I'm sorry, but as of my last knowledge update in September 2021, I don't have any information about a concept called "matrix rectifier" specifically for AC-DC conversion. The term "matrix rectifier" doesn't seem to correspond to any well-known concept or technology in the field of electrical engineering or power conversion up to that point.
If this is a new concept that has emerged after September 2021, I wouldn't have information about it. However, if you could provide more context or details about what the term "matrix rectifier" refers to and how it is related to AC-DC conversion, I might be able to help you understand the concept based on the information available up to September 2021.