Sufei Li

Calculating the unsaturated inductance of 4/2 switched reluctance motors at arbitrary rotor positions based on partial differential equations of magnetic potentials

Phase inductance is a key parameter in switched reluctance motor (SRM) design because torque and the dynamics of phase voltages and currents are directly related to inductance. Therefore, accurate calculation of the inductance at arbitrary rotor positions is important in determining the SRM behavior. Contrary to the popular but time-consuming approach to determine the flux linkage and inductance of a SRM with finite element analysis (FEA), this paper proposes a novel analytical solution based on the partial differential equations of magnetic potentials to calculate the inductance profile of a 4/2 SRM with respect to rotor position, which makes the inductance prediction more time-efficient. The accuracy of this method is validated by comparing its estimated inductance profile to the inductance obtained by FEA.

Multi-objective design and optimization of generalized switched reluctance machines with particle swarm intelligence

This paper proposes a fast and generalized multi-objective design and optimization method for the Switched Reluctance Machines (SRM). An analytical design model for SRMs with any feasible stator and rotor slot combinations is firstly developed, which can accurately evaluate a SRM design much faster than the prevalent finite element analysis (FEA) method. In addition, a novel method for multi-objective optimization of SRM is proposed based on this analytical model, and the number of prime variables to be optimized is reduced to only five. A canonical Particle Swarm Optimization (PSO) algorithm with penalty function is applied to find the optimal solution for a user defined objective function. After several rounds of searching process with the PSO, the optimal regions can be found for the design variables in terms of the performance indices (PIs). Finally, the optimized designs are validated by FEA. This method can generate the optimized SRM designs subject to different design requirements and accelerate the entire optimization process.

Calculating the electromagnetic field and losses in the end region of large synchronous generators under different operating conditions with three-dimensional transient finite element analysis

The significant losses in the end components due to the leakage magnetic field excited by the armature and field end windings can result in partial overheating and is an important consideration in the design of large synchronous generators. This paper describes an approach based on the three-dimensional (3D) transient finite element analysis (FEA) to determine the fields and losses in the generator end region. Taking the nonlinear/anisotropic properties of the stator core, as well as the slitting and stepping shape of core-end packets into consideration, the electromagnetic field and loss distribution in the end region is calculated. The method is validated by the agreement found between the temperatures predicted by the 3D stationary thermal FEA and the temperatures obtained from a physical measurement at various points in the generator. Then, the field and loss distributions in the end region under the open-circuit test condition, power factor lagging condition and leading condition are analyzed and compared using the proposed transient 3D FEA method.

Fast and accurate analytical calculation of the unsaturated phase inductance profile of 6/4 switched reluctance machines

Accurate calculation of the phase inductance profile of switched reluctance machines (SRMs) is of crucial importance in SRM design because it is a key parameter to predict the performance indices such as the torque and core loss. Instead of using the time-consuming finite element analysis (FEA) or the methods that require prior knowledge of magnetic fields from an FEA such as curve fitting and magnetic equivalent circuit (MEC), this paper proposes a fast and accurate analytical approach to determine the unsaturated phase inductance of a 6/4 SRM at arbitrary rotor positions by solving the partial differential equations of magnetic scalar/vector potentials based on Maxwells equations. Conformal mapping is applied to deal with the non-radial or non-tangential geometric structures when calculating the inductance of the SRM. The agreement between the results of the proposed analytical method and FEA validates the analysis.

Analyzing the impact of press plate structure on the flux and loss distributions in the end region of large generators by transient 3-dimensional finite-element method with an improved core loss model

The strong leakage magnetic flux in the end region of large synchronous generators results in significant eddy currents in the end components which can possibly lead to overheating thus threatening the safe operation of large generators and is an essential issue at the design stage. The press plate is a major end component of large generators that fastens the stator end-core packets and shields the stator core back-iron from the intensive leakage flux. This paper describes a transient 3-dimensional (3D) finite-element analysis (FEA) based approach to calculate the magnetic field and loss distributions in the end region of large generators, and incorporates an enhanced laminated core model combining the impacts of anisotropic and nonlinear material properties, hysteresis effects, and the reaction of induced in-plane eddy currents on the magnetic field and loss distributions in the stator core. The method is validated by the agreement between the temperatures predicted by a 3D thermal FEA and the measured results. Then, the influences of different material properties and dimensions of the press plate on the magnetic flux and loss distributions in the end region are evaluated by the proposed 3D FEA.

A multi-objective analytical design approach of switched reluctance machines with integrated active current profile optimization

The large torque ripple of a switched reluctance machine (SRM) caused by commutation and the inherent nonlinear torque-producing nature is a major disadvantage for its widespread application. To mitigate this problem, current profiling for torque ripple minimization has been extensively pursued, however, most current profiling attempts are performed on existing SRM designs and thus will not guarantee a multi-objective optimized design in the entire design space for any specific applications. This paper thus proposes a built-in active current profile optimization approach, which is integrated to the early multi-objective design and optimization stage of SRMs. In addition, the proposed method is very time-saving, especially when the number of prime design variables and the entire search domain are large. Multi-objective optimization process involving 200, 1,000 and 5,000 trail designs are carried out with the multi-objective differential evolution (MODE) algorithm and their Pareto fronts are approximated at a speed more than 100 times faster than the popular finite element analysis (FEA) based electric machine analysis methods, offering machine designers handy, convenient and accurate initial designs, which can be further verified or fine-tuned by FEA in later processes.

A high-frequency rotating flux injection based rotor thermal monitoring scheme for direct-torque-controlled interior permanent magnet synchronous machines

Interior permanent magnet synchronous machine drives have widespread applications in electric traction systems and various industrial processes. However, prolonged exposure to high temperatures while operating can demagnetize the permanent magnets to the point of irreversible demagnetization. In addition, direct measurements with infrared sensors or contact-type sensors with wireless communication can be expensive and intrusive to the machine drive structure. This paper thus proposes a nonintrusive thermal monitoring scheme for the permanent magnets inside the direct-torque-controlled interior permanent magnet synchronous machines. By applying a high-frequency rotating flux offset to the hysteresis controllers in the motor drive, high-frequency currents can be injected into the stator windings of the machine. The permanent magnet temperature can thus be monitored based on the estimated high-frequency resistance, which is the byproduct of the induced magnet eddy current. The method is nonintrusive because it eliminates the infrared sensors and requires no hardware change to the existing motor drive, and the proposed method is validated by real-time experimental results.

Calculating the unsaturated direct and quadrature axes magnetizing inductances of synchronous reluctance machines based on Maxwell's equations and magnetic equivalent circuit

This paper presents an analytical method to calculate the unsaturated direct (d) and quadrature (q) axis magnetizing inductance of synchronous reluctance machines (SynRMs). The d-axis magnetizing inductance is calculated by conformal mapping and solving partial differential equations of magnetic potentials, while the q-axis magnetizing inductance is solved from a magnetic equivalent circuit (MEC) model. With the d and q-axes magnetizing inductance calculated, it will be straightforward to obtain the electromagnetic torque of a SynRM. The analytical method solves much faster than finite element analysis (FEA), and yields a result that matches the FEA simulation.

A survey of electromagnetic — Thermal modeling and design optimization of switched reluctance machines

Switched reluctance machines (SRMs) are gaining interest in the industry and scientific communities owing to the advantages of rigid structures, high reliability, the absence of permanent magnets, robustness, fast dynamic response, and low manufacturing cost. They have become a feasible alternative to conventional electric machines with variable speed drives in many applications. This paper presents a comprehensive review on the status and potential trends of the technology pertinent to the design of SRMs in the following aspects: the mathematical modeling of the electromagnetic and thermal behaviors of SRMs, the enhancement of the performances in terms of torque ripple, efficiency, torque density and acoustic noise, and the multi-objective design optimization. The existing approaches are systematically and comprehensively summarized and compared for each category.

Implementation of surface impedance boundary conditions in the quasi three-dimensional finite-difference simulations of generator end regions

Predicting the distribution of the eddy currents circulating in the press plate or other end metallic components and the impacts of eddy current on the magnetic field in the end region is crucial for the design of large synchronous generators. Compared to the accurate but extremely time-consuming full three-dimensional (3D) finite-element analysis (FEA) that may take several days to complete, a new quasi-3D simulation with finite difference equations can provide acceptable solutions of the magnetic field and eddy current distributions in the generator end region within a few minutes and is thus an appropriate tool at the initial design stage. This paper proposes an approach to estimate the distribution of eddy currents in the end metallic components by implementing the surface impedance boundary conditions (SIBCs) in a quasi-3D finite-difference (FD) scheme. The effects of nonlinear material properties and a compensation method for the near corner effects are incorporated in the proposed formulation of SIBCs to improve the accuracy. The corresponding full 3D FEAs, which are validated by the agreement between their results and the data obtained from physical measurements, are used as the benchmark for this study. The proposed method is validated by the agreement between the results generated by the new quasi-3D simulations and the full 3D FEAs.