Three-level inverter for medium voltage level using series connected IGBTs

Studenteropgave: Kandidatspeciale og HD afgangsprojekt

  • Jan Sundvall
  • Mads Chr. Pilgaard Vaerens
10. semester, Elektronik og IT Ingeniør (Kandidatuddannelse)
Wind turbines of today reach power levels of more than 5 MW, and this puts large requirements to the used electrical components. If the wind turbine inverter setup is based on the back to back topology and full scale power conversion, then all the power is transferred across a common DC link. The voltage rating of the DC link is in the area of 1kV, and this results in a high current rating, and hence large conductors are needed. If the voltage rating of the DC link can be increased, then the conduction losses, and hence the size of the conductors, could be reduced. The goal of this master project is, to analyze the implementation of medium voltage level (+2.4kV) in the DC link, by means of standard IGBTs. The required increase in voltage rating is obtained, by utilizing the three-level inverter topology, and basing it on series connected standard IGBT modules. Also, protection schemes suited for the inverter is analyzed. Based on the results from the analysis, a two phase three-level NPC inverter system rated for a DC link voltage of 2.4kV, and a current rating of 200A was designed, realized and tested. To ensure equal voltage sharing and dynamic performance of the series IGBTs, snubber circuits was analyzed, designed and implemented in the setup. The protection scheme of the inverter was based on desaturation detection and voltage clamping. To perform the required tests of the system, a medium voltage DC power supply and an inductive load was build. The results of the tests was, that by series connecting IGBTs, the voltage rating of an inverter can be increased with acceptable performance due to the incorporated zener clamped snubber circuits. The three-level topology is well suited for the medium voltage level, due to its voltage sharing nature. The voltage clamping protection did not have the expected performance, and therefore this method was not the optimal choice for this project.
Antal sider198
Udgivende institutionIET AAU
ID: 14419917