In a PWM inverter, the PWM signal with the dead-time is usually used to protect the short-phenomenon of a pair of main switching devices in the inverter. The dead-time causes the waveform distortion in the output voltage and interrupts the high carrier frequency drive of the inverter. In order to solve these problems, a novel PWM inverter is proposed in this paper. The proposed PWM inverter is realized by performing zero current switching at the turn-on of the main switching devices and generates the output voltage without a waveform distortion, although the inverter is driven by the PWM signal with the dead-time. The zero current switching is achieved by connecting in series an inductor and a capacitor between the output terminals of a conventional inverter.

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When a servo motor controlled by the conventional PI controller is employed to drive a mechanical load such as a robot manipulator, the response of position control is limited because of the elasticity and the non-linear characteristics of the mechanical load. In order to solve this problem, we propose a new position controller based on the two degrees of freedom control method. In this controller, we incorporate a reference model which is a position control system model with desirable dynamic performance. By utilizing the output signals of this reference model as feedforward control signals, the command input response can be improved to a great extent independent of the disturbance response which is affected by the characterisitics of the mechanical load. We also propose an auto-tuning method of this controller. Experimental results clarify that our controller has excellent dynamic performance compared with the conventinal PI controller and show that the auto-tuning of the controller gains is executed correctly.

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In most voltage-fed inverter drives, three-phase diode bridge rectifiers with a filter capacitor at the DC side are often used. In this type of rectifier, the harmonic levels of the line current are well known to be quite high. So far, a time simulation method has been used to analyze the harmonic current. This method is very accurate, but it requires a long computing time and a complicated algorithm.
This paper proposes a practical new method to easily calculate the harmonic currents for both the continuous and discontinuous current conductions. The proposed method is based on the frequency domain method and the rectifier switching functions. Analytical equations for the harmonic currents on both the DC and AC sides are derived, taking into account the effects of filter capacitance and line reactance. All the calculations are conducted only by algebraic calculation with high accuracy. The effectiveness of the proposed method is confirmed by comparison with the results obtained by the simulation method.

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The vector control is one of the method to obtain superior control performance to a direct current motor for an induction motor driven by the inverter. As to the vector control method, the inverter slip frequency ω₂ of an induction motor is controlled for the purpose of the torque being proportional to the torque current. However, exact vector control cannot be achieved, because the secondary resistance varies extremely by the rotor temperature.
To improve this problem, several countermeasures have been proposed. But most of these methods need complicated system construction or any other parameters exactly.
In this paper, auto-tuning system to adjust phase deviation between γ-δ and d-q axis due to estimating error of secondary resistance to zero by using exciting current differnce is proposed. In this system, only a PI compensator is needed in the loop to decide angular frequency. By using gain and phase margin based on frequency response, optimam gain value or influence of other parameter are evaluated easily. Therefore, stable and high sensible vector control can be achieved.
This paper also describes the field oriented vector control system without magnetic sensor by applying the principle of this method. Furthermore, the method of estimating ω_m and the performance characteristics of the vector control system without speed sensor are discussed. The experimental result of the tested machine shows this method is very useful for practical applications.

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Parametric oscillations occurred in a nonlinear two-phase circuit with nonlinear reactors and capacitors are applied to many kinds of power devices. When the devices are operating under light loading, the output voltage of these devices shows unstable oscillations: subharmonic oscillations, quasi-periodic oscillations or chaotic oscillations. This paper deals with an analysis of the abnormal oscillations and verify the validity of the analysis experimentally. In this paper, the authors offer new circuit equations that can be applied to the analysis of two-phase. nonlinear circuit in which reactor saturation curves are sharp. It is clarified by this analysis that the parametric oscillations of the circuit which contains reactors of moderate saturation characteristics become subharmonic or quasi-periodic oscillations with the existence of resistances of the power supply side; and when the nonlinearity of the reactors in the circuit is sharp, the parametric oscillations may change into chaotic oscillations besides the aforesaid oscillations.

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This paper presents the description and analysis of a half-bridge IGBT inverter suitable for heating ferromagnetic materials at high-frequency. The series-parallel scheme is adopted and, an optimum mode of operation is selected which results in a maximum current gain and practically no voltage spikes in the devices at turn-off. Using the state variable approach, the inverter system circuit model was analyzed including the effect of branch stray inductances and snubber components.
The actual performance was tested on a 50-150kHz prototype rated at 6kW. The developed hybrid inverter is characterized by its simplicity of design and operation, yet is versatile in performance. Experimental evidence is presented to confirm the validity of the inverter system model.
Also, an analytical model for the long billet-short coil induction heating geometry is briefly described. The resulting expressions for the induction heating load parameters are obtained in the form of rapidly converging series. The theoretical results obtained have been experimentally verified.

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This paper considers the identification for linear system of unknown order.
First, we hypothesize some candidate models which have different orders. For each model, we estimate the unknown system parameters and calculate its a posteriori probability by Bayesian theorem. Then we select the optimal model on basis of the a posteriori probability.
Next, we renew the candiate models in consideration of asymptotic property of a posteriori probability, when we have poorly priori information of system order.

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In order to obtain a non-overshoot and fast response in a servo system, approaches using nonlinear compensation actively have been proposed. This paper makes it clear that excelent performence can be obtained by using a hysteresis element in speed control system. This control law can be realized simply by changing the P element of PI controller into a non-linear hysteresis element. The finite time settling response which is non-overshoot and fast can be obtained. Therefore this control law is named Hysteresis plus Integral Control.
In addition, it makes clear that control law is an expansion of Hysteresis feedback control which has been presented.
The approach is examined by some simulations and experiments. As a result, it is confirmed that Hysteresis plus Integral Control is a effective law for finite time settling compensation of a servo system.

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The paper describes analytical and experimental studies on a 2nd-order delta-sigma modulated inverter with a carrier signal. Such a system can be interpreted as a triangular-carrier PWM inverter accomodated by a 2nd-order integral feedback control. An accurate waveform and high immunity to disturbances from the power supply can be expected because of a high loop gain due to the integral control. Being synchronized to a high-frequency carrier, the inverter serves as a moter drive with low acoustic noise. The analysis leads to a condition for a high feedback gain and the synchronism to co-exist. Three types of control schemes based on the condition are tested experimentally. Even with the simplest fixed-parameter configuration, a noise level of more than 70dB below the maximal output is recorded over a range including the DC and the carrier frequencies. Disturbance rejection in this system can be improved by about 10dB by a higher-gain control incorporated with on-line adjustment of transfer parameters.

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The mutual interacton between zero-phase-sequence and negative-phase-sequence circuits in a salient pole synchronous generator is proved experimentally and theoretically. In the method of symmetrical coordinates, it has been believed that positive-, negative- and zero-phase-sequence components are independent. But an experiment driving a synchronous generator with unbalanced load shows that negative-phase-sequence voltage is induced when only zero-phase-sequence current is applied. These interaction between negative- and zero-phase- sequence circuits are proved theoretically by magnetic flux distribution in the air-gap of synchronous generator. The m. m. f. by zero-phase-sequence current generates negative-phase-sequence flux distribution by the saliency of the rotor and the field current 2nd harmonics and vice versa. The revised exprssion for synchronous machine in the symmetric coordinate is proposed.

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Since there are no iron cores in the rotor and stator windings of superconducting synchronous motors, some reactances are intrinsically smaller than the ones of conventional motors. So the low synchronous reactance would be expected to improve the torque-ampere ratio stability and the overload capacity in case of the variable speed drive system of a load commutated inverter due to the small armature reaction. Moreover, the low sub-transient reactance may contribute to lessen the voltage stress during the shortened commutating period, especially in current source type inverter (CSI) systems.
In this paper, after presenting analytical formulas needed for a machine design, one design algorithm is described, citing one example of an experimental CSI fed superconducting motor of 30 kVA which will be fabricated. Further, the distinguished features in its operation, as expected just above, are verified by the computer simulation study in comparison with a conventional machine in terms of a high specific power density, an extension of stable power limit and so on.

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In train speed control system, if we can detect the exact position of the signal section boundary, it can be used for an effective correction of the running distance without using any additional particular devices on the ground-side. However, in the conventional system using a signal detection coil, it has been impossible to detect the section boundary because we can not distinguish the signal change in one section from one caused by passing through two different sections.
In this paper, we propose the novel detection method of the section boundary by using two groups of search coils, which are eqquipped under the floor at the center of the rolling stock. By the experiment on the real test line, we show that the section boundary is effectively detcted based on the difference between the two signals received.

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