This paper describes techniques that Japanese power electronics engineers can use to improve the quality of their technical papers written in English and the accompanying technical presentations. These techniques are based on the experience that the author has gained by participating in international conferences. Such techniques are important to discuss because the significant differences exist in writing and presentation styles between Japanese and American engineers. The author believes that such style differences are caused by differences between the Japanese and American cultures. The objective of this paper is to help Japanese engineers understand these cultural differences and improve their technical communication skills in English. The paper also includes some practical tips on writing and presentation techniques for improving the quality of their technical communications in English.
This paper describes sensor-less vector control method of a synchronous motor with a permanent magnets. We examined the vector control system that used the full order flux observer constituted on the stationary frame. First, a function of this system is explained. This flux observer is converted to the transfer function block diagram which consists of the compensating filter and the vector oscillator. This observer gain can be determined by setting the frequency characteristics of this compensating filter. Then, the design rule that the frequency bandwidth is shown. Lastly, we prove this system has enough stability even in the high-speed region by the experimental results.
This paper proposes new identification laws of an adaptive flux observer for speed sensorless vector controls. In speed sensorless vector controls of an induction motor with the adaptive observer, the speed identification system is known to be unstable in a part of regenerating region. In addition, it is pointed out that the stator resistance variation interferes with the speed identification. Thus it is necessary to find an adaptive scheme which can stabilize the identification system. In this paper, firstly, the stability on the parameter identification is discussed from the viewpoint of Popov’s hyper stability. Secondly, identification laws for the speed and the stator resistance are proposed based on the new identification system which is derived by using the augmented error. Finally, effectiveness of the proposed method is shown by experiments.
It is necessary to estimate the Brillouin scattering power spectrum in a fiber optical strain sensor. This is because optical fiber strain depends on the Brillouin scattering frequency shift. However, this requirement is not met in the strain border area because the Brillouin scattering power spectrum cannot be approximated by one Lorentzian function and therefore the conventional least squares method with linearization cannot be employed. This paper proposes a new power spectrum estimation method that uses two different outputs from a fiber optical strain sensor in the strain border area. The effectiveness of the new method is confirmed by simulation.
In this paper we focus on cooperative transportation by multiple mobile robots. During the transportation, each robot has a load that is influenced by a state of a carrying object and road surface. This paper proposes a method of deciding a grasping position of each robot to equalize the loads based on environmental information estimated by Reaction Torque Observer. Then it is expected that each robot is prevented from becoming overload and stable transportation is realized. Simulation and experimental results show the validity of the proposed method.
A photovoltaic array shows relatively low output power density, and has a greatly drooping Current-Voltage (I-V) characteristic. Therefore, Maximum Power Point Tracking (MPPT) control is used to maximize the output power of the array. Many papers have been reported in relation to MPPT. However, the Current-Power (I-P) curve sometimes shows multi-local maximum points mode under non-uniform insolation conditions. The operating point of the PV system tends to converge to a local maximum output point which is not the real maximal output point on the I-P curve. Some papers have been also reported, trying to avoid this difficulty. However most of those control systems become rather complicated. Then, the two stage MPPT control method is proposed in this paper to realize a relatively simple control system which can track the real maximum power point even under non-uniform insolation conditions. The feasibility of this control concept is confirmed for steady insolation as well as for rapidly changing insolation by simulation study using software PSIM and LabVIEW. In addition, simulated experiment confirms fundament al operation of the two stage MPPT control.
In the permanent magnet (PM) synchronous bearingless motors, radial suspension force components in two-perpendicular axes are mutually interfered by the armature reaction. Then, the magnetic force suspension system has less damping, and it causes unstable rotor suspension with large displacements. In order to eliminate the suspension force interference, some decoupling control methods of the PM bearingless motors have been already proposed. In the decoupling controllers, it is necessary that the radial force parameters are justly identified. The parameters may be varied with the armature reaction or the magnetic saturation in the stator teeth. In this paper, the salient-pole type PM bearingless motors are focused. At first, the parameters are calculated by FEM. However, some problems are found in the FEM parameter identification from a view point of suspension performances of three prototype machines with different structures. Then, a new on-line parameter identification strategy is proposed, and the new strategy is found to be suitable in identification of the parameters considering the armature reaction and the magnetic saturation.
In high-density railroad sections such as metropolitan commuter lines, there is a great demand for increasing train density in order to relieve traffic congestion. However, it becomes more difficult to shorten train headway, which is dependent on the performance of the signaling system and the rolling stock, as the track form, train type, and train performance become more diverse. Therefore, making diagrams needs the expertise of skilled specialists, for train scheduling, operation adjustment, and equipment design. In order to raise the train density to a maximum, this paper aims to calculate the restrictions in the train intervals that exist between all trains within a certain accuracy and derive a train diagram. We propose the “maximum-density diagram" to refer to a diagram whose periodic time is shortest, on the assumption that the actions of the operated trains in one period are fixed. In practice, we obtain the effective results for railroad operation practices, when we derive the “maximum-density diagrams" of model cases.
Power service interruptions cause problems in various facilities. Even an instantaneous voltage drop may give rise to serious problems in computer systems or electronic equipments. The uninterruptible power system (UPS) has been used to compensate for the power service interruptions. And also, the instantaneous voltage drop compensator using the electrolytic capacitor has developed for the instantaneous voltage drop. Recently, the double-layer capacitor is paid attention as a new energy storage element. This capacitor has a lot of advantages such as no maintenance, long lifetime and quick charge/discharge characteristics with large current and it has higher energy density than the electrolytic capacitor. Therefore, we developed the uninterruptible power system using the double-layer capacitor. In this paper, the performance of the uninterruptible power system using the double-layer capacitor is shown by the simulated and experimental results. Furthermore, the discharge characteristics of the double-layer capacitors are investigated on the basis of the equivalent circuit including the capacitors and a voltage booster. Finally, the maximum load capacity to compensate is clarified for the system.
The AC-DC converter, which has three-phase AC power as input and isolated DC power as output is used for the regulated DC power supply of the telecommunication power processing system for several kilowatt class applications. The conventional DC power supply for the telecommunication power system comprises a PWM rectifier with sinewave shaping input current unity power factor and a DC/DC converter connected to the PWM converter, which obtains DC48 V. Since power passes through these two power stage converters, the conversion power loss is difficult to provide high efficiency. In addition, the power components of the power converter make the compact design of the power supply difficult. To resolve these problems, this paper presents a new PWM rectifier as a one-stage power conversion scheme. It experiment, it is proved from a practical point of view that 92.1% of conversion efficiency and input current which can meet harmonics regulation of the Class A in IEC61000-3-2 are achieved.
Tracking control problem of multiple mobile robots is considered. Our system is composed of a reference and follower robots of unicycle type. The robots are assumed to satisfy pure rolling and non-slipping conditions, which lead to nonholonomic velocity constraints. The purpose is to control the followers so that the reference is tracked with arbitrary desired clearance and also to avoid an inter-robot collision. To accomplish this goal, we first introduce a virtual robot (VR) tracking control to establish and maintain the formation when no collision is detected. VR is an ideal robot fixed with each follower and helps in simplifying the control, as the tracking errors become zero in final stage. During the process, if a possibility of collision is detected, a collision avoidance technique (l-ψ or l-l control) will be applied to the lower priority robot. The result of this control gives a monotonic convergence in an internal shape of distance variables, which enables us to predict the movement of the robots during this control and leads to the collision-free movement. These processes are repeated until the desired motion is accomplished. Simulation results prove effciency of our control techniques.
This paper describes novel low loss active voltage clamp circuits for the series connection of RCGCT thyristors. For high voltage converters the series connection of power semiconductor devices is an essential technique for direct switching of high voltages. Several protection circuits have been applied to the series connection of RCGCT thyristors such as CRD snubber circuits which suppress over-voltages across RCGCT thyristors, and voltage balancing resistors to equalize voltage sharing in steady states. However, significant losses in these protection circuits lower the converter’s efficiency. We propose novel low-loss protection circuits, which have active voltage clamp snubber circuits and static voltage balancing circuits. The clamp capacitor voltage of the active voltage clamp snubber circuits are designed to be higher than the equally divided DC-Link voltage. This method can reduce the loss of the clamp circuit to no more than 1/10 of that of the conventional CRD snubber. Also the static voltage balancing circuits compensate for the voltage imbalance generated by the difference in the leakage current between the series connection RCGCT thyristors.
This paper focuses on no-load iron losses of turbine generators. To calculate iron losses of turbine generators a program was developed. In the program, core loss curves of materials used for stator core were reproduced precisely by using tables of loss coefficients. Accuracy of calculation by this method was confirmed by comparing calculated values with measured in a model stator core. The iron loss of a turbine generator estimated with considering three-dimensional distribution of magnetic fluxes. And additional losses included in measured iron loss was evaluated with three-dimensional magnetic field analysis.
Fractional Order Control (FOC), in which the controlled systems and/or controllers are described by fractional order differential equations, has been applied to various control problems. Though it is not difficult to understand FOC’s theoretical superiority, realization issue keeps being somewhat problematic. Since the fractional order systems have an infinite dimension, proper approximation by finite difference equation is needed to realize the designed fractional order controllers. In this paper, the existing direct discretization methods are evaluated by their convergences and time-domain comparison with the baseline case. Proposed sampling time scaling property is used to calculate the baseline case with full memory length. This novel discretization method is based on the classical trapezoidal rule but with scaled sampling time. Comparative studies show good performance and simple algorithm make the Short Memory Principle method most practically superior. The FOC research is still at its primary stage. But its applications in modeling and robustness against non-linearities reveal the promising aspects. Parallel to the development of FOC theories, applying FOC to various control problems is also crucially important and one of top priority issues.
This study proposes an efficient design method of time-varying gain type controller and its application to the positioning control of vibration systems. This method solves a time-varying Riccati equation and the responses of a controlled object simultaneously. Moreover, this study utilizes the random search technique for the tuning of the time-varying weights in the Riccati equation and realizes the efficient controller design under many control constraints.