Wheel-legged mobile robots (i.e., robots that use leg and wheel mechanisms) have the potential for efficient movement in response to the environment. Singular configuration is an inevitable problem in wheel-legged mobile robots and must be solved to realize motion. This paper proposes a simplification of the motion generation method in the singular configuration of a wheel-legged mobile robot. The problem of inverse kinematic calculations in a wheel-legged mobile robot is first modeled, and a solution method is proposed using an extension of the constraints to the acceleration level and the redundancy of the robot. The singular configuration problem in the low-speed region is then solved using the Levenberg-Marquardt method. A simple decision method using a weighted matrix for the damping factor is also proposed. The method is then verified using a three-dimensional simulation and an experiment.
This paper describes a low winding loss design methodology to develop a real-scaled medium frequency transformer (MFT) for an isolated DC-DC converter to be used in a DC-interconnected offshore wind farm system. We assembled a core-type 500kVA MFT consisting of a lap-joint amorphous wound core and windings with a primary Cu sheet and divided secondary Cu sheets, wound alternately in turns. Then, we compared its loss performance with that of a conventionally designed MFT. The alternately wound winding structure suppressed the medium-frequency proximity effect between the Cu sheets and the in-plane eddy current due to the fringing flux crossing the edges of the sheets and fixtures, and the winding loss at 3kHz was 61% lower than that of the conventional MFT. In addition, we propose and discuss an accurate estimation method for the winding loss of core-type MFTs, considering the in-plane eddy current loss at the edge of the Cu sheets based on the finite element method.
The 4ch bilateral control is a teleoperation method that transmits the position and force information between the master and slave, and the reproducibility and operationality are often used to evaluate it. Conventionally, the reproducibility and operationality have been utilized only for performance evaluation, although many controllers based on the 4ch bilateral control scheme have been proposed. Therefore, the aim of this paper is to determine the controller structure based on the target reproducibility and operationality in advance. The contribution of this paper is to develop an appropriate controller from the reproducibility and operationality through numerical computations and analyses. The structure of the proposed controller is verified through simulations and experiments.
The actuators in robot joints are often equipped with reduction gears for increasing the power output. However, a high reduction ratio is required to decrease the backdrivability. In this paper, the backdrivability is improved by installing motor- and load-side encoders in the reduction gear. The proposed method comprises a backdrive assist control, feedforward friction compensation, and estimation and feedback of the load-side disturbance by using a multi-encoder-based disturbance observer. The angular transmission error in the reduction gear is treated as a disturbance that affects the motor. This disturbance is estimated from the motor- and load-side angular accelerations, and provides feedback assistance to the backdrive. The effectiveness of the proposed method is verified through experiments.
This paper proposes voltage control of two battery-operated high-efficiency energy conversion system choppers, which have a very high efficiency of 99.3% and are suitable for power trains of electrical vehicles. However, due to the topology of the choppers, one disadvantage is that the chopper output voltage control has a large transient response, for example, when the duty ratio is changed from zero to a finite value, because of the inherent dead time in the switching phenomena. The minimum pulse width of the gate signal is physically determined by the delay time in the switching phenomena. As a result, there exists a dead time when the duty ratio is changed in this case. Similar phenomena occur when the duty ratio is changed around unity. Consequently, an overcurrent is observed during these types of transient periods and the system shuts down due to overcurrent protection. To solve this problem, intermittent pulse density modulation is proposed such that the output voltage is controlled by the average duty ratio. This makes it possible to output both the very low and the very high average duty ratios with multiple sampling periods. As a result, the transient response was experimentally verified to be improved even though the voltage ripple under this control increased compared with that under simple pulse width modulation (PWM) control.
This paper proposes a solid-state transformer (SST) for a 6.6-kV single-phase grid using multiple cells, which have a power factor correction stage and an isolated DC-DC converter. In the SST, the capacitor voltage of each cell is automatically balanced on the primary side owing to the use of a resonant DC-DC converter. The main focus of this study involves calculating the fundamental loss of the proposed topology assuming a 6.6-kV single-phase grid. The calculations show that the maximum efficiency of the full model of the SST reaches 99%. The scaled model with an input voltage of 1320V, which is 1/5th that of the full model, is tested to confirm the calculation of the power loss and the fundamental operation. The results confirms that the input current is sinusoidal and the total harmonic distortion is 4.3%. Moreover, the automatic capacitor voltage balancing capability is tested. The capacitor voltage on each cell is automatically balanced without any control. Further, the bidirectional operation is verified. Finally, the power loss of the proposed topology is separated into values for each conversion part. The power loss shows good agreement with the calculation with an error of less than 5%.
This paper presents iron loss reduction in the cores of induction heating (IH) coils for a small-foreign-metal particle (SFMP) detector with a 400-kHz SiC-MOSFETs high-frequency inverter. A new core shape for IH coils, which can reduce iron loss, is designed for the stable and continuous operation of the SFMP detector. Magnetic field analysis results using JSOL JMAG software, a 3D full-wave electromagnetic field simulation software, demonstrate that the iron loss caused by the new core shape for IH coils is decreased by 71.8%, compared with that of the previously proposed IH coils, which increase the magnetic flux density to heat SFMPs by 20%. Thus, the stable and continuous operation of the SFMP detector with the newly designed core shape of IH coils can be achieved. It is also shown that SFMP represented by 0.3-mm diameter stainless-steel balls (SUS304) can be detected on the high-performance chemical film (HPCF) with the newly designed core shape of IH coils using JSOL JMAG software. A prototype experimental setup of the SFMP detector with the new core shape of IH coils is constructed and tested. Experimental results demonstrate that a 400-kHz SiC-MOSFETs high-frequency-inverter-based SFMP detector with the newly designed core shape of IH coils can heat SFMPs, which can be observed by a thermographic camera. Therefore, the authors conclude that the 400-kHz SiC-MOSFETs high-frequency-inverter-based SFMPs detector with the newly designed core shape of IH coils is applicable for HPCF production lines.
In this paper, we propose a new control algorithm for a novel fully digital-controlled H-bridge DC-DC converter, which can output the power in both boost and buck mode by only rewriting three digital codes: input voltage, output voltage, and maximum load current. In addition, the proposed algorithm improves the transient response.
An optimization procedure is proposed to determine the shapes and orientations of permanent magnets in interior permanent magnet synchronous motors with concentrated armature windings. In the proposed procedure, 2D finite element analysis coupled with the armature voltage equation is used to take into account the leakage flux at the end windings. The end leakage inductance in the equation is determined by 3D finite element analysis in advance. By using this procedure, the rotor shape of the motor can be optimized within a practical computational time. First, the validity of the analysis is confirmed by comparing measured and calculated characteristics of the motor. Then, the optimal shape and orientation of the permanent magnets in the motor are discussed using the results of the proposed optimization procedure. It is revealed that the consideration of the end-leakage flux is indispensable to estimate the characteristics of the motors with concentrated windings whose core length is relatively short as compared to the diameter, particularly under flux weakening control. An optimized rotor that reduces the iron loss at high speeds without considerable deterioration of the other important characteristics is also obtained by the proposed optimization procedure.
The “optimal” control of a stationary energy storage system in a DC electric railway network is achieved by minimizing the total energy supplied from all the related traction substations. Given a timetable and the speed profiles of all the trains in the network, this paper addresses the problem of finding an optimal charging and discharging power control of the storage system. In this paper, we model the problem as a mixed integer programming problem and show the solutions for several parameter values. We then discuss the validity of our model and estimate the advantages of the energy storage system in terms of energy saving. These processes are useful for designing and installing an energy storage system in a DC electric railway network.
We developed a current commutated hybrid direct current circuit breaker (DCCB) for high-voltage direct current transmission systems. The transmission losses of the developed DCCB are considerably low because a normal current path includes only mechanical switches. Fast mechanical switches and a commutation circuit can achieve a fast current interruption. We also developed a test method for DCCBs, which permits the use of existing facilities such as AC generators. We tested a scaled-down 10-kV hybrid DCCB with the developed test method. The test results proved the operation principle of the hybrid DCCB and the efficiency of the test method.
This paper studies extremely high-precision efficiency measurement by building a back-to-back (BTB) system with a high-power DC-DC converter in order to realize a 100kW high efficiency energy conversion system (HEECS) chopper with 99.5% efficiency. The newly proposed water-cooled 2-phase HEECS BTB chopper system achieves a reduction in input power and enables highly precise measurement of a high-power DC-DC converter with an extremely high efficiency of 99.5%.
This paper proposes a new topology for single-phase photovoltaic PV grid-tied applications. The whole system consists of a two-stage, high-frequency boost inverter cascaded by rectifier-inverter system. A single-phase high-frequency transformer is used to link both stages and provide galvanic isolation between the AC and DC sides. A single-stage high-frequency boost inverter (HFBI), in the first stage, boosts and converts the DC output voltage of the PV array to a high-frequency single-phase square waveform and achieves maximum power point tracking (MPPT). In the second stage, the rectifier-inverter system (RIS) interfaces HFBI to the grid. The proposed topology has many advantages such as increasing the inverter output voltage level, MPPT, high reliability, small size, and light weight. In addition, a proportional integral current control (PI) is used to inject a sinusoidal current into the grid at unity power factor. The proposed topology has been verified analytically using PSIM software and experimentally by using a laboratory prototype.
This paper describes the torque and power factor characteristics of SynRMs (synchronous reluctance motors) considering their magnetic energy and co-energy properties. Since the inductance of SynRM varies drastically due to the magnetic saturation effect, it is not easy for us to understand their characteristics, MTPA (maximum torque per ampere) points, and maximum power factor points, quantitatively applying the frame based on equivalent circuit models. In this study, we focused on the fact that the model constructed by the magnetic energy and co-energy gives more simple expressions to the torque and power factor compared to the equivalent circuit model. A SynRM that consists of a stator, same as a benchmark model (D-model) provided by IEEJ, and a rotor with three layer flux-barrier was simulated by the electromagnetic field analysis, and its magnetic energy and co-energy were calculated. As a result, three states (I, II and III) were defined depending on degrees of the magnetic saturation level. Then, the output torque per square ampere becomes maximum on a boundary region between state II and III. Further, the current phase of the MTPA point moves to the leading phase side with increasing the current magnitude on state III and the phase of the maximum power factor point is larger than that of the MTPA point. It was clarified that the model constructed by the magnetic energy and co-energy are suitable for discussions on the SynRM characteristics taking account of the magnetic saturation.