Abstract: A load-commutated inverter for operating a synchronous motor having two sets of 3-phase windings. The difference of phase angles between the two sets of the 3-phase windings is 30 degrees. The load-commutated inverter is provided with two sets of inverters and a control circuit. Each of the inverters, is formed of thyristors. The inverters are coupled respectively to the 3-phase windings of the motor. The commutation of each of the thyristors is controlled in accordance with a given advanced control angle. The control circuit is coupled to the inverters and is responsive to a commutation overlapping angle of currents (e.g., IU1, IV1 in FIG. 4A) supplied from the inverters to the 3-phase windings of the motor. The control circuit adjusts the given advanced control angle so as to retain a relation:u+.gamma.*.ltoreq.30 degreeswherein u denotes the commutation overlapping angle and .gamma.* corresponds to the reverse-biasing time applied to each of the thyristors.

Abstract: A control system for an AC motor to be driven by an inverter, wherein a control lead angle .beta. of the AC motor drive current is controlled based on the detection of an actual overlapped angle, a set overlapped angle, a detected motor speed, a detected magnitude of the acceleration-deceleration rate of motor speed, a detected amount of current from a power source and/or a detected magnitude of the change rate in the current from the power source.

Abstract: Apparatus and method for controlling a synchronous motor driving a square-law torque load at variable speeds by employing a frequency changer. The armature voltage Va may be controlled so that the ratio Va/N at motor speeds above a predetermined value is greater than Va(100)/N(100), where N(100) is the rated speed of the motor and Va(100) is the armature voltage at that speed. Below a predetermined speed, the armature voltage may be controlled so that the ratio Va/N is less than Va(100)/N(100).

Abstract: A synchronous motor is driven by a plurality of inverting circuits. The inverting circuits are controlled by signals from a position detecting circuit coupled to the shaft of the synchronous motor so as to produce output current signals from the inverting circuits which are shifted by a certain angle from each other.

Abstract: A power converting device including at least one power converting element, and a protection circuit monitoring the switching characteristics of the power converting element and for protecting the power converting element during switching thereof, including a first circuit coupled to detect a reverse voltage applied to the power converting element, a second circuit coupled to the first circuit for receiving the detected reverse voltage and for integrating the detected reverse voltage to produce a reverse voltage/time integral signal, and a third circuit coupled to receive the reverse voltage/time integral signal for producing a decision signal only when the amplitude of the reverse voltage/time integral signal exceeds a first prescribed value, the decision signal indicates that the power converting element is extinguished.

Abstract: In a method and apparatus for controlling a speed of an AC motor energized by a source of alternating current through a frequency converter, a limiter responsive to input voltage and input current is provided for decreasing a primary frequency at a rate faster than a rate of decrease in a number of revolutions of the motor when the source is interrupted for a short interval and for accelerating the motor with a primary current thereof limited to a predetermined value while maintaining the primary frequency and the primary current in a predetermined relation.

Abstract: A frequency converter applies a variable voltage with a variable frequency to an AC motor coupled with a load. At least one frequency region is set up for the variable frequency. The ratio of a percentage input voltage expressed in terms of a percentage of the rated input voltage of the AC motor, to a corresponding percentage input frequency expressed in terms of a percentage of the rated input frequency of the AC motor, is set less than 1 within the frequency region thus set. Also an apparatus for the AC motor control provided.

Abstract: A device for controlling a plurality of parallel connected converters which includes a reference circuit for controlling the converters, a frequency divider having a number of outputs corresponding to a number of the converters, and a plurality of ring counter circuits for driving the converters in response to the output of the frequency divider. Interlocking signals are supplied among the ring counter circuits such that the ring counter circuits recover when a noise signal is applied.

Abstract: In a frequency converter of the type including a polyphase inverter which produces polyphase alternating current inherently containing higher harmonic components, a plurality of polyphase inverters are operated with a predetermined phase difference and the outputs thereof are sythesized by polyphase transformer means so as to eliminate higher harmonic components of relatively low orders, particularly the fifth and seventh higher harmonics.

Abstract: In a control system of an alternating current motor energized by serially connected rectifier and inverter wherein the output DC voltage of the rectifier is controlled by a phase controller which is controlled by a phase control signal and the output frequency of the inverter is controlled by a speed reference signal there is provided a power factor detector which differentiates the phase control signal or the DC voltage and the output of the phase detector is added to the speed reference signal so as to suppress low frequency oscillations of the torque of the motor.

Abstract: In a control system of an alternating current motor energized by a frequency converter including serially connected rectifier and inverter of the type wherein the speed of the motor is controlled by varying the phase of the output current of the inverter by varying the phase of a control signal of the inverter, there are provided a function generator which is supplied with a signal related to the motor torque for generating an analog phase angle signal related to the current phase angle, and a phase shifter responsive to the analog phase angle signal for shifting the phase of the control signal for the inverter.