Iet Electric Power Applications最新文献

Harmonic state estimation, which highly depends on accurate synchronised phasors, is a crucial basis for the location, traceability, and governance of harmonics in power systems. However, most existing synchronous phasor measurement units (PMUs) provide power frequency phasors rather than harmonic phasors. In addition, as the dominant voltage signal provider for PMUs in power systems, capacitive voltage transformers (CVTs) have complex frequency responses and cannot be directly used for harmonic measurement. Therefore, accurate harmonic state estimation is difficult to achieve in applications. A method for harmonic voltage phasor reconstruction and harmonic state estimation based on the measurement data of a CVT is proposed. First, the reasons for harmonic voltage measurement errors were analysed. Second, the scattering parameter method was used to measure the wideband voltage transfer characteristics of CVT. Third, a voltage reconstruction method was proposed to improve the measurement accuracy and expand the frequency range of synchronous phasor measurement. Fourth, this method was applied to harmonic state estimation, and the performance of harmonic state estimation before and after voltage reconstruction was quantitatively compared. Results showed that the proposed method can remarkably improve the accuracy of harmonic state estimation. Finally, some factors, such as state observability, complex error disturbances, CVT structure, and harmonic order, influencing the performance of the proposed method were investigated. Results further demonstrated that the method has high accuracy, strong anti-interference, and adaptability, and can provide basic information for harmonic localisation and traceability.

The utilisation of high-speed motors in cryogenic motors achieves high efficiency and rapid transmission of cryogenic media, and at the same time, the high loss characteristic of high-speed motors enhances the vaporisation rate of cryogenic media and reduces the transmission quality of the media. Comprehensive numerical results on power loss and thermal characteristics of a submersible cryogenic high-speed permanent magnet motor are presented. The electromagnetic and frictional losses are calculated using precise numerical analysis, and these values are then incorporated into the fluid-thermal coupling solution model to obtain the temperature distribution results. In order to mitigate the impact of submerged cryogenic motor temperature on low-temperature medium vapourisation, the response surface optimisation method is employed for designing the rotor cooling diversion orifice, and determining the optimal dimensions, structure, and input conditions for flow velocity. The analysis results indicate that under low-temperature impact, the no-load back electromotive force increased by 9.3 V; the iron loss is increased by 22 W at rated speed and the optimised temperature is reduced by 4.3°C. A 30 kW, 12,000 rpm high-speed permanent magnet motor is utilised for validating the numerical model and the calculated results.

A novel predictive control method with conduction mode detection is proposed to suppress input current distortion of three-level power factor correction (PFC) converters. In PFC converter, the input current is mostly distorted in continuous conduction mode (CCM) with conventional control methods. The proposed predictive control method comprises of a predictive CCM algorithm, a predictive discontinuous conduction mode (DCM) algorithm, and a conduction mode detection technique. By analysing four switching states of PFC converter and based on the inductor current ripple, predictive control duty cycles in CCM and DCM are derived, and the optimal duty cycle is determined by forecasting the next cycle current. According to the duty cycle characteristics, the conduction mode is detected without additional detection algorithms and circuits, achieving the input current tracking the input voltage. Finally, the effectiveness and correctness of the proposed predictive control method are validated through simulation and experiment.

The open-circuit magnetic field of the V-shaped interior PM (IPM) machine is predicted by the analytical method. The method is implemented following the basic principle of the subdomain method. The machine model is divided into five different regions, including rotor slot, magnetic barrier, air gap, stator slot, and stator slot opening. To perform the analytical prediction process in the polar coordinate system, these regions should be transformed into the appropriate subdomains. The last four regions can be transformed into the subdomains with the required shape based on the existing method. The rotor slot cannot be treated as a single subdomain, for the shape of which is irregular. Herein, the PM and vacuum region in the rotor slot is divided into several fan-shaped subdomains. The division method is described clearly. Then, the boundary conditions alongside the interface between adjacent subdomains are derived based on function transformation. On this basis, the open-circuit magnetic field of the IPM machine can be predicted. The magnetic field of the 6p/36 s V-shaped IPM machine is obtained by the proposed method, finite element method simulation, and experiment, respectively. Additionally, the comparison results verify the accuracy and efficiency of the proposed method.

Given the presence of various non-ideal conditions, such as detection errors, converter non-linearity, noise, and parameter mismatches, the flux model experiences the introduction of DC bias and high-frequency harmonics, which subsequently deteriorate the accuracy of flux estimation. To dispose these issues, an improved non-linear flux observer (FOIFFO) using a second-order generalised integrator as an in-loop filter is proposed for the sensorless control of permanent magnet synchronous motors. The observer demonstrates robust performance in eliminating DC bias and having a strong filtering ability for high-order harmonics even without amplitude and phase compensation to accurately estimate the rotational speed and rotor position. The performance of the method is analysed by transfer functions and bode plots, while the discretisation method of the FOIFFO is proposed. Finally, the new sensorless control strategy is verified by synthesising the experimental results.

The end leakage inductance is an important component in the primary leakage inductance of the equivalent circuit. In order to calculate the end leakage inductance of a toroidal winding double-sided linear induction motor (TW-DSLIM) accurately and quickly, the role of ferromagnetic medium is equated by the method of images, the magnetic flux density in the end space is calculated according to the current density of the rectangular coil, end leakage inductance is obtained by calculating the end leakage magnetic energy, the impact of end leakage inductance on the performance of TW-DSLIM is investigated, and finally the TW-DSLIM model is established in finite element analysis to verify the effectiveness of the analytical method.

In this paper, a torque improvement method is presented for a double rotor (DR) permanent magnet motor, where the key is to conduct the study based on effective utilization of magnetic field coupling. To facilitate systematic analysis, the magnetomotive force (MMF) and airgap flux density considering magnetic coupling effect are deduced and analysed. It contributes to building the relationships between the output torque caused by magnetic coupling and magnetic field harmonics. By introducing the coupling sensitivity coefficient, the coupling harmonics in the inner and outer airgap magnetic fields are obtained. Then, two coupling harmonic groups are further determined in terms of phase difference and torque contribution, where one of them is required to be enhanced and the other is needed to be reduced. On the basis of this, a comprehensive coupling factor is defined purposely to realise the design and evaluation of the characteristics of coupling harmonic groups. Some motor performances are analysed in details, including the torque, torque ripple, overload capability, and so on. Finally, a prototype motor is manufactured to verify the feasibility of the presented studies of the DR motor.

Due to the strong coupling effect between the internal magnetic field and the structural field of the transformer, the magnetic-structural coupling should be considered in axial vibration process of the winding short-circuit impact. A 110 kV transformer is taken as the research object. Firstly, the vibration modal characteristics of the transformer are calculated using the classical axial vibration model, and the spatial distribution of the leakage magnetic flux density of the iron core window is obtained based on the image method, which is used as the basis for calculating the excitation electromagnetic force. With the consideration of the non-linear mechanical characteristic of the pad, the dynamic stiffness equation is analysed and established and the magnetic-structural coupling correction model is constructed. Finally, the winding vibration amplitudes obtained respectively by the classical model, the magnetic-structural coupling model, and the magnetic-structural coupling correction model considering the dynamic stiffness are compared. The results show that, compared with the classical model, the vibration amplitude increment with the magnetic-structural coupling correction model is less. The dynamic stiffness will hinder the vibration intensification. The magnetic-structural coupling correction model can provide a more accurate calculation scheme for the winding vibration characteristic analysis.

In order to further improve the output torque and stability of the external rotor permanent magnet synchronous motor, a double-layer non-uniform Halbach external rotor permanent magnet synchronous motor (DNH) structure is proposed and optimised. Finite element models of DNH and other structures are established to compare the electromagnetic characteristics of these motors and verify the superiority of the proposed structure. Secondly, the multi-objective whale optimisation algorithm is improved, and the algorithm is tested by test function to verify the improvement effect. Further, the Spearman correlation of the parameters is calculated, and the parameters are layered. The first layer parameters are optimised by the improved multi-objective whale optimisation algorithm, and the second layer parameters are optimised by parameter scanning. Finally, the motor performance of the initial scheme, single layer optimisation scheme, and hierarchical optimisation scheme is compared by simulation. The simulation results show that the hierarchical optimisation method is superior to the single layer optimisation method. By comparing with other schemes, the performance advantages of hierarchical optimisation DNH in terms of average output torque, cogging torque, torque ripple, permanent magnet cost and other parameters are proved, as well as the effectiveness of the optimisation method.

Managing the high-rate-power transients of Electric Vehicles (EVs) in a drive cycle is of great importance from the battery health and drive range aspects. This can be achieved by high power-density storage, such as a high-speed Flywheel Energy Storage System (FESS). It is shown that a variable-mass flywheel can effectively utilise the FESS useable capacity in most transients close to optimal. Novel variable capacities FESS is proposed by introducing Dual-Inertia FESS (DIFESS) for EVs. The feasibility of the proposed concept is evaluated by deriving the size of a Single-Inertia FESS (SIFESS) for a battery EV, which runs the well-known Urban Dynamometer Driving Schedule. The sizing framework consists of an Energy Management System using the constrained Pontryagin's minimum principle and a proposed sizing algorithm. Then, by splitting the derived SIFESS inertia into two separate inertias, the appropriate engaging control of inertias is determined for some driving cycles including, the Artemis Urban, Braunschweig City, and Worldwide Harmonised Light-duty Vehicles Test Cycle. The dual inertias suitable sizes are derived using a proposed algorithm, which targets maximising the FESS useable capacity. The results show that compared to the SIFESS, the DIFESS can employ the FESS's useable capacity more effectively.