Abstract: A controlled current inverter (CCI) induction motor drive is controlled by controlling motor current and the angle between motor flux and motor current. The angle between motor flux and current is derived directly via a microcomputer phase-locked loop synchronized to the integrated motor voltage. The delay between the application of a firing signal to a thyristor and the initiation of line current is determined and compensated for to achieve the desired angle between motor flux and motor current.

Abstract: A metal rolling mill for reducing the thickness of a metal workpiece passed between a pair of opposed work rolls is controlled to maintain substantially constant tension in the workpiece on the entry side of the work rolls to thereby improve the uniformity of the workpiece gate at the mill output. Working in conjunction with a standard control for delivering the workpiece is a scheme for compensating for thickness variations in the workpiece at the entry side of the work rolls which variations would result in tension changes which would adversely affect output gage consistency.

Abstract: A method of and apparatus for protecting three phase electrical equipment where a signal is derived for each phase representing current in each phase, and the three signals combined to form an analog composite signal. The analog composite signal is converted to digital form. One of the analog signals is used to relate the values of the digital signals to respective phases. The largest value is used to determine heating in the equipent and from the heating the temperature of the equipment is derived. The temperature is compared to critical temperature levels and when a critical level is exceeded, the supply of power to the equipment is interrupted. The digital signals representing the current peaks in each phase are used to determine phase loss and phase unbalance, and the power supply is interrupted when there is a phase loss or when the unbalance exceeds a predetermined critical level.

Abstract: A sine wave generator circuit for providing, as its output, a substantially perfect sine wave signal includes a multiplier responsive to first input and second input signals of varying magnitude for providing as its output the sine wave signal as a function of the two input signals. There is further included a first feedback circuit path connected between the output and one of the inputs of the multiplier which includes a resistance-capacitance network for providing a phase delayed representation of the output signal as the first of the input signals. The amount of phase delay is determined by the relative values of the resistance-capacitance network and determines the frequency of the sine wave output. Further included is a reference signal the magnitude of which will determine the magnitude of the sine wave output signal. The reference signal is applied to a second feedback circuit path connected between the multiplier output and the other one of its inputs.

Abstract: A method of starting an AC motor from any initial speed using open loop control is provided. Sufficient current is provided to the motor so that motor flux can be developed. The frequency provided to the AC motor is varied and the stator frequency at which the motor peak flux occurs is determined. A transition to a control responsive to an external command at approximately the stator frequency at which the peak flux occurred is made.

Abstract: In a metal rolling mill of the type employing automatic gage control (AGC) to control the gap between the rolls utilized to reduce the thickness or gage of a workpiece passed between the rolls, there is provided a method for compensating for roll irregularities (e.g., eccentricity and ovalness). The method provides for developing signals proportional to the roll separation force and the roll rotational speed and isolating from the force signal those cyclic components which have a frequency which is an integral multiple of the roll rotational speed. The values of these cyclic components are then multiplied by a factor greater than unity and the resulting product is subtracted from the original force signal to thus develop a modified force signal which is utilized to control the AGC and hence the roll gap to thus compensate for roll irregularities.

Abstract: A brush wear indicator contact and terminal assembly having a high pressure-per-unit contactor that is formed on a first surface of the plate. A conductor for a brush wear indicator circuit is bonded to the contact plate by a high temperature resistant solder or brazing material and the contact plate is bonded to the surface of the dielectric sheet, which electrically isolates the contact from the spring when the spring is in an extended condition. By the method of the invention, a brush wear indicator contact and terminal assembly is made by adhering a sheet of dielectric material to a brush follower spring with a coating of permanently flexible adhesive, and by bonding a conductor for a brush wear indicator circuit to a contact plate having a contactor ridge on one opposite surface thereof.

Abstract: Apparatus and method for protecting a squirrel cage induction motor against excessive temperatures which can occur in the rotor, provides a thermal model of the rotor. The thermal model has three regions A, B and C representing the starting portion of the rotor conductor, and the rotor core. The rotor is frequency sensitive and currents of higher frequency induced in the conductors tend to be in region A, and currents of lower frequency tend to be in region B. Equipment connected to the stator winding determines values for the positive and negative sequence components of the supply for the fundamental frequency and preferably also for the second and third harmonics present, and provides signals representing these values. Heat calculation circuitry receives the values for all the positive and negative sequence components and a signal representing speed, determines the currents that would be induced in regions A, B and C, and derives equivalent currents which would produce the same heat.

Abstract: A method of adaptively controlling the time of rendering the individual controlled devices of a controllable power conversion bridge includes the sensing of the instant in time at which the current from the bridge to a load becomes discontinuous. From the time of this sensing, the time period to a predetermined time such as a normally calculated time of rendering the controlled devices conductive is derived. This time period is then multiplied by a multiplier and the resultant product is combined with the predetermined time to provide an actual time of rendering the controlled devices conductive.

Abstract: The non-linear control characteristic of a force commutated current source inverter operating as a var generator is linearized to provide a similar dynamic response in both leading and lagging modes of operation by two inter-related control schemes. The first control scheme comprises a linear closed loop feedback which controls a thyristor firing circuit in response to a difference or error signal between a var command signal and an actual var feedback signal while the second control comprises a feed-forward non-linear network having a signal transfer function which models the non-linear control characteristic of the var generator and is operative to control the thyristor firing circuit in response to the summation of scaled values of the var command signal and the actual var feedback signal and wherein the scaled values provide a combined gain which is equal to unity.

Abstract: A method and apparatus for use in conjunction with a power conversion system employing a plurality of switching elements for controlling the electrical power supplied to a load from a source includes the sensing of the instantaneous voltage furnished to the load and providing a signal representing the time derivative of the sensed voltage. The derivative signal thus developed is compared with predetermined reference values to develop output signals which are logically combined to provide a final signal representative of the instant in time at which one of the switching elements is commutated (turned off).

Abstract: A rolling mill stand, including a housing for supporting a pair of opposed rolls for reducing the thickness of a workpiece passed therebetween and an apparatus for adjusting the gap between the rolls, has associated therewith a scheme for controlling the apparatus for adjusting the gap in response to combined results of a first signal representing the force occasioned by the workpiece between the rolls and a second signal representing the strain established in the housing as a result of the workpiece between the rolls.

Abstract: A rolling mill stand which includes roller elements for reducing the thickness of a workpiece which is passed therebetween further includes an adjusting mechanism for adjusting the gap between the roller elements and a sensor for sensing the roll separation force occasioned by passing the workpiece between the roll elements. The stand also includes a sensor for sensing the roller elements position and an automatic gage control device for controlling the gap adjustment mechanism as a function of the roll separation force. Associated with the rolling mill stand is a method of compensating for friction forces within the rolling mill stand occuring as a result of movement of the roller elements so as to improve the accuracy and stability of the automatic gage control.

Abstract: A fault protective system for a load commutated inverter motor drive including an AC to DC source side converter coupled from an AC source to a DC to AC load side converter via a DC link circuit and wherein the load side converter supplies AC power of varying magnitude and frequency to the synchronous motor load. A pair of microcomputers interlinked by a common digital memory respectively control the inverters and interface with hardware type sensor means for detecting the occurrence of a plurality of different types of faults. Additionally, a number of stored instructional sets or programs are respectively included in both microcomputers to detect by software means another plurality of faults. The detection of a fault on either side of the link circuit is communicated to the respective computer which subsequently communicates with the other microcomputer to effect a coordinated protective action in response to thyristor cell failures, circuit failures, and abnormal operating conditions.

Abstract: A voltage controlled oscillator for producing an output signal having a frequency proportional to the magnitude of an input control signal includes a tunable filter circuit for simulating a resistance-inductance-capacitance (RLC) circuit with a resonant frequency approximately equal to the base or center frequency around which the voltage controlled oscillator is to operate. Through appropriate feedback means and multiple gain paths within the simulated RLC circuit, there is provided an output signal whose frequency is a function of the input control signal.

Abstract: A frequency to voltage transducer for producing an output signal having a value proportional to the magnitude of the frequency of an input signal includes a tunable filter circuit for simulating a resistance - inductance - capacitance (RLC) circuit with a resonant frequency approximately equal to the anticipated base frequency of the input signal. Through appropriate feedback means and multiple gain paths within the simulated RLC circuit, there is provided an output signal which is proportional in magnitude to the frequency of the input signal.

Abstract: A control system including a controller for reading temperature values from sensors in a gas turbine, determining the reliability of the sensors, and issuing a fuel control signal for use in controlling the turbine is disclosed. The fuel control signal has a calculated value which is a function of the turbine operating temperature derived from the values of temperature signals generated by the sensors.

Abstract: A scheme for measuring the frequency of an alternating current signal provides for the development of first and second values which are respectively representative of the time the alternating current signal exist in alternate half cycles; e.g., the period of a half cycle. The most recently developed of the first and second values is retained and continuously compared with the other value which is presently being developed to thus provide an output signal representative of the greater thereof. This output signal is indicative of the period and, hence by its reciprocal, a measure of the apparent instantaneous frequency of the alternating current signal.

Abstract: A transistor fault indicator circuit monitors the conduction state of a transistor and compares that state to a commanded state. Differences in states are treated as faults and actuate an alarm or shut down the system including the transistor. In systems in which the transistor may be operated in a continuous conduction mode for long time periods, a control circuit is provided to periodically short circuit the base-emitter bias of the transistor to force a momentary period of nonconduction during which time the proper operation of the transistor can be verified.

Abstract: Overcurrent protection is obtained in a push-pull network by circuitry repeatedly comparing signals indicative of the instantaneous current flow through the push-pull switching elements with a synchronized reference signal whose value is preferably made to decline during the ON periods of the current switches. Thus, the reference signal may initially be set relatively high to accommodate a moderately high in-rush transient and then to decline to lower levels over the remainder of the time the switching elements are on. At any time that the current signals exceed the compared to reference value, the corresponding current switch is deactivated as a protective measure.