A Model Based Digital PI Current Loop Control Design for AMB Actuator Coils

This paper presents a digital PI current loop control design method for AMB actuator coils. The design takes into consideration the dynamics of each function block in the current loop.  For the control of radial bearing actuator current, the digital redesign approach is used: an analog PI controller is designed first with root locus method and then discretized to obtain its digital counterpart. For the control of thrust bearing actuator current, eddy current effects are also considered as they cause frequency dependent inductance and resistance of the thrust coil.  A swept sine test is conducted to measure the impedance of the thrust coil. Then a Matlab/Simulink model is built to carry out a frequency domain design of the digital PI controller with the measured impedance.