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This paper presents a voltage injection method for reconstructing phase currents from current signals measured on single current-shunt circuits with cost-effective and high-performance configurations in the pulsewidth modulation (PWM) inverters that are used for digital appliances. This method involves the injection of voltage signals at the carrier frequency for reconstructing the phase currents in PWM inverters using a single current sensor in the dc-link. It uses minimum signals to reduce the voltage and current harmonics caused by the injected signals. The vector of the injected voltage is at a minimum distance from the original reference to ensure the measurement time in the reconstruction of the phase currents. An injection sequence control method is also proposed to avoid an abrupt change in the injection signals. A PWM scheme for splitting phase voltages is proposed to reduce any audible noise, especially in low-speed operation. The proposed method reconstructs the phase currents with signals from a single current sensor and minimizes the amplitude of the injected signals to reduce the harmonics at audible noise frequencies in the injection signals. Experimental results showed the effectiveness of the proposed method. Index Terms--AC motor drives, current reconstruction, noise, pulsewidth modulated (PWM) inverters.

This paper presents an analysis of inherent position sensors in ac machines. In ac machine drives, the attachment of a mechanical transducer or a structural modification is necessary for zero or low speed operation where the back electromotive force (EMF) is zero or low. However, designs for introducing a measurable saliency in the spatial impedances of structurally symmetrical ac machines without any periodic modulation will make it possible to build sensorless drives at zero or low speed. Thin bridges in the core slots of a stator or rotor take the role of inherent magnetic sensors in ac machines. In structurally symmetric ac machines, such as a surface mounted permanent magnet synchronous machine (SMPMM) or induction machine (IM), the saliency in the spatial impedances is built by the spatial saturation on the leakage flux paths. This can be explained by a machine model that considers the spatial saturation, analyzed by the finite element method, and verified experimentally on test machines. Employing this phenomenon in the design or selection of symmetric ac machines will enable zero- or low-speed operation in sensorless drives. Index Terms--AC machines, ac motor drives, magnetic analysis, transducers.

This paper proposes a hybrid speed estimator that gives the synergetic effect between the model- and the saliency-based field orientations for induction motor drives. The model-based field orientation consists of a flux observer with an adaptive speed estimator that has unstable regions at zero frequency and zero speed. Saliency-based flux orientation utilizes magnetic saliencies caused by saturation and high-frequency injection that causes the torque ripples due to the chattering. The chattering is caused by the higher cutoff frequency of the flux-angle estimation to keep its high dynamics. The proposed method compensates both faults and realizes complete speed estimation from zero to high-speed condition including zero stator frequency. Index Terms--Flux observer, high-frequency voltage injection, hybrid speed estimator, induction motor drives.

This paper presents the analysis of a surface-mounted permanent-magnet (SMPM) machine for the sensorless control scheme based on the high-frequency fluctuating voltage signal injection method. A simplified high-frequency model of an SMPM machine in the estimated rotor reference frame is developed and a sensorless rotor position and speed estimation algorithm is described. To support this, the high-frequency impedances of an SMPM machine are analyzed by finite-element analysis (FEA) and compared with measurement results using a pulsewidth-modulation (PWM) inverter system under various injection conditions. The results of the FEA and measurements are coincident with each other with some errors due to the nonlinear behavior of the PWM inverter and the SMPM machine. The analysis results give physical insights into selecting the injection conditions for sensorless operation of the SMPM machine even though adjustments considering nonlinear behaviors of PWM inverters are required in the actual operation for the desired performance. The experimental results of speed and position control using a commercial SMPM machine are presented based on the analysis of the SMPM machine for the sensorless control algorithm. Index Terms--High-frequency signal injection, sensorless operation, surface-mounted permanent-magnet (SMPM) machine.

This paper presents a new sensorless control scheme of a surface-mounted permanent-magnet (SMPM) motor using high-frequency voltage signal injection method based on the high-frequency impedance difference. In the SMPM motor, due to the flux of the permanent magnet, the stator core around the q-axis winding is saturated. This makes the magnetic saliency in the motor. This magnetic saliency has the information about the rotor position. The high-frequency voltage signal is injected into the motor in order to detect the magnetic saliency and estimate the rotor position. In this paper, the relationship between the high-frequency voltages and high-frequency currents is developed using the voltage equations at the high frequency, and the high-frequency impedance characteristics are analyzed experimentally under various conditions. The proposed sensorless control scheme makes it possible to drive the SMPM motor in the low-speed region including zero speed, even under heavy load conditions. The experimental results verify the performance of the proposed sensorless algorithm. Index Terms--High-frequency signal injection, sensorless drive, surface-mounted permanent-magnet (SMPM) motor.

This paper describes a torque, speed, or position control method at standstill and low speed in the interior permanent-magnet motor (IPMM) drive system without any rotational transducer. While IPMMs have originally magnetic saliency, it varies according to the load conditions and the control performance can be easily degraded. In this paper, the saliency or impedance difference is used as the conventional methods and, nevertheless, in order to amplify the difference containing the information of the rotor angle and to maintain a reasonable performance under any load condition a high-frequency injection scheme is proposed. A speed and position estimation scheme based on the characteristics of the high-frequency impedance is proposed. The scheme extracts the high-frequency impedance components related to the rotor position. An initial angle estimation scheme for starting from an arbitrary rotor position is also proposed. It can distinguish the north magnetic pole position from the south one in several decade milliseconds. The proposed scheme enables position control of a transducerless or position-sensorless IPMM. The experimental results clarify the satisfactory operation of the proposed position control algorithm under any load condition. Index Terms--Motor drives, position estimation, sensorless control.

In this article, a highly efficient battery-balancing circuit with output voltage regulation for mobile applications is proposed and analyzed. The proposed circuit performs a cell-balancing operation for series-connected multiple-battery cells and voltage regulation operation simultaneously without additional power conversion stages. Therefore, it can be integrated into a battery pack with maximized power density and efficiency. These features are essential for recent low-power applications with multiple batteries, such as wireless/smart speakers, drones, and electronic point-of-sale, that require high power density. The operational principle, electrical modeling, and tradeoff relationship between the system power losses and balancing characteristics are derived, and the optimal design candidates of the proposed topology are discussed in terms of Pareto optimization. The effectiveness of the proposed system is verified with a prototype board using GaN switches, and 96.05% efficiency is achieved with a 1.8 V, 0.5 A load. [ABSTRACT FROM AUTHOR]

The CLLC converter is a promising topology for bidirectional power conversation applications, such as vehicle-to-grid (V2G) systems and battery energy storage (BES) systems. Battery charging is one of the most important functions of the CLLC converter in V2G and BES applications. Synchronous rectification (SR) is of vital importance in these applications because it can increase efficiency. In this article, a battery charging method with natural SR features is proposed for the full-bridge CLLC converter. The proposed method consists of a parameter matching design procedure and SR control. A novel SR principle is adopted in this article. Different from the current SR methods, the parameter design process is taken into consideration for the SR realization. After the parameter matching design procedure, the required on-state time of the secondary side switches for the SR is nearly fixed during the whole charging process. As a result, the SR drive signal can be generated directly according to the switching frequency. No sensor detection or software estimation is needed, allowing natural SR to be realized. A lab-level prototype was built to verify the proposed method. The experimental results show an obvious efficiency improvement (up to 2.11%) over the uncontrolled rectification, and the SR of the proposed method is nearly the same as complete SR (with maximum efficiency difference of 0.31%) during the whole battery charging process. [ABSTRACT FROM AUTHOR]

A magnetic manipulation system for medical applications is designed with its coils widely distributed over a sufficiently large space such that a patient can lie down, an operator can enjoy the accessibility, and the workspace is sufficiently large. However, this design makes the current references asymmetrical. Moreover, at the corners, some references might exceed the coil current rating, and the magnetic field cannot be synthesized as desired. To address this overcurrent reference problem, this article proposes a magnetic manipulation system controlled with the minimum infinity-norm current reference. In many magnetic manipulation systems, the current reference for a given motion command of the magnetic field is infinite. And the minimum infinity-norm current reference is the most feasible. The proposed control strategy presents an increased maximum synthesizable magnetic field in an arbitrary direction, including the worst case direction, compared with the conventional field of Moore–Penrose inverse control. To verify the effectiveness, the worst case direction of the magnetic field of each method is analytically derived. And, the controllable areas of the eight-coil magnetic manipulation system are compared. This article also proposes a soft mode transition between the two methods for efficiency enhancement. The experimental results show the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper proposes a method to boost the terminal voltages using a capacitive network. The boosted voltage can improve the power capability of an interior permanent magnet synchronous motor (IPMSM). In the conventional drive system fed by a voltage-source inverter, the terminal voltages of the motor are limited by the dc-link voltage. Such a voltage limitation reduces the torque capability at high speeds. Thereby, the maximum output power is limited. To overcome this feature, series capacitor network between the inverter and the motor is introduced in the proposed IPMSM drive system. The series capacitors boost the motor terminal voltages higher than the inverter voltages to increase the rated speed, resulting in improved power capability. The rated speed in the proposed drive system can be redefined to the desired value through a capacitive network. The enhanced power capability and design freedom in the rated speed are particularly advantageous in fan-load applications where the load torque is proportional to the square of speed. This article presents the structure, d–q equivalent model, operating characteristics, and operable area of the proposed drive. Experimental results are given to verify the feasibility and effectiveness of the proposed system. [ABSTRACT FROM AUTHOR]

Objective: Interventional ultrasound imaging is a prerequisite for guiding implants and treatment within the hearts and blood vessels. Due to limitations on the catheter's diameter, interventional ultrasonic transducers have side-looking structures although forward-looking imaging may provide more intuitive and real time guidance in treating diseased sites ahead of catheters. To address the issue, a magnetically actuated forward-looking interventional ultrasound imaging device is implemented for the first time. Methods: A forward-looking catheter containing a 1 mm ring type focused 35 MHz ultrasound transducer and a micro magnet, was fabricated. For imaging, the transducer was placed at the center of four electromagnetic coils positioned on four sides of a squared acrylic housing. By modifying the magnetic field, the catheter tip could be remotely translated for sector scanning. Results: The scanning angle could reach up to 3° in 1 Hz with 15 mT, while wider angles of 5° could be achieved with a higher magnetic field of 25 mT for ex-vivo imaging. The position of the transducer could be detected by monitoring the motion with a CCD camera, mimicking clinical X-ray imaging. In the wire target and tissue mimicking phantom studies, the measured hole size, spatial resolution and distance between wires by the proposed system were comparable with the values from a linear scanner. Multi-frame real time data acquisition was demonstrated via ex-vivo imaging on a pig's coronary artery. Conclusion/Significance: The feasibility of magnetically actuated forward-looking interventional ultrasound imaging was demonstrated. The remote-controlled scanning method may allow to simplify the structures of forward-looking interventional ultrasound imaging catheters. [ABSTRACT FROM AUTHOR]

This article proposes a method to extend the operating area of the surface permanent magnet motor by inserting the passive power networks between the motor and the voltage source inverter (VSI). In the conventional motor drive system, since the operating area is limited by the maximum voltage, which is synthesized by the inverter, the output torque capability is reduced in the high-speed region. In order to extend the operating area, two types of passive power networks are proposed in this article. The power networks supply the reactive power to the motor for amplifying the motor terminal voltage. Due to the actions, the proposed motor drive system can utilize a higher maximum motor terminal voltage than that in the conventional drive systems. Depending on the network types, the operating point at which the maximum power or torque is generated is shifted to a high speed. The design, control, and analysis methods of the proposed system are presented in this article. The effectiveness of the proposed system is verified through the experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a resonant switching cell model to analyze and design the single-ended resonant dc–dc converters. The single-ended zero-voltage switching (ZVS) converters such as the Class E converter are efficient for megahertz switching because they feature low turn-on and turn-off switching losses. Also, they use only a ground-referenced switch, allowing a simple gate drive circuit. In this paper, we investigate the single-ended resonant converter with the small input inductance, whereas the conventional Class E converter has a large input inductance. The main contribution of this paper is to propose the resonant switching cell as an analytic model that simplifies the analysis and the design of the resonant dc–dc converters. Furthermore, this paper presents the design method of the resonant switching cell model for minimizing the resonant current magnitude and conduction loss while the converter maintains ZVS property. The experimental results from a 10-MHz GaN-based prototype demonstrate the feasibility and effectiveness of the analysis and design based on the proposed resonant switching cell model. [ABSTRACT FROM AUTHOR]

This paper presents a fault-tolerant operation for dual three-phase surface-mounted permanent magnet machines (SPMSMs) that were both electrically connected on three winding phases and mechanically connected on one shaft. The open-phase fault-tolerant operation is considered in dual three-phase SPMSMs drive thus combining motor drive of three-phase and single-phase. The proposed method controls the torque of each motor with different phases using a single inverter. In order to control these motors, the torque and current are distributed between the motors with the specific ratio. Methods for minimizing torque ripple and copper losses and maximizing the output torque of the three-phase motor are stated in this paper. Accordingly, a system with cost-effective and enhanced reliability is proposed without any configuration adjustment or auxiliary switching devices. The mathematical analysis and experiments are presented to verify the feasibility of the proposed method. After the fault, the resulting system is able to provide up to 75% of the rated torque, and up to 50% of the torque can be utilized without any torque ripple. [ABSTRACT FROM AUTHOR]

This paper proposes a d–q cross-coupling current controller for permanent magnet synchronous motor (PMSM) drives. Slotting and cross-coupling effects in PMSMs cause the effective air-gap length to vary with the rotor angle and distort the distribution of the air-gap flux. Such distortions have a significant influence on the current control by changing the relationship between the stator currents and voltages. To investigate their effects, a d–q model is established in this paper, which is suitable for describing the voltage characteristics of the actual PMSMs. The model contains the angle-dependent parameters, the cross-coupling inductance between d–q axes, and the q-axis permanent magnet flux linkage, unlike the ideal d–q model. The transfer function matrix from the d–q currents to d–q voltages of PMSM is newly derived from the model. Based on that, the current controller with the feedback and feedforward terms of 2-by-2 matrix is proposed. It is designed so that the independent gains are in low-pass filter forms and the coupling control gains are zero with eliminating interference between d–q axes. The proposed controller contributes to providing the stable control performance by canceling the slotting and cross-coupling effects. The performance of the proposed current controller is verified by experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a droop control for a stable grid-integrated operation of doubly fed induction generator (DFIG) within microgrid. While the leakage inductances were neglected in the conventional control method, the proposed droop control uses the leakage inductances of DFIG as the output filter inductance by simply just changing the field orientation. This additional output filter inductor improves the system stability by adjusting the output impedance in the microgrid, of which the line impedance is mainly resistive. Also, the virtual impedance method, which is used for the power decoupling and the system stabilization in an inverter-based generator, is introduced to the proposed droop control of DFIG for the case that the leakage inductances are insufficient. To validate the proposed droop control method of DFIG, the simulation and experimental results in the resistive line impedance, where the conventional droop control of DFIG is unstable, are presented. [ABSTRACT FROM AUTHOR]

This paper proposes data transmission method between primary and secondary of the flyback converter without additional communication circuit while simultaneously transferring power. In some application such as a battery charger, the data exchanges between the primary and secondary sides are necessary. In the conventional system, an additional line or wireless communication modules is used for data exchanges, thereby increasing the system and connector size. The proposed system, in comparison, does not use additional signal transceiver but instead exchanges data by simply alternating operation mode of the flyback converter, thus adding communication function while not increasing the volume of the terminal and overall system. The waveform of transformer voltage is used to count the number of resonant pulses, which is used for decoding and encoding the data packet. Bidirectional communication between primary and secondary sides is possible while power is transferred to the output using an appropriate communication protocol. This paper proposes data transmission method for both single output and the multioutput cases. Also, both half-duplex and full-duplex communication using the proposed method is explained. The experimental results are presented to verify the performance of the proposed communication method. [ABSTRACT FROM AUTHOR]

Plasma generation systems represent a particularly challenging load for radio-frequency power amplifiers owing to the combination of high operating frequency (e.g., 13.56 MHz) and highly variable load parameters. We introduce a dynamic matching system for inductively coupled plasma (ICP) generation that losslessly maintains near-constant driving point impedance (for low reflected power) across the entire plasma operating range. This new system utilizes a resistance compression network (RCN), an impedance transformation stage, and a specially configured set of plasma drive coils to achieve rapid adjustment to plasma load variations. As compared to conventional matching techniques for plasma systems, the proposed approach has the benefit of relatively low cost and fast response, and does not require any moving components. We describe suitable coil geometries for the proposed system, and treat the design of the RCN and matching stages, including design options and tradeoffs. A prototype system is implemented and its operation is demonstrated with low pressure ICP discharges with O2 , C4F 8, and SF $_{{6}}$ gases at 13.56 MHz and over the entire plasma operating range of up to 250 W. [ABSTRACT FROM AUTHOR]

The six-step operation of surface-mounted permanent magnet machine drives in a flux weakening region has many advantages compared to the pulse width modulation mode, such as the reduced switching loss and fully utilized inverter output voltage. However, if the ratio of the sampling frequency to the fundamental frequency is low in fixed sampling system, the low-frequency oscillation in the current can be incurred in the six-step operation. The low-frequency current causes a system stability problem and reduces system efficiency due to an excessive heat and high power loss. Therefore, this paper proposes the variable time step controller for six-step operation. By updating an output voltage, sampling phase currents, and executing the digital controller synchronized with the variable sampling time, the turn on and off switch signals for six-step operation can be generated at the exact moment. As a result, the low-frequency oscillation in the phase current can be eliminated. In addition, the system transfer function of the proposed control method is discussed for the system stability and system dynamic analysis. The effectiveness of the proposed method is verified by the comparative simulation and experimental results. [ABSTRACT FROM AUTHOR]

A double inverter fed wound machine (DFWM) needs two inverters on the rotor as well as the stator side. This scheme gives more freedom to operation of an electric machine and improves the output power capability and the efficiency, but its control method becomes more complex because the number of control variables and the operating constraints increase. This paper deals with a control method of DFWM for minimizing the copper loss in maximized operating area. The possible operation area considering all constraints of currents, voltages, and flux is analyzed on the stator currents plane to maximize the operating area. For the minimum copper loss operation in the operating area, different modes are defined and the optimal currents are determined in each mode. Also, the optimal current selection algorithm is proposed to achieve the torque control using the optimal currents. The simulation and experimental results about wound machines are presented to show the feasibility of the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper presents a single-switch isolated dc–dc converter suited for a very high-frequency switching operation, especially above 10 MHz. The converter features a small number of passive components, low-switching loss, and low-voltage stress on the switch. In order to achieve low-voltage stress while maintaining zero voltage switching, the voltage waveform across the switch is shaped by designing the resonant network of the converter. The resonant network includes main parasitic components, such as leakage inductances of the transformer and the junction capacitance of the switch. Furthermore, some resonant elements are entirely replaced by these parasitic components under the specific condition. This paper derives the conditions and then minimizes the number of passive components. To validate the design procedure and the performance of the proposed converter, a GaN-based prototype was implemented. It operates at 10 MHz and provides the output power of 10 W from the dc input voltage of 50 V. The output voltage is regulated to 20 V by the ON–OFF control. Experimental results show that the peak voltage on the switch is reduced to 2.2–2.3 times the dc-input voltage and the efficiency of 69% is achieved under the full load. [ABSTRACT FROM AUTHOR]

This paper presents a novel family of single-switch resonant dc–dc converters with low switch voltage stress. The single-switch resonant converter which has a ground-referenced switch is advantageous for implementing the gate drive circuit and operating at several-MHz switching frequency. However, the conventional ones mostly have high voltage stress on the switch, roughly 4–5 times the input voltage. In this paper, we propose the single-switch converter topologies derived from the drain-source impedance networks consisting of two inductors and two capacitors. The switch voltage of the proposed converters is shaped into a near trapezoid by designing the resonant networks to have the desired drain-source impedance. Furthermore, a simple and specific design scheme is presented here so that the peak switch voltage is lowered to 2.2–2.5 times the input voltage while zero voltage switching is achieved. Experimental results from a 20-W GaN-based prototype operating at 10 MHz demonstrate the feasibility of the proposed converter topologies and the design method. [ABSTRACT FROM AUTHOR]

This paper proposes a novel drive method for interior permanent magnet machines (IPMMs). In the proposed system, a two-phase IPMM is fed from a single-phase H-bridge inverter for low-cost applications. Its main winding in d -axis is connected to the inverter and the auxiliary winding in q-axis is inherently short circuited. This configuration enables the motor to operate in a wider speed range with higher energy efficiency than most other single-phase drive systems. Also, its torque capability in the high-speed range is as high as that of the three-phase IPMM drive despite the reduced power devices, drivers, and current sensors. Accordingly, the proposed system has benefits such as simple structure, low cost, high-power density, and improved efficiency. In this paper, the system is modeled with an equivalent three-phase machine. Based on the model, its torque characteristics and operating areas are analyzed and compared to those of the conventional IPMM drives. A speed control algorithm is also developed. It includes a maximum torque per ampere control to improve drive efficiency and a flux-weakening control to maximize the feasible inverter output voltage. The proposed system and control algorithm are verified by experimental results. [ABSTRACT FROM PUBLISHER]

In this paper, a control method for motor drive system without electrolytic capacitor is proposed. Since dc-link capacitor of this motor drive is about 1% of the conventional one, it can satisfy the grid current regulation of IEC61000-3-2 without bulky filter circuits by directly controlling the electric output power of the inverter. However, dc-link voltage of this drive fluctuates as the rectified grid voltage. It causes higher motor current, especially at the low dc-link voltage area, and severely harms the drive efficiency. To solve this problem, proposed method keeps the dc-link voltage higher than certain limit while controlling the output power. It can improve the efficiency of the drive by lowering the d-axis current at low dc-link voltage area, with satisfying the regulation with small grid current harmonics. The proposed method includes the motor current reference generation for the limited dc-link voltage and selection of the limitation value. The improved performance of the proposed method was verified by the experimental results. [ABSTRACT FROM PUBLISHER]

This paper proposes grid current shaping method using dc-link shunt compensator for three-phase diode rectifier system without electrolytic dc-link capacitor. In the proposed method, the diode rectifier system can satisfy the grid regulation IEC61000-3-12 without any power factor correction circuit or heavy grid filter inductor. The proposed grid current shaping method can be realized by applying DSC with reduced-rating components and without electrolytic capacitor, which is connected parallel to the dc link. Since DSC has no electrolytic capacitor, the system with DSC has high circuit reliability. Furthermore, DSC can enhance the system efficiency, especially in flux-weakening area, since the motor drive inverter recovers the reduced modulation index, which has been spent in the additional control for small passive components. This paper presents the control method for DSC and analyzes the effect of proposed method. The feasibility of proposed method is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

The single-phase diode rectifier system with small dc-link capacitor shows wide diode conduction time and it improves the grid current harmonics. By shaping the output power, the system meets the grid current harmonics regulation without any power factor corrector or grid filter inductor. However, the system has torque ripple and suffers efficiency degradation due to the insufficient dc-link voltage. To solve this problem, this paper proposes the dc-link shunt compensator (DSC) for small dc-link capacitor systems. DSC is located on dc-node in parallel and operates as voltage source, improving the system performances. This circuit helps the grid current-shaping control during grid-connection time, and reduces the flux-weakening current by supplying the energy to the motor during grid-disconnection time. This paper presents a power control method and the design guideline of DSC. The feasibility of DSC is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes the novel control method for a monoinverter dual parallel (MIDP) drive system with interior permanent magnet synchronous machines (IPMSMs). It includes maximum torque per ampere (MTPA) control to elevate drive efficiency and active damping control to alleviate inherent stability problem of an MIDP motor drive system. Due to the combination of reluctance and electromagnetic torques, the d- and q-axis currents of IPMSM are coupled unlike those of induction and surface-mounted permanent magnet machines. For this reason, MTPA and active damping control of a MIDP IPMSM drive system are far more complex than those with nonsalient motors. In this paper, model-based mathematical analysis about MTPA and active damping control for MIDP IPMSM drive system are provided. Experimental results with two 1.6-kW IPMSMs are presented to verify the proposed algorithm. [ABSTRACT FROM AUTHOR]