Traditional rotor position detection schemes typically mount Hall sensors on the stator or motor base to measure the air-gap magnetic field or permanent magnet leakage.However,armature reaction significantly influences detection accuracy.This study proposes mounting Hall sensors on printed circuit boards(PCBs)external to the rotor of an external rotor permanent magnet synchronous motor(PMSM).With the permanent magnet slightly extending beyond the rotor yoke,rotor position is determined by detecting the magnet's field,which is minimally influenced by armature reaction.Theoretical and experimental analyses reveal that when two Hall sensors are placed at a 90° interval on the PCB,the fundamental phases of their signals are not orthogonal,resulting in position errors.To resolve this,it is shown that orthogonal fundamental phases are achieved when the sensors are spaced at an interval of 90°∙Pr/(Pr+1).The theoretical predictions are validated through ANSYS Maxwell finite element simulations and physical motor experiments,confirming the feasibility of the proposed position detection scheme.

To optimize the selection of the bulk capacitor in a flyback converter, this paper proposes a method based on the lifetime and volume of aluminum electrolytic capacitors (Al e-caps). Firstly, mathematical models for the low-frequency and high-frequency harmonic currents of the bulk capacitor are established. The accuracy of these models has been verified by comparing the Saber simulation results and experimental results with calculated results, providing a basis for accurately calculating capacitor losses. Secondly, a lifetime model for the capacitor is established based on capacitor losses. The Pareto frontier of capacitor loss lifetime and volume is obtained using the multi-objective particle swarm optimization (MOPSO) algorithm, providing a basis for the optimal selection of the bulk capacitor. Finally, a 75 W flyback converter prototype is built based on the results obtained from the optimization process according to personalized requirements. The results show that the optimized capacitor has almost no effect on efficiency, and the volume decreases by 36.8 % with a sacrifice of 4.21 % in loss lifetime.

AbstractGiven 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 flux-estimation model employs a third-order generalized integrator frequency-locked loop to effectively eliminate DC bias. However, this method has two limitations. First, the frequency estimation performed by the frequency-locked loop (FLL) can sometimes be inaccurate at times, resulting in frequency oscillations when the EMF fluctuates, impacting the dynamic performance of the method. Second, the method has restricted capability when it some to suppressing high harmonics. To address the disadvantages of the dynamic performance, a more advanced method called dual TOFO-FLL (DTOFO-FLL) is proposed to improve the dynamic response. Furthermore, the coefficient k of the generalized integrator is crucial for both harmonic suppression and dynamic performance. In an effort to improve the suppression of high-order harmonics, while maintaining a robust dynamic performance, a flux-observer parameter adaptive method, DATOFO-FLL, is brought forth based on DTOFO-FLL. A theoretical analysis demonstrates that this technique delivers strong harmonic suppression during steady-state operation and upgraded dynamic performance in terms of response speed and disturbance rejection. Experimental validation was conducted on a platform controlled by an STM32G431RB digital signal processor to test a sensorless drive method using DATOFO-FLL. The results verified the effectiveness of this approach in driving a permanent magnet synchronous motor.

随着风电场规模的不断增大,电网不对称短路故障期间,风电场与电网之间的耦合作用不断增强,电压失稳风险增大.针对现有风电场接入电力系统技术规定,在电网发生不对称短路故障持续阶段,研究辐射状风电场的静态电压稳定性分析方法.建立了考虑多风电场与连接线路的阻抗模型,根据不对称故障时的动态无功支撑要求,对多风电场的电压稳定性进行分析,获得了风电场和电网正负序阻抗之间的电压相互作用关系.分析结果表明,多风电场满足现有风电并网导则时,所提方法可准确判断电网不对称短路故障持续阶段的静态电压是否稳定.最后,通过仿真验证了理论分析的正确性和所提方法的有效性.

The coherence factor (CF) can improve the image contrast and side lobe suppression ability of traditional delay and sum (DAS) beamformer. However, it always leads to dark-region artifacts. In this paper, in order to reduce the dark-region artifacts while maintaining the image resolution and contrast as much as possible, a truncated-composite-based condition coherence factor (TC-CCF) is proposed for ultrasound imaging. Initially, the condition coherence factor (CCF) is defined as the ratio between the number of sampling time which should satisfy the condition of sign consistency and the total number of sampling time within the duration of a transmitting pulse. Then, setting a truncation threshold to truncate the CF and CCF, and the proposed truncated-composite condition coherence factor is obtained by combining the two truncated coherence factor. To evaluate the performance of the proposed methods, the simulation, the geabr_0 experiment, and the in vivo rat mammary tumor study is conducted. The simulated cyst indicates that TC-CCF can obtain better performance than CF and SCF in speckle quality. The geabr_0 experimental results demonstrate that the TC-CCF can gain 34.1% lower full width at half-maximum (FWHM) and 41.7% higher contrast ratio (CR) than traditional DAS. Furthermore, for experimental cysts, a maximal improvements of noise contrast ratio (CNR) and speckle signals-to-noise ratio (sSNR) is 137% and 114.5% respectively. In general, the proposed methods can effectively address the inherent limitation of the standard CF to improve the speckle quality.

Photovoltaic modules are long-term exposed outdoors, and the surfaces are easily covered by dust, which seriously affects the power generation efficiency and increases the workload of maintenance. An anti-reflective and superhydrophobic coating with excellent durable and self-cleaning properties was proposed to improve this problem. The prepared coating has multiple structures to improve the durability. Firstly, the coating consists of a double-layer film structure, and the bottom layer is connected to the substrate through covalent bonding to improve the adhesion of the coatings; secondly, the hydrophobic silica particles in the top layer can be embedded in the pore structure of the bottom layer to improve the connection strength between the top and bottom layers; thirdly, hydrophobic silica particles in the top layer are fixed in a three-dimensional mesh structure formed by long-chain silica, which can improve the mechanical stability of the coatings. In addition, the preparation conditions of the hydrophobic particulate silica sols and the ratio of long-chain silica sol in the top layer solution can be adjusted to control the durable, anti-reflective, and superhydrophobic properties of the coatings. The experimental results indicate that the transmittance of the coated glass is increased by 5 % compared to the bare glass, and the coating has 6H pencil hardness test grade and 5B tape adhesion test grade. The maximum output power of the coated PV modules can be increased by 5.67 %. After simulating dust accumulation and rainfall, the power of coated and uncoated photovoltaic modules can be restored to 96.6 % and 83.0 % respectively, indicating that the prepared coating also has excellent self-cleaning ability.

为了进一步提高动磁式直线振荡电机的推力密度,在传统E型铁心结构基础上提出一种3C型直线振荡电机,采用有限元法建立两种结构电机的2D分析模型,在此基础上,计算了电机的磁场分布和电磁推力,研究了共振状态下电机的动态性能.分析表明3C型电机可以有效缓解电机局部磁饱和,提升气隙磁密,相同激励下拥有更大的电磁推力,更好的动态性能.最后,在有限元分析基础上制作了一台3C型直线振荡电机样机,并进行了电机的静态推力测试,实验结果与有限元仿真取得了较好的一致性.研究结果对推动直线振荡电机的大功率应用具有重要意义.

In this paper, we propose a dual projection generalized sidelobe canceller (DPGSC) based on mixed subspace (MS) for ultrasound imaging, which aims to improve the speckle signal-noise-ratio (sSNR) and decrease the dark-region artifacts. A mixed signal subspace based on the correlation between the desired steering vector and the eigenvectors is constructed to further optimize the desired steering vector and the final weight vector. The simulated and experimental results show that the proposed method can greatly improve the speckle uniformity. In the geabr_0 experiment, the standard deviation of background and sSNR of MS-DPGSC can be improved by 48.07% and 58.49% more than those of eigenspace-based generalized sidelobe canceller (ESGSC). Furthermore, for a hyperechoic target, the maximal improvement of contrast ratio is 95.29%. In terms of anechoic cyst, the contrast-to-noise ratio of MS-DPGSC is increased by 123.08% than that of ESGSC. The rat mammary tumor experimental data show that the proposed method has better comprehensive imaging effect than traditional generalized sidelobe cancellers and ESGSCs.

Accurate position signals are essential for a vector control system. To obtain accurate position signals, high-precision position sensors such as optical encoder and resolver are employed. However, they are usually restricted by the environmental condition and cost. Linear Hall-effect sensors, possessing tiny size, light weight and low cost, are usually used to detect position signals. However, the position signals detected by linear Hall-effect sensors in low cost conditions always contain a large part of high-order harmonics, which will decrease the validity and reliability of sensor measurement. In this paper, to eliminate the influence of harmonics, a short-distance harmonic suppression method without any low-pass filter is proposed. The proposed method utilises three linear Hall-effect sensors displaced a certain electrical angle to dissolve the position signal. Through simulation analysis and experimental verification, the proposed method has been proven to be effective in suppressing the third-order and fifth-order harmonics.

Crystalline silicon (c-Si) solar cells cannot make full use of solar energy at present, especially the short wavelength (300-500 nm) energy. Owing to the inherent problem, c-Si photovoltaic (PV) modules are still facing the trouble of low PV conversion efficiency. Applying spectral down-conversion (DC) materials to transform underutilized solar spectrum is an effective way to improve the problem. In this study, inspired by chlorophyll (Chl) fluorescence phenomenon, Chl film were specially prepared by encapsulating Chl with oxygen insulating material as spectral DC material. Then, to enhance Chl stability, nano SiO2 was added to the film-forming solution. The spectroscopic properties of the Chl films were analyzed, and the output power characteristics of the PV modules coated with the Chl films were inspected. The experimental results indicate that the prepared Chl film has good spectral conversion performance, and can convert light of about 400 nm into about 670-680 nm which is suitable for PV modules. After being exposed outdoors for about 30 days, the maximum power of the PV module coated by the Chl film with SiO2 is still improved by 9.2%. Since the Chl can be obtained from nature by an economical way, the Chl film is a promising material to improve the power generation efficiency of c-Si PV modules.

Conductive hydrogels featuring a modulus similar to the skin have flourished in health monitoring and human-machine interface systems. However, developing conductive hydrogels with self-healing and tunable force-electrical performance remains a problem. Herein, a hydrogen bonding cross-linking strategy was utilized by incorporating silk sericin-modified carbon nanotubes (SS@CNTs) into sodium alginate (SA) and polyvinyl alcohol (PVA). Hydrogels synthesized with desirable tensile strength and self-healing ability (67.2 % self-healing efficiency in fracture strength) assembled into strain sensors with a low detection limit of 0.5 % and a gauge factor (GF) of 4.75 (0-17 %). Additionally, as-prepared hydrogels exhibit high sensitivity to tiny pressure changes, allowing recognition of complex handwriting. Notably, resulting hydrogels possess self-powered property, generating up to 215 V and illuminating 100 commercial green LEDs. This work stems from the pressing need for multifunctional hydrogels with prospective applications in human motion sensing and energy harvesting.

Triboelectric nanogenerator (TENG) has proved an effective ambient mechanical energy collection and conversion technology for power supply to distributed sensors in internet of things. Rational stack of TENG units is a way to enhance its output performance in a limited space. However, the output does not linearly increase with the number of stack units due to narrow working gaps and low contact electrification ability of materials. It is still a great challenge to obtain a high output performance TENG by stacking units. Herein, a V-shape multiple stacking TENG (V-TENG) is proposed, which largely increases effective contact area and improves space utilization. A self-charge excitation circuit and a Zener diode are used to enhance its output performance and maintain output stability. The peak power of the V-TENG with self-charge excitation (VSE-TENG) reaches to 3.96 mW, which increases by more than 22 times compared with that without excitation. Furthermore, the VTENG with power management can collect water flow energy and serve as a portable power supply for powering LEDs, a temperature and humidity sensor, and a calculator. This work provides a new strategy for boosting TENG output performance in a fixed device space.

Abstract The slotless tubular permanent magnet linear motor (STPMLM) offers obvious advantages when it is applied to the punching system, such as space saving and controllable impact strength. Herein, the mechanical and electromagnetic coupled differential equations were established to present a comprehensive analysis of the relationship between mover mass and motor performance in the punching system. The travel time of the punching movement was expressed analytically under the condition of the mover obtaining the same impact kinetic energy, and the relationship between the mover mass and the resistive energy consumption in one punching process was also deduced under the same condition. Then the analytical results were validated by a numerical model. The studies show that a lighter mover mass can contribute to less resistive energy consumption and faster dynamic response in the punching applications. Based on that, a STPMLM with special‐shaped yoke was designed for lighter mover mass. Moreover, prototype experiments including static thrust characteristic and dynamic performance were conducted. The experimental results proved that the proposed permanent magnet linear motor with special‐shaped yoke can improve the dynamic performance and reduce resistive energy consumption while ensuring that the electromagnetic performance is not affected.

The linear voice coil motor (VCM) is widely used in many applications. Many research studies have been done to improve its thrust density. This article proposes a novel end-iron-free VCM topology to suppress the end effect on thrust loss. As the end iron yoke is removed, the reverse flux near the end of VCM has been greatly reduced. For a higher thrust density, the arrangement of unequal length between magnets is studied in terms of magnetic equivalent circuit (MEC) method. Through further electromagnetic analysis, the optimal permanent magnet (PM) length ratio is determined based on finite element analysis (FEA). The results from both FEA and practical experiments show that thrust characteristic and dynamic performance of the end-iron-free structure with appropriate PM length ratio is much better than those of the original structure, which proves the superiority of the proposed structure. Moreover, its cost and weight have been decreased. The proposed design plays a significant role in enhancing VCM performance and efficiency.

In the case of designing linear voice coil motors (LVCMs), the aluminium tube is usually used to support and fix the windings. Due to the high-speed linear reciprocating motion, the eddy-current damping force in aluminium tube has a large effect on the dynamic characteristic of LVCMs and weakens the resultant force. In this study, an LVCM with forward winding is studied. The cause of eddy current damping force in the original structure of the aluminium tube is analysed, and the corresponding mathematic model is established which is verified by finite element method. To restrain the damping effect, three restraining measurements have been discussed. Then a novel structure of aluminium tube with axial slits and ribbed stiffeners is proposed according to the simulation analysis. During the experimentation process, the mover resultant force is replaced with its acceleration. Results show that the mover acceleration of LVCM with stiffened aluminium tube is bigger than that of the initial one. Hence the resultant force of the proposed structure is improved effectively and the new structure has a good inhibition effect on eddy-current damping effect.

Due to the ironless structure of the toroidal winding in the tubular linear voice coil motor (TLVCM), the winding thickness is one of the critical parameters that have an impact on air-gap flux density, and hence affects the copper loss at rated thrust. This paper investigates and determines the thickness of the ironless toroidal winding of the TLVCM for the purpose of a minimum copper loss. Magnetic equivalent circuit (MEC) method is used to analyze the air-gap flux density with respect to winding thickness, and the corresponding copper loss at the rated thrust is assessed by considering the slot fill factor. The optimal solution is obtained according to the U-shaped curve of the copper loss. Moreover, the finite-element analysis is combined to validate the results of MEC method, and a good agreement is reached. Two prototypes of TLVCMs having similar slot fill factor are made, one of which is with the optimal winding thickness. The expected current at the rated thrust is obtained by a test platform of static thrust, so as to obtain the corresponding copper loss for each prototype. The experimental results show that the TLVCM with optimal winding thickness features a lower copper loss. Hence, the attempt to minimize the copper loss by designing the thickness of the ironless winding is highly effective.

A Halbach permanent magnet (PM) tubular linear voice coil motor (LVCM) with a semi-closed structure is developed to enhance the thrust density in this study. Generally, the end of conventional LVCM is open and suffers from the considerable end reluctance. The usage of Halbach array in LVCM makes this problem more prominent although it improves the air-gap flux density greatly. The flux at the end of LVCM can be guided to improve the air-gap flux density. Therefore, this study aims to constrain and direct the magnetic field at the end of a Halbach PM LVCM by using a ferromagnetic auxiliary yoke to construct a semi-closed structure. Magnetic equivalent circuit method is utilised to analyse the effect of the auxiliary yoke on air-gap flux density. Besides, finite element analysis is used to analyse the magnetic circuit and design the parameters of LVCM. The semi-closed tubular LVCM topology is manufactured and the effectiveness of this topology is validated by experimental measurements. Results show that the thrust density of LVCM is improved effectively by using an auxiliary yoke at the end.

In this paper,the mechanical air gap of a natural air-cooled slotless tubular permanent magnet (PM) linear actuator (TPMLA) was investigated,trying to constrain and direct the heat flow in well-defined paths and minimize the PM temperature.Generally,the heat generated by slotless windings must pass through the surrounding air first.For this reason,the heat dissipation condition is much worse than slotted machines.Although a small mechanical air-gap length tends to increase the air-gap flux density,it makes a large portion of heat generated by windings being transferred to the PM side,heating the PM and lowering the remnant flux density of PM.Therefore,a proper mechanical air gap is of great importance for PM temperature of slotless TPMLA.Electromagnetic and thermal models were established,and were compared with finite element models.Three prototypes of slotless TPMLAs having different mechanical air-gap lengths were built and tested.The effect of mechanical air gap on constraining and directing the heat flow is greatly prominent,which shows that the attempt to minimize PM temperature of TPMLA by increasing its mechanical air-gap length properly is highly effective.

Generally, for small- and medium-sized tubular permanent-magnet (PM) linear actuators, PM structures can be divided into two categories. One is interior PM (IPM) structure and the other is surface-mounted PM (SPM), involving a compromise between flux per pole and magnet leakage flux. This study proposes a novel semi-IPM (s-IPM) structure for a tubular linear actuator having the advantages of high flux per pole of IPM and small magnet leakage flux of SPM. The air-gap flux density and the average thrust are analysed and compared with IPM and SPM by the magnetic equivalent circuit and finite element analysis. Moreover, the s-IPM structure is also compared with Halbach PM array in terms of the average thrust and the magnet utilisation. Four prototype actuators with different PM structures are built and tested. Both the theoretical and experimental results show that the magnet utilisation of the s-IPM structure is the largest while its cost and volume are approximately unchanged. The proposed s-IPM actuators are of great prominence in high-magnet-utilisation and low-cost applications.