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
  • H02P25/10—Commutator motors, e.g. repulsion motors
  • H02P25/14—Universal motors
• • 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
  • H02P25/16—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring
  • H02P25/18—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the circuit arrangement or by the kind of wiring with arrangements for switching the windings, e.g. with mechanical switches or relays

Definitions

• the present invention refers to a device for control of the speed of a series motor powered from an AC power source, the free end of the rotor winding being connected to one terminal of the power source and the free end of the stator winding being connected to the other terminal of the power source via a first two-way silicon controlled rectifier, and the stator winding being provided with a tap connected to the other terminal of the power source via a second two-way silicon controlled rectifier.
• a device for control of the speed of a series motor powered from an AC power source the free end of the rotor winding being connected to one terminal of the power source and the free end of the stator winding being connected to the other terminal of the power source via a first two-way silicon controlled rectifier, and the stator winding being provided with a tap connected to the other terminal of the power source via a second two-way silicon controlled rectifier.
• a device of the kind indicated is described in DE-A-3200753.
• a control circuit is provided for the purpose of generating trigger pulses applied to the control electrodes of the respective one of the two-way silicon controlled rec- tifiers.
• the tap provided in the stator winding the full stator winding can be used when operating the motor in a lower speed range whereas a reduced winding with a corresponding lower magnetization of the stator can be utilized for operating the motor in a higher speed range.
• the described device has proved useful in avoiding problems of increased degree of harmonics in the current taken from an AC mains network when driving a series motor of the kind referred to above in a power range exceeding about 1000 watts.
• phase control of silicon controlled rectifiers of the type thyristor or triac may give cause to transients which in turn generate sinusoidal harmnonics. If a motor of the kind referred to is operated in a power range exceeding about 1000 watts the degree of harmonics will be unallowably high causing interference acting upon other appliances connected to the network.
• filters comprising inductive or capacitive means or the use of a PWM regulator.
• a common feature of these solutions is that in connection with motors in vacuum cleaners, for example, with a maximum power of about 1.500 watts high costs will be involved which of course increase the overall cost of the product in an undesirable way.
• the object of the invention is to provide a control device for a series motor of the kind referred to above which permits a power loading up to about 1.500 watts without any increase of the degree of harmonics in the current drawn above predetermi- ned acceptable values.
• the object is achieved by a control device incorporating the features of claim 1. the invention will now be described more in detail in connection with two embodiments with reference to the enclosed drawings, in which: Fig. 1 shows a circuit diagram of a control device according to the invention in a first embodiment; fig. 2 shows a circuit diagram of a control device according to the invention in a second embodiment, and Fig. 3 is a diagram showing waveforms of the motor current and of the tap voltage, respectively, in the device according to Fig. 1.
• FIG. 1 a series motor 10 is shown which in the usual way is provided with brushes 11, 12 and a rotor winding, schemati- cally designated by 13, the ends of which being connectible to the respective brush 11, 12 via a commutator 14.
• the brush 11 Via a conduc ⁇ tor 15, the brush 11 is connected to one terminal 16 of an AC source providing, for example, an AC voltage of 230 volts and the frequency 50 Hz.
• the opposite terminal of the AC source is designated by 17 and is connected to a common junction P in the circuit via a conductor 18.
• the brush 12 in the motor is connected to one end of the stator winding formed by coils Ll and L2 between which a tap U is provided.
• the free end of the coil L2 is connected to the junction P via a first two-way silicon controlled rectifier 19, such as a triac.
• the tap U is connected to the junction P via a second silicon controlled rectifier 20 of the type triac.
• the motor can be provided with a split stator winding in which one half of the winding, corresponding to the winding Ll, L2, is provided between the brush 11 and the conductor 15. This winding half has no tap.
• a first trigger circuit for the triac 19 comprises a potentiometer PI connected to the junction P via a capacitor 22.
• the junction between the potentiometer Pi and the capacitor 22 is connected to the control electrode of the triac 19 via a trigger component 23 of the type DIAC.
• a second trigger ciruit for the triac 20 is formed by a potentiometer P2 connected to the junction P via a capacitor 24.
• the opposite end of the potentiometer P2 is connected to the terminal 16 of the AC source via a conductor 25 and the conductor 15.
• the junction between the potentiometer P2 and the capacitor 24 is connected to the the control electrode of the triac 20 via a trigger component 25 of the type DIAC.
• the two potentiometers Pi and P2 are mechanically interconnected for reasons to appear in the following. The interconnection has been indicated by a dashed line 26.
• the triac 19 is used for controlling the speed of the motor 10 to a desired level. Due to the phase control used, up to that power level the corresponding current draw will not cause harmonics of a rate exceeding acceptable values.
• the triac 19 with associated trigger circuit comprising the potentiometer PI, the capacitor 22 and the DIAC 23, functions in the conventional way and, as appears from Fig. 3a, the trigger circuit emits a trigger signal at the desired time tl, determined by the setting of the potentiometer 19, and the triac 19 starts to conduct. Then, the triac continues to conduct for the rest of the half period. During a following negative half period the course is similar.
• the phenome- non When the motor is to be driven in a higher speed range corresponding to power levels up to maximum power the phenome- non is used according to which a lower magnetization in the motor makes it possible for the motor to operate at higher speed.
• the driving of the motor is then controlled by the triac 20 via the tap ⁇ and coil L2 is disconnected.
• the prerequisite for this to happen without problems is that before the triac 20 can start conducting triac 19 is fully conducting, i.e. has been conducting from the beginning of the half period.
• the potentiometers can be ganged, i.e. they can be arranged on the same shaft and in such a way that before P2 is allowed to leave its zero position, or position with the maximum resistance, potentiometer Pi has taken a position of minimum resistance.
• Fig. 3b illustrates how triac 19 conducts right from the beginning of the half period to the point t2 where P2 is operated so that trigger pulses are emitted to the triac 20 causing the latter to conduct.
• the current increases in a step from a value II to a higher value 12 and then follows a higher curve I'up to the end of the half period.
• the tap voltage U is shown which is also the voltage across the conducting triac 19. The voltage goes negative at the time t2 when triac
• triac 19 starts conducting thereby turning off triac 19. This is important for the desired function to be obtained. If triac 19 should continue conducting heat problems may occur in coil Ll.
• Fig. 2 illustrates an alternative embodiment of the in- vention in which the simple trigger circuits of Fig. 1 have been replaced by an integrated electronic control circuit 27 of a common type.
• the motor is controlled by triacs 19, 20 and same reference numerals as in Fig. 1 have been used to designate identical parts.
• the control circuit has an output TRl connected to the control electrode of the triac 19 via a conductor 28.
• the control circuit has an output TR2 connected to the control electrode of the triac 20 via a conductor 29.
• An input IN of the control circuit 27 has a voltage or current applied which can be varied by means of a potentiometer P3 for the purpose of setting the desired speed within the full speed range of the motor.
• the potentiometer P3 can be replaced by another setting means, such as a pressure sensitive device (vacuum box) for automatic setting and control of the desired speed.
• the setting means can apply at the input IN a digital signal containing information on the desired speed.
• a terminal A on the control circuit 27 is connected to the junction P.
• Fig. 2 The function of the embodiment according to the invention shown in Fig. 2 is similar to that of the embodiment of Fig. 1. However, same conditions apply as before in that triac 19 has to be fully conducting before triac 20 can start conducting.
• This condition can be put in the control circuit 27 so that, for example, trigger pulses are emitted on the output TR2 only if the setting means (P3) has been set for a speed higher than that for which the trigger pulses on the first output (TRl) causes the first two-way silicon controlled rectifier (19) to be fully conducting.
• the control circuit can be a microcomputer and the control parameters can be programmed in a known way.

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

Applications Claiming Priority (3)

Publications (1)

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• 1995
  • 1995-01-24 SE SE9500244A patent/SE505506C2/sv unknown
• 1996
  • 1996-01-19 WO PCT/SE1996/000055 patent/WO1996023349A1/en not_active Ceased
  • 1996-01-19 JP JP8522806A patent/JPH10513036A/ja active Pending
  • 1996-01-19 CN CN96191587A patent/CN1169214A/zh active Pending
  • 1996-01-19 KR KR1019970704950A patent/KR19980701559A/ko not_active Withdrawn
  • 1996-01-19 EP EP96901595A patent/EP0872012A1/de not_active Withdrawn
  • 1996-01-19 CA CA002208071A patent/CA2208071A1/en not_active Abandoned

Non-Patent Citations (1)

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