Multi-pulse rectifier for ac drive systems having separate dc bus per output phase and multiple isolation transformers

Abstract

An 18n-pulse rectifier for AC drive systems having a separate DC bus for each output phase is provided, where n=any positive integer. The rectifier uses three separate phase rectifiers, one for each output phase of a transformer, each comprised of 2n six-pulse diode bridges connected in series or parallel. Each phase rectifier may be supplied with n unique sets of phase inputs from a transformer secondary winding. In some configurations, the n sets of inputs provided to each rectifier are separated by 60/n degrees of phase (when n is greater than 1), while the corresponding inputs to neighboring rectifiers are separated by 20/n degrees of phase. In a 36-pulse example, the phase offsets for the inputs provided to the rectifiers may be −25° and +5° from the transformer primary winding (for the first rectifier), −15° and +15° from the primary winding (for the second rectifier) and −5° and +25° from the primary winding (for the third rectifier). Each set of inputs may include three lines of in-phase current, and may be coupled to one of the six-pulse diode bridges. In some configurations, two identically-wound transformers may be used to supply output voltages to the rectifiers. The transformers may each supply the same phase offsets to each rectifier, in accordance with the methodology above, which may support higher-capacity applications.