ா (5)
∗
ܸா = ܸௗ௖ − ܴ஻ ‫ܫ‬஻ (6)

Fig 4 Droop characteristic of controllable loads
30


Where RE and RB are expressed by the following equations
௏∗
ܴா = ೎೘ ∆ܸௗ௖ (7)
௉ ಶೝ
∗
௏೏೎೘
ܴ஻ = ௉ಳೝ
∆ܸௗ௖ (8)
The grid side inverter control system with the feedback loop, here voltage and frequency
is maintained. Bus voltage and frequency maintained within the acceptable range by applying
power control of photovoltaic's and wind generator.

4. SIMULATION DIAGRAM

The Fig 5 shows the voltage and frequency fluctuations are reduced by Photovoltaics and
varying pitch angle of wind generator. In that wind turbine and photovoltaic are connected to
AC bus through the converter and inverter circuit the controllable load is connected to Ac
bus. When a big grid disturbance occurs, voltage and frequency fluctuate during transition
from emergency mode to islanding mode of a micro grid so we can control the power of wind
turbine and PV cell.

Fig 5 Simulink diagram

Thus the overall simulation diagram as shown in Fig 5. In this simulation model
consists of Solar and Wind power generation. And also hybrid inverter placed in the output of
the simulation diagram.
Fig 6 shows the Simulink diagram for Wind Power generation. In this simulation
consists of Wind Turbine, Asynchronous Generator and Controller.

31


Fig 6 Simulink Model for Wind Power Generation

And Fig 7 and Fig 8 shows Simulink model of Boost Converter and Simulink model
of inverter for Photo Voltaic in the Smart Grid system

.
Fig 7 Simulink Model for Boost Converter

PWM inverter model is shown in Fig 8. There are used six IGBT switches in normal
PWM inverter.

Fig 8 Simulink Model for Inverter for PV

5. RESULTS AND ANALYSIS

From the simulation model, PV array generating 22V after that 22V boosted to 257V
using boost converter and wind turbine output 440V, the output of the boost converter DC
voltage, DC voltage converted into AC .Finally PV generating voltage and wind turbine
generating voltage are integrated to grid so we can avoid the voltage and frequency
fluctuation in the grid.

32


Fig 9 shows the output voltage of Photo Voltaic Cell. It generates 22.265 V.

Fig 9 Output of PV Cell

Thus the input voltage of 22.265 V to the boost converter. This is shown in Fig 10.

Fig 10 Input of Boost Converter
Output of the boost converter output voltage is shown in Fig 11. It produces 257. 5 V
and given to the normal PWM Inverter.

Fig 11 Output of Boost Converter

Wind generator generates 440 V. This is shown in Fig 12.

Fig 12 Wind Turbine Output Waveform

33


Fig 13 Output Waveform
The Fig 13 shows the overall output waveform. After integration of solar and wind
turbine the deviation of output voltage can be reduced. By controlling the pitch angle and
boosting of PV system.

6. CONCLUSION

Due to big disturbance in a micro grid, voltage and frequency fluctuation occurs
during transition from emergency mode to islanding mode. The AC bus voltage and
frequency fluctuation is suppressed considerably by the use of renewable energy sources,
such as wind turbine and PV array. Voltage and frequency fluctuations caused are reduced by
applying power control of photovoltaic and varying pitch angle of wind generator. Stable
power supply can be achieved even during islanding operation.

REFERENCE

[1] Tomonobu Senjyu, Ryosei Sakamoto, “Tatsuto Kinjo, Katsumi Uezato, and Toshihisa
Funabashi, “Output Power Leveling of Wind Turbine Generator by Pitch Angle Control
Using Generalized Predictive Control”, The Papers of Joint Technical Meeting on Power
Engineering and Power Systems Engineering, IEE Japan, PE-04-77/PSE-04-77, pp. 17-
22, 2004. (in Japanese)
[2] Tomonobu Senjyu, Tatsuto Kinjo, Katsumi Uezato and Hideki Fujita, “Terminal Voltage
and Output Power Control of Induction Generation by Series and Parallel Compensation
Using SMES”, T. IEE Japan, vol. 123-B, no. 12, pp. 1522-1529, 2003. (in Japanese)
[3] Youichi Ito, Zhongqing Yang, and Hirofumi Akagi, “A Control Method of a Small-Scale
DC Power System Including Distribution Generators”,T. IEE Japan, vol. 126-D, no. 9,
pp. 1236-1242, 2006. (in Japanese).
[4] E. B. Muhando, Tomonobu Senjyu, Atsushi Yona, Tatsuto Kinjo, and Toshihisa
Funabashi,
[5] “Disturbance rejection by dual pitch control and self-tuning regulator for wind turbine
generator parametric uncertainty compensation ”, IET Control Theory And Applications,
vol. 1, pp. 1431-1440, 2007.
[6] Ming Yin, Gengyin Li, and Ming Zhou, “Modeling of the Wind Turbine with a
Permanent Magnet Synchronous Generator for Integration”, IEEE Trans. on Power
Electronics, vol. 6, no. 25, pp. 903-911, 2007.
[7] Tomonobu Senjyu, Ryosei Sakamoto, Naomitsu Urasaki, Toshihisa Funabashi, Hideki
Fujita, and Hideomi Sekine, “Output power leveling of wind turbine generator for all
operating regions by pitch angle control”, IEEE Trans. on Energy Conversion, vol. 21,
no. 2, pp. 467- 476, 2006.

34


[8] De Battista, H., Puleston, P.F., Mantz, R.J., and Christiansen, C.F., ‘Sliding mode
control of wind energy systems with DOIG – power efficiency and torsional dynamics
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K.Raja received B.E (Electrical and Electronics) & M.E (Power System) in
2010and 2012, respectively. Now he is working as an Assistant Professor in
Knowledge Institute of technology in the Dept of Electrical and Electronics
Engineering. His areas of interest are Power-Electronic applications in
Renewable Energy Systems, Hybrid Renewable Systems, Isolated Wind Electric
Generator and Power Quality.

I.Syed Meer Kulam Ali was born in Tamil Nadu, India. He received B.E degree
in Electrical and Electronics Engineering and M.E degree in Power System
Engineering in Anna University Chennai. Now he is working as an Assistant
Professor in EBET Group of Institutions, Tirupur in the Dept of Electrical and
Electronics Engineering. His areas of interest are Power Electronic and its
applications, Renewable Energy Systems and Power System.

P.Tamilvani was born in Tamilnadu, India. She received B.E degree in
Electrical and Electronics Engineering in Bharathiyar University and M.E degree
in Power Electronics and Drives in Anna University Coimbatore. Now she is
working as an Assistant Professor in EBET Group of Institutions, Tirupur in the
Dept of Electrical and Electronics Engineering. Her areas of interest are Power
Electronic and its applications and Renewable Energy Systems.

K.Selvakumar received B.E degree in Electrical and Electronics Engineering
in Anna University Chennai and he pursuing the M.E degree in Power System
Engineering in KSR College of technology, Tiruchengode. He is
currently working as a Assistant Professor in Muthayammal Engineering
college, Rasipuram. His research interests include Unit Commitment, Economic
Dispatch, Power System Optimization and smart grid, Distributed generation in
power system.

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Wind and solar integrated to smart grid using islanding operation

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