This paper presents the new concept of voltage transient sag compensator and the experimental results of its 400V class compensator. This compensator is composed of the series connection of some inverter units with gradational output voltages. Because each output voltage is different by 2n times, an approximate sinusoidal voltage is generated by controlling operation of each inverter and compensates voltage sag of the power line. The new compensator can be directly installed in a power line without an insertion transformer and a large filter, and thus it is expected to be compact and economical system.
This paper presents the efficient operation method by interdependent use of condenser energy on the new concept of voltage transient sag compensator. This compensator consists of the series connection inverter units, and each inverter unit generates a different output voltage by 2n times. Namely, in this system, the compensation energy is accumulated in each inverter unit's condenser charged with different voltage by 2n times. The method proposed here, in any case of various levels of transient voltage sags on the power line, provides the efficient use of condenser energy of all these inverter units. The method of interdependent use of condenser energy is also verified by the experiment.
The superconducting magnetic levitation railway system (MAGLEV) under development in Japan uses a pulse-width-modulation (PWM) inverter for driving a linear synchronous motor (LSM). The inverter output voltage contains non-negligible harmonics which cause harmonic resonances in the LSM system, and therefore harmonics of the output voltage have been analyzed in order to control such harmonic resonances. This paper applies a third-harmonic injection method to the inverter for the purpose of enhancing the output voltage without changing the circuit configuration. It performs harmonic analysis of the output voltage of the inverter based on the third-harmonic injection. Validity of the harmonic analysis is verified by computer simulation.
In a large-scale inverter system that uses a semiconductor switching device, a rectifier and an inverter are connected through a DC circuit. In this circuit, the harmonic magnification phenomenon is often induced by the inductance of distribution wires and the condenser to absorb the harmonic voltage and current. To suppress this harmonic magnification phenomenon, we propose a new suppression method to use the initial phase of the carrier wave. When some inverters operate in parallel at the same frequency, such as the inverters to drive LSM, it is possible to reduce the specific harmonic component of the total inverter input current due to PWM control by changing the phase of the carrier wave of each inverter. We studied a method of suppressing the magnification phenomenon of the specific harmonic near the resonant frequency of the DC circuit by using this principle and confirmed its performance by the digital simulation.
A normally-off type 5kV class 4H-SiC JFET with low specific on-resistance, called SEJFET (Static Expansion channel JFET), has been fabricated. Its normally-off operation is realized at the temperature from RT to 600K. A very fast switching time of the 4H-SiC SEJFET are realized. The turn-on time at RT is 20ns and the turn-off time at RT is 47ns. In this SEJFET, temperature dependences of the output characteristics and transfer characteristics are evaluated. Its specific on-resistance has a large positive temperature dependence, and its transconductance has a large negative temperature dependence.
This paper describes commutation characteristics of snubber circuits of the PWM rectifier for the converter without DC link components. The DC link part of this converter has no smoothing circuit such as electrolytic capacitors and reactors. Therefore, one of the switches in the upper arms and one of the switches in the lower arms of the rectifier must be on-state in order to assure the path of the load current. The rectifier section of this converter requires the LC filter to improve the AC source current waveforms. Consequently, dead time should be applied to each of the commutation switches to prevent short circuit through the filter capacitors. The currents of the load are kept through the snubber circuit during the dead-time period. In this paper, we discuss an analytical method of the converter with the snubber circuit of the rectifier, and the experimental results are used to verify the analytical method. Next, the optimal snubber parameters are determined by calculation for 0.75kW induction motor driven by this converter. Finally, suitable snubber circuits for bidirectional switches are discussed.
With prevalence of information technology into our modern society and advance of automation technology in modern production process, the UPS market is assumed to make sustainable expansion. Error-Tracking-Mode PWM scheme offers novel constantly-sampled current-regulated switching algorithm to voltage-source power converters. This paper proposes a UPS in which Error-Tracking-Mode PWM scheme is applied to the current minor loop. The upper voltage control loop (ac-AVR) is developed afresh, that makes best of the PWM attributes. The equivalent output impedance of the UPS is derived theoretically for not only small signal but also large signal operation, that value can be arbitrarily specified by the ac-AVR parameters. A 3 kVA experimental setup was designed and fabricated, which has demonstrated the theoretical characteristics satisfactorily. The paper discusses the experimental results in detail. The authors believe that the paper presents a clue to realize independent and autonomic operation of dispersed PWM converters.
In this paper, a new visual feedback control for a swirling-flow melting furnace is proposed. This method control the furnace combustion by manipulating the burner fuel based on image data, which shows the melting situation inside the furnace. The feature of this control system is that, a visual-tracking property is realized by using an adaptive control algorithm which changes the control gain based on image evaluation as if the melting point varies. Through actual experiments, it is clear that its combustion can be controlled very precisely by this visual feedback control system.
This paper gives an analysis and design of a static synchronous compensator (STATCOM) using a series-connected hybrid multi-converter system. The hybrid multi-converter system consists of two GTO converters and an IGBT converter connected in series by transformers. The proposed STATCOM has advantages that the harmonic components of the output voltage/current would be less than a conventional configuration STATCOM composed of a 12-, 24-, or 48-pulse converter; the total switching losses would be less than a PWM STATCOM; and the response would be as rapid as a PWM STATCOM. One problem of the hybrid configuration STATCOM is that it tends to operate in an over-modulation range if a considerable compensating reference change occurs. To solve this problem, this paper also proposes a variable DC voltage control strategy, where the DC voltage is adaptively adjusted in accordance with the required reactive power. The validity of the proposed configuration STATCOM and control strategies are verified by simulation and experimental results.
The three-dimensional magnetic field analysis has clarified the effect of several structural and manufacturing factors on the properties of the outer rotor type stepping motors. (1) The number of rotor teeth, 128, can make a unit step angle under 0.5 degree and a cogging torque under 1mNm for the outer rotor type stepping motor with the outer diameter under 60mm and with the output torque above 0.4Nm. (2) The permanent magnet flux has an optimal value dependent on the thickness of the laminated core to maximize the motor torque. (3) The lamination stacking error of the small teeth of the rotor and stator has a large effect on the cogging torque of the stepping motor.
Recently, contaminated groundwater remediation is very important for human health. At present, human risk is calculated with in some assessment model. However, these methods can not reflect an optimizing control. Therefore, this paper proposes a decision support system for effective pumping rate by using risk assessment model. New DSS uses a fuzzy inference to be optimum pumping rate. And human risk was calculated by using monitoring data. Thereby, Engineer becomes possible to remediation with public acceptance. In this paper, outline of numerical method is explained and the numerical examination results are shown.
This paper describes a prioritization scheme for robot-control-related data that are transmitted via a real-time network system. The network system is constructed by a device named Responsive Processor and the network is applied to a bilateral robot system. The robot system is driven by a controller based on impedance matching theory. Due to a limitation of the network capacity, the priority order of the robot-control data must be determined. We analyzed a control system with time delay and assigned the priority order considering the robustness against time delay. To evaluate the priority assignment, we conducted experiments on a network based bilateral robot. The experimental results verified both the prioritization scheme and the order of the priority assignment.