With the continuously increasing demand for energy and the limited supply of fossil fuels, renewable power sources are becoming ever more important. Knowing that future energy demand will grow, manufacturers are increasing the size of new wind turbines (WTs) in order to reduce the cost of energy production. The reliability of the components has a large impact on the overall cost of a WT, and press-pack (PP) insulated gate bipolar transistors (IGBTs) could be a good solution for future multi-megawatt WTs because of advantages like high power density and reliability. When used in power converters, PP IGBTs are stacked together with other components in a clamping mechanism in order to ensure electrical and thermal contact. Incorrect mechanical clamping of PP IGBTs has a negative impact on their reliability and consequently on the reliability of the WT. In this study the impact of mechanical clamping conditions on the static thermal distribution among chips in PP IGBTs is investigated.

View full abstract

In this paper, a grid connected variable speed wind turbine (VSWT) PMSG integrated with the NaS-type battery energy storage system (BESS) is modeled in the real-time digital simulator (RTDS) to analyze the performance in a real system. This study is also a part of the future power hardware-in-loop (PHIL) test; therefore, individual components are modeled from the practical standpoint. The wind turbine, power grid, and control system are modeled in the large-time-step main network; however, the wind generator (PMSG), frequency converter (FC), and BESS integrated with STATCOM are modeled in the RTDS VSC small-time-step network to take into consideration the higher-switching-frequency phenomena. The interface transformer is used to connect the different-time-step subnetworks. The option of integrating the anemometer is kept open for a future PHIL test. The simulation results are compared with those obtained from the laboratory standard power system software PSCAD/EMTDC to validate the model developed in the RTDS/RSCAD.

View full abstract

With the rapid increase in the aging population of Japan, the need for robotic gait training has grown. This paper presents a novel gait training device that guides the leg movements during gait. Conditions for correct gait movement were defined through previous gait analysis, and the gait training system presented in this paper is based on those conditions. This paper focuses on designing a controller for gait guidance. The proposed power-assist using variable gain position controller was compared to a normal position controller and also to a force controller, and the characteristics a controller must have for most effective gait guidance is discussed.

View full abstract

Interior permanent magnet synchronous motors (IPMSMs) are generally driven by current control based on a vector control system. Usually, in such a system, the harmonic current appears in the current control loop. Some harmonic current suppression control methods using repetitive control have been proposed. In earlier repetitive control techniques, the amount of memory for implementation was not considered explicitly. Furthermore, optimality was not ensured in our earlier studies. In this paper, we present a novel harmonic current suppression method using the generalized repetitive control. Compared with the conventional method, the proposed method achieves better control performance while taking into account the amount of memory for implementation. The effectiveness of the proposed method is verified through simulations and experiments.

View full abstract

This paper presents a maximum torque response control for interior permanent magnet synchronous motors based on a maximum torque control frame. The maximum torque control frame separates a current vector into two components: t-axis and f-axis. The t-axis represents the torque component; the f-axis, the magnetic flux component. Therefore, the maximum torque response control is realized by using the current change in the t-axis. The effectiveness of the t-axis is first established theoretically, and then verified thought simulations and experiments.

View full abstract

This paper proposes a force-based compliance control method utilizing visual information that can be integrated with a haptic system for motion navigation tasks. The force generated on the basis of useful image information of the tracked object is utilized to provide a response to the bilateral control system. An eye-to-hand approach is used to magnify the information from the vision sensor. The control strategy, image processing method, and integration techniques are elaborated upon in detail. Four experiments were conducted using different distances between the camera and object to validate the proposed integration method. The effectiveness of the proposed method was evaluated through a comparison with the conventional bilateral control method.

View full abstract

Industrial robots require high-speed and high-precision motion for improvements in productivity and product quality. However, high-speed motion excites residual vibration because the joint axis of the industrial robot has axial torsion. In addition, the inertia moment of the industrial robot is changed by the end-effector tool. Therefore, robust vibration suppression control is required. However, achieving both robust vibration suppression control and high-speed motion control is difficult. This paper proposes a new final state control method that considers the convergence time and inertia variation for an industrial robot. The proposed method applies final state control to the entire motion control system of each joint. To achieve the desired convergence time for the end-effector, the final state control profile is redesigned by using a proposed flowchart. The effectiveness of the proposed method is confirmed by a numerical simulation and an experiment using a 3-degree-of-freedom robot manipulator.

View full abstract

A motion-copying system is characterized by its ability to preserve and reproduce the motions of a human operator. The performance of a motion-copying system based on bilateral control is affected by friction and harmonic disturbances. To improve the performance of this system, we propose a friction-free disturbance observer with a dither signal for both motion-saving and motion-loading systems. The dither signal reduces the effect of friction, while the friction-free disturbance observer suppresses oscillatory disturbances in force estimation. Moreover, the friction-free disturbance observer achieves effective harmonic disturbance suppression in force estimation. All control algorithms are implemented in a field-programmable gate array to achieve a short sampling period that reduces the controller execution time and enables a wider force-sensing bandwidth. The effectiveness of the proposed method is verified by experimental results.

View full abstract

In this study, we extended the conventional admittance control and developed a new power augmentation technology that supports the upper extremity movements of humans using only the electromyography (EMG) signals of agonists. First, we selected the EMG signals of two agonists, the biceps brachii and clavicular part of the deltoid, to control the elbow and shoulder joints, respectively. We then developed an extended admittance control to augment the subject's strength and support the movements of the subject's upper extremity in flexion, keeping still, and extension while holding a heavy load. The experimental results showed that the performance of the proposed extended admittance control can be arbitrarily adjusted by control parameters to reduce the load “felt” by the user.

View full abstract

Motion control techniques are employed for nanoscale positioning in industrial equipment such as numerical control (NC) machine tools and exposure systems. The advanced motion control techniques are based on precise current control. However, speeding up the precise current response causes a serious limitation owing to the carrier period of the inverter. In addition, the position response has to be slower than the current response. In a previous paper, we designed and fabricated an experimental precision stage, achieving novel ultrahigh-speed nanoscale positioning based on multirate pulse width modulation (PWM) control. However, it was difficult to achieve faster and more precise positioning because of the resonance modes of the stage. In this paper, we propose a multirate PWM control in which the resonance mode is considered. Simulations and experiments are performed to demonstrate the advantages of the proposed method.

View full abstract

In this paper, diode-clamped linear amplifiers (DCLAs) are developed for achieving low-noise and fine force control. Class-B and Class-D power amplifiers are not suitable for driving a motor, owing to their power efficiency and high switching noise. In particular, a force control system using Class-D power amplifiers cannot generate appropriate fine force because of the switching operations by PWM or PDM. For that reason, we focus on DCLAs, which are capable of solving the problems both power efficiency and force noise. Furthermore, the force noise generated by the linear motor is less than that generated by the Class-D power amplifiers. Through a theoretical analysis, simulations, and experiments, the validity of the force control system using DCLAs is verified.

View full abstract

Three-phase four-wire distribution systems are widely used in many countries. These distribution systems are used for both three-phase three-wire loads and single-phase two-wire consumer appliances, e.g., in South Korea and Myanmar. Because of the time-dependent load characteristics, unbalanced load conditions frequently occur, resulting in the unbalanced voltages for the three-phase and single-phase loads. In addition, these unbalanced load conditions cause more loss in the distribution transformer. This paper proposes a novel reference current generation method for active load balancer (ALB) in the three-phase four-wire distribution systems. The main advantages of the proposed method is that it uses only a constant DC capacitor voltage control for reference current generation without calculating the active and reactive currents in the three-phase four-wire distribution systems. The basic principle of the novel reference generation method in ALB is discussed and then confirmed on the basis of results of digital computer simulation using PSIM software.

View full abstract