Method and detector device for monitoring current sensors and electric drive system

Description

Technical area

[0001] The present invention relates to a method and a detector device for monitoring current sensors, in particular current sensors for phase currents in a multi-phase electrical drive system. The present invention further relates to an electrical drive system with such a device for monitoring current sensors. State of the art

[0002] Electric drive systems are used in numerous applications. Electrical energy can be provided by an electrical energy source, such as a battery or similar. The provided electrical energy can be converted by means of a power converter into a single-phase or multi-phase electrical voltage, which is then applied to the terminals of an electrical machine in order to set a predetermined operating state. To control the electric drive system and to set predetermined setpoint values ​​on the electrical machine, for example, the electrical currents from the power converter to the phase terminals of the electrical machine can be detected. For this purpose, a current sensor can be provided for each phase of the electrical machine, which current sensor provides an analog or digital signal corresponding to the electrical current.

[0003] The document DE 10 2011 003 566 A1 describes a method and a device for calibrating a current sensor, in particular a current sensor for detecting a phase current of an electrical machine controlled by an inverter. For this purpose, it is proposed to compare a detected actual value or a variable derived from a detected actual value with a predetermined target value and to determine a deviation from a standard state. The document DE 10 2018 251746 A1 discloses a method for determining a gain error of a current measuring device of a sensor unit of an electrical machine, wherein the machine has a stator winding with at least three phases and a rotor that is rotatably mounted about a rotational axis. The method excludes the influence of a rotor angle of the rotor on the determination of the gain error by means of a low-pass filter. Disclosure of the invention

[0004] The present invention provides a method and a device for monitoring current sensors, as well as an electric drive system, having the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims.

[0005] Accordingly, the following is provided: A method for monitoring current sensors, in particular for monitoring current sensors for phase currents in a multi-phase electrical drive system. The method comprises a step for detecting sensor values ​​for the phase currents. In particular, each current sensor can determine a phase current of the multi-phase electrical drive system and provide a sensor value corresponding to the determined phase current. The method further comprises a step for calculating a current sum using the detected sensor values ​​from the current sensors. Furthermore, the method comprises a step for determining a real part and an imaginary part of a complex current sum. The real part and the imaginary part of the complex current sum can be determined using a rotor angle of the electrical machine in the electrical drive system.The method further comprises a step for calculating a complex gain error of the current sensors. The complex gain error is calculated from a quotient of the real part of the complex current sum and a current effective phase current amplitude, as well as a quotient of the imaginary part of the complex current sum and the current effective phase current amplitude. Finally, the method comprises a step for calculating an absolute value of the complex gain error.

[0006] Furthermore, a detector device for monitoring current sensors, in particular for monitoring current sensors for phase currents in a multi-phase electrical drive system, is provided. The detector device comprises an input interface and a computing device. The input interface is designed to detect sensor values ​​from current sensors, with each current sensor detecting a phase current of the multi-phase electrical drive system and providing a sensor value corresponding to the detected phase current. In particular, sensor values ​​from current sensors can be detected at the phase connections of an electrical machine of the electrical drive system. Alternatively, detection of the phase currents at a different location is also possible. The computing device is designed to calculate a current sum using the detected sensor values ​​from the current sensors.Furthermore, the computing device is designed to calculate a real part and an imaginary part of a complex current sum. The real part and the imaginary part can be calculated using a rotor angle of the electric machine in the electric drive system. Furthermore, the computing device is designed to calculate a complex gain error. The complex gain error is calculated from a quotient of the real part of the complex current sum and a current effective phase current amplitude, as well as a quotient of the imaginary part of the complex current sum and the current effective phase current amplitude. Finally, the computing device is designed to calculate an absolute value of the complex gain error.

[0007] Finally, the invention provides an electric drive system comprising a multi-phase electric machine, a plurality of current sensors, and a detector device according to the invention. The current sensors are each designed to detect an electrical phase current and output a sensor value corresponding to the detected phase current. Advantages of the invention

[0008] The present invention is based on the finding that current-based control of an electric drive system places high demands on the accuracy and reliability of the current sensors that measure the electrical currents in the drive system. This requires checking and validating the sensor data provided by the current sensors in order to detect malfunctions such as a gain error (current sensor gain error).

[0009] It is therefore an idea of ​​the present invention to take this finding into account and to provide a diagnosis of current sensors in an electric drive system, which enables a reliable and rapid diagnosis of the current sensors even in the case of dynamic processes and asymmetrical resistances in the various phases of the electric drive system.

[0010] For this purpose, the measured values ​​of the current sensors for the individual phases of the electrical machine are first summed and from this a current sum is calculated. The current sensors can be provided, for example, within the power converter, at the phase connections of the electrical machine or along the supply lines between the power converter and the electrical machine. The current sensors can output an analog or digital signal that corresponds to the respective detected electrical current. The signal output by the current sensors can thus correspond to a value that is, for example, proportional to the electrical current in the respective phase line. In this way, the current sensors can each provide a sensor value that corresponds to a phase current of the multi-phase electrical drive system.

[0011] With fault-free current sensors and a fault-free electrical machine, this current sum is usually zero. However, in the event of a fault, for example, due to different amplification factors in the individual current sensors, the current sum may deviate from zero. In conventional systems, the current sensors can be detected, for example, by observing the minima and maxima in the phase currents over several electrical periods. However, such methods generally only work in steady-state conditions. If, on the other hand, the current varies excessively within one electrical revolution, the minima and maxima of the phase currents differ. As a result, a reliable diagnosis for such operating conditions is not possible using conventional methods.Furthermore, even in the steady state, different values ​​for the minima and maxima can occur due to different electrical resistances in the different phases, for example in the inverter, in the electrical machine or the supply lines.

[0012] The present invention therefore provides a method which takes into account the aforementioned disadvantages of conventional methods and enables a reliable diagnosis of the current amplification factor of the current sensors even under dynamic operating conditions.

[0013] The present invention considers the current sum described above, i.e. the sum of all electrical currents in the individual phases of an electrical machine. From this sum, a complex current sum is formed using a measured or calculated rotor angle, i.e. the calculated current sum is broken down into a real part and an imaginary part. The real part and imaginary part of the complex current sum can then be filtered separately if necessary. For this purpose, for example, low-pass filtering, combined low-pass and band-pass filtering or, if necessary, averaging is possible. The current effective current, which can be obtained, for example, from a dq transformation, is filtered with the same filter time constant as that used for filtering the real and imaginary parts of the complex current sum.For filtering the current sum, especially for separate filtering of the real and imaginary parts, it is preferable to consider the corresponding temporal profiles. Accordingly, the terms "current sum," "real part," or "imaginary part" preferably refer to temporal profiles of the corresponding quantities.

[0014] Furthermore, a complex gain error can be calculated from the complex current sum and the current phase current amplitude. The real part of the complex gain error results from the quotient of the real part of the complex current sum and the current phase current amplitude, and the imaginary part of the complex gain error results from the quotient of the imaginary part of the complex current sum and the phase current amplitude.

[0015] Finally, the magnitude of the complex gain error can be calculated. This amplitude value can be compared, for example, with a threshold value to check whether the gain error is still within a specified tolerance range.

[0016] In this way, the current sensor gain of the current sensors for detecting the phase currents can be reliably verified even in the event of a dynamic change in the phase currents.

[0017] According to one embodiment, the method comprises a step for comparing the calculated magnitude, i.e., the amplitude, of the complex gain error with a predetermined threshold. Furthermore, the method may comprise a step for detecting a sensor error. A sensor error may be detected if the calculated magnitude of the complex gain error exceeds the predetermined threshold. The predetermined threshold may be selected such that deviations in the current sensor gain within a predetermined tolerance range are accepted, while deviations in the current sensor gain outside the predetermined tolerance range are classified as faulty. If a current sensor gain is detected in this way that lies outside the acceptable tolerance range, i.e., is greater than the predetermined threshold, appropriate measures may then be taken if necessary.For example, the sensor values ​​from the current sensors can be classified as unreliable in such a case and may no longer be used to control the electric drive system. If necessary, the electric drive system can be switched to emergency operation or even shut down completely. Of course, any other suitable measures are also possible depending on the application.

[0018] According to one embodiment, the method for monitoring the current sensors comprises a step of filtering the calculated current sum. This can be a low-pass filter, a combined low-pass and band-pass filter, or possibly also an averaging step. Accordingly, the real part of the complex current sum and the imaginary part of the complex current sum can be calculated using the previously filtered current sum.

[0019] According to one embodiment, the method comprises steps for filtering the real part of the complex current sum and the imaginary part of the complex current sum. Furthermore, the method comprises steps for determining an effective phase current and for filtering the time profile of the effective phase current. In particular, during such filtering, both the real part and the imaginary part of the complex current sum as well as the profile of the effective phase current are filtered with the same time constant. Thus, the complex gain error can be calculated using the filtered real part and the filtered imaginary part of the complex current sum as well as the filtered effective phase current. Here, too, the filtering can comprise low-pass filtering, combined low-pass and band-pass filtering, or averaging.

[0020] Alternatively, it is also possible to perform filtering after calculating the complex phase current amplitudes.

[0021] The invention is defined by the appended claims. Short description of the drawings

[0022] Further features and advantages of the invention are explained below with reference to the figures. These show: Fig. 1: a schematic representation of an electric drive system with a detector device according to one embodiment; and Fig. 2: a flowchart underlying a method for monitoring current sensors according to one embodiment. Description of embodiments

[0023] Figure 1shows a schematic representation of a block diagram of an electric drive system according to one embodiment. In the example shown here, the electric drive system comprises an electrical energy source 3, for example a DC voltage source, a power converter 1 and an electric machine 2. In the example shown here, the power converter 1 is an inverter which, according to a setpoint specification S, generates a multi-phase AC voltage from the DC voltage provided by the electrical energy source 3 and provides this voltage to the phase connections of the electric machine 2. Although the example shown here is a three-phase electric machine 2, the present invention is in principle also applicable to any multi-phase electric machines which may also have a number of phase connections other than three.

[0024] In principle, the present invention is also applicable to any winding arrangement within the electrical machine 2, for example, star or delta connections. The only essential requirement here is that the electrical machine 2 has a winding arrangement in which the entire electrical current flows via the phase connections, and no additional current flow, for example, via a second star point or the like, is provided.

[0025] The power converter 1 can, for example, have power electronics with multiple switching elements. The switching elements of this power electronics 30 can, for example, be controlled by means of control signals from a control device 20. In this way, a multi-phase alternating voltage can be generated from the direct voltage provided by the electrical energy source 3, for example by means of pulse-width modulation, in order to control the electric machine 2 based on a setpoint value S. The setpoint value S can, for example, be a torque to be set or something similar.

[0026] To control the electrical machine 2 according to the setpoint S, the control device 20 can detect the electrical currents in the phase lines between the power converter 1 and the electrical machine 2 and adapt the control of the power electronics 3 according to the detected electrical currents and the setpoint S. For this purpose, the electrical currents can be detected using corresponding current sensors 21 to 23. The current sensors 21 to 23 can be provided, for example, within the power converter 1, at the phase connections of the electrical machine 2, or along the supply lines between the power converter 1 and the electrical machine 2. The current sensors 21 to 23 can output an analog or digital signal that corresponds to the respectively detected electrical current.The signal output by the current sensors 21 to 23 can thus correspond to a value which is, for example, proportional to the electrical current in the respective phase line.

[0027] For correct control of the electric drive system, it is necessary that the control is based on correct measured values ​​of the electrical phase currents. For this purpose, the sensor signals output by current sensors 21 to 23 can be checked and verified for plausibility using a detector device 10. A method according to the invention for checking the sensor values ​​from sensors 21 to 23 is described below.

[0028] First, the sensor signals provided by the current sensors 21 to 23 are detected at an input interface 11 of the detector device 10. Since, as already described above, the electrical current between the power converter 1 and the electrical machine 2 flows exclusively via the phase lines, which are monitored by the current sensors 21 to 23, the sum of the currents detected by the sensors 21 to 23 is always zero in a fault-free state. The computing device 12 of the detector device 10 therefore first calculates a total current I_sum from the sensor values ​​provided by the current sensors 21 to 23 by summing the real values ​​of the respective phase currents corresponding to the sensor values. Various factors can lead to a total current deviating from zero. For example, the individual current sensors 21 to 23 can have different, at least slightly different, current sensor gains.

[0029] If the total current is zero or below a specified limit, this can be interpreted as an indication that current sensors 21 to 23 are functioning correctly. Otherwise, i.e., if the total current deviates from zero or exceeds a specified limit, the diagnostic scheme described below can be applied to diagnose a malfunction in current sensors 21 to 23, particularly deviating sensor current gains. Alternatively, the diagnostic scheme described below can also be permanently active.

[0030] If necessary, the total current I_sum determined based on the sensor values ​​provided by current sensors 21 to 23 can be filtered. For example, low-pass filtering, combined low-pass and band-pass filtering, or averaging are possible. Such filtering can determine a filtered total current I_f_sum. If such filtering is applied to the total current, the filtered total current I_f_sum can also be checked to determine whether it deviates from zero or exceeds a specified limit.

[0031] If the total current I_sum or the filtered total current I_f_sum deviates from zero or exceeds the specified limit, a complex current sum is first generated from the determined total current I_sum. The real part I_Re and the imaginary part I_Im of the complex current sum are calculated as follows: l_Re = l_sum − l_f_sum * sin phi * 2 l_Im = l_sum − l_f_sum * cos phi * 2 where phi represents the rotor angle of the electric machine 2. This rotor angle phi can be measured, for example, by means of a rotor angle sensor 2a or provided as a calculated value by the control device 20.

[0032] Furthermore, the control device 20 can also provide a value for the current effective current I_eff. This value of the current effective current I_eff can be obtained, for example, from a dq transformation.

[0033] In a further step, the real and imaginary parts of the complex current sum can be filtered. For example, low-pass filtering, combined low-pass and band-pass filtering, or averaging can be applied. This results in a value for the filtered real part of the complex current sum, I_Re_f, and a value for the filtered imaginary part of the complex current sum, I_Im_f.

[0034] Furthermore, the effective current I_eff is filtered with the same filter time constant that was used to filter the complex current sum. This results in the filtered effective current value I_eff_f.

[0035] From the filtered real and imaginary parts of the complex current sum as well as the filtered effective current, a complex current gain error can be calculated as follows: F_err_Re = l_Re_f / l_eff_f F_err_Im = l_Im_f / l_eff_f where F_err_Re represents the real part of the complex current gain error and F_err_Im represents the imaginary part of the complex current gain error.

[0036] From this complex current amplification error, the amplitude, i.e. the amount of the complex current sum, can then be calculated as follows: F_err_abs = sqrt F_err_Re ∧ 2 + F_err_Im ∧ 2

[0037] The amount or amplitude calculated in this way can then be compared with a predefined threshold value. If the calculated amount or amplitude is below the predefined threshold value, the current amplification factors of the current sensors 21 to 23 are within an acceptable tolerance range. However, if the amount exceeds the predefined threshold value, this is an indication that the current amplification factors of the current sensors 21 to 23 deviate outside of an acceptable tolerance range. In such a case, suitable measures can be taken if necessary. For example, the sensor values ​​provided by the current sensors 21 to 23 can no longer be considered for the control of the electric drive system, or can only be considered to a limited extent. If necessary, the electric drive system can be switched to emergency mode or even shut down completely.

[0038] In addition to the previously described processes, it is also possible to perform the filter operations differently from the previously described scheme. For example, the filter operations can be performed only after the complex gain factor has been calculated. Furthermore, depending on the application, it is also possible to apply filter operations at times different from the scheme described above. The filter operations or averaging can be applied to either one or more electrical periods of the phase currents in order to create a filtering effect that is appropriate for the respective application.

[0039] Figure 2shows a schematic representation of a flowchart underlying a method for monitoring current sensors in a multi-phase electric drive system. The method described below can, in principle, comprise any steps as previously described in connection with the diagnostic device 10.

[0040] In addition, the previously described diagnostic device 10 can of course also have any components in order to carry out the method steps described below.

[0041] In step S1, sensor values ​​from current sensors for the phase currents of an electrical machine 2 are first recorded.

[0042] In step S2, a current sum is calculated from the recorded sensor values. In step S3, the real and imaginary parts of a complex current sum are determined. This complex current sum can be calculated, as previously described, using the rotor angle of the electric machine 2 in the drive system.

[0043] In step S4, a complex gain factor is then calculated. As previously described, the calculation is performed from the quotient of the real part of the complex current sum and the current effective phase current, as well as the quotient of the imaginary part of the complex current sum and the current effective phase current.

[0044] Finally, in step S5, an amount or amplitude of the complex gain factor is calculated.

[0045] The thus calculated amount of the complex amplification factor can be compared with a predetermined threshold value in order to determine an inadmissible deviation of the current amplification factor in one of the current sensors 21 to 23.

[0046] In summary, the present invention relates to the diagnosis of current sensors in an electric drive system. A total current is calculated from the sensor values ​​provided by the current sensors. If this total current deviates significantly from zero, a complex current sum can be calculated using the rotor angle of the electric machine. This complex current sum is related to the current effective current in the electric drive system to determine deviations in the current amplification factors of the current sensors used.

Claims

1. Method for monitoring current sensors (21-23) for phase currents in a multi-phase electric drive system, having the steps of: acquiring (S1) sensor values for the phase currents, wherein a respective current sensor (21-23) ascertains one phase current of the multi-phase electric drive system and provides a sensor value corresponding to the ascertained phase current; calculating (S2) a total current by using the acquired sensor values from the current sensors (21-23); characterized by determining (S3) a real part and an imaginary part of a complex total current by using a rotor angle of the electric machine (2) in the electric drive system; calculating (S4) a complex gain error from a quotient of the real part of the complex total current and of a present effective phase current amplitude and a quotient of the imaginary part of the complex total current and of the present effective phase current amplitude; and calculating (S5) an amount of the complex gain error.

2. Method according to Claim 1, having the steps of: comparing the calculated amount of the complex gain error with a predetermined threshold value; and detecting a sensor error if the calculated amount of the complex gain error exceeds the predetermined threshold value.

3. Method according to Claim 1 or 2, having a step for filtering the calculated total current, wherein the real part and the imaginary part of the complex total current are calculated using the filtered total current.

4. Method according to one of Claims 1 to 3, having the steps of: filtering the real part and the imaginary part of the complex total current, determining an effective phase current, and filtering a time characteristic of the effective phase current, wherein the real part and the imaginary part of the complex total current and the time characteristic of the effective phase current are filtered with an equal time constant, and wherein the calculation of a complex gain error is performed using the filtered real part and the filtered imaginary part of the complex total current and the filtered effective phase current.

5. Method according to Claim 3 or 4, wherein the filtering of the total current, of the real part and of the imaginary part of the complex total current and / or of the time characteristic of the effective phase current comprises averaging, low-pass filtering or combined low-pass filtering and band-pass filtering.

6. Detector apparatus (10) for monitoring current sensors for phase currents in a multi-phase electric drive system, having: an input interface (11) which is designed to acquire sensor values for phase currents, wherein a respective current sensor (21-23) ascertains one phase current of the multi-phase electric drive system and provides a sensor value corresponding to the ascertained phase current; a computing device (12) which is designed to calculate a total current by using the acquired sensor values from the current sensors (21-23), to determine a real part and an imaginary part of a complex total current by using a rotor angle of the electric machine (2) in the electric drive system, to calculate a complex gain error from a quotient of the real part of the complex total current and of a present effective phase current amplitude and a quotient of the imaginary part of the complex total current and of the present effective phase current amplitude, and to calculate an amount of the complex gain error.

7. Electric drive system, having a multi-phase electric machine (2), a plurality of current sensors (21-23), each designed to acquire an electric phase current and to output a sensor value corresponding to the acquired phase current; and a detector apparatus (12) according to Claim 6.