In this study, a simple and smooth voltage controller for a three-pole active magnetic bearing (AMB) system is proposed. It is designed with the backstepping procedure. The first step assumes the currents as the control inputs and designs the smooth current controller that has been proposed in the literature. The second step considers that the currents are not actual inputs, but part of the states. Then, the actual control inputs (voltages) are designed using simple proportional and integral (PI) control to make the error states from the first step to be zero asymptotically. Based on the voltage-controlled AMB system, an observer is designed for the rotor displacement estimation. The observer is based on the input voltages and coil currents that drive the magnetic poles. Such an observer can be utilized in the sensorless control of the AMB system. Due to the strong nonlinearity in the dynamics of 3-pole AMB system, the theory of nonlinear high-gain observer is adopted to design the observer. First, it is shown that the strong nonlinear 3-pole AMB system is observable under the zero input condition, which guarantees the existence of a high-gain observer. Then, the system is transformed into a regular form for the design of observer. Finally, a nonlinear observer is designed following the theory of high-gain observer. The proposed smooth voltage controller and nonlinear observer are verified numerically and experimentally. The results show the effectiveness of the smooth voltage controller and the feasibility of the nonlinear high-gain observer. and Hsiao, Mechanical Engineering Journal, Vol.4, No.5 (2017) [DOI: 10.1299/mej.16-00718] therein). Several methods have been proposed, including linear observer based, linear observer with parameter identification, switching ripple (from switching amplifier) based, and interrogation signal based.The objectives of this study are to propose a smooth voltage controller and to design an observer for the 3-pole AMB system. Due to the strong nonlinearity of the 3-pole AMB system, the stable levitation controller is in general complicated. Although a simple and smooth current controller for the 3-pole AMB system was proposed in (Chen, 2011, Meeker andMaslen, 2006), voltage controller is in general more cost-effective. Based on the voltage-controlled system, the estimation of the rotor position will be achieved by designing an observer. A Luenberger type observer with Kalman filter has been proposed in (Darbandi et al., 2014) based on the linearized 3-pole AMB system. However, the results are valid only when coil currents and rotor displacements are relatively small. The overall stability and observability cannot be guaranteed by linear controller and observer. Due to the nonlinearity of magnetic force, the observability and/or parameter estimation of magnetic bearing system is in general difficult (Delpoux and Floquet, 2015, Mizuno et al., 2016). The 3-pole configuration makes the problem even more difficult. In view of the strong nonlinearity of the 3-pole system...