High-power regenerative converter for ore transportation under failure conditions

The use of three-level neutral point clamped (3LNPC) voltage source inverters for drive applications in the megawatt range is becoming a standard solution. In combination with the same converter circuit in rectifier operation as Active Front End (AFE) it is able for four-quadrant operation. An existing plant, which has been in operation with eight converters since several years, has shown some failures, which lead to considerations of failure mechanisms and failure rates. All failures were on the AFE. A first failure of a power semiconductor leads to subsequent breakdown of others. Some failures are analyzed and failure conditions are described. Some failure reasons can be excluded and a probable reason is pointed out. Finally, a recommended solution is described and its result after its implementation is discussed.