back-EMF Research Articles

Speed Control Strategy of Low-Cost Modular Permanent Magnet Synchronous Linear Motor Based on Sliding Mode Vector Tracking Observer

In order to achieve the low-cost position detection of modular permanent magnet synchronous linear motor (MPMSLM), three switching Hall sensors space 120° apart are designed. Two groups of Hall detection board are installed to ensure the position detection is effective throughout the process. The motor speed and electrical angle are extracted from Hall signals using Taylor expansion. In addition, a sliding mode observer (SMO) is designed to estimate the back EMF. Then, the information of SMO and Hall sensors is integrated by vector tracking observer. Eventually, a closed-loop speed control system based on sliding mode vector tracking observer is established. The experiments are carried out on the linear segment of MPMSLM. The results show that the proposed method can estimate motor speed and electrical angle accurately at the full-speed range.

Back EMF Measurement Method and Consideration for Predicting Vibration of Brushed DC Motor

Back EMF Measurement Method and Consideration for Predicting Vibration of Brushed DC Motor

A Novel Methodology to Enhance the Smooth Running of the PM BLDC Motor Drive Using PWM-PWM Logic and Advance Angle Method

This paper addresses the active torque ripple compensation of a permanent magnet brushless direct-current motor (PMBLDC) drive with a new pulse width modulation (PWM) technique and advance angle method. Torque ripple is a well-known problem in BLDC motors which is produced by a discrepancy between the stator current and the back electromotive force (back-emf) waveforms. The advanced angle method proposed in this paper generates a maximum torque in the PM BLDC motor by decreasing the displacement between the phase voltage and phase current in proportion to the load. Further, a simple and comprehensive PWM-PWM logic is proposed in this paper to reduce the torque ripples. The test results show that the BLDC motor drive achieves good steady-state performance while maintaining a quick dynamic response. The performance of the PWM-PWM logic and advance angle method, have been tested and compared with the practical results for the characteristics of DC bus voltage, DC bus current, electromagnetic torque, shaft torque, mechanical torque, phase voltage, phase current and PWM signal.

Wide-Speed Range Sensorless Control of Five-Phase PMSM Drive under Healthy and Open Phase Fault Conditions for Aerospace Applications

This paper presents a speed sensorless control of a five-phase PMSM in healthy operation and under the Open-Phase Fault on any phase of the machine. The solution is recommended for mission-critical applications requiring high reliability capacities, such as Aerospace applications. An adapted Active Fault Tolerant Control is proposed with the aim of obtaining electromechanical torque as close as possible to that normally developed by a machine working in healthy condition. In instances of a loss of power to one phase of the machine, a reconfiguration of the control law is performed to ensure the continuity of service and to maintain acceptable control performances without requiring a hardware rearrangement of the power architecture. The motor rotation speed and position, required for the Field Oriented Control (FOC) of the stator currents, are estimated using a Back-Electromotive Forces (Back-EMF) observer based on a mathematical model of the motor and implemented in the stator diphase reference frame. Different electrical models that describe the behavior of the five-phase machine in the normal and degraded operations are given. Experimental results on a 1.25 kW synchronous PM machine are shown to confirm the effectiveness of the motor control.

Design Optimization of a New Hybrid Excitation Drive Motor for New Energy Vehicles

In this paper, a new hybrid excitation drive motor (HEDM) was proposed to solve the problem of an uncontrollable magnetic field of a permanent magnet motor. The rotor part of the motor was composed of a combined magnetic pole permanent magnet rotor and a brushless electric claw rotor, in which the combined magnetic pole permanent magnet rotor has a parallel magnetic circuit structure. According to the characteristics of the parallel rotor structure, the equivalent magnetic circuit model was established, and the no-load leakage flux coefficient of the claw pole rotor was calculated. The Taguchi method was used for objective optimization of the permanent magnet rotor structure. The distortion rate of no-load back electromotive force (EMF) was taken as the first optimization goal; the cogging torque and the average torque were taken as the second optimization goal; and the torque fluctuation coefficient was a constraint condition. The optimal parameter matching under the mixed horizontal matrix was obtained. The parameters of the claw pole were optimized by using the method of uniform variables, and the dimension parameters of the motor were obtained. Finite element analysis and prototype tests were carried out for the optimized motor structure. The rationality and feasibility of the new HEDM as a vehicle motor were verified, which provided a possibility for the application of the new energy vehicle drive motor field.

Irreversible Demagnetization Improvement Process of Hybrid Traction Motors with Dy-Free Magnets

Permanent magnet synchronous motors (PMSMs), with their high power density, high efficiency, and thermal stability, are widely used nowadays. PMSM magnets are composed of rare earth elements. However, rare earth elements are subject to severe price fluctuations because of their limited availability and the monopoly of some countries. Therefore, extensive research on magnets devoid of rare earth elements has been conducted recently. Although a magnet devoid of rare earth elements has a high irreversible demagnetization rate at high temperatures owing to its low coercive force, an irreversible demagnetization improvement process is proposed in this paper to compensate for this disadvantage. This process analyzes the contribution of the magnet’s back EMF (electromotive force) using the flux linkage equation, which does not change with time. Next, the location of irreversible demagnetization is moved to a position with a low contribution to the back electromotive force. Consequently, even if irreversible demagnetization occurs at the same size, the irreversible demagnetization ratio is reduced. The proposed process can minimize irreversible demagnetization while maintaining performance.

A Generalized Fault Tolerant Control Based on Back EMF Feedforward Compensation: Derivation and Application on Induction Motors Drives

In this paper, a fault-tolerant three-phase induction drive based on field-oriented control is studied, and an analytical approach is proposed to elucidate the limitations of FOC in flux-torque regulation from the controller perspective. With an open-phase fault, the disturbance terms appear in the controller reference frame and degrade the controller performance when operating in a d-q plane with DC quantities. In addition, the hardware reconfiguration, which is essential to operate faulted three-phase drives, causes substantial change in the way the control parameters vd, vq are reflected onto the machine terminals. An accurate understanding of the feedforward term, by considering the open-phase fault and the hardware modifications, is provided to re-enable the FOC in presence of an open-phase fault. Furthermore, the concept of feedforward term derivation is generically extended to cover multiphase induction drives encountering an open-phase fault whereby no hardware reconfiguration is intended. The proposed method is explained based on a symmetrical six-phase induction and can be extended to drives with a higher number of phases. The effectiveness of the proposed derivation method, which is required to form a feedforward fault-tolerant controller, is verified and compared through the simulation and experiment, ensuring smooth operation in postfault mode.

A Study on The Electromagnetic Multi-Step Transmission Characteristics of Interior Permanent Magnet Synchronous Motors

In this paper, electromagnetic multi-step transmissions are introduced as a method for increasing the torque and efficiency of electric vehicle driving motors. Motors using permanent magnets have a limited ability in increasing the speed as the back electromotive force increases as the speed increases. The electric vehicle driving motor performs field-weakening controls to increase the speed after the rated point. Field-weakening control increases the rotor’s speed by weakening the magnetic flux of the field. At this time, the output is constant as the speed increases. Motors have voltage limits, which also affect the maximum speed of the motor. In order to improve these constraints, there is a case study of electromagnetic shifting phenomena. Examples of the research include the wye-delta method and the method of changing the number of equivalent serial turns. As in the case of previous studies, the problem of increasing back electromotive forces as the speed increases is solved. In this paper, we propose a method to increase the maximum speed by changing the number of parallel paths. In order to lower the back electromotive force at high speeds, the number of parallel paths of the stator windings changed via the thyristor. As the number of stator parallel paths increases, the back electromotive force decreases. When the back electromotive force is lowered, the torque that can be output is reduced, but the maximum speed can increase as the voltage is also lowered. Before shifting, the number of parallel paths is set to two to satisfy high torque at low speeds. After shifting, the maximum speed can be increased to 4 with the number of parallel paths, which can broaden the operating range of the motor. In addition, the resistance of the stator windings is reduced by increasing the number of parallel paths in the high-speed region. The loss that accounts for the largest proportion of the electromagnetic loss of the motor is copper loss, and by reducing it, the efficiency increased. As a result, it increases the operating area and simultaneously increases the high-efficiency area. In order to analyze the electromagnetic characteristic, a finite-element-method-based simulation was used.

Sensor Fusion of Self-Sensed Measurements for Position Control of a Constant Air-Gap Solenoid

This article presents a novel constant air-gap solenoid (CAS) actuator design that can perform accurate and wide-bandwidth closed-loop position control with two fused self-sensed plunger measurements. The recently patented CAS actuator is experimentally validated to be the first electromagnetic actuator with the ability to simultaneously produce two plunger position measurements with complementary bandwidth characteristics. First, a variable reluctance differential solenoid transducer (VRDST) is converted into a stacked CAS actuator through minor geometry modifications. Next, two complementary self-sensing methods that are based on inductance and back electromotive force (BEMF) are selected. Then, a complementary filter design is proposed to fuse the inductance- and BEMF-based self-sensing methods. Afterward, the design and fabrication of the prototype CAS actuator and the experimental setup are discussed. The experimental setup is then used to characterize the prototype CAS actuator and observe the performance of the individual self-sensing methods. Finally, the fused measurement is used for feedback in closed-loop position control. The closed-loop position control experiments show that the self-sensed feedback performs comparably with a dedicated high-end laser vibrometer. Furthermore, the results show that the sensor fusion output performs better than the individual self-sensing methods.

A Review of Torque Ripple Reduction Design Methods for Radial Flux PM Motors

Nowadays the efficient use of energy is a major issue in applications such as electric vehicles. However, there are some phenomena that affect electric vehicle performance. One of those phenomena is the torque ripple of electric motors, which interferes with traction and the suspension system (causing vibration that stresses this system), and it can also introduce electric current harmonics into the battery, reducing its life, since torque ripple is partly a consequence of non-sinusoidal back EMF. For those reasons this is a topic worth investigating. The torque ripple of permanent magnets (PM) motors can be reduced in design or through control. Since control techniques have been reviewed and design methods have not, this paper presents a comparison of several design techniques to reduce torque ripple by different approaches and categorize them to show the characteristics of each group. A discussion is then made about the advantages and disadvantages of the designs, in general, as well as some comments about the missing, but important information, in the papers, such as the effects on efficiency. The study shows that a combination of methods provide the best results, although it complicates fabrication and suggests that this is a promising line of future investigation on torque ripple reduction methods.

A Study on Reduction of Cogging Torque and Magnet Usage through Intersect Magnet Consequent Pole Structure

Owing to the shortage of rare-earth magnetic materials, various methods are being examined to reduce the use of magnets. One of these is a consequent pole. The consequent pole model can reduce the use of magnets by 50% using only one pole of the magnet and replacing the other pole with iron. However, the consequent pole has the disadvantage of generating back EMF asymmetry and a high cogging torque. In this study, an intersect magnet consequent pole structure is proposed to overcome the disadvantages of the existing consequent pole. Two methods have been proposed to improve axial leakage magnetic flux caused by the intersect magnet consequent pole structure. Finally, we propose a method to reduce the cogging torque and minimize the use of magnets with the same performance standard. For motor design, two-dimensional and three-dimensional finite element analysis was used, and comparative analysis was performed via simulations for several models. The existing model and the final model were compared and verified.

An Efficient and Robust I-f Control of Sensorless IPMSM With Large Startup Torque Based on Current Vector Angle Controller

Interior permanent magnet synchronous motor (IPMSM) with back electromotive-force (EMF) based sensorless field-oriented control (FOC) is widely used in medium-high speed applications. Unfortunately, the back EMF is too small to be estimated accurately during low speed operation. Hence, the current-frequency ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I–f</i> ) control with controllable current vector is used for startup. However, the conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I–f</i> control is hard to realize the tradeoff between startup speed and load capacity, suffering high-acceleration and high-load startup failure. In this article, a current vector angle controller for sensorless IPMSM startup is proposed to adjust speed-up-stage current acceleration and constant-speed-stage current amplitude with load automatically. The proposed angle controller guarantees the current vector angle close to the maximum torque per ampere angle, which contributes to large startup torque, high operating efficiency and smooth transition from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I–f</i> startup to sensorless FOC. Furthermore, the robustness against parameters variation of angle controller is evaluated quantitatively. These theoretical advantages are verified in experiments with a 380 V, 1.5 kW IPMSM. In particular, the experimental results demonstrate that the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I–f</i> control realizes full-load startup even with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{ \pm }}$</tex-math></inline-formula> 50% flux linkage and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\rm{ \pm }}$</tex-math></inline-formula> 30% inductance variation. Furthermore, the startup acceleration auto-adjusts with load to reconcile startup speed and load capacity.

PMSM Demagnetization Fault Diagnosis Based on Back-EMF Signal

To study the irreversible demagnetization fault of the permanent magnets (PMs) in the permanent magnet synchronous motor (PMSM), a two-dimensional Finite Element (FE) model of the PMSM is built by the Finite Element Method (FEM). Analysis of demagnetization faulty mechanism of the electric and magnetic signals under local demagnetization conditions is conducted. The no-load Back-EMF signal is adopted as the indicator of the demagnetization faults of PMSM. In this paper, the faults of uniform demagnetization and single magnet demagnetization are studied through FEA. Therefore, the relationship between the amplitude of the back EMF and the degree of demagnetization is obtained. Moreover, the fitting curve is obtained by using the least squares method from multiple sets of FEA results. The results show that the method can effectively diagnose the demagnetization fault of the PMs of the PMSM, and could provide the guideline for online health monitoring of the PMSM in future research works.

Research of a Stator PM Excitation Solid Rotor Machine for Flywheel Energy Storage System

A typical flywheel energy storage system (FESS) includes an electrical machine, a flywheel, and magnetic bearings, which are independent of each other. Therefore, the structure of FESS is complicated, which leads to the problems of high cost and low integration. This article presents a novel stator PM excitation solid rotor machine (SPE-SRM) for FESS, which integrates an electrical machine, flywheels, and a magnetic bearing. The design method of the SPE-SRM is presented specifically. First, the structure and operation principle of the SPE-SRM are illustrated. Second, the design and optimization of the flywheel-rotor are presented with considering of power, energy storage, and mechanical strength. Third, the magnetic equivalent circuit of the SPE-SRM is established to simplify the design. Besides, the armature reaction and leakage flux factor are investigated. Fourth, the performance indexes, including torque, suspension force, no-load back electromotive force (back-EMF), losses, and temperature rise are fully analyzed by the finite element analysis. Finally, a 22 kW prototype is manufactured and tested. The rationality of the concept and design is validated by experiments. The SPE-SRM has the merits of high integration, robust structure, and low cost, so it has the potential for wide application in FESS.

Complex-Coefficient Synchronous Frequency Filter-Based Position Estimation Error Reduction for Sensorless IPMSM Drives

Accurate rotor position is significant for the back electromotive force (EMF)-based sensorless interior permanent-magnet synchronous motor (IPMSM) control. However, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">±</i> (6 h±1)th harmonics will appear obviously in the estimated back-EMF due to the effect of the inverter nonlinearity and flux spatial harmonics. These harmonics will subsequently result in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">±</i> (6 h)th harmonic pulsation in the estimated rotor position. In order to deal with this issue, a new complex-coefficient synchronous frequency filter (CCSFF)-based sliding mode observer combined with a quadrature phase-locked loop (PLL) is proposed to mitigate the back-EMF voltage distortion. Therefore, the performance of the position estimation is remarkably improved. The proposed CCSFF possesses both bandpass-filtering and frequency-adaptability characteristics. It can pass the fundamental component without magnitude attenuation and phase delay in different frequency scenarios. Moreover, the linearized model of the proposed CCSFF-PLL-based position estimation system is established and a systematic parameter design is presented to obtain promising dynamic performance. The effectiveness and feasibility of the proposed method are confirmed by experiments on a 1.5-kW IPMSM test platform.

A Lag Compensation-Enhanced Adaptive Quasi-Fading Kalman Filter for Sensorless Control of Synchronous Reluctance Motor

A novel position estimation strategy based on lag compensation-assisted adaptive quasi-fading Kalman filter (LC-AQFKF) is proposed for synchronous reluctance motor (SynRM) sensorless drive in this article. In LC-QFKF, the quasi-fading factor is derived to avoid the harsh assumptions of conventional adaptive fading Kalman filter, and accessibility of the method is improved while ensuring the estimation accuracy. The computational efficiency of LC-AQFKF is promoted by introducing the quasi-fading factor into the prediction error covariance matrix. Moreover, the frequency characteristic of AQFKF-based active back electromotive force observer is analyzed, and the phase lag problem in high-speed situations caused by the low-pass filtering property of AQFKF is overcome. In this way, the estimation accuracy of the rotor position is significantly enhanced. Besides, the double dynamic position compensation method is put forward to strengthen the position estimation performance of sensorless SynRM drive under dynamic conditions. The effectiveness of the proposed scheme is validated at a 1.5 kW SynRM drive.

Online Inductance Identification Using PWM Current Ripple for Position Sensorless Drive of High-Speed Surface-Mounted Permanent Magnet Synchronous Machines

Back–electromotive force estimation-based rotor position estimation methods are usually adopted for high-speed surface-mounted permanent magnet synchronous machines (SPMSM) drive to deal with the limitations of position sensors in high-speed applications. Considering inductance mismatch is the main cause of the position estimation error, this article proposes a novel pulsewidth modulation (PWM) current ripple-based online inductance identification method to improve the position estimation accuracy. The proposed method utilizes the inherent PWM current ripple of the voltage source inverter for inductance identification. In addition, the transient circuit equations on the estimated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\gamma \delta$</tex-math></inline-formula> frame are adopted as the identification model, and the recursive least squares method is used to obtain the estimated inductance. Compared with the traditional parameter identification methods, the proposed method does not need to inject additional signals or fix parameters. During the sensorless drive of high-speed SPMSM, the proposed method can accurately identify the inductance while not affecting the normal operation of PMSM at all, which is the main contribution of this article. With the proposed method, the estimated inductance can rapidly converge to the accurate value, and then the position estimation error will be eliminated. Finally, the effectiveness of the proposed method is verified by simulations and experiments.

Improved AVF-PLL-Based Position Estimation Scheme for SPMSM Sensorless Drives

The combination of a high-performance filter and phase-locked loop (PLL) has been presented as an effective alternative for the position estimation of a permanent magnet synchronous motor (PMSM) drive. However, the feedback delays existing in the practical implementation of the filter and PLL usually lead to position estimation deviation. To enhance the accuracy of position estimation, this paper proposes a sensorless control technology based on an improved adaptive vectorial filter (AVF) and PLL. First, the effect of feedback delay on the filtering performance of the AVF and the tracking performance of the PLL are analyzed. Then, corresponding delay compensation methods for the AVF and PLL are proposed. A compensation term based on the prediction of the filtered back electromotive force (EMF), which can repress the filtering performance degradation caused by feedback delays, is introduced and combined with the conventional AVF. As a result, the amplitude and phase shifts with the filtered back EMF can be effectively eliminated before applying it to the PLL. A differential calculation structure, which can ensure that the closed-loop transfer function of the equivalent ideal PLL is the same as the ideal PLL under the condition of feedback delay, is proposed to replace the cascade calculation structure of the conventional PLL. In addition, an open-loop deviation compensation method is integrated to eliminate the position estimation static deviation. The effectiveness of the proposed sensorless control technology is investigated by experimental tests.

Sensorless Brushless Motor Phase Compensation Speed Control

This paper proposes angular velocity vector feedback speed control system, the amplitude and phase signals of diagonal velocity are extracted, and signals are converted into current and voltage vector signals to achieve high efficiency and speed precision. Brushless motor rotational stability on speed and torque are classified, comparative characteristics analysis of dynamic speed and torque between conventional method and proposed method are simulated, results consisting of speed accuracy, the waveform of stator current and back electromotive force of each phase are all compared and analyzed, verifying fitness and validation of the proposed method.

Improved Position Sensorless Piston Stroke Control Method for Linear Oscillatory Machine via an Hybrid Terminal Sliding-Mode Observer

Since the piston stroke of linear oscillation machine (LOM) is very important for the safe and reliable operation of the system, it is necessary to effectively control the piston stroke. Besides, considering that the use of position sensor will reduce the system reliability, so the accurate position sensorless method is needed to obtain the stroke signals. In this article, a hybrid terminal sliding-mode observer is designed by combing a second-order nonsingular terminal sliding mode (SNTSM) and a high-order sliding-mode (HOSM) to estimate the back-electromotive force signals of the LOM. The SNTSM surface is selected to ensure that the system state variables can converge in a finite time and the HOSM control law is designed by introducing a variable exponential reaching law, which can strengthen the stability of the observer and greatly reduce the sliding chattering. Since the piston stroke is calculated by integrating the estimated piston velocity, the pure integral saturation will occur due to the presence of dc components in the measured current and voltage. In order to cope with this problem, one self-adaptive band-pass filter is introduced to replace the pure integrator, which can obtain smooth stroke signals with almost no amplitude and phase offset. Moreover, the current amplitude controller is designed to improve the control accuracy and response speed. Finally, comprehensive simulation and experimental results are provided to verify the effectiveness and the superiority of the proposed method.