The role of Power Electronics in Photovoltaic Power Generation Systems Lecturer: Prof. Dr. Mário L. da Silva Martins. Federal University of Technology -Parana 1
Outline: Motivation: World Energy Outlook; Energy and Environment. Renewable Energy: Renewable Energy Outlook; Future Energy Systems. Photovoltaic Energy: Photovoltaic Basics; Photovoltaic Systems. Some conclusions. 2
Motivation Conceito: O que é? 3
World Energy Outlook: Energy production and use is fundamental to modern, industrialised economies, and supports all economic activity. Energy is used to move vehicles, heat homes, and power industry. In the industrial sector, final energy consumption has been falling slightly in OECD countries, (shift from industrial manufacturing to services). The commercial and residential sectors are continuing to increase their energy use, with greater use of electrical goods, more floor space per capita, and higher levels of cooling and heating comfort. 4
World Energy Outlook: Nowadays there is a huge energy consumption and growing demand. High levels of economic growth in the new giants of the world economy. China and India together account for nearly half of the entire growth in world energy demand. By around 2010, China will overtake the United States to become the world s largest consumer of energy. 5
World Energy Outlook: Share of China and India in Incremental Energy Demand (2000-2006) 50% 85% 35% 6
World Energy Outlook: Increase in World Primary Energy Demand by Fuel Perspective 2005-2030 100% 50% 7
World Energy Outlook: The most important trend in energy production over the last few decades has been the rapid increase in the share of energy from electricity. This is partly the result of increased growth in the electricity-intense residential and commercial sectors. Furthermore, there has been a shift in all sectors to greater electricity use. This reflects the wide range of uses of electricity, its flexibility, safety and cost. 8
World Energy Outlook: Electricity Demand and Generation 15 016 TWh in 2005 29 737 TWh in 2030 9
World Energy Outlook: China and India need to sustain a phenomenal rate of economic growth. There are still over 400 million people in India without access to electricity. Access to clean burning fuels for cooking and space heating in rural China is still very limited. The aspirations of a burgeoning middle class are driving social and economic change. 10
World Energy Outlook: Per-Capita Primary Energy Demand in China, India and Other Selected Countries (2005) 8toe <1.5toe < 0.5toe 11
World Energy Outlook: There can be no moral grounds for expecting China and India selectively to curb their economic growth simply because world energy demand is rising unacceptably, with associated risks of supply interruptions, high prices and damage to the environment. These are global problems to be tackled on a global basis. 12
Energy & Environment: lectricity Idealized energy-depletion curves of the world. Electricity generation by fuel types for selected countries. 200 13
Energy & Environment: Energy production and use can affect the environment in many ways, with very diverse impacts from different fuel sources. Table 1. Contribution of energy use to air pollutants. Air pollutant SO 2 Transport 4% Electricity production 23% NO 2 52% 28% CO 85% 2% Particulates 17% 12% The power sector is the dominant source of SOx emissions, where coal use is highest. Ecosystems impacts: acid rain! Coal extraction: land degradation! 14
Energy & Environment: Per capita CO 2 emission vs. population of some selected countries (2004). 50 years Global fossil fuel CO 2 emissions. 15
Energy & Environment: Long-term effect of global warming: The gradual melting of the world s glaciers and polar ice caps will inundate low-lying areas of the earth. Severe droughts in tropical countries near the equator, such as Africa and India. The circulation of more air with heavy moisture will cause more hurricanes, tornados, heavy rains, and floods. Some animal species (such as polar bears, penguins, and corals) will gradually become extinct. RENEWABLE ENERGY. 16
Renewable Energy Conceito: O que é? 17
Renewable Energy Outlook Definition: Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are naturally replenished. Renewable energy replaces conventional fuels in four distinct areas: Power generation; Heating (water / space); Transport, and Rural (off-grid) energy services. The most explored: Hydro-electric; Photovoltaic; and Wind. 18
Renewable Energy Outlook Annual growth rates of electricity generation sources (world). Source: REPP, Worldwatch 1998/99. Future electricity generation = wind and solar PV 19
Future Energy Systems: Renewable energy systems involve many aspects: Efficiency (production & conversion); Reliability and cost of the energy conversion; Capability to forecast energy production; Safe connection to the electric grid (microgrids); Efficient energy storage and transport (low environmental impact); and, Development of advanced control and monitoring algorithms; Distributed Generation 20
Future Energy Systems: Distributed Generation RESs cannot directly replace the existing electric energy grid technologies. RESs will gradually be infused into existing grids. 21
Future Energy Systems: Sources Loads Power Electonics Energy network Communication network 22
Future Energy Systems Power Electronics Buildig BLocks The Smart Grid model. 23
Future Energy Systems Why PEBB? Connecting hundreds and thousands of RESs to the utility network introduces different dynamics to the system. If the distributed sources are not properly controlled, the grid can become unstable and even fail. The Smart Grid model. 24
Future Energy Systems Why PEBB? This challenge is solved by electronic power converters that handle two main tasks: Maximum Power Transfer and Power Limit. Active/Reactive Power Control and Power Quality Control. 25
Future Energy Systems PEBB tasks: On the input side (Source): Power Electronics control and transform the load characteristics so that maximum power is extracted from the source. On the grid side: Power Electronics must control active power injection even in view of contributing to frequency control ensure low harmonic content (THD), low electromagnetic interference (EMI), and low leakage current. 26
Photovoltaic Energy Conceito: O que é? 27
Photovoltaic Basics History Edmond Becquerel (1839) Bell Laboratories (1954) Solar Cell Space applications since 1958 Solar Pannel Global energy (oil) 1973 Solar PV as energy source. 28
Photovoltaic Basics Modeling of the Solar Cell Semiconductor PN junction Elecrons/holes mobility Solar Cell electric model ( ) I = I I + I L D Sh Math model 29
Photovoltaic Basics Operation and Characteristics (i x v) Irradiance dependence Temperature dependence I Irradiation V Temperature 30
Photovoltaic Basics Power and Characteristics Solar Cell: P V = 1 2W = 0.5 0.6V MPP varies during the day. To enhance the power an array with several cell is required. 31
Photovoltaic Basics PV Modules: One silicon solar cell produces about 0.5 volt. Modules are arrangement of solar cells connected in series that produces about 18 volts at (60 to 300 W). Module is the basic building block of PV systems. Monocrystalline modules. Multicrystalline modules. Thin film (Amorphous) modules. PV module. 32
Photovoltaic Basics PV Arrays Individual modules can be connected in series, parallel, or both to increase either output voltage or current. This also increases the output power. Circuit diagram of the PV array. 33 Flexibility in power capability
Photovoltaic Basics Partial Shading Partially shaded conditions is quite common (e.g., due to clouds, trees, etc.) Reduces the effectiveness of the MPP tracking (MPPT) schemes. Damage the module due to hot spot phenomenum. MPP Local MPP Nonideal Characteristic curve. 34
Photovoltaic Systems PEBB tasks: MPPT Maximum Power Point Tracker Means that the PV generator is always supposed to operate at maximum output voltage/current rating. In principle, a MPPtracker is a dc/dc converter that sets the solar generator to operate at MPP independently of the load. Its main function is to adjust the panel output voltage to a value in which the panel transfers maximum energy to the load. 35
Photovoltaic Systems PEBB tasks: MPPT Maximum Power Point Tracker The two most frequently used MPPT algorithms are perturb and observe (P&O) and incremental conductance (IC). Measured variables 36
Photovoltaic Systems PEBB configuration: Stand Alone Grid Connected PV battery systems Only PV systems PV hybrid systems PV battery systems 37
Photovoltaic Systems Stand Alone Series configuration Grid Connected Parallel configuration Single-stage configuration PEBB config.: Parallel Single-stage Series 38
PEBB config.: Photovoltaic Systems Stand Alone Grid Connected Decentralized Centralized Team concept Multi-string String Module integrated 39
Photovoltaic Systems MPPT stage Voltage Gain issue Grid Connected Boost converter with voltage multiplier Boost converter with coupled inductor 40
Photovoltaic Systems MPPT stage Voltage Gain issue Grid Connected Integrated Boost-flyback converter 41
Photovoltaic Systems MPPT stage Efficiency issue Grid Connected Decentralized Multi-string 42
Photovoltaic Systems MPPT stage Efficiency issue Grid Connected Decentralized Multi-string 43
Photovoltaic Systems Inverter stage Control issue Syncronization (PLL) Active/Reactive Power Control THD voltage Islanding 44
Photovoltaic Systems Inverter stage Efficiency/ weight issue In PV transformerless systems, the switching converter has to be designed not only for high efficiency and low THD but also to guarantee low ground current injection. It is required to avoid the current circulation from DC bus to the load during the output voltage zero state. 45
Photovoltaic Systems Inverter stage Efficiency issue Operate with a lower switching frequency (lower losses). Lower dv/dt stress. Generate smaller CM voltage. Hybrid NPC 9-level output voltage 46
Photovoltaic Systems Inverter stage Hybrid Output voltage Low freq. Low freq. High freq. 47
Photovoltaic Systems Semiconductors S i C have a high potential for enhancements of the efficiency of PV systems. On state resistance x Rated Voltage 48
Some Conclusions Conceito: O que é? 49
Some Conclusions: 50
Some Conclusions: System level chalenges: Maximum Power Transfer and Power Limit. Active/Reactive Power Control and Power Quality Control. Component level chalenges: Efficiency Voltage-gain Performance Low cost 51
Thanks to: G r u p o d e P e s q u i s a e m Análise e Processam ento de Energia 52