In the AC servo system, the output voltage is restricted by inverter output limitations. Voltage saturation occurs as a result of these limitations. The settling time of the current and speed increases because of voltage saturation. This paper proposes a new control system for improving the transient response of the surface permanent magnet synchronous motor (SPMSM) by using the proposed flux-weakening control based on the current differential signal. Because the current differential signal is taken into consideration, the suppression of voltage saturation is achieved with a smaller d-axis current in a transient state. Finally, this paper proposes a new combination method of flux-weakening control and an inverter modulation scheme, which makes it possible to improve the voltage utilization on condition of flux-weakening region. The proposed speed control system achieves a quick and stable speed and current response. The effectiveness of the proposed control methods is confirmed by both the numerical simulation results and the experimental results.

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This paper describes an inverter control method for reducing the input current harmonics and vibration in an electrolytic capacitor-less inverter for an interior permanent magnet synchronous motor (IPMSM). Typically, the back electromotive force (EMF) on an IPMSM is not sinusoidal and contains harmonics caused by the rotor structure, which leads to harmonic distortion in the motor control system and generation of harmonics in the input current. Moreover, the input current vibration occurs at the source side, which is caused by resonance with the line impedance and the DC-link capacitor.  This paper proposes three control methods to reduce the current harmonics distortion and vibration. The first method filters out the harmonics of the feedback d-q axis current using a notch filter. The second method compensates the d-q axis voltage references to reduce the input current harmonics. To prevent the input current vibration, the third method adds a cancellation voltage pulse to the three-phase voltage reference of the inverter. The superior performance of these proposed methods are demonstrated through experimental results. The experimental results confirm that the proposed methods meet guideline EN61000-3-2.

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Point of load (POL) converters require a small size and high-efficiency performance for IT industrial applications. In addition, the interleaved technique, magnetic integration, and application of GaN FETs are well known as good approaches to satisfy these demands in the power converters. Although coupled inductors for POL converters have been proposed in several studies, a coupled multilayered chip inductor has not been examined because of the difficulty of its construction. In this paper, a novel coupled multilayered chip inductor for interleaved POL converters is proposed. This novel coupled inductor has a pair of windings with inverse coupling in the magnetic core. Further, the magnetic material of the coupled inductor is an Fe-based metal composite powder (Fe-Si-Cr). Additionally, an Fe-based powder in the magnetic core has been processed with electrical insulation by a highly crystallized oxide nanolayer in order to reduce the eddy-current losses. Finally, the high efficiency performance of the coupled multilayered chip inductor is evaluated by prototypes of interleaved buck converters using normally off-type GaN FETs with a switching frequency of 1MHz.

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A promising topology to interconnect wind power plants is proposed. The advantages of this series-connected system over the conventional parallel system are first discussed, and a control strategy for the series-connected system is examined in order to realize optimum wind energy usage. The dynamic performance of the series-connected system is investigated through simulation and experiments while an effective method of realizing high-quality output power is also shown. Finally, a novel topology featuring wind turbine/generators connected in series that is suitable for DC power transmission is introduced, which can enlarge the scale of the wind power plant without increasing the system voltage level.

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Several virtual synchronous generator (VSG) controls for three-phase inverters have been proposed in order to extend the advantages of synchronous generators to inverters. The VSG controls facilitate smooth transitions between the grid-connected mode and the island mode. The governor and the automatic voltage regulator (AVR) realized in the VSG stabilize the frequency and the voltage respectively in the island mode. In addition, they can control the active and reactive power of the inverter in the grid-connected mode. The objective of this paper is to extend these useful properties of VSG to single-phase inverters. The proposed single-phase inverter with a VSG is based on two synchronous d-q reference frames, i.e., the positive and negative sequences. The double decoupled synchronous reference frame (DDSRF) theory is applied to generate these two reference frames. The simulation and experimental results indicate that the properties of a three-phase inverter with a VSG can be extended to a single-phase inverter effectively.

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Hybrid electric vehicles (HEVs) and electric vehicles (EVs) improve the efficiency of a drive and reduce CO₂ emissions by regenerative braking and operating the engine under optimum conditions. To minimize the driving units, the motor size should be decreased and the maximum torque should be increased. Therefore, motors employing permanent magnets have been commonly used recently. For HEV and EV motors, Toshiba developed a motor that delivers a high reluctance torque, known as PRM, and has been applying it to various vehicles. This paper describes the current motor development status in TOSHIBA.

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This paper proposes a reactive power control strategy for the active load balancer (ALB) in three-phase four-wire distribution systems. The proposed reactive power control strategy is based on constant DC capacitor voltage control only, which is always used in active power line conditioners. Therefore, the proposed approach does not require active and reactive calculation blocks of load currents for the reference source current calculation. The power factor of the source side currents can be adjusted under the balanced load condition using the proposed reactive power control strategy. The basic principle of the reactive power control strategy for the ALB is discussed in detail and verified via digital computer simulation using power electronic simulation (PSIM) software. A prototype experimental model is constructed and tested to demonstrate the validity and high practicability of the proposed control strategy. Simulation and experimental results indicate that balanced source currents with a predefined power factor are achieved when the proposed control strategy is applied to the three-phase four-wire distribution systems.

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The integration of differential-mode (DM) and common-mode (CM) inductors onto a single core has been expected to miniaturize EMC filters. On the other hand, this technique possibly leads to lower tolerance to magnetic saturation caused by the DC flux, hindering the miniaturization effect due to integration. Particularly, this problem seems to be exacerbated in the previously reported magnetic structure. The reason may lie in the fact that this conventional structure tends to induce a large DC flux because its equivalent number of turns for the DM inductance is restricted to only half of the total number of turns. This paper addresses this problem by proposing a novel structure that assigns more turns to the DM inductance to suppress the DC flux more effectively. A theoretical analysis and experiments verified that the proposed structure is equivalent to series-connected DM and CM inductors. Additionally, an analytical estimation revealed that the proposed structure reduced the core volume by 41% compared to the conventional structure for the same wire length. These results demonstrate effectiveness of the proposed structure for miniaturizing EMC filters.

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This paper presents a comparison study of various motors for application to an electric vehicle (EV) and the potentiality of a ferrite magnet motor as a candidate for rare-earth-less motor for an EV. The rotor shape of the proposed ferrite magnet motor is based on a spoke-type shape. Further, we developed two types of prototypes: one has a large magnetic torque equivalent to a conventional rare-earth permanent magnet motor for an equal volume, and another has a wide variable-speed range suitable for an EV.

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Methods for sensorless control involving the injection of a high-frequency signal into the low-speed range of an interior permanent-magnet synchronous motor (IPMSM) have been proposed. However, audible noise is a concern for these methods. We propose a method to reduce the audible noise due to a high-frequency current by minimizing the injection-signal amplitude suitable for IPMSM driving states.

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A higher-order passive power filter (LLCL filter) for a grid-connected inverter is becoming attractive for the industrial applications owing to the possibility of reducing the cost of copper and the magnetic material. To avoid the well-known resonance problems of the LLCL filter, it is necessary to use either passive or active damping methods. In this study, the stability of the LLCL-filter-based grid-connected inverter is analyzed and a critical resonant frequency for the LLCL filter is identified when sampling and transport delays are considered. In the high-resonant-frequency region, active damping is not required; however, active damping is necessary in the low-resonant-frequency region. The basic LLCL resonance damping properties of different feedback states based on a notch filter concept are also studied. Then, an active damping method using capacitor current feedback for the LLCL filter is introduced. On the basis of this active damping method, a design procedure for the controller is given. Last, both simulation and experimental results are provided to validate the theoretical analysis of this study.

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This paper proposes a novel variable speed motor drive, a wound field synchronous motor (WFSM) drive integrated with a Z-source inverter (ZSI). The proposed WFSM is a nonpermanent magnet machine and employs two field coils as dc field mmf sources. On the other hand, the ZSI has an impedance network that consists of two dc reactors and two capacitors. In the proposed drive, the two field coils of the WFSM act not only as dc field mmf sources but also as dc reactors in the ZSI, resulting in size and cost reductions in the drive system. In order to achieve voltage boost-up and field current controls simultaneously, the control algorithm for this integrated system is examined. Experimental results using a test drive system show that the proposed drive under the proposed control works properly.

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This paper proposes fast initial position estimation of IPMSMs (interior permanent magnet synchronous motors) that is based on intentional pulse voltage injection and comb filters. Most initial position estimation methods utilize the amplitude or differential values of high-frequency currents, and the performance of sensorless control depends on the algorithm to reconstruct these values. Although Fourier series expansion, which requires some low-pass filters (LPFs), is utilized generally, the filters degrade the response of position estimation. This paper focuses on the algorithm for initial position estimation of IPMSMs at standstill, and proposes a new algorithm using comb filters that can rapidly calculate the amplitude values of high-frequency currents and improve the initial position estimation performance. In addition, this paper experimentally shows the performance of the initial position estimation, starting characteristics of sensorless control, and characteristics of sensorless control including standstill under the load.

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This paper discusses the volume of an electromagnetic compatibility (EMC) filter and a cooling system that are used for a pulse width modulation (PWM) inverter with wide band-gap devices. First, the volume of reactors that are used in EMC filters such as common mode choke coils and differential mode choke coils is theoretically estimated. Then, the relationship between the carrier frequency of the PWM inverter and the total volume of filter reactors is clarified via simulation. Moreover, the relationship between the carrier frequency and the volume of the cooling system is calculated on the basis of on experimental results. The total volume of the inverter system that contains the filter reactors and cooling systems is reduced by 54% at a carrier frequency of 300kHz using a two-stage filter, as compared to the case of a carrier frequency of 150kHz with a single-stage filter. In addition, an induction motor is driven by a prototype GaN-FET inverter system having a carrier frequency of 300-kHz. As a result, the conducted emission is suppressed below the limit prescribed by CISPR-11 Group 1. Therefore, the proposed design method for EMC filters is validated experimentally. Furthermore, the power loss of the EMC filter is less than 2% as compared with the total loss of the GaN-FET inverter system.

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Wireless power transmission (WPT) utilizing magnetic-field resonance has been given increasing attention by power electronics engineers and industries. Actually, many technical papers related to WPT circuits based on magnetic-field resonance have been published to verify their high-efficiency power transmission characteristics. However, a 10MHz-class high-frequency power supply suitable for high-power transmission systems has not been studied sufficiently, although small power rating converters such as the direct-current resonance class-E multi-resonant ZVS WPT system with a 74.9W output power have been proposed. Hence, the authors propose a new circuit topology for high-power and high-frequency inverter systems suitable for high-power WPT.  In this paper, the authors propose a novel high-frequency current-output-type inverter circuit topology utilizing an immittance conversion element and WPT circuit, which utilize LC anti-resonant circuits suitable for the proposed current-output-type inverter.  As a result of the prototype test, the proposed inverter provides a high conversion efficiency of more than 88.8% at 11.33MHz operation with a 142.1W output power rating. Also, the proposed WPT circuit suitable for the current-output-type inverter provides a high transmission efficiency of more than 94.1% at 11.33MHz with 2cm transmission gaps and a 46.1W output power.

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Plasma-assisted ignition technology has been proposed to boost the combustion efficiency of scramjets during high-speed flight. One technique utilizes high-voltage nanosecond-duration pulses, which can generate free radicals, thereby initiating ignition earlier in the combustion chamber and improving fuel efficiency. A high-voltage nanosecond pulse generator is an integral part of the system. In this study, a modular nanosecond pulse generation system, utilizing multiple high-speed high-voltage MOSFETs, is developed and tested. The modular system can generate width-adjustable pulses (from 20ns to 50ns) with a fast rise time (< 6ns), fast fall time (< 6ns), and variable amplitude using multiple switch cells. The system is also scalable in voltage and current. By employing the inductive voltage adder, the system is configured in two different ways: two switch cells coupled in parallel and two switch cells coupled in series. These configurations demonstrate scalability and the fundamental sizing constraints.

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This paper presents a PWM control method for a variable-voltage single-stage bidirectional buck AC/DC converter for suppressing the output voltage ripple with a high source power factor. The proposed method maintains the minimum number of commutations during the control period for realizing three voltage levels close to the output reference voltage. The overall loss of the converter is reduced using the proposed method, which is verified experimentally.

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This paper describes two-triangle carrier sinusoidal pulse-width-modulation (SPWM) for a five-level diode-clamped PWM inverter and compares it to the SPWM-based neutral-point-clamped (NPC) PWM inverter and the original SPWM-based five-level diode-clamped PWM inverter for use in medium-voltage motor drives. The characteristics of the three techniques are compared by analysis and experiment for an adjustable-speed motor drive for pumps and blowers without a transformer. The experimental systems are 380-V 5.5-kW downscale models. The experimental systems were designed, constructed, and tested for the comparison study and were based on a 16-bit digital signal processor with the use of insulated gate bipolar transistors as switching devices. A 5.5-kW four-pole induction motor coupled with a permanent-magnet synchronous generator was used as the electrical load.

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The realization of a new communication medium that realizes the transmission of haptic information between distant places is required. A bilateral control system is an effective technique that can share tactile sensation between two systems. However, the performance of the bilateral control tends to destabilize, and the haptic information deteriorates under a communication delay because haptic information has the bilateral information flow property. This is because the control goals cannot be achieved in real time owing to the delay time. Therefore, a novel method is proposed to realize simultaneity in a bilateral control system under a communication delay. The proposed control system is designed to realize the control goal equations for bilateral control regardless of the delay time and is designed symmetrically. Buffering the force information of the system resolves the interference between the modal space caused by the communication delay. The entire control system is stabilized by using a phase-lag compensator that has the equivalent meaning of acceleration response feedback with a high pass filter. The validity of the proposed method is confirmed by experiments.

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This paper proposes a motion-reproduction method for a multi-degree-of-freedom system. For storing and reproduction of haptic information, a motion-copying system was proposed. Reproducing the saved motion using this method is difficult when the environmental configuration in the motion-loading phase is different from that in the motion-saving phase. There are several methods for adapting to the variation in environmental configuration. In the conventional method, it is considered that the orthogonal axes are controlled independently. However in the tracing motion, friction and interference exist between the orthogonal axes. Thus, it is impossible to reproduce the saved motion when the coefficient of friction varies. In this paper, friction in a two degree-of-freedom system is modeled and a motion-copying system using the modeled friction is proposed. The proposed method reproduces the saved motion even when the coefficient of friction varies. To validate the proposed method, experiments were conducted.

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A pickup system for optical disks operates in the horizontal and vertical directions for tracking and focusing, respectively. The conventional optical disk system is designed for each direction of operation. The conventional system becomes slow in moving to the next point because it does not consider the operation trajectory. Thus, because the point-to-point movement becomes longer, there is possibility that the tracking performance is deteriorated in high-speed rotation. In order to achieve faster operation, we develop a concurrent control method of tracking and focusing on an optical disk and realize short trajectory control. In this paper, a new two-dimensional feedforward control system is proposed, which has concurrent control of focusing and tracking. The feedforward controller is based on equivalent-perfect tracking control (E-PTC). The experimental results show the effectiveness of the proposed control system.

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A PWM converter generally includes a low-pass filter to remove the high-frequency switching currents that flow into the power grid. If the inductance of the power grid greatly increases, the response of the automatic current regulator (ACR) deteriorates. When the ACR response deteriorates, the power grid is affected by low-frequency oscillations, making the power supply unstable. A type of low-pass filter is proposed to suppress the resonance, but several problems still remain. Active dampers achieve resonance suppression without a damping resistor. However, they need additional sensors to achieve a high performance and a sensorless type becomes more sensitive to the inductance changes in the power grid. In this study, we propose an observer-based active damper to control the resonance using an LCL filter. The deterioration in the current loop's response can be prevented, even if the power grid's inductance increases, preventing low-frequency disturbances. The proposed control method is achieved without needing to tune to the corresponding power grid's inductance.

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This paper proposes a method to prevent overshoot and undershoot (OS/US) problems for final-state control (FSC) and updating final-state control (UFSC). The FSC is an optimal feedforward control technique to drive a dynamic system to a specified state in a specific time period by an external input. The UFSC is a version of FSC that is modified to deal with a varying final state by updating the FSC control input at each sample. However, both FSC and UFSC algorithms do not guarantee that no overshoot or undershoot occurs in the transient state between the initial state and the final state. This paper proposes an OS/US prevention technique via tuning the FSC or UFSC activated time. The technique is developed by adding a constraint that all the FSC or UFSC control input should be in the same direction. In this paper, the effectiveness of the algorithm is verified by simulations for a plural-cart connection problem.

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As the aging problem becomes increasingly significant, robots are being widely applied as walking-assist devices for elders or patients suffering from walking disabilities. In this paper, a novel walking-assist multi-legged device that is fixed on the waist, with two machine legs independent from human legs, helps elders walk and climb stairs without any manipulation of the machine. In the proposed device, an inertial measurement unit (IMU) sensor is employed; the IMU contains a triaxial accelerometer, a triaxial gyro (angular rate sensor), and a triaxial magnetometer. The sensor is fixed on the waist of the elder in order to gauge the posture of the waist thereby preventing an emergency such as a fall. Further, based on the zero-moment point (ZMP), the stability of the device is analyzed to confirm the feasibility and effectiveness of this device.

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