Suspension Force Research Articles

Design and Terminal Sliding Mode Control of Double Stator Bearingless Switched Reluctance Motor

This paper proposes an 18/15/8-pole bearingless switched reluctance motor (BSRM) with good decoupling performance, which optimizes the distance and number of teeth between the inner and outer stator and rotor, reduces the hysteresis force existing during phase change, improves the electromagnetic conversion efficiency, and reduces the interference of forces between torque and levitation. A three-layer rotor structure is used to design the magnetic separation frame, which eliminates the interference of magnetic lines between the torque system and the suspension system. The direct control idea is applied to control the torque and levitation forces. A new reaching law (RL) is proposed, and a torque sliding mode controller and a suspension force sliding mode controller are designed, which replace the traditional terminal sliding mode control and PID control, and improve the robustness of the control system and dynamic response. Ansoft Maxwell 2D software is used to perform electromagnetic analysis to verify the decoupling, and the control simulation model is established by MATLAB/Simulink simulation analysis, and the results are compared with the traditional controller method. The results show that the proposed control system effectively improves the dynamic response speed and robustness of the system, and verifies the effectiveness and superiority of the proposed control method.

Parameter Measurement of a Hybrid Active Magnetic Bearing and Control of Tilt Moment

Recently, many rotors used in industrial rotating machines trend to less weight, long span, and high-speed rotation, therefore, it should be considered not only rigid modes but also bending modes of the rotor. Active magnetic bearings can control the suspension force, then it is suitable to suppress the resonance at high order bending modes. We aim to control the resonance at bending mode using hybrid active magnetic bearings (HAMBs). The HAMB consists of control and bias sections, with negative stiffness in each section. Therefore, it generates not only the radial force but also the tilting moment, then, it is possible to give the damping moment for the tilting of the rotor. In this paper, the mathematical model of the HAMB is derived, and the measured results of the stiffnesses are shown. Then, the control of the tilting moment is discussed.

Mechanism Model of Suspension Force for Spherical Bearingless Flywheel Machine

Mechanism Model of Suspension Force for Spherical Bearingless Flywheel Machine

Speed Sensorless Control of Bearingless Synchronous Reluctance Slice Motor Considering the Effect of Suspension Force Windings

Speed Sensorless Control of Bearingless Synchronous Reluctance Slice Motor Considering the Effect of Suspension Force Windings

Comparison among limit performances of various chassis control methods by numerical optimization

Since the limit performance of an integrated chassis control vehicle depends on the combination of control inputs such as steering angle, braking torque, and so on, it is important to clarify how the combination of control inputs affects the limit performance. In this study, the performances of integrated chassis control systems with various input combinations are evaluated in an obstacle avoidance situation. The obstacle avoidance problem is formulated as an optimal control problem that maximizes the avoidable obstacle width at the predefined distance and is solved by using a numerical optimization technique. In the optimization, a full-vehicle model equipped with actuators that can independently control the steering angles, braking torques, and active suspension forces of four wheels is used, and the optimization results are compared for various combinations of control inputs. From the optimization results for four combinations of control inputs, the effects of integrated control are examined.

Model predictive direct suspension force control of a bearingless induction motor based on sliding mode observer

PurposeThe purpose of the control method proposed in this paper is to address the problem of the poor anti-interference of the suspension winding current in the traditional bearingless induction motor (BL-IM) direct suspension force control process.Design/methodology/approachA model predictive direct suspension force control of a BL-IM based on sliding mode observer is proposed in this paper. The model predictive control (MPC) is introduced to the traditional direct suspension force control to improve the anti-interference of the suspension current. A sliding mode flux linkage observer is designed and applied to the MPC system, which reduces the error of the parameter observation and improves the robustness of the system. The strategy is designed and implemented in the MATLAB/Simulink and the two-level AC speed regulation platform.FindingsThe simulation and experimental results show that the performance of the BL-IM under the control method proposed in this paper is better than that under the traditional direct suspension force control, and the suspension performance of the motor and the anti-interference of the control system are improved.Originality/valueThis study helps to improve the suspension performance of the motor and the anti-interference of the control system.

A piecewise analytical model of bearingless switched reluctance motor for full rotor angular positions

PurposeThis paper aims to establish a piecewise Maxwell stress analytical model of bearingless switched reluctance motor (BSRM) for the full rotor angular positions. The proposed model varies from the existing models, which are only applicable to the partial-overlapping positions of stator and rotor poles. By extending the applicable rotor angular positions, this model provides a basic analytical model for the multi-phase excitation control of BSRM.Design/methodology/approachThe full rotor angular positions are classified into the partial-overlapping positions and the non-overlapping positions. At first, two different air gap subdividing methods are proposed, respectively, for the two-position ranges. Then, different integration paths are selected accordingly. Furthermore, two approximate methods are presented to calculate the average flux density of each air gap subdivision. Finally, considering the mutual coupling between the two perpendicular radial suspension forces, a piecewise Maxwell stress analytical model is derived for the full rotor angular positions of BSRM.FindingsA piecewise Maxwell stress analytical model of BSRM is built for the full rotor angular positions, and applicable to the multi-phase excitation mode of BSRM. For the partial-overlapping positions and the non-overlapping positions, two sets of air gap subdividing methods, integration paths and approximate calculation methods of air gap flux densities are proposed, respectively. The accuracy and reliability of the proposed model are verified by the finite element method.Originality/valueThe piecewise Maxwell stress analytical model of BSRM for the full rotor angular positions is proposed for the first time. The novel air gap subdividing methods, integration paths, approximate calculation methods of air gap flux densities and the coupling between the two radial suspension forces are adopted to improve the modeling accuracy. As the applicable range of rotor angular position is extended, this model overcomes the limitation of the existing models only for single-phase excitation mode and contributes to the accurate control of BSRM multi-phase excitation mode.

A Novel Current Limitation Technique Exploiting the Maximum Capability of Power Electronic Inverter and Bearingless Machine

This article presents a current limitation technique for a multiphase bearingless machine featuring a combined winding system. This winding structure allows the machine to produce both suspension force and motoring torque. The main challenges with the combined winding configuration consist of decoupling the suspension force and torque generation and designing a proper current limitation algorithm. The former topic has been already tackled and presented in previous publications, while the latter will be addressed in this article. In particular, the proposed suspension force control technique will allow to prioritize either suspension force or torque generation. In this article, the priority is given to the rotor levitation, hence the suspension force rather than the torque is essential. Finally, simulation results and experiment validation on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{1.5}\,\text{kW}/3000\,\text{r/min}$</tex-math></inline-formula> prototype machine are provided.

Asymmetrical Four-Phase Combined Winding Arrangement for Bearingless PM Motors

Conventional bearingless motors typically comprise two sets of independent windings in the stator to produce torque and suspension force, denoted by a separated winding in this study. However, several approaches to combine suspension and rotation windings into one set of windings, known as combined winding, have been investigated for torque density improvement and for increasing the instantaneous suspension force production at start-up. This study proposes a method to convert a typical three-phase brushless dc motor into a four-phase bearingless motor with combined winding, based on the magnetomotive force (MMF) distribution. As an example, a 12-slot/10-pole surface-mounted permanent magnet motor was investigated. The calculation results demonstrate that the suspension force cannot be generated at certain rotational angles when the four phases are symmetrically located. This study introduces torque and force current factors based on the MMF distribution to select several asymmetrical four-phase winding arrangements. The radial force trajectory calculated by the finite element method was evaluated to determine the final model. To verify the proposed method, the prototype was built and tested, and the test results showed that the rotor was levitated successfully and could be driven up to 5000 r/min.

Development of Axial-Flux Single-Drive Bearingless Motor With One-Axis Active Positioning

This study proposes a novel axial-flux bearingless permanent magnet motor with one-axis active positioning. This bearingless motor consists of an axial-flux surface permanent magnet motor with coreless coils and a repulsive permanent magnet coupling located at its center. Therefore, it has a single three-phase winding and needs only one three-phase inverter for both rotation and magnetic suspension; it is, thus, referred to as a single-drive bearingless motor. The axial position of the rotor is actively controlled, whereas the radial and tilting motions are passively stabilized. The suspension force and torque are regulated by the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis currents, respectively. The structure of the proposed axial-flux single-drive bearingless motor is presented, and its torque and suspension force are obtained by both theoretical derivation and numerical modeling (using the finite-element method). A prototype machine is fabricated, and the obtained experimental results are presented and discussed.

A Novel Combined Winding and Test Result of a 20-Pole/24-Slot Consequent-Pole Bearingless Motor With Parallel Motor Winding

A novel consequent-pole bearingless motor is proposed with a unique combined winding structure of parallel motor windings for mixing applications, such as agitators used to mix fluids in the pharmaceutical or food industry. Bearingless motors can be used to achieve high purity and no contamination in these mixing applications. The principles of the magnetic suspension force and torque generation are presented by calculating the magnetomotive force (MMF) distributions with two different magnetic field. In addition, the error angle of the suspension force is evaluated in several pole/slot combinations with the proposed combined winding using 3-D finite element analysis. As a result, 20-pole/24-slot was found to be the best configuration, because it has the least direction and amplitude variations in the radial suspension force generation. A prototype of the proposed 20-pole/24-slot bearingless motor was built and tested. The stable magnetic suspension start-up and rotation can be successfully achieved in the experiment. The measured waveforms of the rotor displacement and the U-phase current while the rotor is magnetically suspended and rotated are shown. It is confirmed by calculations and experiments that the proposed combined winding is effective for stable radial magnetic suspension and rotation.

Self-Bearing Machine Modeling Reflecting Rotor Position Induced Non-Linearity Based on 7-D Lookup Table

The rotor of self-bearing machines can be in an off-centered position as they lack of physical bearings. The air-gap length and effective area with respect to each phase become nonuniform, which results in inductance and back EMF non-linearities. Evaluation of self-bearing machines performance in time domain is inaccurate without a model that includes non-linear inductance and back EMF constants. To reflect non-linearities, finite element analysis (FEA) is often used. However, FEA requires large computational power to run in time-domain simulation. In this article, a 7-D lookup table (7-D LUT) model of inductance and back EMF constants, suspension forces, and torque is proposed for time-domain simulation, including non-linearity from the rotor translational and rotational displacement. Pre-evaluated FEA results are post-processed to construct the 7-D LUT model to enable fast and accurate time-domain simulation reflecting non-linearities from the input of rotary position (slotting effect), translational position in horizontal and vertical directions (unbalanced air-gap field effect), and magnetic saturation effect. A combined winding self-bearing machine is evaluated using the proposed method and verified with FEA and experimental results.

The Single-peak and “V” Shaped Combined Permanent Magnet Guideway for High-Temperature Superconducting Magnetic Levitation

With the merits of the excellent self-stabilization, the high-temperature superconducting (HTS) magnetic levitation (maglev) system is relatively appropriate for high-speed railway transportation. The suspension force and guidance force are mainly produced by the interaction between the HTS bulks and the permanent magnet guideway (PMG). Before the HTS bulks turn into the superconducting state, it will capture the magnetic field generated by the PMG and interact with the magnetic field of PMG after turning into the superconducting state, which creates the suspension phenomena. Therefore, the research of the magnetic flux density of external magnetic fields excited by the PMG is very significant to an intensive discovery of HTS maglev properties. However, the previous single-peak guideway needs to be improved to supply HTS maglev with sufficient vertical magnetic fields gradients. Otherwise, it might cause the guidance force to be not great enough for practical engineering application. Hence, this paper proposed a better “V” shaped PMG, by combining the single-peak and “V” shaped PMG. Under the typical work condition of 30 mm field cooling height, 10 mm work height and 10 mm lateral displacement, the levitation force and guidance force of HTS bulks could attain 6779 N and 2778 N, respectively. Compared to the levitation force and guidance force produced by using single-peak PMG, these two forces increase by 12.6% and 137%. As a result, the new “V” shaped PMG will provide HTS maglev with more adequate guidance performance and load capacity.

Suspension principle and verification of 6/4 pole bearingless switched reluctance motor with permanent magnets in its stator yoke

In order to overcome the disadvantages of 12/8 pole bearingless switched reluctance motors (BSRMs), such as high commutation frequency, more stator windings, and more power devices, a 6/4 pole BSRM with half the commutation frequency and number of windings is studied. The structure characteristics and operation characteristics of the 6/4 pole BSRM are investigated through modeling, simulation, and prototype experiment, and the main performance indices, such as suspension force, inductance performance, and air-gap flux density, are evaluated to reveal the levitation control mechanism of the 6/4 pole BSRM with permanent magnets in its stator yoke. The motor can suspend stably in the radial direction, and the correctness and feasibility of the theoretical analysis are verified.

Design, Manufacture and Performance Evaluation of HTS Electromagnet Wound by YBCO Tape

Heat generation and serious energy consumption of normal-conductive suspension electromagnets influence the performance and stability of suspension systems. With the development of second generation (2G) high temperature superconducting (HTS) technologies, HTS suspension electromagnets are being considered for energy saving purpose. In this paper, a suspension system with three suspension electromagnets is designed, which is comprised of two normal-conductive suspension electromagnets and a 2G-HTS suspension electromagnet. A three-dimensional (3D) electromagnetic field simulation based on finite element method (FEM) is carried out, and the force test platform of suspension electromagnet is built for performance evaluation of the HTS suspension electromagnet. The experimental results show that the current of HTS suspension electromagnet is steady loaded from 0 A to 70 A under 77 K working conditions, with the suspension force meet the requirements. This work provides a certain theoretical and practical foundation for the future superconducting suspension projects.

Comparison of Combined Winding Strategies for Radial Nonsalient Bearingless Machines

This paper investigates and compares two popular combined winding configurations for bearingless machines, the multi-phase (MP) and dual-purpose no-voltage (DPNV) windings. Each of these winding configurations has the ability to independently create suspension force and drive torque using the same stator coils. The paper develops analogous bearingless motor force and torque models, space vector equivalent circuits, and a current regulation architecture for each combined winding approach. A comprehensive comparison is made between the two combined winding topologies by using these analogous models and through an experimental study. It is shown that, from a motor design perspective, these combined winding topologies are equivalent for certain design conditions, but that each winding places very different demands upon the drive power electronics. The paper concludes that the optimal choice of winding configuration depends on the machine parameters and the expected loading and drive cycle. When compared in terms of total current stress exerted on the bearingless drive, the MP winding is preferred when over half of the coil current is used to produce torque rather than force. In terms of the drive's volt-ampere rating, the DPNV winding is shown to be advantageous for high operating speeds and low torque values.

Performance Evaluation of a Homopolar Bearingless Motor for Ultrahigh Speed Applications

This study evaluates the performance of a homopolar bearingless motor driven at 100 000 r/min with a mechanical output power of 120 W. The rotor has two salient iron core parts assembled into the shaft in tandem. The stator comprises two units located axially in tandem and an axially magnetized permanent magnet that is sandwiched between these two stator units. This magnet provides three-dimensional magnetic bias flux to polarize the rotor core parts, resulting in single polarity of one rotor core; thus, this type of motor is called homopolar motor. Each stator has two separated three-phase windings for the motor rotation and magnetic suspension, and the bearingless motor examined in this study has active suspension control with four-degrees-of-freedom (radial and tilting motions). The rotating part consists of only iron cores, and hence, it has the advantage of a rigid robust structure. Additionally, no angle detection is needed for the active magnetic suspension control. Therefore, the homopolar bearingless motor is suitable for high-speed applications. The conventional homopolar bearingless motors have an eight-pole rotor, but the proposed structure has a six-pole rotor to reduce the driving electrical frequency. Although this six-pole homopolar bearingless motor has 20% suspension force variation and 4.5° of force error angle, the rotor is driven up to 100 000 r/min without touchdown. This study presents the structure and principle of the proposed homopolar bearingless motor and the experimental results of the load test.

Three-Coil Combined Winding Configuration for a 2-DOF Actively Controlled Bearingless Permanent Magnet Motor

This study describes a simple combined winding configuration for a two-degrees-of-freedom (DOF) controlled bearingless motor with a six-slot/six-pole permanent magnet (PM) structure. This bearingless PM motor has only three concentrated coils that are wound alternately on six teeth of the stator and employs only one three-phase inverter for both the two-DOF radial magnetic suspension and single-phase motor drive. Theoretical calculation and finite element method (FEM) analysis demonstrated that the proposed three-coil combined winding configuration generates a four-pole rotating field and six-pole alternating field for generating radial suspension force and torque, respectively. To verify the proposed configuration, we built and tested an outer rotor bearingless PM motor with a diameter of 58 mm and a height of 5 mm. The rotor was successfully levitated and driven up to 7500 rpm. The calculated and measured results were compared for both the proposed combined winding configuration and the previously developed separated winding configuration. The measured motor efficiency of the prototype with the combined winding at 5000 rpm with 20 mNm output is improved by 5% due to the copper loss reduction when compared to that with the separated winding.

Investigation on the Depth of Slip Hanger Teeth Bite into Casing and the Mechanical Properties of Casing under Different Suspension Loads in Ultra-Deep Wells

There is great difficulty in controlling the setting load of the large-size slip casing hanger in the Northwest Oilfield in China, and a reasonable setting load is of great significance. This paper studied the relationship between slip hanger bite depth and suspension load in the Ф 273 mm WE-type slip hanger in the Northwest Oilfield in China through experiment, theoretical computation, and finite element analysis. The accuracy of the finite element model was proved by comparing the finite element simulation results with the experimental bite marks on the casing surface. The study results show that the bite mark of the slip insert in the casing is deeper in the lower part of the sitting position. When the hanging load increases from 1000 kN to 6000 kN, the maximum bite depth of the slips in the casing gradually increases with the suspension load. The residual collapse strength of the casing decreases correspondingly. When the residual collapse strength decreases to a certain value, the maximum suspension force corresponding to the bite depth of the slip insert can be obtained. Based on the finite element research results and theoretical equations, the stress distribution on the casing wall where the slips bite the deepest is obtained by derivation. The suggestions on improving the material structure of the casing under this stress were proposed. The limit of the setting load of the large-size casing wellhead for avoiding casing collapse was obtained, which is of great significance for guiding field-casing setting.

Window+: Electrostatic levitation enabled Polymer-Air multilayer (EPAM) structures for highly transparent energy efficient windows

The poor thermal insulating building windows, especially single-pane windows, are wasting ∼ 7% of the total energy consumed by the U.S. every year. This paper presents an electrostatic levitation enabled polymer-air multilayer (EPAM) structure as a highly transparent and energy efficient window retrofitting solution for low-income single-pane window users. To provide controllable and stable suspension force between large size compliant polymer films without deteriorating their visual transmittance (Vt) in the multilayer polymer/air structure, corona discharge (CD) was used to induce quasi-permanent charges for non-conductive polymer films, leading to controllable and long-lasting surface electric potential difference between two sides of CD charged films. Liquid-solid contact electrification (LS-CE) was combined with CD to realize precise control of the electrical potential of each side of polymer films. CD + CE treated films can obtain programmable and stable electrostatic forces to form resilient EPAM structures for cost and energy effective window retrofitting purpose. The resilient EPAM retrofitted clear windows can provide U-factor lower than 3 W·m−2·K−1, Vt higher than 70%, haze lower than 1.6% at cost lower than $79.7/m2, at least 10 times cheaper than double pane windows. The energy saved by EPAM can reach as much as the order of 106 kJ/m2 per year. The CD + CE surface potential programming solution also provides a highly repeatable and controllable way for other electrical potential related technologies, such as energy harvesting and storage.