Research On Constant- Current Source Biased Magnetic Bearing System

Constant-current source biased Magnetic bearing is one type of Active Magnetic Bearing (AMB), it is characterized by the bias coils and control coils separated, which can use a power amplifier to provide bias current for the five degrees of freedom.The characteristics principle of the magnetic bearing with constant-current source is discussed, which is that the electromagnetic force of constant-current source biasing magnetic bearing is generated by the magnetic field superposition, while the traditional active magnetic bearing electromagnetic force is generated by current superposition. The derivate expression of the electromagnetic force has been included and the controlling of the magnetic bearing with constant-current source has been studied.A six-way bi-directional power amplifier control system is used to realize the five degrees of freedom stable suspension of the magnetic bearing with constant-current source, and further discussed about the turn ratio of constant-current part and control current part in theory.Theoretical analysis and experimental validation attain the differences of the copper loss, iron loss, wind loss and power loss of the power devices between the constant-current source biased structure and the traditional structure of active magnetic bearing. It analyzes the specific circumstances that under the different bias current conditions, the losses will increase with the control current increasing. It was proved that magnetic bearing with constant-current source has less power loss than conventional active magnetic bearings.