iesl/pub/guide/01
A SMART CONTROL SYSTEM BETWEEN DIFFERENT RENEWABLE ENERGY SOURCES WITH MAXIMUM POWER POINT TRACKING Lankapura L.N.T, Lansakara M.W.N.S, Navoda K.K., Weerasekara W.M.W. Abstract: Due to the ever increase in price of Electricity, many countries are switching to Renewable sources of Energy. Energy from Sun in the form of Solar, Wind and Bio mass Energy can be used by any electricity consumer in Sri Lanka. With the Net Metering approved by the CEB high end Domestic consumers and all Commercial consumers will benefit by installing such renewable energy systems connected to the grid through an interface which will maximize the energy from these installed through a SMART system. Hear is described the designing, making and testing of such a system. The fetching the optimal energy is based on Maximum Power Point Tracking concept and the project was implemented for solar power generation. Considering the parameters the panel Voltage, insolation and ambient temperature an algorithm was prepared to adjust the output to fetch maximum power. The battery could be charged by the three renewable sources and is connected through the inverter and a power management system. If renewable power source is not providing energy and if the battery is discharged then the system will shift to redundant grid supply. Keywords:
Solar, MPPT, Irradiation, Tidal
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iesl/pub/guide/01
1. Introduction In modern living style, power needs are unlimited. Because of that energy demand increases day by day. Therefore, supply has to be increased. With the demand for energy increasing around the world, it was recognized the need for using renewable energy like solar, wind, tidal wave and bio mass. It is essential to connect those sources together to the grid . In order to provide smart power supply and smart power management of the grid the maximum power has to be fetched to load and control the switching power sources.
2.
Problem Statement and Proposed System
Renewable power mainly depends upon the variation of the environmental conditions. A major problem with renewable energy such as wind and solar power is that supply is often intermittent, causing fluctuations on the grid system. So it is not possible to get constant power
output from renewable sources. Because of this problem it is necessary to have a power storage system. Not only that but also the power produced in the renewable source is not effectively passed to the load, some percentage mostly which less than half of the produced power is effectively sent to take the load. Project was to find solutions to these main two problems. Since this project has to be “Smart" it introduced that all the renewable power sources should connect through the MPPT to fetch the effective power potion for load and the power controlling system was developed to keep a smart power management system between the renewable power sources. Figure 1 shows the block diagram of the project scope.
3.
Maximum Power Point Tracking (MPPT)
There are several methods of MPPT methods which are used to collect the available maximum power to the load. In this project the method used was the P&O algorithm. That operates by periodically perturbing terminal voltage or current and comparing the PV output power with that of the previous perturbation cycle. If the PV array operating voltage changes and power increases (dP/dVPV>0), the control system moves the PV array operating point in that direction; otherwise the operating point is moved in the opposite direction. In the next perturbation cycle the algorithm continues in the same way [1]. A common problem in P&O algorithm is that the array terminal voltage is perturbed every MPPT cycle; therefore when the MPP is reached, the output power oscillates around the maximum, resulting in power loss in the PV system. This is especially true in constant or slowlyvarying atmospheric conditions [2].
Figure 1- Block Diagram of the Smart power to a load
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4. Solar Power MPPT System
The power of the PV module depends upon the specific solar radiation, ambient temperature and the panel voltage. The power of the PV module given by a fourth order polynomial function [3], PPV = P1VPV4 + P2VPV3 + P3VPV2 + P4VPV+P5 (1) Here, Ppv - Power of the PV module Vpv – Voltage of the PV module P1, P2, P3, P4, P5 – Coefficients depending upon the Properties of the panel. The cell temperature can be calculated by sun radiation and ambient temperature. The cell temperature is given by [3][4], T
cell
= T
ambient
+
(2) Here, T cell – Cell Temperature T ambient – Ambient Temperature NOCT The nominal operation condition temperature (NOCT) which is the temperature of the cell at 800W/m2 and 0 20 C ambient temperature. I - Irradiation Level
iesl/pub/guide/01 So the Coefficients P1, P2, P3, P4, P5 are given by the functions of cell temperature Tcell [3], P1 = 5.75*10-7 T cell 2 -2.3*10-5 T cell - 2.1*10-3 (3) P2 = -4*10-5 T cell 2 +1.17*10-3 T cell - 0.101 (4) P3 = 7.25*10-4 T cell 2 -1.26*10-2 T cell – 1.9 (5) P4 = -4.1*10-3 T cell 2 +2.37*10-2 T cell +19.35 (6) P5 = 4.18*10-3 T cell 2 +3.4*10-2 T cell – 12.4 (7) The rated values of the PV module are given in the data sheet of the particular PV panel. The rated voltage and NOCT are taken from the datasheet and the cell temperature and the coefficients are calculated by using above equations [3].
5. Power Management System Since the renewable energies are not 100% reliable power sources, there should be a power management system which sense the power level and operates according the state of the power sources. When at the discharged state of the battery which is charged by a renewable source may not able to provide sufficient
power to the load through the inverter, to provide a reliable and continuous supply to the load this project introduce a smart power controlling system based on power electronics which may able to switch to another power source. (the grid)
In order to obtain the maximum power point the boost converter was designed to fetch the power from PV panel. To determine an optimum PV voltage at which the PV power is equal to its maximum value, from the fourth order polynomial function, the condition is,
(8) Therefore the obtained function is, P1VPV3
+
3P2VPV + 2P3VPV+ P4 =0 2
Figure 2- Block Diagram of the Power Management System
The PV module’s voltage, ambient temperature and sun radiation were sensed by the sensor circuits and the sensor output is an input to the controller and by using above equation determine the dPpv/dVpv value. If it is equal to zero, it means that the PV generator is operated at its optimum voltage whereas if it is greater than zero, the process of searching the optimum voltage is repeated by incrementing or decrementing the PV voltage with a constant, set at a value of 0.5. After finding the optimum PV voltage, the
The system is consists with battery charge level indicator, when the battery level indicator indicates low charge level of the battery to the micro controller and it generates a signal to operate relays as shown on the figure 2. Then one relay operates and cuts the power to the inverter from the discharged battery and another relay operates and switches the other power source to the inverter.
6. Performance Analysing 3
optimum duty cycle is calculated for the boost converter. The duty cycle (D) of the boost converter is given by, D=1(9) Here Vin and Vout are respectively the input and output voltages of the boost converter. The boost converter fetches the current from the available maximum power of the PV at particular radiation level and ambient temperature. Then passing through a charge controller circuit the power feeds to a battery. The implemented boost converter is shown in the figure 3.
Figure 3- Boost Converter Circuit The system component ratings and electronic design depends upon the ratings of the input sources. The system that was
iesl/pub/guide/01 implemented is for a panel with the ratings of maximum power 120W and the optimum operating voltage and current and 17.2V and 6.98A respectively. This system cost was about Rs.18000 ($145) with component costs in Sri Lanka. Figure 4 shows the final hardware outcome of the whole project.
project. According to the calculated efficiency of solar power outputs for with MPPT controlling system and without MPPT it can be seen that the efficiency of the power delivered to the load is increased by the system which is with MPPT controlling method. Before connecting to the inverter it is needed to have a controlling system to manage the power sources according to the available power of the renewable to keep a reliable supply to the load. Mainly this system can be implemented in domestic and industrial consumers places. Finally, this can be introduced as a best power solution for the power shortage problems to the present situation of the worlds energy.
Figure 5: The Graph of Power Efficiency Vs Time for the System with MPPT and without MPPT Systems
Figure 4: Smart Solar Power Generation System
7. Testing Results During the MPPT controller testing, the solar radiation, ambient temperature, panel output voltage, output current and boost converter voltage were measured. The values were taken during 1200h to 1300h on a sunny day. The efficiency of the system with MPPT and without MPPT is given in Figure 5.
According to the graph in figure 5 it can be seen by Square pointed curve the panel average power efficiency without MPPT system was around 71.4% and by considering dotted line curve the average power efficiency with MPPT was 92.9%. Therefore, since the power efficiency without MPPT is less than the power efficiency with MPPT this is a smart and effective implementation in power generation.
8.
References 1.
Conclusions
A MPPT system for solar power generation which works according to the variation of the sun irradiation, ambient temperature and panel voltage was developed in this
2.
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T., Kerekes &
R., Teodorescu, “MPPT algorithm for voltage controlled PV inverters”, IEEE TRANSACTI ONS ON POWER ELECTRONI CS, pp.21, 2008. N.,
K.,
Sooriyaarachc hi, N., S., D., B., Liyanage,
P., A., G., Abenayaka & S., G., Abeyrathne “Comparative analysis of speed of convergence of MPPT techniques” IEEE TRANSACTI ONS ON POWER ELECTRONI CS, pp.04, 2011. 3.
Tamer, T., N., Khatib, A.,
Mohamed & N., Amin “An Efficient Maximum Power Point Tracking Controller for Photovoltaic Systems Using New Boost Converter Design and Improved Control Algorithm” pp.1-8, 2009. 4.
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