For microwave ovens, the transformer needs reducing the weight. The continuous adjustability of output power is also required to improve cooking performance. Recently resonant inverter type power supplies for microwave ovens have been examined, but the output power ability has not been examined in datail. We studied the relation between circuit parameters and the characteristics of the power supply with a transformer that works also on resonant reactor. As a result the output of the power supply was related to the leakage inductance of the transformer. Finally, we discussed about the experimental result using this instrument. The output of the power supply can be continuously controlled in the range of 10 to 100%. Furthermore, adoption of this inverter can reduce the weight of the power supply to about 2/3.
A DC brushless motor is a kind of a synchronous motor driven by the inverter and needs sensors to detect the rotor position. As one of the methods, the induced voltages of a brushless motor have been utilized practically. However, there are some problems in this method, such as the motor can get insufficient torque on account of the low induced voltages in a low-speed range. This paper proposes a new method which controls the inverter angular frequency ω1, by using inherent characteristics that the torque current ir, is almost proportional to the internal phase angle φ where the primary flux of a synchronous motor is controlled to be constant. If the parameters of a motor are given exactly, the speed regulation is quite little and the transient characteristics with high response and high starting torque are obtained. Furthermore, it is possible to operate a synchronous motor in the field weakening range. Here, the principle of the control method and the performance characteristics of a DC brushless motor having no position sensors are discussed. The simulation and the experimental results of the tested machine show that the proposed method is very useful for practical applications.
A dual type inverter for increasing the capacity of a current source inverter with sinusoidal outputs is presented. Its main circuit configuration is very simple. Only one rectifier is used for supplying the dc power to two unit inverters, and the ac output terminals of each unit inverter are directly connected in parallel without a transformer. Since the dc power source is shared, the mean dc link voltage of each unit inverter must be equalized for current balancing. This can be achieved by supplying pulse-width modulated gate signals in the period of 120° and 180° in each unit inverter alternately. According to the experimental results obtained when a 1.5-kW induction motor is driven by a 2.5-kVA inverter, good current balance between the unit inverters is achieved. Both output voltage and current waveforms become almost sinusoidal. The 2-μF output terminal capacitor for overvoltage absorption and GTO switching frequency of about 1.2kHz are sufficient to produce sinusoidal output waveforms in the tested equipment. Since the harmonics contained in output voltage and current in the wide frequency range are decreasing even in the low GTO switching frequency, this strategy is suitable for increasing the capacity of a current source inverter with sinusoidal outputs.
Recently, advances in office and factory automation equipment have led to the development and commercialization of direct drive systems using linear motors. In fact, it has also been reported that X-Y plotters have been marketed as plotters that use two linear motors (one for the X direction and another for the Y direction) and air bearings. However, the authors have yet to withness the practical development of a direct-drive Surface Motor (“SFM”) that can operate in these two directions under direct drive and using only one motor. In view of this situation, the authors proposed an SFM that enables bidirectional motion and reported upon its basic structure and specifications. The SFM's stator is a checkerboard arrangement of N-pole and S-pole magnets, laid atop a back iron plate. The mover is a bakelite truck platform that includes core coils. The SFM and the PM-type linear pulse motor both use the same operation principle. In this paper, the authors will show the mathematical development that supports its bidirectional control system, and report on the results of prototype drive tests. The authors have developed a drive system that enables excitation. The excitation sequence is generated by a computer. The authors conducted drive tests based on the drive principles described above.
Recently, adjustable speed hydroelectric power systems have been developed. In those power systems, AC exciting synchronous generators are used, instead of ordinary salient-pole type synchronous machines. However, some higher harmonic sequences are included in the distribution of air gap magnetic flux density and in the terminal voltage waveform of the AC exciting synchronous machines, because these machines have open winding slots. In order to develop better machines without terminal voltage waveform distortions, an evaluation method of the terminal voltage harmonics has been needed. The authors describe mechanism of higher harmonics generation qualitatively and propose an analytical method of no-load terminal voltage waveforms, on the basis of two-dimensional magnetic field analysis considering movement of the rotor, for quantitative higher harmonics analysis. The analytical results of higher harmonics show good agreement with the experimental ones.
Analysis of DC brushless motors has been done without considering the inductance of the stator windings. Therefore, characteristics of velocity (N) -torque(T) -current(I) have been straight lines. The effects of the inductance are not negligible and the actual N-I-T characteristics are quite different from calculated ones. We set up circuit equations taking into account the drive circuit, resistance and inductance of the stator windings and waveform of back e. m. f., to analyze small DC brushless motors. Obtained characteristics showing curved lines agree well with actual ones. With the results, trial-and-error design process became possible to be removed and efficiency of the motor design was improved.
When a large crane is used near a medium wave radio broadcasting antenna, it operates as an effective receiving antenna and a voltage induced at a crane hook which gives a worker an electric shock. In a practical experiment, we successfully developed an attenuator which employs a passive electric circuit to install those cranes, and announced the experiment results. In this time, we theoretically analyzed this attenuator which employs a passive electric circuit and show the design method of a passive attenuator from the results of analysis. In this paper, first the equivalent circuit of the crane equipped with the passive attenuator as a receiving antenna is induced. We show that the attenuated characteristics of a passive attenuator by the model experiment accords with the theoretical attenuated characteristics which employ an equivalent circuit under the same condition.
The squirrel cage type induction generator is suitable for small water power stations and wind power stations because of its simple and rugged structure, and low construction cost. But the transient rush current flows into the primary and secondary windings when an induction generator is abruptly connected to a utility power network. The inrush current causes the voltage fluctuation in the power system. Therefore the electric power company needs the control method with low cost of the inrush current of the induction generator. So we have to know many properties of the inrush current in detail. The factors affecting inrush currents are system voltages, controlling the system voltage phase angle, rotary speed, residual magnetism of the core, and residual electric charge of the primary windings. In this paper, the inrush current is analyzed by the instantaneous value symmetrical coordinates. The experimental study of the inrush current using phase controll equipment and a small induction generator is mentioned. The conclusions of this investigation are summarized as follows: (1) The factor that gives the strong influence on the inrush current is the voltage phase angle. (2) Although rotary speed changes from 0.9 to 1.15 times as much as the synchronous speed, the maximum value of the inrush current is nearly constant. (3) The maximum amplitude of the inrush current is definitely seen in the first or second wave.