PV Emulator: New Designing & Testing Approach

To achieve the target of solar generation by 2022, the approach and methodology opted should be made faster, efficient and cheap. PV Emulator is contributing towards this by providing an easy platform for testing and designing in dynamic conditions along with less space and capital requirements…

Electricity generation from the Photovoltaic (PV) systems is a major renewable energy source as it involves zero greenhouse gas emission and no fossil fuel consumption. India is a tropical country where sunshine is available for longer hours per day and in great intensity. This provides an added advantage to solar energy in India. Various renewable power projects using different forms of energy like wind energy, biomass energy; hydro power and hybrid systems are being established in the country to meet the energy requirements of isolated communities and areas which were still not electrified. India’s renewable energy sector is amongst the world’s most active players in renewable energy utilization, especially, solar and wind electricity generation. The broad aim of Ministry of New and Renewable Energy (MNRE) is to develop and deploy new and renewable energy for supplementing the energy requirements of the country. As of October 2017, the country’s solar grid had a cumulative capacity of 15.60 GW. India has shown tremendous improvement in this sector by increasing its solar generation capacity from 2,650 MW (as on 26 May 2014) to 12,289 MW (as on 31 March 2017). The average current price of solar electricity has dropped to 18% below the average price of its coal-fired counterpart. Indian government targets to plans of producing 100 GW of solar capacity including 40 GW from rooftop solar by 2022. The improvements in solar power technology in recent years have helped in spreading awareness and adopting efficient ways to lower prices.

  As per the data collected in 2016, the top five countries with their installed solar power capacity ratings (in descending order) are:

• China (78.7 GW)
• Japan (42.75GW) 
• Germany (41.22GW) 
• United States (40.3GW)
• Italy (19.27GW)

  India ranked seventh with capacity of 9.01GW. But in June 2017, China and India have taken over as the leading developers of large scale solar projects. The top five largest power plants of world are Tengger Desert Solar Park (1500MW) China, Datong Solar Power Runner Base (1000MW) China, Kurnool Ultra Mega Solar Park (900 MW) India, Longyangxia Dam Solar Park (850MW) China, Kamuthi Solar Power Project (648 MW) India. As per reports till date, the world’s largest solar power park is located in the Kamuthi, Tamil Nadu, India.

  Governments around the world have recognised the need of sustainable sources for electrical energy production. One of the reasons of PV technology gaining popularity is the incentives provided by the governments across the globe. The introduction of regulatory policies has broadened the research area of PV solar interconnection. Increasing interests in solar power have made PV systems a promising alternative to conventional energy sources. PV systems are interfaced with power electronic components to enable its interconnection to the power system network and are explored to attain the advantages of lower carbon emissions and decreasing capital investment. However, research conducted on them encountered sensitive issues related to high price coated for purchasing photovoltaic panels including designing and testing issues. One of the alternatives to such problems is PV Emulator.

  PV Emulators have current voltage (I-V) characteristics similar to that of real PV generator. Several studies for emulating the I-V characteristics of PV systems have focused on using different power converter topologies. A PV Emulator is required to study new PV inverters and MPPT tracking algorithms in the laboratory to improve their performance under varying conditions. They are less bulky and provide a good alternative to installation area problem which is a prime concern due to increasing population. Moreover, Emulators are independent of weather conditions thereby, making them more reliable and cheap. The total capacity of PV systems is not firm, because of the unreliable nature and changing behaviour of PV systems.
Few problems faced by existing PV panels include:

• Requirement of large space for installation.
• Dependence on weather conditions
• Big budget requirement for onsite testing process
• Selection of panel among large variety of available choices of solar panels.

  Figure 1 represents the basic block diagram of PV Emulator with converter for increasing or decreasing the output voltage according to applied load and application. The output power of PV system is highly dependent on random and uncontrollable meteorological conditions, therefore, the use of an actual PV system for research, investigation concerning problems with power management as the MPPT testing, interfacing the PV generator to the grid and load is difficult.

  Keeping this in view, researchers are focussing on PV Emulators.

Approaches for Designing of a PV Emulator

  There are three widely used approaches for designing PV Emulator:

• Use of the equivalent circuit of PV generator: It comprises of power devices, resistors and diodes. The performance of diode is badly affected due to dissipated power thereby, requiring an efficient cooling system.
• Practically exposing photovoltaic cell to a source of light under adequate conditions of Temperature and Irradiation: It is efficient for low power levels as factors like heat dissipation and size of testing setup results in difficulties at high power applications.
• Utilizing the modern power electronic components: The power supplies are based on converter controllable power like DC-DC converters and this is most efficient way among all approaches. DC-DC converters together with maximum power point tracking systems (MPPT) are used to avoid losses occurring due to mismatch in characteristic curve and load line.

  Different converters used in emulators include Buck, Boost, Buck-Boost, Cuk, Sepic, Zeta etc. PWM with P, PI, PID perform well for fixed switching frequency and small signals. An Emulator can reproduce different desired characteristics quickly with no extra cost by just making some minor changes in controller. The controllers of Emulator reported in literature include Sliding Mode Controller that are robust with respect to load and has better dynamic response compared to other controllers, Voltage and Current Control Mode, some non-linear controllers include Hysteresis Controller which requires devices to sense input voltage variations, Fuzzy Logic Controllers, Lyapunov based for regulation of duty cycle. It is also utilised to assess the stability of controller. Mathematical expressions also provide alternative to obtain the characteristics of desired panel using State Space Approach.

Conclusion

  To achieve the target of solar generation by 2022, the approach and methodology opted should be made faster, efficient and cheap. PV Emulator is contributing towards this by providing an easy platform for testing and designing in dynamic conditions along with less space and capital requirements. Emulators employing artificial intelligence techniques for controller or memory storage device is a new area to be explored for better results.


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