Jiongjiong Cai

Multi-turn encoders receives great attentions recently, especially the gear-type ones with mechanical structure and permanent magnets, which has the function of multi-turn mechanical memory. However, the current gear-type multi-turn encoders still have many challenges, such as complex structure, large volume, complex calculation method, etc. To provide a more flexible multi-turn magnetic encoder that can encode position information in an analytical way, this paper studies the principle, system model, encoding algorithm, and design policy of a novel multi-layer magnetic Vernier group (MVG) method. The weakness of the conventional multi-turn magnetic Vernier encoder is firstly analyzed. Then, the new principle, system model and general encoding algorithm of the investigated multi-layer MVG method are introduced. The design policy of the novel multi-layer MVG method are carefully discussed: (1) from the tooth number of the minimum common period (TNMCP) perspective, all possible combinations of two lower-layer MVGs to upgrade to a higher-layer MVG are analyzed. (2) The gear and tooth number decision policy for lower layers are investigated when the top-layer TNMCP is decided. A gear-saving scheme is established, and the corresponding parameter selections are analyzed. (3) The general process of upgrading the current MVG into a higher-layer alternative is shown out. Finally, a two-layer MVG encoding system with three gears is designed as an example for experimental verification. The results demonstrate that angle information and multi-turn encoding can be realized according to the proposed multi-layer MVG method. The correctness of the gear-saving scheme is also verified. The turn values decoded from the multi-layer MVG are consistent with those from the reference motor encoder.

Electrically-excited flux-switching machines are advantageous in simple and reliable structure, good speed control performance, low cost, etc., so they have arouse wide concerns from new energy field. However, they have much lower torque density/thrust density compared with the same type PM machines. To overcome this challenge, electromagnetic-thermal coupled analysis is carried out with respect to water-cooled electrically-excited flux-switching linear machines (EEFSLM). The simulation results indicate that the conventional fixed copper loss method (FCLM) is no longer suitable for high thrust density design, since it is unable to consider the strong coupling between the electromagnetic and thermal performance. Hence, a multi-step electromagnetic-thermal joint optimisation method is proposed, which first ensures the consistency between the electromagnetic and thermal modelling and then considers the effect of different field/armature coil sizes. By using the proposed joint optimisation method, it is found that the combination of relatively large size of field coil and relatively low field copper loss is favourable for achieving high thrust force for the current EEFSLM design. Moreover, the thrust force is raised by 13-15% compared with using the FCLM. The electromagnetic and thermal performance of the EEFSLM is validated by the prototype test.

When the electromagnetic (EM) force ${F}_{\mathrm{M}}$ is used to balance the dynamical axial gas separation force ${F}_{\text{gas}}$ of scroll compressors, the control effect, system complexity, reliability, and cost are severely restricted by the dynamic force sensor systems. For this consideration, a scroll compressor without online force sensors is designed, and an innovative EM force control method based on “EM force-current ( ${F}_{\mathrm{M}}{\rm{ - }}{i}_{\mathrm{M}}$ )” nonlinear model is proposed. The “ ${F}_{\mathrm{M}}{\rm{ - }}{i}_{\mathrm{M}}$ ” nonlinear relationship changes with frequency and EM gap, so it is difficult to determine the relationship online. Even when the target EM force is precise, it is difficult to obtain the corresponding control current to generate the actual EM force. Given this difficulty and challenge, this article creatively puts forward a method. When the target EM force is always kept as the final target curve, the “ ${F}_{\mathrm{M}}{\rm{ - }}{i}_{\mathrm{M}}$ ” relationship, used to decode the control current, is adjusted by adjusting the estimated value of the EM gap to control the actual EM force. The best dynamic contact seal and high-quality steady-state operation can be realized by optimizing the estimated EM gap value. This method consists of two stages: set up an offline database and carry out online control. At the offline stage, the “ ${F}_{\mathrm{M}}{\rm{ - }}{i}_{\mathrm{M}}$ ” nonlinear relations with different frequencies and EM gaps are sampled with force sensors and then stored using Prandtl–Ishlinskii (PI) model. At the online stage, no online feedback force sensors are needed. The current needed to produce exact F _M is decoded from the chosen “ ${F}_{\mathrm{M}}{\rm{ - }}{i}_{\mathrm{M}}$ ” PI model established at the offline stage. The creative “ ${F}_{\mathrm{M}}{\rm{ - }}{i}_{\mathrm{M}}$ ” model choosing method is proposed, which relies on the iterative estimations of EM gap value. The results of the quasi-prototype experiment show that the aforesaid control method is feasible.

To help the reverse Brayton cycle cool the refrigerant from 100 K to 50 K, an auxiliary generator, with a housed stator, is studied and optimized, and the influences of weights in the cost- function on the results are discussed. The power demand and adiabatic characteristics of reverse Brayton cycle expansion are analyzed, after which the optimization indexes, including output rated power, efficiency, the air gap between rotor and stator, loss, and volume, are decided. The initial model of the auxiliary generator is then constructed and the parameters to be optimized are also determined. Taking the low loss and sinusoidal back-EMF as the evaluation indexes, the single parameter optimizations of the auxiliary generator are carried out. The co-simulation of the generator and its corresponding driving circuit is investigated, with which the power generation efficiency is calculated. The global optimizations of the generator parameters are carried out using a genetic algorithm. A suitable analytic hierarchy process (AHP) model is proposed, with which a three-order judgment matrix is constructed, and the effects of different weight combinations, in the cost-function, on generator performance are compared. The experimental results show that the output back-EMF amplitude is 28.2 V, which is about 10% smaller than the simulation results; the output power of the auxiliary generator under load is about 3.7 W, meeting the rated demand.

In order to explore the axial electromagnetic dynamic balance force curve of a scroll compressor under the action of thermal energy, radial clearance, mechanism friction, and other factors in actual working conditions, an axial force exploration method that can automatically approach sections is proposed in this paper. Considering the dynamic response ability of the electromagnetic balance system, an automatic optimization algorithm of the partition number was proposed to find the optimal partition number in order to achieve the optimal tracking effect. An experimental platform was built to test the effect of the segmented tracking method on calibrating the deviation between the theoretical axial force curve and the real curve. The results show that the curve construction method proposed in this paper has convergence. This method can automatically and accurately construct the axial balance force curve required by the electromagnetic dynamic balance. Through the automatic optimization algorithm, the standard error (RMSE) between the target curve and the theoretical curve was reduced from 290 to 22.6, and the number of partitions with the lowest standard error was 20. The results provide a useful reference for the accurate, automatic, and efficient exploration of the actual axial sealing force of the scroll compressor.

In order to reduce the transverse edge effect of a single-sided linear induction motors (SLIMs) for a low-speed Maglev train, this article proposes novel SLIMs with symmetry/asymmetry double-slit secondary. First, the end effects of the conventional SLIMs with flat-solid and cap-solid secondaries are investigated based on three-dimensional (3-D) finite-element model. For the latter one, the influences of slip frequency and secondary structure parameters are obtained as well. Second, the structures of the proposed double-slit secondaries are introduced, and the topology parameters are investigated by a single-variable optimization method. Third, the force performances of SLIMs with proposed two kinds of double-slit secondaries are compared with those of the SLIMs with the traditional cap-solid secondary. Finally, a prototype of SLIM with asymmetry double-slit secondary is manufactured and tested to validate the predictions. The results show that the SLIM with the proposed asymmetry double-slit secondary can improve the force performances due to reduction in the transverse end effect.