The research topic revolves around improving the conversion efficiency of large-scale solar inverters. Firstly, the gradual reduction of traditional fossil fuels was introduced, and new energy has become the direction of future development. At this time, the photovoltaic industry has received unprecedented development opportunities. The development of the photovoltaic industry has also played a significant role in promoting the development of solar inverters. Currently, solar inverters are increasingly unable to meet the needs of the photovoltaic industry, especially centralized photovoltaic power generation systems that require large-scale solar inverters that can adapt to high-power, high-frequency, high-altitude and other situations.
(1) In order to meet the requirements of photovoltaic power generation and efficiency improvement, the optimization of control algorithms was first considered. Three widely used MPPT algorithms, namely constant voltage method, disturbance observation method, and incremental conductance method, were introduced. This article briefly introduces the principles, advantages, and disadvantages of three algorithms, and compares them with the commonly used variable step size algorithms. Combining perturbation observation method and conductance increment method, an improved perturbation observation method with conductance increment as the relaxation factor is proposed. By comparing pure MPPT efficiency simulation with RTDS based semi physical simulation, it was found that the improved algorithm is more stable and efficient in static characteristics compared to traditional variable step size algorithms; In terms of dynamic characteristics, it can make faster dynamic responses based on changes in external conditions. The superiority and feasibility of the improved algorithm have been verified, meeting the requirements of efficiency.
(2) The vigorous development of solar inverters has also attracted the attention of many experts and scholars, so the structure of solar inverters has also shown diversified development. Therefore, a more reasonable selection of solar inverter structure is particularly important for the development of large-scale solar inverters. Analyzed three types of solar inverter topologies – traditional two-level, E-type three-level, and T-type three-level. Theoretical calculations were conducted on the on state loss and switching loss of three types of solar inverters, and the power loss, junction temperature, and heat sink temperature of the three structures were analyzed through semi physical simulation experiments. It was found that T-type three-level solar inverters have the advantages of fewer open devices, less total power loss, lower heat sink requirements, and higher efficiency compared to the other two structures of solar inverters, More in line with the requirements of improving the efficiency of large-scale solar inverters.
(3) In response to the requirements of the experimental platform, the key component parameters of the solar inverter were calculated, selected, and tuned. By selecting DC bus capacitors, the instability of solar inverter output and the lifespan of components caused by excessive ripple current have been effectively controlled; By tuning the parameters of the filtering circuit, the high-order harmonic components of the output voltage are reduced, thereby improving the output quality of the solar inverter; By selecting heat sinks, the heat generated by power losses in high-frequency switching tubes such as IGBTs can be reduced in a timely manner, ensuring the long-term stable operation of the switching tubes; By designing a stacked busbar, the parasitic inductance in the circuit is reduced, thereby protecting the normal operation of the switching transistor; By adjusting the dead time, the problem of the upper and lower switching tubes on the same bridge arm not being able to conduct simultaneously has been effectively solved, ensuring the normal operation of the switching tubes. Finally, an experiment was conducted on the full load power grid connected power generation of the entire photovoltaic inverter system, and it was found that the grid connected voltage, DC voltage, and grid connected current could meet the design requirements. This also verified the rationality of the selection of solar inverter components and parameter tuning. At the same time, the efficient and stable output also proved the feasibility of the control algorithm and the selection of solar inverter structure.
With the booming development of the photovoltaic industry, research on solar inverters will gradually deepen. Therefore, solar inverters with higher power, higher efficiency, and stronger adaptability will receive more and more attention from the world. Therefore, this puts forward higher requirements for the research of solar inverters. How to further optimize solar inverters with higher efficiency, lower cost, and better stability still needs further improvement.
(1) In the MPPT control algorithm, the dynamic characteristics of the algorithm only consider changes in lighting. In fact, photovoltaic cells are also limited by other factors such as temperature. At present, research mainly focuses on changes in lighting, and there is relatively little research on temperature changes. Therefore, if the influence of temperature changes can be considered and the algorithm can be further optimized, better results can be achieved.
(2) When selecting the structure of solar inverters, only the influence of power loss is considered. For example, modulation methods such as SVPWM and SPWM also have a certain impact on different solar inverter structures, especially under different modulation methods, the power loss of solar inverters is also different. This article only compares and analyzes the loss situation under the same modulation method. Therefore, the power loss of various solar inverter structures under multiple modulation methods will be the direction of future research.
(3) When comparing the losses of three solar inverter structures, the same switching frequency of 5kHz was used. The power losses of different solar inverter structures vary nonlinearly under different switching frequency conditions and do not follow general patterns. Therefore, this will be the direction for improvement.
(4) Different solar inverter structures have certain differences in on state losses, switch losses, and switch quantities in different situations. Therefore, this article only selected and designed for a specific power generation environment, and concluded that the T-type solar inverter structure has more advantages. However, its adaptability has not been verified yet, which is related to whether this type of solar inverter can be promoted to other power generation environments, and therefore has certain research value.