Hironori Okuda

Analytical Model for Magnetic Field Analysis of Induction Motor Performance

A numerical method of calculating the performance characteristics of three phase squirrel cage induction motors, which is based on the magnetic field analysis, is presented. A magnetic field is analyzed over a radial cross-section of a motor with a finite element method. Core saturation and induced rotor bar currents are calculated, and the actual configuration of a motor is analyzed, with this method.

Development of PWM Inverter Employing GTO

Application techniques of a gate turn-off thyristor (GTO) to a pulse-width modulation (PWM) inverter are presented. The switching characteristics of a GTO greatly depend on those peripheral circuits, so that it is very important to establish the application techniques to design the gate circuit and the main circuit of the GTO. For the gate circuit, the relations of the GTOs turn-off characteristics to impedance elements of an off-gate circuit and to the circuit system are described. For an on-gate circuit, a new narrow-pulse method is developed which can keep the conduction of the GTO in spite of the performance state of an inverter depending on the power factor of a load. Using this new on-gate circuit, the power dissipation of the gate circuit is reduced to one-fourth compared with a commonly used wide-pulse method. The transmitting section of a control signal is evaluated for disturbance of a PWM inverter, caused by switching operations. It is concluded that the gate circuit which is provided with separate power supplies used to turn the device on and off would be most advantageous. For the main circuit, the effects of the snubber capacitors capacitance and wiring inductance on GTO turn-off characteristics are considered. Also discussed is a protection method for the GTO at the occurrence of a short-circuit fault, which utilizes its self-extinguishing capability. Some practical examples of the PWM inverter employing the GTO for driving induction motors (IM) are presented. These inverters have been made smaller in volume or much higher in performance.

Microprocessor Control System with I/O Processing Unit LSI for Motor Drive PWM Inverter

In order to increase the performances and decrease the size and cost of control circuits for pulsewidth modulated ( PWM) inverters, a microcomputer control system has been developed. It consists of a microcomputer and an I/O processing unit large-scale integration (LSI) to control a variable-speed motor. The microcomputer performs complicated calculations and analyses of driving conditions. The I/O processing unit LSI detects motor driving states (analog to digital convsrsion and pulse count, etc.), generates PWM pulse outputs, and protects the inverter against overcurrents and power outages. The I/O processing unit LSI functions using the command data from the microcomputer. Conversion and count data can be sent to the microcomputer from the I/O processing unit LSI. For the convenience of interfaces to the microcomputer, all-digital logic circuits are developed for the I/O processing unit LSI. For example, PWM pulse outputs are generated by comparing digital data of a carrier timer and step level of a modulation wave. Undesirable harmonic components can be reduced easily by command data from the microcomputer.