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Knowledge of micro inverter

Nov 02, 2020

Knowledge of micro inverter

In the design of solar photovoltaic grid-connected, the role of inverter is very important. The inverter can convert sunlight energy into direct current electric energy, and then through inversion to form single-phase alternating current electric energy suitable for all kinds of equipment.


  Inverter classification


   Based on different uses at present, inverters can be divided into two types, one is an independent power supply, and the other is a grid-connected power supply.


   According to the waveform modulation method, it can be divided into square wave inverter, step wave inverter, sine wave inverter and combined three-phase inverter.


   For inverters used in grid-connected systems, they can be divided into transformer-type inverters and transformer-less inverters according to the presence or absence of transformers.


  The background of the emergence of the new architecture


   At present, the most widely used photovoltaic system in the market is the centralized inverter. The so-called centralized inverter is to connect a solar photovoltaic cell in series to reach a high voltage direct current, which is converted to alternating current through the inverter. However, in photovoltaic power plants, solar photovoltaic modules, partial shadows, different tilt angles and orientations, dirt, different degrees of aging, small cracks, and different temperatures of different photovoltaic panels can easily cause system mismatch and reduce output efficiency. The shortcomings of this led to a significant reduction in the overall output power, so this has also become a difficult problem for centralized inverters.


   In order to solve this problem, new architectures of "micro inverter" and "micro converter" have appeared in recent years. Since each solar cell module is equipped with a micro inverter power supply, the overall output power is maximized by optimizing the output power of each module. Even if some of the panels are affected by shadows, dust coverage, etc., the inverter power optimizer can still track the best local MPP and recover more than 57% of the lost power generation. At the same time, the power optimizer converts the input voltage/current into different output voltages/currents to maximize the energy transfer in the system.


  Micro inverter definition


Micro-inverter technology proposes to directly integrate the inverter with a single photovoltaic module, and equip each photovoltaic module with an inverter module with AC/DC conversion function and maximum power point tracking function, and directly convert the electric energy generated by the photovoltaic module AC power is used by AC loads or transmitted to the grid.


   When one of the panels does not work well, only this [industrial electrical appliances network-cnelc] block will be affected. All other photovoltaic panels will run in the best working condition, making the overall system more efficient and generating more power. In practical applications, if the string inverter fails, it will cause the panels of several kilowatts to fail to function, and the impact of the failure of the micro-inverter is quite small.


   Several advantages of micro inverter


   1. Increase the power generation of each inverter power module as much as possible and track the maximum power. Since the maximum power point of a single module is tracked, the power generation of the photovoltaic system can be greatly increased by 25%.


  2. Adjust the voltage and current of each row of photovoltaic panels until they are all balanced to avoid system mismatch.


  3. In addition, each module has a monitoring function, which reduces the maintenance cost of the system and makes the operation more stable and reliable.


  4. Flexible configuration. In the household market, the size of photovoltaic cells can be installed according to the user's financial resources.


  5. No high-voltage electricity, safer, simpler and faster installation, low maintenance and installation costs, and less dependence on installation service providers, so that the solar power system can be DIY by users.


  6. The cost is equivalent to or even lower than that of a centralized inverter.


   The development of micro-inverters


The concept of    micro-inverter has a long history. A certain company considered developing this product 10 years ago, but finally decided not to do it. Since then, other companies have continued to improve hardware and software to make microinverters more attractive. Located in California, USA, Enphase company, founded by 3 engineers from NASA, began commercial mass production in 2008, and sold tens of thousands of sets of products that year. Subsequently, Enphase was listed on the Menasdaq exchange this year after receiving several venture capital investments, becoming the world's number one manufacturer of micro inverters.


   In September 2009, the inverter industry ushered in a major event in the history of its development. ISM, the leading manufacturer of inverters, announced the acquisition of OKE, a company engaged in the development of micro-inverters. The company was founded in 1984 and started the research and development of micro-inverters very early. After the completion of the acquisition, SMA immediately applied OKE’s technology to its own products. This acquisition is of extraordinary significance to the inverter market, because after the acquisition, the inverter market has undergone tremendous changes. The change can be said to directly affect the development of the inverter market today.