A Wide Input Range Non-Isolated Three-Port Converter for Stand-Alone PV Storage Power Generation System
Gao Shengwei1,2, Zhu Qingtong1,2
1. School of Electrical Engineering TianGong University Tianjing 300387 China; 2. Tianjin Key Laboratory of Intelligent Control of Electrical Equipment Tianjing 300387 China
Abstract：Due to the increasing scarcity of traditional fossil energy sources such as oil and coal, new energy sources represented by solar energy have been commonly developed. Conventional two-port converters are used in new energy generation systems with energy storage ports, which have problems such as a large number of converters, large size, and low power density. In contrast, a three-port converter (TPC) only needs one converter to complete the power management and energy control between the PV, battery, and load, which has the advantages of high efficiency, high integration, and centralized energy management. Non-isolated TPCs are limited in application because they do not have transformers for port voltage matching, and the voltage constraints between ports are often severe. In recent years, some non-isolated TPC proposed still have problems such as serious inter-port voltage constraints, many power devices, and low efficiency. Therefore, this paper proposes a non-isolated TPC with a wide input range. This topology can work when the PV cell voltage is greater or less than the battery voltage, and the energy from the PV port flows to the load port without passing through the battery port. It meets the application requirements of the PV port voltage variation with a wide input range and improves the system’s efficiency. First, this paper uses the conventional Buck, Boost, and Buck-Boost converters as the channel connecting the PV port and the load port, and the bidirectional boost FSBB converter as the channel connecting the PV and the battery. A power flow path is added for connecting the battery and the load to obtain the proposed wide input range non-isolated TPC. Then, three topologies of FS-Boost TPC, FS-buck TPC, and FS-Buck-Boost TPC are compared and analyzed from the number of devices, voltage constraint range, and whether the output voltage at the load side is negative polarity. The FS-Boost TPC is superior. Finally, the operating principle and steady-state characteristics of this converter under the three constraints of Vo>Vpv>Vb, Vo>Vb>Vpv, and Vb>Vo>Vpv are analyzed with FS-Boost as an example. Secondly, the control strategy of FS-Boost TPC is designed. For realizing three functions of constant output voltage, battery protection, and maximum power point tracking (MPPT), the designed strategy can be switched between Single Input Single Output-Battery (SISO-B) mode, Double-Input (DI) mode, Double-Output (DO) mode and Single Input Single Output-PV (SISO-P) mode according to the power relationship between ports. Finally, the control strategies are described in detail with Vo>Vpv>Vb, and Vo>Vb>Vpv as examples, and the corresponding modulation strategies are given. Finally, the FS-Boost TPC experimental prototype is built, and the steady-state and dynamic switching experiments are completed under the two constraints of Vo>Vpv>Vb and Vo>Vb>Vpv. The experimental study shows that the proposed FS-Boost TPC can operate stably in four operating modes and complete the switching between modes with the switching time within 4 ms.The efficiency of the system in DI mode and DO mode is tested, and the maximum output efficiency of the topology is 97.8% in the test range. The topology efficiency decreases with the increase of the input power. The smaller the PV voltage is for the same PV input power, the lower the output efficiency of the converter. Through theoretical and experimental analysis, the following conclusions can be obtained: (1) The proposed topology can work in applications where the PV voltage is greater or less than the battery voltage and meets the practical application requirements of a wide input range of PV voltage variations. (2) The control strategy design can ensure constant output voltage at the load side and fast switching between the four operating modes. Therefore, the proposed wide-input-range three-port converter is suitable for stand-alone PV storage power generation systems consisting of PV, batteries, and loads.
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2023, Vol. 38 
