Control apparatus for motors and the like

Abstract

Abstract A SPEED CONTROL CIRCUIT FOR A D.C. SHUNT-FIELD MOTOR OF THE CLASS IN WHICH THE CURRENT TO THE MOTOR ARMATURE IS CONTROLLED BY A PHASE-CONTROLLED SCR CIRCUIT, THE PHASE ANGLE OF OPERATION OF THE SCR CIRCUIT BEING IN TURN DETERMINED BY THE TIMING OF TRIGGER PULSES FROM A UNIJUNCTION RELAXATION OSCILLATOR. THE INPUT D.C. CONTROL VOLTAGE, WHICH MAY BE MANUALLY GENERATED OR PRODUCED BY AN EXTERNAL INSTRUMENT, IS COMPARED IN A CLOSED-LOOP SERVO ARRANGEMENT WITH A FEEDBACK VOLTAGE, DEVELOPED ACROSS A FEEDBACK RESISTOR, WHICH IS INDICATIVE OF THE VOLTAGE ACROSS THE ARMATURE, THE BASE-TO-EMITTRER DYNAMIC CHARACTERISTIC OF A CONTROL TRANSISTOR IS USED IN THE ERROR DETECTION PROCESS TO COMPARE THE FEEDBACK VOLTAGE WITH THE INPUT CONTROL VOLTAGE. THE COLLECTOR CURRENT OF THE CONTROL TRANSISTOR DETERMINES THE CURRENT FED TO THE RELAXATION-OSCILLATOR TIMING CAPACITOR SO AS TO VARY THE FIRING ANGLE OF THE SCR CIRCUIT. THE INTERNAL BASE-EMITTER VOLTAGE OF THE CONTROL TRANSISTOR COMBINED WITH THE VOLTAGE DROP IN THE ABOVE-MENTIONED FEEDBACK RESISTOR PROVIDES A CONVENIENT VOLTAGE-OFFSET LEVEL WHEN AN EXTERNAL INSTRUMENT IS USED TO PRODUCE THE CONTROL VOLTAGE. THE ADVERSE EFFECTS OF PULSATIONS IN THE FEEDBACK VOLTAGE ARE MITIGATED BY A NEUTRAILIZING CIRCUIT WHICH FEEDS THE HIGHERFREQUENCY PULSE COMPONENTS BOTH TO THE EMITTER AND TO THE BASE OF THE CONTROL TRANSISTOR, AN ARRANGEMENT WHICH AT THE SAME TIME RETAINS ADEQUATELY FAST RESPONSE TO TRANSIENTS AND GOOD CIRCUIT STABILITY. AN IMPROVED AND SIMPLIFIED TRANSISTOR CIRCUIT IS UTILIZED FOR LIMITING THE MAXIMIUM CURRENT THROUGH THE ARMATURE, IN WHICH CIRCUIT A VOLTAGE INDICATIVE OF ARMATURE CURRENT IS APPLIED BETWEEN BASE AND EMITTER OF A TRANSISTOR SO THAT, WHEN THE ARMATURE CURRENT EXCEEDS A PREDETERMINED VALUE, THE INHERENT BASE-EMITTER JUNCTION VOLTAGE OF THE TRANSISTOR IS EXCEEDED, CAUSING THE TRANSISTOR TO TURN ON AND TO BYPASS THE NOMINAL CONTROL CIRCUIT FOR THE CONTROL TRANSISTOR. THE EFFECTS OF LINE VOLTAGE VARIATIONS AND OF MOTOR WARMUP ARE COMPENSATED BY DERIVING A VOLTAGE RELATED TO THE FIELD CURRENT OF THE MOTOR AND COMBINING IT WITH THE INPUT CONTROL VOLTAGE OF THE SYSTEM BY WAY OF A ZENER DIODE.

Inventors

• 👤 Franklin O Wisman

Bibliographic Details