Primary Permanent Magnet Linear Motor Research Articles

A General Control Method for Half-Centralized Open Winding Permanent-Magnet Motor Drive System

In this paper, a general control method based on duty ratio selection for half-centralized open winding primary permanent-magnet linear motor (HCOW-PPMLM) drive system is proposed. The proposed control method is designed from the perspective of single-phase subsystem. The novelty of this paper is the voltage process and modulation, which can realize the expansion from two movers to multi movers. The design of voltage process and modulation contains voltage preprocessor, saturation limiter and duty ratio distributor. In the voltage preprocessor, phase voltages are transferred to phase modulation index. The saturation limiter deals with excessive phase modulation indexes based on the independent over-modulation principle. The duty ratio distributor distributes the voltage demand into inverters by the common-leg-based distribution principle. Compared to existing method, the proposed control method can realize the expansion from two movers to multi movers and has less computation burden. In addition, more mover quantities will not increase the complexity of analysis and design. Finally, the effectiveness of the proposed control method has been verified by experimental results.

Adaptive backstepping control of primary permanent magnet linear motor via radial basis function neural network and command filter

This paper studies the displacement and speed control of primary permanent magnet linear motor (PPMLM) under the influence of unmodelled load interference, time-varying parameters and end effects. Adaptive backstepping control is first proposed to ensure system stability in the presence of time-varying parameters during motor movements. Then, radial basis function (RBF) neural network is used to compensate for the effect of the unmodeled load disturbance of the system. Furthermore, the command filter is implemented in the backstepping control to counteract the differential expansion phenomenon. The compensation signal is set to reduce the filtering error induced by the filter. Simulation results are given to verify the good performance of the proposed control in comparison with the adaptive backstepping controller and the command filter adaptive backstepping controller.

Fault-Tolerant Predictive Control for Five-Leg Dual-Mover Permanent-Magnet Motor Drives

In this paper, a fault-tolerant predictive control (FTPC) is proposed for the post-fault operation of five-leg dual-mover primary permanent-magnet linear motor (PPMLM) drives with open circuit fault (OCF). In the post-fault operation, one phase winding and one voltage-source-inverter (VSI) leg are lost. As a result, there are four VSI legs and five healthy phase windings from two movers. Especially, one VSI leg is shared by two movers. The objects of FTPC are to reduce the computation burden and improve the performances. Firstly, A minimum copper loss principle is designed to distribute the reference current for two movers. Secondly, two global optimal mover voltage vectors (MVVs) for two movers are respectively determined by geometrical location. Thirdly, the two global optimal MVVs are respectively modified as two local optimal MVVs, in which the influence of the common leg is considered. Finally, two synthesized voltage vectors are obtained to improve the steady-state performances. Meanwhile, 60% of the computation burden can be reduced by using FTPC. The effectiveness of the proposed FTPC have been verified by experimental results.

Electromagnetic design and temperature field analysis of hybrid excitation primary permanent magnet linear motor

Hybrid excitation primary permanent magnet linear motor has the dual advantages of high thrust density of primary permanent magnet linear motor and the flexibility on adjusting the air gap magnetic field of hybrid excitation motor. In this paper, two new 36/4 hybrid excitation primary permanent magnet linear motors with different secondary structures are proposed. Based on the detailed introduction of the motor topology and operation mechanism, the structural parameters are optimized, and the pole arc coefficient of the primary pole shoe and the secondary are finally determined to be 0.4. The secondary is magnetoresistive, and the final thrust adjustment range is about 16.8% under the conditions of optimal armature current and current lead angle. The temperature field of the motor in the magnetizing state is analyzed. The results show that the temperature of the motor decreases gradually from the center to both sides after 7200 s of operation of the new hybrid excitation structure, while the permanent magnet will not be demagnetized permanently. It shows an acceptable reliability.

Direct Thrust Force Fault-Tolerant Control of Primary Permanent Magnet Linear Motor With Single DC-Link Current Sensor for Metro Application

In order to improve the fault-tolerant control (FTC) ability of the current sensor of the primary permanent magnet linear motor (PPMLM) drive system, the direct thrust force control (DTFC) strategy with single DC-link current sensor is proposed. According to the principle of voltage vector equivalence, the present basic voltage vector is equivalent to two adjacent sub-basic voltage vectors to achieve the equivalence of the present candidate voltage vector. The principle of different phases based on the fact that the DC-link current is equal to or opposite to one of the phase currents is introduced. The output sequence of the two sub-basic voltage vectors is determined by the principle of different phase mode to ensure that the measured currents in the two adjacent periods are any two-phase currents in the three phases, and then the third-phase current is calculated. Finally, the effectiveness and correctness of the proposed DTFC (P-DTFC) is verified by simulation and experiment.

Unified Maximum Voltage Utilization Controls for Half-Centralized Open-End Winding Permanent-Magnet Motor Systems

In order to extend the speed range and reduce power electronics devices of the primary permanent-magnet linear motor traction system, a half-centralized open-end winding topology is studied in this article, in which <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> movers are supplied by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> +1 voltage-source inverters. In order to maximize the speed range, two unified maximum voltage utilization control (UMVUC) methods are proposed for the studied traction system, which can be easily implemented for any number of movers. The first UMVUC is named as the original UMVUC, and it requires a heavy computation burden, which makes the implementation difficult when the number of movers is large. For the linear motor system, the relative positions of all movers are approximately constant. Based on this feature, the second UMVUC named as simplified UMVUC is proposed, which can significantly reduce the computation burden. In order to suppress the zero-sequence current (ZSC) and reduce the switching loss, a zero-sequence polarity assignment method is employed in the proposed UMVUCs. An experiment platform is developed, and the effectiveness of the proposed UMVUCs has been validated by experimental results.

Direct Thrust Force Control of Primary Permanent Magnet Linear Motor Based on Improved Extended State Observer and Model-Free Adaptive Predictive Control

A model-free adaptive predictive control algorithm based on an improved extended state observer (IESO) is proposed to solve the problem that the primary permanent magnet linear motor is susceptible to time-varying parameters and unknown disturbances. Firstly, a model-free adaptive control algorithm based on compact format is designed to achieve high control precision of the system and reduce thrust fluctuation, only through the input/output data of the system. Because the traditional model-free adaptive control is too sensitive to the internal parameters of the controller, a combination of model-free adaptive control and predictive control is further developed. By predicting the data for a future time in advance, the sensitivity to the internal parameters of the controller is reduced and the control performance is further improved. Since the load change and other nonlinear disturbances in practical applications have a great impact on the control effect of the system, an improved extended state observer is further used to compensate for the impact of nonlinear disturbances on the control system. In addition, the stability of the closed-loop system is analyzed. Comparable simulation results clearly demonstrate the good tracking performance and strong robustness of the proposed control.

Collaborative Control for Half-Centralized Open-End Winding Permanent-Magnet Linear Motor Drive Systems

Inthis article, a half-centralized open-winding primary permanent-magnet linear motor (HCOW-PPMLM) drives system is proposed, in which two independent voltage-source-inverters (VSIs) and one common VSI are required to supply two open-winding movers. Compared to the traditional open winding motor topology, the proposed topology requires less half-conductor switches, which can reduce the construction cost, system volume, system weight, operation and maintenance cost, and failure rate. To achieve high-performance operation, a collaborative control is proposed for the proposed topology. Based on the principle that minimizes maximum voltage of VSIs, the voltage distributor in the proposed collaborative control is designed to maximize the dc bus voltage utilization. The effectiveness of the proposed topology and the proposed collaborative control have been verified by experimental results. The proposed topology is also compared with conventional open-winding PPMLM topology by variable speed and load experiments.

Deadbeat two-vector model predictive current control for open-winding primary permanent-magnet linear motor

The structure of open-winding motor fed by the dual-inverter can increase the winding terminal voltage of the primary permanent-magnet linear motor (PPMLM). So, it is an effective method to improve the thrust performance of the PPMLM. Based on the detailed derivation of the mathematical model of the open-winding PPMLM and the in-depth analysis of the space voltage vector distribution characteristics of the dual-inverter, a deadbeat two-vector model predictive current control (MPCC) model is proposed in this paper. First, the optimal vector of the inverter 1 is determined by judging the position of the large sector. Second, two optimal vectors of the inverter 2 is determined by judging the position of the small sector. Finally, the duty cycle of the two optimal vectors of the inverter 2 is calculated to realize the proposed deadbeat two-vector MPCC algorithm. Compared with the traditional model predictive torque control (MPTC) and MPCC strategies, the proposed algorithm has the advantages of lower current harmonics (lower 34 % and 44 % under rated conditions, respectively) and better thrust performance (higher 77 % and 61 % under rated conditions, respectively) as well as lower computational complexity. Simulation and experimental results show that the proposed two-vector MPCC has good steady-state and dynamic performances, which can reduce the current harmonics and thrust ripple, and thus improve the motor drive performance compared with the traditional method.

Direct Thrust Force Control of Half-Open Winding Primary Permanent Magnet Linear Motor

In this paper, a direct thrust force control (DTFC) strategy is proposed for the half-open winding primary permanent magnet linear motor (PPMLM) drive system in order to improve the dynamic response and performance of flux weakening control. The independent voltage active vector (IVAV) is selected as the candidate voltage vector to suppresses the zero sequence current in the proposed DTFC (P-DTFC). Meanwhile, a new switch table is designed to determine the control vector while the complexity of control method is greatly simplified in P-DTFC. The simulation and experimental results verify that P-DTFC maintains better steady-state and dynamic-state performance with lower complexity compared with traditional DTFC (T-DTFC).

Phase-Shifting Fault-Tolerant Control of Permanent-Magnet Linear Motors With Single-Phase Current Sensor

In this article, a phase-shifting fault-tolerant control (PS-FTC) method with single-phase current sensor is proposed for primary permanent-magnet linear motor traction system. The phase with healthy sensor is defined as the first phase, while the other two phases without healthy sensors are, respectively, defined as the second and third phases. In PS-FTC, hysteresis current control is adopted. The actual currents of the second and third phases are replaced by the estimated values, while the reference values are obtained by phase shifting of the estimated first-phase current. Although the linear motor parameters have been used in the calculation of the estimated currents, the parameter variations do not affect the performances of PS-FTC. Compared with the conventional fault-tolerant control (C-FTC) method and the existing fault-tolerant control schemes with single-phase current sensor, PS-FTC is robust and shows better steady-state performances. Furthermore, a hybrid strategy combining PS-FTC and C-FTC is adopted to improve the transient-state performances. The effectiveness of PS-FTC and the hybrid strategy are verified by the theoretical analysis and experimental results.

System construction of a four-side primary permanent-magnet linear motor drive mechanical press

A primary permanent-magnet linear motor (PPMLM) has a robust secondary structure and high force density and is appropriate for direct-drive mechanical press. The structure of a four-side PPMLM drive press is presented based on our previous research. The entire press control system is constructed to realize various flexible forming processes. The control system scheme is determined in accordance with the mathematical model of PPMLM, and active disturbance rejection control is implemented in the servo controller. Field-circuit coupling simulation is applied to estimate the system’s performance. Then, a press prototype with 6 kN nominal force is fabricated, and the hardware platform of the control system is constructed for experimental study. Punch strokes with 0.06 m displacement are implemented at trapezoidal speeds of 0.1 and 0.2 m/s; the dynamic position tracking errors are less than 0.45 and 0.82 mm, respectively. Afterward, continuous reciprocating strokes are performed, and the positioning errors at the bottom dead center are less than 0.015 mm. Complex pulse trajectories are also achieved. The proposed PPMLM drive press exhibits a fast dynamic response and favorable tracking precision and is suitable for various forming processes.

Coupled Fault-Tolerant Control of Primary Permanent-Magnet Linear Motor Traction Systems for Subway Applications

In this article, a coupled fault-tolerant control (C-FTC) is proposed for primary permanent-magnet linear motor traction system in subway applications. By coupling the faulty mover with a healthy mover, the proposed C-FTC can achieve continuous operation of the faulty mover, in which one or more current sensors fail. A healthy mover is determined as the reference mover. The switch-states of the reference mover are also applied to its mathematical model. As a result, synchronous currents of the reference mover are also estimated from its mathematical model, and they are treated as the reference currents of the mathematical model of the faulty mover. Hence, the switch-states of the faulty mover can be determined. Therefore, the faulty mover can be controlled without any current sensors. The key of C-FTC is to compensate the parameter variations and the nonlinear effects of the faulty mover drive system with those of a healthy mover drive system, which is the main contribution of this article. Comparing with the conventional current-sensorless control, C-FTC has stronger robustness to the parameter variations and the nonlinear effects. The effectiveness and robustness of the proposed C-FTC are verified by simulation and experimental results.

A Fault Diagnosis Method for Current Sensors of Primary Permanent-Magnet Linear Motor Drives

In this article, a fault diagnosis method is proposed to detect current sensor faults for the studied primary permanent-magnet linear motor (PPMLM) traction system, in which only two current sensors are required, and the gain fault and zero-offset fault can be distinguished. In this proposed fault diagnosis method, synchronous currents are estimated by the PPMLM model. By comparing the estimated and measured synchronous currents, estimation errors are calculated, and ac components can be extracted by corresponding filters. In the synchronous frame, the zero-offset fault and the gain fault can be detected by the single-frequency and double-frequency components, respectively. Furthermore, the fault phase also can be located. Compared with conventional fault diagnosis methods, the proposed one can distinguish gain fault and zero-offset fault but only two current sensors are required. Simulation and experimental results verify the effectiveness of the proposed fault diagnosis method.

Dual-Level Located Feedforward Control for Five-Leg Two-Mover Permanent-Magnet Linear Motor Traction Systems

Based on the model predictive current control (MPCC), a dual-level located feedforward control (DLFC) is proposed for the five-leg dual-mover primary permanent-magnet linear motor traction system, in which, two three-phase movers are fed by one five-leg voltage-source inverter (VSI). In the proposed DLFC, the studied traction system is divided into dual-level subsystems, including mover level and system level. In the mover level, it is assumed that one mover is fed by one three-leg VSI. The reference synchronous currents are replaced by the reference static voltages, and the model current predictions are eliminated by the discrete mover voltage vectors (MVVs). Furthermore, the global optimal MVVs are determined by the mover-level geometrical location. If the implementation conflicts between two global optimal MVVs, two local optimal MVVs will be determined by the system-level geometrical location to replace one former global optimal MVV. Compared with MPCC, the computation burden of DLFC can be significantly reduced. If both control methods use the same sampling period, they have the same performances. On the other hand, DLFC can use shorter sampling period, and it can perform better than MPCC. All the theoretical analyses are verified by simulation and experimental results.

Magnetic field analysis of Primary Permanent Magnet Linear Motor Based on Halbach Distribution

The rail transit system driven by linear motor has outstanding advantages in climbing ability, traction performance, vibration and noise. However, with the increase of traffic travel and other situations, how to ensure that the linear motor still has a large thrust and stability in the air gap condition is the key technical problem. In order to solve this problem, three Halbach permanent magnet array structures are proposed and applied to the magnetic barrier coupled primary permanent magnet unilateral excitation linear motor (MBCPPMUELM). The finite element software is used for simulation and analysis. By comparing the harmonic distribution of air gap magnetic field of the three Halbach permanent magnet array motors, a topology structure with high magnetic field modulation effect is obtained It provides a useful reference for the further design and analysis of this kind of motor.

Fault-Tolerant Control of Primary Permanent-Magnet Linear Motors With Single Phase Current Sensor for Subway Applications

Because both magnets and windings can be mounted in the mover, the primary permanent-magnet linear motor (PPMLM) has a low-cost advantage for subway applications. In this paper, a fault-tolerant control (FTC) with single phase current sensor is proposed for PPMLM traction system in subway applications. In the proposed FTC, d - and q -axis currents are estimated from the reference synchronous currents and the surviving measured phase current. The estimation is robust since no machine parameters are required. In steady-state operation, the estimated current errors are half the actual ones. As a result, the current response is slowed but the current command can be achieved. However, the achievement of control target depends on the current tracking accuracy, which is enhanced by the voltage decoupler. Compared with existed FTC schemes, the proposed one is robust and has better transient-state performances. The effectiveness of the proposed FTC is verified by theoretical analysis and experimental results.

Simplified Model Predictive Current Control of Primary Permanent-Magnet Linear Motor Traction Systems for Subway Applications

In this paper, a simplified model predictive current control (MPCC) is proposed for the primary permanent-magnet linear motor traction system in subway applications, which is fed by one two-level voltage-source-inverter (VSI). Based on the deadbeat concept, the reference voltage vector is calculated to eliminate the difference between the measured and reference currents in the next sampling period. Due to the discrete feature of the VSI, the reference voltage vector usually cannot be provided. Hence, the distance of a voltage vector is defined, and the voltage vector with the shortest distance is selected as the optimal one, which is called as the shortest distance principle in this paper. According to the shortest distance principle, the distribution of the reference voltage vector is divided into seven sectors, and the optimal voltage vector can be easily determined considering the location of the reference voltage vector. As a result, the computation cost is significantly reduced. However, the performances of MPCC are not affected by this simplification. The equivalence between the proposed and conventional MPCCs is proved in theory. All the theoretical analyses are verified by experimental results.

Direct Thrust Force Control of Primary Permanent-Magnet Linear Motors With Single DC-Link Current Sensor for Subway Applications

Because both magnets and windings can be mounted in the mover, the primary permanent-magnet linear motor (PPMLM) has a low-cost advantage for subway applications. In this paper, a novel direct thrust force control (DTFC) with single dc-link current sensor is proposed for PPMLM traction system in subway applications. The first phase current is directly measured by the dc-link current sensor. The second phase current is sensed with a limited delay, which is strictly limited by the limited measurement delay principle. The third phase current is calculated based on the condition that the summation of the three phase currents is zero. During the current reconstruction, no motor parameters are required. Because PPMLM may sink in the same phase for a long time and affect the current reconstruction accuracy, the single optimal target is proposed to re-select the original voltage vector. Compared with the conventional DTFC scheme, the proposed one has nearly the same performances; especially, the maximum speed and response time remain nearly unchanged. The effectiveness of the proposed DTFC scheme is verified by experimental results.

A Primary Permanent-Magnet Linear Motor for Urban Rail Transit

In this paper, a new permanent-magnet (PM) linear motor is proposed, in which both the magnets and armature windings are placed in the short mover, while the long stator consists of iron core only. Hence, this new PM linear motor can be called a primary permanent-magnet linear motor. It exhibits the advantages of robustness, low cost, high efficiency, high power factor, and high thrust force density. It is especially suitable for long stator applications such as urban rail transit. In this paper, the topology and operation principle of this motor are discussed in detail. The steady-state characteristics including field distributions, flux-linkage, back-EMF, phase inductance and thrust force are investigated. In addition, the technique of skewing stator teeth is adopted to improve the electromagnetic performance. Results from finite element method (FEM) verified the theoretical analysis results.