This paper presents an overview of the key technologies and solutions adopted in utility-scaled photovoltaic inverters for large scale photovoltaic plants. The overview starts by presenting the circuit topology and cooling system. Subsequently, it focuses on the on-site integration and deployment of the system and finally on the introduction of a modular-type solution that enables photovoltaic and energy storage in the same low voltage bus.

In recent years, AC servo drives have been required not only to play the role of high-speed and high-precision positioning devices but also as information devices that acquire various data through sensor networks. Our current flagship product: the Σ-X series, is a component that maximizes the performance of our customers' equipment and provides data acquisition functions to realize digital solutions such as preventive maintenance and failure prediction.

In this paper, we explain our solution concept: i³-Mechatronics, and introduce the lineup, basic performance, and the latest functions of Σ-X based on this concept. In addition, as a case study of the control technology development, the motion control function that has both high vibration suppression performance and easy-to-use adjustment guidelines for the user will be described.

Considering that the hysteresis described by the classical Prandtl-Ishlinskii (CPI) model is usually symmetric, this paper presents a modified generalized Prandtl-Ishlinskii (MGPI) model for pneumatic artificial muscles (PAMs), which can describe dynamic hysteresis nonlinearities by considering different loads and frequencies. Currently, it is still a challenging issue to achieve tracking control of PAMs because of their inherent characteristics such as dynamic hysteresis nonlinearities, output saturation, and creep. Unlike the commonly used rate-dependent PI model which linearly changes the weights or thresholds with the input rate, the proposed model changes the shape of envelope functions in GPI play operators. The MGPI model, in particular, has the advantage of directly describing the output-to-input relationship with fewer to-be-identified parameters, which reduces the computational burdens in real-time applications. To validate the efficacy and accuracy of the proposed model, a self-built PAM experiment platform is performed, and the obtained experimental results show that the proposed method achieves satisfactory tracking performance.

This paper presents a method for robust velocity control of electromagnetic friction brakes for constant velocity (isokinetic) training in rehabilitation. Rehabilitation treatments using robots have become an attractive option due to labor shortages. In robot rehabilitation, isokinetic exercises are a form of highly efficient training. In rehabilitation machines, passive machines (brakes and clutches) are commonly utilized because they are inexpensive and safe. We focus on electromagnetic friction (EF) brakes which have a higher torque-to-weight ratio than magneto-rheological and powder brakes. Owing to such characteristics, the size and weight of the rehabilitation robots can be reduced by using EF brakes. Consequently, it can reduce the burden on subjects. Although EF brakes generate high torque, they have hysteresis and offset torque, which deteriorates the control performance. This paper proposes three contributions of an EF brake. First, the analysis and modeling of the EF brake are proposed. Second, a disturbance observer is proposed for the EF brake. The proposed method can design the disturbance suppression characteristics independent of the tracking performance. Finally, a robust velocity control scheme that considers the sign of the velocity for isokinetic exercises is proposed. The proposed method is compared with the conventional proportional-integral controller and its effectiveness is experimentally confirmed.

Patients diagnosed with bronchial asthma or chronic obstructive pulmonary disease (COPD) are required to use inhalers to control their symptoms. However, approximately 70% of the patients use their inhalers incorrectly because of misunderstandings regarding their use or habituation owing to long-term use. Currently, in-person instructions provided by pharmacists or doctors are the only remedy to this problem. Therefore, new evaluation method, which eliminates the input of a doctor or pharmacist, is urgently needed. This study aims to realize automatic evaluation of individual inhaler motion. A new sensing attachment with inertial measurement unit (IMU) is developed for an inhaler device. We propose an evaluation method using data from the sensing attachment, without doctor or pharmacist issued instructions. The proposed evaluation method for inhaler motion is based on a dynamic programming (DP) matching algorithm. Furthermore, the evaluation method is verified via suitable clinical experiments. Based on the experimental results, all clinical data could be classified by the proposed method.

Proximity and tactile sensors have been widely used to control robots. However, each of these sensors has its own shortcomings. Visual sensors have blind spots, whereas tactile sensors cannot acquire information when non-contact. To overcome these problems, this study develops an optical sensor that can measure the distance and two-axis forces using a beam structure and photo reflectors. The sensor is inexpensive owing to its simple structure. Moreover, the sensor is demonstrated to have sufficient accuracy for both the distance and force measurements at 0.2, 0.5, and 1.0Hz. Additionally, the usefulness of the sensor is confirmed based on reduced impact control at the time of contact and force control.

This paper proposes a novel extended electromotive force (EEMF) observer of a dual three-phase permanent magnet synchronous motor (DTP-PMSM) operable to the position sensorless overmodulation drive. The overmodulation drive occurs in current harmonics, and the estimated EEMF also contains harmonic components, leading to ripple error in the estimated position. Based on the vector space decomposition (VSD) utilized in DTP-PMSM current control, the proposed method can decrease the current harmonics in the overmodulation and the harmonic components in the estimated EEMF, and it can also improve position estimation. The effectiveness of the proposed EEMF observer and the improvement in the position estimation were experimentally verified.

An accurate target tracking system improves the quality of flyby imaging of the target and consequently aids effective planetary exploration. A vision-based tracking system is one of the more popular systems, utilizing imaging data to achieve the required tracking accuracy. However, recent high-accuracy target tracking requirements cannot be achieved with targeting error feedback only. This paper summarizes the asteroid flyby mission characteristics and requirements, shows how possible error sources in the tracking system, and displays an exemplar control system design. The tracking error source is generally divided into a navigation error, which is a tracking profile generation error, and a control error, which is caused by the control system. A high-quality onboard relative-trajectory determination system is required to improve the navigation accuracy of the control system, because the pre-designed or offline-estimated relative trajectory contains uncertainties that cause the tracking profile generation error. Previous studies focused on this navigation error because of its sensitive effect on control system performance, showing some methods for improvement. This paper discusses how the control system can be improved to achieve greater precision during target tracking by considering the navigation and system characteristics. A realistic case study scenario is defined and analyzed based on an actual target tracking interplanetary probe mission. The characteristics of the designed control system are presented and its performance is analyzed via numerical simulation, using the case study data.

The mitigation of delay propagation owing to excessive station dwell time is crucial for ensuring stable transport in a highly frequent urban train service. The precise departure time of the preceding train from the station is difficult to predict; however, control methods with predictions are effective in mitigating the delay of the following train. The train trajectory is generated using real-time continuous position information from the communication-based train control (CBTC) system, which can mitigate the delay propagation of the following train without predictions. In this study, a control method for mitigating delay propagation without predictions is proposed. Furthermore, introducing a finite-departure prediction for the preceding train can allow the following trains to avoid stops between stations. We numerically verify the effectiveness of reducing the delay time based on case studies with and without departure prediction. The results show that departure predictions effectively reduce headway and the duration of stops between stations for the following trains.

This paper provides an overview of a circuit analysis model for a DC brush motor, taking into consideration showering arc events. A mechanical contacts model that reproduces showering arc behavior is developed by combining new variable resistors with the steady arc model. As a result, spike surge waveforms can now be simulated via circuit analysis. It is also become clear that spike surges with continuous showering arcs constitute the maximum condition of conducted EMI. The measured and simulated conducted EMI show good agreement within 9dB up to 108MHz, in accordance with the CISPR 25 standard. Moreover, it is now possible to quantitatively predict the amount of conducted EMI in a system comprising a step-down DC-DC converter and a DC brush motor, by considering a dominant magnetic coupling and parasitic impedances.

Wireless power transfer based on magnetic resonant coupling can be used to supply power to a mobile robot within a few meters of a transmitter coil. However, when the robot moves or its power consumption fluctuates, its input impedance varies significantly and, in case of impedance mismatch, power reflection may occur. To address this issue, we employed a driver coil on the transmitter side to match input impedance. By regulating the coupling coefficient between the driver and the transmitter coils, the input impedance is matched and power reflection is eliminated. Input impedance regulation is achieved by moving the driver coil mechanically. As confirmed by our experiments, the transmitting efficiency matched with the analytically calculated value, and the input impedance was matched for a vast range of distances from 0 to 1m and load resistances from 4 to 210 Ω by moving the driver coil properly. Therefore, the proposed system successfully addresses the power reflection problem in wireless power transfer for mobile robots.

A cell capacitor is one of the most fragile components in a modular multilevel converter (MMC). Capacitance decreases and equivalent series resistance (ESR) increases, as the capacitor deteriorates. This paper proposes an online monitoring method for both the capacitance and ESR of the cell capacitors in an MMC without any additional components or operation. The proposed method measures the impedance of the cell capacitor not only at a low frequency but also at a switching sideband-frequency of the cell without current sensors for capacitor current. The high-frequency components around the switching frequency improve the estimation accuracy compared with the previous methods that measure only impedance at low frequencies. The experimental results confirm that the proposed method estimates the capacitance and ESR with errors of 3.1% and 8.8%, respectively.

This paper presents optimal current-control methods for driving two different synchronous motors using a single inverter. When one inverter drives two motors, system efficiency will deteriorate if their loads are not identical. Moreover, even with identical loads, system efficiency will deteriorate if the parameters of the two motors are not identical. To address this issue, this paper proposes optimal current-control methods for systems with two different motors driven by a single inverter.

The compressor motor of an air conditioner is subjected to the a fluctuating load torque during the suction and discharge of refrigerant, resulting in a speed ripple in the machine angular cycle. This paper proposes a new predictive feedforward control system that predicts and suppresses the speed ripple cuased by the periodic disturbance of compressor motor by using error data of speed PI controller. The speed ripple suppression performance of proposed control method is experimentally confirmed by applying it to achieve speed control of an air conditioner compressor motor.

This study proposed a control method to reduce the torque ripple vibration of an integrated on-board charger using the windings of an interior permanent magnet synchronous motor (IPMSM). During a battery-charging operation, stopping the motor results in noise, as well as damage to the motor and other components from the torque vibration caused by the charging current. In the proposed control method, the generated torque was estimated using a back-electromotive force table, and the phase current was controlled to eliminate the torque. The proposed method can suppress torque vibration, irrespective of the angle of the rotor in the IPMSM. The effectiveness of the proposed method was verified experimentally, with the torque vibration suppressed by 94% compared with that of the conventional control method.

This study proposes a control method for an electrolytic capacitor-less dual-inverter with an aim to reduce the interharmonic currents. Owing to the low-energy buffer of the electrolytic capacitor-less inverter, load fluctuations superimpose harmonic currents on the input current. The proposed control method facilitates output power pulsation control of main inverter, which is a constant frequency regardless of load fluctuations. The experimental results exhibit a reduction in the interharmonic currents at 20 and 80Hz by 68 and 72%, respectively. Moreover, the power factor is improved by 11 pt., and total harmonic distortion (THD) of the input current is reduced by 26 pt. under rated load conditions. Therefore, the proposed control method can effectively reduce the interharmonic currents and improve the power factor and THD of the input current.

Many contact-rich tasks in factories are still executed manually because it is often difficult for robots to adapt to variable environmental conditions. To incorporate the adaptability of humans to the environment into robots, a machine learning technique called learning from demonstration (LfD) has been well studied. A popular approach for automating complex tasks involves selecting the appropriate action from several segmented motions, called movement primitives. In this study, we propose a method for autonomously selecting a recovery action and correcting the trajectory when the task is determined to have failed based on force. Although conventional technologies can divide motions into time series, they are unable to recognize the presence of failures in detail in response to slight environmental variations. Therefore, we propose a two-stage clustering method, which consists of time segmentation of trajectories and labeling of segmented motions, to recognize failures and generate of recovery actions in response to the failures. The proposed method was able to perform the task even in cases of a 20mm position error by accurately selecting recovery actions and correcting the trajectory.

Wind energy conversion systems (WECS) have become increasingly common in recent years as a result of global warming. WECS needs to release the wind through pitch control during high winds. In this study, a novel method for individual pitch control (IPC) via pitching moment estimation is designed. The conventional IPC method considers the blade load, without keeping the rotor speed at the rated value. This study proposes the application of a reaction force observer (RFOB) to the pitch actuators to estimate the pitching moment of each blade. Using the pitching moment information, we estimate the wind speed for each blade, enabling IPC to simultaneously achieve load reduction and maintain the rotor speed at the rated value. The effectiveness of the proposed method is verified via simulations and experiments.

This paper discusses operation characteristics of discontinuous current mode (DCM) for an ac-dc isolated converter for on-board battery chargers of electric vehicles. The converter discussed in this paper consists of a front-end diode-bridge rectifier, an active energy buffer, and a dual-active-bridge dc-dc converter. The energy buffer circuit absorbs the power pulsation from the single-phase ac line into a small-rated capacitor, and thus, makes it possible to reduce a required capacitance of the dc-link capacitor. This paper explains details of the DCM control method including a technique of the ripple cancel of the inductor current, to realize the power factor correction of the line current and the voltage control of the buffer capacitor at the same time without complex calculations. Then, a reference value of the inductor current and an operation range of the dc-output voltage are discussed. Experimental results obtained by a 220-V, 6.6-kW experimental setup demonstrate a sinusoidal-line current and a controlled buffer capacitor voltage as well as a smoothed dc-output current.