Bearingless Switched Reluctance Motor Research Articles

Multi-Physics Multi-Objective Optimal Design of Bearingless Switched Reluctance Motor Based on Finite-Element Method

The bearingless switched reluctance motor (BSRM) integrates the switched reluctance motor (SRM) with the magnetic bearings, which avoids mechanical bearings-loss and makes it promising in high-speed applications. In this paper, a comprehensive framework for the multi-physics multi-objective optimal design of BSRMs based on finite-element method (FEM) is proposed. At first, the 2-D electromagnetic model of a fabricated initial design prototype is built and solved by the open-source FEM software, Elmer. The iron loss model in Elmer based on the Fourier series is modified by a transient iron loss model with less computation time. Besides, a simplified lumped-parameter (LP) thermal model of the BSRM is applied to estimate the temperature rise of BSRM in the steady state. Then, the comprehensive framework for the multi-physics multi-objective optimal design of BSRMs based on FEM is proposed. The objectives, constraints, and decision variables for optimization are determined. The multi-objective genetic particle swarm optimizer is utilized to obtain the Pareto front of optimization. The electromagnetic performance of the final optimal design is compared with the initial design. Comparison results show that the average electromagnetic torque and the efficiency are significantly enhanced.

Design and Analysis of a Novel Bearingless Segmented Switched Reluctance Motor

A novel bearingless segmented switched reluctance motor (BSSRM) is proposed in this paper to solve the coupling problem of the traditional bearingless switched reluctance motor (BSRM). Different from traditional BSRMs, the proposed BSSRM adopts the double stator and segmented rotor structure, thereby making the motor operate in short flux paths and the magnetic flux path isolated between torque and suspension system. On the basis of introducing the structure and working principle of the BSSRM, the mathematical model of torque and suspension force is deduced. The 2D finite element simulation model is established by the Ansoft software. The influence of structural parameters on torque and suspension system is analyzed, and its electromagnetic characteristic and decoupling characteristic are analyzed. Compared with the double stator bearingless switched reluctance motor (DSBSRM), the BSSRM not only improves the torque and suspension output but also weakens the coupling between torque and suspension system. Finally, the simulation results verify the effectiveness of the BSSRM.

Comprehensive analysis of suspending force for improved bearingless switched reluctance motor with permanent magnets in stator yoke

Comprehensive analysis of suspending force for improved bearingless switched reluctance motor with permanent magnets in stator yoke

Analysis of a hybrid double stator bearingless switched reluctance motor

A hybrid double stator bearingless switched reluctance motor with advantages of high suspension output, small loss and weak coupling is presented. This motor can realise electric/power generation and radial two-degree-of-freedom suspension. The biased magnetic field for producing radial force is provided by a permanent magnet, which reduces system power consumption. Self-decoupling is realised between a torque system and suspension system according to the mechanical structure design. Furthermore, the radial force is approximately constant when the suspension current is constant, thereby improving the controllability of the system. The operation principle is introduced and the electromagnetic characteristics are analysed through the time-stepping finite element method. This analysis verifies the effectiveness of the theoretical analysis.

Levitation control of an improved modular bearingless switched reluctance motor

In order to reduce coupling between torque and suspending force in conventional bearingless switched reluctance motor (BLSRM), one 12/12 hybrid-stator-pole structure BLSRM was investigated. In this structure, motor consists of two single phase motor. Biased flux is provided by axial permanent magnet, which is installed between two motor in axial direction. However, axial permanent magnet occupies axial space, which results in increased axial length and decreased critical speed. Therefore, an improved modular BLSRM is proposed in this paper. In order to reduce axial space and improve critical speed, permanent magnet is designed to install in stator yoke. To realize steady levitation during rotor rotating, one simple levitation control strategy is put forward, which is benefitted from natural decoupling between torque and suspending force. In addition, digital control system including torque and suspending force is designed by means of TMS320F28335 and experimental platform is established. Finally, the improved BLSRM can be steadily levitated in the static and rotating conditions by experimental results.

Rotor autocentering and speed control of hybrid bearingless SRM using single-neuron adaptive PID controller

The bearingless switched reluctance motor (BLSRM) is emerging as an attractive option for modern industrial applications because of the features, such as compact size, lubrication and seal free performance, long lifeand ability to rotate at very high speed and high power. The control approach is extremely fundamental to a steady operation because of itshighly nonlinear, multi variable and open loop unstable nature. This paper presents a single neuron based rotor suspension control of a 12/14 Hybrid Pole BLSRM with autonomous rotation and suspension poles. This hybrid pole structure produces the suspension force linearly with respect to rotor position and independent of the torque characteristics. Implementation of a non model based Single neuron adaptive PID Controller by avoiding the modeling complexity is proposed. Experimental results demonstrate that the proposed controller maintains the rotor in the center position as well as the speed tracking and disturbance elimination performances independently.

Rotor Suspension and Stabilization of Bearingless SRM using Sliding Mode Controller

Motors working in extreme conditions such as ultra high and low temperatures, high contamination, high purity etc. require high maintenance of mechanical bearings and the regular lubrication. Hence there is a need of a motor without mechanical bearings and lubrication in addition to simple in control and less maintenance. There by, bearingless motors (BLMs) gain more attention. The bearingless switched reluctance motor’s (BLSRM) is simple in construction and economical in addition to high speed capacity and high torque to inertia ratio. The magnetic nonlinearity arising due to double salient structure makes rotor eccentric displacement control and speed regulation complicate and needs robust control methodology such as sliding mode control (SMC) which has integrity, high certainty and rapid dynamic response when compared to typical controllers. Sliding mode can be realized with distinct classical reaching laws. This paper presents design and implementation of a SMC for a 12/14 BLSRM and the dynamic performance is endorsed by simulation using Matlab software.

Multi-Objective Optimal Design of Bearingless Switched Reluctance Motor Based on Multi-Objective Genetic Particle Swarm Optimizer

In recent decades, bearingless switched reluctance motors (BSRMs) have been proposed. However, few researchers focused on the optimal design of the BSRMs. In this paper, the multi-objective optimal design of BSRMs is investigated. At first, an analytical design model is derived from the mathematical model of the BSRMs. An initial design is calculated by the analytical design model. The electromagnetic performance is compared with calculation results from the finite-element method (FEM). Then, the objective functions, constraints, and decision variables are also determined. Corresponding sensitivity analysis of the decision variables is implemented. Besides, aiming at solving the optimization problem with disconnected, non-uniformly distributed Pareto front and multiple local optimums, a novel multi-objective genetic particle swarm optimizer (MOGPSO) is presented. The algorithm performance of the proposed MOGPSO is validated by solving the standard test functions. Then the proposed MOGPSO is applied for the optimal design of BSRMs. Optimization results solved by MOGPSO, conventional multi-objective particle swarm optimizer, and non-dominated sorting genetic algorithm II are compared and analyzed. Comparison results reveal that the proposed MOGPSO can achieve more non-dominated solutions in Pareto front and is particularly suitable for optimization of BSRMs. The final optimal design is selected from the obtained Pareto front. The electromagnetic performance is compared with the initial design and verified by the FEM. Verification results show that the optimal design of BSRMs based on the analytical design model and the proposed MOGPSO is feasible and effective.

A Novel Technique for Controlling Speed and Position of Bearingless Switched Reluctance Motor Employing Sensorless Sliding Mode Observer

High-speed motors working in harsh environments such as high temperatures, radiation, and poisonous substances are limited because of motor breakdown due to vibrations of mechanical bearings. The concept of magnetic bearings is an alternative to the issues of slide or ball bearings because of its advantages of friction-free, negligible thermal problems, and lubrication free. Rotor vibration control during start-up, acceleration and deceleration phases are one of the key problems besides stable levitation, in high-speed applications of bearingless switched reluctance motor (BSRM). The use of linear control strategies alone is not effective in suppressing vibration due to residual unbalance and external disturbances. In this paper, a global sliding mode controller (GSMC) is proposed to control the speed and position of BSRM and also sensorless operation with sliding mode observer. In this method, rotor displacement tracking error functions are used in the sliding mode switching functions and the new sliding mode displacement control and speed tracking equations are obtained with an extra exponential fast decaying nonlinear function along with conventional linear sliding mode switching surface. Simulation is carried on 12/14 BSRM with the proposed controller and observer and the results of rotor displacements and speed are presented. In addition to the improvement of performance characteristics when compared to sliding mode controller, GSMC cancels the reaching mode, reduce the chatting, and overcome the disturbance and the time delay.

Advanced Control Method for a Single-Winding Bearingless Switched Reluctance Motor to Reduce Torque Ripple and Radial Displacement

Because of the current commutation and the double-salient pole structure of single-winding bearingless switched reluctance motors (SWBSRMs), the torque and radial forces have large ripples when present control methods are used. In order to solve those problems, a novel solution is proposed in this paper, which can achieve direct torque control (DTC) and direct force control (DFC) simultaneously. With the hysteresis-loop control of torque and flux linkage, the power switches of converter can be directly controlled based on the proposed space voltage vectors. First, the basic space voltage vectors are transformed correspondingly to realize DTC for BSRMs. After that, considering the generation principle of levitation forces, the basic space voltage vectors are transformed into equivalent space voltage vectors to facilitate the implementation of DFC. As a result, the torque and levitation forces can be controlled at the same time only with the developed equivalent space voltage vectors. The complicated current control algorithm is not needed, which is necessary for conventional methods. Moreover, the levitation performance is improved with the proposed method. Experimental results show that the torque ripple and radial displacements of SWBSRMs can be reduced approximately by 80% and 29%, respectively.

Design methodology for a special single winding based bearingless switched reluctance motor

Bearingless switched reluctance motors (BSRMs) have both magnetic bearing as well as conventional motor characteristics which make them suitable for diverse industrial applications. This study proposes a design methodology for a BSRM in order to calculate the appropriate geometrical dimensions essential for realising a minimum levitation force at every orientation of rotor. It is based on the stator–rotor overlap angle and helps in reducing the complexities associated with the self-bearing operation of a switched reluctance motor (SRM). Different from a conventional SRM, the motor under study deploys a special single set parallel winding scheme for simultaneous production of torque as well as radial force. An analytical model incorporating this single set winding is developed for calculating the torque and the radial force. The proposed bearingless design is verified by developing a two-dimensional finite-element model of a 12/8 SRM in ANSYS Maxwell.

Direct control of torque and levitation force for dual-winding bearingless switched reluctance motor

In dual-winding bearingless switched reluctance motors (BSRMs), an additional winding is placed on the stator poles in conventional switched reluctance motors (SRMs), which is mainly to achieve the function of levitation. Due to the hysteresis current control in existing control strategies for dual-winding BSRMs, the complicated derivation of winding-current expression was necessary, and some constraints were also introduced that increased the difficulties on designing the current control algorithm. In order to solve these problems, the direct control concept of torque and levitation forces is proposed and developed in this paper, named as direct torque control (DTC) and direct force control (DFC). Moreover, the torque ripple can also be reduced greatly. Firstly, the space voltage vectors of dual-winding BSRMs are defined for the main and levitation windings, respectively. After that, the rules and procedures for selecting the space voltage vectors are demonstrated in detail, and the system control block is also presented to facilitate the implementation of proposed control strategy. Finally, experimental results are provided to demonstrate the performance.

A novel mathematical model of bearingless switched reluctance motor considering air-gap edge effect

PurposeThis paper aims to propose a novel mathematical model of bearingless switched reluctance motor (BSRM). This model differs from conventional mathematical models in the calculation of torque and suspension forces. Conventional mathematical models neglect the coupling relationship between the α- and β-axes or ignore the magnetic saturation of the Si-Fe material. This study considers these issues simultaneously. Additionally, considering the air-gap edge effect, the fringing coefficient is used to establish a high-precision mathematical model.Design/methodology/approachAn innovative mathematical model of BSRM based on the Maxwell stress method was established by selecting an appropriate integration path. The fringing coefficient of the air-gap was computed based on the finite element analysis results at the aligned position of the stator and rotor poles. Using the least squares fitting method, the piecewise fitted magnetization curve of the Si-Fe material was utilized to calculate flux density.FindingsThe appropriate integration path of the Maxwell stress method was selected, which considered the coupling relationship of the suspension forces in the α- and β-axes and was closer to the actual situation. The fringing coefficient of the air-gap improved the calculation accuracy of air-gap flux density. The magnetomotive force was consumed by the magnetic resistance of the stator and rotor poles considering the magnetic saturation.Originality/valueA novel mathematical model of BSRM is proposed. Different from conventional mathematical models, the proposed model can effectively solve the coupling relationship of the suspension forces in the α- and β-axes. Additionally, this model is consistent with the actual situation of motor as it includes a reasonable calculation of the air-gap flux density, considering the air-gap edge effect and magnetic saturation.

Decoupling Control for Dual-Winding Bearingless Switched Reluctance Motor Based on Improved Inverse System Method

Dual-winding bearingless switched reluctance motor (BSRM) is a multivariable high-nonlinear system characterized by strong coupling, and it is not completely reversible. In this paper, a new decoupling control strategy based on improved inverse system method is proposed. Robust servo regulator is adopted for the decoupled plants to guarantee control performances and robustness. A phase dynamic compensation filter is also designed to improve system stability at high-speed. In order to explain the advantages of the proposed method, traditional methods are compared. The tracking and decoupling characteristics as well as disturbance rejection and robustness are deeply analyzed. Simulation and experiments results show that the decoupling control of dual-winding BSRM in both reversible and irreversible domains can be successfully resolved with the improved inverse system method. The stability and robustness problems induced by inverse controller can be effectively solved by introducing robust servo regulator and dynamic compensation filter.

Suspending control scheme of 8/10 bearingless SRM based on adaptive fuzzy PID controller

Suspending control scheme of 8/10 bearingless SRM based on adaptive fuzzy PID controller

Improved Radial Force Modeling and Rotor Suspension Dynamics Simulation Studies for Double-winding Bearingless Switched Reluctance Motor

The rotor radial force is changed by adjusting the windings current value to control rotor suspension for various kinds of bearingless switched reluctance motor (BSRM). To accomplish the BSRM's suspension control, the radial force analytical model is necessary. Currently the mathematic relationship among radial force, winding currents, and rotor rotation angle has been built for double-winding BSRM, but the rotor eccentricity displacement has not been considered. That is, the existing radial force analytical model only can be used to analyze rotor radial force when rotor shaft is located in the central position. Actually, the rotor radial force is significantly affected by the rotor shaft eccentricity displacement. It is difficult for the bearingless motor to keep the rotor shaft staying in the central position, and the rotor shaft always runs around the central position with an eccentricity displacement. The rotor eccentricity caused by the radial force is considered in the paper to obtain the air-gap permeance and the windings inductances. Furthermore, the radial forces analytical model considering the rotor eccentricity displacement is derived. Finally, the finite-element method (FEM)-based results are applied and the dynamics simulation using the proposed model is accomplished to verify the correctness of the model.

Compensation Strategy of Levitation Forces for Single-Winding Bearingless Switched Reluctance Motor With One Winding Total Short Circuited

In order to take advantage of conventional switched reluctance motors (SRMs), the SRM is integrated with the bearingless motor technology and then a reluctance type of bearingless motor is created, named as bearingless SRM (BSRMs). Not only electromagnetic torque but also the levitation forces should be controlled in BSRMs, which is different from SRMs. The levitation forces should always exist even when winding fault occurs. Therefore, the absent levitation forces that ought to be produced by the fault winding should then be compensated by other winding. This paper proposes the compensation strategy of levitation forces for BSRMs when one stator winding is short circuited. The short-circuit fault is investigated and the short-circuit current is expressed for the derivation of radial forces. Then, the winding compensation rule and the mathematical model of levitation forces are developed to facilitate the compensation control for the motor levitation. After that, the proposed compensation strategy is verified by simulation results in MATLAB/Simulink. Experimental results are also presented to demonstrate the performance.

Equivalent Transformation and Control for Single-winding Bearingless Switched Reluctance Motors

The single-winding bearingless switched reluctance motor has a simple structure of windings in which the winding current produces the magnetic torque and levitation forces simultaneously. In the proposed control strategy, the average torque and average levitation force are regulated simultaneously to ease the current calculation and reduce the processing time of the digital signal processor. Moreover, to simplify the algorithm and investigate the relationship between the two kinds of bearingless switched reluctance motors, the equivalent transformation between single-winding and dual-winding bearingless switched reluctance motors is developed. After that, the average levitation-force control strategy is developed to regulate the torque and the radial force simultaneously. Accordingly, the system control block is established to achieve the closed-loop control, and experimental results verify that the proposed control strategy is effective for a stable levitation.

New type 12/14 bearingless switched reluctance motor with double windings

In this paper, a new type 12/14 bearingless switched reluctance motor with double windings is presented. The stator includes two types of poles such as suspending pole and torque pole. Different from the previous 8/10 structure, double windings including bias winding and control winding are installed on the same suspending pole. In addition, in order to reduce the coupling between torque and levitation force, the stator torque poles are shifted with one angle. Windings of two adjacent torque poles are connected in series. Therefore in order to explain advantages of proposed motor, structure and basic operating principle are introduced. In the meanwhile, levitation force is derived by means of equivalent magnetic circuit. The force characteristics with respect to current and displacement are analysed. In addition, by means of finite element analysis, coupling characteristic and self-starting characteristic are investigated. The validity of the structure is verified by the analysis and experimental results.

Control of Suspending Force in Novel Permanent-Magnet-Biased Bearingless Switched Reluctance Motor

Recently, bearingless switched reluctance motor (BLSRM) has been received more and more attention. To realize the stable levitation and rotation, the corresponding suspending force and torque should be controlled. In this paper, different from the conventional bearingless SRM control, one independent control scheme for levitation force and torque is presented. In the control, a complex control algorithm based on a lookup table is not needed. Torque control is separated from radial force control, and each channel of radial force is independently controlled. Therefore, the control is very simple to be implemented. First, based on the brief introduction of the BLSRM structure and operating principle, the mathematical relationship of levitation force with respect to current and displacement is derived. Furthermore, the rotor dynamics model, in which levitation force in four degrees of freedom is considered, is established. Based on the given analysis, the digital control system, which includes torque and suspending force, is designed by means of TMS320F28335, and an experimental platform is established. According to the experimental results, the proposed BLSRM can be steadily levitated in the static and rotating conditions.