Comparative Study of 100kW Three-Level Bidirectional DC-DC Converters for Battery Storage Integration with 1500V PV Inverter

With more and more photovoltaic (PV) generation in the power system, the grid is in need of more and more energy storage systems in order to provide critical grid functionalities such as inertia support and primary frequency regulation. Thus, DC coupled PV plus storage system is becoming an important solution in the industry. In a DC-coupled PV plus storage system, a bidirectional DC-DC converter is used to interface the PV and battery storage. Improving the performance of the DC-DC converter is important in this high-power application. For 1500V PV systems, the DC-DC converter needs to support a high output voltage of 1500V. While using higher breakdown voltage SiC is one options, a three-level converter based on lower voltage SIC is another more attractive solution. In this study, a SiC three-level bidirectional (TLB) DC-DC converter and a three-level flying capacitor (FCC) bidirectional DC-DC converter, are compared in terms of the operation principle, capacitor voltage balancing control, and power losses. A prototype TLB converter is developed and verified with a 99.4% peak efficiency.