Solar based grid tie integration system for efficient power management

International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS-2017)

Solar based Grid Tie Integration System for Efficient Power Management R. Vaira Vignesh

T. Abinaya (Corresponding author)

Department of Mechanical Engineering, Department of Electronics and Communication Engineering, Amrita School of Engineering, Coimbatore, Nadar Saraswathi college of Engineering & Technology, Amrita Vishwa Vidyapeetham, Amrita University, India. Affiliated to Anna University, Chennai, India. [email protected] [email protected] T. Muthu Vijayan Robert Bosch Engineering and Business Solutions, Coimbatore, India.

Abstract— Solar power is currently been used in many commercial applications such as solar water heaters, solar pumps, stand-alone solar powered houses etc. The extensive power of the Sun can be used for power generation with the help of solar cells. The power demand in our country is at its peak level and will tend to increase in the upcoming days. This project mainly focuses on the conversion of excessive solar energy into useful power to eliminate the power scarcity, where the solar power can be converted into electricity and can be synchronized with the grid. The solar power is trapped with the help of solar cells, which will produce a DC voltage. This DC voltage will be converted into AC using IGBT based three phase six pulse inverter. Filters are used to remove the higher order harmonics present in the signal inverter output signal. This filtered AC voltage can be synchronized with the grid through Phase Locked Loop (PLL) base control system. Keywords— Solar cells, Grid, Dc chopper, Phase Locked Loop

I. INTRODUCTION A. Solar Energy Solar energy is an important source of renewable energy and its technologies are broadly characterized as either passive solar or active solar depending on the way they capture and distribute solar energy or convert it into solar power. Active solar energy methods like the photovoltaic systems, concentrated solar power and solar water. Solar energy in one form or another is the source of nearly all energy on the earth. Passive solar like a building to the Sun, selecting materials with suitable thermal mass or light dispersing properties, and designing spaces which circulate air in the atmosphere. Photo Voltaic (PV) devices directly convert the incident solar radiation into electricity. It does this process with noiseless, pollution, makes them robust, reliable and long lasting. Photo voltaic is a simple and elegant method which harnesses the sun's energy.

B. Grid Tie Systems A grid-connected power system is connected to the utility grid which generates solar PV. A grid connected system consists of solar panel, power condition unit, electronic converters and grid synchronizer. It also includes integrated battery. Based on their utility they are classified into small residential to commercial rooftop. It gets connected to the utility grid and perfectly connected it supplies excessive power. Photovoltaic wattage may be less than average consumption, whereas the consumer will purchase grid energy. They can feed excess power to the grid A meter is fixed to monitor the transfer of power is done through feedback. Gridconnected rooftop systems which have a capacity less than 10 kilowatts can meet the load of most consumers. Depending on their expectation with their local grid energy company, the consumer needs to pay the cost of electricity which is consumed less the value of electricity generated. This will be a negative number if more electricity is generated than consumed by the company. II. SOLAR CELLS A solar cell is an electronic device which directly converts sunlight into electricity. It also produces both a current and a voltage to generate electric power. Here this process makes the absorption of light which raises an electron to a higher energy state, and this movement makes the higher energy electron from the solar cell into an external circuit. The electron then dissipates its energy in the external circuit and returns to the solar cell. The basic operation of a solar cell and its arrangement is shown in Fig 2.1. It generates light generated carriers and generation of voltage across solar cells. The requirements for photovoltaic energy conversion satisfy the process and variety of materials.

978-1-5386-1887-5/17/$31.00 ©2017 IEEE

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International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS-2017) generated current. Voc is found by setting the net current equal to zero in the solar cell equation which is given by (2)

D. Fill factor The fill factor is defined as the ratio of the maximum power from the solar cell to the product of Voc and Isc. It is a parameter which determines the maximum power from a solar cell. While it is in combination with Voc and Isc, It determines the maximum current and voltage from a solar cell. However, at both of these operating points, the power from the solar cell is zero and it is a measure of the squareness of the solar cell and is also the area of the largest rectangle which will fit in the IV curve. The IV characteristics of Fill Factor is shown in Fig 2.2

Fig 2.1 IV curve of a solar cell showing the short circuit current and open circuit voltage. A. IV Curve The IV curve of a solar cell is the superposition of the IV curve of the solar cell diode with the light-generated current. The light shifts the IV curve down into the fourth quadrant where power can be extracted from the diode. The diode law becomes by illuminating a cell adds to the normal dark currents in the diode so that:

Fig. 2.2 Characteristics showing Fill Factor Since fill factor is the measure of squareness then solar cell with larger voltage is preferable and the less area is occupied by the rounded space. The Fill Factor can be determined theoretically from a solar cell by differentiating the power from a solar cell with respect to voltage where this is equal to zero. (3)

(1)

(4)

where IL = light generated current B. Short Circuit Current When the voltage across the solar cell is zero then the shortcircuit current is produced through the solar cell. The shortcircuit current is as ISC and shown on the IV curve is shown in Fig 2.1. For an ideal solar cell at most moderate resistive loss mechanisms, the short-circuit current. The short-circuit current is due to the generation and collection of light-generated carriers which is identical. Therefore, the short-circuit current is the largest current which may be drawn from the solar cell. The short-circuit current depends on a number of factors which are area of the solar cell, number of photons, spectrum of the incident light. C. Open circuit voltage The open-circuit voltage, denoted as VOC, occurs at zero current and it is the maximum voltage available from a solar cell. It corresponds to the amount of forward bias on the solar cell due to the bias of the solar cell junction with the light-

(5) where Voc is defined as a "normalized Voc" The above equation explains that the fill factor will be higher only at higher voltage. The FF will be lower due to the presence of parasitic resistive losses. Therefore, the FF is most commonly determined from measurement of the IV curve and is defined as the maximum power divided by the product of Isc*Voc. E. Efficiency Efficiency is defined as the ratio of energy output from the solar cell to input energy from the sun. In addition to reflecting the performance of the solar cell itself, the efficiency depends on the spectrum and intensity of the incident sunlight and the temperature of the solar cell. The efficiency measured must be carefully controlled in order to compare the performance of one

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International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS-2017) device to another. The efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity and it is given by

characteristics of converters improve with increasing operating frequencies. A. Functions of DC-DC converters The functionalities of a DC – DC converter are as follows.

(6)

• Used to step up or step down the input DC voltage based on the duty cycle ratio.

(7)

• It regulates the DC output voltage against fluctuation in load and line variations.

Where Voc isopen circuit voltage, Isc is short-circuit current, FF is fill factor , Ș is efficiency

• Reduces the voltage ripples on the dc output voltage below the required level. • Provides isolation between the input source and the load B. Step-up or Boost converter It consists of DC input voltage source VS, boost inductor L, controlled switch S, diode D, filter capacitor C, and load resistance R. The circuit diagram of boost converter is given below in Fig 3.1. When the switch S is in the ON state, the current in the boost inductor increases linearly and the diode D is off at that time. When the switch S is turned OFF, the energy stored in the inductor is released through the diode to the output RC circuit.

Fig 2.3 Array of solar cells connected in Series

Fig 3.1 Step-up or Boost Converter

Fig 2.4 IV and PV characteristics of the Solar Array III. DC CHOPPER The output from the solar array is a variable DC and based on the solar irradiance of the cell the variable DC has to be converted to a fixed DC. Since the Inverter needs a fixed DC for its proper and a long term operation, DC-DC chopper is used to convert the varying DC output of the solar cell into a fixed DC quantity. Electronic devices operate in their active (linear) mode at higher power levels switching regulators in linear regulators. It works based on a voltage or current divider, which is inefficient because they are limited to output voltages than the input voltage, and also their power density is low because they require low frequency line transformer. Switching regulators can achieve high energy conversion efficiencies. So they use power electronic switches and their modes are on and off state. If the operating frequency is higher then, the transformers, filter inductors, and capacitors will be lighter. Switching regulators use power electronic semiconductor switches in on and off states. Modern power electronic switches can operate at high frequencies. The higher the operating frequency, the smaller In addition, the dynamic

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Fig 3.2 Matlab – Simulink circuit for Boost Converter

Fig: 3.3 Output of Boost Converter

International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS-2017)

The main purpose of the inverter is to provide a three-phase voltage, where the amplitude, phase, and frequency of the voltages should always be controllable. sinusoidal voltage waveforms are used in most of the Industrial applications is shown in Fig 4.1. The output voltage and current from DC chopper need to be converted into AC quantities, so the output is fed to the Inverter. A. Matlab Simulation of Three Phase Voltage Source Inverter The voltage source inverter produces the output voltage as AC with the input as DC voltage source. The Inverter employed here is a three phase six pulse IGBT based voltage source inverter operating at 180 degree mode of operation. In this mode the IGBT switching happens exactly at 180 degree phase difference and the phase difference between the switches on the same arm will operate with a phase difference of 120 degrees.

Fig 3.4 Pulse Generator Specifications The chopper used here is to step up the input variable DC into fixed voltage at the output. The value of the output voltage depends on the duty cycle of the pulse generator that controls the switch. The boost converter is selected instead of BuckBoost and it is the output of the solar panel which is always less than the required voltage. If there is a higher voltage in the source side, then buck converters can be used. But the output of the solar panel never exceeds the load requirement. C. Booseter converter Using Matlab the Boost converter shown in Fig 3.2 is simulated as the Switching device and also the pulse generator of 100 kHz frequency. With the duty cycle of 50%, the output for the given circuit can be calculated. The capacitor and Inductor values for the given duty cycle and the input and output voltages can be calculated. The output voltage can be varied based on switching frequency and the duty cycle. The output image of boost converter is shown in Fig 3.3. The configuration of the converter can be changed with the help of the Pulse generator is shown below in Fig 3.4.

Fig 4.2 IGBT based 3 Phase Inverter The inverter is connected to the output from the DC chopper through the capacitors bridge. The output from chopper is a fixed signal. The life time of the inverter is extended as shown in Fig 4.2. B. Harmonics and Filter

IV. INVERTER

Fig: 4.3 Second Order Low pass filter

Fig 4.1 Three Phase Inverter

The fundamental component of waveform which have the frequency as integral multiples of the fundamental component is called the Harmonics.

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International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS-2017) The output of the filter will be in non-sinusoidal form. Second order low pass filter is shown in Fig 4.3. The two kinds of filters are active and passive. The passive filter can eliminate only one component, while the active filter can eliminate most of the higher order contents. Filters are used to eliminate the higher order harmonics to reduce total harmonic distortion. Passive filter is cost effective.

Fig 4.5(b) Output waveform after filter V. SYNCHRONIZATION Digital Phase lock loop (DPLL) used in communications and signal processing systems that require phase tracking and synchronization. The circuit can synchronize an inverter to the grid and also can re-gain synchronization and its phase, amplitude, or distortion of the grid voltage. There are many types and forms of DPLLs, and are normally classified according to the nature of the sampling process as uniform or non-uniform DPLLs. The non-uniform type of DPLLs has better acquisition time and less circuit complexity compared to the uniform type with a fixed time-delay unit as proposed in the time-delay digital tan lock loop (TDTL).

Fig 4.4(a) FFT analysis of the waveform before filter

The output from the inverter after filtering will be pure sinusoidal and it will be given to the grid. The grid frequency, voltage and phase must be compared with the inverter output and it will be synchronized with the help of a feedback loop that monitors and controls the synchronization.

VI. CONCLUSION Fig 4.4(b) FFT analysis of the waveform after filter The DC voltage output from the chopper is converted to sinusoidal AC voltage of 50 Hz power frequency using a six pulse inverter. Since the output from the inverter contains large amount of harmonics, it is filtered using a second order low pass passive filter. The FFT analysis of waveform before applying filter and after applying filter is shown in Fig 4.4(a) and 4.4(b) respectively. The output wave form of the filter is shown in above mentioned Fig 4.5(a) and 4.5(b)

The solar panel of given specification is modeled in Simulink and the characteristics obtained from the simulation for various levels of irradiance and load is matched with the characteristics of the given panel. The output voltage from the solar panel is fed to a boost DC chopper and a constant DC voltage output is obtained from the chopper. The DC chopper duty cycle is adjusted in a way that it provides a constant output with the varying solar output voltages. This autonomous system without batteries has resistive load. [1]

[2] [3]

[4] [5] [6]

Fig 4.5(a) Output waveform before filter

[7]

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REFERENCES B.K.Bose, “Global warming: Energy, environmental pollution, and the impact of power electronics,” IEEE Ind. Electron. Mag., vol. 4, no. 1, pp. 6–17, Mar. 2010. M.Malinowski, K. Gopakumar, J. Rodri Renewable Energy Policy Network, (2014, Apr.). Renewables 2014 global status report. B.J.Huang, ,W.L. Ding and Y.C. Huang, 2011 “Long-term field test of solar PV power generation using one-axis 3-position sun tracker” Solar Energy, Volume 85,Issue 9,Sept., pp 1935-1944 http://www.mathworks.inc/ Power Electronics’ by M. Rashid Synchronization of a renewable energy inverter with the grid’ by Nader Anani, Omar Al-Kharji AlAli, Mahmoud Al-Qutayri, and Saleh AL-Araji C.S.Chin, A. Babu, and W. McBride, 2011 “Design, modeling and testing of a standalone single axis active solar tracker using MATLAB/SIMULINK” Renewable Energy, Volume 36,Issue 11, Nov, PP 3075-3090

International Conference on Energy, Communication, Data Analytics and Soft Computing (ICECDS-2017) [8]

S.Ozcelik, H. Parkash, and R. Challoo, “Two-axis solar tracker analysis and control for maximum power generation,” Procedia Computer Science, vol. 6, pp. 457–462, 2011. [9] Lewis Fraas and Larry Partain, Solar Cell and its Applications, Wiley Publications, 2010. [10] A.Chikh and A. Chandra," An optimum Method for Maximum Power Point Tracking in Photovoltaic Systems", IEEE Power and Energy Society General Meeting, San Diego, CA, pp. 1-6, July 2011.

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