A Variable Frequency Device Based on BDFM and Its Application

Variable frequency transformers, as an energy conversion device, have important applications in wind power low-frequency transmission systems and isolated variable frequency power supply systems. At present, there is a brush slip ring structure in variable frequency transformers, which reduces the reliability of the motor. In order to solve the above problems, this paper proposes a frequency conversion device based on brushless doubly fed machine (BDFM) and its usage method, mainly including BDFM, driving motor, back-to-back converter, etc. The BDFM can be any form of wound rotor BDFM, salient pole rotor BDFM, permanent magnet field modulation BDFM, etc. The driving motor can be any form of permanent magnet synchronous motor, stator permanent magnet motor (including flux switching motor, flux reversing motor, doubly salient motor), homopolar inductor alternator, etc. The connection method between the drive motor rotor and the BDFM rotor can be radial coaxial connection or axial series connection according to the application scenario. The control winding of the BDFM is connected to the 50 Hz power grid through a back-to-back converter. The power winding and the winding of the driving motor are connected to a 50 Hz grid or low-frequency grid (or load) depending on the application scenario and the type of BDFM. The frequency conversion device based on BDFM proposed in this paper has the advantages of simple rotor structure and high reliability, and is very suitable for application in wind power low-frequency transmission systems and isolated frequency conversion power supply systems.