Non-Linear Control of Magnetic Bearings for High-Speed Flywheels

Depending on the level of bias, the control system for an active magnetic bearing can be classified as either linear, non-linear or hybrid. For a given design of bearing, the minimum bias current which facilitates linear control, and which is therefore commensurate with low iron/copper losses and amplifier VA ratings, can be specified. However, non-biased, nonlinear control is the most energy efficient mode, and, hence, is particularly appropriate for applications in which precise position control is not required, such as high-speed energy storage flywheels. The determination of the amplifier VA ratings and the effects of control current ripple are discussed, and a simple computer simulation is used to illustrate nonbiased, non-linear controller design.