Linear Switched Reluctance Machine Research Articles

Dynamic Coding-Based Control Scheme Under Lossy Digital Network: An Optimized Time-Varying Packet Length Approach.

This work proposes a design scheme of the desired controller under the lossy digital network by introducing a dynamic coding and packet-length optimization strategy. First, the weighted try once-discard (WTOD) protocol is introduced to schedule the transmission of sensor nodes. The state-dependent dynamic quantizer and the encoding function with time-varying coding length are designed to improve coding accuracy significantly. Then, a feasible state-feedback controller is designed to attain that the controlled system subject to possible packet dropout is exponentially ultimately bounded in the mean-square sense. Moreover, it is shown that the coding error directly affects the convergent upper bound, which is further minimized by optimizing the coding lengths. Finally, the simulation results are provided via the double-sided linear switched reluctance machine systems.

System design, analysis, and experimental investigations of linear switched reluctance machines with double mover configuration

This paper proposes a new double mover configuration of a linear switched reluctance motor (LSRM). The proposed design is established for optimization of the motional forces and to ensure a high-grade electromechanical energy conversion process. The major drawback of the traditional linear machine is that its force densities within and throughout its area is produced in its radial direction of the yoke and does not contribute to its motion or twisting force of the rotor. If these normal forces happen to be in the direction of motion, a larger motional force profile for SRM is yielded. Based on these guidelines, a new LSRM is developed. In order to compare the energy conversion efficiency of LSRM with that of the conventional SRM, a finite element model is constructed. The proposed system is simulated using the FEM software and tested under four conditions. Further, an experimental prototype of the proposed machine is also developed and tested in the laboratory. The results obtained from the prototype indicate that the proposed geometry offers superior performance in terms of high-power density and higher percentage of the national forces.

Comparative Study of Linear Variable Flux Reluctance Machine with Linear Wound Field Flux Reversal Machine

As members of doubly salient magnetless linear machines, linear variable flux reluctance (LVFR) and wound field flux reversal (LWFFR) machines inherit the merits of conventional magnetless linear machines such as low cost, high flux adjustment capability and high reliability. Furthermore, like linear switched reluctance machine, they have a very simple and compact long secondary, which are very attractive for long stroke applications. However, low force capability is their major defect. To solve this issue, new LVFR and LWFFR machine topologies were proposed in recent work, while lacking studies on their force improvement mechanism and further force evaluation. In this paper, LVFR and LWFFR machines with improved force performance are comparatively studied with the emphasis on their force capabilities. The operation principle of the two machines is analyzed based on magnetic field harmonics produced by flux modulation. Contributions of air-gap flux density harmonic components to no-load back electromagnetic forces of the two machines are analyzed and the average force equation is derived. Moreover, force capabilities of the both machines are investigated by means of the time-stepping finite-element analysis to verify the theoretical analysis.

Low-Ripple Continuous Control Set Model Predictive Torque Control for Switched Reluctance Machines Based on Equivalent Linear SRM Model

In this article, a low-ripple continuous control set (CCS) model predictive torque control (MPTC) method for switched reluctance machines (SRMs) is proposed. The inherent high nonlinearity of the SRMs makes it difficult to solve the optimization problem in the CCS MPTC algorithm analytically. To address this issue, an equivalent linear SRM model is adopted, and the cost function is also properly modified. Then, with the torque boundary values provided by executing the voltage vectors of an improved switching table, the optimization problem in the CCS MPTC method becomes simple and analytically solvable. The Lagrange multiplier method is employed to solve this optimization problem analytically and generate the optimum torque reference values for the active phases. Based on the estimated torque variation rates, the duty cycles for each phase are calculated. Extensive simulation and experimental tests are carried out in a four-phase 8/6 SRM setup. These testing results reveal that the proposed CCS MPTC method shows much lower torque ripples and current ripples in a wide speed range with a low computational burden than the existing finite control set MPTC methods.

Computational-Efficient Model Predictive Torque Control for Switched Reluctance Machines With Linear-Model-Based Equivalent Transformations

In this article, a novel model predictive torque control (MPTC) method for switched reluctance machines (SRMs) is proposed based on the equivalent linear SRM model and the improved switching table. First, an improved switching table with only six switching states is developed based on the inductance characteristics. The adoption of this improved switching table not only reduces the computational burden by 25% but also improves the torque control performance and system efficiency at high-speed region. However, the look-up-table (LUT) based MPTC methods suffer from occupying numerous storage space. To ease this issue, the simple linear SRM model is utilized. The flux-linkage and torque equivalent transformations are introduced to address the difference between the linear and nonlinear SRM models. With these transformations, the MPTC realized on the linear SRM model is proposed. Compared to 1530 storage units consumption to store three two-dimensional (2-D) LUTs in the LUT-based MPTC methods, the proposed method only occupies 228 storage units. Experimental results on an 8/6 SRM setup verify that the proposed method effectively eliminates the commutation torque ripple with lower execution time, less storage space, and improves the torque control performance at a high-speed range compared with the conventional LUT-based method.

Proportional Predictive Control of Networked Linear Switched Reluctance Machine System With Time-Varying Delay

In this article, a proportional predictive (PP) control strategy is proposed and a high-precision position tracking controller is designed for the networked linear switched reluctance machine system (NLSRMS) with time-varying delay. The closed-loop system model of the NLSRMS is constructed based on the PP control strategy. The stability conditions of the system are proposed by combining the optimal control value calculated by the cost function. The controller of the closed-loop NLSRMS is designed by using continuously updated predictive output equation information based on calculation. The comparative study of the proposed PP and PID control methods is presented by tracking several types of signals. The maximum steady errors of PP and PID control strategies are 0.2 mm and 2 mm under the sinusoidal signal, respectively. The maximum steady errors of PP and PID control strategies are 0.07 mm and 0.7 mm under the square signal, respectively. The simulation results show the effectiveness of the proposed PP control strategy.

Design and Control of a Transverse Flux Linear Switched Reluctance Machine for Rail Transit Application

The design, optimization and control methods of a transverse flux Linear Switched Reluctance Motor (LSRM) for the rail transit application are introduced. Two structures of LSRMs, EI type and EE type, are compared and analyzed. The structure of EE type machine is optimized from the perspective of average electromagnetic thrust per unit mass through finite element calculations. The initial sizes of the motor are calculated according to the design theory of the rotary SRM. After obtaining the initial sizes, the sensitivities of the LSRM sizes are analyzed by the three-dimensional finite element calculation, and then the sizes such as the slot depth, the slot width and the tooth width of the motor are optimized. The hardware test platform is built, the electromagnetic characteristics of the prototype are tested, and the motor characteristics of the LSRM with different secondary materials are compared. The control method of the LSRM with position sensors is proposed, and then the sensorless control of the motor is also realized based on the pulse injection strategy. The experimental results verify the effectiveness of the design and control strategies.

Corrections to “A Novel Tubular Switched Reluctance Linear Machine Shielding From Longitudinal End Magnetic Effect” [Jun 20 Art. no. 3601407

Presents the front cover for this issue of the publication.

Corrections to “Three-Dimensional Magnetic Equivalent Circuit Research of Double-Sided Switched Reluctance Linear Machine” [Jun 20 Art. no. 3603608

Corrections to “Three-Dimensional Magnetic Equivalent Circuit Research of Double-Sided Switched Reluctance Linear Machine” [Jun 20 Art. no. 3603608

Design and Analysis of a Novel Transverse-Flux Tubular Linear Switched Reluctance Machine for Minimizing Force Ripple

This article proposes a novel transverse-flux tubular linear switched reluctance (TF-TLSR) machine for long-stroke applications, in which the armature windings are placed on the short primary, while the long secondary is made of only low-cost iron ring. The key for the proposed machine is to innovatively introduce the complementary tooth structure into the primary salient-pole design and equip the complementary machine unit configuration in the primary construction for the purpose of minimizing the force ripple. The principle of force ripple reduction by using these complementary structure configurations is illustrated in depth. The analytical calculations of the winding inductance and thrust force of the proposed machine are developed with the air-gap magnetic path modeling. By using the 3-D finite element analysis (3-D-FEA), the sensitivity study of two key structural parameters on the force characteristics is also carried out, based on which a satisfactory TF-TLSR machine is finally determined. Consequently, a prototype is fabricated for experimentation testing, and the FEA and experimental results are comparatively demonstrated, which verifies the validity of the design ideas of using a complementary concept for minimizing force ripple in the proposed machine.

A Novel Three-Phase Tubular Switched Reluctance Linear Machine With Transverse-Flux Path

Several tubular switched reluctance linear machines (TSRLMs) with transverse flux are proposed for improving thrust density recently. Owing to the particularity of the structure of transverse-flux TSRLMs, how to maximize the electrical utilization becomes a key to improve these machines’ performance. A novel three-phase transverse-flux TSRLM is proposed in this paper, whose stator sleeve is composed of six ferromagnetic rings and five spacer rings. And the mover is composed of an aluminum tube and several fan-shaped poles. The adjacent fan-shaped poles are placed at 120 degree intervals. In the novel structure, each half of the windings corresponding to a phase constitute a single coil without the need of intermediate connections. This winding way avoids the limitation of stator ferromagnetic ring spacing, and increases the space for wire placement compared with the other existing transverse-flux TSRLMs. In order to verify the superiority of the novel TSRLM, a conventional transverse-flux TSRLM which has the same volume and main dimensions is presented to compare their performances. Finally, the finite element calculation results show that the average thrust per unit core mass of proposed TSRLM is greater than conventional TSRLM, which shows its superiority for speed control systems. It proves that the novel structure can help increasing the use of TSRLMs.

Three-Dimensional Magnetic Equivalent Circuit Research of Double-Sided Switched Reluctance Linear Machine

This paper proposes a three-dimensional magnetic equivalent circuit (3D MEC) method to analyze the flux linkage characteristics and electromagnetic force characteristics of double-sided switched reluctance linear machine (DSRLM). The 3D finite element model (3D FEM) of DSRLM is established to analyze the magnetic field line distribution of the motor. The magnetic field distribution of two representative positions (unaligned and aligned position) is mainly analyzed, and the reluctance of each part was obtained by the magnetic flux tube method. According to the similarity principle, the magnetic flux tube with irregular shape is equivalent to a simple magnetic circuit that is easy to calculate. According to the similarity of the magnetic circuit and electric circuit, the 3D MEC model of DSRLM was established. The Gauss–Seidel iteration method is used in MATLAB to solve the flux linkage-current curves at two representative positions. Then the flux linkage curves calculated by the MEC method are compared with the 3D-FEM results and experimental results. After that, the flux linkage curves obtained by MEC are used to solve the electromagnetic force curves. And the electromagnetic force curves are compared with the curves obtained by FEM and experiment. It can be found that the error is within an acceptable range, indicating that the scheme is more feasible.

Electromagnetic design method for a TLSRG with application in ocean wave energy conversion

The tubular linear switched reluctance machine (TLSRM) has shown potential for applications as generator in direct drive conversion of ocean wave energy devices. However, the design of this type of machine is a difficult task and there is no methodology to provide an explicit solution. This work aims to contribute for the solution of this problem with the proposal of a new procedure to design tubular linear switched reluctance generators (TLSRG). With the proposed procedure the TLSRG can be designed to develop a given linear force and to achieve better generation efficiency. The design is defined as a minimization problem where an optimization process is used to find the optimal solution for the dimensional parameters. Finite element method (FEM) analysis is applied to compute the relevant electromagnetic characteristics. The mathematical model of the generator conversion system is formulated to evaluate its dynamic performance. An H-Bridge asymmetric converter is adopted to control the energy flow in the generator. The electric currents in the generator phases are adjusted with a hysteresis controller. A TLSRG with a maximum mean force of 120 kN is designed by applying the proposed procedure, implemented in Matlab® and combined with MagNet® (FEM commercial software) to compute the electromagnetic characteristics of the machine. The system mathematical model is solved in Simulink®. The dynamic simulations are performed for a constant velocity of 1.3 m/s. For these operating conditions, the generator is characterised with an output power of 126.2 kW and an efficiency of 82.1%. The control proposed to drive the TLSRG is experimentally tested on a small-scale prototype. The experimental results show the effectiveness of the controller in keeping the phase current near the reference value.

Four-quadrant force control with minimal ripple for linear switched reluctance machines

Linear switch reluctance machine (LSRM) has been tried to act as an alternative generator for direct drive linear wave energy converter (WEC). Many researchers have proposed new topologies of LSRM to improve the power density, efficiency and reliability. However, the control methods for LSRM applied in direct drive WEC have been paid little attention, especially control methods considering the wave energy generator operating characteristics. In this paper, according to the generator control requirements of the direct drive WEC, force control algorithm for LSRM operating in four quadrants without a speed closed loop is put forward. The force ripple of LSRM is suppressed using force sharing function method. The four-quadrant control is easy to realize requiring only phase currents information. Simulation results validate the proposed method and indicate that LSRM is able to be used as the generator for direct drive WEC.

High‐precision non‐linear modelling method for a switched reluctance linear machine by interpolation with using variant sigmoid function

This study presents a non-linear modelling method for a switched reluctance linear machine (SRLM), which achieves high modelling precision while requiring no prior knowledge regarding the specific structural dimensions of an SRLM. The proposed modelling method provides accurate flux linkage data based on limited experimental measurements through an interpolation process using a variant sigmoid function. The accuracy of the interpolation process is further increased by considering mutual coupling among the three phases. The performance of the proposed method is validated experimentally by comparing it with the performances of the Fourier series method and the two-dimensional finite element method. The results demonstrate that the proposed method achieves greater modelling precision than the other methods considered in modelling an SRLM.

A Novel Tubular Switched Reluctance Linear Machine Shielding From Longitudinal End Magnetic Effect

Traditional linear machines are under great influence of longitudinal end effect because of their finite stacking lengths in transverse and longitudinal directions. Longitudinal end effect causes imbalance of phase performance so that linear machine's force fluctuation is aggravated. The negative impact of longitudinal end effect on a flat type switched reluctance linear machine (SRLM) is verified in this paper. In order to avoid this problem, a novel tubular switched reluctance linear machine (TSRLM) is proposed, which can shield from unexpected impact of end effect. In structure, there is no transverse cut in tubular linear machines, so tubular linear machines can evade the influence of the transverse end effect. The equivalent magnetic circuit of this TSRLM is analyzed in this paper, which proves that the TSRLM is also not influenced by longitudinal end effect. A prototype is manufactured, and its corresponding hardware platform is established. A series of simulations and experiments verify that there is no deviation performance among phases in the proposed TSRLM. Accordingly, the traditional longitudinal end effect in linear machines caused by longitudinal cuts can be thoroughly evaded in proposed TSRLM.

Compensation analysis of longitudinal end effect in three‐phase switched reluctance linear machines

The longitudinal end effect of switched reluctance linear machine (SRLM) makes the electromagnetic characteristics of different phases unbalanced, especially in magnetic flux distributions. These discrepancies unbalance phase currents and aggravate the force ripple of SRLM, which are verified on a double-sided SRLM. This study aims to analyse the influence of the longitudinal end effect on SRLMs and to investigate simple but practical compensation methods for the performance improvement of linear machines. Through magnetic circuit analysis, a new compensation method which is widening stator end poles is proposed for the first time. Three-dimensional finite element analysis (3D FEA) shows that this new method can decrease the force factor by about 93.9%, while the previously used method which is adding auxiliary stator poles can decrease the force ripple factor by only about 27.5%. In addition, the proposed method needs less extra space than the previous method. Hence, the new compensation method is more practical and more efficient. Furthermore, the theoretical value of optimal width of stator end poles is expressed, and its effectiveness is confirmed by sensitivity analysis.

Instantaneous Thrust Control of the Linear Switched Reluctance Motors with Segmental Translator

The linear switched reluctance machine (LSRM) has all advantages of rotary switched reluctance machine including simple and rugged structure, absence of magnetic material and windings on translator, high reliability and appropriate performance over a wide range of speed. Like rotary switched reluctance motor with segmental rotor, segmental translator linear switched reluctance motor (STLSRM) has capability to produce higher output power/weight in comparison to the conventional linear switched reluctance motors. Due to high advantages of the STLSRM drive, various control algorithms including current control, model predictive control, direct force control, universal control and force distribution function are investigated for the first time to control the instantaneous thrust of this motor. Applying these algorithms to a typical three-phase STLSRM, simulation results are presented and they are compared together from the force ripple reduction point of view.

Tracking Control of Networked Multiple Linear Switched Reluctance Machines Control System Based on Position Compensation Approach

This paper proposes the precise tracking control for the multiple linear switched reluctance machines (LSRMs) with network-induced time delays by using the motor positions compensation method. Considering the mutual position disturbances among the multiple motors, two network topologies are proposed for the multiple LSRMs control system. In order to improve the tracking precision, the motor position signals are used to compensate the tracking errors among the three motors. The encoders-to-controller and the controller-to-actuator time delays are modeled as a discrete-time Markov chain which denotes the whole random time delay step for the closed-loop control system. The stability conditions and the tracking controller design method for the networked LSRMs control system are proposed by using Lyapunov theory and the inequality techniques. Several groups of experimental results are presented to verify the effectiveness and practicability of the proposed method for the networked multiple LSRMs control system.

Flux Characteristics Analysis of a Double-Sided Switched Reluctance Linear Machine Under the Asymmetric Air Gap

This paper analyzes the flux characteristics and normal force of the double-sided switched reluctance linear machine (SRLM) under the asymmetric air gap. The magnetic equivalent circuit (MEC) of the machine and the details of the flux paths configuration at six distinct mover positions under the asymmetric air gap are included. Then, six special mover position magnetization curves are calculated by solving the MEC with the method of Gauss–Seidel. The magnetic flux-linkage model and thrust model based on six distinct mover positions are established by analytical polynomial. Three-dimensional (3-D) finite-element method (FEM) simulation and the experimental study with the prototype hardware are carried out to validate the accuracy of the MEC model calculated for the flux linkage and normal force. The six distinct mover positions flux linkage and normal force calculated by the MEC are consistent with the 3-D FEM calculated data and experimental data. It indicates that the proposed method to calculate the flux linkage and the normal force is feasible and effective. The dynamic analysis is also conducted. The simulated phase current waveforms are also consistent with the experimental results. It indicates that the presented method can be used to simulate the phase current under the asymmetry air gap effectively. The normal force under different asymmetry rates is analyzed, which provides the theoretical basis for reducing the unbalanced force of the double-sided SRLM.