Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
  • H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
  • H02P25/04—Single phase motors, e.g. capacitor motors

Definitions

• the present invention relates to a circuit for con ⁇ trolling the speed of an electric motor, particularly a shaded pole motor, in accordance with a control voltage and including a ramp generator for generation of a saw- tooth voltage, a comparison circuit with two inputs which are supplied with the control voltage and the sawtooth vol ⁇ tage, respectively, a trigger circuit the input of which is connected to the output of the comparison circuit and a triac connected in series with the electric motor, the control electrode of which is connected to the trigger circuit.
• Such a circuit may for instance be used to control a heating element or the speed of a fan in accordance with e.g. a temperature as the said control voltage can thus be formed by means of a voltage divider consisting of a fixed resistor and a temperature-dependent resistor.
• the comparison circuit controls 0-passage/not-O-passage impulses to the triac by scanning the sawtooth voltage at one input and scanning a temperature-dependent threshold value at the other input.
• a control circuit of the above-mentioned kind is not suitable for control of shaded pole motors as such motors and other asynchronous motors have a greatly varying torque which is very low at slow speeds and high at optimum motor speed.
• this disadvantage is avoided by the output of the comparison circuit being connected to a control input of the ramp generator, and by the generator being arranged to supply a steep ramp when the comparison circuit is OFF and a slightly less inclined ramp when the comparison circuit is ON.
• fig. 1 shows schematically a block diagram of a known control circuit
• fig. 2 graphic representations of voltages in the known circuit
• fig. 3 schematically a block diagram of a control circuit according to the invention
• fig. 4 graphic representations of voltages in the circuit according to fig. 3.
• a ramp generator 1 generating a sawtooth voltage
• a vol ⁇ tage divider consisting of a fixed resistor 2 and a temperature-dependent resistor 3 producing a tempera ⁇ ture-dependent control voltage
• a comparison circuit 4 whose two inputs are supplied with the sawtooth voltage and the control voltage, respectively, a trigger circuit 5, the input of which is supplied with the output signal of the comparison circuit 4, and a triac 6 connected in series with a load 7, for instance a heating element to be controlled, the control electrode of the triac being connected to the trigger circuit 5.
• Fig. 2 is graphic representations of the sawtooth voltage, the control voltage and the voltage across the load at different temperatures. In dotted line is also shown the load power which is lowest when the tempera ⁇ ture and hence the control voltage is highest.
• Fig. 3 shows the control circuit of fig. 1 with the modifications which are made according to the pre ⁇ sent invention.
• the output signal from the comparison circuit 4 is in this case applied not only the trigger circuit 5 but also the ramp generator 1 which is hereby controlled in such a way that the ramp inclination has a first value when the comparison circuit is OFF and a second value when the comparison circuit is ON.
• the result is the voltage sequences suggested in fig. 4, and where the ramp inclination is relatively small when the motor 7 is ON, and relatively steep when the motor is OFF.
• the coefficient of inclina ⁇ tion of the two ramps can be adapted to the individual motor.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Ac Motors In General (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8139666

Family Applications (1)

Country Status (5)

Cited By (1)

Citations (3)

• 1985
  • 1985-11-07 DK DK512685A patent/DK512685A/da unknown
• 1986
  • 1986-11-07 FI FI872976A patent/FI872976A0/fi not_active IP Right Cessation
  • 1986-11-07 WO PCT/DK1986/000124 patent/WO1987003151A1/en not_active Ceased
  • 1986-11-07 JP JP61506165A patent/JPH01500398A/ja active Pending
  • 1986-11-07 EP EP86906795A patent/EP0245395B1/en not_active Expired

Patent Citations (3)

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