Hybrid-excited Switched-flux Permanent Magnet Research Articles

Electromagnetic-Thermal Analysis of a Hybrid-Excited Flux Switching Permanent Magnet Generator for Wind Turbine Application

An accurate thermal analysis needs to be performed on the machines with new structures to ensure that their electromagnetic performance is not negatively affected. In this regard, this paper details an investigation into the electromagnetic-thermal analysis of an outer rotor hybrid-excited flux switching permanent magnet generator that gains from ferrite PMs in stator yoke and neodymium PMs in rotor segments. Incorporating ferrite PMs and barriers in the stator core enhances the power density of the proposed generator compared to the basic topology. Also, the temperature of the stator and windings of the HEFSG decreases due to the presence of barriers. As a result, the HEFSG can be a potential candidate for DDWT applications. In this study, the thermal modeling started with a 3-D FEM electromagnetic analysis to calculate the losses as heat sources. Afterward, an accurate thermal network was plotted to elucidate the thermal behaviors between various parts of the generator, where the heat sources, heat transfer coefficients, thermal resistances, and heat capacitances form the thermal characteristics of the network, which was then followed by the 3-D FEM thermal analysis. Finally, the experimental test results from the prototyped generator confirmed the accuracy of the simulation results.

Investigation of DC Winding Induced Voltage in Hybrid-Excited Switched-Flux Permanent Magnet Machine

The dc winding induced voltage in hybrid-excited machines can lead to dc winding current ripple and hence, fluctuating field excitation. It may also challenge the dc power source and increase the difficulty of machine control, especially at high speed. The dc winding induced voltage in a hybrid-excited switched-flux permanent magnet (HESFPM) machine is investigated in this article. The phenomenon and mechanism of the dc winding induced voltages under both open-circuit and on-load conditions are analyzed, with particular emphasis on on-load operation which consists of open-circuit induced voltage and armature current induced voltage, respectively. Two techniques, i.e., rotor step skewing and unequal rotor teeth, are proposed and comparatively investigated by the finite-element (FE) method to suppress the dc winding induced voltage under on-load condition. FE results show that the peak-to-peak value of on-load dc winding induced voltage can be effectively suppressed by 96.15% or 89.05% by rotor step skewing or unequal rotor teeth, respectively, while the average on-load electromagnetic torque can be maintained at 89.4% or 87.8%. A prototype HESFPM machine is built and tested to verify the FE results.

Vector Control of a Hybrid Axial Field Flux-Switching Permanent Magnet Machine Based on Particle Swarm Optimization

A hybrid axial-field flux-switching permanent magnet machine (HAFFSPMM) is a novel hybrid excited flux-switching permanent magnet motor, which combines the advantages of the axial-field flux-switching permanent magnet machine and hybrid excited synchronous machine. In this paper, based on the vector control method, the mathematical model of the HAFFSPMM is deduced and the operating performance of the HAFFSPMM in the entire operating region is investigated. A novel control scheme for the HAFFSPMM drive system, including the $i_{d }=0$ and flux-weakening strategy, is proposed. To improve the robustness of the control system, the parameters of the proportional-integral (PI) controller are optimized using the particle swarm optimization (PSO) algorithm. The experimental results demonstrate that the proposed control strategy can maximize the output torque and speed range of the drive system, and the PSO-PI controller can reduce the torque ripple and improve the stability of the control system. Moreover, the strong flux-weakening ability, large load capacity, high power, and torque density of the HAFFSPMM are validated.

Control strategy for hybrid‐excited switched‐flux permanent magnet machines

Hybrid-excited permanent magnet (PM) machines utilise the coordinated operation between the PM and the field excitation current. To enhance the effectiveness of the field excitation current, iron flux bridges are applied to hybrid-excited switched-flux PM machines. This study proposes a new control strategy in which the d-axis current is utilised, while the field excitation current is controlled towards zero rather than negative in the flux-weakening mode. These reference currents are determined by the voltage error regulation method. The special magnetic circuit can effectively reduce the d-axis flux-linkage by either partially short-circuiting the PM flux via the iron bridge or removing the field excitation current. The proposed method exhibits advantages, such as highly enhanced torque response in the constant torque region, extended speed range, robustness against machine parameters, and higher efficiency in flux-weakening region. The feasibility of the proposed method is verified by detailed experimental results.

Hybrid-Excited Flux-Switching Permanent-Magnet Machines With Iron Flux Bridges

Hybrid-excited machines utilize the synergies of permanent magnet (PM) and wound field machines. Flux-switching PM machines have emerged as an attractive machine type due to the fact that the excitation sources are located in the stator allowing a simple robust rotor whilst providing high torque density. This paper proposes topologies of hybrid-excited flux-switching PM machines incorporating iron flux bridges to enhance the effectiveness of the field coil excitation. A simple lumped parameter magnetic circuit model is developed to predict the effect of adjusting various parameters. Two-dimensional finite-element analysis has also been used to predict the machine performance, while a prototype machine has been built and tested to validate the predicted results.