Method for controlling an electric motor in the event of a speed measurement anomaly

Abstract

The invention relates to a method for controlling a synchronous electric motor, the method comprising: generating (400) a torque reference based on a mechanical setpoint; measuring (405) the position and determining the speed of the motor; measuring (410) the current generated by the motor; generating (445) voltage references based on the torque reference; and generating (450) control voltages based on the reference voltages. It comprises: detecting an anomaly in the position measurement; adapting (440) the electrical control gains according to whether or not an anomaly in the position measurement of the electric motor has been detected; and the voltage references being dependent on the values of the electrical control gains.

Description

[0001] Description

[0002] Title of the invention: Method for controlling an electric motor in the event of a speed measurement anomaly

[0003] Technical Field

[0004] The invention relates to the control of an electric motor and more particularly the control of an electric motor following an anomaly in the measurement of the speed of its rotor.

[0005] Prior art

[0006] For a control system configured to control an electric motor configured in speed or position, a rotor speed sensor is generally used in order to construct a robust and efficient control law.

[0007] When the position information becomes unusable, the system becomes inoperative due to a lack of information to supplement the measurement. When the anomaly occurs during a controlled movement, it is necessary to react instantly to continue the movement and maintain the expected level of performance.

[0008] There are different methods for controlling a sensorless electric motor which can be classified into two categories: on the one hand, methods operating from electrical quantities as applied or measured on an electric motor, the electrical quantities being able to be instantaneous quantities or quantities averaged over a period of time which depends on the power stage and its control strategy, and, on the other hand, methods operating from high frequency components of the electrical quantities, added to the main control.

[0009] As schematically illustrated in Figure 1, the principle of controlling an electric motor without a position sensor from fundamental electrical quantities includes a motor controlled in voltage by an electrical controller.

[0010] The electrical controller receives as input a measurement of the current in the motor, a value of the motor speed estimated from the voltage and current of the motor and a mechanical torque reference provided by a mechanical controller, the mechanical controller determining the mechanical torque reference from a speed or position reference, the speed estimate and control parameters of the electrical controller.

[0011] As schematically illustrated in Figure 2, the principle of controlling an electric motor without a position sensor from high-frequency electrical quantities differs from the principle of Figure 1 in that it includes a high-frequency module upstream of the motor and the estimation carried out is made on the speed or position of the motor.

[0012] In the definition of known electrical system architectures, the presence of a position or speed measurement is known at the time of control system configuration. It is in this phase that the choice is made of a controller that manages or not the position or speed measurement.

[0013] Either the control law is configured to operate with the information given by the position sensor, or the control law is configured to operate without this information. Reconfiguration from one to the other can only be done after a stop phase. This causes the current movement to end in an uncontrolled manner. A faulty position / speed measurement value will, through the regulation, generate voltages on the motor that do not correspond to the state of the motor. This can induce a set of inappropriate behaviors that will have to be captured through different monitoring functions.

[0014] In known systems, when a fault is detected, it is only proposed to generate a warning or a fault.

[0015] Statement of the invention

[0016] The main purpose of the present invention is therefore to propose a solution for reconfiguring the engine control mode on the fly, to overcome the failure of an engine position sensor. By reconfiguring the engine control mode on the fly, we mean reconfiguring it in operation. That is to say, reconfiguring the engine control mode while maintaining the engine and its control means in operation.

[0017] In a first subject of the invention, a method for controlling a synchronous electric motor is proposed, comprising a generation of a mechanical torque reference from a mechanical setpoint, a measurement of the position and a determination of the speed of the electric motor from the position measurement, a measurement of the current generated by the electric motor, a generation of voltage references from the mechanical torque reference, and a generation of control voltages from the reference voltages.

[0018] The method further comprises monitoring an anomaly in the position measurement of the electric motor, adapting the electrical control gains depending on whether or not an anomaly in the position measurement of the electric motor is detected, the voltage references generated depending on the values ​​of the electrical control gains.

[0019] The method according to the invention thus makes it possible to provide continuity of control of the voltage of the electric motor even in the presence of a major failure, namely the loss of measurement information of the position of the motor. The detection of the failure and then the reconfiguration of the electrical control means through the adaptation of the gains, and alternatively of the current reference, makes it possible to guarantee the performance of the mechanical movement of the electric motor. And this without having to stop the motor, and without having to stop the control, that is to say without having to switch off and reset the control of the motor.

[0020] Monitoring an electric motor position measurement anomaly also includes checking the consistency of the position or speed information with the current information.

[0021] Current information means data from current measurements and transformations of current measurements.

[0022] In one aspect of the method, monitoring for an electric motor position measurement anomaly includes estimating the speed of the electric motor from the speed determined from the position measurement and the current measured at the motor terminals, comparing the estimated speed to the determined speed, and reporting a measurement anomaly based on the result of the comparison relative to a detection threshold.

[0023] According to another object of the invention, there is proposed an electrical system for controlling a synchronous electric motor comprising a mechanical control unit configured to receive a mechanical setpoint and deliver a mechanical torque reference, an electrical control unit configured to deliver a voltage reference as a function of the torque reference delivered by the mechanical control unit, a power unit configured to deliver a control voltage to the electric motor as a function of the voltage reference delivered by the electrical control unit, a position sensor of the rotor of the electric motor that said electrical system controls, and means for measuring the current at the terminals of the electric motor controlled by the electrical control system.

[0024] According to a general characteristic of the system according to the invention, the electrical control unit further comprises:

[0025] - a means of detecting a measurement anomaly of the position sensor,

[0026] - an electrical control gain adaptation module configured to adapt the gains depending on whether or not an anomaly in the position measurement of the electric motor is detected, and

[0027] - a control module configured to deliver voltage references from the mechanical torque reference, the current measured at the terminals of the electric motor, and the electrical control gains delivered by the adaptation module (94).

[0028] In a first aspect of the system according to the invention, the anomaly detection means comprises a module for estimating the speed of the motor from the voltage and current of the motor, a comparator configured to compare the determined speed with the speed measured by the sensor, and a module for signaling a measurement anomaly as a function of the result of the comparison with respect to a detection threshold.

[0029] In a second aspect of the system according to the invention, the power control block further comprises a power converter.

[0030] According to another object of the invention, there is provided an electrical system comprising an electric motor coupled to a load, and an electrical control system as defined above coupled to the electric motor.

[0031] Brief description of the drawings

[0032] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate an exemplary embodiment thereof without any limiting character. [Fig. 1] Figure 1 schematically represents an electrical system 1 comprising a synchronous electric motor 2 and a control circuit 4 according to one embodiment of the invention.

[0033] [Fig. 2] Figure 2 shows schematically in more detail an electrical control system 4 of the synchronous electric motor 2 of Figure 1.

[0034] [Fig. 3] Figure 3 is a schematic representation in more detail of an electrical control block 9 of Figure 2.

[0035] [Fig. 4] Figure 4 schematically presents a logic diagram of a control method implemented by the electrical control system 4 of the synchronous electric motor 2 according to an embodiment of the invention.

[0036] Description of the embodiments

[0037] In Figure 1 is schematically represented an electrical system 1 comprising a synchronous electric motor 2 with permanent magnets coupled to a load 3 and an electrical control system 4 coupled to the electric motor 2.

[0038] The electrical control system 4 of the synchronous electric motor 2 comprises a control assembly 5, a position sensor 6 configured to measure the speed of the rotor of the synchronous electric motor 2, and means for measuring the voltage and current at the terminals of the synchronous electric motor 2.

[0039] As illustrated in Figure 2 which schematically presents in more detail an electrical control system 4 of the synchronous electric motor 2, the control assembly 5 comprises a mechanical control block 8 configured to receive a mechanical setpoint Cm and deliver a mechanical torque reference R c, an electrical control block 9 configured to deliver a voltage reference R T according to the torque reference Rc delivered by the mechanical control block 8, and a power block 10 configured to deliver a control voltage T c to the electric motor 2 depending on the voltage reference R T delivered by the electrical control unit 9.

[0040] As illustrated in Figure 3 which schematically represents an electrical control block 9 in more detail, the electrical control block 9 comprises a means 92 for detecting a measurement anomaly of the position sensor 6, a module 94 for adapting the electrical control gains configured to adapt the gains depending on whether or not a position measurement anomaly of the synchronous electric motor 2 is detected, a control module 96 configured to deliver voltage references R T from the mechanical reference R c, of the current measured at the terminals of the electric motor 2 by the current measuring means 7, and of the electrical control gains delivered by the adaptation module 94.

[0041] Furthermore, the anomaly detection means 92 comprises a module 922 for estimating the speed of the motor from the voltage and current of the motor, a comparator 924 configured to compare the determined speed with the speed measured by the position sensor 6, and a module 926 for signaling a measurement anomaly as a function of the result of the comparison with respect to a detection threshold.

[0042] In Figure 4 is shown a flowchart of a control method implemented by the electrical control system 4 of the synchronous electric motor 2. The method comprises a first step 400 of generating a mechanical torque reference from a mechanical setpoint. In a second step 405, a measurement of the position is then carried out using the position sensor 6 and a determination of the speed of the electric motor 2 from the position measurement, and, in a step 410, a measurement of the current generated by the electric motor 2.

[0043] A measurement anomaly monitoring of the position sensor 6 is then carried out. For this, in a step 430, the consistency of the position or speed information with the current information is checked, and it is determined whether or not there is an anomaly, in a step 435, between said information. The consistency check of the information notably comprises an estimation of the speed or the position of the motor from the electrical quantities such as the current generated by the motor and a comparison of this estimated speed or this estimated position with respect to the measured position or a speed determined from the measured position, this comparison being able to be carried out by calculating the difference between the estimated speed and the measured speed and by verifying that this difference remains limited to an expected variation range with regard to the measurement noise and the regulation dynamics.

[0044] Following the check of the consistency of the information, it is possible to deliver, in a step 420, an estimate of the speed of the electric motor 2 from the position measurements and the current measured at the terminals of the motor in particular. In a following step 445, the voltage references for the selected electrical control gains are delivered to the power block 10.

[0045] Finally, in a step 450, the voltage block delivers a control voltage to the synchronous electric motor 2.

[0046] Estimating the speed of the permanent magnet synchronous electric motor 2 from the electrical quantities (voltage and current) of the electric motor can be done in different ways.

[0047] The following mathematical model represents a modeling of a synchronous electric motor with surface permanent magnets (without saliency) with the physical quantities of three phases S1, S2, S3, with the resistance R s, the current i on each of the phases i S i, is2, iss, and the voltage on each of the phases u s1 , U s2 , u S 3, and the electric flux on each of the phases φ S1 , φ s2 , φ s3 . [Math [Math [Math

[0048] With the flux φ expressed by the magnetic coupling matrix equation:

[0049] [Math 4]

[0050] With M representing the value of stator mutual inductance, L representing the value of stator self-inductance, <4> M representing the permanent flux value, and 0 representing the position of the magnet. And the electromagnetic torque TEM expressed by the following equation:

[0051] With n p representing the number of pole pairs.

[0052] In steady state, the quantities (u s i, Us2, u s3 ) are sinusoidal quantities phase-shifted by 2K / 3.

[0053] We know from the construction of the electric machine that i S1 + i s2 + i s3 = 0. By applying the Clarke transform on the three-phase quantities, that is to say by applying the following two transformation matrices: we can define for each quantity X a new coordinate vector

[0054] (or variables): [Math

[0055] We obtain the relations:

[0056] [Math

[0057] [Math

[0058] [Math

[0059] With by construction that is z = 0, and

[0060] [Math

[0061] [Math

[0062] Where L dq = LM, and Ly = L + 2.M.

[0063] This model shows that the third component has no functional role since the current magnitude is zero and that this component does not intervene in the generation of torque. This gives the writing of the classical two-phase system: [Math

[0064] [Math

[0065] With by construction that i Sz = 0, and

[0066] [Math [Math

[0067] [Math

[0068] In steady state, the quantities (u sa , u s p) are sinusoidal quantities phase-shifted by TI / 2.

[0069] By replacing the flux variables, we obtain the equations for the permanent magnet synchronous motor without salience:

[0070] [Math

[0071] [Math

[0072] [Math

[0073] [Math

[0074] The following model represents in matrix form a permanent magnet synchronous electric motor in the following fixed frame:

[0075] [Math

[0076] [Math

[0077] [Math

[0078] With the following notations:

[0079] [Math 26] the voltage of the motor, [Math 27] the current of the motor, 0, the position of the magnet, co, the speed of the magnet, and the matrices: [Math

[0080] [Math

[0081] In mechanical and electrical steady states, the system reaches stationary equilibrium. The motor rotates at speed co=d0 / dt under a load torque constraint T EM = TLOAD- The following expression of the couple:

[0082] [Math allows the current to be expressed in a general form:

[0083] [Math With any value (which is often set by the controller).

[0084] Then comes the expression:

[0085] [Math which allows us to write [Math

[0086] With variables

[0087] [Math 35]

[0088] In practice, it is not possible to know the phase e precisely from the electrical signals taken individually. It is possible to estimate the pulsation of the electrical signals, an image of the velocity, that is to say the derivative of the position.

[0089] To estimate the speed from the phase of the electrical quantities, it is sufficient to calculate the angle of the voltage vector with a direct calculation of the inverse of the tangent function for example.

[0090] It is also possible to use a PLL (Phase lock loop) type algorithm.

[0091] In any case, there is a phase shift <p entre la phase des grandeurs électriques et la position du rotor (qui dépend de la stratégie de contrôle en premier lieu) qui est à prendre en compte sur les expressions précédentes du repère tournant. Il vient :

[0092] [Math 36]

[0093] [Math 37] and

[0094] [Math 38] The speed of the electric motor can also be determined from the amplitudes of the electrical quantities. From the expression [Math 38], we can also extract an estimate of the speed, this time based on the amplitude of the voltage and current, by solving the following equation: [Math 39] That's to say

[0095] [Math

[0096] And [Math

[0097] With :

[0098] [Math 42]

[0099] [Math 43]

[0100] [Math 44]

[0101] [Math 45]

[0102] Note that there is no objection to using the quantities in the fixed frame instead of a rotating frame in the previous formulas.

[0103] The previous expression gives two solutions (one positive, one negative). It is possible to remove the indeterminacy by selecting the speed which has the sign consistent with the direction of movement of the voltage vector (whether its phase increases or decreases).

[0104] By taking the model of the engine in the fixed frame (equations [Math 23] and [Math 24]), to construct a dynamic estimate, we choose to place ourselves in a frame rotating at the speed:

[0105] [Math 46] with:

[0106] [Math 47]

[0107] [Math 48]

[0108] We then have: [Math 49]

[0109] [Math 50]

[0110] [Math

[0111] We can then construct the observer: [Math 53]

[0112] It remains to define the structure of the gains K which guarantees that the quantity ω, corresponding to the estimate of the speed, tends towards ω. With the notation 6X = X - X, then the difference between the motor model and the observer can be written: [Math 54] [Math 55]

[0113] [Math 56]

[0114] The choice: [Math 57]

[0115] [Math 58] leads to

[0116] [Math 59] [Math 60] [Math

[0117] The classical study of this system shows the convergence of the speed estimator based on electrical quantities [Math 53] towards the real speed.

[0118] The comparison between, on the one hand, the information obtained by the speed measurement, and on the other hand the information obtained by a speed estimation makes it possible to validate the consistency of the position or speed measurement. The speed estimation can be directly a value obtained from the electrical quantities, for example [Math 41] or [Math 52]; it is also possible to use a static or dynamic combination of the speed measurement and the speed estimation from the electrical quantities. Validating the consistency consists, for example, of calculating the difference between the two pieces of information, and defining an acceptable threshold of difference between these two estimates, which must be equal in steady state, for example 1 Hz.

[0119] A classic control of the permanent magnet electric motor consists of calculating a reference voltage vector in the following control frame: [Math

[0120] [Math

[0121] [Math

[0122] With

[0123] [Math

[0124] [Math or corresponds to the reference voltage, œ s corresponds to the pulsation of the control mark, 0 S corresponds to the pulsation of the control mark, corresponds to the reference current, corresponds to the motor current in the control mark, and œ corresponds to the estimated engine speed.

[0125] The K payoff matrices CTRL-P and K CTRL-r are to be calculated to ensure control performance. This performance depends on the dynamics of the estimated speed. It is necessary to determine a set of gains (K CTRL-P , K CTRL-I) by speed estimation strategy, whether the estimated motor speed comes from measurement, or from an estimation strategy based on electrical quantities, or from a mixture of the two.

[0126] The reference voltage is then transformed into the three voltages to be applied to the motor phases, in two stages: from a rotation of the angle of the control mark

[0127] [Math then a

[0128] [Math

[0129] The invention thus makes it possible to provide continuity of control of the voltage of the electric motor even in the presence of a major failure, which is the loss of measurement information of the position of the motor. The detection of the failure and then the reconfiguration of the electrical control means through the adaptation of the gains, and alternatively of the current reference, makes it possible to guarantee the performance of the mechanical movement of the electric motor. In other words, the invention consists of reconfiguring on the fly the control mode of the motor to compensate for a failure of the position sensor, by controlling the movement. This on-the-fly reconfiguration is made possible by the invention thanks to a control of the consistency of the speed / position information with regard to the electrical measurements, and an adaptation of the controller according to this measurement consistency.

[0130] The invention thus proposes a control of the consistency of the speed / position information with regard to the electrical measurements, thus allowing detection of position measurement anomalies from an electrical / mechanical behavioral analysis, a reconfiguration of the electrical and mechanical controllers to control the movement, and an adaptive control between a control means with the speed / position measurement information and a control means with the information of the measurements of the electrical quantities, without speed / position measurement information.

Claims

Demands

1. A method for controlling a synchronous electric motor, comprising generating (400) a mechanical torque reference from a mechanical setpoint, measuring (405) the position of the electric motor and determining the speed of the electric motor from the position measurement, measuring (410) the current generated by the electric motor, generating (445) voltage references from the mechanical torque reference, and generating control voltages (450) from the reference voltages, characterized in that it further comprises monitoring for an anomaly in the position measurement of the electric motor, adapting (440) the electrical control gains according to whether or not (435) an anomaly in the position measurement of the electric motor is detected, and in that the voltage references depend on the values ​​of the electrical control gains,monitoring of an anomaly in the position measurement of the electric motor, including a check (430) of the consistency of the position or speed information with the current information.

2. A method according to claim 1, wherein the monitoring of an anomaly in the position measurement of the electric motor includes an estimation (420) of the speed of the electric motor from the speed determined from the position measurement and the current measured at the terminals of the motor, a comparison of the estimated speed to the measured speed, and a reporting (435) of a measurement anomaly based on the result of the comparison with respect to a detection threshold.

3. An electrical control system (4) for a synchronous electric motor (2) comprising a mechanical control block (8) configured to receive a mechanical setpoint (Cm) and deliver a mechanical torque reference (Rc), and an electrical control block (9) configured to deliver a voltage reference (R T ) depending on the torque reference delivered by the mechanical control block (8), a power block (10) configured to deliver a control voltage (T c ) to the electric motor (2) as a function of the voltage reference (R T ) delivered by the electrical control unit (9), a position sensor (6) of the rotor of the electric motor (2) which said electrical control system (4) controls, and means (7) for measuring the current at the terminals of the electric motor (2) controlled by said electrical control system (4), characterized in that the electrical control unit (9) further comprises: - a means (92) for detecting a measurement anomaly of the position sensor (6) via a check of the consistency of the position or speed information with the current information, - an electrical control gain adaptation module (94) configured to adapt the gains according to whether or not an anomaly in the position measurement of the electric motor is detected, - a control module (96) configured to deliver voltage references from the mechanical torque reference, the current measured across the terminals of the electric motor, and the electrical control gains delivered by the adaptation module (94).

4. Electrical control system (4) according to claim 3, wherein the anomaly detection means (92) comprises a module (922) for estimating the motor speed from the motor voltage and current, a comparator (924) configured to compare the determined speed to the speed measured by the sensor, and a module (926) for reporting a measurement anomaly based on the result of the comparison with respect to a detection threshold.

5. Electrical control system (4) according to any one of claims 3 or 4, wherein the power control block (10) further comprises a power converter.

6. Electrical system (1) comprising a synchronous electric motor (2) coupled to a load (3), and an electrical control system (4) according to any one of claims 3 to 5 coupled to the synchronous electric motor

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