Actuator arrays that consist of a planar arrangement of actuators are widely used for transportation of objects or shaping a rough surface by controlling the actuators cooperatively. In particular, thermal displays that consist of multiple heat sources spread over a surface have been developed for many years. Generally, the expression ability is determined by the number of actuators in actuator arrays, and accordingly, thermal displays require many heat sources to ensure a high spatial resolution of temperature distribution. However, the number of usable heat sources is limited because of mechanical issues. In order to solve this problem, a control method that employs a model derived from a thermal diffusion equation and is used between two heat sources, is proposed in this paper. By using the proposed method, any selected point of the heat conduction can be expressed using only one heat source. Therefore, infinite number of nodes of propagation can be reproduced by selecting a desired node. The method is expected to extend the technology for controlling multiple actuators or heat sources on a surface.
In this research, a new estimation method for the sensorless control of a permanent magnet synchronous motor (PMSM) in the low speed range is proposed using a speed observer and an opened phase voltage. An approximate linear equation of the opened phase voltage, which varies depending on the rotor position, is calculated using the least squares method with constant time intervals. This estimated position is used as the input of the speed observer instead of the actual position information. The position detection method based on the opened phase voltage can be applied to a non-saliency and closed shelf motor in a low speed range where back-EMF (Electro-Motive Force)-based methods are difficult to apply. In the proposed method, the current waveform is satisfactorily controlled in a sinusoidal waveform during the period when the opened phase voltage is not measured. Compared to conventional methods, it improves the energy efficiency and reduces the torque ripple. In this paper, we present the proposed position estimation method and the experimental results.
An auto-tuning damper for grid-connected converters (GCs) is proposed in this paper to improve the stability of GCs when there is an increase in the penetration of renewable energy sources (RES). Increasing number of GCs are being connected to the power grid for supporting the power generation of RES systems, and this makes the equivalent output impedance of GCs becomes closer to the system impedance of the power grid. This increases the influences of the operation of GCs on the output voltage, and there is a greater risk of GCs becoming instable. In addition, system operations such as switching of transmission lines will result in larger variations in the system impedance than before in this situation. This could induce large changes in the resonance characteristics between the system and GCs. In this situation, conventional active damping control, which is designed based on the known conditions of system impedance, could have less controllability due to the changes in resonance characteristics. The harmonic resonance could become instable if the active damping control has insufficient damping effect. For this reason, an auto-tuning damper for harmonic resonance is proposed in this paper. It makes the active damping control capable of taking action in response to the changes in resonance characteristics. Therefore, it can improve the stability of operation of GCs. The operational principle, simulation, and scale-down prototype validation are presented to show the improvements achieved by the proposed solution. In addition, a problem investigated during prototype validation is explained and described.
This paper presents an integrated design of train scheduling, use of onboard energy storage, and traction power management for urban railways. The proposed design aims to integrate the design of train operation and infrastructure to improve energy-saving operation and the flexibility of energy management. The design problem is formulated as the minimization of the energy supplied from substations and the energy capacity of onboard energy storage. By varying the weighting factor, energy-saving purpose and cost-saving purpose can be compromised. To demonstrate the performance of the proposed design, numerical case studies are performed and evaluated on the Bangkok Mass Transit System. From the comparisons of nominal operation and design operating conditions, it is seen that the energy-saving performance is improved by up to 9.65% and the peak power at a substation is reduced by approximately 40%. The design scenario can be simply classified into cheap, moderate, and expensive designs depending on the appropriate adjusting weighting factor. Furthermore, the effect of pantograph voltage is evaluated and discussed. From the results, it is seen that the energy-saving performance is reduced by approximately 1% due to the fluctuation of the pantograph voltage. Even though the variation of pantograph voltage affects the design scheduling, a small deviation in the running time in some sections must be allowed. The proposed design still provides considerable improvement with regard to the energy-saving operations. The proposed design employs an offline design and planning because the design process requires considerable computation time.
This paper proposes a novel discontinuous pulse width modulation (DPWM) strategy to reduce the switching-frequency-order DC-link current harmonics for a two-level three-phase voltage source inverter (VSI). The proposed modulation method realizes a long lifetime of the smoothing capacitor to the motor drive system. Furthermore, the proposed strategy requires only one carrier; thus, high cost hardware such as field-programmable gate arrays are unnecessary. The DC-link current harmonics are reduced by shifting two unclamped modulating signals in every half control period. In addition, the injection of the zero sequence signal to all discontinuous modulating signals optimizes the phase of the clamped modulating signal and its clamped value according to the conditions of the output phase currents; consequently, the DC-link current harmonics are reduced even when the load power factor varies. Experiments confirm that the proposed DPWM strategy can reduce the DC-link current harmonics by a maximum of 18.3% at a modulation index of 0.705 and a load power factor of 0.819.
This paper presents a design of efficient urban railways based on an integrated design of train schedule and use of wayside energy storage. The main objective is to simultaneously design the train operation, infrastructure, and traction power management scheme to enhance energy-saving operation and the flexibility of energy management. The proposed design aims to minimize the energy supplied from substations and the energy capacity of the energy storage system (ESS). The objective function is formulated as the weighted sum of the energy-saving term and cost-saving term. Numerical case studies are performed on the Bangkok mass transit system (BTS) to demonstrate the performance of the proposed design. From the results, it is seen that the designed timetable parameters and the appropriate installation scenario of ESS (i.e. capacity and location) obtained from the proposed design can improve the energy-saving performance by up to 10.35% compared with the nominal operation. Moreover, the reduction of peak power and voltage regulation at substations can be achieved. By adjusting the weighting factor, the design scenario can be classified into categories ranging from a cheap infrastructure design to an expensive design; and the decision of an optimal solution can be simply finalized by considering the Pareto curve. To simplify the optimization process, the effect of voltage is excluded. Therefore, the performance of the design operation may be degraded by the variation of the pantograph voltage. From the comparison, it is seen that the variation of voltage entails small deviations in the design scheduling and degrades the energy-saving performance, especially in the off-peak hour condition. Even though such deviations are allowed in the operation of some running sections without any modification of the designed condition, the energy-saving performance is still improved.
This paper proposes fine and fast discretization, which is based on the Finite Difference Time Domain (FDTD) method without a matrix exponential function. The proposed method is more accurate than the conventional discretization based on the first-order Pade approximation. Moreover, compared with that of the conventional method, the computational cost of the proposed method is very small. Although the Pade approximation is impossible to realize broadband real-time control, the FDTD method achieves the broadband real-time control. The proposed method and the conventional Pade approximation are analyzed by the Taylor expansion in a symbolic expression. According to the theorical analysis, the error of the FDTD discretization method is smaller than that of the conventional method. Numerical simulations also compare the errors and computational cost associated with the proposed and conventional methods. The FDTD discretization method is applied in admittance control for rendering the time-variant haptic sensation. In the case of the conventional method, owing to the limitation due to computation cost, the parameter update is not completed within the sampling period. On the other hand, the FDTD method completes the discretization within the sampling period. The gain and phase characteristics of the proposed method are close to the ideal responses. The validity of the method is verified by an experiment involving linear motor systems.
Stopping control is very important in public transportation systems. It is used to precisely match where a vehicle is boarded at a station and the positions of the doors of the vehicle. Although it is necessary to estimate self-localization with high accuracy, the cost of implementing it using balises, which is currently popular, is very high. To accelerate the introduction of stopping control to public transportation systems, a low-cost self-localization estimation technology is required. We propose a vision-based self-localization method for underground railway, which does not use expensive balises as that in conventional method. The method uses image recognition to calculate the relative distance to a ground target, whose position is known, and estimates the position of a vehicle from the absolute position of the target and the relative distance. In this paper, we evaluate the accuracy of the self-localization estimation using the proposed method under outdoor conditions that are more severe compared with underground conditions. From the results of six trials, we confirmed that the accuracy of position estimation of all trials satisfied the required accuracy of 0.8m, when the distance between the vehicle and ground target was 20m.
This paper proposes a new three-inertia model that considers new transmission factors to achieve quick reaction force control. New transmission factors are confirmed by the analysis results of load-side dynamic characteristics. The load-side dynamic characteristics are measured via input impact torque using a hammer and motor-side velocity response. The experimental results of the input impact torque using a hammer confirm a new anti-resonance frequency with regard to the load-side dynamic characteristics. Therefore, new transmission factors are obtained based on the new anti-resonance frequency. However, the conventional three-inertia model has no new anti-resonance frequency. The consistency of the proposed three-inertia model that considers new transmission factors against plant system is confirmed by using a state observer based on the proposed three-inertia model. Additionally, the effectiveness of the force control system based on the proposed three-inertia model is confirmed by numerical simulations and experiments.
The dual inverter drive system feeding an open-end winding permanent magnet (PM) motor has been studied for developing autopilot technologies of hybrid vehicles. Autopilot systems require fault-tolerant functions, which enable it to continue to drive the motor even if some failure occurs in the motor drive system. The fault-tolerant function of a dual inverter drive system, which assumes that the DC-bus battery power source of the dual inverter drive system has failed, is discussed in this paper. In the dual inverter drive system that is considered, both the inverters have a capacitor in parallel with a battery across each DC-bus. The capacitor drives the motor continuously even if the DC-bus battery has failed. The inverter, in which the DC-bus battery has failed, is operated with the capacitor instead of the failed battery. It is required to both control the capacitor voltage at a constant value and simultaneously generate multilevel voltage waveforms across the motor windings with the space vector modulation (SVM). In this paper, the fault-tolerant function of the DC-bus battery in a dual inverter drive system is proposed, and its operation characteristics are examined through several experiments and compared with those of a normal system.
This paper presents a novel algorithm for simultaneous position and interaction force control. In the classical algorithms, position and force control are executed concurrently by switching between two separate controllers: the position and force controller. Thus, one can consider the control system working in two modes, namely the position control and force control modes. Switching between these two modes often leads to oscillations in the controlled position and force. Therefore, the safe interaction between a controlled mechanical system and its environment is jeopardized. The above issues are tackled in this study by introducing a new control strategy. The proposed algorithm combines position and force control into a single controller, in which the transition between position and force control is smooth, removing the oscillations of classical methods. Therefore, the safe interaction between a mechanical system and its environment is enabled. In addition, using this method one can equip actuators with a control system capable of performing both position and force control. Thus, a step towards “smart actuators” is possible.
This paper proposes a hybrid motion reproduction structure using a master-slave structure manipulator based on a motion-copying system. Data-driven control will be an important technique in the near future. Learning from Demonstration (LfD) using a robot manipulator is already used in manufacturing. Unlike other motion observation methods based on visual or trajectory responses, a motion-copying system can obtain not only trajectory response but also force response during contact motion, which is necessary to realize contact tasks. A motion-copying system has two phases, the motion saving phase and motion reproduction phase. In the motion reproduction phase, the motion stored in the motion saving phase obtained from the bilateral control can be used to reproduce specific motion. Existing control methods for a motion-copying system have only one system in the reproduction phase, a slave system. It is necessary to consider the case where there are two systems in the phase to widen the application of a motion-copying system. The additional system can provide flexibility to the reproduced motion. In this case, data, human, and a robot are involved in reproducing the motion. In this paper, the control structure is proposed when there are two systems in the motion reproduction phase. Because there are two systems, it is necessary to design the controllers for each system. The proposed method uses a coordinate transformation technique to design two motions in each system separately. The paper also introduces a novel index called the reproduction ratio. It determines the motion to be reproduced in the motion reproduction phase. The ratio is used as an element of a coordinate transformation matrix. The experimental results show the validity of the proposed method.
Power factor correction converters are widely used in industrial drive systems. Several different configurations and topologies exist for such converters and it is difficult to choose one. Therefore, in this work, a comprehensive selection of possible configurations are optimized and compared against each other. The analysis shows the important aspects of converter design and how the semiconductor technology used (Si, SiC, and GaN) affects the total converter volume. A sensitivity analysis of certain power semiconductor parameters is performed to highlight the benefit of possible future developments of components and materials. In addition, the differences between the rectifier stage, where an electromagnetic interference filter stage is necessary, and the inverter stage, where the harmonic motor losses are influenced by the modulation scheme, are presented.
High step-up converters have been widely used in renewable energy systems and, recently, in automotive applications, owing to their high voltage gain capability. In these applications, power losses, mass, and volume are quite restrictive, because they affect the system operation and cost. However, it is difficult to optimize these characteristics simultaneously. Consequently, multi-objective optimization through the design automation of power electronics is useful to meet the efficiency and power density requirements. This paper presents a procedure to optimize the efficiency and power density of a coupled inductor used in a high step-up converter. In this procedure, a complete modelling of power losses and size is evaluated by comparing different materials and dimensions. In addition, 3D and 2D finite element modelling simulations are used to validate the magnetic core shapes and sizes. The results of this modelling stage are introduced into a multi-objective optimization algorithm to obtain a Pareto front. Finally, the optimization methodology is experimentally validated.
To improve the resolution of a magnetic absolute encoder, we propose a new magnetic encoder with an eccentric structure. Since the proposed magnetic encoder consists of only one eccentrically rotating multi-pole magnet and four Hall elements, its structure is very simple and cost efficient. By calculating the absolute offset by combining the look-up table and least squares method, it is possible to calculate the absolute angle even when a multipolar magnet is used for resolution improvement. Furthermore, since the quadrature signal can be calculated, it is possible to configure the converter using the conventional method, and it is very versatile. Experimental results show that the proposed method can achieve both improvements of accuracy by increasing the number of pole pairs and calculation of absolute angle.
In this paper, an output voltage accuracy improvement method for an asynchronous PWM inverter is proposed. This method is suitable for control conditions where the ratio of the carrier frequency to output voltage frequency is lower than 9. In such a situation, the inverter output voltage contains disturbance voltage composed of the beat component. The proposed method suppresses the disturbance voltage by adding a compensation term to the voltage command. The details regarding an analytic derivation method of the above compensation term is written in this paper. The validity of the proposed method is confirmed by computer simulation and experiment.
Recently, from the viewpoint of vibration and noise reductions, torque ripple reduction of motor-equipped electrical machines is the need of the hour. The authors have already proposed to improve torque characteristics of a synchronous reluctance motor using the topology optimization method. The evaluated rotor structure succeeded in substantial torque ripple reduction, but the cause for this reduction was unknown. In this paper, we investigate the reason for torque ripple reduction using the improved rotor structure of the motor by a topology optimization method known as R-SLP, by comparing it to the reference model using finite element analysis. A calculation method is proposed to analyze the circumferential magnetic force density of spatial and time harmonic orders using the magnetic density in the air gap. By focusing on the time order at which the torque waveform was evaluated, we estimate which circumferential magnetic force density orders affect torque ripple reduction. Then, we clarify the reason for torque ripple reduction to examine the influence of local shape of rotor structure using 12th time-harmonic magnetic fields. As a result, the modified flux barrier rotor structure is obtained, which further reduces the torque ripple in comparison to the previous structure.