Variable Flux Memory Machines Research Articles

Novel Magnetization State Closed-Loop Control for Variable Flux Memory Machine

Novel Magnetization State Closed-Loop Control for Variable Flux Memory Machine

Investigation of the over-load unintentional remagnetization effect in series hybrid magnet variable flux memory machine

Variable flux memory machines (VFMMs) have become a research hotspot due to their adjustable air-gap flux with the employment of low coercive force (LCF) permanent magnets (PMs). Series hybrid magnet VFMMs (SHM-VFMMs) utilizing series-magnetic-circuit high coercive force (HCF) and LCF PMs are extensively investigated due to their excellent unintentional demagnetization (UD) withstand capability. Nevertheless, the existing researches still focus on the UD of LCF PMs under heavy load operation, and the remagnetization issue remains unreported. Therefore, in this paper, the over-load unintentional remagnetization (UR) effect of the a dual-layer-SHM-VFMM (DLSHM-VFMM) is first revealed, and its mechanism is investigated and analyzed in depth based on finite element (FE) analyses. A DLSHM-VFMM prototype is manufactured and tested to verify the effectiveness of the theoretical analyses.

Winding Characteristics and Magnetization State Regulations of Variable Flux Memory Machines With Segregated Distributed Windings

The variable flux memory (VFM) machine with segregated multiple three-phase windings is investigated, with particular reference to its winding characteristics and magnetization state (MS) regulations. The overlapped distributed windings are separated into multiple three-phase winding sets with each set non-overlapped, which contributes to the independent relationship between the winding set and corresponding permanent magnet (PM) pole-pairs. Consequently, the single winding set can independently complete the MS regulation, and thus the overall current requirement is reduced. Moreover, it is revealed that the amplitude of de/re-magnetizing magneto-motive force (MMF) with single winding set operation is actually higher than those with multiple winding sets operation thanks to the asymmetric winding layout, resulting in the enhanced de/re-magnetizations and thus the further reduced de/re-magnetizing currents. The winding function, MMF distribution, inductance, and torque of the machine are analyzed, and intentional MS regulations with different methods are compared. A prototype machine is fabricated and tested for experimental validations.

An Improved Observer-Based Current Decoupling Method for Mitigating Speed Fluctuation of Variable Flux Memory Machines

An Improved Observer-Based Current Decoupling Method for Mitigating Speed Fluctuation of Variable Flux Memory Machines

Multi-objective Hierarchical Optimization Method with Decoupling Capability for Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Multi-objective Hierarchical Optimization Method with Decoupling Capability for Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Sensorless Control of Variable Flux Memory Machines Based on Improved Extended EMF Model and Adaptive Extended State Observer

Sensorless Control of Variable Flux Memory Machines Based on Improved Extended EMF Model and Adaptive Extended State Observer

Q-axis Current Reverse Control of Variable Flux Memory Machines With High Salient Ratio During Magnetization Process for Speed Fluctuation Reduction

For variable flux memory machine (VFMM) with high salient ratio, a negative torque occurs when applying a positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_d</i> ) pulse to magnetize the machine under positive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> ), causing a large speed drop. Since traditional speed controllers tend to increase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> at this point to increase the speed, unfortunately the higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> will generate stronger negative torque and further exacerbate the speed drop. To deal with this unique problem, a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis current reverse control (QCRC) concept is proposed to achieve non-negative torque by reversing <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i_q</i> current during the period of negative torque occurrence. Specifically, based on QCRC concept, three control methods are newly designed, including look-up-table-based QCRC method (Method I), disturbance observer assistance + Method I (Method II) and disturbance-observer-based QCRC method (Method III). A super-twisting sliding mode torque observer (STSMTO) is newly structured as the disturbance observer. Furthermore, a linear active-disturbance-rejection-based feedforward decoupling (LADR-FFD) current controller is utilized to improve the current tracking performance, and the effect of its intrinsic time delay is also investigated. Finally, the effectiveness and feasibility of the proposed three control methods are validated through experimental measurement on a separated series-parallel VFMM (SSP-VFMM).

Comparative Investigation on Dual Three-Phase Variable Flux Memory Machines for Vehicle Tractions

Comparative Investigation on Dual Three-Phase Variable Flux Memory Machines for Vehicle Tractions

A Novel Dual Magnetizing Current Controller to Mitigate Speed Fluctuation During Magnetization State Manipulation for Variable Flux Memory Machines

A Novel Dual Magnetizing Current Controller to Mitigate Speed Fluctuation During Magnetization State Manipulation for Variable Flux Memory Machines

Finite Set Model Predictive Current Control for Variable Flux Memory Machine with a Novel ThreeLayer Optimization Strategy

Finite Set Model Predictive Current Control for Variable Flux Memory Machine with a Novel ThreeLayer Optimization Strategy

A Novel Separated Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Aiming at the problems of the existing hybrid-magnetic-circuit variable flux memory machine (HMC-VFMM), such as weak flux regulation (FR) capability and low efficiency in high-speed region, etc., this article proposes a novel separated HMC-VFMM (SHMC-VFMM), which innovatively arranges a series magnetic circuit on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis and a parallel magnetic circuit on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis. The SHMC design can simultaneously reduce the PMs fluxes through low-coercive-force PMs configured on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis, which will improve the FR capability. The magnetic saturation is alleviated by reducing the usage of high-coercive-force PMs, which further broadens the FR range. The proposed design also simplifies the rotor mechanical structure, thereby improving the rotor design flexibility. Firstly, the topological evolution process and the working principle of the proposed machine are interpreted in in succession. Then, the mechanism of further expanding the FR range of the proposed machine is revealed by comparing its equivalent magnetic circuit model with that of the existing machine. Subsequently, the electromagnetic characteristics of the two compared machines are analyzed by using the finite element method, which validates the performance advantages of the proposed machine. Finally, an SHMC-VFMM prototype is manufactured and measured to verify the superiority of the proposed SHMC design.

A Novel Series Magnetic Circuit Variable Flux Memory Machine With Self-Flux Leakage Paths

Variable flux memory machine (VFMM) applying low coercivity force (LCF) permanent magnets (PMs) is suitable for electric vehicles (EVs) since its air-gap flux can be adjusted easily. In this article, a novel series magnetic circuit VFMM with self-flux leakage paths (SMC-VFMM-SLP) is proposed, in which the design concept of self-flux leakage is introduced to enhance air-gap flux regulation (FR) range and keep high torque density simultaneously. The self-flux leakage paths can control the self-flux leakages based on the magnetization states (MSs) of the employed LCF PMs. The machine can thus keep a high torque density under the positive MS and achieve excellent flux-weakening ability under the negative MS when it is loaded. First, the topology and the FR range expansion principle of SMC-VFMM-SLP are interpreted in detail, in which the magnetic circuits under different MSs are qualitatively analyzed. The electromagnetic performance of SMC-VFMM-SLP under the positive and negative MSs is subsequently investigated by the finite element method, including no-load characteristics, torque abilities, and efficiency maps. Finally, an SMC-VFMM-SLP prototype is manufactured and measured, which confirms the feasibility of the proposed self-flux leakage paths design for the air-gap FR range improvement.

Investigation of Delta-Type Variable Flux Memory Machines Considering Magnetizing Current Limits

A simple delta-type interior-permanent magnet (PM) variable flux memory (VFM) machine exhibiting series-parallel magnetic coupling is investigated, and the limits of magnetizing current capacity are considered. The series-parallel coupled high coercive force (HCF) PMs and low coercive force (LCF) PMs integrate the merits of stable PM working point in series-type VFM machines with the high torque output in parallel-connected cases. Moreover, it is revealed that the iron bridges between the two kinds of the PMs play an essential role on magnetic coupling, de-/re-magnetization and torque capability. The VFM machines with wider iron bridges normally require higher magnetizing currents. The effects of the iron bridges are investigated based on the theoretical analysis and finite element methods. It is found that the narrower iron bridges contribute to the more significant series coupling and wider flux variation range, while the wider iron bridges sacrifice the flux variation but facilitate the torque improvement. A prototype machine is manufactured and the experiments are carried out to verify the investigations.

Improved Adaptive Sliding-Mode Observer Based Position Sensorless Control for Variable Flux Memory Machines

This paper focuses on the position sensorless control for variable flux memory machine (VFMM), of which the magnetization state (MS) can be flexibly changed by applying a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current pulse to achieve the so-called MS manipulation. First, the unique challenges in VFMM sensorless control are in depth analyzed and summarized based on experimental results. An improved adaptive sliding mode observer (SMO) and an improved phase-locked loop (PLL) are then proposed. Specifically, a newly developed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axis voltage pulse injection method is employed to accurately measure the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axis inductances of VFMM during MS manipulations and update them into SMO to increase its convergence speed. An adaptive law is proposed for tuning sliding mode gains to obtain satisfying estimation performance of SMO under different conditions of speed and MS. In addition, to enhance the position tracking performance against the position estimation error resulted from MS manipulation or speed change, an improved PLL is structured, whose bandwidth can be adaptively adjusted by using fuzzy logic control. Finally, the feasibility and effectiveness of the proposed sensorless control strategy are verified through experimental measurements on a hybrid magnetic circuit VFMM (HMC-VFMM) prototype.

A Novel Variable Flux Memory Machine With Separated Series--Parallel PM Structure

Variable flux memory machine (VFMM) with hybrid magnetic circuit (HMC) is regarded as a potent solution for electric vehicles owing to its flexible flux control and fine accidental demagnetization withstand capability. However, existing HMC-VFMMs generally suffer from insufficiently wide flux regulation range and relatively high magnetization current level, hindering overall efficiency enhancement, particularly under high-speed region. This article proposes a novel separated series–parallel VFMM (SSP-VFMM), which features that the used high-coercive-force and low-coercive-force magnets are placed in a dual-layer arrangement to form SSP magnetic circuits, respectively. The second permanent magnet layer employs different magnet materials in the same rotor hole, which alleviates the magnetic saturation so as to achieve an excellent flux regulation range, and maintain a satisfactory accidental demagnetization withstand capability. The topology structures and operating principles of the existing HMC-VFMM and the proposed SSP-VFMM are illustrated and introduced first, and then their performance metrics are analytically assessed by using magnetic circuit models. The electromagnetic characteristics of the two machines are subsequently evaluated and compared, including air-gap magnetic flux densities, torque characteristics, and efficiency maps. Finally, some relevant experiments on HMC- and SSP-VFMM prototypes are undertaken to verify the effectiveness of the proposed new topology.

Hybrid-Magnet Variable Flux Memory Machine With Improved Field Regulation Capability for Electric Vehicle Applications

This article aims to investigate a novel hybrid-magnet variable flux memory machine (VFMM) with improved field regulation capability for electric vehicle applications. Two sets of permanent magnets (PMs), i.e., high-energy-density neodymium–iron–boron PM and low coercive force (LCF) PM, are arranged in a delta array to improve field regulation capability and torque density. The machine topology, key features, and operating principle of the presented machine are demonstrated. Based on the simplified magnetic circuit model, the underlying design tradeoffs of the presented machine are revealed qualitatively. The nonlinear magnetic circuit model of the presented machine taking saturation and hybrid-magnet leakage flux into consideration is built for machine analysis. Electromagnetic performance comparisons are carried out by finite element analysis between the presented VFMM and the existing VFMM. The results show that the presented machine can achieve significantly improved flux regulation capability while maintaining the high output torque due to the improved arrangement of hybrid magnetic branches and enhanced flux concentration effect. Finally, the investigated VFMM is prototyped. The operating principle and predicted results are verified by experimental results.

Thermal Modeling and Analysis of Hybrid-Magnetic-Circuit Variable Flux Memory Machine

Variable flux memory machine (VFMM) can be regarded as a promising candidate for electric vehicles (EVs) owing to its advantages of excellent flux adjustment capability and overall efficiency improvement over an extended operating range. However, the uncertain internal thermal behavior due to magnetization state (MS) change has an immense influence on electromagnetic performance of permanent magnet, which makes the precise MS estimation of low coercive force PM a challenging issue. To explore the benefits of MS manipulation on temperature rise reduction and provide an effective method to accurately evaluate temperature rise in VFMM, a magnetic-thermal coupling model of the newly developed hybrid-magnetic-circuit VFMM accounting for different MSs is established in this article. The lumped parameter thermal network (LPTN) model and computational fluid dynamics based finite-element (FE) method are employed to analyze the temperature characteristics, respectively. First, the losses of the investigated machine are calculated by adopting both the FE method and analytical equations. Afterward, the equivalent thermal resistances and heat transfer coefficients are determined by employing the LPTN model. Meanwhile, FE modeling is employed to analyze the three-dimensional thermal field distribution. Finally, a prototype machine is fabricated and experimentally measured, which can confirm the validity of the theoretical analyses.

Design Tradeoff Between Saliency Ratio and PM Flux Linkage in Variable Flux Memory Machines

To achieve flexible flux regulation, variable flux memory machines (VFMMs) are normally characterized by a high permanent magnet (PM) flux linkage design, which generally reduces the saliency ratio of the machine. In order to further reveal the internal performance tradeoffs, this paper investigates the relationship between the saliency ratio and PM flux linkages of VFMMs by combining the equivalent magnetic circuit models and the finite element (FE) method. Three hybrid-magnetic-circuit (HMC) VFMMs having different PM grades and saliency ratios are chosen as the case studies to analyze and reveal the influence of flux linkages and saliency ratios on the major electromagnetic characteristics. First, the no-load and dq-axes equivalent magnetic circuit models of the investigated machines are established successively to obtain the PM flux linkages and dq-axes inductances of the machines. Then, the relationships between the electromagnetic torque and the key design parameters are obtained based on the space vector model. Next, the maximum torque per ampere (MTPA) trajectory is portrayed to determine the flux-weakening characteristics of the VFMMs. Afterwards, the electromagnetic characteristics of the three machines are compared and analyzed to confirm the previous theoretical analyses. Finally, an HMC-VFMM prototype is fabricated and tested to verify the effectiveness of the analysis.

Improved MTPA Control for Variable-Flux Memory Machine With Operating Envelope Prediction-Based MS Manipulation

This article proposes an improved maximum torque per ampere (MTPA) control method for variable-flux memory machine (VFMM) with operating envelop prediction-based magnetization state (MS) manipulation. The proposed method can achieve the MTPA control under the voltage limitation and simplify the MS adjustment process for expanding the operating region. The mathematical model of the studied VFMM is established to calculate the reference current for MTPA control online as well as to predict the operating envelop at each MS. According to the calculated operating envelop, the proposed MS manipulation method can separate the magnetization and demagnetization processes by setting two MS manipulation boundaries correspondingly, which is easily implementable and can avoid frequent MS manipulation processes. Besides, the inductance characteristics of the machine are measured to improve the model accuracy and control performance. Experiments are carried out on a VFMM prototype to validate the feasibility and effectiveness of the proposed method.

A Novel Three-Stage Optimization Design Method of Asymmetric-PM Variable Flux Memory Machine Considering Magnet-Axis-Shifting Effect

Asymmetric-permanent-magnet variable flux memory machine (APM-VFMM) commonly suffers from the optimization issues, i.e., variable magnet-axis-shifting (MAS) effects result in distinctly differentiated electromagnetic characteristics under multiple magnetization states (MSs). Thus, this article proposes a novel three-stage optimization method for APM-VFMM considering the MAS effects to achieve efficient optimization. In the first stage, an analytical model based on the magnetic equivalent circuit (MEC) and torque models considering the MAS effects is developed to determine the key optimization objectives of the investigated machine while theoretically revealing the internal mechanisms for the improvement of the flux regulation range and torque capability. In the second stage, the comprehensive sensitivity analyses of the main geometric parameters are implemented based on a self-organizing map (SOM) method. Subsequently, the geometric parameters with higher sensitivity are selected for the multiobjective optimization process, thus effectively reducing the computational burden. In the third stage, a multimode circuit control model is developed and utilized in a single finite element analysis (FEA) case to consider multiple MSs and different MAS effects simultaneously for multiobjective optimization. The FEA predictions and experimental tests carried out on an APM-VFMM prototype confirm the effectiveness of the proposed three-stage optimization method.