태양광발전 양방향 배터리 충방전 DC-DC 컨버터에 관한 연구

Abstract

The advancement in science and technology, industrial development, and rapid population growth increased the demand for energy over the years. Consequently, fossil fuels, such as oil, coal, and gas widely served as the primary energy sources for multiple purposes. This has led to several global environmental problems, including the depletion of fossil energy sources and waste disposal issues owing to the expansion of nuclear power plants. Therefore, the international standards of environmental protection are being reformed worldwide, increasing the utilization of various renewable energy sources for sustainable development. Among the commonly used renewable energy sources, the photovoltaic power generation system utilizes unlimited solar energy. Therefore, it can be designed diversely based on its capacity. Additionally, the absence of moving parts enhances the system operation and ensures easy maintenance. However, the power generation relies on multiple factors, such as the variations in weather conditions, the amount of solar radiation, and temperature. Thus, the power fluctuations in the photovoltaic systems can restrict their applications, particularly based on the amount of energy required by the load. Therefore, several researchers have studied various techniques to charge and discharge a battery using direct current (DC). When a battery is applied to a photovoltaic power generation system, the DC–DC converter technology performs peak-reduction and load-leveling by generating maximum power during the peak power consumption. This is essential for both the charging and discharging roles in the system as the battery is charged using the photovoltaic cells or systems and discharged by supplying the required power to the load in the event of a power outage or low power generation. Therefore, the efficiency enhancement of the DC converters is constantly researched owing to their ability to convert and manage energy effectively. In this thesis, a novel topology was proposed for the bidirectional charging and discharging system integrated with the DC–DC converter with a maximum power point tracking (MPPT) control function that tracks the maximum power point. To verify the performance for the photovoltaic power generation systems, a PSIM of a simulation tool was employed for a 500-W low-power portable bidirectional battery charging and discharging DC-DC converter. Additionally, the hardware system demonstrated the feasibility of the bidirectional charging and discharging through experiments. Unlike the conventional unidirectional buck-boost DC–DC converter, the proposed topology can charge and discharge in both directions with identical voltage variable ranges. Moreover, the ripple current and inductor volume can be reduced as the frequency of the inductor is twice that of the inductor used in a conventional DC–DC converter. Furthermore, as the output stage of the power supply transforms into a pulse current source, it can be maintained stable despite the unexpected load fluctuations. Thus, the condenser capacity is reduced owing to the decreased ripple in the overshoot of the capacitor current. The 500-W bidirectional battery charging and discharging DC–DC converter was fabricated and tested for the photovoltaic power generation systems. The experimental results verified the enhanced performance more than 500-W class, with the proposed system exhibiting an efficiency of 95.17% as opposed to the 91.12% efficiency of the conventional systems. The proposed topology of the DC–DC converter can contribute to the development of photovoltaic power generation systems that are capable of charging batteries of different voltages or supplying power to outdoor electrical systems. It can also be used as a power source in case of emergency power outages. Additionally, these systems can satisfy the power demand if other renewable energy sources fail to supply sufficient power.