WO2005117246A2 - Method and device for determining the mechanical load of an alternating current synchronous electric motor with a permanent magnet rotor - Google Patents

Method and device for determining the mechanical load of an alternating current synchronous electric motor with a permanent magnet rotor Download PDF

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Publication number
WO2005117246A2
WO2005117246A2 PCT/EP2005/052464 EP2005052464W WO2005117246A2 WO 2005117246 A2 WO2005117246 A2 WO 2005117246A2 EP 2005052464 W EP2005052464 W EP 2005052464W WO 2005117246 A2 WO2005117246 A2 WO 2005117246A2
Authority
WO
WIPO (PCT)
Prior art keywords
motor
alternating
phase difference
supply voltage
rotor
Prior art date
Application number
PCT/EP2005/052464
Other languages
French (fr)
Other versions
WO2005117246A3 (en
Inventor
Sebastiano Acquaviva
Domenico Diacono
Original Assignee
Emerson Appliance Motors Europe S.R.L.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Emerson Appliance Motors Europe S.R.L. filed Critical Emerson Appliance Motors Europe S.R.L.
Publication of WO2005117246A2 publication Critical patent/WO2005117246A2/en
Publication of WO2005117246A3 publication Critical patent/WO2005117246A3/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/34—Testing dynamo-electric machines
    • G01R31/343—Testing dynamo-electric machines in operation
    • 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
    • H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
    • H02P23/14—Estimation or adaptation of motor parameters, e.g. rotor time constant, flux, speed, current or voltage
    • 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
    • H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
    • H02P6/14—Electronic commutators
    • H02P6/16—Circuit arrangements for detecting position

Definitions

  • the present invention relates in a general way to alternating current synchronous electric motors with permanent magnet rotors .
  • a first object of the invention is to provide a method for determining in a simple, reliable and economical way the mechanical load of a synchronous electric motor of this type.
  • the rotor of the motor is associated with an electrical position sensor, stationary in operation, which can supply an alternating electrical position signal,
  • the determined phase difference is compared with at least one predetermined reference.
  • a further object of the invention is to provide a device for determining the mechanical load of an alternating current synchronous electric motor with a permanent magnet rotor, and according to the invention this further object is achieved with a device whose essential characteristics are defined in Claim 5. Further characteristics and advantages of the invention will be made clear by the following detailed description, provided purely by way of example and without restrictive intent, with reference to the attached drawings, in which:
  • Figure 1 is a block diagram of a device according to the present invention associated with an alternating current synchronous electric motor with a permanent magnet rotor;
  • Figure 2 is a set of three diagrams which show, in a qualitative way, as a function of the time t shown on the horizontal axis, the variation of the motor supply voltage and of two voltages generated in a device according to the present invention.
  • Figure 3 is a diagram which shows in a qualitative way the variation of the phase difference ⁇ p between the position signal and the supply voltage of a synchronous electric motor used for driving a hydraulic pump, as a function of the liquid flow rate Q shown on the horizontal axis.
  • the letter M indicates a single-phase alternating current synchronous electric motor with a permanent magnet rotor, of a known type.
  • the motor M is associated with a control circuit D which is also of a known type .
  • the motor M is supplied for operation with an alternating voltage V, such as the ordinary mains voltage at 50 (60) Hz.
  • the rotor of the motor M is associated with an electrical position sensor S, such as a Hall effect sensor.
  • This sensor which is mounted in a stationary way, supplies at its output in operation an alternating electrical position signal, indicated by H in Figures 1 and 2.
  • this signal is a square wave having the same frequency as the alternating supply voltage V.
  • ZCD indicates a squaring circuit, to whose input the supply voltage V is applied during operation.
  • a square-wave signal indicated by Vsq in Figures 1 and 2, appears at the output of the squaring circuit ZCD during operation, this signal being isochronous and in phase with the voltage V.
  • the present invention is based on the finding that the phase difference ⁇ varies significantly with a variation of the mechanical load (resistive torque) of the synchronous electric motor .
  • the squaring circuit ZCD (which, incidentally, can be what is known as a zero crossing detector) and the electrical position sensor S are connected to a phase detector PD, which supplies at its output a signal indicating the phase difference ⁇ between the two signals H and Vsq.
  • the output of the phase detector PD is connected to a first input of a comparator TC, which compares the determined phase difference ⁇ with at least one predetermined reference, supplied to this comparator by a (constant or variable) threshold generator circuit TG .
  • the comparator circuit TC can also be designed to compare the phase difference ⁇ with a plurality of predetermined reference values .
  • a device can be used, for example, to determine the liquid flow rate Q of a hydraulic pump driven by an alternating current synchronous electric motor of the type defined above.
  • a device is used to determine the phase difference between the alternating supply voltage and the electrical signal indicating the position of the rotor of the motor, and this phase difference is compared with at least one predetermined reference indicating a corresponding value of the liquid flow rate Q.
  • Figure 3 shows a graph of the experimentally determined variation of the phase difference ⁇ as a function of the variation of the liquid flow rate Q of an electric pump of the type in question .
  • the determination of the liquid flow rate of a hydraulic pump driven by a synchronous electric motor can be useful, for example, in a dishwasher, in which an electrical resistance heating device for heating the washing liquid is associated with the intake of the electric pump which supplies the washing liquid to the spray arms of the dishwasher.
  • an electrical resistance heating device for heating the washing liquid is associated with the intake of the electric pump which supplies the washing liquid to the spray arms of the dishwasher.
  • a thermal cut-out which switches off the electrical resistance heater when, for any reason, the flow of washing liquid through the electric supply pump decreases or stops altogether.
  • a device in such an application, could be used to supply an electrical signal indicating the instantaneous flow rate of the pump, and also to detect a reduction or interruption of the liquid flow through this electric pump, so that the electrical resistance heating device could then be switched off without the use of a thermal cutout.
  • Another useful advantage of a device according to the present invention is the possibility of detecting the jamming of the rotor, which may occur in conditions such that the sensor (S) is switched not by the rotor' s magnetic ield, but by the magnetic field dispersed in the winding (a condition which may occur when, for example, the rotor is jammed in such a position that the strength of the magnet's magnetic field acting on the sensor is zero) .
  • the angle ⁇ which is present is unstable, but in any case is very different from the angle which would be present in correct operation (in normal operation, the angle can vary between 100 and 180 , while when the rotor is jammed it oscillates between 0 ° and 100°) .

Abstract

For determining the mechanical load of an alternating current synchronous electric motor (M) having a permanent magnet rotor, - the rotor is associated with an electrical position sensor (S), stationary in operation, which can supply an alternating electrical position signal (H); - the phase difference (φ) between the said position signal (H) and the alternating supply voltage (V) of the motor (M) is determined, and - the determined phase difference (φ) is compared with at least one predetermined reference.

Description

Method and device for determining the mechanical load of an alternating current synchronous electric motor with a permanent magnet rotor
The present invention relates in a general way to alternating current synchronous electric motors with permanent magnet rotors .
A first object of the invention is to provide a method for determining in a simple, reliable and economical way the mechanical load of a synchronous electric motor of this type.
This object is achieved according to the invention with a method characterized in that
- the rotor of the motor is associated with an electrical position sensor, stationary in operation, which can supply an alternating electrical position signal,
- the phase difference between the said electrical position signal and the alternating voltage supplied to the motor is then determined, and
- the determined phase difference is compared with at least one predetermined reference.
A further object of the invention is to provide a device for determining the mechanical load of an alternating current synchronous electric motor with a permanent magnet rotor, and according to the invention this further object is achieved with a device whose essential characteristics are defined in Claim 5. Further characteristics and advantages of the invention will be made clear by the following detailed description, provided purely by way of example and without restrictive intent, with reference to the attached drawings, in which:
Figure 1 is a block diagram of a device according to the present invention associated with an alternating current synchronous electric motor with a permanent magnet rotor;
Figure 2 is a set of three diagrams which show, in a qualitative way, as a function of the time t shown on the horizontal axis, the variation of the motor supply voltage and of two voltages generated in a device according to the present invention; and
Figure 3 is a diagram which shows in a qualitative way the variation of the phase difference <p between the position signal and the supply voltage of a synchronous electric motor used for driving a hydraulic pump, as a function of the liquid flow rate Q shown on the horizontal axis.
In Figure 1, the letter M indicates a single-phase alternating current synchronous electric motor with a permanent magnet rotor, of a known type.
The motor M is associated with a control circuit D which is also of a known type .
The motor M is supplied for operation with an alternating voltage V, such as the ordinary mains voltage at 50 (60) Hz. The rotor of the motor M is associated with an electrical position sensor S, such as a Hall effect sensor. This sensor, which is mounted in a stationary way, supplies at its output in operation an alternating electrical position signal, indicated by H in Figures 1 and 2. When the rotor reaches synchronism, this signal is a square wave having the same frequency as the alternating supply voltage V.
In Figure 1, ZCD indicates a squaring circuit, to whose input the supply voltage V is applied during operation. A square-wave signal, indicated by Vsq in Figures 1 and 2, appears at the output of the squaring circuit ZCD during operation, this signal being isochronous and in phase with the voltage V.
In general, there is a phase difference, indicated by φ in Figure 2, between the square-wave signals H and Vsq.
The present invention is based on the finding that the phase difference φ varies significantly with a variation of the mechanical load (resistive torque) of the synchronous electric motor .
With reference again to Figure 1, the squaring circuit ZCD (which, incidentally, can be what is known as a zero crossing detector) and the electrical position sensor S are connected to a phase detector PD, which supplies at its output a signal indicating the phase difference φ between the two signals H and Vsq.
The output of the phase detector PD is connected to a first input of a comparator TC, which compares the determined phase difference φ with at least one predetermined reference, supplied to this comparator by a (constant or variable) threshold generator circuit TG .
The comparator circuit TC can also be designed to compare the phase difference φ with a plurality of predetermined reference values .
A device according to the present invention can be used, for example, to determine the liquid flow rate Q of a hydraulic pump driven by an alternating current synchronous electric motor of the type defined above. For this purpose, a device according to the invention is used to determine the phase difference between the alternating supply voltage and the electrical signal indicating the position of the rotor of the motor, and this phase difference is compared with at least one predetermined reference indicating a corresponding value of the liquid flow rate Q.
Figure 3 shows a graph of the experimentally determined variation of the phase difference φ as a function of the variation of the liquid flow rate Q of an electric pump of the type in question .
The determination of the liquid flow rate of a hydraulic pump driven by a synchronous electric motor can be useful, for example, in a dishwasher, in which an electrical resistance heating device for heating the washing liquid is associated with the intake of the electric pump which supplies the washing liquid to the spray arms of the dishwasher. In a prior art application of this type, use is made of what is known as a thermal cut-out, which switches off the electrical resistance heater when, for any reason, the flow of washing liquid through the electric supply pump decreases or stops altogether. In such an application, a device according to the present invention could be used to supply an electrical signal indicating the instantaneous flow rate of the pump, and also to detect a reduction or interruption of the liquid flow through this electric pump, so that the electrical resistance heating device could then be switched off without the use of a thermal cutout.
However, the application described above is mentioned purely by way of example.
Another useful advantage of a device according to the present invention is the possibility of detecting the jamming of the rotor, which may occur in conditions such that the sensor (S) is switched not by the rotor' s magnetic ield, but by the magnetic field dispersed in the winding (a condition which may occur when, for example, the rotor is jammed in such a position that the strength of the magnet's magnetic field acting on the sensor is zero) . In the conditions described above, the angle φ which is present is unstable, but in any case is very different from the angle which would be present in correct operation (in normal operation, the angle can vary between 100 and 180 , while when the rotor is jammed it oscillates between 0° and 100°) . Clearly, provided that the principle of the invention is retained, the forms of application and the details of construction can be varied widely from what has been described and illustrated purely by way of example and without restrictive intent, without thereby departing from the scope of protection of the invention as defined in the attached claims .

Claims

1. Method for determining the mechanical load of an alternating current synchronous electric motor (M) having a permanent magnet rotor, the method being characterized in that
- the rotor is associated with an electrical position sensor (S) , stationary in operation, which can supply an alternating electrical position signal (H) ;
- the phase difference (φ) between the said electrical position signal (H) and the alternating supply voltage (V) of the motor (M) is then determined, and
- the determined phase difference (φ) is compared with at least one predetermined reference.
2. Method according to Claim 1, in which use is made of a position sensor (S) for supplying a square—wave signal at the same frequency as the said alternating supply voltage (V) of the motor (M) , and in which the latter voltage (V) is squared before the phase difference (φ) is determined.
3. Method according to Claim 2, in which the alternating supply voltage (V) of the motor (M) is squared by means of a zero crossing detector circuit (ZCD) .
4. Method for determining the liquid flow rate (Q) of a hydraulic pump driven by an alternating current synchronous electric motor (M) with a permanent magnet rotor, in which the mechanical load of the motor (M) is determined by a method according to any one of the preceding claims, by comparing the determined phase difference (φ) with at least one predetermined reference indicating a corresponding liquid flow rate (Q) .
5. Device for detecting the mechanical load of an alternating current electric or synchronous motor (M) with a permanent magnet rotor, characterized in that it comprises
- an electrical position sensor (S) associated with the rotor of the motor (M) and stationary in operation, for supplying an alternating electrical signal (H) indicating the position of the said rotor,
- phase detector means (PD) connected to the said electrical position sensor (S) , for supplying a phase signal indicating the phase difference (φ) between the said position sensor (H) and the alternating supply voltage (V) of the motor (M) , and
- comparator means (TC) for comparing the said phase signal with at least one predetermined reference.
6. Device according to Claim 5, comprising an electrical position sensor (S) for supplying a square-wave signal (H) having the same frequency as the said alternating supply voltage (V) of the motor (M) , and squaring means (ZCD) for supplying to the said phase detector means (PD) a square-wave voltage having the same frequency as the said alternating supply voltage (V) .
7. Device according to Claim 6, in which the said squaring circuit (ZCD) is a zero crossing detector circuit.
PCT/EP2005/052464 2004-05-31 2005-05-30 Method and device for determining the mechanical load of an alternating current synchronous electric motor with a permanent magnet rotor WO2005117246A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITTO2004A000367 2004-05-31
ITTO20040367 ITTO20040367A1 (en) 2004-05-31 2004-05-31 PROCEDURE AND DEVICE FOR DETECTING THE MECHANICAL LOAD OF A SYNCHRONOUS ELECTRIC MOTOR IN ALTERNATING CURRENT WITH PERMANENT MAGNET ROTOR.

Publications (2)

Publication Number Publication Date
WO2005117246A2 true WO2005117246A2 (en) 2005-12-08
WO2005117246A3 WO2005117246A3 (en) 2006-04-13

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Application Number Title Priority Date Filing Date
PCT/EP2005/052464 WO2005117246A2 (en) 2004-05-31 2005-05-30 Method and device for determining the mechanical load of an alternating current synchronous electric motor with a permanent magnet rotor

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WO (1) WO2005117246A2 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH294384A (en) * 1948-10-01 1953-11-15 Licentia Gmbh Electrical measuring device with a mechanical pressure contact driven by a synchronous motor.
EP0407253A1 (en) * 1989-07-07 1991-01-09 Thomson-Csf Dynamic measuring device for the torque of an ac motor and ac-motor-control apparatus utilising this device
US4991429A (en) * 1989-12-28 1991-02-12 Westinghouse Electric Corp. Torque angle and peak current detector for synchronous motors

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CH294384A (en) * 1948-10-01 1953-11-15 Licentia Gmbh Electrical measuring device with a mechanical pressure contact driven by a synchronous motor.
EP0407253A1 (en) * 1989-07-07 1991-01-09 Thomson-Csf Dynamic measuring device for the torque of an ac motor and ac-motor-control apparatus utilising this device
US4991429A (en) * 1989-12-28 1991-02-12 Westinghouse Electric Corp. Torque angle and peak current detector for synchronous motors

Also Published As

Publication number Publication date
ITTO20040367A1 (en) 2004-08-31
WO2005117246A3 (en) 2006-04-13

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