DE102014223096A1 - Method for determining a current sensor error in an EC motor - Google Patents

Abstract

The invention relates to a method for determining a current sensor error in the evaluation of current sensor signals of at least two current sensors (S1, S2), the phase currents (Iu, sens, Iv, sens) of at least a first and second motor phase (U, V) connected in a star-shaped Motor phases (U, V, W) of a three-phase EC motor (1) detect, wherein the EC motor (1) in response to the measured phase currents (Iu, sens, Iv, sens) in a current-regulated control mode by means of the motor phases (U , V, W) applied field-controlled PWM voltage signals. According to the invention, the motor phases are subjected to PWM measurement signals whose duty cycles (DCu, DCv, DCw) have a size causing a standstill of the EC motor (1), from the current sensor signals of the two current sensors (FIG. S1, S2) of the first and second motor phase (U, V) the associated phase currents (Iu, sens, Iv, sens) are determined from the duty cycles (DCu, DCv, DCw) to the motor phases (U, V, W) applied PWM measurement signals to a respective to the phase currents (Iu, sens, Iv, sens, Iw, sens) of the first and second motor phase (U, V) proportional first and second setpoint (Tu, Tv) are determined, the quotients (Iu, sens / Iv, sens) on the one hand from the phase currents (Iu, sens, Iv, sens) of the first and second motor phase (U, V) and on the other hand from the first and second setpoint (Tu, Tv) are compared, and in case of deviation of the two Quotients (Iu, sens / Iv, sens, Tu, Tv) by a given measure a current Sensor error is detected.

Description

The invention relates to a method for determining a current sensor error in an EC motor according to the preamble of patent claim 1.

In today's motor vehicles a variety of electrical or electronic devices with inductive loads, such as. Valves, electric motors or relays are used, which are driven by means of driver stages, usually switching transistors, usually pulse width modulated.

Brushless motors (also known as EC motors or BLDC motors) are increasingly being used as electric motors, whose activation in the case of a 3-phase EC motor is known to be carried out by means of three half-bridges. For field-oriented control of the EC motor, a current sensor for current measurement and possibly a sensor for detecting the motor position is provided in each motor phase.

An operation in the current-regulated control mode can also be done with two current sensors, as for example. From the DE 10 2010 028 097 A1 is known.

If a current sensor fails in such a control with two current sensors, the operation of the EC motor can not be maintained, because usually can not be located by which error in the motor control chain (mechanical components, motor angle sensor, bridge electronics, etc.) the misconduct was triggered.

This problem solves the above DE 10 2010 028 097 A1 in that a target value for the phase current measured by a second current sensor is determined from the phase current measured by a first current sensor, and a current sensor error is identified on the basis of a difference between the measured phase current of the second current sensor and the target value. In this known method, the target value for the measured phase current of the second current sensor is determined on the basis of a peak value of the phase current of the first current sensor.

The object of the invention is to a known method according to the DE 10 2010 028 097 A1 specify alternative method, which also works without additional electronic components or additional sensors that are not already required as a prerequisite for a field-oriented control of the EC motor.

This object is achieved by a method having the features of patent claim 1.

• – die Motorphasen mit PWM-Messsignalen beaufschlagt werden, deren Tastverhältnisse eine einen Stillstand des EC-Motors bewirkende Größe aufweisen,
• – aus den von den PWM-Messsignalen bewirkten Stromsensorsignalen der beiden Stromsensoren der ersten und zweiten Motorphase die zugehörigen Phasenströme bestimmt werden,
• – aus den Tastverhältnissen der an die Motorphasen angelegten PWM-Messsignale eine jeweils zu den Phasenströmen der ersten und zweiten Motorphase proportionale erste und zweite Sollgröße bestimmt werden,
• – die Quotienten einerseits aus den Phasenströmen der ersten und zweiten Motorphase und andererseits aus der ersten und zweiten Sollgröße verglichen werden, und
• – bei Abweichung der beiden Quotienten um ein vorgegebenes Maß ein Stromsensorfehler erkannt wird.

This method of determining a current sensor error in the evaluation of current sensor signals from at least two current sensors detecting the phase currents of at least a first and second motor phase of star connected motor phases of a three-phase EC motor, the EC motor depending on the measured phase currents in a current regulated Control mode is controlled field-oriented by means of applied to the motor phases PWM voltage signals, according to the invention is characterized in that

• - The motor phases are subjected to PWM measurement signals, the duty cycles have a causing a standstill of the EC motor size,
• The associated phase currents are determined from the current sensor signals of the two current sensors of the first and second motor phase which are produced by the PWM measuring signals,
• From the duty cycles of the PWM measurement signals applied to the motor phases, a respective first and second setpoint variable proportional to the phase currents of the first and second motor phases are determined,
• - The quotients are compared on the one hand from the phase currents of the first and second motor phase and on the other hand from the first and second setpoint, and
• - If the two quotients differ by a predetermined amount, a current sensor error is detected.

With this method according to the invention, it is possible to detect the failure of a current sensor in a 2-sensor system of a DC motor at standstill. For this purpose, the current sensor error is detected on the basis of the known applied control patterns of the PWM measurement signals, which are set in relation to the ratio of the measured phase currents of the first and second motor phases.

• – mittels eines weiteren Stromsensors der Phasenstrom der dritten Motorphase des EC-Motors detektiert wird,
• – aus den Tastverhältnissen der an die Motorphasen angelegten PWM-Messsignale eine zu dem Phasenstrom proportionale dritte Sollgröße bestimmt wird,
• – die Quotienten aus den Phasenströmen der ersten, zweiten und dritten Motorphase jeweils mit einem Quotienten jeweils aus den zugehörigen drei Sollgrößen verglichen werden, und
• – bei einer Abweichung von wenigstens zwei Vergleichsergebnissen von einem vorgegebenen Maß derjenige Stromsensor als defekt erkannt wird, dessen detektierter Phasenstrom in dem Quotienten der beiden Vergleichsergebnisse verwendet wird.

According to a further advantageous embodiment of the invention, it is provided that

• The phase current of the third motor phase of the EC motor is detected by means of a further current sensor,
• From the duty cycles of the PWM measurement signals applied to the motor phases, a third desired variable proportional to the phase current is determined,
• - The quotients of the phase currents of the first, second and third motor phase are each compared with a quotient of the associated three desired values, and
• - Is detected in a deviation of at least two comparison results of a predetermined level that current sensor as a defect whose detected phase current is used in the quotient of the two comparison results.

According to this embodiment of the invention, not only a current sensor error can be detected, but also the faulty current sensor itself can be detected beyond.

It is further provided according to the development that a sum of the duty cycles of the PWM measurement signals of the two further motor phases is formed to determine the desired value of a phase current, from which twice the amount of the duty cycle of the PWM measurement signal of a motor phase is subtracted.

This method according to the invention can be implemented in a simple manner by software, without additional hardware being required.

In the following, the method according to the invention will be explained and described in more detail with reference to a single figure. These 1 shows a block diagram of an arrangement for operating an EC motor 1 for explaining the method according to the invention. With this EC motor 1 a vehicle function of a vehicle is realized.

This arrangement includes an EC motor 1 with a stator with three switched in star connection and each designed as a winding motor phases U, V and W. These three motor phases U, V and W are interconnected on the one hand in a neutral point S and on the other with a half bridge HB1, HB2 and HB3 for feeding connected by PWM signals. These half bridges HB1, HB2 and HB3 each have a high-side and low-side transistor and are connected to the energy supply to a vehicle electrical system voltage U _{batt of} a vehicle. From a control unit 2 For example, the half-bridges HB1, HB2 and HB3 are driven to generate PWM signals with predetermined duty cycles, which are supplied to the motor phases U, V and W.

For field-oriented control of the EC motor 1 For example, a first current sensor S1 and a second current sensor S2 are connected in the motor phase U and the motor phase V, whose current sensor signals of the control unit 2 are fed, which determines the phase currents I _{u, sens} and I _{v, sens of} the motor phases U and V, in dependence of which the PWM signals for the motor phases U, V and W are generated.

Furthermore, a functional monitoring of these current sensors S1 and S2 is carried out, which will be explained below. An alternative method for monitoring the function, in which a further, arranged in the third motor phase W current sensor S3 is provided, will be described below.

This function monitoring is provided by the control unit 2 PWM measuring signals with duty cycles DCu, DCv and DCw generated by means of the half bridges HB1, HB2 and HB3, wherein these duty cycles of the PWM measurement signals have such a size that the EC motor 1 remains at a standstill, so does not start. The phase currents I _{u, sens} and I _{v, sens} caused by these PWM measuring signals in the motor phases U and V are detected by the current sensors S1 and S2 as current sensor signals and used to evaluate the control unit 2 fed.

Mathematically, the phase currents I _u and I _{v of} the motor phases U and V can be determined from the applied phase voltages of the motor phases U, V and W and the star voltage U _s , as will be derived below.

und

wobei U_s die Sternspannung der Sternschaltung der drei Motorphasen U, V und W ist, U_u und U_v die Strangspannungen der Motorphase U bzw. V und R_u und R_v die Wicklungswiderstände der Motorphasen U und V sind.Thereafter, the phase currents I _u and I _{v are} first determined according to the following formulas (1) and (2):

and

where U _{s is} the star voltage of the star connection of the three motor phases U, V and W, U _u and U _{v are} the phase voltages of the motor phase U and V and R _u and R _{v are} the winding resistances of the motor phases U and V.

For the sake of completeness, the formula (3) for the phase current I _{w of} the third motor phase W is given, which, however, is only necessary for the alternative method for functional testing of three current sensors S1, S2 and S3:

wobei DCu, DCv und DCw die Tastverhältnisse der PWM-Messsignale der Motorphasen U, V und W sind und U_batt die Bordnetzspannung des Fahrzeugs ist.The phase voltages or motor voltages U _u , U _v and U _{w of} the motor phases U, V and W and the phase voltage U _{s are} determined according to the following formulas (4), (5), (6) and (7): D _U = DCu · U _batt, (4) U _v = DCv · U _batt , (5) U _w = DCw · U _batt , (6) and

where DCu, DCv and DCw are the duty cycles of the PWM measurement signals of the motor phases U, V and W and U _{batt is} the vehicle electrical system voltage of the vehicle.

By inserting the formulas (4), (5) and (6) in (7), the formula (8) for the star voltage U _s results:

With the formulas (4) and (8), the phase current I _{u can be represented} by being substituted into the formula (1) as follows:

Accordingly, for the phase current I _v by substituting the formulas (5) and (8) in formula (2):

If all three half-bridges are at the same supply voltage U _batt and the winding _resistances R _u and R _{v of} the motor phases U and V have the same values, the following proportionality to the phase currents I _u and I _v exists: I _u ~ (DCv + DCw - 2DCu), and I _v ~ (DCu + DCw - 2DCv).

The two terms (DCv + DVw-2DCu) and (DCu + DCw-2DCv), which are each formed from the duty cycles of the PWM measurement signals, therefore represent setpoint values T _u and T _v for the phase currents I _u and I _v .

wobei die Phasenströme I_u und I_v durch die Formeln (9) und (10), also durch die Sollwerte T_u und T_v ersetzt sind. Now, the quotient I _u / I _v from the mathematically calculated phase currents I _u and I _{v of} the motor phases U and V with the quotient I _{u, sens} / I _{v, sens} detected by the two current sensors S1 and S2 phase currents I _{u, sens} and I _{v, sens} , since the value of these two quotients in the case of fully functional current sensors S1 and S2, assuming that the winding resistances R _u and R _{v are} equal and the half bridges HB1, HB2 and HB3 are supplied with the same supply voltage, theoretically have to agree according to the following relationship:

wherein the phase currents I _u and I _{v are} replaced by the formulas (9) and (10), ie by the setpoint values T _u and T _v .

The quotient T _u / T _v represents the expected ratio of the two phase currents I _u and I _v , which is determined by the quotient I _{u, sens} / I _{v, sens of} the phase currents I _{u, sens} and I _v detected with the current sensors S1 and S2 _{, sens is} mirrored. The deviation of these two quotients T _u / T _v and I _{u, sens} / I _{v, sens} by a predetermined amount therefore indicates that there is a sensor error that is due to a defective current sensor S1 and / or S2.

As already stated above, a third current sensor S3 can also be provided in the third motor phase W for measuring the phase current I _w (cf. 1 , dashed line of the current sensor S3). Is the control of the EC motor 1 carried out on the basis of these three current sensors S1, S2 and S3, a high control quality and high functional availability can be achieved, especially in safety-critical aspects.

In order to test the functionality of these three current sensors S1, S2 and S3, PWM measurement signals with duty cycles DCu, DCv and DCw are also generated, which are applied to the three motor phases U, V and W and have a size such that the EC engine 1 is at standstill, so is not rotated due to these PWM measurement signals. The current sensor signals of the current sensors S1, S2 and S3 generated on the basis of these PWM measurement signals become the control unit 1 fed, which determines therefrom the phase currents I _{u, sens} , I _{v, sens} and I _{w, sens} the motor phases U, V and W.

wobei U_batt die Bordnetzspannung des Fahrzeugs, R_w der Phasenwiderstand der Motorphase W ist und DCu, DCv und DCw die Tastverhältnisse der PWM-Messsignale sind. Damit ergibt sich für den Phasenstrom I_w eine den Phasenströmen I_u und I_v entsprechende Proportionalität: I_w ~ (DCu + DCv – 2DCw). Now, according to formulas (9) and (10), a formula (12) can also be established for the two phase currents I _u and I _v for the phase current I _w :

where U _batt the vehicle electrical system voltage of the vehicle, R _{w is} the phase resistance of the motor phase W and DCu, DCv and DCw are the duty cycles of the PWM measurement signals. This results in a proportional to the phase currents I _u and I _v for the phase current I _w proportionality: I _w ~ (DCu + DCv - 2DCw).

This term (DCU + DCV - 2DCw) is next to the target values T _u and T _v for the phase currents I _u and I _v a third reference value T _w represents.

sondern es lassen sich auch die Quotienten

bilden. Unter der Annahme, dass alle drei Phasenwiderstände R_u, R_v und R_w gleich sind und alle drei Halbbrücken HB1, HB2 und HB3 an der gleichen Versorgungsspannung U_batt liegen, kann nicht nur der Quotient I_u/I_v aus den mathematisch berechneten Phasenströmen I_u und I_v der Motorphasen U und V mit dem Quotient I_u,sens/I_v,sens der von den beiden Stromsensoren S1 und S2 detektierten Phasenströme I_u,sens und I_v,sens verglichen werden, sondern auch die Quotienten I_u/I_w bzw. I_v/I_w mit den Quotienten I_u,sens/I_w,sens und I_v,sens/I_w,sens.This is not just the quotient

but it can also be the quotients

form. Assuming that all three phase resistances R _u , R _v and R _{w are} equal and all three half-bridges HB1, HB2 and HB3 are at the same supply voltage U _batt , not only the quotient I _u / I _v can be calculated from the mathematically calculated phase currents I _u and I _{v of} the motor phases U and V with the quotient I _{u, sens} / I _{v, sens} the detected by the two current sensors S1 and S2 phase currents I _{u, sens} and I _{v, sens} , but also the quotients I _u / I _w or I _v / I _w with the quotients I _{u, sens} / I _{w, sens} and I _{v, sens} / I _{w, sens} .

Substituting formulas (9), (10) and (12) into formulas (13), (14) and (15) leads to the following formulas:

These quantities proportional to the phase currents I _u , I _v and I _w (DCv + DCw - 2DCu), (DCu + DCw - 2DCv) and (DCu + DCv - 2DCw) formed from the duty ratios of the PWM measurement signals are the setpoints T _u , T _v and T _w .

The quotients T _u / T _v , T _u / T _w and T _v / T _w represent the expected ratio of the two phase currents I _u and I _v , I _u and I _w and I _v and I _w , respectively, which are represented by the quotients I _{u, sens} / I _{v, sens} , I _{u, sens} / I _{w, sens} and I _{v, sens} / I _{w, sens} the detected with the current sensors S1, S2 and S3 phase currents I _{u, sens} , I _{v, sens} and Iw _{, sens be} mirrored.

By a threefold comparison of the quotients T _u / T _v and I _{u, sens} / I _{v, sens} , T _u / T _w and I _{u, sens} / I _{w, sens} and T _v / T _w and I _{v, sens} / I _{w, sens} , a current sensor error due to a defective current sensor S1, S2 or S3 can again be detected if the deviation between one of the two quotients exceeds a predetermined level.

If one of the three current sensors S1, S2 or S3 is defective, the defective current sensor can also be identified. In this case, the quotients involved in the formulas (16), (17) and (18) deviate from the given dimension in the case of two of these formulas. The phase current used simultaneously in these two formulas is therefore defective, i. H. the current sensor measuring this phase current is defective.

For example, if a comparison of the quotients involved in the formulas (16) and (17) shows a deviation from the predetermined dimension, this indicates a faulty phase current I _u , ie the current sensor S 1 is defective.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102010028097 A1 [0004, 0006, 0007]

Claims (3)

A method for determining a current sensor error in the evaluation of current sensor signals from at least two current sensors (S1, S2), the phase currents (I _{u, sens} , I _{v, sens} ) of at least a first and second motor phase (U, V) of star-connected motor phases (U, V, W) of a three-phase EC motor ( 1 ), the EC motor ( 1 ) is field-controlled in dependence on the measured phase currents (I _{u, sens} , I _{v, sens} ) in a current-regulated control mode by means of the motor phases (U, V, W) applied PWM voltage signals, characterized in that - the motor phases with PWM Measuring pulses are applied whose duty cycles (DCu, DCv, DCw) a standstill of the EC motor ( 1 ) have effective size, - the associated phase currents (I _{u, sens} , I _{v, sens} ) are determined from the current sensor signals of the two current sensors (S1, S2) of the first and second motor phase (U, V) produced by the PWM measuring signals, - From the duty cycles (DCu, DCv, DCw) of the motor phases (U, V, W) applied PWM measurement signals to each of the phase currents (I _{u, sens} , I _{v, sens} , I _{w, sens} ) of the first and second motor phase (U, V) proportional first and second setpoint (T _u , T _v ) are determined, - the quotients (I _{u, sens} / I _{v, sens} ) on the one hand from the phase currents (I _{u, sens} , I _{v, sens} ) of the first and second motor phase (U, V) and on the other hand from the first and second setpoint (T _u , T _v ) are compared, and - in deviation of the two quotients (I _{u, sens} / I _{v, sens} , T _u , T _v ) is detected by a predetermined amount of a current sensor error. A method according to claim 1, characterized in that - by means of a further current sensor (S3) of the phase current (I _{w, sens} ) of the third motor phase (W) of the EC motor ( 1 ) is detected, - from the duty cycles (DCu, DCv, DCw) of the applied to the motor phases (U, V, W) PWM measurement signals to the phase current (I _{w, sens} ) proportional third target variable (T _w ) is determined, - The quotients (I _{u, sens} / I _{v, sens} , I _{u, sens} / I _{w, sens} , I _{v, sens} / I _{w, sens} ) from the phase currents (I _{u, sens} , I _{v, sens} , I _{w , sens} ) of the first, second and third motor phase (U, V, W) in each case with a quotient (T _u / T _v , T _u / T _w , T _v / T _w ) in each case from the associated three desired values (T _u , T _v , T _w ) are compared, and - is detected in a deviation of at least two comparison results of a predetermined amount of that current sensor (S1, S2, S3) as defective whose detected phase current (I _{u, sens} , I _{v, sens} , I _{w, sens} ) is used in the quotient of the two comparison results. A method according to claim 1 or 2, characterized in that for determining the desired value (T _u , T _v , T _w ) of a phase current (I _{u, sens} , I _{v, sens} , I _{w, sens} ) a sum of the duty cycles of the PWM Measuring signals of the two other motor phases (U, V, W) is formed, from which twice the duty ratio of the PWM measurement signal of a motor phase (U, V, W) is subtracted.

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