This paper discusses the efficiency of an induction motor when periodic fluctuation occurs in a load. A high-efficiency control method for induction machines achieves minimum copper loss by adjusting the excitation current depending on the load condition. When the load torque varies rapidly, the high-efficiency control method increases the copper loss because the transient current flows in the excitation current. This paper clarifies the boundary condition for high-efficiency control. When the load fluctuates faster than the boundary condition, high-efficiency control based on the effective value of the load torque is used. The copper loss under load fluctuation is analyzed in order to derive the boundary condition at which copper loss is minimized. Finally, the validity of the boundary condition is confirmed experimentally using a 3.7-kW induction motor.
Interior permanent magnet synchronous motors (IPMSMs) are widely used for many applications because of their many attractive characteristics. In order to realize high power and high efficiency, maximum torque per ampere (MTPA) control has been proposed for current-controlled IPMSM drive systems. On the other hand, direct torque control (DTC) is also used for IPMSM drive systems. However, DTC requires not current but torque and stator flux linkage as references. Therefore, it is difficult to make references for MTPA control, and a look-up table is often used instead. This paper proposes an MTPA control strategy for DTC-based IPMSM drive systems that does not rely on a look-up table. The proposed method is based on a motor model in a d-q rotating frame, which is often used in synchronous motor drives. This method does not require any look-up tables, so estimated parameters can be applied easily. In addition, inductance variation can be considered if inductances are modeled as functions of the current. The simulation and experimental results validated the proposed method.
This paper proposes new three-phase current control methods for ac motor drives, which detect only a phase current from among three-phase currents. The first proposed method first detects a phase current, and then estimates the two-phase current in the stationary reference frame using the detected single phase current. The second proposed method first detects a phase current, then synthesizes the two-phase quasi-current in the dq rotating reference frame, and finally produces two-phase current estimates by extracting the positive-phase component from the quasi-current. The third proposed method produces two-phase current estimates by filtering out the negative-phase component from the quasi-current. This paper presents the principles and detailed characteristic analyses of the proposed methods and validates them on the basis of extensive experiments.
This paper describes the design of an induction motor to decrease the stray load loss of an electrical train based on magnetic field analysis. The stray load loss of the current motor accounted for about 30% of the measured total motor loss. The sensitivity of the loss to various motor design parameters was evaluated by using magnetic field analysis. The stray load loss showed high sensitivity to the magnetic flux density in the stator, the gap width, and the rotor slit height. Base on these results, a motor was developed to reduce the stray load loss by 50% and total loss by 15% compared to the current motor.
This paper proposes controlled voltage source (CVS) vector control for switched reluctance motors (SRMs) using the PWM method. This proposed technique can achieve high controllability for variable speed drives, low current ripple and low noise operation, and high motor efficiency at high speed. Moreover, its implementation is easy because the controller design does not require complicated offline data such as the magnetization characteristics. To verify the effectiveness, an experiment was conducted to compare the performances of the proposed technique and a conventional unipolar drive using the hysteresis comparator method.
Unacceptable levels of congestion can be seen in a number of commuting railway lines across Japan and elsewhere in the world. To ease congestion, several scheduling schemes have been proposed for high frequency train operation on these railways. Generally, most of the trains in the schedule generated using these schemes make much fewer calls at stations en route. Operating railways using such schedules inevitably have different impact on the whole system performance of the railway power supply network compared with conventional scheduling schemes. In this paper, the authors present the results of the evaluation of such impact by using the DC railway power feeding system simulator RTSS and the train schedule evaluator Sujic. The results show that significant decrease in passenger travel times is possible without significant increase in energy consumption by applying the high frequency scheduling scheme.
This paper examines the shapes of cores for secondary coils of the wireless power transfer (WPT) system for a railway. An infinitely long cable-type coil is utilized as the primary coil for the WPT system because it is economical. Thus, this paper examines the ferrite core shapes for the secondary coils that are suitable for an infinitely long primary coil. The cores should be as thin as possible to reduce weight. However, bonding small cores to manufacture larger thin cores reduces the performance of the secondary coils. As a result, the cores are paradoxically required to be thicker. Therefore, this paper proposes the adaptation of thicker discrete-type cores with the same volume as conventional flat-type cores for the secondary coils.
Computational efficiency is very important for reducing the system development time and cost of a power electronic (PE) system simulator. A PE system often consists of various subcircuits that convert electric energy between different combinations of AC and DC. The subcircuits are linked by DC voltages and currents with large energy storage elements of inductors and/or capacitors in most cases. The DC-link voltages and currents vary very slowly. This paper describes a parallel circuit simulation method that divides the whole system into subcircuits by applying an explicit integration formula to selected energy storage elements such as series inductors and/or parallel capacitors. A new automatic partitioning method of a system into subcircuits is proposed. The method mainly consists of three steps: detection of parallel capacitors, that of series inductors, and reconnection consideration by control circuits. The proposed method is applicable to power electronic systems. A parallel simulation was performed to investigate how the proposed method works and to demonstrate the effectiveness of circuit partitioning.
The theory of functionally different effective muscles allows for detailed measurement of the muscle strength of limbs by separating mono-articular and bi-articular muscles. The theory represents the output force distribution (OFD) at the end of a limb as a hexagon whose opposite sides are parallel and of the same length. The measured OFD is used to derive the muscle strength under an assumption. The muscle strength is affected by the assumption and all sides of OFD. This paper proposes a new method for obtaining the muscle strength from corresponding sides of the OFD without the assumption. The method is based on minimizing the sum of the square of the muscle strength induced by the central nervous system which is called cosine tuning. The slope of each side of the OFD is formulated from the limb posture, which is applied to the measurement of the OFD. The muscle strength is independently derived from the corresponding side only. The proposed and conventional methods were applied to three subjects, and the result of the OFD and the muscle strength were presented.
This paper presents a simple method for determining synchronous machine quantities: d- and q-axes time constants and reactances. This method determines them only by drawing additional lines in the frequency characteristics of operational impedances. A new systematic drawing strategy for determining transient/subtransient open-circuit time constants and the d-axis transient reactance is proposed. The frequency characteristics of operational impedances are obtained by the standstill DC test using a small DC power supply. Since the rotational test becomes unnecessary, the proposed method is suitable for tests in a factory. The validity of the proposed method was demonstrated with a numerical calculation example on a large-capacity machine (800MVA, 25kV, 2 poles, 60Hz) and an implementation test on a small-capacity machine (10kVA, 200V, 31.9A, 4 poles, 50Hz).
This paper proposes a method to determine the regenerative brake characteristics of a battery-powered railway vehicle to increase its running distance on the non-electrified line and to decrease the required distance of the electrified line, considering two-quadrant chopper power. The proposed method is verified through experimental results.
This paper deals with a frequency domain based power controller for overhead line and electric double layer capacitor (EDLC) hybrid railway vehicles. The loss of EDLC causes an error in the proportional feedback control of the EDLC energy management. In this paper, a design method of the energy reference for compensating the error of the EDLC energy by using assumed average loss is proposed to improve the energy management accuracy of this controller. The effectiveness of this design method is verified by a small-scale experimental system.
Our researches focus on the haptics for remote operation based on motion control technology. These researches can apply to medical application and mobility system. Students can acquire design method for control-system as well as mechanical and electrical design by graduation work.