Hitachi, Ltd.

Shigetoshi Okamatsu

Hiroshi Narita

Masahiko Ibamoto

Toshiaki Okuyama

Takashi Tsuboi

Koichiro Nagata

Koichi Miyazaki

Hirohisa Satomi

Daisuke Tan

Hiroshi Fujii

Masato Suzuki

Akira Horie

Tokunosuke Tanamachi

Eiji Kozu

Tadashi Takaoka

Yoshio Nozaki

Yoshitoshi Akita

Kingo Abe

Noboru Oouchi

An induction motor drive includes a plurality of inverters, a changeover switch which changes over outputs of the plurality of inverters to be supplied to one induction motor and a changeover controller which controls the changeover switch on the basis of a failure detection signal of one inverter to change over from the one inverter to another inverter to start the other inverter so that the induction motor is driven. The changeover controller includes a frequency/phase detector which always detects a frequency and a phase of a terminal voltage of the induction motor and a starting frequency/phase setting device which controls a frequency and a phase at starting of the other inverter in accordance with detected values of the frequency/phase detector when the failure signal is inputted.

Apparatus and method for driving an induction motor

An electric power converter apparatus having a function of converting a power source voltage into an AC voltage having an arbitrary frequency and maintaining an output voltage constant even on the power source variation, in which the electric power converter apparatus decreases the output voltage when the output voltage drops to equal to or less than a predetermined value, afterward, increases the output voltage in response to a predetermined rate of change when the power source voltage rises.

Electric power converter suppressing output voltage variation due to input voltage fluctuation

A motor driving apparatus including inverter apparatuses, inverter control circuits, and a plurality of inverter control apparatuses for performing variable-speed driving of a single motor, breakers each of which being provided between each inverter apparatus and the motor, the inverter control circuits being connected in parallel to each other. Here, a motor rotation frequency/phase detection circuit of each inverter control circuit is set up on a closer side to the motor than the breakers, then frequency and phase of a terminal voltage at the motor are detected and inputted into failure-time input frequency/phase setting circuits regardless of close/open of each breaker. This feature allows computation by the failure-time input frequency/phase setting circuits to be carried out at all times, thereby making it possible to shorten a computation time needed for computing inverter-apparatus start frequency/phase.

Motor driving system and motor driving method

For use in a system in which a capacitor is connected between an AC machine and an inverter in order to improve the power factor, a controller for an AC machine capable of even when the overvoltage occurs due to the self-excitation between the AC machine and the capacitor, reactivating stably the inverter to continue the running. When the operation of the inverter is stopped and then the inverter is reactivated, the manipulation of starting the switching of the inverter is performed after a DC voltage of the inverter has been decreased to the operating voltage in the running, whereby the reactivation is performed stably without stopping the system.

Controller of AC machine

An electric motor is rotated at a velocity &ohgr; . After that, during &Dgr;t seconds, the 1st acceleration is executed at a rate (&ohgr; &minus;&ohgr; )/&Dgr;t . During this acceleration, the torque &tgr; is calculated so as to execute the time integration. After the lapse of &Dgr;t , the integrated result is stored. Next, the velocity is set to be &ohgr; . After that, during &Dgr;t seconds, the 2nd acceleration is executed at a rate (&ohgr; &minus;&ohgr; )/&Dgr;t . At the 2nd acceleration, although the integration-starting and the integration-terminating velocities are each equal to those at the 1st acceleration, the acceleration rate is modified (&ohgr; &equals;&ohgr; , &ohgr; &equals;&ohgr; , &Dgr;t &ne;&Dgr;t ). During this acceleration, the torque &tgr; is calculated so as to execute the time integration, after the lapse of &Dgr;t , storing the integrated result. The inertia J is calculated using the 1st and 2nd integrated results.

Method for calculating inertia moment and driver for electric motor

A DC voltage on an electric car stringing is supplied to a variable voltage and variable frequency PWM inverter so as to be converted into a three-phase alternating current which is supplied to a plurality of three-phase induction motors. The motors are connected to different wheels to drive an electric car. The inverter is controlled on the basis of an operating frequency command determined by adding or subtracting a slip frequency command to or from a motor speed and a voltage command proportional to the operating frequency command. On the other hand, a motor current command is set and compared with a maximum current value of currents of the plurality of motors, and the slip frequency command is corrected in accordance with a difference therebetween. In a constant torque region of the electric car, a correction value increasing in proportion to the speed is then added to the motor current command, so that torque of motors other than a motor to which the maximum current flows compensates for a decrease in torque caused as the speed increases to improve constant torque characteristics.

Control system for induction motor driven electric car

A power converter such as an inverter or chopper using self-turn-off type semiconductor devices supplies power to an inductive load and free wheel diodes are provided so that the current flowing through this load circulates not through the power supply but through the free wheel diodes. When it is detected that the load current exceeds a predetermined value, the self-turn-off-type semiconductors which are conductive are turned off. At this time, the self-turn-off-type semiconductors which are turned on and immediately thereafter cause the recovery current to flow in the free wheel diodes are turned off not immediately but after the recovery current disappears.

Control system for power converter

An inverter using gate turn-off thyristors (GTOs) is controlled by means of pulse width modulation (PWM) to control the speed of an induction motor. If the current flowing through the induction motor becomes an overcurrent which can still be cut off by the GTOs, a gate off signal is supplied to respective GTOs to interrupt the overcurrent. If any one of arms respectively corresponding to phases is short-circuited, a gate on signal is supplied to all GTOs to distribute the short circuit current among the arms, and the main circuit is interrupted by a high-speed breaker. At this time, a simultaneous gate on signal is given priority. If the simultaneous gate on signal is present, a simultaneous gate off signal is disabled. Owing to this configuration, destruction of the GTOs due to consecutive guard operation can be prevented.

Guard system for inverter apparatus

For controlling the rotational speed of an induction motor, an inverter is provided which converts direct current to alternating current and feeds the converted current to the motor. The output voltage and frequency of the inverter is controlled by a pulse-width modulated control device. The number of pulses contained in a half cycle of the inverter output voltage are changed every time the inverter output frequency reaches one of plural predetermined reference values. The plural predetermined reference values are adjusted in accordance with the DC supply voltage and/or with the motor current.

Control of induction motor using PWM inverter

A sine wave of a frequency to be generated in an inverter is compared with a triangular wave having a frequency N times (N: 15, 9, 3, 1) the frequency of the sine wave, so that a modulated pulse train is generated thereby to control the inverter. This inverter supplies power to an induction motor. With the increase in motor speed, N is reduced until it finally becomes 1. When the inverter transfers from an idle state to an active state, N is inhibited from becoming 1 but set to 3 even if the motor is running at high speed.

Induction motor control system and method

A control system for an electric motor vehicle adapted to be driven by a group of induction motors, comprises a converter for producing an a.c. output to energize the group of induction motors, a frequency command circuit for producing a value representing a minimum number of rotations among those of at least two induction motors of the group added with a slip frequency in a power running mode of the vehicle on one hand and a value representing a maximum number of revolutions among those of at least two given induction motors of the group subtracted by the slip frequency in a regenerative braking mode, respectively, the values being utilized as frequency control commands, and a frequency control circuit for controlling the output for controlling the output frequency of the converter in dependence on the frequency control commands, thereby to improve the adhesion performance of the electric motor vehicle.

Control system for electric motor vehicle

A control apparatus is disclosed for an electric car having an induction motor supplied with polyphase AC power of variable frequency from a power converter so as to drive a driving wheel. This control apparatus comprises a detector for detecting the actual running speed of the electric car irrespective of whether the driving wheel causes adhesion or non-adhesion, a device for establishing a slip frequency of the induction motor, and a device for generating a frequency command based upon a signal of the actual running speed and the slip frequency, this frequency command being used to control the output frequency of the power converter.

Control apparatus for electric car

A control system for an electric car driven by an induction motor which is supplied with electric power of a variable frequency and a variable voltage from an inverter comprises means for detecting the car speed, means for setting a slip frequency of the motor, a frequency command generator, control means for controlling the output frequency of the power converter in accordance with the frequency command and controlling the output voltage of the power converter, a current command generator, and a voltage command generator. The output voltage of the power converter is controlled in accordance with selected one of the current command and the voltage command while being limited by the other command.

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Katsuta, Japan

Shigetoshi Okamatsu