Iet Electric Power Applications最新文献

Aiming at resolving the parameter uncertainty of the servo system under multi-working conditions, a flatness-based switched linear system model is proposed. Firstly, a fifth-order linear switched discrete-time system with uncertain parameters is established. The flatness properties of switched system is described and a de Bruijn's graph-based framework is introduced for graphical description of the switched system. In addition, non-linear bode diagrams are obtained via sweeping signals with multiple amplitudes. The discrete equations of the electromechanical servo system are established by the bode plots. The unknown parameters of the subsystems in switched model are identified by the simulated annealing algorithm, and compared with the least squares method to verify the accuracy of the identified parameters. Finally, the simulation model and experimental platform are constructed to verify the effectiveness of the proposed method. The switched model is compared with the classical transfer function model and single subsystems. The results indicate that the resolution of parameter uncertainty in servo systems is effective. The accuracy of the established switched model is about 99.5%. The accuracy of the switched linear system model of the electromechanical servo system is verified and the proposed modelling method is validated.

An efficient method for the detection of the stator winding faults (SWFs) of induction motors was dealt based on Park's vector of rotor slot harmonics (RSHs). The induced harmonic voltages of the RSHs in the stator windings are the supreme signatures for fault detection, which can be monitored in the motor currents. Using such a signature, unbalanced supply voltage and stator windings fault situations could be segregated straightforwardly. On the other hand, despite some merits, Park's vector analysis-based methods suffer from low sensitivity and unreliability in the case of low-severity faults. To have the advantages of both methods while tackling the shortcomings, Park's vector approach and the RSH signatures are combined in the proposed method. The RSHs are extracted using the fast Fourier transform method and the least squared approach is employed for pattern recognition. Different experimental results under various scenarios, even in the case of low severity faults, confirm that the locus of Park's vector is an elliptical shape in SWFs, while it is shapeless in other cases, such as healthy and unbalanced supply voltage cases.

Demagnetisation fault (DF) is a common rotor fault in the permanent magnet synchronous motor (PMSM). DF can cause obvious changes in the magnetic field of PMSMs. As a result, previous DF diagnosis methods mainly depends on magnetic field analysis. However, conventional analysis methods based on the magnetic potential-permeability method, sub-domain method and magnetic equivalent circuit method are not suitable for DF condition. In addition, DF diagnosis is further complicated by various operating conditions. To address these issues, a robust DF diagnosis method is proposed for PMSM based on d-axis magnetic network model using magnetic field reconstruction. The proposed fault diagnosis method employs magnetic field reconstruction to obtain the radial air-gap flux density under the open-circuit condition. Subsequently, a d-axis magnetic network is established to solve the demagnetisation coefficient matrix in the DF state. Finally, the effectiveness of the proposed method is validated through simulations and experiments. Both results demonstrate that the proposed method can accurately recognise uniform DF and partial DF with multiple demagnetised permanent magnets, exhibiting great robustness against different operating conditions.

A stacked polyphase bridge converter consists of multiple standard, three-phase two-level voltage source inverters connected in series to the same dc voltage source. The authors present a decentralised and dynamic dc-bus reconfiguration strategy for this type of converter. The innovation of the proposed strategy lies in its ability to isolate or reactivate one of the inverters in the series connection online, even in motoring mode, enabling increased fault tolerance and an extended speed range. Both the required hardware alterations and the multi-agent control strategy are addressed. Its major benefits compared to the state-of-the-art are that only two additional active, unidirectional semiconductor switches are required per inverter, and that the control is based on local computations, local measurements and neighbour-to-neighbour communication only. Hence, the scalability and reliability of the hardware are extended towards the control. Simulations and experimental results on a 4 kW modular axial-flux PMSM prove the feasibility of the concept, and validate that the dc-bus can be reconfigured in 100 ms, without torque interruption.

Aiming at the problem of high-speed motors being limited by multiple physical fields, which makes it difficult to achieve ultra-high-speed stable operation and develop towards higher speeds and higher power, an ultra-high-speed bearingless permanent magnet synchronous motor (UBPMSM) is proposed. Based on the mathematical model of suspension force for the bearingless permanent magnet motor considering the rotor eccentricity and load condition, the electromagnetic design method for UBPMSM is proposed. According to this method, the topology, torque system and suspension force system of a 10 kw 100k r/min UBPMSM are theoretically designed. The finite element method (FEM) is used to analyse the electromagnetic performance, which verifies the correctness of the proposed design method for UBPMSM. Further analysis and selection of winding span combinations are conducted to obtain better torque and suspension performance.

Axial Flux-Switching Permanent Magnet motors are broadly used in various industrial applications due to their high torque density and low rotor inertia. However, one major drawback of these motors is their cogging torque, which results in torque ripple and vibration. Existing methods for reducing cogging torque have often led to a decrease in useful electromagnetic torque, thereby compromising motor efficiency. To address this issue, a novel hybrid structure for the simultaneous improvement of cogging torque and electromagnetic torque in Axial Flux-Switching Permanent Magnet motors is presented. The proposed structure combines the optimal arc coefficient of the rotor pole technique with the notching rotor technique, resulting in a new motor configuration that exhibits both reduced cogging torque and increased torque density. Analytical equations for calculating cogging torque are derived, and 3D finite element analysis is conducted to evaluate the effectiveness of the proposed structure design. Furthermore, the optimal values of the arc coefficient and forming angle of the rotor pole are determined using the Taguchi analysis. Comparing the results of the optimal motor structure with the previous design shows that the new structure can improve the cogging torque, average electromagnetic torque, torque ripple, torque density, and peak torque output of the motor, which confirms the effectiveness of the proposed structure.

In the field of electric aircraft, the axial force of the conical motor is used to offset propeller thrust and reduce bearing wear. For the problem of accurate calculation of the no-load axial force of the conical motor, combined with the characteristics that the rotor magnetic bridge of the hybrid conical inner-mounted permanent magnet synchronous motor (HC-IPMSM) is easy to be saturated and difficult to be calculated analytically, an equivalent analytical calculation method is proposed. According to the principle of constant air-gap magnetic flux, the HC-IPMSM is equivalent to many cylindrical surface-mounted permanent magnet synchronous motors (CY-SPMSM), and an analytical model is gained. Combining with the scalar magnetic potential Laplace equation and Poisson equation, the air-gap flux density distribution on the rotor surface is calculated. And finally, the no-load axial force of the motor is obtained by using the cone angle and the Maxwell stress method. Simulation and experiments verify the correctness and validity of the analytical model.

The lumped element network model has been proven to be an efficient tool for the interpretation of transformer Frequency Response Analysis. However, it is challenging to obtain parameters of the model if transformer design information is unavailable. In such a case, optimisation algorithms can be used for gray-box model parameter estimation. A methodology is developed by the authors to establish a transformer network model without winding design data, and instead, end-to-end open circuit Frequency Response and other terminal test results are utilised; and Genetic Algorithm is applied to approximate the unknown parameters of the model. The modelling approach developed is independent of the unit number of the network model and therefore guarantees the accuracy of optimisation. Furthermore, it can deal with transformers with a complicated winding structure such as interleaved disc type winding. Two single windings, helical and interleaved disc type, and a single-phase 144/13 kV 60 MVA transformer are used to demonstrate the method. FRA spectra produced by the best estimated gray-box model and the corresponding white-box model are compared. The main features in amplitude and phase spectra are well matched, with low values of Relative Standard Deviation, for both single windings and transformer. Estimated electrical parameters show a high consistency with reference values, which are calculated based on winding design data. This validates the methodology and gives confidence to apply grey-box modelling for FRA interpretation.

In-plane eddy-current loss in permanent-magnet synchronous machines has been comprehensively and analytically studied by using three-dimensional (3D) finite element method. Considering the accuracy and calculation time, the electrical conductivity in the stack direction should be set to zero in 3D analysis. Stacking factor is also an important analytical parameter in this kind of calculation. The influences of slot number and coil-end height have been clarified. Harmonics caused by an inverter in pulse-width-modulation or one-pulse mode result in additional in-plane eddy-current loss, which is independent of the slot number. This behaviour can be explained by a theoretical equation of the eddy-current loss. These results are useful for the analysis and design of highly efficient electrical machines.