WO2023174500A1 - A method of estimating induction motor speed - Google Patents

A method of estimating induction motor speed Download PDF

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Publication number
WO2023174500A1
WO2023174500A1 PCT/EP2022/025216 EP2022025216W WO2023174500A1 WO 2023174500 A1 WO2023174500 A1 WO 2023174500A1 EP 2022025216 W EP2022025216 W EP 2022025216W WO 2023174500 A1 WO2023174500 A1 WO 2023174500A1
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Prior art keywords
rated
motor
state
supply frequency
speed
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PCT/EP2022/025216
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French (fr)
Inventor
Gurmeet Singh
Sneha ABHYANKAR
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Eaton Intelligent Power Limited
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Publication of WO2023174500A1 publication Critical patent/WO2023174500A1/en

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    • 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
    • H02P6/18—Circuit arrangements for detecting position without separate position detecting elements
    • 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
    • H02P2207/00—Indexing scheme relating to controlling arrangements characterised by the type of motor
    • H02P2207/01—Asynchronous machines

Definitions

  • the present invention relation to a method of estimating induction motor speed.
  • Speed estimation is important in applications related to speed control, condition monitoring, estimating motor efficiency and in motor fault diagnosis. Correct speed estimation provides improved control and helps in avoiding performance issues. Speed may be measured using either direct or indirect methods.
  • the direct method uses speed measurement sensors, such as a tachometer, a stroboscope and encoders.
  • speed measurement sensors such as a tachometer, a stroboscope and encoders.
  • Siliang Lu et al describes: “Tacholess Speed Estimation in Order Tracking: A Review With Application to Rotating Machine Fault Diagnosis”, published in IEEE transactions on Instrumentation and Measurement, Vol. 68, No. 7, July 2019.
  • These sensors are very sensitive and can be damaged with dust, vibrations and shock.
  • the use of sensors increases the cost.
  • Indirect methods of measuring speed do not directly measure the speed but they estimate the speed using other characteristics.
  • a Rotor Slot Harmonics (RSH) and eccentricity method may be used, which uses motor current spectrum analysis for speed estimation.
  • vibration analysis uses the fundamental rotational frequency component for speed estimation, as described by Gurmeet Singh et al.; in “Speed estimation of rotating machinery using generated harmonics”; Computers and Electrical Engineering 72 (2018) 420-430. Both of these methods use complex digital signal processing techniques, and implementing them on motors requires hardware to collect current data at high sampling rates. This increases the hardware and memory requirements, as well as increasing the cost.
  • the method of the present invention has adapted the LSE method to improve its accuracy in estimating speed by using a rated motor efficiency, and it is further considered that Name Plate Information (NPI) may change with time (e.g. due to ageing or because of repairs) and so this method further considers how to determine a revised (i.e. re-calibrated) rated motor efficiency and a rated motor speed.
  • NPI Name Plate Information
  • a method of estimating induction motor rotational speed comprising: measuring motor operational parameters, the parameters comprising input power, a supply frequency at a first state and a supply frequency at a second state; wherein the first state is the state at a first synchronous speed at a first output power and the second state is a state at a second synchronous speed at a second output power; determining, using motor name plate information (NPI), rated motor information, wherein the rated motor information comprises rated motor efficiency, rated supply frequency, rated motor slip and a rated output power at the measured supply frequency at the second state; calculating motor slip at the measured supply frequency at the second state using the rated motor slip, the rated supply frequency and the measured supply frequency at the second state; calculating rated synchronous speed at the measured supply frequency at the second state using rated synchronous speed at the measured supply frequency at the first state the rated supply frequency and the measured supply frequency at the second state; calculating a rated speed at the measured supply frequency at the measured supply frequency at the measured supply frequency at the second state;
  • the method further comprises: calculating a revised rated motor efficiency and a revised motor rated speed by performing the steps of: measuring, using a speed sensor, a motor rotational speed; iteratively perform the steps of the invention according to the first aspect by reducing the rated motor efficiency by a first predetermined value and changing the rated speed at the measured supply frequency by a second predetermined value until the calculated motor rotational speed is within a preset range of the measured motor rotational speed; and storing the revised rated motor efficiency and the revised motor rated speed.
  • the first predetermined value is 2% of the rated motor efficiency
  • the second predetermined value is 5rpm
  • the motor operational parameters further comprise a motor supplied voltage.
  • the rated motor information further comprises rated motor output power and rated motor voltage.
  • a non-transitory computer readable storage medium for storing instructions to perform the method of the first aspect of the invention.
  • Figure 1 depicts a schematic of a method of estimating motor rotational speed in accordance with a first aspect of the present claimed invention
  • Figure 2 depicts a graph of the power-speed characteristics of an induction motor at various supply frequencies
  • Figure 3 depicts a method of revising the rated motor efficiency and the rated motor speed in accordance with a preferred aspect of the present claimed invention in accordance with the first aspect
  • Figure 4 depicts an example of the method of Figure 3 in further detail
  • Figure 5 depicts a schematic of an experimental set-up used to test the accuracy of the method of estimating induction motor speed in accordance with the first aspect of the present claimed invention
  • Figure 6 depicts a result of the experiment used to test the accuracy of the method of estimating induction motor torque in accordance with the first aspect of the present claimed invention when compared with the LSE method;
  • Figure 7 depicts a table of NPI information for two test induction motors
  • Figure 8 depicts a table of results for a 2013 induction motor
  • Figure 9 depicts a table of results for a 2006 induction motor.
  • Step 110 comprises measuring motor operational parameters.
  • the measured operational parameters comprise input power (Pi2), a supply frequency at a first state (f s i) and a supply frequency at a second state (f S 2); wherein the first state is the state at a first synchronous speed at a first output power and the second state is a state at a second synchronous speed at a second output power.
  • Step 120 comprises determining, using motor name plate information (NPI), rated motor information.
  • the rated motor information comprises rated motor efficiency (e), rated supply frequency (f s ), rated motor slip (s ra ted) and a rated output power at the measured supply frequency at the second state (P mra ted2).
  • Step 130 comprises calculating 130 motor slip (s ra ted2) at the measured supply frequency at the second state using the rated motor slip (s ra ted), the rated supply frequency (f s ) and the measured supply frequency at the second state (f S 2).
  • Step 140 comprises calculating rated synchronous speed (w syn _2) at the measured supply frequency at the second state using rated synchronous speed (w syn ) at the measured supply frequency at the first state the rated supply frequency (f s ) and the measured supply frequency at the second state (f S 2).
  • Step 150 comprises calculating a rated speed (w ra ted_2) at the measured supply frequency at the second state using the calculated rated synchronous speed (w syn _2) and the calculated motor slip (s ra ted2).
  • step 160 comprises calculating the motor rotational speed (Wr2) using the input power (Pj2), the rated motor efficiency (e), the rated output power at the measured supply frequency at the second state (P mra ted2), the rated synchronous speed (w syn _2) at the measured supply frequency at the second state and the rated speed (w ra ted_2) at the measured supply frequency at the second state.
  • this depicts a graph 200 of the power-speed characteristics of an induction motor at various supply frequencies.
  • Figure 2 depicts the rated synchronous speed (W syn _i), in radians per second, with supply frequency (f s i) as a function of rated output power (Pmratedi) with supply frequency (f s i).
  • the rated synchronous speed (W syn _2), in radians per second, with supply frequency (f S 2) as a function of rated output power (P mr ated2) with supply frequency (f S 2) is shown.
  • Figure 2 depicts a first state and a second state as described in relation to the method of the present invention as described in relation to Figure 1. Accordingly, it is shown that the first state and the second state are values of supply frequency for a given graph 200 of the power-speed characteristics of an induction motor at various supply frequencies.
  • this depicts a preferred method 300 of revising the rated motor efficiency and the rated motor speed, comprising steps 310 to 330.
  • a motor rotational speed is measured using a speed sensor, for example a tachometer.
  • the method of estimating induction motor rotational speed is iteratively performed. This comprises changing the rated motor efficiency by a first predetermined value and the rated speed at the measured supply frequency by a second predetermined value until the calculated motor rotational speed is within a preset range of the measured motor rotational speed.
  • Step 330 comprises storing the revised rated motor efficiency and the revised rated motor speed.
  • this depicts an example method 400 of the method described in relation to Figure 3 in accordance with a preferred aspect of the present claimed invention in accordance with the first aspect.
  • This method 400 comprises steps 410 to 490.
  • step 410 a motor rotational speed is measured using a speed sensor.
  • step 420 the method of estimating induction motor rotational speed (w r 2) is used and an estimate is produced.
  • step 430 it is determined whether the difference between the measured motor rotational speed of step 410 differs from the estimated motor rotational speed of step 420 by more than a first predetermined threshold (e.g. 5rpm). If the difference is less than or equal to the first predetermined threshold, then the method proceeds to step 470. If the difference is greater than the first predetermined threshold then the rated motor speed used in the estimation of step 420 is increased by a predetermined value and the motor rotational speed is re-estimated in step 440.
  • a first predetermined threshold e.g. 5rpm
  • step 450 it is determined whether the re-estimated motor rotational speed differs from the measured motor rotational speed of step 410 by a smaller value than that produced in step 430 (i.e. it is determined in step 450 whether there is less difference between the difference of step 430). If the difference in step 450 is smaller than the previous difference of step 430, then the method proceeds to step 470, discussed below. If the difference in step 450 is not smaller than the previous difference of step 430, then the rated speed is decreased by the first predetermined value (e.g. 5rpm) in step 460.
  • the first predetermined value e.g. 5rpm
  • step 470 it is determined whether the difference of step 450 is less than or equal to a second predetermined threshold (e.g. 3rpm). If the difference is less than or equal to the second predetermined threshold then the method 400 proceeds to step 490. If the difference is greater than the second predetermined threshold then the method 400 proceeds to step 480.
  • a second predetermined threshold e.g. 3rpm
  • step 480 a revised (i.e. decreased) value of the rated motor efficiency is used in the speed estimation method of 420, where the revised rated motor efficiency is decreased by a second predetermined value (e.g. 2% of the original rated motor efficiency).
  • the steps of 470 and 480 are iteratively performed until a revised rated motor efficiency is determined which produces a difference between the measured motor rotational speed and the estimated motor rotational speed which is less than or equal to the second predetermined threshold. Once the difference is less than or equal to the second predetermined threshold, then the method 400 proceeds to step 490.
  • step 490 the revised rated motor speed and the revised rated motor efficiency are stored.
  • this depicts a schematic 500 of an experimental set-up used to test the accuracy of the method of estimating induction motor speed in accordance with the first aspect of the present claimed invention.
  • a 25 horse power (HP) induction motor 510 was used to drive a mechanical load 520.
  • the system 500 had a speed sensor and a torque sensor 530 used to determine the speed and torque output from the induction motor 510. The determined speed and torque outputs were then displayed on a display 540.
  • the system 500 further comprises a motor operational parameters unit used to measure the motor operational parameters from the induction motor 510.
  • Table 1 shows the NPI for two 25 HP induction motors, including their manufacturing year (i.e. 2013 and 2006), and their motor rated information, including their rated voltage and rated current (which is used to determine the rated power), and their rated frequency, rated speed, rated torque and rated efficiency.
  • Figure 6 depicts a result of the experiment, as described in relation to Figure 5, used to test the accuracy of the method of estimating induction motor torque, in accordance with the first aspect of the present claimed invention when compared with the LSE method.
  • Figure 6 depicts a result of an error in speed estimation, in units of rpm, for multiple samples of a particular model of engine, where (a) is an induction motor manufactured in 2006, and (b) is an induction motor manufactured in 2013.
  • the known LSE method produces larger errors when compared to the results of the method of the present invention. For example, it is seen in Figure 6 (a) that the maximum error produced using the LSE method is 13.7rpm, whereas the maximum error produced using the method of the present invention is 3.7rpm.
  • the rated motor information is determined from the NPI, where the NPI is information which is found by using an electrical vehicles nameplate (i.e. its licence plate or another identification number/code which identifies the vehicle or an induction motor engine) and which allows the determination of rated information of a particular vehicle.
  • an electrical vehicles nameplate i.e. its licence plate or another identification number/code which identifies the vehicle or an induction motor engine
  • the motor operational parameters described in relation to Figure 1 may further comprise a motor supplied voltage (V2).
  • the rated motor information may further comprise rated motor output power (P m ) and rated motor voltage (Vi).
  • Wsyn is rated synchronous speed (w syn ) at the measured supply frequency at the first state
  • f s _i is the motor operational supply frequency at a first state.
  • Pi2 is input power
  • e efficiency
  • P02 is a motor operational output power
  • P m-ra ted_2 is the rated output power at the measured supply frequency at the second state.
  • Pm_rated_2 is calculated using Equation 8 below, where T ra ted_2 is a rated motor torque at a second state and is found using Equation 7 and T ra ted_i is a rated torque motor torque and found using Equation 6:
  • Wratedi is a rated speed at the measured supply frequency at the first state
  • Pmratedi is the rated output power at the measured supply frequency at the first state
  • Vi is the rated motor voltage
  • V2 is the motor supplied voltage.

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Abstract

A method of estimating induction motor rotational speed comprising measuring motor operational parameters, the parameters comprising input power, a supply frequency at a first state and a supply frequency at a second state; wherein the first state is the state at a first synchronous speed at a first output power and the second state is a state at a second synchronous speed at a second output power; determining, using motor name plate information (NPI), rated motor information, wherein the rated motor information comprises rated motor efficiency, rated supply frequency, rated motor slip and a rated output power at the measured supply frequency at the second state.

Description

A METHOD OF ESTIMATING INDUCTION MOTOR SPEED
Field of the Invention
The present invention relation to a method of estimating induction motor speed.
Background to the Invention
Speed estimation is important in applications related to speed control, condition monitoring, estimating motor efficiency and in motor fault diagnosis. Correct speed estimation provides improved control and helps in avoiding performance issues. Speed may be measured using either direct or indirect methods.
The direct method uses speed measurement sensors, such as a tachometer, a stroboscope and encoders. For example, Siliang Lu et al; describes: “Tacholess Speed Estimation in Order Tracking: A Review With Application to Rotating Machine Fault Diagnosis”, published in IEEE transactions on Instrumentation and Measurement, Vol. 68, No. 7, July 2019. These sensors are very sensitive and can be damaged with dust, vibrations and shock. In addition, the use of sensors increases the cost.
Indirect methods of measuring speed do not directly measure the speed but they estimate the speed using other characteristics. For example, a Rotor Slot Harmonics (RSH) and eccentricity method may be used, which uses motor current spectrum analysis for speed estimation. Alternatively, vibration analysis uses the fundamental rotational frequency component for speed estimation, as described by Gurmeet Singh et al.; in “Speed estimation of rotating machinery using generated harmonics”; Computers and Electrical Engineering 72 (2018) 420-430. Both of these methods use complex digital signal processing techniques, and implementing them on motors requires hardware to collect current data at high sampling rates. This increases the hardware and memory requirements, as well as increasing the cost.
A further known method of estimating speed using an indirect method is found in US 2014/009102 A1 which describes a linear speed estimation (LSE) method for speed estimation of motors operated using variable speed drives (VFD). This method works well for motors having a higher motor rating, where these motors have low slip due to high inertia, in comparison to motors of lower ratings. Therefore, this method has errors when applied on high slip motors of lower motor rating. Additionally, when motors get old or are overhauled, there can be a divergence of the name plate information (NPI) from what has been recorded, leading to a large error when estimating speed using the LSE method.
Therefore, there is a requirement for an indirect, sensor-less, speed estimation method. Advantageously, such a method would reduce the cost and hardware resource requirements.
The method of the present invention has adapted the LSE method to improve its accuracy in estimating speed by using a rated motor efficiency, and it is further considered that Name Plate Information (NPI) may change with time (e.g. due to ageing or because of repairs) and so this method further considers how to determine a revised (i.e. re-calibrated) rated motor efficiency and a rated motor speed.
Summary of the Invention
According to a first aspect of the invention, there is provided a method of estimating induction motor rotational speed, comprising: measuring motor operational parameters, the parameters comprising input power, a supply frequency at a first state and a supply frequency at a second state; wherein the first state is the state at a first synchronous speed at a first output power and the second state is a state at a second synchronous speed at a second output power; determining, using motor name plate information (NPI), rated motor information, wherein the rated motor information comprises rated motor efficiency, rated supply frequency, rated motor slip and a rated output power at the measured supply frequency at the second state; calculating motor slip at the measured supply frequency at the second state using the rated motor slip, the rated supply frequency and the measured supply frequency at the second state; calculating rated synchronous speed at the measured supply frequency at the second state using rated synchronous speed at the measured supply frequency at the first state the rated supply frequency and the measured supply frequency at the second state; calculating a rated speed at the measured supply frequency at the second state using the calculated rated synchronous speed and the calculated motor slip; and calculating the motor rotational speed using the input power, the rated motor efficiency, the rated output power at the measured supply frequency at the second state, the rated synchronous speed at the measured supply frequency at the second state and the rated speed at the measured supply frequency at the second state.
Preferably, the method further comprises: calculating a revised rated motor efficiency and a revised motor rated speed by performing the steps of: measuring, using a speed sensor, a motor rotational speed; iteratively perform the steps of the invention according to the first aspect by reducing the rated motor efficiency by a first predetermined value and changing the rated speed at the measured supply frequency by a second predetermined value until the calculated motor rotational speed is within a preset range of the measured motor rotational speed; and storing the revised rated motor efficiency and the revised motor rated speed.
Preferably, the first predetermined value is 2% of the rated motor efficiency, the second predetermined value is 5rpm, and the preset range of less than or equal to 3rpm.
Preferably, the motor operational parameters further comprise a motor supplied voltage.
Preferably, the rated motor information further comprises rated motor output power and rated motor voltage.
Preferably, calculating the rated motor slip at the measured supply frequency
Comprises.
Figure imgf000005_0001
wherein calculating the rated synchronous speed at the measured supply frequency at the second state comprises: wsyn-2 =
Figure imgf000005_0002
wherein calculating the rated speed at the measured supply frequency at the second state comprises: wrated 2 = Wsyn 2(1 - srated 2).
Preferably, the motor rotational speed is calculated using: wr2 = (mPg2) + Wsyn _2 = (m * e * wherein:
Figure imgf000005_0003
Wherein. Pm_rated_2 ~ Prated_2 wrated_2 ’
Figure imgf000006_0001
Jm rated l wherein. 7 ated_i rated
According to a second aspect of the invention, there is provided a non-transitory computer readable storage medium for storing instructions to perform the method of the first aspect of the invention.
Detailed Description of the Drawings
Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:
Figure 1 depicts a schematic of a method of estimating motor rotational speed in accordance with a first aspect of the present claimed invention;
Figure 2 depicts a graph of the power-speed characteristics of an induction motor at various supply frequencies;
Figure 3 depicts a method of revising the rated motor efficiency and the rated motor speed in accordance with a preferred aspect of the present claimed invention in accordance with the first aspect;
Figure 4 depicts an example of the method of Figure 3 in further detail;
Figure 5 depicts a schematic of an experimental set-up used to test the accuracy of the method of estimating induction motor speed in accordance with the first aspect of the present claimed invention;
Figure 6 depicts a result of the experiment used to test the accuracy of the method of estimating induction motor torque in accordance with the first aspect of the present claimed invention when compared with the LSE method;
Figure 7 depicts a table of NPI information for two test induction motors; Figure 8 depicts a table of results for a 2013 induction motor; and
Figure 9 depicts a table of results for a 2006 induction motor.
With reference to Figure 1 , this depicts a method 100 of estimating motor rotational speed in accordance with a first aspect of the present claimed invention which comprises steps 110 to 160. Step 110 comprises measuring motor operational parameters. The measured operational parameters comprise input power (Pi2), a supply frequency at a first state (fsi) and a supply frequency at a second state (fS2); wherein the first state is the state at a first synchronous speed at a first output power and the second state is a state at a second synchronous speed at a second output power.
Step 120 comprises determining, using motor name plate information (NPI), rated motor information. The rated motor information comprises rated motor efficiency (e), rated supply frequency (fs), rated motor slip (srated) and a rated output power at the measured supply frequency at the second state (Pmrated2).
Step 130 comprises calculating 130 motor slip (srated2) at the measured supply frequency at the second state using the rated motor slip (srated), the rated supply frequency (fs) and the measured supply frequency at the second state (fS2). Step 140 comprises calculating rated synchronous speed (wsyn_2) at the measured supply frequency at the second state using rated synchronous speed (wsyn) at the measured supply frequency at the first state the rated supply frequency (fs) and the measured supply frequency at the second state (fS2). Step 150 comprises calculating a rated speed (wrated_2) at the measured supply frequency at the second state using the calculated rated synchronous speed (wsyn_2) and the calculated motor slip (srated2). Finally, step 160 comprises calculating the motor rotational speed (Wr2) using the input power (Pj2), the rated motor efficiency (e), the rated output power at the measured supply frequency at the second state (Pmrated2), the rated synchronous speed (wsyn_2) at the measured supply frequency at the second state and the rated speed (wrated_2) at the measured supply frequency at the second state. With reference to Figure 2, this depicts a graph 200 of the power-speed characteristics of an induction motor at various supply frequencies. In particular, Figure 2 depicts the rated synchronous speed (Wsyn_i), in radians per second, with supply frequency (fsi) as a function of rated output power (Pmratedi) with supply frequency (fsi). Additionally, the rated synchronous speed (Wsyn_2), in radians per second, with supply frequency (fS2) as a function of rated output power (Pmrated2) with supply frequency (fS2) is shown.
Figure 2 depicts a first state and a second state as described in relation to the method of the present invention as described in relation to Figure 1. Accordingly, it is shown that the first state and the second state are values of supply frequency for a given graph 200 of the power-speed characteristics of an induction motor at various supply frequencies.
With reference to Figure 3, this depicts a preferred method 300 of revising the rated motor efficiency and the rated motor speed, comprising steps 310 to 330. In step 310, a motor rotational speed is measured using a speed sensor, for example a tachometer. In step 320, the method of estimating induction motor rotational speed, as described in relation to Figure 1 , is iteratively performed. This comprises changing the rated motor efficiency by a first predetermined value and the rated speed at the measured supply frequency by a second predetermined value until the calculated motor rotational speed is within a preset range of the measured motor rotational speed. Step 330 comprises storing the revised rated motor efficiency and the revised rated motor speed.
With reference to Figure 4, this depicts an example method 400 of the method described in relation to Figure 3 in accordance with a preferred aspect of the present claimed invention in accordance with the first aspect. This method 400 comprises steps 410 to 490.
In step 410, a motor rotational speed is measured using a speed sensor. In step 420, the method of estimating induction motor rotational speed (wr2) is used and an estimate is produced. In step 430, it is determined whether the difference between the measured motor rotational speed of step 410 differs from the estimated motor rotational speed of step 420 by more than a first predetermined threshold (e.g. 5rpm). If the difference is less than or equal to the first predetermined threshold, then the method proceeds to step 470. If the difference is greater than the first predetermined threshold then the rated motor speed used in the estimation of step 420 is increased by a predetermined value and the motor rotational speed is re-estimated in step 440. In step 450, it is determined whether the re-estimated motor rotational speed differs from the measured motor rotational speed of step 410 by a smaller value than that produced in step 430 (i.e. it is determined in step 450 whether there is less difference between the difference of step 430). If the difference in step 450 is smaller than the previous difference of step 430, then the method proceeds to step 470, discussed below. If the difference in step 450 is not smaller than the previous difference of step 430, then the rated speed is decreased by the first predetermined value (e.g. 5rpm) in step 460.
In step 470, it is determined whether the difference of step 450 is less than or equal to a second predetermined threshold (e.g. 3rpm). If the difference is less than or equal to the second predetermined threshold then the method 400 proceeds to step 490. If the difference is greater than the second predetermined threshold then the method 400 proceeds to step 480.
In step 480, a revised (i.e. decreased) value of the rated motor efficiency is used in the speed estimation method of 420, where the revised rated motor efficiency is decreased by a second predetermined value (e.g. 2% of the original rated motor efficiency). The steps of 470 and 480 are iteratively performed until a revised rated motor efficiency is determined which produces a difference between the measured motor rotational speed and the estimated motor rotational speed which is less than or equal to the second predetermined threshold. Once the difference is less than or equal to the second predetermined threshold, then the method 400 proceeds to step 490. In step 490, the revised rated motor speed and the revised rated motor efficiency are stored.
With reference to Figure 5, this depicts a schematic 500 of an experimental set-up used to test the accuracy of the method of estimating induction motor speed in accordance with the first aspect of the present claimed invention. In system 500, a 25 horse power (HP) induction motor 510 was used to drive a mechanical load 520. The system 500 had a speed sensor and a torque sensor 530 used to determine the speed and torque output from the induction motor 510. The determined speed and torque outputs were then displayed on a display 540. The system 500 further comprises a motor operational parameters unit used to measure the motor operational parameters from the induction motor 510.
In the experimental set up depicted in Figure 5, two test induction motors were measured. The NPI information for these two test induction motors is seen in Table 1 , as depicted in Figure 7. Table 1 shows the NPI for two 25 HP induction motors, including their manufacturing year (i.e. 2013 and 2006), and their motor rated information, including their rated voltage and rated current (which is used to determine the rated power), and their rated frequency, rated speed, rated torque and rated efficiency.
The results of these test are seen in Table 2, as depicted in Figure 8, for the 2013 induction motor of Table 1 ; and in Table 3, as depicted in Figure 9, for the 2006 induction motor of Table 1 .
With reference to Figure 6, this depicts a result of the experiment, as described in relation to Figure 5, used to test the accuracy of the method of estimating induction motor torque, in accordance with the first aspect of the present claimed invention when compared with the LSE method. In particular, Figure 6 depicts a result of an error in speed estimation, in units of rpm, for multiple samples of a particular model of engine, where (a) is an induction motor manufactured in 2006, and (b) is an induction motor manufactured in 2013. It is shown that the known LSE method produces larger errors when compared to the results of the method of the present invention. For example, it is seen in Figure 6 (a) that the maximum error produced using the LSE method is 13.7rpm, whereas the maximum error produced using the method of the present invention is 3.7rpm.
It will be appreciated that the above described embodiments of the first and second aspects of the present invention are given by way of example only, and that various modifications may be made to the embodiments without departing from the scope of the invention as defined in the appended claims. For example, in use the rated motor information is determined from the NPI, where the NPI is information which is found by using an electrical vehicles nameplate (i.e. its licence plate or another identification number/code which identifies the vehicle or an induction motor engine) and which allows the determination of rated information of a particular vehicle.
The motor operational parameters described in relation to Figure 1 may further comprise a motor supplied voltage (V2). The rated motor information may further comprise rated motor output power (Pm) and rated motor voltage (Vi).
The method 100 comprises calculating the motor slip (srated2) at the measured supply frequency at the second state using Equation 1 : srated 2 = Srated (— ). Srated is rated motor slip from the NPI, fs is rated motor supply frequency and fs_2 is motor operational supply frequency at a second state.
The method 100 comprises calculating the rated synchronous speed (wsyn_2) at the measured supply frequency at the second state using Equation 2: wsyn 2 =
Figure imgf000011_0001
Wsyn is rated synchronous speed (wsyn) at the measured supply frequency at the first state, and fs_i is the motor operational supply frequency at a first state.
The method 100 comprises calculating the rated speed (wrated_2) at the measured supply frequency at the second state using Equation 3: wrated _2 = Wsyn 2(1 - srated 2), where these terms are defined above in relation to Equations 1 and 2.
The method 100 comprises calculating the motor rotational speed (wr2) using Equation 4: wr2 = (mPo2) + Wsyn 2 = (m * e * Pi2) + wsyn 2,
Where the parameter, m, is found using Equation 5: m = Wrated-2 w‘-yn ' Additionally, Pm_rated_2
Pi2 is input power, e is efficiency, P02 is a motor operational output power and Pm-rated_2 is the rated output power at the measured supply frequency at the second state. Pm_rated_2 is calculated using Equation 8 below, where Trated_2 is a rated motor torque at a second state and is found using Equation 7 and Trated_i is a rated torque motor torque and found using Equation 6:
Equation 6: P m_rated_i Trated l = rated_i
Equation
Figure imgf000012_0001
Equation 8. Pm_rated_2 Prated_2 ^rated_2
Wratedi is a rated speed at the measured supply frequency at the first state, Pmratedi is the rated output power at the measured supply frequency at the first state, Vi is the rated motor voltage and V2 is the motor supplied voltage.

Claims

1. A method of estimating induction motor rotational speed (wr2), comprising: measuring motor operational parameters, the parameters comprising input power (Pj2), a supply frequency at a first state (fsi) and a supply frequency at a second state (fS2); wherein the first state is the state at a first synchronous speed at a first output power and the second state is a state at a second synchronous speed at a second output power; determining, using motor name plate information (NPI), rated motor information, wherein the rated motor information comprises rated motor efficiency (e), rated supply frequency (fs), rated motor slip (srated) and a rated output power at the measured supply frequency at the second state (Pmrated2); calculating motor slip (srated2) at the measured supply frequency at the second state using the rated motor slip (srated), the rated supply frequency (fs) and the measured supply frequency at the second state (fS2); calculating rated synchronous speed (wsyn_2) at the measured supply frequency at the second state using rated synchronous speed (wsyn) at the measured supply frequency at the first state, the rated supply frequency (fs) and the measured supply frequency at the second state (fS2); calculating a rated speed (wrated_2) at the measured supply frequency at the second state using the calculated rated synchronous speed (wsyn_2) and the calculated motor slip (srated2); and calculating the motor rotational speed (wr2) using the input power (Pi2), the rated motor efficiency (e), the rated output power at the measured supply frequency at the second state (Pmrated2), the rated synchronous speed (wsyn_2) at the measured supply frequency at the second state and the rated speed (wrated_2) at the measured supply frequency at the second state.
2. The method of claim 1 , wherein the method further comprises: calculating a revised rated motor efficiency (e*) and a revised motor rated speed (Wrated 2*) by performing the steps of: measuring, using a speed sensor, a motor rotational speed; iteratively perform the steps of claim 1 by reducing the rated motor efficiency (e) by a first predetermined value and changing the rated speed at the measured supply frequency (Wrated2) by a second predetermined value until the calculated motor rotational speed (wr2) is within a preset range of the measured motor rotational speed; and storing the revised rated motor efficiency (e*) and the revised motor rated speed (Wrated_2*).
3. The method of claim 2, wherein the first predetermined value is 2% of the rated motor efficiency, the second predetermined value is 5rpm, and the preset range of less than or equal to 3rpm.
4. The method of claim 1 , wherein the motor operational parameters further comprise a motor supplied voltage (V2).
5. The method of claim 1 , wherein the rated motor information further comprises rated motor output power (Pm) and rated motor voltage (Vi).
6. The method of claim 1 , wherein calculating the rated motor slip at the measured supply frequency comprises: srated 2 = Srated (- ;
\JS_2/ wherein calculating the rated synchronous speed (wsyn_2) at the measured supply frequency, fs_2, at the second state comprises: wsyn-2 = and
Figure imgf000014_0001
wherein calculating the rated speed (wrated_2) at the measured supply frequency at the second state comprises. wraded 2
Figure imgf000014_0002
7. The method of claim 1 , wherein the motor rotational speed (wr2) is calculated using: wr2 = (mPo wherein: m
Figure imgf000014_0003
Figure imgf000014_0004
8. A non-transitory computer readable storage medium for storing instructions to perform the method of claims 1 to 7.
PCT/EP2022/025216 2022-03-15 2022-05-10 A method of estimating induction motor speed WO2023174500A1 (en)

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US20140009102A1 (en) 2010-06-16 2014-01-09 Eaton Corporation System and method of speed detection in an ac induction machine
US20190074787A1 (en) * 2017-09-01 2019-03-07 Schneider Toshiba Inverter Europe Sas Method for identifying magnetic saturation parameters of an asynchronous electric motor

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US20110050142A1 (en) * 2009-08-26 2011-03-03 Bin Lu System and method for motor speed estimation of an electric motor
US20140009102A1 (en) 2010-06-16 2014-01-09 Eaton Corporation System and method of speed detection in an ac induction machine
US20190074787A1 (en) * 2017-09-01 2019-03-07 Schneider Toshiba Inverter Europe Sas Method for identifying magnetic saturation parameters of an asynchronous electric motor

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