Hitachi, Ltd.

The Kansai Electric Power Co., Inc.

Keiji Saito

Akira Bando

Hiroto Nakagawa

Yasuteru Oono

Chikara Tanaka

Tadao Kawai

Eizo Kita

Keiichi Mitsuhashi

Hiroshi Koyama

Osamu Nagura

Hashime Nagai

Yasuteru Ohno

Ikuro Miyashita

A semiconductor power conversion system comprising a multiphase bridge circuit which includes semiconductor devices having a controllable firing function and a reverse blocking characteristic, a gate control circuit which gives firing commands to the semiconductor devices, a short circuiting switch in which switching devices having a controllable firing function and a reverse blocking characteristic are connected in parallel with a DC output side of the multiphase bridge circuit, and a protection control device for performing a control for protecting the multiphase bridge circuit. The protection control device includes a device for detecting a commutation failure of the multiphase bridge circuit, and a device in response to the detection of the commutation failure for producing a blocking command for blocking the firing of the semiconductor devices of the multiphase bridge circuit and producing a short-circuiting command for firing the switching device which is short-circuited which bypasses current of the commutation failure. The protection control device further includes a device for detecting ending of a short-circuit based on the ceasing of current conduction of the short circuiting switch and for halting the blocking of the firing of the semiconductor devices of the multiphase bridge circuit.

Fault protection for a multiphase bridge power converter

An improved electric power conversion system comprising a multi-phase bridge circuit composed of semiconductors such as thyristors and an associated firing circuit. It is so constructed that: if the AC input current Iac flowing in the bridge circuit is equal to or larger in value that the DC output current Idc flowing out of the bridge circuit, it will be decided than an inner defect or fault is caused, and possible expansion of inner defect will be prevented by disabling the firing circuit to extinguish the thyristors in the bridge circuit, and if the AC input current Iac is smaller than the DC output current Idc in value, the bridge is permitted to continue the operation of power conversion, thus eliminating unnecessary interruption which otherwise would be caused by exterior disturbances. Also, an improved electric power conversion system may be equipped with a device to prevent an adverse effect from being caused by abnormal rise of thyristors' temperature.

Semiconductor electric power conversion system enabling fault and/or

A generator-motor apparatus with economical protection measures for use in a variable speed pumping-up electric power plant, having a main transformer, a secondary winding of which is coupled to an electric power system, a power system breaker connected to a primary winding of the main transformer, a syncronizing breaker connected in series with the power system breaker, a generator-motor, a rotor of which is mechanically coupled to the pump-turbine and an armature winding of which is connected to the power system through the synchronizing breaker, the power system breaker and the main transformer, and an excitation circuit, including a frequency converter for supplying a field winding of the generator-motor with AC voltage of the variable frequency and a converter transformer for feeding the converter, which is branched from a junction of the power system breaker and the synchronizing breaker.

Power system and synchronizing breakers for a variable speed generator

In a rolling mill having a pair of upper and lower work rolls, defining a pressure gap therebetween through which a material is passed to be rolled, a method and apparatus for controlling the rolling mill under the different peripheral-speed rolling operation in which one of the rolls is driven at a predetermined peripheral speed by controlling the speed of a motor for driving the one roll, and the other roll is controlled to generate a torque corresponding to a difference, between a total torque required for the rolling operation and a torque generated by the one roll by controlling the torque of the motor for driving the other roll on the basis of a torque command corresponding to the torque difference.

Control method and apparatus for rolling mill

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Hitachi, Japan

Keiji Saito