This paper presents an efficient pulse-width modulation (PWM) method to optimally reduce switching (SW) losses in three-phase neutral-point clamped (NPC) inverters in one switching cycle using a new two-phase modulation scheme. The proposed method digitally selects an optimum switching vector (SV) pattern, which minimizes an estimation function based on switching losses considering phase currents among possible reduction patterns for one switching cycle. The proposed modulation method is further extended to reduce common-mode voltages in three-phase NPC inverters. The basic principle involves elimination of the common-mode voltage by limiting the combinations of the output phase voltage levels of the three-level NPC inverter. A modified space vector generation technique based on the two-phase modulation method is proposed to reduce both common-mode voltages and switching losses. The proposed PWM method was experimentally verified for output voltages of the NPC inverter connected to a universal load. The method reduced the number of switching transitions for the largest or second largest current, and it can automatically adapt to different load conditions. The method was also experimentally validated for its EMC and switching loss reduction capability.

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A sampling algorithm to immunize digital control power converters with triangular carrier waveforms against switching noise is introduced. Many converter circuits employ a sawtooth carrier waveform; however, no optimal sampling method has been presented that avoids switching noise. As demonstrated by the experiments conducted in this research, there are cases where converter circuits are not correctly controlled and sample values are affected by switching noise via current sensors or AD converters. As a result, the output is unstable and inaccurate thus reducing the reliability of the converter.  This paper proposes an adaptive sampling method for a digital control current-mode power converter circuit on an FPGA (Field Programmable Gate Array) with the PWM (Pulse Width Modulator) sawtooth carrier waveform. To avoid noise overshoot and undershoot during the MOSFET's switching process, the sampling timing of the AD converter is adaptively tuned according to the duty ratio of each switching cycle. We further introduce a random phase noise generator, to conduct simulations as realistic as practical experiments. We also present simulation and experimental results of the proposed methodology illustrating cases of successful noise avoidance. Thus, we verify that the proposed sampling method improves the reliability of power converter circuits.

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This paper presents a method for calculating the eddy current loss in a permanent magnet (PM) of a surface PM (SPM) motor based on a reluctance network analysis (RNA). First, an RNA model of the SPM motor that accounts for the rotor rotation is described. Then, the eddy current loss in the magnet of the SPM motor including the carrier harmonics is calculated by the proposed model. Finally, it is demonstrated that the RNA model can consider the effect of the division of the magnet to reduce the eddy current loss in the magnet.

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Recently, the four-leg inverter and the four switch inverter, which have fewer of switches, have been studied for their advantages of low cost and compactness^(1)-(12). In particular, the four-leg inverter^(13)-(15) can drive two motors independently. Applications of the four-leg inverter are factory automation, electric vehicles and crane trucks. The inverter consists of four legs and two capacitors connected in a series. However, many of conventional studies on the four-leg inverter and the four switch inverter have used open-loop control systems such as the volts per hertz (V/f) control system. This paper proposes capacitor voltage balancing control of the four-leg inverter for two vector-controlled induction motor drives. In this a study, the source of the capacitor voltage fluctuation caused by the current flow through the capacitors is analyzed by using the space vector and a compensation method is described. The capacitor voltage fluctuation compensation method and the independent drives of the two induction motors fed by the four-leg inverter with the vector control method are demonstrated with experimental results.

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In electric vehicles (EVs), cooperative control between a regenerative brake system (RBS) and the conventional hydraulic brake system (HBS) enhances the brake performance and energy regeneration. This paper presents an integrated antilock braking control system based on estimating the wheel slip to improve the anti-slip performance of a four wheel drive in-wheel motor EV. A novel anti-slip control method for regenerative braking was developed and integrated with a hydraulic antilock braking system (ABS) according to the logic threshold concept. When combined with the features of driving motors, the proposed method can improve the brake performance under slip conditions. Comparative simulations showed the proposed control approach provided a more effective antilock braking performance than the conventional ABS.

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This paper proposes an optimal d-axis current to suppress the 2nd radial force, which is caused by the fundamental permanent flux. Under the no-load condition, the flux distribution is approximated in order to calculate the radial force. Considering the cyclic nature of 3-phase, the optimal d-axis current reference to suppress the 2nd radial force is derived. Simulations and experiments under both load and no-load conditions are performed to demonstrate the validity of the proposed optimal d-axis current reference.

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Mechanical and electrical system control conventionally uses the Lagrange motion equation for general mechanical and electrical motions. However, using the Lagrange approach for the control system is difficult to understand physically and intuitively.  This paper proposes estimation and control methods for the reaction energy of a mechanical synchronous motor and an electrical LR circuit. The reaction energy is the inflow energy from outside the actuator; it is estimated and controlled by the newly defined energy disturbance observer and reaction energy observer. A generalized Heaviside operator is also introduced to simplify the representation of the energy control system. The effectiveness of the proposed methods was verified by simulation of a mechanical synchronous motor and an electrical LR circuit.

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At present, many kinds of robots are being developed for medical care. In medical care, operations often need to be performed at the micro-scale. This study was focused on a macro-micro bilateral control system that can transmit haptic sensations of a micro-environment between master and slave systems. The macro-micro bilateral control system amplifies disturbances; therefore, analysis, modeling and compensation of the disturbances were considered.

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This study presents the guidance control provided by a rehabilitation support robot that is intended to assist with the movement of a patient's arm. The guidance control is accomplished using a stiffness ellipse. The characteristic that the direction of force acted upon changes depending on the settings of the stiffness ellipse is used for guiding the movement. The system developed in this study adjusts the stiffness ellipse by using a musculoskeletal manipulator with biarticular mechanism. It was verified that the movement of a subject could be guided by changing the stiffness ellipse and assisting the movement. The experimental results demonstrate that it is possible to guide the movement without any dependency on the control bandwidth of the actuator.

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Reliability is an issue that has recently captivated the attention of researchers. Its goal is to develop new techniques to design more reliable systems, which can operate without failing during operation. A result of this growth in technology is an increase in the complexity and susceptibility of more complex systems. The principal objective of redundancy allocation is to maximize the availability of a system while reducing the cost, volume or weight. This paper proposes an Estimation-of-Distribution Algorithm (EDA) approach as a new meta-heuristic method to solve a redundancy allocation problem (RAP) for a high security control system.

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This paper describes a wide angle fovea (WAF) telescope developed to help rangers save the people floating on the sea in the aftermath of tsunamis and other disasters. The WAF telescope is designed using a proposed Multiple-Stage WAF model having both a wide field of view (FOV) so that it never misses a moving target once it is captured and a high magnification in the central FOV that can resolve detail. This design concept is inspired by the smart function of the eyes of humans and raptors. In other words, the authors design an optical telescope with the dual functions of both wide angle surveillance and resolution of detail in order to improve its usability and convenience. The specification of the prototype has been determined paying attention to this point. The produced prototype has a handy size because it uses two aspherical surfaces in the entire lens compound system. We have tested the prototype and discussed its performance.

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[in Japanese]

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