High power electrical conversion, sinusoidal inverter which converts dc source to ac source has been widely employed in such as the ac motor drive control systems. The off-line calculated optimal pulse width modulation (PWM) scheme has been proposed so far. By this scheme, the following high performances are available. 1) selective lower-order harmanics elimination. 2) adjusting the fundamental part to the desired amplitude. 3) the reduction in switching losses and the size of dc link filter. However, in practice, the fluctuation in dc voltage caused by the inevitably uncertainty of ac load offers poorr performance to ac output such as the remaining of error between its fundamental part and the desired value. In this paper, we propose an optimum switching control real-time scheme using the output feedback. This scheme attempts to adjust the switching angles of each period so that the cost function which measures the specific lower-order harmonics and fundamental harmonic error is minimized. Basicaly, it is difficult to control such switching angles because the cost function is nonlinear in the switching angles. To avoid such this problem the virtual pulseamplitude-modulation (VPAM) is introduced. Instead of calculation the switching angles directly we calculate the amplitudes of VPAM that linear for the cost function first. The switching angles or PWM, now, are calculated by approximation its pulsewidth with the pulseamplitude of this VPAM. The simulation and experiment are performed and these results show the effectiveness of proposed scheme.
Nonlinear loads using power semiconductor devices produce harmonic currents and reactive power in AC power lines. As they are popular in many fields, the elimination of harmonic currents and reactive power is one of the important research projects. This paper describes a control method and compensation characteristics of the combined filter system of a current source active filter and a high-pass-filter. The system senses three signals, load currents, source currents and line voltages, to create the reference signals of the active filter. The goal of this paper is to solve the problems: (1) A harmonic-enlarging effect due to the parallel resonance, (2) Filtering of the harmonic currents produced by source-side harmonic voltages, and (3) Drawbacks of analog control such as being sensitive to noises, etc. The transfer function of the current source converter is identified, and is used for designing the control system of the active filter. Digital control based on a DSP is adopted to remove the drawbacks stemming from analog counterpart, but it is found that it introduces a new problem, a computational delay in the output, that results in serious deterioration of the fiter performance. It is shown that the addition of the source current feedback can solve not only the delay problem but ones due to the parallel resonance and source-side harmonic voltages. Finally a small setup controlled by a DSP was built, and the validity of the proposed method was demonstrated by experimental results.
V/f constant controlled induction motor system is widely used in various industrial fields. However, this control has some unfavorable aspects particularly at low speed. To improve these problems, primary flux control is discussed in this paper. In this system, the primary flux of induction motor is controlled to be constant. If primary resistance is estimated exactly, this method can improve transient and torque characteristics excellently as compared with V/f constant control method introduced in the general purpose method inverter. In this paper, the principle of the control method and system configuration are discussed. By detecting primary voltages of induction motor using RC filter, the primary flux is dominated constantly. Since the primary resistance varies extremely by the motor temperature, compensating primary resistance variation automatically is also described. This paper also deals with performance characteristics of induction motor. The experimental results of the tested machine shows that the proposed method can be expected for the high performance general purpose inverter.
A new PWM method of the three-level inverter using a digital signal processor, which is useful for large capacity instantaneous current controlled GTO inverters is presented. In case of the three-level inverter, short pulses are always necessary to output medium voltage vectors. The output waveform deteriorates from the ideal PWM waveform by the influence of the minimum pulse width limit of the GTO thyristors. In this PWM method, firstly, the switching sequences of voltage vectors which enable the neutral voltage balance control are selected. And then, from these sequences of voltage vectors, sequences which are not affected by the minimum pulse width limit of GTO are selected. Using these switching sequences, the voltage vector mean value control PWM method based on the space-vector control is proposed.
This paper analizes some features of estimation error on the observer which estimates disturbance torque and velocity. This observer inputs the information of driving torque and current position, and outputs the information of disturbance torque and velocity. Although this observer is a practical tool to compose a robust control system, we have never enough information to make the most of it. So the study to grasp some basic features of the observer is needed now. And it is very inportant to analize the estimation error on it. Then, this paper considers the estimation error caused by disturbance torque and observation noise, because these seem to be the most significant causes. And the result of analysis gives the practical way to select a pole allocation of the observer. Finally, the simulation and the experimental results are shown.
A new control technique for voltage-fed and current-fed PWM three-phase converters (inverters and rectifiers) is presented. Approach is based on the application of the sliding mode design methods. A general mathematical description of the three-phase converters (buck and boost inverters and rectifiers) is developed. On the basis of this description the sliding mode controller is designed to obtain optimal PWM and desired closed-loop dynamics. Both, the PWM switching pattern and the closed-loop dynamics are addressed as a single control problem and the output of the controller provides direct commands for the converter's switches. It is shown that the same controller can be applied for all analyzed converters. The controller has a simple structure and is suitable for digital implementation. Simulation results are provided to confirm theoretical predictions.
When magnetic fields in electrical machines with moving conductors such as linear induction motors are analyzed, eddy currents due to the movement of conductors should be taken into account. Although two kinds of coordinate systems (moving and fixed coordinate systems) can be applicable to the analysis of eddy currents in moving conductors, the advantages and disadvantages of both coordinate systems are obscure. In this paper, methods for analyzing magnetic circuits with moving conductors are systematically classified, and the moving and fixed coordinate systems are compared with each other from the standpoints of accuracy, memory requirement and CPU time. It is shown that the moving coordinate system is superior to the fixed coordinate system for transient analysis.
A couple of pulse septum magnets is used to inject a 800MeV electron into the superconducting electron storage ring of Mitsubishi Electric Corp. The beam orbit simulation indicates that the apparent septum width of the magnet should be less than 3mm to obtain the good injection efficiency into the ring. To perform the requirement and overcome the problems of heat dissipation and Lorentz force, the molded type septum magnet is designed and fabricated. The fabricated magnet is 1m long and has an aperture of 10mm height and 10mm width. The vacuum pipe of 0.3mm thickness is settled through the aperture for beam transport line (HBT line). The magnet is excited by a single turn coil to 1.8T at 17kA of a sine wave with a width of 4ms which provides a peak field uniformity of 0.1% for a duration of 12μs as required for injection. As for the apparent septum width, the width of 2.5mm, which includes the coil, coil holder, and thickness of the vacuum chamber of storage ring and HBT line, is achieved. The experiment of high energy electron beam transportation through the magnet has been done and the stable extraction from the magnet is observed.
In this paper we deal with a generator system by use of variable energy like a wind power. The variable energy has influence voltage and frequency of a generator system. However, load requires constant voltage and frequency. Therefore, this paper proposed that a generator system have good points as follews: (1) This generator is brushless system make used of Multi-Field induction machine. (2) Frequency converter of small capacity used for constant voltage and frequency in load at variable speed. (3) PWM Inverter can supplying reactive power to Self-Excited generator. (4) Voltage wave of load is sine wave by LC filter of the frequency converter. The Multi-Field induction machines of this generator system have 4 poles and 8 poles as a same stator winding. The rotor of Multi-Field machine is especially cage type. This rotor can transform among 4 poles field and 8 poles field on the stator. In the present paper, we described an experimental study of the brushless, Self-Excited, constant voltage, constant frequency, variable speed and sine wave generator system by Multi-Field induction machine. We described component of this generator system, operation of Multi-Field induction machine, characteristics of generator system, and effect of LC filter in frequency converter.