Power coordination control strategy of microgrid based on photovoltaic generation

MATEC Web of Conferences 355, 03065 (2022) ICPCM2021 https://doi.org/10.1051/matecconf/202235503065 Power coordination control strategy microgrid based on photovoltaic generation of Zhongxiao Chen *, Jiarui Chen, Kaiqing Fu, and Longkun Xue School of Electronic and Information Engineering, Xi’an Technological University, Xi’an, 710021, China Abstract. In order to solve the large-scale grid-connected photovoltaic cells caused by power fluctuations, power quality decline and other issues. This paper proposes and researches a power coordination control strategy for microgrid based on photovoltaic power generation. The principle of photovoltaic cells and the switching of maximum power point tracking and limited power mode are studied. The stability control methods of DC bus voltage, AC bus wire and frequency are studied. The model of microgrid is established and moreover, based on the power of microgrid and the charging state of storage battery, the operation of microgrid is divided into different working modes. The stable operation of microgrid is realized by adjusting the output power of each unit in different working modes. The calculation shows that the control strategy can effectively reduce the power fluctuation in the microgrid and improve the output power of renewable energy. Finally, the feasibility and effectiveness of the proposed methods are verified by experiments. 1 Introduction Due to the global energy over-consumption and environmental pollution are becoming more and more serious, the renewability and non-pollution of solar power let it be favored by social development. Photovoltaic cells convert light energy directly into electricity through photovoltaic effect, which has sufficient cleanliness, While protecting the environment, it effectively solves the problem of limited conventional energy[1]. However, the large-scale use of photovoltaic cells can cope with the energy crisis, because of its own intermittent shortcomings of power generation, when grid-connected, it will cause power fluctuation and reduce power quality, thus limit power generation, while the proposal of microgrid proposes to solve such problems. Microgrid can be divided into DC microgrid, AC microgrid and AC-DC hybrid microgrid according to different forms of electric energy[2-3]. AC-DC hybrid microgrid has AC bus bar and DC bus bar, which can provide electric energy for AC load and DC load at the same time. It not only omits multiple power conversion links, simplifies microgrid structure and distributed power supply mode, but also improves operation efficiency and economy. And the control methods are more flexible. Therefore, in islands[4], remote mountainous areas and other places which cannot be connected to the * Corresponding author: © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 355, 03065 (2022) ICPCM2021 https://doi.org/10.1051/matecconf/202235503065 large grid, AC-DC hybrid microgrid operation is more effective. This paper takes the isolated island mode of optical storage diesel AC-DC hybrid microgrid as the research object, focusing on its control strategy. The control objective of AC-DC hybrid microgrid is to ensure the stability of DC bus bar voltage, AC bus bar voltage and frequency[5]. The coordinated control strategy of hybrid microgrid was studied in Reference[6-7]. The operation effects of microgrid power balance, maximum power output of micro-source and minimum energy interaction between AC and DC buses were achieved. Literature[8] presents a hierarchical control strategy for AC/DC hybrid microgrid, which solves the power control problem of parallel bidirectional AC/DC converters. However, the above control strategies do not take the frequent switching of control strategies into account due to bus voltage fluctuations. Reference[9] considers the power control strategy of DC microgrid and divides DC microgrid into four working modes based on power. However, it does not consider the shortage of photovoltaic power supply. Considering the limitation of energy storage capacity, mode switching of photovoltaic power generation units and combined power supply of diesel generators, this paper proposes a power coordination control strategy under islanding mode of AC/DC hybrid microgrid. Based on the system power and the state of charge (SOC) of storage battery, this method determines the different working modes of each module in the microgrid under different operating conditions, and realizes the coordinated power control of the microgrid based on photovoltaic power generation. 2 Principle of photovoltaic power generation Photovoltaic power generation is a way of conversion of light energy into electricity through photovoltaic effect of semiconductor materials[10].The surface of photovoltaic cells is covered with a thin sheet of metal-film semiconductor. When sunlight illuminates the semiconductor materials and electromotive force is generated at both ends of the semiconductor materials. The principle of photovoltaic power generation is shown in Figure 1. solar negative pole load positive pole I current Fig. 1. The principle of photovoltaic power generation. The photovoltaic cell is equivalent to a PN junction. When P-type and N-type semiconductor materials are combined, The electrons in the N-type region will diffuse into the P-type region, holes in the P-type region will diffuse into the N-type region, forming barrier wall. At this time, N-type is charged positively, P-type is charged negatively, and the whole is not charged. At this time, strong built-in electrostatic field will be generated inside the semiconductor, forming P-N junction, as shown in Figure 2. When sunlight irradiates the PN junction, a new pair of holes-electrons will be formed in the barrier area. Because of the strong built-in electrostatic field in the barrier area of PN junction, the pair of holes-electrons in the barrier area will be generated or the pair of holes-electrons in the barrier area will be generated outside the barrier area but spread to the 2 MATEC Web of Conferences 355, 03065 (2022) ICPCM2021 https://doi.org/10.1051/matecconf/202235503065 inside of the barrier area. Under the action of the built-in electrostatic field, the direction of the movement begins, electrostatic field, the direction of movement begins. As the electrons leave the barrier region, the potential in P region increases and the potential in N region decreases. Photogene rated electromotive force is generated at both ends of PN junctions. As shown in the principle of photovoltaic power generation in Fig. 1, Assume that PN junctions are connected to loads, there is an uninterrupted potential difference at both ends of the circuit when sunlight illuminates. P-type N-type a P region Barrier electric field Barrier area b N regi (...truncated)