The Development of Power Amplifier for the High-Power Magnetic Suspension Bearing Blower

The nonlinear dynamics are studied for an active magnetic bearing (AMB) system under the low-frequency sinusoidal excitation, which can affect the operational stability of a high-speed magnetic bearing. A single-degree-of-freedom nonlinear dynamics model of magnetic bearing was developed with a c-type active magnetic bearing as the research target. The characteristics of the magnetic bearing system show positive and negative stiffness for different feedback gains. The amplitude–frequency response curves of the vibration characteristics of the positive stiffness magnetic bearing system were obtained by using the method of multiple scales. The influence of each parameter on the resonance amplitude and nonlinearity of the magnetic bearing system is understood by analyzing the amplitude–frequency response curve. The bifurcation diagram for the rotor with rotor mass, and control parameters is derived from the numerical simulation of the negative stiffness magnetic bearing system. The parameter intervals that cause single-cycle vibration, double-cycle vibration, and chaotic state of the magnetic bearing rotor are discovered by analyzing the bifurcation diagrams of each parameter. The simulation results show that the magnetic bearing system exhibits complex nonlinear dynamic characteristics when it is a negative stiffness system.

For a traditional two-level current switching power amplifier (PA) used in a magnetic bearing system, its current ripple is obvious. To increase its current ripple performance, three-level amplifiers are designed and their current control is generally based on analog and logical circuits. So the required hardware is complex and a performance increase from the hardware adjustment is difficult. To solve this problem, a FPGA-based digital current switching power amplifier (DCSPA) was designed. Its current ripple was obviously smaller than a two-level amplifier and its control circuit was much simpler than a tri-level amplifier with an analog control circuit. Because of the field-programmable capability of a FPGA chip used, different control algorithms including complex nonlinear algorithms could be easily implemented in the amplifier and their effects could be compared with the same hardware.

Rotors with speeds more than 20000 rpm, like Flywheel Energy Storage System (FESS), are fully or partially evacuated to reduce drag but have to be geometrically constrained except in the rotation axis. Magnetic bearings are preferred over a rolling element or journal bearings. The high-speed rotor is supported on active magnetic bearings. Though magnetic bearings with multi-axis support are possible, we look at building the support using desired passive compliance along five DOFs and one contactless support using a magnetic field with high stiffness at the set gap. A single DOF active magnetic bearing system is designed to precisely position a shaft along the longitudinal direction. The shaft is supported on a pair of compliant ortho-planar mechanisms at the two ends. The compliant structure is designed to provide bearing support along the radial directions. The position of the shaft along the longitudinal direction is actively controlled using the magnetic bearing system. A two-unit system based on magnetic attraction, one at either end, is designed. A candidate compliant ortho-planar mechanism is designed to support the shaft and fabricated using rapid prototyping. Stresses and bearing stiffness along different axes are calculated and analyzed using FEM. The 3D printed part was used for visualization and tested for compliance in the active magnetic bearing direction. The active magnetic bearing system is modeled. The controller will be optimized for disturbance rejection and minimize excursion around a desired axial location. The developed setup can be used to study and develop multi-axis AMB for high-speed rotating applications.

Switching power amplifier is an essential component for magnetic bearing system. However, the current ripple resulted from the conduction and shutoff operation of power switch component inevitably affects the performance of active magnetic bearing. To reduce the current ripple of switching power amplifier, the characteristics of current ripple are first analysed. In response to the spectrum character of current ripple, an online lifting wavelet transform de-noising algorithm, unlike the conventional power filter circuit, is proposed in this study. Moreover, the sliding data window and an improved threshold function are introduced to realise the feasibility of online processing and to improve the de-noising performance, respectively. Finally, plentiful comparative experiments, taking the magnetically suspended flywheel as subject, are implemented. The results illustrate that the proposed algorithm could dramatically reduce the current ripple and that the rotor displacement jitter and the vibration force are suppressed accordingly.

Under the background of intelligent new manufacturing, rotating machinery is developing towards the direction of high speed, high precision, intelligence and automation. Bearing, as the key component of high-speed precision rotor, has higher and higher requirements. As a high performance electromechanical integrated bearing, active magnetic bearings(AMBS) have a wide application prospect. In this paper, based on Simplorer and Ansoft Maxwell, the converter field-circuit coupling joint simulation of active radial magnetic bearing is carried out, including the structural design of active radial magnetic bearing and the establishment of the finite element model of active radial magnetic bearing in Maxwell. The mathematical model of single-degree-of-freedom of active radial magnetic bearing is established and the PID controller is designed. Power amplifier circuit is established in Simplorer, active radial magnetic bearing control program C module is created, and active radial electromagnetic bearing finite element model created in Maxwell is imported into Simplorer for joint simulation. Finally, the simulation results of magnetic force line, magnetic density, current stiffness and displacement stiffness of active radial magnetic bearing based on PID controller are given. Research shows that applying control strategy based on Simplorer field-circuit coupling joint simulation method combining software and hardware features, the simulation results more close to reality, the whole design of the active magnetic bearing system is verified.

Nowadays, high-frequency switching power amplifiers (SPA) have been studied widely; bulk of the researches were focused on audio power amplifiers. In active magnetic bearing (AMB) systems, high-frequency electromagnetic excitation caused by rotor imbalance can affect the performance of the SPA, so the traditional SPA cannot meet the requirements of the AMB systems. Therefore, on the premise of ensuring larger power, the frequency of the SPA should be improved to ensure the normal operation of the AMB system. Two-level pulsewidth modulation (PWM) current-mode SPAs are widely used in AMB systems. In order to broaden the bandwidth and to reduce the average steady-state error current, SiC power devices based SPA with a high bus voltage and a high switching frequency was designed. The basic principle and the linearized control model of SPAs are introduced. Then, the duty ratio stability and average steady-state error current of the SPAs are analyzed based on the output ripple current. When the PWM modulator is designed by either the discrete devices or the integrated chips, the critical gains to ensure the duty ratio stability are, respectively, analyzed based on the slope matching and the nonideal characteristic of operational amplifiers. Hence, two methods to reduce the average steady-state error current are proposed, respectively. One is to adjust the offset voltage of triangular carrier for the P controller, the other is to use a proportional integral (PI) controller. The offset adjusting method allows the SPA to achieve better dynamic performance and wider bandwidth. The proportional integral (PI) controller can reduce the average steady-state error current but narrows the bandwidth. Finally, the experiment results are in good agreement with the theoretical analyses.

A rotor spinning within an active magnetic bearing (AMB) system will normally be levitated and hence operate without rotor-stator contact. External disturbances and inherent unbalance may be compensated with appropriate control to keep rotor deviations within the clearance gap. However, AMBs have limited dynamic load capacity due to magnetic material field saturation. Hence overload conditions may result in rotor-stator contact. A touchdown bearing (TDB) and rotor landing sleeve are usually included to protect the expensive rotor, magnetic bearing and sensor components from damage. Once rotor-TDB contact has been made, rotor dynamic conditions may ensue resulting in persistent rotor bouncing or rubbing limit cycle responses. Prolonged exposure to these severe dynamics will cause TDB degradation and require regular replacement. If possible, a clear aim should be to restore contact-free levitation through available control capability in an efficient manner. This paper is used to guide the control options that are available to restore contact-free levitation. The use of AMB control is appropriate if the required control forces are within saturation limits. It is also possible to actuate TDBs and destabilize persistent rotor dynamic contact conditions. For example, piezo-based actuation offers larger control forces than those from magnetic bearing systems. Hybrid control action involving both types of actuation system has the greatest potential for completely robust restoration of contact-free levitation.

In order to meet the requirement of magnetic suspension bearings for high speed machine, the three-level PWM switching power amplifiers are designed and tested. The carrier triangular wave phase shift method is used in the design. The comparative study on the three-level PWM switching power amplifier with the two-level PWM switching power amplifier indicates that the three-level PWM technique can effectively reduce the current ripple of the suspension force control windings. The experimental results of the prototype verify the feasibility and effectiveness of the proposed three-level switching power amplifier.

Magnetic bearings use magnetic forces to support various machine components. Because of the non-contact nature of this type of suspension, magnetic bearing technology offers a number of significant advantages over conventional bearings, such as rolling element and fluid film bearings. An active magnetic bearing basically consists of an electromagnetic actuator, position sensors, power amplifiers, and a feedback controller. All of these components are characterized by nonlinear behavior and therefore the entire system is inherently nonlinear. However, in simulations of the dynamic behavior of magnetic bearing systems, the nonlinearities are usually neglected to simplify the analysis and only linear models are used. Moreover, many control techniques currently used in magnetic bearing systems are generally designed by ignoring nonlinear effects. The main reason for simplification is the intractability of the complexity of the actual model. In fact, the inherent nonlinear properties of magnetic bearing systems can lead to dynamic behavior of a magnetically suspended rotor that is distinctly different from that predicted using a simple linearized model. Therefore, the nonlinearities should be taken into account. This literature review is focused on the nonlinear dynamics of magnetic bearing systems and it provides background information on analytical methods, nonlinear vibrations resulting from a rotor contacting auxiliary bearings, and other active topics of research involving the nonlinear properties of magnetic bearing systems, such as nonlinear self-sensing magnetic bearings and nonlinear control of magnetic bearings. The review concludes with a brief discussion on current and possible future directions for research on the nonlinear dynamics of magnetic bearing systems.

The self-sensing magnetic bearing technology offers significant cost savings and the potential for dynamics advantages due to its fundamental sensor-actuator collocation. This paper proposes a rotor displacement self-sensing scheme for the permanent magnet bias magnetic bearings (PMB) using three-level amplifier demodulation. Based on the proposed structure of radial PMB, the self-sensing principle is presented by the magnetic circuit analysis. Then a mathematical expression which includes voltage of the coil, neutral point voltage of the coil and coil current is derived. Based on the derived formula, a practical self-sensing algorithm adapting for three-level switching power amplifier (PA) is proposed. In three-level switching PA, voltage of the coil is non-ideal at high level or low level because of inductive load. If signals are sampled at these non-ideal times, the detection precision becomes worse. The problem is solved through sampling at zero level and singular point will not appear. The experiment on a magnetically suspended motor show that this method can satisfy the performance demand of magnetic bearings system and the rotor speed can reach 3342 RPM.

A switching power amplifier (SPA) provides the driving current for an active magnetic bearing (AMB) to achieve magnetic suspension (MS) control. The performances of the current bandwidth and current ripple should be significantly considered in the SPA of the AMB. The SPA can obtain a wide bandwidth by increasing the dc-link voltage. However, a high dc-link voltage will cause a high current ripple. To achieve a wide bandwidth and low current ripple, a new GaN-device-based SPA for the AMB of a flywheel energy storage system (FESS) is proposed in this article. The GaN SPA can operate at a high switching frequency and high dc-link voltage. Thus, the GaN SPA can improve the performance of the current bandwidth and current ripple compared to the conventional SPA. According to the characteristics of the GaN SPA, a low-loss PWM method and an optimal dead time strategy is proposed to increase the efficiency of the SPA. Furthermore, a high-response control approach of dead-beat model predictive control is proposed to further improve the current bandwidth. The proposed GaN SPA is applied in a 500-kW MS FESS prototype. The effectiveness of the SPA is verified experimentally.

Magnetic levitation is a fundamental requirement for implementing a magnetic bearing (MB). In a magnetic bearing system, it provides a contact-free support for the rotating shaft. This is achieved through an attractive magnetic levitation force, produced by passing current(s) through electromagnet(s). The magnetic force is controlled with the help of adjustable current by implementing a control system. The gap between stator and rotor is measured with a position sensor and is used as a means of controlling the levitation force of the magnetic bearing. In this chapter the implementation of the control system for magnetic levitation based on an embedded microcontroller has been described. If the implementation of magnetic bearing system is done by using only electromagnets, it is known as Active Magnetic Bearing (AMB) system.

High speed flywheel energy storage systems normally use magnetic bearings to reduce friction loss. Bearing load consists of radial forces with or without axial forces according to drive configuration and requirements. The magnetic bearing system may be passive magnetic bearing (PMB), active magnetic bearing (AMB) or superconducting magnetic bearing (SMB) according to the required application. In this paper, a design example for an 8-pole radial AMB used for flywheel energy storage is presented. The design details along with finite element simulations are given to verify the design requirements. Finite element analysis is also used to obtain the bearing parameters. Based on calculated system parameters, a Matlab model is built to simulate the magnetic bearing in different cases.

To address the issue that current ripple in traditional switching power amplifiers (SPA) for active magnetic bearing (AMB) systems is constrained by the switching frequency, this paper proposes a novel LCL filter-based switching power amplifier (LCL-SPA) along with its parameter design and high-performance control strategy. Without altering the original full-bridge topology or the switching frequency, the proposed scheme achieves superior ripple suppression. To tackle the inherent resonance problem of the LCL filter, a sensorless capacitor current feedback active damping (CCFAD) strategy is proposed. This approach effectively suppresses resonance without additional hardware sensors and ensures system stability under digital control delays. Furthermore, to overcome the limitations of traditional PI controllers in terms of the dynamic performance and parameter tuning of the LCL-SPA, a high-performance LESO-based control algorithm within the Linear Active Disturbance Rejection Control (LADRC) framework is designed. By utilizing a Linear Extended State Observer (LESO) to estimate and compensate for total lumped disturbances in real-time, the algorithm simplifies the parameter tuning process and achieves rapid current tracking with nearly zero overshoot. Experimental results demonstrate that the proposed LCL-SPA achieves extremely low current ripple across various reference currents, with the ripple minimized to 20 mA at a 3 A load. Frequency response tests confirm that the system possesses a closed-loop bandwidth of up to 2 kHz, satisfying the high dynamic requirements of magnetic bearings.

Switching power amplifier is an essential part for active magnetic bearings (AMBs). Proportional control method is widely used in AMB's switching power amplifiers for it has many advantages. The gain of the proportional controller will affect the dynamic response and steady-state response of the system and lead to nonlinear behavior of the system. The nonlinear phenomenon of switching power amplifier will lead to the increase in current ripple and harmonic, and even damage the switching elements. Thus, when choosing the gain of the proportional controller, we need to take into account the response effect of the system and the nonlinear phenomenon. During AMB operation, the equivalent inductance of the coil will change as the position of the rotor changes. This will also complicate the switching power amplifier control, which may make the system's nonlinearity more serious. To bridge this gap, this article analyzes the nonlinear phenomenon of the proportional control of the AMB's switching power amplifier and proposes an adaptive control method considering the rotor's position. This method can use the optimal proportional control gain according to the change in the equivalent inductance, and the nonlinear phenomenon can be avoided. The control method has been verified by simulation and experiments.