SE1550848A1 - A method of monitoring an electric motor - Google Patents

A method of monitoring an electric motor Download PDF

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Publication number
SE1550848A1
SE1550848A1 SE1550848A SE1550848A SE1550848A1 SE 1550848 A1 SE1550848 A1 SE 1550848A1 SE 1550848 A SE1550848 A SE 1550848A SE 1550848 A SE1550848 A SE 1550848A SE 1550848 A1 SE1550848 A1 SE 1550848A1
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SE
Sweden
Prior art keywords
time period
motor
during
current supply
rotational speed
Prior art date
Application number
SE1550848A
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Swedish (sv)
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SE538929C2 (en
Inventor
Sommansson Joakim
Källkvist Kurt
Original Assignee
Scania Cv Ab
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 Scania Cv Ab filed Critical Scania Cv Ab
Priority to SE1550848A priority Critical patent/SE538929C2/en
Priority to DE102016006472.2A priority patent/DE102016006472A1/en
Publication of SE1550848A1 publication Critical patent/SE1550848A1/en
Publication of SE538929C2 publication Critical patent/SE538929C2/en

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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
    • H02P29/00—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors
    • H02P29/02—Providing protection against overload without automatic interruption of supply
    • H02P29/024—Detecting a fault condition, e.g. short circuit, locked rotor, open circuit or loss of load
    • H02P29/0241—Detecting a fault condition, e.g. short circuit, locked rotor, open circuit or loss of load the fault being an overvoltage
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
    • H02H7/0811—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors for dc motors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
    • H02H7/085—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load
    • H02H7/0851—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load for motors actuating a movable member between two end positions, e.g. detecting an end position or obstruction by overload signal
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
    • H02H7/085—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load
    • H02H7/0854—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against excessive load responsive to rate of change of current, couple or speed, e.g. anti-kickback protection
    • 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
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
    • A61M5/00—Devices for bringing media into the body in a subcutaneous, intra-vascular or intramuscular way; Accessories therefor, e.g. filling or cleaning devices, arm-rests
    • A61M5/14—Infusion devices, e.g. infusing by gravity; Blood infusion; Accessories therefor
    • A61M5/168—Means for controlling media flow to the body or for metering media to the body, e.g. drip meters, counters ; Monitoring media flow to the body
    • A61M5/16831—Monitoring, detecting, signalling or eliminating infusion flow anomalies
    • A61M2005/16863—Occlusion detection

Abstract

16 ABSTRACT A method of monitoring an electric motor, comprising monitoringa current supply (I) and a rotational speed of the motor during afirst time period (T1) and a second time period (T2). The methodfurther comprises comparing the current supply and the rotationalspeed during the second time period to stored data relating tothe current supply and the rotational speed during the first timeperiod to determine a current supply difference (Al) between thefirst time period and the second time period. On the basis of saidcurrent supply difference and said rotational speed difference, itis determined whether a load on the motor has changed from thefirst time period to the second time period. The method is particularly suitable for monitoring a brushless DC motor. (Pig. 2)

Description

A method of monitorinq an electric motor TECHNICAL FIELD OF THE INVENTION The invention relates to a method of monitoring an electric motoraccording to the preamble of claim 1. The invention also relatesto a computer program product, an program, a computer electronic control unit and a motor vehicle.
BACKGROUND AND PRIOR ART both brushed DC motors and brushless DC motors, are used for numerous applications in many different Electric motors, fields. ln particular, brushless DC motors (BLDC motors), i.e.electric DC motors having their windings in a stator of the motorinstead of in a rotor, are nowadays commonly used in theautomotive industry, e.g. to power fuel pumps, pumps in ureadosage systems and cooling systems, throttles, actuators, etc. inmotor vehicles, and such motors may also be used in thepowertrain of a vehicle. The motors used are often provided withbuilt-in drivers and are either speed controlled or simple on/offmotors. Generally for electrical motors of both brushed type andbrushless type, it is useful to be able to detect situations in whichno load, an unusually small load or an unusually large load isapplied to the motor, in order to e.g. protect the motor fromin the overheating or overspeeding, or for detecting errors system in which the motor is used.
US 2013/0186661 discloses a method of monitoring a brushlessDC motor in a power tool and of determining whether the motor isin a non-load state, in which the motor is running without loadapplied to an end bit of the power tool. The method comprisesmonitoring a current supply and a rotational speed of the motorthe detected rotational speed to pre-defined threshold levels. Based on the and comparing the detected current and/orcomparison, it is judged whether a load is applied to the motor ornot.
However, a method disclosed in US2013/0186661 is that it requires detailed knowledge of expected current levels and rotational speeds. The method is therefore problem with the limited to applications in which these parameters are well-known.For applications in which current levels and rotational speeds are unknown or more difficult to predict, the method lacks precision.
SUMMARY OF THE INVENTION lt is an object of the present invention to solve the aboveidentified problem and thus provide a solution by means of whichan unexpected load situation can be identified also forapplications with little knowledge about expected current levels or rotational speed levels.
According to a first aspect of the present invention, this object isachieved by means of the method initially defined. The methodcomprises: - monitoring a current supply to the motor and a rotational speed of the motor during a first time period, monitoring a current supply to the motor and a rotational speed of the motor during a second time period.
The method is characterized in that it further comprises: storing data relating to the current supply and the rotationalspeed during at least the first time period, comparing the current supply during the second time periodto stored data relating to the current supply during the firsttime period to determine a current supply differencerepresenting a difference in current supply between the firsttime period and the second time period, comparing the rotational speed during the second timeperiod to stored data relating to the rotational speed duringrotational the first time period to determine a speed difference representing a difference in rotational speedbetween the first time period and the second time period, on the basis of said current supply difference and saidrotational speed difference, determining whether a load onthe motor has changed from the first time period to the second time period.
By means of the method according to the invention, the current and speed during a first time period are compared to the current and speed during a second time period, and the results of these comparisons are used to determine whether a change in load applied to the motor has changed. Thus, the method does not rely on pre-defined threshold levels, but it is rather the detection of a relative current increase or decrease and/or a relative increase or decrease in rotational speed that indicate that a load on the motor has changed. A drop in current supply without drop in rotational speed of the motor, or an increase in rotational speed without increase in current supply, indicates that the loadon the motor has decreased. Similarly, an increase in currentsupply without increase in rotational speed, or a reduction of therotational speed without reduction of current supply, indicatesthat the load has increased. Very little knowledge about therelies on relative application is needed since the detection changes in current supply and/or rotational speed.
The method according to the invention is very useful for earlydetection of possible errors in the system in which the motor isworking and prevention of more severe consequences of sucherrors. For example, if the motor is used to power a pump in aurea dosage system, a situation in which the rotational speed ofthe motor increases rapidly, i.e. the load on the motor hasdecreased, may indicate the presence of air bubbles in the ureadosage system. lf instead the rotational speed decreases withoutcorresponding drop in current supply, i.e. an increase in load onthe motor, this may indicate that the flow of urea through theurea dosage system is for some reason restricted, e.g. due to flow blockages.
The method according to the invention has the further advantageof not requiring any additional sensors or signals apart from thecurrent feedback from the motor. The method is therefore veryversatile and can be used in numerous applications in which anelectric motor is used. ln particular, this is advantageous forbrushless DC (BLDC) commonly monitored from such motors. The method is however motors, since current feedback is best suited for applications running under reasonably static conditions, or under conditions which vary according to well-known or controlled schemes.
According to an embodiment of the invention, the step ofcomparing the current supply during the second time period tostored data relating to the current supply during the first timeperiod comprises comparing a second average current supplyduring the second time period to a first average current supplyduring the first time period. By looking at the average currentsupply, a more accurate determination of an unexpected loadsituation can be made since the influence of occasional current peaks or drops is reduced.
According to another embodiment of the invention, the step ofcomparing the rotational speed during the second time period tostored data relating to the rotational speed during the first timeperiod comprises comparing a second average rotational speedduring the second time period to a first average rotational speedduring the first time period. The influence of occasional rotational speed peaks or drops is hereby reduced.
According to another embodiment of the invention, the step ofdetermining whether a load on the motor has changed comprisesrotational comparing the speed difference to a pre-defined threshold. By comparing the difference in rotational speedbetween the first time period and the second time period to athreshold, it is easy to discriminate between smaller, normalfluctuations in load and larger fluctuations which indicate that thesystem or the motor is not functioning properly. Since a difference in rotational speed, and not an absolute value of the rotational speed, is compared to a threshold, it is not necessaryto know anything about normal rotational speed levels of the motor in the current application.
According to another embodiment of the invention, the step ofdetermining whether a load on the motor has changed comprisescomparing the current supply difference to a pre-definedthreshold. Also in this embodiment, it is easy to discriminatebetween normal fluctuations in load and larger fluctuations. Thefunction of the motor can be analyzed without knowledge about the current application of the motor.
According to another embodiment of the invention, the methodfurther comprises the steps: - monitoring an input signal for controlling the motor duringthe first time period and the second time period, - storing data relating to the input signal during at least thefirst time period, - comparing said input signal during the second time periodto stored data relating to said input signal during the firsttime period.
The rotational requested torque, or another requested output from the motor. By input signal can be e.g. requested speed,comparing the input signals during the first and the second timeperiods, it is possible to determine whether a detected change inload on the motor is reasonable or not. A change in input signalsindicates that a simultaneous change in rotational speed and/orcurrent is expected, while the absence of a change in inputsignals indicate that the change in load might not be normal. lf the motor is controlled by a control unit which is also used to control other parameters of the system in which the motor isworking, it may easily be checked whether the change in load isa result of an expected change in the system, or if the change in load is unexpected.
According to another embodiment of the invention, the methodfurther comprises the step: - based on the comparison of input signals and a determined change in load on the motor, generating an error code.
The error code can be generated e.g. when there is a change inload without corresponding change in input signals. By setting anerror code, it is possible to e.g. request the attention of a driverof a vehicle in which the motor is located, or to introduce asearch for an error in the system in which the motor is working.Generation of an error code may therefore be useful to prevent or remedy secondary issues in the system.
According to an embodiment of the invention, the method iscarried out for a brushless DC motor. The inventive method isparticularly suitable for monitoring a BLDC motor, since currentfeedback is commonly monitored from such a motor, and thus noextra sensors or other equipment is required.
According to another aspect of the invention, the object isachieved by a computer program comprising computer programcode for causing a computer to implement the proposed methodwhen the computer program is executed in the computer. ln other aspects, the invention also relates to a computer program having the features of claim 9, a computer program product having the features of claim 10, an electronic control unithaving the features of claim 11 and a motor vehicle according to claims 12 and 13.
Further advantages as well as advantageous features of the present invention will appear from the following detailed descnpüon.
BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will in the following be described with reference to the appended drawings, in which: Fig. 1 is a flow chart showing the method according to anembodiment of the invention, Fig. 2 is a schematic diagram showing current supply as afunction of time for a BLDC motor, Fig.3 is another diagram showing current supply as afunction of time for a BLDC motor, and Fig.4 shows a schematic drawing of a control unit for implementing a method according to the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THEINVENTION A flow chart illustrating a method according to a first embodimentof the invention is shown in fig. 1. ln a first step A1, a currentsupply I and a rotational speed w of a brushless DC (BLDC)motor are monitored during a first time period T1 by means of a monitoring device. ln a step A2, data relating to the current supply I and the rotational speed w are stored in a databaseonce a stable current and rotation have been found. A firstaverage value |_avg1 of the current supply I during the first timeperiod T1 and a first average value w_avg1 of the rotationalspeed w during the first time period T1 are calculated and storedin a step A3. ln a step A4, the current supply I and the rotationalspeed w of the motor are monitored during a second time periodT2. Second average values l_avg2 and w_avg2 of the currentsupply I and the rotational speed w respectively are calculated ina step A5. ln a step A6, the second average current supplyl_avg2 is compared to the stored first average current supply|_avg1 and a current supply difference Al is determined. Thiscurrent supply difference Al can be in the form of an actualdifference, i.e. AI=l_avg2-|_avg1, but it may also be calculatedas e.g. a ratio. ln a step A7, the second average rotational speedw_avg2 is compared to the stored first average rotational speedw_avg1 and a rotational speed difference Aw is determined. Alsoin this case, the difference Aw may be in the form of an actualdifference or e.g. in the form of a ratio. Based on the detectedcurrent supply difference Al and rotational speed difference Aw,in a step A8, it is determined whether a load on the motor haschanged between the first time period T1 and the second time period T2. ln another embodiment, the method comprises all the steps ofthe first embodiment. ln addition to monitoring the current supplyI and the rotational speed w, input signals to the motor aremonitored, such as requested torque T and/or requestedrotational speed w_req during the first time period T1 and the second time period T2. The input signals, or values representing the input signals, are stored in a database. When it is determinedin step A8 that a load on the motor has changed, it is checkedwhether also the input signals to the motor have changed. lf theinput signals have changed so that the decreased/increased loadon the motor was expected, no action is taken. lf however theinput signals to the motor have not changed, and a change inload was unexpected, an error code is generated. The error codemay be used to communicate an error message to an operator of the motor.
Fig. 2 schematically shows a current feedback signal from aln the diagram, current supply I as a function of time t is shown. During BLDC motor being subjected to a decrease in load. a first time period T1, the average current supply l_avg1 is stableand the motor is running at an average rotational speed w_avg1.For a BLDC motor with n coils, the rotational speed w is given by1/(t1-n), peaks. After the time period T1, the load on the motor is reduced. wherein t1 is the time between successive currentThe time t2 between current peaks is equal to the time t1between current peaks during the first time period T1, so themotor runs at a maintained rotational speed w. However, thereduced load results in a reduced current supply I to the motor,so that the average current supply l_avg2 during the second timeperiod T2 is smaller than the average current supply l_avg1during the first time period T1. The difference between the average current supplies is here shown as Al=l_avg1-l_avg2.
Also fig. 3 schematically shows a current feedback signal from a BLDC motor being subjected to a decrease in load. However, in 11 this case, the average current supply is stable, |_avg1=|_avg2, but instead the rotational speed w increases since t2 lf a stable current supply I and a stable rotational speed wcannot be found during startup of a motor monitored using themethod according to the invention, it can be assumed that themotor is overspeeding and that there is an unexpectedly small load on the motor.
Fig. 4 illustrates very schematically an electronic control unit 1comprising an execution means 2, such as a central processorunit (CPU), for executing a computer program. The executionmeans 2 communicates with a memory 3, for example of the typeRAM, through a data bus 4. The control unit 1 also comprises anon-transitory data storing medium 5, for example in the form ofa Flash memory or a memory of the type ROM, PROM, EPROMor EEPROl\/I. The execution means 2 communicates with the datastoring medium 5 through the data bus 4. A computer programcomprising computer program code for implementing a methodaccording to the invention is stored on the data storing medium The invention is of course not in any way restricted to the embodiments described above. On the contrary, many possibilities to modifications thereof will be apparent to a personwith ordinary skill in the art without departing from the basic idea of the invention such as defined in the appended claims.

Claims (13)

1. A method of monitoring an electric motor, the methodcomprising:- monitoring a current supply (I) to the motor and a rotationalspeed (w) of the motor during a first time period (T1),- monitoring a current supply (I) to the motor and a rotationalspeed (w) of the motor during a second time period (T2),characterized inthat the method comprisesand the rotational speed (w) during at least the first time period (T1), -storing data re|ating to the current supply (I) - comparing the current supply (I) during the second timeperiod (T2) to stored data re|ating to the current supply (I)during the first time period (T1) to determine a currentsupply difference (Al) representing a difference in currentsupply (I) between the first time period (T1) and the secondtime period (T2), - comparing the rotational speed (w) during the second timeperiod (T2) to stored data re|ating to the to the rotationalspeed (w) during the first time period (T1) to determine arotational speed difference (Aw) representing a difference inrotational speed (w) between the first time period (T1) andthe second time period (T2), - on the basis of said current supply difference (Al) and saidrotational speed difference (Aw), determining whether a loadon the motor has changed from the first time period (T1) to the second time period (T2). 13
2. The method according to claim 1, wherein the step ofcomparing the current supply (l) during the second time period(T2) to stored data relating to the current supply (l) during thefirst time period (T1) comprises comparing a second averagecurrent supply (l_avg2) during the second time period (T2) to afirst average current supply (l_avg1) during the first time period (T1).
3. The method according to claim 1 or 2, wherein the step ofcomparing the rotational speed (w) during the second time periodto stored data relating to the rotational speed (w) during the first(T1) rotational speed (w_avg2) during the second time period (T2) to time period comprises comparing a second averagea first average rotational speed (w_avg1) during the first timeperiod (T1).
4. The method according to any of the preceding claims,wherein the step of determining whether a load on the motor haschanged comprises comparing the rotational speed difference (Aw) to a pre-defined threshold.
5. The method according to any of the preceding claims,wherein the step of determining whether a load on the motor haschanged comprises comparing the current supply difference (Al) to a pre-defined threshold.
6. The method according to any of the preceding claims, furthercomprising the steps:- monitoring an input signal for controlling the motor during the first time period (T1) and the second time period (T2), 14 - storing data relating to the input signal during at least thefirst time period, - comparing said input signal during the second time period(T2) to stored data relating to said input signal during the first time period (T1).
7. The method according to any of the preceding claims, furtherincluding the step:- based on the comparison of input signals and a determined change in load on the motor, generating an error code.
8. The method according to any of the preceding claims, wherein the method is carried out for a brushless DC motor.
9. A computer program comprising computer program code forcausing a computer to implement a method according to any ofthe claims 1-8 when the computer program is executed in the computer.
10. A computer program product comprising a data storagemedium which can be read by a computer and on which theprogram code of a computer program according to claim 9 is stored.
11. An electronic control unit (1) of a motor vehicle comprising an execution means (2), a memory (3) connected to theexecution means (2) and a data storage medium (5) which isconnected to the execution means (2) and on which the computerprogram code of a computer program according to claim 9 is stored.
12. A motor vehicle comprising an electronic control unit (1) according to claim 11.
13. A motor vehicle according to claim 12, wherein the motor vehicle is a truck or a bus.
SE1550848A 2015-06-18 2015-06-18 A method of monitoring an electric motor SE538929C2 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
SE1550848A SE538929C2 (en) 2015-06-18 2015-06-18 A method of monitoring an electric motor
DE102016006472.2A DE102016006472A1 (en) 2015-06-18 2016-05-25 Method for monitoring an electric motor

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE1550848A SE538929C2 (en) 2015-06-18 2015-06-18 A method of monitoring an electric motor

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Publication Number Publication Date
SE1550848A1 true SE1550848A1 (en) 2016-12-19
SE538929C2 SE538929C2 (en) 2017-02-21

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DE102019105749A1 (en) * 2019-03-07 2020-09-10 Ebm-Papst Landshut Gmbh Method for detecting incorrect operation of a gas blower driven by a direct current motor

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DE9001867U1 (en) * 1990-02-16 1990-04-19 Siemens Ag, 1000 Berlin Und 8000 Muenchen, De
SE516155C2 (en) * 1997-10-28 2001-11-26 Emotron Ab load guard
EP1772960B1 (en) * 2005-10-07 2009-03-04 Emotron AB Load monitor
DE102008029910C5 (en) * 2008-06-24 2020-03-05 BSH Hausgeräte GmbH Method for recognizing the load status of a pump
JP2012076160A (en) 2010-09-30 2012-04-19 Hitachi Koki Co Ltd Power tool

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DE102016006472A1 (en) 2016-12-22

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