Power electronic activation for active magnetic bearings

Abstract

The School of Electrical, Electronic and Computer Engineering of the North-West University is currently doing research on active magnetic bearing (AMB) systems. One of the latest developments is the flexible rotor double radial AMB model. Various studies on the AMB sub-systems are being conducted using the model. The focus of this study is on AMB power amplifiers (PAS). The aim is to develop a platform to facilitate the analysis of the two-state and the three-state switching techniques that are possible for the AMB switch-mode PAS. An average current controlled PA prototype board is designed to facilitate the study. The design of the switch-mode PA for the two-state and the three-state switching techniques is conducted and analysed based on the design specification. The switching techniques are realised in a digital signal processing (DSP) environment with a TMS320P2812 eZdsp DSP starter kit (DSK). A TMS320P2812 eZdsp DSK is programmed in visSim® development software. The simulation model for the two switching techniques was developed in MATLAB® simulink. The simulation models are used to verify the design specifications, to predict the experimental set-up behaviour and to compare the two-state and the three-state switch-mode PA topologies. The two switching techniques showed good correlation in system performance, small signal bandwidth and power bandwidth. The simulation models' responses are also in agreement with the theoretical analysis. Testing of the PA's switching techniques was conducted on the double radial AMB system. The two switching techniques are analysed on the basis of how well they can regulate the coil current. The power bandwidth as well as the power loss analysis was used to evaluate the two switching techniques. The experimental results showed good correlation with the simulation results in terms of the dynamic response and the power losses. The power bandwidth measurements could not be performed at the specified dc levels due to noise problems. The power bandwidth prediction was however verified by reducing the voltage level to minimum values and the switching frequency to lower value. Recommendations for future improvements on the PAS are given based on the results.