Hybrid Excitation Synchronous Machine Research Articles

Electromagnetic performance analysis of a new high‐speed hybrid excitation synchronous machine

AbstractTo facilitate the regulation of the air‐gap magnetic field of permanent magnet synchronous machines, a novel topology of a high‐speed hybrid excitation synchronous machine (HESM) was presented. The electromagnetic performance of the proposed HESM was evaluated. The air‐gap magnetic field regulation principle was introduced first. Then, a mathematical model of the HESM was established. Based on the characteristics of a 3D magnetic circuit, the HESM equalled three types of 2D magnetic circuit machines in axial parallel superposition, and thus the expressions of inductance parameters were deduced. Subsequently, the voltage regulation performance of the HESM was assessed according to the mathematical model and inductance parameters. The loss and efficiency were calculated. Finally, a HESM prototype was tested and verified.

Theoretical Analysis for Rapid Design of Hybrid Excitation Synchronous Machine With Consequent Pole Rotor

Theoretical Analysis for Rapid Design of Hybrid Excitation Synchronous Machine With Consequent Pole Rotor

Finite-Time Control for Dual Three-Phase Hybrid Excitation Synchronous Machine Based on Torque Sensorless Current Coordinative Strategy

In this paper, the finite time speed regulation problem is investigated for a dual three-phase hybrid excitation synchronous machine (DTP-HESM) without a torque meter. The electromagnetic torque estimation required in the current coordinative strategy is obtained through the disturbance estimation technology. This method increases fault tolerance and reduces the cost as well as complexity of the DTP-HESM system. In contrast to the existing controllers in the speed loop, the non-singular terminal sliding mode control method is adopted to ensure the finite-time convergence of speed tracking in the whole speed region. To achieve better dynamic performance in the presence of lumped disturbances, including unknown load torque and unmodeled dynamics, the disturbance estimations are introduced into the sliding mode variable to establish a composite speed regulating controller. Simulations and experiments are carried out to validate the feasibility and effectiveness of the proposed control scheme.

Overview of the technology behind hybrid excitation synchronous machines

The objective of this paper is to present a comprehensive analysis of hybrid excitation synchronous machines, including an examination of various structures found in scientific and technical literature, along with their advantages and drawbacks. Additionally, different methods of classification for these structures will be explored. The paper also delves into the contributions of the hybrid excitation principle for both motoring and generating modes and provides an overview of various models used in designing these structures.

An Analytical Method for Calculating the Cogging Torque of a Consequent Pole Hybrid Excitation Synchronous Machine Based on Spatial 3D Field Simplification

Consequent pole hybrid excitation synchronous (CPHES) machines have the advantage of symmetrical bidirectional magnetomotive force increments. Compared with a traditional hybrid excitation motor (HEM), a CPHES machine improves the disadvantage of asymmetry in the adjustment range when magnetization and demagnetization occur. The calculation and analysis of the cogging torque of the CPHES machine are complex due to the complicated structure. This paper proposes an analytical method for calculating the cogging torque of a CPHES machine. This analytical method converts the complex three-dimensional magnetic field problem into a two-dimensional magnetic circuit problem and, through the accumulation method, can quickly and accurately calculate the cogging torque of the CPHES machine. In contrast with the finite element method, the calculation results basically follow each other, but the analytical method is more efficient and omits complicated meshing. This is of great significance to the preliminary electromagnetic design and performance optimization of a CPHES machine.

Mechanical Design and Analysis of a High-Torque Modular Hybrid Excitation Synchronous Machine for Electric Vehicle Propulsion Applications

Although hybrid excitation synchronous machines (HESMs) can provide an attractive flux-regulating capability, the fabrication and mechanical strength of the complex rotor are with significant challenges and need great efforts especially for high torque machines. In this article, a modular fabrication method of the dual-end magnetic-shunting rotor is proposed for high torque hybrid excitation synchronous machine. Then, by using numerical methods, the thermal stress of the rotor is calculated and compared with the 3-D FEA methods. To improve the mechanical strength of the rotor, the size of the screw, lug boss and filler is optimized, meanwhile, the rotor loss is optimized and thermal stress is evaluated. The results show that the proposed modular fabrication method demonstrates the improved mechanical strength and material utilization rate compared with the conventional fabrication process. Based on the three-dimensional finite-element analysis (3-D FEA) results, a 100 kW HESM prototype is successfully designed and manufactured using the proposed modular magnetic-shunting rotor. The experimental tests validate the effectiveness of the modular fabrication method and mechanical strength analysis.

System-Level Optimization of Hybrid Excitation Synchronous Machines for a Three-Wheel Electric Vehicle

In this article, a two-level methodology is proposed to optimize the design of a hybrid excitation synchronous machine (HESM) for a given electric vehicle (EV) over an arbitrary-selected driving cycle. We are looking at a huge analysis problem of finding an optimal hybridization ratio (HR) between the two excitation sources, namely, permanent magnet (PM) and wound excitation (WE). To find the optimal HR, the HR is scanned from 0 to 1 or from pure WE to pure PM excitation. For each HR, the motor is optimally designed at the component level, its cost is minimized, and its global efficiency over the selected driving cycle is calculated. Then, at the system level, the global efficiencies associated with each HR are compared in order to find the optimal HR. The complexity of the design optimization at the component level is addressed by nondominated sorting genetic algorithm II (NSGA-II). To make a compromise between the accuracy and speed of calculations, a nonlinear 3-D dynamic magnetic equivalent circuit (MEC) model is developed and evaluated by commercial finite element analysis (FEA) software. Following the proposed methodology and due to 300 h of computations with 48 CPU cores in parallel, the final HESM design can achieve up to 18.65% higher global efficiency than pure WE and 15.8% higher than pure PM excitation.

Component-Level Optimization of Hybrid Excitation Synchronous Machines for a Specified Hybridization Ratio Using NSGA-II

In this article, a Hybrid Excitation Synchronous Machine (HESM) is optimally designed for a specified Hybridization Ratio (HR). A new formulation of the design problem is proposed to be tackled by the Non-dominated Sorting Genetic Algorithm II (NSGA-II), while minimizing the material cost. This formulation includes a more comprehensive explanation of the key concept, HR, which considers the soft and hard saturation effects in the HESM design. The HESM model is based on a 3D nonlinear Magnetic Equivalent Circuit (MEC). For faster convergence, the number of design variables is reduced using two statistical analyses, namely Analysis of Level and Analysis of Variance (ANOVA). A HESM is optimally designed for HR = 0.5 and validated by a commercial Finite Element Analysis (FEA) software.

Pre-optimization of hybridization ratio in hybrid excitation synchronous machines using electrical circuits modelling

Hybridization ratio α is an additional degree of freedom offered by the hybrid excitation principle in the design of synchronous electrical machines. The first goal of this contribution is to present the tool developed for analysing the effect of the hybridization ratio. This software tool is based on the electrical circuits modelling of hybrid excitation synchronous machines. This tool can also be advantageously used for the pre-optimization of this parameter. The used model and the optimization algorithm are first thoroughly detailed. Finally, a parametric study intended to investigate the effect of some design specifications and parameters on this optimal value is presented.

Equivalent Magnetic Circuit Model for Consequent Pole Hybrid Excitation Synchronous Machine with AC Field Control

At present, almost all hybrid excitation machines (HEMs) apply DC field current to control the air-gap flux. However, the DC field control mode results in a problem that the capability of field-weakening is not equal to that of field-strengthening. This paper briefly explains the mechanism of asymmetric bidirectional field control capability in present HEMs, proposes a consequent pole hybrid excitation synchronous (CPHES) machine with AC field control mode to solve the asymmetric problem. The structure and principles of CPHES machine are presented. Additionally, the equivalent magnetic circuit model of CPHES machine is derived to reduce the computational complexity of analyzing CPHES structure by using three-dimensional finite element analysis (3DFEA). The proposed equivalent model and 3D-FEA are compared, the results verify the proposed model is basically consistent with the 3D-FEA, and the proposed model is able to reduce the computational complexity greatly.

Optimization and Performance Improvement of a Hybrid Excitation Synchronous Machine With Modular Magnetic-Shunting Rotor

Hybrid excitation synchronous machines (HESMs) are regarded as special permanent magnet synchronous machines (PMSMs), in which flux linkage, inductances, and characteristic current change with field current. The machine topology, optimized structure design, and modular fabrication method of an HESM with magnetic-shunting rotor are presented in this paper. To solve the thermal problems, an optimized cooling system considering the rotor losses is proposed. Then, the feature of adjustable d -axis inductance and flux linkage are theoretically analyzed and calculated. As a result, the characteristic current changes with the field current, which is significant to the constant power range. The adjustable d -axis inductance, flux linkage, and characteristic current are validated by finite-element analysis results. According to the feature of adjustable characteristic current, an optimized control strategy is proposed to improve the output power capacity of the HESM with modular magnetic-shunting rotor in the whole speed range by taking full advantage of the adjustable characteristic current feature, in which the characteristic current is adjusted close to the rated current at high speed. To validate the feasibility and superiority of the optimized design and control methods, a 100-kW HESM with modular magnetic-shunting rotor prototype is designed, manufactured, and tested.

Study of a Hybrid Excitation Synchronous Machine: Modeling and Experimental Validation

This paper deals with a parallel hybrid excitation synchronous machine (HESM). First, an expanded literature review of hybrid/double excitation machines is provided. Then, the structural topology and principles of operation of the hybrid excitation machine are examined. With the aim of validating the double excitation principle of the topology studied in this paper, the construction of a prototype is presented. In addition, both the 3D finite element method (FEM) and 3D magnetic equivalent circuit (MEC) model are used to model the machine. The flux control capability in the open-circuit condition and results of the developed models are validated by comparison with experimental measurements. The reluctance network model is created from a mesh of the studied domain. The meshing technique aims to combine advantages of finite element modeling, i.e., genericity and expert magnetic equivalent circuit models, i.e., reduced computation time. It also allows taking the non-linear characteristics of ferromagnetic materials into consideration. The machine prototype is tested to validate the predicted results. By confronting results from both modeling techniques and measurements, it is shown that the magnetic equivalent circuit model exhibits fairly accurate results when compared to the 3D finite element method with a gain in computation time.

A HESM-Based Variable Frequency AC Starter-Generator System for Aircraft Applications

With the development of more electric aircraft, higher demand for electrical energy is put forward in generation systems. The constant speed drive is eliminated in variable frequency ac (VFAC) generation systems, which makes integrated starter-generator (SG) can be realized. Considering the inherent defects of wound rotor synchronous SG systems, such as the complex starting excitation methods and rotating rectifiers, this paper proposes a VFAC SG system based on hybrid excitation synchronous machines (HESMs) for aircraft applications. The key technology of HESM-based VFAC SG system is to regulate the field current in such a way that three major modes of VFAC SG system operation for aircraft applications, namely, engine starting operation, transition mode, and generating operation, can be realized effectively. The simulation model of HESM-based VFAC SG system is built and analyzed. A prototype HESM-based VFAC SG system has been designed and developed for experimental verification. The starting operation, transition mode, and generating operation of the prototype HESM-based VFAC SG system are implemented. The feasibility of HESMs to VFAC SG system for safety-critical aircraft applications has been validated.

Hybrid excitation synchronous machine adaptive speed region control and experimental verification

Hybrid excitation synchronous machine adaptive speed region control and experimental verification

Electromagnetic Performance Analysis of a New Hybrid Excitation Synchronous Machine for Electric Vehicle Applications

In this paper, a new hybrid excitation synchronous machine (HESM) with dual-end built-in field windings is designed for electric vehicle traction applications with consideration of electromagnetic performance. This HESM topology inherits the features of brushless HESMs with magnetic shunting rotor and benefits from better space utilization. The fundamental structure and operating principle of the HESM are introduced in detail. The electromagnetic performance of the HESM, including back-electromotive force waveform, cogging torque, torque ripple, no-load flux regulation capability, and output torque capability, is analyzed by the 3-D finite-element method. The predicted results reveal that the output torque ripple of the HESM can be optimized by the coordinated operation between field current and armature current. A 100 kW prototype HESM has been designed and manufactured for experimental verification. The advantages and feasibility of the HESM in EV traction applications are validated by the test results.

An analytical method of calculating back-emf in dual consequent hybrid excitation synchronous machine

In order to solve the problem of asymmetric bidirectional flux control capability in hybrid excitation machine, a novel structure called dual consequent hybrid excitation synchronous (DCHES) machine is presented in this paper. Generally, the analysis of back-EMF for the machine with complex electromagnetic structure such as DCHES machine should utilize 3-D finite element analysis (FEA), which will require huge resources and computing time. In order to avoid using 3-D FEA to analyze the back-EMF of complex structure, an analytical method of calculating back-EMF is presented in this paper. The electromagnetic field in 3-D space can be simplified as a 2-D field by dividing the 3-D field into several simple zones, the resultant effect equals to the summation of every single 2-D field's effect. According to electromagnetic theory, the analytical formula of back-EMF is obtained on the basis of Fourier series. The influence of main parameters on back-EMF waveform under sine and trapezoidal flux distribution is discussed respectively. The theoretical result shows that the trapezoidal air-gap flux distribution would generate a sine back-EMF. Finally, the presented analytical method is verified and evaluated with experimental results.

Design and Optimization of Hybrid Excitation Synchronous Machines With Magnetic Shunting Rotor for Electric Vehicle Traction Applications

In this paper, a hybrid excitation synchronous machine (HESM) with magnetic shunting rotor is designed for electric vehicle traction applications with consideration of electromagnetic performance and mechanical strength. The HESM with magnetic shunting rotor is a topology of brushless HESM with extended magnetic bridge to embed field windings. The rotor core extends along the axial direction and the increase of rotor length is inevitable, which reduces torque density. In order to improve torque density, the excitation structure is optimized by built-in field windings and the HESM with one-end built-in field windings is presented. To improve the flux regulation capability and decrease the magnet consumption further, the HESM with dual-end built-in field windings is proposed and investigated. The comparative study of the performances of the original HESM and the HESMs with one/dual-end built-in field windings is carried out by three-dimensional finite element method (FEM). An original HESM prototype and a permanent magnet synchronous machine prototype have been developed and the experimental results, which agree well with the FE-predicted results, confirm the advantages of HESM and the validity of FEM used in predictions in this paper.

A Simplified Finite-Element Model of Hybrid Excitation Synchronous Machines With Radial/Axial Flux Paths via Magnetic Equivalent Circuit

In this paper, a novel modeling method for hybrid excitation synchronous machines (HESMs) with radial/axial flux paths via magnetic equivalent circuit (MEC) is proposed. 3-D finite-element analysis (FEA) is essential when analyzing a machine with radial/axial flux paths due to the asymmetry in the axial direction. However, 3-D FEA is computationally expensive and time-consuming, especially during the preliminary design stage. The proposed modeling method is analyzed and validated based on an HESM with magnetic shunting rotor. The fundamental structure and working principle of the HESM with magnetic shunting rotor are introduced. On the basis of 3-D structure, an MEC considering saturation and leakage flux distribution is built and illustrated, as well as field analysis is performed. A 2-D equivalent finite-element model via MEC is built and illustrated. A prototype HESM with magnetic shunting rotor has been designed by the proposed modeling method and developed for experimental verification. With the proposed modeling method, the computational efficiency is significantly improved in the design stage. The proposed modeling method is verified by the good agreement between the predicted and measured results.

Overview and development of variable frequency AC generators for more electric aircraft generation system

With the development of more electric aircraft (MEA), higher demands for electrical energy are put forward in generation systems. Compared to constant frequency AC (CFAC) generation systems, the constant speed drive (CSD) is eliminated and integrated starter/generator (SG) can be realized in variable frequency AC (VFAC) generation systems. In this paper, an overview of VFAC generators for safety-critical aircraft applications is presented, with a particular focus on the key features and requirements of candidate generators and the starting control strategies. Wound rotor synchronous machines (WRSMs) are typical generators used in VFAC generation systems so far. Meanwhile, hybrid excitation synchronous machines (HESMs) and cage-type induction machines are promising candidates for VFAC generation systems. The generation operation of WRSM is relatively mature, however, the SG technology of WRSM is still full of challenges. As one of the most important issues, the starting excitation methods of WRSM are summarized. An HESM-based VFAC SG system is proposed and developed in this paper. The experimental results show that the starting mode, transition mode and generating mode of the VFAC SG system are realized. The continuous progress of VFAC generation system makes great contributions to the realization of MEA.

Comparative study of new axial field permanent magnet hybrid excitation machines

Hybrid excitation synchronous machines (HESMs) are permanent magnet machines which allow the control of the air-gap flux density. In this study, three new axial field HESM structures, each having two rotors and one stator, are proposed. The operation principles of these machines, considering weakening or supporting the air-gap flux density, are described. The magnetostatic and transient analyses of the proposed models have been carried out by using finite element method. To have reliable analysis results, the stator length and input and output diameters of the models have been chosen to be identical. Results are compared in terms of efficiency, power density and range of flux control between each other and another axial field HESM in the literature. In conclusion, the proposed HESM models demonstrate satisfactory performance for the generator mode and they are suitable for wind energy applications. Furthermore, because of their field weakening operation ability they can be used as motors in the vehicle industry.