We propose a novel speed sensorless vector control method for induction motors, which is applicable to industrial drive systems.
This method calculates the flux axis angular velocity and rotor speed of an induction motor from the induced voltages, without using any delay components. According to this method, the system can directly estimate an accurate motor speed, and precisely generate torque.
In addition, this system can smoothly restart operation after an instantaneous power interruption.
We show the validity of the proposed control method through several experiments.

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Three-phase small squirrel cage induction motors have been used in a variety of industries for many years. Reduction of vibration and noise caused by electromagnetic forces has been recently urged due to environmental concerns.Vibration is produced by a deformed stator core caused due to electromagnetic force. The relationship between the shape of the deformed stator core, the wave of electromagnetic force and the natural frequency of the stator core was numerically analysed and compared with measured results.
First, the motor's natural frequencies and modes were analysed through FEM analysis and experiments. Next, the induction motor vibration due to various electromagnetic forces was analysed using FEM and was measured. From these analyses and experiments, it was confirmed that the mode of electromagnetic vibration was dependent on the mode of a nearby natural frequency.

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We have already proposed a six-phase pole change induction motor (six-phase PCIM) for electric vehicles (EV), and have been making clear about its operation principle and steady state characteristics. The six-phase PCIM further expands the constant power operation range using the pole change technique without mechanical contactors, therefore it possesses the superb characteristics to miniaturize the EV's driving systems.
This paper proposes a new analyzing method for the six-phase PCIM in order to derive the basic equations which can be utilized to analyze the transient phenomena caused by pole change and to create the control methods. First, a “six-phase tensor-transformed rotational d-q axis” (provisional name) will be defined, and its physical meanings will be made clear. By using this axis, the voltage and torque equations which can uniformly deal with the steady state and the transient state will be derived.
Next, comparative examinations between the measured results and the simulated results regarding the voltage, current and torque characteristics on the steady state and the transient state at the pole change operation and the both poles dual operation will be achieved. Through these examinations, the propriety of this theory and its effectiveness in the further detail performance analysis and the application to the control method for the six-phase PCIM will be discussed.

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A study on efficient excitation system must be important to enhance the potential of superconducting AC generators further. Based on this thought, we have fabricated a model machine for generating actual electricity with a brushless exciter system, which consists of aa supercondudcting dynamo or “magnetic flux pump”. The fully superconducting generator has also been studied, in which both of armature and field windings are made of superconductors.The paper presents actual power output tests and calculated results in transients as well as static electrical characteristics of the model machine with the magnetic flux pump when operated as a fully superconducting brushless generator in persistent current mode.

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Auxiliary power supply systems, or SIVs (Static Inverters), which feed electric loads in rolling stocks have been used instead of motor-generator systems (MGs), because they have many advantages over the MGs including weight, seize and ease of maintenance. Recently, SIVs using the IGBTs (Isolated Gate Bipolar Transistors) with high switching frequency have been developed, which are expected to achieve stable and high response of the output voltage. In the SIVs, it is needed to suppress resonance of LC filter which is connected to reduce harmonics of the output voltage. Therefore, in order to realize high response of the output voltage, instantaneous voltage control which can suppress the resonance is needed. This paper proposes a new instantaneous voltage control method for SIV, which can suppress the resonance of LC filter and achieve high response to disturbance without static error with simple structure of control system. Simulation results show effectiveness of the method.

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In this paper, different sliding surfaces are analyzed for the SEPIC converter. The simplest discontinuity surface leading to a stable equilibrium point corresponds to the constant input current. A fast transient response is obtained when a linear combination of the input and the output voltage is used to control the converter. Other sliding surfaces providing adaptative control schemes are also investigated to attenuate perturbation effects in the input voltage or in the output load.

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A new AC/AC power converter topology, in which all the switches perform soft switching to reduce switching losses is proposed. The topology enables conduction-period control of individual current pulses, whereby PWM has been achieved. The scheme implements current peak (resonant) limiting by a simple diode clamp. Improved switch utilization (voltage. current) and reduced part-count could be cited as the merits of the circuit over the previous soft-switched, current-sourced AC/AC configurations. Moreover a simple controller, that generates “PWM current controlled, AC output voltages” is introduced, and experimental results are presented. In the scheme an indirect current feed-forward scheme which makes the system robust is introduced; scheme results in smooth controllable motor currents. Therefore, its applicability for a V/F drive is highlighted. For cases, where PWM is not possible, an alternative, current-controlled voltage-synthesizing method is introduced and simulation results are presented.

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A single phase high efficiency flywheel (FW) uninterruptible power supply (UPS) rating of 5kW and 200V-lmin is described. The UPS has following characteristics.
(1) Battery less system which makes maintenance free and long life about three times of a battery UPS.
(2) Simple power conversion circuit of 3 arms configuration which can realize high efficiency and small size.
Inside of the new flywheel unit rotating 15000rpm is vacuumized to eliminate windage losses by a zirconium getter pump. The flywheel rotor is made no mechanical touch by a pivot bearing in high speed states so as to get long life. Charging or discharging of the mechanical energy of the FW is achieved only by controlling the instantaneous slip frequency of the induction machine. The power conversion circuit is consisted of a 3 arms bridge which has a common arm of the both inverter and converter bridges. All control of the UPS is realized by simple programs on the single chip floating point DSP.

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The authors have previously presented a control scheme for synchronous reluctance motors where the motor current is controlled to keep the MMF phase angle constant, and made it clear that a simpler control scheme is possible by using a N-speed synchro for a 2N pole motor. However, conventional brushless synchros are expensive and bulky due to the intricate construction where the rotary transformer supplies current to the exciting winding on the rotor core. The authors have therefore developed a novel VR (variable reluctance) synchro without a rotary transformer, consisting of a stator core with both the exciting and output windings and a uniquely shaped rotor core with no winding.
This paper describes the theory of the novel VR synchro and presents measured waveforms of the output voltages of a prototype VR 4-speed synchro. In addition, a variable speed drive system for 8-pole reluctance motors which uses the new control scheme is introduced. In this system, the VR synchro is directly connected to the motor shaft, whose output voltages are demodulated and directly used as the current phase command for the inverter current supplied to the motor. Experimental results show a satisfactory speed response for 4 quadrant drive.

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Permanent magnet synchronous motors (PM motors) are used in many industrial applications as AC servo motors. Particularly surface mounted PM motors are most used in low power range. With recent developments of magnet materials, their high torque capability makes them suitable in middle power range.
In this paper, different magnet configurations are presented to get high torque to current ratio, and then electro motive forces (EMF) are distorted by a non-sinusoidal flux density distribution. In this case, a sinusoidal current produces torque pulsations.
To eliminate these pulsations, an adequate instantaneous current is computed. Consequently high torque to current ratio are obtained with adequate current.

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A capacitor-filtered single phase rectifier circuit has been widely used in the household electronic apparatuses. This rectifier circuit generates many harmonic components in the AC side current. This generated harmonics may cause various disturbances.
So, in this paper, we propose a reduction method of the harmonic currents based on the principle of constant resistance circuit. And we carry out the analysis of the circuit, and describe the design method of the circuit constants on the DC side of the rectifier circuit. Furthermore, as an example, we consider the application to a television set, which occupies a majority of harmonic currents on the power distribution systems, and clarify the reduction effects of this method.

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