HV submodule technology based on press pack IGBT for largest scale VSC-HVDC application

In the last five year Power rating of VSC-HVDC application has dramatically increased in Voltage and Current. Higher and higher rating is also driven by increasing interest to apply VSC-HVDC in large scale B2B and in overhead line transmission where with present LCC technology is now possible to reach 6.5kA DC at ±800 - 1100 kV DC. Higher and higher VSC-HVDC rating has been possible thanks to two main aspects: Modular Multilevel Converter (MMC) topology that allows increasing converter voltage in very simple way, continuous increase in performances and rating of new power semiconductors. In MMC Converter, each HV valve is made of certain number of Modular Units, commonly called submodules, connected in series. Normally, IGBTs are controllable power devices used as switches in submodule and half-bridge or full-bridge are typical submodule conversion topologies. Actually there're two main families of devices: · Plastic Modules named PMI · Press pack modules named PPI Plastic modules IGBT and Diode (PMI) are the most popular devices used. However, it is well known that PMI devices have some drawbacks if compared to Press-Pack devices (PPI) expecially when applied in highest power and in most severe applications. RXPE, basing on its positive experience accumulated in many large Statcom and large MV drives in operation from some years, decided to extend the application of PPI solution also in VSC-HVDC. The paper describes the application of this technology in NanHao multiterminal converter rated ±160kV, 200MW and Yunnan B2B converter rated ±350kV, 1000MW. The positive results of these testing have allowed extending R&D activity on higher power PP devices and the development of new 3kA DC generations of submodules able to realize converters up to 3GW at ±500kV DC Voltage.