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As it is well recognized, LLCL filter effectively reduces the total inductance of the sinewave filter. In this article, a unified single-current feedback active damping method is proposed for LLCL-equipped high-speed permanent magnet synchronous motor. With the unified discrete model, this method can be utilized in both inverter current feedback-only and motor current feedback-only systems. The coefficient selection and simple digital implementation methods are developed to design the damping system efficiently. The proposed method performs well even with mismatched parameters, such as a $\pm$15% error in filter parameters and a $\pm$40% error in motor inductance. In addition, the study confirms the advantages of LLCL filter over LCL filter in terms of total inductance in high-speed motor drives. Finally, the effectiveness of the proposed method is validated by experimental results of a 12 kr/min(1000 Hz) HSPMSM.

This article proposes a single-motor-current feedback resonance suppression method for LCL-equipped high-speed permanent-magnet synchronous motor drives based on capacitively coupled active damper. The proposed method does not require any additional sensors or high-bandwidth current controllers, and an adaptive controller is designed to dynamically adjust the feedback gain. Compared with the active damping methods, the proposed method not only allows the filter resonant frequency to be higher than the Nyquist frequency, but also has strong parameter robustness. Compared with the existing active damper control method, the number of current sensors is reduced by 50%. In addition, thanks to the low harmonic characteristics of the motor current, the output voltage of the damper in the proposed method can be greatly reduced, which helps reduce the damper dc-link voltage from 30% of the inverter to 5%. The low dc-link voltage helps reduce the power loss and makes it possible to use low-voltage mosfets to construct the high-frequency damper. The experimental results of a 3-kW 12-kr/min (1000 Hz) test motor verify the proposed method.

In this article, the dual resonance problem is first described in LCL-equipped high-speed permanent magnet synchronous motor drives. Since the synchronous coordinate transformation, the natural resonance in stationary coordinate will be converted into two resonances, which are located at $f_{\text{res}}-f_{e}$ and $f_{\text{res}}+f_{e}$, respectively. ($f_{\text{res}}$ is the natural resonant frequency and $f_{e}$ is the motor frequency). Theoretical analysis and experimental results indicate that the traditional notch filter-based methods cannot ensure stability when the $f_{\text{res}}$ is located between $f_{s}/3-f_{e}$ and $f_{s}/3+f_{e}$ because of the dual resonance problem. To address this issue, a robust notch filter-based active damping with a magnitude attenuator is proposed. Besides, the coefficient selection method of the magnitude attenuator is analyzed in detail. Finally, the effectiveness and robustness of the proposed method are verified by the experimental results of a 72 kr/min motor.

In this article, a nonlinear semianalytical model (SAM) is presented to predict the magnetic field distribution (MFD) and electromagnetic performances (EPs) in the cubic spoke-type permanent magnet (PM) machine. To model the rectangular PMs, the rectangular PM is simplified as a combination of fan-shaped regions with different arc angles. Then, the MFD and EPs of the cubic spoke-type machines can be obtained by the harmonic modeling technique. Particularly, the saturation of the magnetic bridges is considered by the nonlinear iterative algorithm. The proposed nonlinear SAM is studied on a 12-slot/8-pole cubic PM prototype, and the nonlinear finite element model and experiment verify its correctness. The main contribution of this article is to present a general analytical modeling method for cubic spoke-type PM machines and consider the magnetic saturation of magnetic bridges.

This article proposes a dynamic decoupling active damping current control method for the current-source inverter (CSI)-fed high-speed permanent magnet synchronous machine (HSPMSM) drive with low carrier ratios. In this system, the natural resonance frequency is relatively high compared with the conventional CSI-fed system due to the high fundamental frequency and low inductance of the HSPMSM, which makes the traditional capacitor-voltage-feedback-based active damping fail. To achieve the desired resonance damping effects, the discrete-time-model-based multistate feedback active damping is proposed, which can configure the resonance pole arbitrarily. Then, to solve the serious cross coupling under low carrier ratios, a low-frequency-equivalent-transfer-function-based dynamic decoupling method is proposed for the parts where the traditional decoupling method cannot be applied. On the above basis, an outer-loop proportional–integral controller is adopted to adjust the magnitude and phase of the open-loop transfer function. In this way, the desired open-loop cutoff frequency with enough phase and gain margin can be achieved under the wide fundamental frequency changes of the HSPMSM. Finally, the effectiveness of the proposed method is verified by experiments.

This article proposes a hybrid analytical model (HAM) for predicting ac copper losses in hairpin windings. The HAM combines the nonlinear semi-analytical model (SAM) and the 1-D ac copper loss computation model to solve the inaccurate boundary solutions of the 1-D ac copper loss computation model when magnetic saturation occurs in the stator teeth. The HAM is used to study the ac losses of the hairpin windings with four different conductor arrangements under different current excitation conditions, and the versatility of the HAM is verified. The HAM has high calculation accuracy, and the calculation speed is 66% faster than the finite element (FE) model. The primary contribution of this research is to present a quick and simple approach for accurately predicting ac copper losses in hairpin windings with arbitrary conductor arrangements.

In this article, a new analytical model for predicting the magnetic field of the U-shaped interior permanent magnet motor (IPMM) is proposed. In the polar coordinates, rectangular permanent magnets are equivalent to the combination of consistent fan-shaped subdomains, and after that, the Laplace or Poisson equation of each solution domain can be obtained. Furthermore, based on the harmonic modeling (HM) technique, the saturation characteristics of the magnetic bridge are accurately considered, and then its magnetic field distribution (MFD) and electromagnetic performances (EPs) can be obtained. The approach proposed in this article includes but is not limited to U-shaped IPMMs, and it can also be applied to spoke-type or V-shaped IPMMs with a minor modification.

This article proposes a pole placement-based current control method for the current-source inverter (CSI) fed permanent magnet synchronous machine (PMSM) drive with eliminating capacitor voltage sampling. First, a generalized $N$-order feedback form of motor current and CSI output current is proposed in the stationary $\alpha \beta$ frame, for the arbitrary pole placement of the control plant. With the proposed pole placement method, the resonance frequency is moved closer to the Nyquist frequency and the resonance peak is damped. On this basis, a linear controller is proposed in the synchronous $dq$ frame for the high-performance current control of PMSM. Moreover, the control parameter selection method is presented based on the consideration of open-loop crossover frequency and phase margin (PM). In this way, the desired PM and enough gain margin can be achieved, thus guaranteeing the stability and robustness of the system. Finally, the effectiveness of the proposed method is verified by lab-scaled experiments.

DC-link capacitor is one of the significant parts of traction converters. Due to the impact of electrical stress, high temperature and humidity, its capacitance degrades faster than expected. Accurate capacitance estimation is critical to the condition monitoring of DC-link capacitors, which is also the basis of online capacitor life prediction. Currently, there is a big challenge for capacitor capacitance estimation in railway applications. The noise fluctuation of the voltage sensor may be nearly equal to that of ripple voltage, leading to the considerable errors of the existing capacitor condition monitoring methods. Therefore, a capacitance estimation method based on precharging model and noise evaluation is proposed in this article. The capacitance is estimated by improved recursive extended least square. The influence of the noise can be effectively reduced and both the calculation accuracy and convergence speed can be well guaranteed through an independent noise estimation model. The proposed method has good immunity in a certain range of signal-noise ratio or signal bias. It shows good performance in experiments.

This article proposes a flexible active damping method for an LCL-equipped high-speed permanent magnet synchronous motor. The damping ratio of the LCL resonance can be freely designed by the proposed high-order partial-state (virtual output voltage and the capacitor current) feedback. Moreover, a coefficient selection method is developed to complete the design of the damping system quickly and efficiently. As the main contribution, the proposal can be easily applied to single-sensor (motor current feedback only) applications to eliminate the sensor of the capacitor current with high parameter robustness. The experimental results of a 72-kr/min test motor verify the stability and robustness of the proposed control strategy.

Tooth-coil permanent magnet synchronous machines (TC-PMSMs) are commonly used in wind power generation and wheel-hub propulsion applications. These machines operate at low speeds and have a large number of poles and slots, providing various pole/slot combinations as options. Typically, these combinations have similar performances, making it challenging to choose the best one from different perspectives. This study focuses on 32-pole TC-PMSMs with different slot numbers to understand how key electromagnetic and thermal performance indicators vary with slot numbers. Using the finite element method, parameters such as torque density, cogging torque, inductance, flux-weakening capability, losses, and temperature rise are evaluated and compared. Prototypes of the wheel-hub TC-PMSM are manufactured and tested on a back-to-back test rig, to validate the analysis results. The findings and conclusions derived from this research can assist in determining the optimal slot number or narrowing down the selection range of competitive pole/slot combinations during the scheme comparison stage.

In order to shorten flanging process and improve manufacturing efficiency, an electromagnetic punching-flanging (EMPF) process was proposed in this work. The EMPF experiments were performed with 6061 aluminum alloy sheets and an electromagnetic-mechanical-fracture numerical simulation was established. The flange formation mechanism and relationships between die-fitting gaps/flange heights and discharge energies were analyzed. The thickness reductions of flanged parts were measured to characterize the flange forming quality. Results showed that sheet deformations during EMPF process mainly occurred in the flanging stage of sheets, and the relationship between flange heights and discharge energies could be represented by a quadratic function. The appropriate increase of discharge energies could reduce the die-fitting gaps. The die-fitting gap (0.506 mm) was minimum under the discharge energy of 7 kJ, which was an optimum discharge energy in this work. The thickness reduction gradually slowed down from this position to fillet positon. The maximum and average thickness reduction rates relative to sheet thickness were 13.6 % and 8.2 % for optimum discharge energy, respectively. Numerical simulation and experimental investigations illustrated that the electromagnetic punching-flanging process can be used for manufacturing flanged parts with high quality.

The zero-sequence inductance is a vital parameter for the performance analysis of permanent magnet machines, especially under faulty conditions or in open-winding machines. This paper focuses on the zero-sequence inductance calculation of fractional slot concentrated winding permanent magnet synchronous machines (FSCW-PMSMs), and reveals the variation regularity of this kind of inductance and its various components against pole/slot combinations, using the winding function and finite element methods. Moreover, based on the analysis of 36-slot FSCW-PMSMs with different pole numbers, the dependency of each inductance component on the pole/slot combination is discussed in detail. To validate the regularities, experimental measurements of zero-sequence inductance are implemented in the prototype of the 36-slot stator. It is found that the regularities are independent of specific slot or pole numbers, which provide guidelines for optimum pole/slot combination selection, to mitigate the problems caused by zero-sequence current.

This paper proposed an electromagnetic loading process with the high-speed impact. Al-4.2% Cu alloy bars were used to employ electromagnetic impact (EI) experiments. Deformation mechanism and microstructure evolution of EI samples were revealed by theoretical model and microstructure characterizations. The EI process had impact force (peak value 40 kN) and impact velocity (peak value 6.7 m/s) during a short time period (1.25 ms). Adiabatic shearing mechanism dominated the whole deformation process, causing that significant microstructure characteristic was adiabatic shear bands (ASBs). The theoretical analysis implied that the formation of ASBs was accounted for the radial velocity gradient. Most plastic deformations concentrated in ASBs, and approximately pure shear deformations resulted in adiabatic temperature rise of 0.33–0.42 Tminside ASBs. The width of ASBs was about 135 μm, in which original equiaxial grains were elongated into laminated sub-structures. TEM observations showed multi-slip systems were simultaneously actuated due to severe shear deformations. High dislocation density and dislocation tangles distributed with the ASBs. Adiabatic temperature rise and distorted energies drove sub-grains rotate into recrystallization grains (70–280 nm) with large angle grain boundaries. The needed maximum time (45 μs) for rotational dynamic recrystallization was far less than that of plastic deformation, indicating that rotational dynamic recrystallization mechanism contributed to the formation of recrystallization grains.