Hitachi, Ltd.

Motonobu Hattori

Kenji Nandoh

Akira Ishibashi

Nobuyoshi Mutoh

Hideyuki Shimonabe

Satoshi Ibori

Akiteru Ueda

Keijiro Sakai

Yuuzi Yamasawa

Yasuharu Tamuro

Yuichiro Nagato

Shigeru Murasaki

Hiromi Ishida

Noritoshi Tuji

A method and apparatus are disclosed for controlling a pulse width modulated (PWM) inverter controlled for ignition by a (PWM) pulse produced with a carrier wave and a modulation wave. The method comprises sampling an amplitude of the modulation wave at a cycle rate related to the frequency of the carrier wave. The modulation wave and the carrier wave are synchronized when the sample modulation wave amplitude has a peak value greater than an amplitude of the carrier wave. The modulation wave and the carrier wave are asynchronized when the sampled modulation wave has a peak value less than the amplitude of the carrier wave.

Method and apparatus for selectively controlling an operation mode of a

A control system for controlling a PWM inverter so that the inverter drives an induction motor at a variable voltage and a variable frequency while keeping constant a ratio of the output voltage of the inverter to the output frequency thereof, is disclosed which includes current component detecting means for detecting an effective current corresponding to a load, from the input current of the induction motor, frequency setting means for setting the output frequency of the PWM inverter, flux setting means for setting the amount of magnetic flux generated in the induction motor, correcting-frequency calculating means for calculating a frequency correcting quantity proportional to the effective current, and correcting-flux calculating means for calculating a flux correcting quantity proportional to the effective current. In a case where the detected effective current is judged to be less than a predetermined value, the frequency correcting quantity is added to the set output frequency to obtain an output frequency command, and the sum of the flux correcting quantity and the set amount of magnetic flux is multiplied by the value of the output frequency command to obtain an output voltage command, for the purpose of controlling the operation of the PWM inverter on the basis of the output frequency command and the output voltage command.

Control system for PWM inverter

When an abnormality is detected during driving of an inverter, the output of the inverter is interrupted for a period of several milliseconds and then operated again. At this time, if no abnormality is detected, driving is continued, while if an abnormality is again detected, driving is stopped.

Electric power control apparatus with first and second fixed time

An inverter for converting DC power to AC power, an oscillation control circuit for stepwise generating a command value concerning the conversion condition of the inverter, and an operation controller which, when the command value from the oscillation control circuit changes, controls the oscillation control circuit to repetitively generate alternate new and old or present command values before and after change of the command value. Particularly, this invention provides an inverter capable of continuing smooth operation even when the control system has a limited resolution.

PWM inverter apparatus with digital control

A control apparatus for producing a pulse width modulating signal to be used for operation of a PWM inverter wherein a modulating wave of a sinusoidal waveform corresponding to the desired AC output voltage of the inverter is sampled at selected periodical time intervals to obtain a level of the modulating wave at each sampling point and the interval is arithmetically determined between each sampling time point and a time point which appears between the sampling point and the next sampling point and at which time point a virtual triangular waveform, which has positive and negative peaks of a predetermined amplitude occurring alternately at the selected periodical time interval, takes the same level as the sampled level of the modulating wave. On the basis of the time interval, the PWM signal is produced.

Control apparatus for PWM inverter

A power inverter including a converter unit for rectifying AC power into DC power, an inverter for inverting the DC power into AC power for driving a load apparatus, and a protection apparatus for protecting the load apparatus from being overloaded. The load protecting apparatus comprises current detecting means for detecting a current supplied to the inverter unit from the converter unit, a memory for storing a thermally limited operation time characteristic determined in consideration of cooling effect proper to the load apparatus, and an abnormality detecting circuit for producing an abnormality signal to stop the operation of the inverter unit when an accumulated value calculated on the basis of the current value detected by the current detector at a predetermined sampling interval exceeds the characteristic value previously stored in the memory. The load apparatus can be positively protected from overload notwithstanding variations in the output voltage and the output frequency of the power inverter.

Power inverter with overload protection apparatus

A method and apparatus for controlling an induction motor, in which an AC power source is connected to the induction motor through a switch and a frequency converter, and the motor speed is controlled by controlling the output frequency and output voltage of the frequency converter. In the starting operation, the induction motor in a free-running state is supplied with an initial voltage in a given frequency which is expected to make the absolute value of the motor current minimum or near minimum, and then the supply voltage is increased gradually from the initial voltage with its frequency being retained at the given voltage. When the output frequency of the frequency converter reaches a predetermined value, the output frequency and voltage thereof are increased gradually with the ratio therebetween being maintained at a given value.

Growing community of inventors

Funabashi, Japan

Motonobu Hattori