Abstract: A controlled current inverter system forms the basis of an AC motor drive system for furnishing the motor load 18 with a variable frequency, variable magnitude AC current from an inverter 14 which is supplied from a variable DC current source such as a converter 12 by way of a DC link including an inductor 17. Motor speed and torque are controlled through the control of motor current I.sub.M and angle .theta., which is the angle formed between vectors designating motor current and flux through first and second control signal channels 39 and 59 coupled to the DC source 12 and the inverter 14, respectively. A control function of this angle, defined in terms of both method and apparatus, is implemented by means 61 and 63 which limits this angle to predetermined values for relatively low levels of motor current, for example, values of current corresponding to the current required for maintaining a minimum amount of motor flux.

Abstract: Apparatus and method for high slip operation of an AC electric motor at substantially zero rotation and substantially zero torque in an AC electric motor drive system is disclosed. The electric motor produces a rotation in response to an outgoing signal, such as a drive current, of variable magnitude and frequency supplied by the drive system. An idle control signal is furnished when the drive system is in a substantially zero rotation and substantially zero torque state, where the frequency of the current is approximately zero. The idle control signal causes substantially simultaneously an adjustment of the magnitude of the current to a predetermined magnitude level and a rapid raising of the frequency of the current to a higher frequency value to produce per-unit slip s=(n.sub.1 -n)/n.sub.b greater than 0.1, where n.sub.1 is the synchronous rotation of the stator field of the motor, n is the rotation of the rotor of the motor, and n.sub.b is the synchronous speed of the stator field at motor rated rpm.

Abstract: A fixed gating sequence apparatus and method for an inverter is disclosed. In one aspect of the invention, an outgoing signal of variable frequency is generated by the inverter in response to gating signals provided by an inverter control. The gating signals effectively are provided by a shift register of an inverter control to the gates of the conduction controlled rectifying devices in the inverter in response to a clocking signal. The clocking signal is provided to the clock input of the shift register at a normal system rate when an idle condition (idle control signal) is not present and at a predetermined cycling rate from when the idle condition occurs until a desired fixed gating pattern effectively is provided by the shift register to the inverter. The shift register remains at the stage providing the desired fixed gating pattern until the idle condition no longer is present, whereupon the normal clocking signals are again provided to the shift register.

Abstract: A circuit for detecting the conductive state of a semiconductor device (e.g., a thyristor) which exhibits a substantial terminal to terminal voltage difference between its conducting and nonconducting states and which utilizes a gating signal to render the device conductive includes a bistable circuit (e.g., a flip-flop) which is placed into a first stable state with the occurrence of the gating signal. A voltage sensing circuit disposed across the semiconductor device is utilized to develop an additional signal which is applied to the bistable circuit to thereby place that latter circuit into its second stable state. The state of the bistable circuit is representative of the conductive state of the semiconductor device.

Abstract: A controlled current inverter motor control system including a controlled source of direct current for supplying a variable frequency inverter by way of a direct current link circuit which includes, within the link circuit, a selectively insertable dynamic braking resistive element. Upon a call for a dynamic braking mode of operation, the source of direct current is short circuited and the normal operational or running control of the motor is discontinued. Special circuitry is provided which then forces a special frequency control of the inverter to thus control the angle between the motor flux and motor current to a prescribed value proportional to the extant value of a motor operating parameter (motor current or motor flux) prior to the insertion of the dynamic braking resistive element into the link circuit.

Abstract: Disclosed is an overload protective circuit for an electric motor which is adaped to monitor and track motor temperature as a function of an operating parameter, namely armature current. The motor's armature current is sensed and converted to a multi-bit digital signal which is used to address a programmable read only memory (PROM) which has been pre-programmed with discrete digital values of temperature for a plurality of armature currents for the motor being protected. The digital address signal for the armature motor current is periodically updated at a relatively rapid rate and depending upon the armature current sensed, multi-bit temperature values are outputted from the PROM to a digital latch which operates a relatively slower rate to output another address back to the PROM so as to predict what the temperature will be at the next time increment based on the present current value and the present temperature.

Abstract: A substantially zero rotation and substantially zero torque detector and method for an AC electric motor drive system includes an AC electric motor producing a rotation in response to an outgoing signal, e.g., drive current, of variable magnitude and frequency. An actual rotation signal is generated and is proportional to the rotation of the AC electric motor or to the frequency of the outgoing signal. A rotation reference signal proportional to a desired level of rotation is established. A rotation difference signal representative of any difference between the rotation reference signal and the actual rotational signal is generated. A torque command signal is provided as a function of the rotation difference signal and is used to produce a frequency control signal and a current control signal. Alternatively, the torque command signal is generated proportional to a desired level of torque when the drive system utilizes a desired torque level as opposed to a desired rotation level.

Abstract: A repeater for use in a data communications link, particularly of the type to provide the exchange of process control information with external controlled equipment, includes a detector for detecting incoming data presented on the data communications link. Through the use of a free running internal clock, the data is retimed, reconstructed through the use of a modulator and presented to a transmitter for placement back on the data link. The repeater further provides data and clock signals to the external controlled equipment and receives signals from that equipment which serve, by way of logic circuitry within the repeater, to effect the modification of the data received by the repeater to thus enable the controlled equipment to communicate with other elements connected to the link.

Abstract: Disclosed is an exciter circuit for an electrical load such as the field winding of a direct current (DC) motor. The exciter circuit regulates the DC current applied to the load from an alternating current (AC) source in response to an isolated feedback signal developed by means of a saturating square loop current transformer. The current signal developed is compared against a signal corresponding to the desired current value and an error signal is generated which is fed to photo-optical firing circuit means which are coupled to and operative to control at least one thyristor (SCR) which, when rendered conductive, is adapted to provide a freewheeling current path for the load current during the half cycle of the AC line voltage when it is disconnected from the load by at least a half wave rectifier. The present invention includes embodiments for both single and bidirectional current flow through the load which, as noted above, preferably comprises the field winding of a DC motor.

Abstract: Disclosed is an AC motor drive system having a variable frequency, variable magnitude AC current supplied from a controlled inverter coupled to a variable DC current source in the form of a converter by way of a DC link including an inductor. The AC motor load is controlled so as to have dual modes of operation in order to optimize torque at any speed which can be produced within the voltage and current limitations of the variable frequency power source. The first mode comprises a constant slip or constant angle mode for operating speeds up to the corner point speed which is defined as the speed at which the motor voltage at full torque matches the maximum voltage the variable frequency inverter coupled thereto can provide. Thereafter, the system enters the second mode by automatically shifting to a constant horsepower variable slip or changing angle mode for operating speeds beyond the corner point speed.

Abstract: An apparatus and method for providing signals indicative of the magnitude and angular position of the DC motor flux of an AC induction motor is disclosed. The AC induction motor provides controllable rotation and torque in accordance with a drive current of variable magnitude and frequency. A first signal is provided proportional to the rate of change of the flux of the motor. A second signal is supplied proportional to the magnitude of the drive current. A flux signal is generated proportional to the integral of the first signal when the frequency of the output signal is above a preselected value and which is proportional to the second signal when the frequency of the output signal is below the preselected value. A representative value for the preselected frequency value is 3 Hertz in a 60 Hertz drive system. The flux signal is effective to control the generation of the drive current.

Abstract: A motor drive system having a direct current, shunt motor utilized in a web coiling operation and operated in a tension control mode includes circuitry to automatically provide compensation for inertial effects of the drive and the web coil during periods of acceleration and deceleration.

Abstract: A method for controlling the temperature of a workpiece in a hot strip mill includes calculating temperature changes of the strip at each mill stand location by determining changes in workpiece deformation resistance and correlating the changes in deformation resistance to changes in temperature. Error corrections are made for changes in rolling speed. The calculated temperature change at each mill stand is used to control water sprays positioned adjacent the mill stands. A temperature sensor is placed downstream of the last mill stand to act as a check on the desired delivery temperature of the workpiece. Temperature discrepancies from the temperature sensor are fed upstream to modify temperature corrections.

Abstract: Disclosed is a three phase AC motor drive system wherein a variable frequency variable magnitude AC current is fed to an AC motor load from a thyristor controlled DC to AC inverter which is supplied from a thyristor controlled AC to DC converter by way of a DC link including an inductor. The DC load current is commanded to rise at a rate limited by the difference between the output voltage of the converter and the input voltage to the inverter which voltage appears across the inductor. As a result of the inherent commutation transport lag encountered for commands in the negative direction, an error signal clamp is placed in a feedback signal path controlling the AC to DC converter for limiting the command for changes in the positive direction thereby providing a system response in the positive direction which is more nearly like the response in the negative direction.

Abstract: An inverter system including a controlled direct current (d.c.) power source for providing a variable d.c. voltage to a variable output frequency inverter circuit by way of a suitable d.c. link, includes suitable circuitry for detecting a commutation fault or shoot-through condition within the inverter circuit and for taking appropriate remedial action to correct such condition. The shoot-through condition is determined as a function of the d.c. input current to the inverter circuit, the output alternating current (a.c.) of the inverter circuit and the extant condition of the load. In the particular embodiment of the invention illustrated, the load is an a.c. motor and the load condition sensed is whether the motor is in the running or idle mode of operation.

Abstract: A circuit for controlling the rendering conductive of the controlled rectifiers of a power conversion unit to thereby control the power supplied to a load from a source of alternating current voltage employs a single means to sense a prescribed phase relationship between adjacent phase to neutral voltages of the source which means is utilized to develop a digital count representing a time-phase relationship with respect to the point determined. The digital count thus developed is supplied to a memory system to address that system and based upon the contents of the locations within the memory system thus addressed there is provided an output which determines the time and firing sequence of the rectifiers of the power conversion system. This output is then utilized to generate suitable signals which are applied to the rectifiers of the power conversion system to thereby control the power supplied to the load.

Abstract: The flatness of metal strip being rolled in a hot strip mill is improved by applying higher than normal interstand tensions with maximum permissible tensions being based upon preestablished maximum allowable width reductions due to interstand tensions. The relationships between interstand tension and interstand plastic deformation are predetermined functions of strip material properties, strip temperature, and assumed tensile stress distribution across the strip width.

Abstract: A polyphase inverter system for supplying alternating current power to a load through the use of conduction controlled devices such as controlled rectifiers which are selectively rendered conductive in a sequence and at a rate which determines the frequency of the electrical power delivered to the load, includes an inverter control employing a source of pulses and an open-ended, bidirectional shift register. The contents of the register are shifted in response to the application thereto of the pulses, in combination with a direction signal. The instantaneous contents of the register serve to initiate gating signals for rendering conductive the controlled rectifiers. Logic means associated with and responsive to a specified configuration of the register contents develop, in combination with the directional signal, a predetermined bit pattern to be inserted into the register.

Abstract: In controlling a slab reheat furnace, the average temperature of each slab in a zone, is predicted as a function of the radiation heat source temperature in the zone, and the thermal properties, dimensions, location, velocity, and past thermal history of the slabs. The predicted slab temperatures are compared with a range of desired slab temperatures and the slab requiring the greatest time to be heated to its desired temperature is identified. The furnace is controlled in such a manner that the identified slab will be heated to the desired temperature. Slabs likely to be overheated are identified and, if a predetermined temperature limit is to be exceeded, the furnace is controlled to prevent further heating of the slabs. Gas temperatures throughout the zone are predicted based upon only one sensed temperature in the zone.

Abstract: A circuit and method is disclosed for detecting the presence of charges of appropriate magnitude and polarity on commutating capacitors of an inverter that converts a DC output current to a drive current of variable magnitude and frequency for driving an AC electric motor producing controllable rotation and torque. The presence of charges of appropriate magnitude and polarity is detected by measuring the voltages across the conduction controlled rectifying devices in the inverter. In addition, the existence of conduction controlled rectifying devices in the conducting state is determined by measuring the magnitude of the DC output current. An output signal is generated when the charges of appropriate magnitude and polarity are detected, which output signal is effective to allow the inverter to generate normal drive current.