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A SQUID tandem is a two-stage amplifier consisting of the front end SQUID at T << 1 K and the booster SQUID at T ∼ 4 K. We give an overview of the dc SQUID design for the tandem used in the recent 37-pixel frequency domain multiplexed (FDM) readout demonstration of X-ray calorimeters. The SQUID devices were fabricated with pillar-type Josephson junctions at the nominal JC = 500 A/cm2 critical current density. We further discuss possible improvements to the FDM tandem configuration, including (i) the class-B operation for better power efficiency, (ii) the input power combiner as an improvement over the simple T-junction summing, with the promise for larger multiplexing factors, and (iii) the new booster SQUID device. The new improved booster is a 8-parallel 66-series SQUID array fabricated with SWAPS Josephson junctions at the nominal JC = 1.5 kA/cm2 critical current density, and it shows dV/dΦ > 30 mV/Φ0 gain in the symmetric-slope operation, as well as ΦN ≈ 0.05 μΦ0 / Hz1/2 flux noise.

The inertia of a power system decreases with the increasing penetration of renewable energy, and the stability of power systems is facing great challenges. A virtual synchronous generator (VSG) has become one of the effective schemes for the high permeability of distributed generation, due to its similar characteristics to a synchronous generator. However, the coupling of the VSG in the power transmission from the actual power output point to the grid-connected point may lead to a steady-state error and dynamic oscillations, which limits the power output capability of the grid-connected converter and the grid support ability. To solve this problem, first, the power coupling mechanism of VSG is studied. Second, a virtual-inductor and virtual-capacitor control strategy is proposed for power decoupling, which eliminates the power coupling and improves their capability in suppressing the reactive power fluctuation. Finally, simulation and laboratory experimental results verify the effectiveness of the proposed decoupling strategy.

Magnetic circuit components have long been the largest and most difficult components to miniaturize. Printed circuit board (PCB) fabrication methods cannot achieve small diameter, high aspect-ratio vias for high winding turn numbers to achieve high inductance, and microelectronics methods cannot achieve the high-quality and thick ferrite core materials. In this paper, we present an alternative breakthrough method of printed circuit fabrication to significantly reduce the effective via diameter for embedded magnetic devices, boosting the inductance per unit area. To reduce the effective via diameter, high-density via plugs are ex-situ fabricated and shaped, and then embedded into PCB substrate in the same process as standard magnetic core embedding. The structure of the plug is such that precise placement within the substrate, or alignment to the plug with the winding pattern, is not necessary. Devices presented in this paper use via plugs with an effective diameter of 40 μm and a theoretically unlimited aspect ratio, though refinements in the plug fabrication process are expected to reduce the via diameter down to 10μm. The process is experimentally demonstrated with a 14-turn racetrack shaped transformer; novel diagnostic methods using magneto-optic garnet films to image current paths are also demonstrated.

Thomson coil actuators consist of an electric coil repelling a metallic disk. They are considered the fastest electromagnetic actuators for short travels and for this reason are favored for DC circuit breakers. Although the basic physics are understood, the actuator’s few components are very interdependent, making for a difficult analysis. Actuator design so far has thus been limited to trial and error based on finite-element models. In this paper, a novel approach is presented based on the electromagnetic frequency response of the actuator. This method is shown to be an intriguing analysis tool and various actuator design directions are presented. Experimental results provide a confirmation of the analysis.

Grid-connected inverter failure may be caused by outliers of a population of units in field operation, due to the LCL filter parameter uncertainty. This paper proposes a probabilistic framework to analyze the impact of multiple filter parameter variances due to component tolerances, operating points, and aging effects. Both robust stability and filter performance are selected as the risk of failure. The robust stability of the grid-connected inverter is quantified by the structured singular value (SSV). The total harmonic distortion (THD) of the grid current is estimated to evaluate the filter performance. A case study on a three-phase inverter is performed to verify the proposed method through Hardware-in-the-Loop (HIL) simulation and physical prototype testing.

Mission profile emulation for submodules (SMs) in the modular multilevel converter (MMC) is a crucial step before a full-scale system is put into field operation. Existing methods suffer from limitations of the testing accuracy due to the staircase-like arm voltages which result in distorted loading current and require large filter inductance. This is especially the case when limited number of SMs are under test. In this paper, an efficient MPE method is proposed to emulate the loading behaviors of multiple SMs in MMC. The testing circuit allows two arms of MMC with flexible SM number, operating in inverting and rectifying mode under nearest level modulation (NLM), to be tested simultaneously with reduced DC supply voltage. A common H-bridge circuit is introduced in the testing circuit, with each arm of the H-bridge circuit functioning as the voltage compensator by using feed-forward control. In this way, the current distortion can be significantly suppressed and testing accuracy can be guaranteed in a cost-efficient manner even though no large inductor is included in the testing circuit. The proposed method allows SMs under test to be loaded as in the actual back-to-back MMC system. Simulations and experimental measurements are given to validate the proposed method.

Power filters have been widely used to suppress switching harmonics caused by the modulation of grid-connected inverters. In order to save the total inductance and cost and reduce the volume, different power filters were proposed for the three-phase three-wire grid-connected voltage source inverter. However, in industrial applications, due to the consideration of production cost, the difficulties caused by the deviation of actual parameters have to be addressed. In this article, we propose a new three-phase three-wire power filter with a simple structure, almost the smallest total inductance, and strong resistance to the adverse effects of parameter shifts. The parameters of the proposed filter and the design of the grid-connected system controller are introduced in detail. When studying the influence of parameter offset, a comparison between different types of notch power filters is also given. Simulation and experimental results on a 380 V/50 Hz/6 kW three-phase inverter prototype verify the performance of the proposed power filter.

Impedance-source inverters with coupled inductors can provide much higher voltage gains, but occasionally at the expense of discontinuous input currents and large voltage spikes at their dc-links. The former is caused by absence of inductances at their inputs, while the latter is due to unintentional interruptions of leakage currents through their coupled inductors. These problems have now been solved here by a new family of dual-winding impedance-source inverters (DW-ISIs). Each DW-ISI can recycle leakage energy from its two windings to a few clamping capacitors, which in turn help to prevent voltage spikes. This, together with the presence of an inductance for smoothing its input current, renders the family of DW-ISIs to be highly effective, while not compromising voltage and current stresses when compared to other precedent inverters. In addition, to simplify the circuit analysis, a reactive component elimination method has been proposed in this paper. Simulation and experimental results have confirmed the validity of the proposed topologies.

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.

Lisää artikkeli, kun julkaistu. The use of multiple transmitters (Tx) has been an attractive solution for enabling free-positioning wireless power transfer (WPT) in a large area. One of the key challenges in such multi-Tx WPT systems is the cross-coupling between Tx coils. This letter proposes a compact self-decoupled Tx coil solution for multi-Tx WPT systems. The measured cross-coupling between Tx coils has been reduced by 95% compared to conventional coil designs. Additionally, an integration method for a compensation inductor with the main Tx coil is proposed. Therefore, the coil design proposed in this letter facilitates creation of fully modular and scalable Tx coils for multi-Tx WPT systems. The proposed designs are experimentally verified in a laboratory prototype.

This paper presents a new method for estimating the fault location in voltage source converter interfaced dc system. The proposed dc fault location estimation method evaluates the distance from the fault point to the dc line terminal by estimating the line inductance, hence it is designated as L location. Since the fault impedance usually only includes resistance, the proposed L location is less affected by the variation of fault resistance. In addition, the ripple caused by the distributed capacitive discharge is excluded from the dc line current when the proposed L location is applied in the dc system with the distributed-parameter transmission line. The cubic curve fitting method is used to reconstruct the current signal based on the least square method. The effectiveness of the proposed L location is verified with an OPAL-RT based multi-terminal dc system and experimental point-to-point and MTDC systems. The comparison with other methods, including the impedance estimation and the voltage travelling wave based location substantiates the comprehensive performance of the proposed method.

A Phase-shifted full-bridge (PSFB) converter is widely used in various applications due to its soft-switching characteristics. However, one of the recognized shortcomings of the PSFB converter is that it cannot simultaneously have a wide soft switching range and a small secondary-side duty cycle loss. The shortcoming hinders the high frequency and high efficiency of the converter. In this paper, the change of the energy demand of the converter on the external series inductor with input voltage and load is analyzed. On this basis, a variable saturation inductor with controllable energy is proposed to meet the energy demand and solve the problem of core heating. The controllable change characteristics of the inductor energy are studied directly instead of the controllable change of the inductance value. By adjusting the inductor energy, the PSFB can not only achieve soft switching under light loads, but also reduce duty cycle loss under heavy loads. Theoretical analysis and experimental verification are carried out on the soft switching and duty cycle loss of the converter. Since the transformer ratio can be increased due to the smaller duty cycle loss. The efficiency of the converter can be further improved.

The high-frequency (HF) signal injection methods have been widely used for the low-speed sensorless control of permanent magnet motor under vector control framework. However, for the fault tolerant permanent magnet synchronous motor (FTPMSM) system under fault condition, the fault tolerant control is usually based on independent control of each phase current, rather than the vector control, which prevents the existing sensorless control from being directly applied. To cope with this issue, this paper proposes a novel sensorless control by HF signal injection in any non-fault two phase windings for the FTPMSM system with no coordinate transformation, which can ensure the low- and zero-speed sensorless control performance both in fault-free and fault tolerant operation conditions. This sensorless control scheme is based on independent control framework of each phase current, which consists of the real-time inductance observer, the non-orthogonal phase-locked loop (NPLL), the notch filter and the polarity discrimination of magnet pole. The real-time inductance observer is proposed to estimate the differential mode inductances of two non-fault phase. The NPLL is proposed to achieve the rotor position and speed estimation based on the obtained two phase inductances. To enhance the sensorless control performance, a new notch filter is proposed to filter out the injected HF response component in phase current. The proposed sensorless FTPMSM system has preeminent low-speed control performance and robustness in non-fault and fault tolerant operation process, which is also verified via experiments on a six-phase FTPMSM platform.

Fundamental harmonic analysis (FHA) model is widely used for wireless power transfer (WPT) due to its physical insight and compact form (for example, 8RL/2) of diode rectifier equivalent resistance. Because this compact form is valid for continuous conduction mode (CCM), and resonant tank parameters such as inductance and capacitance are independent of equivalent resistance when designing these parameters based on double side LCC (DS-LCC) FHA model, the selected optimal parameters may not satisfy the CCM prerequisite. This will make actual system characteristics deviate from the FHA model predictions, especially the output voltage and power. Therefore, the original optimal design is invalid and designer needs to execute a circular design, namely designing resonant tank parameters based on FHA model, then judging or simulating whether satisfy CCM operation, redesigning parameters if not satisfy CCM. In order to validate the original optimal design even if CCM isn`t established and make design process straightforward, an effective remedy which is adding a series LC filter in secondary side is proposed, and a computation method about the required minimum filter parameter is provided. Effectiveness of proposed remedy is verified by simulation and experiment. Besides, computation method is packaged as a program to help researchers design rapidly.

A hybrid excitation generator is proposed as a brushless solution for aircraft low-voltage DC power system applications. This topology distinguishes itself from the commonly used electrically excited generator in aircraft power systems, because it features an open-circuit voltage without field current. This feature is an advantage but it also includes a risk. As a too high open-circuit voltage has detrimental influences on the generation system, the limitation of this open-circuit voltage needs to be guaranteed at all times. The key design parameters, such as the slot-pole combination, stack length, and number of turns of the armature winding, are determined to make sure that generators meet the open-circuit voltage limitation. These key design parameters influence also the inductance characteristics of the generator and put consequences on the load characteristics thereby. Therefore, this paper also analyzes the load and short-circuit characteristics of these hybrid excitation generators as function of these parameters. Theoretical deduction and simulation are conducted to reveal the influence law of the parameters on the performance of the hybrid excitation generator under the limitation of open-circuit voltage. A 12300rpm 12kW prototype is developed. The experiments verify the analysis and show the hybrid excitation generator is appropriate for aircraft applications.

This paper investigates a dc solid state transformer (DCSST) with dc fault ride-through (FRT) capability for medium voltage dc (MVDC) systems. The fault ride through requirement for DCSST in dc gird is investigated. Short circuit fault clearance on the medium voltage (MV) side is realized by introducing full bridge converters with cascaded dc converter modules on the MV side of the DCSST. The fault ride-through strategy under typical voltage sags is analyzed. Factors affecting the fault clearing and system recovery are considered, including the number of full bridge converters, the values of dc inductance and the voltage of dc-link bus. The concept is verified with both simulations and experiments.

The bipolar pad is one of the most promising topologies in inductive power transfer systems for electric vehicles. However, there is scant literature on the analytical model of the bipolar pad. In this paper, a 3-D analytical model of the inductive power transfer system including a bipolar transmitter and a square receiver is developed based on the superposition of two 2-D subdomain analytical models. Ferrite and the aluminum shields with finite dimension are taken into account on the transmitter and receiver sides. An analytical calculation of the mutual inductance is then carried out with respect to the main parameters of the inductive power transfer system, namely the dimension of the coils, the conductivity and the permeability of the shield. Two study cases are demonstrated to highlight how the proposed method can accelerate speed up the pad design process. Calculation results of the proposed model are compared with both a finite element analysis model and experimental measurements, demonstrating that the proposed model is 9 times faster than the finite element analysis method. When comparing with the experimental results, computational error of the proposed model is less than 6% in most of the study cases

Direct model predictive control (DMPC) has become an effective control alternative for the grid-tied modular multilevel converter. However, classical DMPC of the grid-tied MMC relies on accurate system model. System parameter variations will deteriorate the control performances of power, grid current, and circulating current. Besides, the inherent fewer switching actions of DMPC will also lead to poor circulating current performance. To solve these issues, this work proposes a robust DMPC solution for the grid-tied MMC. Novelties lie in two aspects. First, a virtual-flux (VF) based online inductance estimator is proposed, which utilizes the VF estimation error caused by inductance deviation. It achieves fast and accurate estimation of AC equivalent inductance, and reduces the dependency on system parameters. Thereafter, we propose a hybrid predictive control frame with a simple proportional-resonant (PR) controller, which considerably suppresses the circulating current. Finally, experimental results verify the effectiveness of the proposed solution.

Resistance emulating control is attractive due to the advantages of ease to use and less voltage sensor. However, it is only suitable for rectification mode. This letter presents a simple stabilized negative resistance emulating control for inverter mode, which overcomes the limitation of the conventional resistance emulating control. To stabilize the converter, a stabilizer based on negative inductance emulating is designed. Moreover, the unity power factor is realized by the steady-state inductance emulating technique. Since only the input current information is required, this control scheme is cost-effective and robust. Experimental results verify the effectiveness of the proposed method.

DC short-circuit current calculation is necessary to design and protect modular multilevel converter-based (MMC-based) multi-terminal DC (MTDC) grids. In this paper, a general and analytical short-circuit current calculation method is proposed for bipolar MTDC grids. For pole-to-pole (P2P) faults, the superposed fault equivalent network of the MTDC grid is first developed in the frequency-domain. Then, a decoupling method based on the network inductance ratio is proposed, which simplifies the high-order network into the superposition of several independent two-order RLC circuits. As a result, the short-circuit current can be expressed as the sum of the currents of these RLC circuits. For P2G faults, the phase-domain DC line impedance considering the coupling effects is determined based on its modal-domain parameters, so that the P2G fault current can be calculated using the method of the P2P fault. The proposed methods effectiveness is verified through simulations and experiments, and the calculation error is classified and analyzed. Compared with the existing methods, the proposed method is more accessible, more accurate, and available for hand-solution.

Oil condition monitoring is an important way to achieve mechanical equipment health assessment, condition early warning, fault diagnosis, and intelligent maintenance. A microsensor integrated with inductance-resistance and capacitance sensing units is presented, which can comprehensively detect metal debris, air bubbles, and moisture in oil based on impedance analysis. The inductance-resistance sensing unit not only detect traditional inductance parameter, but also proposes a resistance detection method based on coil to further improve the detection sensitivity for non-ferromagnetic metal debris. The capacitance sensing unit can detect air bubbles, and a new moisture measurement method is also proposed. Based on the signal characteristics of inductance, resistance and capacitance detection results, the microsensor can effectively distinguish 16-500 m iron debris, 60-500 m copper debris, >170 m air bubbles and moisture in oil. The ultrasensitive microsensor can obtain more oil status information, which has important value and wide engineering application prospect for modern fault diagnosis and prediction theory based on information fusion.

Ultralow-noise microwave amplification and detection play a central role in different applications, going from fundamental physics experiments to the deployment of quantum technologies. In many applications the necessity of reading multiple detectors, or cavities or qubits, calls for large bandwidth amplifiers with the lowest possible noise. Current technologies are based on High Electron Mobility Transistors and Josephson Parametric Amplifiers. Both have limitations, the former in terms of the minimum noise, the latter in terms of bandwidth. Superconducting Traveling Wave Parametric Amplifiers (TWPAs) have the potential of offering quantum limited noise and large bandwidth. These amplifiers are based on the parametric amplification of microwaves traveling along a transmission line with embedded nonlinear elements. We are developing superconducting TWPAs based both on Josephson junction arrays (Traveling Wave Josephson Parametric mplifiers) and on nonlinear kinetic inductance (Dispersion Engineered Traveling Wave Kinetic Inductance Amplifiers). Our goal is to achieve large bandwidth (in the 5 to 10 GHz range), large gain (more than 20 dB), large saturation power (more than -50 dBm), and near quantum limited noise (noise temperature less than 600 mK). Current achievements in the design and development of the high performance TWPAs are here reported and discussed, together with current limitations and possible future developments.

Dual three-phase permanent magnet synchronous motors (DTP-PMSMs) feature a satisfactory capability of the fault-tolerant operation due to the inherent multiphase configuration. To improve the control performance of the DTP-PMSMs under the open-phase fault, accurate inductances are critical. This paper presents an extended Kalman Filter (EKF) based inductance estimation strategy for DTP-PMSMs with one phase opened. Firstly, the multi-synchronous-rotating frame (MSRF) based DTP-PMSMs modeling under the single open-phase fault is presented. Secondly, the system space-state model and proposed EKF based estimation algorithm considering inverter nonlinearity are presented. Finally, the inductance estimation is performed by experiments under both steady and transient states. The estimation results have been verified by torque measurements which confirm the validity of the proposed method.

The grid-connected inverters (GCIs) that use droop control can avoid instability issues caused by the phase lock loops (PLLs) when connected to weak grids. Thus, the droop-controlled GCIs (DGCIs) have attracted more and more attentions. However, one of the limitations of the droop control is that its performance is highly influenced by the line impedances. Virtual inductances (VIs) can be used to overcome this limitation. However, if LCL filters are used by the GCIs to attenuate current harmonics, the interference between the VIs and the LCL filters will cause a new type of system oscillations. In this paper, the effects of the VI on the stability of the LCL filter have been explored when the grid-side current (GC) or the inverter-side current (IC) of the LCL filter is used as the feedback for the VI. It has been revealed that the stabilities of the system when using these two currents by the VI are different. The feasible ranges of the parameter values of the VI have been derived, with which the VI can be used without affecting the stability of the DGCIs. Simulation and experimental results have been provided, which verify the correctness of the analysis in this paper.

In this paper, an inductance on-line identification method is proposed for model predictive control (MPC) of vehicle-to-grid (V2G) inverter with enhanced robustness against grid frequency deviation. Firstly, a full-order sliding mode observer is established to observe the virtual-flux of the power grid. Secondly, a new inductance on-line identification method based on the dot product of the grid voltage vector and the observed virtual-flux vector is creatively proposed. A detailed theoretical analysis is carried out, which shows that the robustness of the proposed inductance identification method against frequency deviation can be enhanced by properly selecting sliding mode gains. Finally, by substituting the identified inductance into the MPC algorithm, the current control accuracy of the V2G inverter is improved accordingly. Detailed comparative experimental results verify the effectiveness and feasibility of the proposed strategy. When there is a frequency deviation of 5Hz, which may occur in a weak grid system, the inductance identification errors of the conventional gradient correction method, the forgetting-factor least squares method, and the direct calculation method are 2mH, 2.3mH, and 3mH, respectively, while it is reduced to 1.75mH for the proposed method.

The mutual inductance is the core parameter of electrodynamic suspension (EDS) as it couples the onboard coils and ground coils to realize the stable suspension. The precise and efficient calculation of mutual inductance is therefore of great significance to understand and optimize the characteristics of EDS train, which has achieved a manned speed in excess of 600 km/h. In this paper, we proposed a calculation method of mutual inductance, considering the geometrical details of coils and the attitude of bogie, by means of the 3-D discretization of coils and the spatial coordinate transformation of discrete units. Based on this methodology, the analytical model was established, and the dependence of computation time and precision on the discretization degree is intensively discussed. Afterwards, the finite element analysis (FEA) was adopted to check the accuracy and effectiveness of the proposed methodology. Compared with FEA, the computation time has been reduced by 97% with accuracy reserved. Finally, a testing platform was constructed to further verify the availability of the proposed model. In summary, the proposed methodology can realize efficient calculation of mutual inductance in consideration of more realistic situations, providing an invaluable tool for the complex studies of superconducting EDS train.

With the increase in number of VSC based HVDC systems, it is inevitable that there would be interconnections with weak ac grids. The paper presents the analytical basis for identifying coupling in the power loops which is dependent on grid inductance and operating point by utilizing the impedance-based modeling technique. The formulation is used to define an inverse-based decoupling outer-loop controller for VSC-HVDC system. The concept is extended to HVDC grids and it is shown that the gains obtained using simple inverse may lead to instability. Robust controller tuning with pole-placement and minimization of $H_\infty$ norm is presented for HVDC grids, which form a restricted feedback system. The results show that the proposed method of decoupling results in effective decoupling of the power loops over a large range of SCR values as compared to that with traditional vector control. The system stability is also maintained over a large range of SCR values and PLL gains when a sudden variation of parameters is considered. The stability margins can be enhanced by pole-placement. The observations from the small-signal models are confirmed using detailed time-domain simulations. The proposal is expected to be useful in controller design for HVDC grids.

In this paper, a novel model predictive torque control (MPTC) method for switched reluctance machines (SRM) is proposed based on the equivalent linear SRM model and the improved switching table. Firstly, an improved switching table with only 6 switching states is developed based on the inductance characteristics. The adoption of this improved switching table not only reduces the computational burden by 25% but also improves the torque control performance and system efficiency at high-speed region. However, the look-up-table (LUT) based MPTC methods suffer from occupying numerous storage space. To ease this issue, the simple linear SRM model is utilized. The flux-linkage and torque equivalent transformations are introduced to address the difference between the linear and nonlinear SRM models. With these transformations, the MPTC realized on the linear SRM model is proposed. Compared to 1530 storage units consumption to store 3 2-dimensional (2-D) LUTs in the LUT-based MPTC methods, the proposed method only occupies 228 storage units. Experimental results on an 8/6 SRM setup verify that the proposed method effectively eliminates the commutation torque ripple with lower execution time, less storage space, and improves torque control performance at a high-speed range compared with the conventional LUT-based method.

In this letter, a solution to achieve changeable inductance without any other auxiliary circuit based on PWM modulation for coupled inductor is proposed to reduce the circulating current at steady-state and limit the inrush current during start-up for input-serial-output-parallel (ISOP) dual-active-bridge (DAB) converter in solid-state-transformer (SST) applications. By modulating the PWM signals, the equivalent inductance of coupled inductor can be changed without any other auxiliary circuit. The smaller equivalent inductance is adopted in steady-state to reduce the circulating current and increase the power transfer capability. And the larger equivalent inductance is used to limit the inrush current during the start-up. The analysis based on the modulated coupled inductor for the steady-state and the start-up process is given. The design consideration for the coupling coefficient is introduced according to the optimization of leakage inductor root-mean-square (RMS) current, inrush current and the filter capacitance. Finally, the comparison of experimental results between the proposed solution and the conventional method from a 1600W/250kHz prototype verifies the effectiveness.

This paper proposes a novel approach to the modelling of HTS transformer-rectifier flux pumps that can charge HTS magnet-ic loads without the need for bulky current leads or expensive cryogenic requirements. The model was built in MATLAB/Simulink for a flux pump with 2 HTS switches, an HTS transformer with a primary inductance of 15 mH, second-ary inductance of 50 H and an HTS magnetic load with an in-ductance of 2 mH. With a 5 A pk-pk triangular current wave-form at 2 Hz the system can load the HTS load to 34.63 A in 5 s. This incremental addition of flux to the load demonstrates the advantage of flux pumps as they can charge high-field magnets without the need for large power sources. The speed of flux pumping is improved by increasing the system frequency, the magnitude of the dynamic voltage developed in the HTS switches and by increasing the primary inductance of the trans-former. This has widespread industrial applicability in fields such as the charging of high-field magnets for MRI systems.

Permanent magnet synchronous motor (PMSM) is widely used in electric vehicles due to its high power density. New requirements are constantly proposed with the development of PMSM, one of which is torque ripple. Current harmonic injection is a common method to minimize torque ripple. Designing effective controller to realize current harmonic injection is the key technology. In this paper, the transient voltage-current coupling equation considering magnetic saturation is derived by introducing incremental inductance. After appropriately simplifying, it is shown in form of the harmonic state space (HSS) equation. Considering that PMSM parameters varies with current due to magnetic saturation, robust controller is adopted to ensure stability. In order to eliminate the influence of motor speed change on control stability, the HSS is transformed into a spatial form. Then the speed adaptive robust (SAR) controller is designed. At last, the SAR controller is used in simulation and test bench experiment to verify dynamic response and stability. Compared with traditional PI and PR controller, the SAR controller can ensure good dynamic response, steady-state error and robust stability when speed and PMSM parameters vary. Moreover, SAR controller can well resist the harmonic coupling effect and system lag.

This experimental study aimed to obtain the actuation properties of Shape Memory Alloy (SMA) spring actuators available under the commercial names of Biometal® NiTiCu and KRL® NiTi NiTiCu, NiTiFe. An objective is to characterize the electro-thermo-mechano-electro behavior of shape memory spring through experimentation via simultaneous measurement techniques. These measurements are synchronized by embedding an impedance analyzer and data acquisition module through a unique program. Moreover, to obtain the mathematical model by parts of the SMA spring and equivalent circuit analysis of active spring through their electro-thermo-mechano-electro characteristics exhibited during shape memory effect. Based on the experimental results, the SMA spring's equivalent circuit is considered a series resistance - inductance​ circuit. It was found from the experimental results that the Biometal® actuator produced more resistance, inductance variation and offered more displacement as compared to KRL® actuators.

in order to enhance motor torque performance of existing two-phase 8/10 E-Core SRM, an improved modular permanent magnet (PM)-assisted Switched Reluctance Motor (SRM) structure is presented. Firstly, basic structure and operation principle of the proposed structure are introduced. To further evaluate performance improvement, effects of various parameters on the design such as inductance, flux-linkage, average torque and cogging torque are compressively investigated by finite element method (FEM) software subsequently. In the meantime, comparisons with other two-phase SRM structures are also performed including average torque, torque/PM volume, torque/ motor volume, torque/current, etc. Finally, a prototype is fabricated, and simulation and experimental results verify that the proposed design has high torque performance.

Cross-coupling effect and complicated control are the main drawbacks in multi-port structures such as multi-active bridge (MAB) converters. This paper discusses existing solutions for decoupling power flow in the MAB and proposes a new strategy. The suggested solution requires an external inductor and two more switches per bidirectional port, and one inductor per output unidirectional port. The theoretical analysis shows that each output port can be controlled independently in all scenarios. The proposed strategy does not require a decoupling matrix, and each port behaves like a separated dual-active bridge converter. In the end, the functionality and performance of the proposal are validated in PLECS simulator, demonstrating an appropriate selection of the inductances can decouple the power flow effectively, besides it reduces the circulating power and enhances the possibility of fault tolerance.

To design simple and efficient inductive power transfer (IPT) systems, minimum number of conversion stages and effective maximum efficiency tracking (MET) are the primary design criteria. The MET control uses a fast mutual inductance estimation (MIE) algorithm to achieve fast tracking of the maximum efficiency point especially when the variation of the gap distance and misalignment of the magnetic coupler are significant. The feedback control of the MET-MIE IPT system should be designed without a wireless communication channel to improve stability and robustness. In this paper, a novel MET-MIE control strategy is proposed for achieving simplicity and high efficiency in IPT systems. Verifications are provided by simulations and experiments. It is shown that maximum efficiency can be tracked with less than 4% error in MIE under significant variation of the gap distance and misalignment of the magnetic coupler.

The dynamic response of conventional doubly salient electro-magnetic generator (DSEG) system with uncontrolled rectification is slow, owing to its large time constant resulting from the large energy storage capacitance and field winding inductance. In this paper, the minimum field-current-increment (MFCI) control strategy is proposed for the DSEG system with angular position control (APC) rectification to solve this problem. Based on the ampere-second balance of the energy storage capacitor on the load side, the output voltage estimation model of APC is established to analyze the working characteristics of APC under different conditions in detail. Then, the method to minimize the field-current-increment by controlling the conduction angle is put forward to improve the dynamic response, because the smaller variation corresponds to the better dynamic performance. Finally, the experiments on a 12/8 pole DSEG system with controlled rectification are implemented to validate the effectiveness of the proposed control strategy, and the improved dynamic performance is observed in the results.

In three-phase three-wire (3P3W) voltage-source converter (VSC) systems, utilization of filter inductors with deep saturation characteristics is often advantageous due to the improved size, cost, and efficiency. However, with the use of conventional synchronous frame current control methods, the inductor saturation results in significant dynamic performance loss and poor steady-state current waveform quality. This article proposes an inverse dynamic model-based compensation (IDMBC) method to overcome these performance issues. For this purpose, two-phase exact modeling of the 3P3W VSC control system is obtained. Based on the modeling, the inverse system dynamic model of the nonlinear system is obtained and employed such that the nonlinear plant is converted to a virtual linear inductor system for linear current regulators to perform satisfactorily. Further, to control phase currents in the synchronous frame, a two-phase coordinate transformation is proposed. The IDMBC method is tested via dynamic command response and waveform quality simulations and experiments that employ saturable inductors reaching down from full inductance at zero current to 1/9th inductance at full current. The results obtained demonstrate the suitability of the method for 3P3W VSCs employing saturable inductors. Publisher's Version

The rapid discharge of the dc-link capacitors during the short-circuit fault would cause the transient current with fast propagation speed in the VSC based dc system. It is necessary to limit the dc fault current and lower the requirement of fault detection speed. However, the traditional fault current limitation method with directly installed inductors in the dc line will prolong the fault isolation time, resulting in the system instability during the power flow shifting. In this paper, an adaptive solid-state circuit breaker (SSCB) is proposed for the low and the medium voltage dc system, bypassing the installed inductors during the normal state and connect them into the dc line when the fault occurs. Besides, the energy dissipation circuit and the snubber circuit are applied to release the energy stored in the installed inductors and the dc line inductance after tripping. Hence, the fault isolation speed can be accelerated, and it is not necessary to use the metal oxide varistors in the proposed SSCB. By comparing with other SSCB schemes with the fault current limitation function, the effective fault current limitation, fault isolation and the ride-through of the proposed SSCB is verified in the OPAL-RT based simulation and the hardware test.

High-voltage DC (HVDC) circuit breaker is the necessary equipment for multi-terminal HVDC grids, which is a prospective power transmission method in the future. Therefore, the research about HVDC interruption ushered in an explosive development in recent years. The mechanical DC circuit breaker based on the pre-charged capacitor for current commutation and interruption is considered to be one of the most promising HVDC interruption solution. However, the commutation capacitor requires a complicated pre-charging circuit, especially in high voltage applications, which brings a great challenge to the promotion of mechanical interruption solution. In this paper, a novel self-charging mechanical HVDC circuit breaker is proposed. It utilizes the induced voltage generated by part of current limiting reactor to adaptively charge the commutation capacitor under different fault current conditions without extra auxiliary charging circuit. By investigating the influence of capacitance and inductance on the charging time and current commutation process, the optimized parameters are determined. Then the breaking performance of proposed HVDC breaker under different rising rates of fault current is evaluated in a two-terminal HVDC system. Finally, a low-power prototype is developed to verify the feasibility of the proposed topology and an improved scheme for rated current breaking is discussed.

The integrated two-stage Buck-Boost-LLC isolated DC-DC converter is suitable for wide-voltage regulation range, high-frequency and high-efficiency application. However, the choke inductor current of Buck-Boost stage injecting into LLC stage will cause non-sinusoidal resonant current and asymmetric secondary current under the conventional modulation strategy. This will result in synchronous rectification problems. Traditionally, a large resonant inductor is utilized to improve the situation, but it sacrifices power density and efficiency. Therefore, this paper proposes a bipolar symmetric phase shift modulation strategy to reduce the resonant inductance and correct resonant current with high power density and high efficiency. Moreover, LLC stage is improved. The RMS current of primary switches is decreased by the entrance of the choke inductor current. Zero-voltage-switching is achieved by choke inductor current instead of magnetizing current, so that the transformer can be designed without air gap and has lower winding loss caused by leakage flux. With minimum magnetizing current, the resonant current is minimized. The conduction loss of primary switches and winding loss of transformer shows 75% and 26% reduction, respectively. Finally, a 500kHz 400W prototype with 97.6% peak efficiency and 142W/in3 power density is built up. The experimental results verify that the proposed modulation strategy corrects resonant current effectively and improves efficiency and power density.

Wireless power transfer (WPT) systems are widely applied in many scenes due to their safety, convenience, and flexibility. This letter proposes a novel control strategy named Periodic Energy Control (PEC) in WPT systems. It is suitable for all kinds of compensation topologies of WPT systems. Specifically, it takes the energy input to the resonant network as the control target, which calculates the energy input by measuring the capacitor voltage or the inductor current, thereby controlling the switching action of the inverter. Meanwhile, it not only effectively suppresses the overvoltage (or overcurrent) when system parameters such as load and mutual inductance change, but also features low sensitivity to mutual inductance, which has advantages in the scene where mutual inductance changes. Moreover, this letter presents the principle of PEC and derives the energy input to the resonant network in various compensation topologies of WPT systems. Finally, experiments are presented to verify the effectiveness of this control method.

It is essential to estimate stator inductance and rotor flux linkage online for fault diagnosis and high-performance control of surface-mounted permanent magnet synchronous machine (SPMSM). Current injection method is a popular way to estimate the two parameters. However, the dead-time influence of voltage-source-inverter (VSI) and the stator inductance variation caused by injected current could not guarantee the converge of the estimation. To solve the above two problems, a method of injecting square-wave angle for online parameter estimation is proposed in this paper. Firstly, the theory of eliminating dead-time influence with and without square-wave angle injection is analysed. Next, the least square algorithm is adopted to estimate stator inductance without injection. Then the rotor flux linkage is estimated with injecting square-wave angle. The saturation effect on estimation is also analyzed and both parameters are estimated without acquiring any nominal values. At last, the appropriate amplitude and frequency of square-wave angle are determined by the parameter error and convergence analysis. The proposed method is evaluated with simulation and extensive experiments under various speed and load conditions. It is noteworthy that not less than two parameters are estimated without the dead-time influence and the injection will not cause inductance variation, which is different from the previous work.

A predictive current control with parameter robustness (PR-PCC) method of permanent magnet synchronous motor (PMSM) is proposed in this paper. First, a cost function is designed to calculate the increment of the optimal voltage vector at the current instant, which is based on incremental PMSM model. The incremental PMSM model is used to eliminate the influence of the motor flux parameter. Second, the optimal voltage vector that minimizes the cost function is obtained by combining the increment of optimal voltage vector with the idea of iteration. At the same time, a current observer based on the incremental model is designed to compensate the one-step sampling delay. In this way, the feedback current of dq-axis accurately followed the reference current. In comparison with the conventional pulse width modulation predictive current control (PWM-PCC) method, the proposed method can significantly reduce the steady-state error of dq-axis current caused by inductance, flux and resistance parameters mismatch quickly. Finally, experimental results of the proposed method and the conventional PWM-PCC are presented in this paper to verify the validity of the proposed method.

In a typical wireless power transfer (WPT) system, the load, the mutual inductance and the required tuning frequency can vary in a particular range. Variation of each parameter can substantially impact the dynamic characteristics of the system. Thus, they can be considered as the sources of uncertainty in the system. To address this issue, robust control methods such as -synthesis are developed to deal with possible system uncertainties. In this paper, first, the generic dynamic analysis of the series-series WPT compensation network for two modes of operation, i.e. Constant Output Voltage (COV) mode and Constant Output Current (COC) mode, in the presence of three aforementioned uncertainty sources is carried out. Subsequently, the frequency detuning as a function of the compensation capacitor variation is explored and broadened as a technique to obtain the optimized compensation capacitor value that can lead to a plant with minimized dynamic deviations from its nominal system in the operating range between COC and COV modes. As such, this approach offers a design procedure for a least conservative robust controller which can significantly improve the system performance. The optimized structure and the corresponding designed -synthesis controller are comprehensively elaborated.

Aiming at the problem that the traditional doubly salient electro-magnetic machine (DSEM) can not work when the excitation-loss occurs, this paper designs and analyzes a fault-tolerant DSEM for excitation-loss, and the torque ripple suppression strategy under the fault-tolerant operation is studied. Firstly, the characteristics of the output torque of DSEM before and after excitation-loss is analyzed, and a DSEM with novel winding configuration is proposed to improve the fault tolerance. Secondly, under normal/excitation-loss conditions, the structure parameters of the fault-tolerant DSEM are analyzed to reveal the influence of the motor structure on its performance. Then the steady-state torque of the fault-tolerant DSEM is compared to the traditional DSEM and the switched reluctance motor (SRM) with the same size, which proves the effectiveness of fault-tolerant design. By analyzing the inductance and torque characteristics, a torque ripple suppression strategy is proposed for the fault-tolerant DSEM without increasing the complexity of the system. Finally, a prototype is developed, and the experimental results verify the fault tolerance capability of the prototype and the effectiveness of the proposed torque ripple suppression strategy. The research results of this paper provide a specific implementation method for the fault-tolerant system design of DSEM under excitation-loss.

the capability of misalignment tolerance is vital for an IPT (inductive power transfer) system. A new loosely coupled transformer structure with series solenoid and DD pads (SDDP) was proposed in this paper to improve the misalignment tolerance of the IPT system. The designed loosely coupled transformer not only has strong misalignment-tolerant capability in the X-direction, but also has strong misalignment-tolerant capability in the Y-direction. The fluctuation of mutual inductance is 3.15% within 67.0% misalignment distance of largest size of the SDDP in the X-direction and 44% misalignment distance of largest size of the SDDP in the Y-direction. Finally, an LCC/S compensated IPT system with 300W power was built as an example to demonstrate the performance of the proposed LCT. The output voltage fluctuates with rated load is less than 3.2%. And the efficiency is 90.2%91.3%.

Fault diagnosis and condition monitoring of electric machines using readily available drive sensors are highly critical in safety critical applications. This paper presents an accurate method to detect stator Inter-Turn Short Circuit (ITSC) fault using the spatial inductance profile which can be implemented both at start up (standstill) or in real-time. For this purpose, AC motor drive spatially scans the motor at each start up in milliseconds by injecting high-frequency signal to obtain spatial inductance profile, analyze the fault status and locate faulty phase. Using the start-up inductance profiling as reference, online detection version is implanted successfully which is essential for real-time condition monitoring. This approach is highly sensitive ITSC faults, agnostic to temperature variations and takes inverter nonlinearities into account caused by dead time and voltage drop across the power devices. To demonstrate the efficacy and practicability of the proposed algorithm, it is experimentally verified on two PMSMs, IPMSM and an induction motor, all re-wounded to mimic inter turn short circuit faults. It is shown that, the algorithm can detect ITSC faults very accurately in the order of milliseconds even if the number of shorted turns is very low.

This paper presents a post-fault current control strategy for dual three-phase Interior Permanent Magnet (IPM) synchronous machines. The current controllers are designed based on the Vector Space Decomposition (VSD) algorithm. This take into account the equivalent harmonic inductance variation, which is then used to introduce the post-fault compensation control. A double three-phase IPM machine is modelled and operated in three different operating conditions: nominal, one three-phase set in short-circuit (SC), and one three-phase set in open-circuit (OC). By keeping the current loop bandwidth constant, the proposed fault-tolerant current controllers guarantee the same dynamic performance of the remaining healthy module after the faults occurred. In OC fault, the proportional and integral (PI) controllers are redesigned while adapting the inductance variation. For the SC case, constant stability margins are provided by cascading a novel lag compensator to the nominal controller. The current dynamics responses are analysed in both healthy and faulty conditions by means of Matlab/Simulink simulations. Experimental results on a 30kW six-phase IPM machine prototype with isolated neutral points and supplied by two custom three-phase converters, are demonstrating the effectiveness of the proposed control strategies.

This article introduces the analytic modeling optimal control with kinetic inductance fine turning method in detail, aiming at solving special control problems of pulsed power supply for heavy-ion accelerator magnet. The inductance of the accelerator magnet is time-varying, unclear, and affecting the control precision. In order to solve this difficulty, the hypothesis of the kinetic inductance and identification task with control objective is presented. The kinetic inductance fine turning method has been proposed by the experimental phenomenon. The analytic model of power supply with magnet is calibrated by identified kinetic inductance during the operation. In simulations, the kinetic inductance has been designed and assumed to be unknown. This method can identify kinetic inductance and control precision to meet the design requirements. In experiments, the current of the power supply can track two different triangle waveforms. The final identified kinetic inductance waveforms are significantly different. At the end of each switching cycle, the absolute margin of current error is lower than 0.015A, except for individual interference values. Control precision is close to measurement accuracy. Therefore, the excellent agreement between the results of simulations and experiments verifies this introduced method.

High frequency and high efficiency inductor design method is proposed for the application of critical soft switching with large current ripple to improve the power density and efficiency of electrified energy conversion systems. Firstly for the theoretical design section, the core/coil size, number of turns, airgap, inductance are optimized to minimize the inductor losses. Secondly for the structural design section of coil, a 3D routing method of litz PCB winding is developed to reduce the AC copper losses. The strand number, trace width, thickness and layout of litz PCB are analyzed in detail. Different types of coil, including solid/litz types of PCB/wire windings, are compared and analyzed based on the high frequency copper loss reduction and space utilization. For the structural design section of core, E and I cores are optimized to reduce the volume and core losses. Specifically, E-E, E-I, I-I and E-Air types of core structures are designed and compared considering the core loss, volume reduction and airgap limitation for the stack of turns. Ten derived prototypes are built to benchmark with the commercial inductors. Power losses, temperature rise and cost are reduced by a factor of 10, 2.5 and 3 with the proposed core and coil structures.