In this paper, we describe the theoretical aspects of the flux feedback type vector control system based on the flux observer, giving emphasis on its robust stability to the secondary resistance variation. The main reason for our success in realization of this control system is the desensitization of the flux observer. Actually, robustness of this control system entirely depends upon that of the flux observer. First, we clarify a class of flux observers and derive its general structure and pole allocation to accomplish its desensitization to the secondary resistance variation. Then, we show that in our proposed vector control system, right half plane zeros (i.e., unstable zeros) may appear in the open loop system with changes of the secondary resistance; we, however, can avoid their occurrence by the pole allocation method of the flux observer. Furthermore, we establish the design criterion for the feedback gain and the pole allocation of the flux observer which guarantees robust stability of this control system, by exploring the influence of such zeros on the flux feedback control system. Finally, by theoretical and experimental approaches, it is shown that our proposed vector control system has an extremely low sensitivity to the secondary resistance variation in comparison with the slip frequency controlled type vector control system.
For the voltage source type inverters, it is easy to improve the output waveforms, and the influence to the switching devices by the surge voltage is small. For power regeneration, however, it is necessary to add another converter to the AC power source. Among such converters for regeneration, the PWM converters have been often reported, which are excellent circuits. For the weak points, however, high cost could not be avoided as the capacities increase, because three AC reactors, and relatively high speed GTOs or power transistors should be employed. From such a viewpoint, the authors have investigated how to accomplish that the thyristor rectifier could be used even for regeneration. In the proposed equipment, the usual rectifier bridge can be also used for inversion through the medium of the DC reactor. The commonly used current smoothing reactor for rectification could be also used for the operation of this DC reactor. In the proposed method, by using one transistor of self commutation and six thyristors of external commutation, the PWM waveform control can be accomplished. For the frequency analysis of output current waveforms, the authors have proposed a frequency analysis method which can give definite output equations. The validity of its theory has been confirmed experimentally.
For the pulling in performance of synchronous motors, it is desired generally to improve the limit of synchronization and to eliminate the rotor transients as fast as possible. Since the system of the motor is represented with a nonlinear differential equations, the analysis of pulling-into-step phenomena is difficult to treat quantitatively by conventional methods. In this paper, a method is presented for deciding the most favorable angle to improve the synchronization by using performance index and the on-off excitation control is proposed for removing rotor transients. A Lyapunov function is used for performance index, which can evaluate the stability of a nonlinear system. The most favorable angle and the instants of the excitation control can be derived quickly even in on-line system. The on-off excitation control is a new control strategy differing from conventional optimal control method, that is valuable for implementation to remove rotor transients. The proposed method is applied to the practical system, and the possibility to improve the synchronism is shown experimentally.
This paper describes a new type of a simulator for solar cell module which can represent both its static and dynamic characteristics also. The way of generating the static characteristics is made through the use of piecewise linear approximation. The complete piecewise curve is obtained by the summation of individual line segments whose breakpoint currents and slopes are determined separately for each segment. Such segments can be generated with diode bridge type analog switch circuits and summed by the series connection of those analog switch circuits. On the other hand, as the dynamic behavior can be represented by the C-R first order lag circuit, it is necessary for the simulation of the dynamic characteristics that the capacitor in switched in accordance with the slope of the straight line segment. The switching of this capacitor is achieved easily with the diode analog switches also. The proposed simulator is practical and represents both the static and the dynamic characteristics of the actual solar cell module.
This paper deals with the analyzing results of rotating resistance of a magnet base from both the sides of theory and experiment. The value of rotating resistance of the magnet base has been decided mainly by materials of the permanent magnet in the magnet base through the experiences, but the suitable explanation on the rotating resistance has not yet been established. In this paper, the following points are discussed. (1) An actual permanent magnet within a magnet base is rotated on the yoke in eccentric contact condition. Here, it was assumed that the permanent magnet was rotated on the yoke in non-contact condition with gaps from 0.1 to 0.3mm. The theoretical expression of the rotating resistance was derived by the permeance analysis method. (2) The calculated values of rotating resistance by the theoretical expression with ferrite and alnico magnets are almost consistent with the measured values. (3) It is clarified that the rotating resistance of the magnet base with the ferrite magnet is about 50% less than that with the alnico magnet from a viewpoin of the theory as well as experiment. It can be explained that the values of rotating resistance mainly depend upon the recoil permeability of permanent magnets.
The effects of chopping frequencies and sampling periods on the stability of a digitally-controlled magnetic suspension device using a DC chopper have been studied. The use of a DC chopper for controlling the magnetic coil current gives low loss and high-current control capability in comparison with the use of a conventional linear amplifier. Digital control enables the system to be more flexible and advanced than analog control. However, the DC chopper causes current ripple and control dead time, and the digital control system causes control delays due to computation time. These factors will affect the stability of the suspension device. First, we neglect the chopping operation and deduce a linearized state equation around the neighborhood of an equilibrium position, and then design an optimal regulator. Next, we consider the control delay and calculate the eigen values of the system. Further we take the ON/OFF operation of the chopper into consideration and neglect the control delay and then calculate the eigen values. The both calculations show that the two factors have relatively small effect on the stability when the sampling period is less than 7 ms. The experiment revealed that the major factor which makes the device unstable was the noise of the current feedback signal produced by the asynchronous operation of chopping and sampling. When the ripple is filtered out, the lower stable operation limit of the PWM frequencies is close to the theoretical values. As a result, the device is unstable regardless the chopping frequencies when the sampling period is very long. When the sampling period become shorter than 7 ms and at high PWM frequencies we can use a simplified model neglecting the control delay and the chopping operation. At lower PWM frequencies a model considering the control delay is effective when using a current filter.
The DC source of an inverter is, in many cases, composed of a diode bridge rectifier circuit with a smoothing capacitor in the DC link. Due to the existence of a large amount of harmonics in the AC line current, the inductive interference and low effective power factor have been serious problems. In this paper, the authors propose a new current control scheme of the three-phase PWM converter, which can suppress the harmonics of the input current and achieve the unity power factor. The current control is performed with the instantaneous voltage equation of the converter and the system parameters in the equation are identified by the model reference adaptive system. Therefore, the high performance current control is achieved even if the converter parameters are unknown. In the parameter identification, the number of the identified parameters can be halved to reduce the calculation time by introducing the complex plane to describe the state equation. Furthermore, the identified parameters can converge to the real parameters even if constant control input is given. The stability of the identification algorithm is proved with the hyperstability approach. The effectiveness of the proposed current control has been demonstrated by simulations and experiments. In the prototype, a DSP (TMS 320C25) can perform all necessary controls by software, and, as a result, a simple controller has been constructed. The sampling period was 255 μs and the switching frequency of the converter was 1.5 kHz. The time required to converge the identified parameters was within 5 ms and the current was settled with one sampling (255 μs) when reference current was changed from 2 A to 10 A.
Recently, in ordor that rotational speed of DC machines may become faster, conditions on commutation are strict more than ever. In these cases, it is important to evaluate the performance of carbon brush materials accurately. This paper describes the new method evaluating brush materials and experimental results based on the new proposed method. Performance of brush materials has been evaluated by the tests obtaining characteristics of sliding contact and of commutation. However, a tendency of results obtained by these tests has not agreed with that of experimental results by using DC machines. In this paper, the authors propose a new method to evaluate characteristics of commutation and sliding contact. The features of a proposed method are as follows: (1) ‘Degree of contact disturbance’ is used as a way of estimations for sliding contact characteristics. The degree is time-dependent fluctuation of sliding contact voltage. (2) Performance of commutation is reviewed by using a new expression of the spark region. In order to realize these evaluation, testing machine for observation of flash was produced. The tendencies between obtained characteristics by produced testing machine and experimental results tested by DC machine, show good agreement. The validity of these evaluating method is confirmed.
We have already proposed a linear actuator which is very simple in the structure. In the previous paper, the analyzed results of its static and transient characteristics have been reported. The analyzed results have shown good agreement with the measured results. The analytic method to get the calculated values is very simple and easy without the complicate mathematical technique. It is important only to know the permiance distribution in the magnetic circuit exactly. The calculated values of the flux density, the phase angles, the thrust force, etc. agree well with the measured values of them. However, when the exciting voltage raises to high, the magnetic saturation phenomenon occurs in the iron core and affects the calculated values. In this report, the improved method is explained which was taken account of the influence of this magnetic saturation as a numerical expression of the magnetizing curves of the iron core. By use of this advanced method, the calculated values of the ring velocity and the variations of the coil current have good agreement with the experimental results.
On a variable speed control of motors used in industrial plants and industrial robots, a shaft torsional oscillation is often generated when a motor and a load are elastically coupled with a shaft. Such an oscillation may result in damage to the machine. This paper is intended to theoretically explain the fact that a shaft torsional oscillation can be suppressed by using the digital observer regardless of the presense of the gear. In this paper, we conducted tests on two shafts with resonant frequencies at 10.5 Hz and 16 Hz using a full-digital control equipment for controlling DC motors with the digital observer in order to confirm the oscillation control effects.
This paper deals with the flux distribution in Ferrite Orthogonal Cores. The Flux distribution must be known to understand the operation of an FOC. We classify the components of flux into four parts according to the flux pattern by using a diagram of flux distribution. The flux control characteristics can be obtained by considering the component fluxes. The result of the analysis is a better understanding of the roll of the component fluxes in improving the performance of the flux control characteristics.