Method and device for determining estimate of measurement offset of phase current sensor

Abstract

The invention relates to a device (101, 300) for determining an estimated value (314, 315) of a measurement offset of a phase current sensor (115) for a phase current (112) of an electric machine (103). The device (101, 300) is configured to determine a measured value (215) of a control error of a current controller (200) for adjusting a phase current (112) of an electric machine (103) at a point in time. The device is further provided for determining a model value (313) of the control error at the point in time on the basis of an estimated value (314, 315) of the measured offset of the phase current sensor (115) at the point in time by means of a model (302) dependent on the stator inductance of the electric machine (103). Furthermore, the device is designed to determine, by means of the filter unit (301), an estimated value (314, 315) of a measured offset of the phase current sensor (115) at the next point in time on the basis of the measured value (215) of the control error and on the basis of the model value (313) of the control error.

Description

Technical Field

[0001] The present invention relates to a method and a corresponding device for determining the offset of a phase current sensor of an electric machine. Background Art

[0002] An electric drive vehicle has an electric drive that can operate with a plurality of, typically N (e.g., N = 3) phase currents. The phase currents can be generated by an inverter based on a direct current provided by an electrical energy storage. Each phase current can be detected and monitored by a current sensor arranged on the corresponding phase line. Here, the measured values of N - 1 current sensors can be used to control the phase currents. The Nth current sensor can be used for a total current credibility test.

[0003] During the service life of the phase current sensor and / or due to temperature fluctuations, it is possible that the measured values of the phase current sensor have a measurement offset and / or the measurement offset of the phase current sensor changes. This can lead to inaccuracies in the operation of the electric drive of the vehicle. Summary of the Invention

[0004] The technical task to be solved herein is to enable an efficient, accurate, and robust determination of the measurement offset of the phase current sensor, in particular to enable a persistent and reliable operation of the electric machine.

[0005] The above task is solved by each independent claim. In addition, advantageous embodiments are described in the dependent claims. It should be noted that the additional features of the claims dependent on the independent claims can, without the features of the independent claim or only in combination with some of the features of the independent claim, form an independent invention on their own and independent of all combinations of the features of the independent claim, which can be the technical solutions of the independent claim, a divisional application, or a subsequent application. This also applies to the technical teachings described in the specification, which can form an invention independent of the features of the independent claim.

[0006] According to one aspect, a device for determining an estimated value of the measurement offset of a phase current sensor for a (optionally three-phase) electric machine (such as a synchronous machine) is described. The device can be arranged to determine, respectively for the d-axis and the q-axis of the dq coordinate system of the electric machine, an estimated value of the measurement offset of the phase current sensor. The estimated value of the measurement offset of the phase current sensor can then be transformed from the dq coordinate system of the electric machine to the three-phase system of the electric machine by means of an inverse Park transformation, in order to determine an estimated value of the measurement offset of the first phase current sensor for the first phase of the electric machine and an estimated value of the measurement offset of the second phase current sensor for the second phase of the electric machine.

[0007] Therefore, the estimated value can be determined in the dq coordinate system of the electric machine. In addition, the determination can be performed iteratively on a sequence of consecutive time points.

[0008] The device is arranged to repeatedly determine, at each time point of a sequence of successive time points, a measured value of the control error of a current controller for regulating the motor phase currents at that time point (for the d-axis and for the q-axis respectively). The control error of the current controller typically depends on the measurement offset of said one or more phase current sensors.

[0009] The device is also arranged to repeatedly determine, at each time point of a sequence of successive time points, a model value of the control error at that time point (for the d-axis and for the q-axis respectively) based on an estimated value of the measurement offset of the phase current sensors at that time point by means of a model depending on at least one stator inductance of the motor. The (mathematical) model can depend on L q stator inductance and L d stator inductance, where L q stator inductance and L d stator inductances are different.

[0010] Thus, a mathematical model can be used to determine a model value of the control error based on an estimated value of the measurement offset determined so far, which model value should correspond to the measured value of the control error. The estimated value of the measurement offset can be adjusted iteratively in order to reduce (in particular minimize) the deviation between the model value of the control error and the measured value of the control error and in this way determine the estimated value of the measurement offset efficiently and precisely.

[0011] The device can in particular be arranged to determine an estimated value of the measurement offset of the phase current sensors at a time point (immediately) following the respective time point based on the measured value of the control error and based on the model value of the control error by means of a filter unit. The device, in particular the filter unit, can be arranged to determine an estimated value of the measurement offset of the phase current sensors by means of a phase-locked loop (PLL). The PLL can depend here on the electrical frequency of the motor and / or on the (electrical) speed of the motor. By using the (PLL-based) filter unit, the estimated value of the measurement offset can be determined in a particularly robust and precise manner.

[0012] The filter unit can comprise a band-pass filter (or be configured as a band-pass filter). The device can be arranged to determine the electrical frequency and / or the (electrical) speed of the motor at the respective time point. The band-pass filter, in particular the passband of the band-pass filter, can then be adjusted as a function of the electrical frequency and / or the (electrical) speed of the motor. As an alternative or in addition, the model can be adjusted as a function of the (electrical) speed of the motor. Thus, the estimated value of the measurement offset can be determined in a particularly precise and robust manner.

[0013] The device can be configured to filter a measurement value depending on a control error at that time and a model value of the control error at that time, in particular a signal depending on the difference between the measurement value and the model value, by means of a filter unit, in particular by means of a band-pass filter of the filter unit. Then, an estimated value of the measurement offset of the phase current sensor at the next time point can be determined in a particularly precise and robust manner based on the filtered signal.

[0014] The device can be configured to determine an input value of the filter unit based on a measurement value of the control error at that time and based on a model value of the control error at that time, in particular based on the difference between the measurement value of the control error at that time and the model value of the control error at that time. Then, an estimated value of the measurement offset of the phase current sensor at the next time point can be determined by means of the filter unit based on the input value of the filter unit. Here, the filter unit can be configured to adjust the estimated value of the measurement offset of the phase current sensor along a sequence of time points in such a way that the input value (optionally the input value accumulated over the sequence of time points) is reduced. Thus, the estimated value of the measurement offset can be determined in a particularly precise and robust manner.

[0015] As described above, a measurement value of the control error, a model value of the control error, and an estimated value of the measurement offset of the phase current sensor can be determined separately for the d-axis and the q-axis of the motor dq coordinate system in order to enable particularly precise current control of the motor.

[0016] The (mathematical) model can depend on and / or include, in particular correspond to

[0017]

[0018] where i d_m 、i q_m is the model value of the measurement value of the (at least one) phase current sensor for the d-axis or the q-axis of the motor dq coordinate system;

[0019] is the target value of the phase current for the d-axis or the q-axis of the dq coordinate system (current controller);

[0020] is the model value of the control error for the d-axis or the q-axis of the dq coordinate system;

[0021] Δi d_off ,Δi q_off is the estimated value of the measurement offset of the phase current sensor for the d-axis or the q-axis of the dq coordinate system;

[0022] ω cc is the bandwidth of the current controller;

[0023] Rs is the stator resistance of the electric machine;

[0024] L d and L q are the stator inductances for the d-axis and q-axis of the dq coordinate system;

[0025] ω e is the electrical speed of the electric machine.

[0026] The above mathematical model enables a particularly precise determination of the estimated value of the measurement offset.

[0027] The device can be set up to detect (and transform into the dq coordinate system) the measured value of the phase current at a next time point by means of the (at least one) phase current sensor. The measured value of the phase current can be corrected at the next time point by means of the estimated value of the measurement offset of the phase current sensor (in the dq coordinate system) in order to determine the corrected measured value of the phase current at the next time point. Furthermore, the phase current can be adjusted, in particular in the context of current control, as a function of the corrected measured value of the phase current, in particular to a target value of the phase current. As a result, a particularly precise operation of the electric machine can be achieved.

[0028] According to another aspect, a (road) motor vehicle (in particular a car or a truck or a bus or a motorcycle) is described which comprises the device described herein. The vehicle also comprises an electric drive.

[0029] According to another aspect, a method for determining an estimated value of the measurement offset of at least one phase current sensor for the phase current of an electric machine is described. One or more estimated values in the dq coordinate system can be determined here and transformed into the three-phase system of the electric machine.

[0030] The method comprises repeatedly determining at each time point of a sequence of successive time points the measured value of the control error of a current controller for adjusting the phase current of the electric machine at the respective time point. Furthermore, the method comprises determining a model value of the control error at the respective time point on the basis of a model which depends on at least one stator inductance of the electric machine and on the estimated value of the measurement offset of the phase current sensor at the respective time point.

[0031] The method further comprises determining, by means of a (PLL) filter unit, the estimated value of the measurement offset of the phase current sensor at the time point (immediately following in the sequence of time points) after the respective time point on the basis of the measured value of the control error at the respective time point and on the basis of the model value of the control error at the respective time point.

[0032] According to another aspect, a software (SW) program is described. The SW program can be set up to be executed on a processor (for example on a controller of a vehicle) and thereby to carry out the method described herein.

[0033] According to another aspect, a storage medium is described. The storage medium may include an SW program that is configured to be executed on a processor and thereby perform the methods described herein.

[0034] It should be noted that the methods, devices, and systems described herein can be used not only individually but also in combination with other methods, devices, and systems described herein. Additionally, any aspects of the methods, devices, and systems described herein can be combined with each other in various ways. In particular, the features of the claims can be combined with each other in various ways. Furthermore, the features listed in parentheses should be understood as optional features. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be described in detail below with reference to embodiments. The accompanying drawings are as follows:

[0036] Figure 1a Shows an exemplary inverter or converter for a vehicle motor;

[0037] Figure 1b Shows an exemplary curve of the phase voltage;

[0038] Figure 2 Shows an exemplary current control loop for current control of a motor in the dq coordinate system;

[0039] Figure 3 Shows an exemplary device for determining an estimated value of the offset of a current sensor; and

[0040] Figure 4 Shows a flowchart of an exemplary method for determining an estimated value of the offset of a phase current sensor. DETAILED DESCRIPTION

[0041] As mentioned at the beginning, the present invention is dedicated to efficiently and accurately determining the measurement offset of the phase current sensor of a multiphase motor. In this context, Figure 1a An exemplary inverter 100 is shown, which is configured to generate a phase voltage 111 (i.e., an alternating voltage) for the stator windings of a motor 103 (e.g., a vehicle motor) based on the on-vehicle grid voltage U DC 110 (i.e., a DC voltage). The inverter 100 may have an intermediate circuit with an intermediate circuit capacitor 105, and the on-vehicle grid voltage U DC 110 is applied to this intermediate circuit capacitor.

[0042] The inverter 100 (or converter or current transformer) includes a plurality of switches or switching elements 102, 104, which are each arranged in a half-bridge for each phase 121, 122, 123 in the example shown. The switching elements 102, 104 are controlled by a control device 101 in order to generate the phase voltage 111 for the motor 103.

[0043] Figure 1b An exemplary phase voltage 111 is shown, which can be generated by the switching elements 102, 104 of the half-bridge. As Figure 1b can be seen, the switching elements 102, 104 are switched (i.e., turned on or off) in a specific pulse pattern in order to generate the (sinusoidal) alternating voltage 111. The pulse pattern for a specific (static) operating point of the electric motor 103 can be determined in advance, for example by means of an optimization method such as SOPWM (Synchronous Optimal Pulse Width Modulation), by means of which a specific optimization criterion (e.g., the harmonic distortion of the phase current) can be optimized, in particular minimized. The determined pulse patterns for different operating points of the electric motor 103 can be stored, for example, in a look-up table (LUT). Each pulse pattern has a specific number M of pulses for each wave or half-wave of the alternating voltage to be generated, where M is an integer (e.g., M = 1, 2, 3, 4, 5, 6 or more).

[0044] The different operating points of the electric motor 103 can include, for example, different torques and / or different rotational speeds to be set.

[0045] The device 101 can be set up to implement current control in order to adjust a specific operating point of the electric motor 103, in particular the control of the phase currents 112 of the different phases 121, 122, 123 of the electric motor 103. For this purpose, the measured values of the phase currents 112 in the different phases 121, 122 can be detected by means of the current sensors 115. In the case of N different phases 121, 122, 123 (e.g., N = 3), it is usually sufficient to detect the measured values of N - 1 phases, since the phase current 112 on the Nth phase 123 results as the sum current of the other N - 1 phases 121, 122 (e.g., zero). Therefore, the inverter 100 advantageously has only N - 1 current sensors 115 for the N - 1 corresponding phase currents 112.

[0046] When N = 3, the measured values of the phase currents of the respective phases a (121), b (122) and c (123) can be defined as follows:

[0047] i as_m = i as + Δi as_off (1)

[0048] i bs_m = i bs + Δi bs_off (2)

[0049] i cs_m = -i as_m - i bs_m = i cs -(Δi as_off + Δi bs_off ) (3)

[0050] Here, i as , i bs and i cs are the correct values of the phase currents of the first phase a, the second phase b, and the third phase c, respectively. Δi as_off is the measurement offset of the first current sensor 115 of the first phase, and Δi bs_off is the measurement offset of the second current sensor 115 of the second phase. i as_m and i bs_m are the actual measured values of the current sensor 115 of the first phase or the second phase, and i cs_m is the actual measured value of the current sensor 115 of the third phase (if any).

[0051] The above currents can be transformed to the dq coordinate system by means of the Park transformation, thereby obtaining

[0052]

[0053] or, correspondingly, in matrix form

[0054]

[0055] Here, θ e is the electrical rotation angle of the motor 103. Δi d_off is the d-axis component of the measurement offset in the dq coordinate system and Δi q_off is the q-axis component of the measurement offset in the dq coordinate system. In particular, Δi d_off describes the influence of the measurement offset of the phase current sensor 115 on the d-axis component of the current, and Δi q_off describes the influence of the measurement offset of the phase current sensor 115 on the q-axis component of the current.

[0056] The above equations can be rewritten as follows:

[0057] △i d_off = k off sin(θ e + α) (7)

[0058] Δi q_off = k off cos(θ e + α) (8)

[0059] where

[0060]

[0061] As can be seen from equations (7) and (8), the measurement offset of the phase current sensor 115 causes high-order harmonics in the phase current 112 in the dq coordinate system, and the high-order harmonics have a frequency corresponding to the electrical rotational speed or rotational speed ω of the rotor. e of the frequency.

[0062] Figure 2 An exemplary current control circuit 200 for the d-axis component (upper) and q-axis component (lower) of the current is shown. The control loop 200 has a controller 211 and a system to be controlled 212 respectively. Here, the system to be controlled 212 can be modeled by the formulas shown respectively. The actual values 213 of the d-axis component or q-axis component of the current are provided by the system to be controlled 212, and these actual values are distorted due to the corresponding measurement offset, so as to obtain the measured value 216 of the current. The control loop 200 shown in Figure 2 can also be used for a current-excited synchronous motor.

[0063] Assuming that the bandwidth of the controller 211 (especially the PI controller) is ω cc , the following formulas can be determined for the d-axis component and q-axis component of the current:

[0064]

[0065] or

[0066]

[0067] Figure 3 An exemplary device 300 is shown, which is configured to determine the estimated value 314 of the measurement offset Δi d_off , Δi q_off in the dq coordinate system) based on the above formulas, especially based on formulas (11) and (12). The device 300 includes a model unit 302, which is set to determine the measured value i d_m , i q_m of the model value 313i d_obs and / or (based on formulas (13) and (14)) determine the model value of the control error based on the above formulas, especially based on formulas (11) and (12) and based on the estimated value 314 of the measurement offset. Therefore, based on the above formulas, an observer can be provided to estimate the phase current measured by the sensor 115 and / or to estimate the control error 215 of the current control loop 200.

[0068] The model value 313 of the control error can be subtracted from the corresponding measured value 215 of the control error of the current controller 200 to determine the input value 311 to the filter unit 301, especially the phase-locked loop (PLL) filter unit 301. The input value 311 should ideally be zero.

[0069] The filter unit 301 can be configured as a band-pass filter, by means of which an electrical frequency fe(θ e = 2π*fe*t) signal can be extracted from the input value 311, in particular from the difference between the input value 311 and the output value 314 (i.e., the estimated value of the measurement offset) of the filter unit 301. As described above, the measurement offset depends on this electrical frequency.

[0070] The filter unit 301 is also provided for iteratively reducing the input value 311, in particular minimizing it (to zero). If this is the case, the model value 313i of the control error determined by the model unit 302 d_obs agrees with the measured value 215 of the control error and thus provides an accurate estimated value 314 of the measurement offset.

[0071] The filter unit 301 can be constructed according to the literature of M. Karimi-Ghartemani and A. K. Ziaran, "Performance characterization of a non-linear system as both an adaptive notch filter and a phase-locked loop" (published in the International Journal of Adaptive Control and Signal Processing, Vol. 18, pp. 23-53, 2004, especially see Figure 2 and 5), the content of which is incorporated herein by reference in its entirety.

[0072] The estimated value 314 of the measurement offset can be transformed from the dq coordinate system to the abc coordinate system in the transformation unit 303 in order to provide an estimated value 315 of the measurement offset Δi as_off , Δi bs_off .

[0073] Figure 4 The flowchart of a (possibly computer-implemented) method 400 for determining the estimated values 314, 315 of the measurement offset of the phase current sensor 115 for the phase current 112 of the electric machine 103 is shown. The method 400 can be designed to determine the estimated value 314 of the measurement offset of at least one phase current sensor (in particular exactly two phase current sensors) 115 for the d-axis and q-axis of the dq coordinate system, respectively. Alternatively or additionally, the estimated value 315 of the measurement offset of the phase current sensor 115 can be determined for different phases 121, 122 in the three-phase system of the electric machine 103, respectively.

[0074] Method 400 can be repeatedly executed at each time point in a sequence of successive time points. Here, the current estimates 314, 315 of the measurement offset can be determined, in particular updated, recursively respectively.

[0075] Method 400 includes (at each time point in a sequence of successive time points) determining 401 the measured values 215 (for the d-axis and for the q-axis respectively) of the control error of the current controller 200 for regulating the phase current 112 of the electric machine 103 at this time point. The measured values 215 of the control error can here (in the steady state of the current controller 200) depend on the measurement offset of the phase current sensor 115.

[0076] Furthermore, method 400 includes determining 402 the model value 313 of the control error at this time point based on the estimated values 314, 315 of the measurement offset of the phase current sensor 115 at this time point by means of a model 302 that depends on the stator inductance of the electric machine 103.

[0077] Method 400 further includes determining 403 the estimated values 314, 315 of the measurement offset of the phase current sensor 115 at a time point after this time point based on the measured value 215 of the control error at this time point and based on the model value 313 of the control error at this time point by means of a filter unit 301 (with a band-pass filter).

[0078] By the measures described herein, it is possible to determine the measurement offset of at least one phase current sensor 115 of the electric machine 103 particularly efficiently and precisely, thereby improving the current control and thus the reliability of the operation of the electric machine 103.

[0079] The invention is not limited to the embodiments shown. In particular, it should be noted that the description and the drawings are only to illustrate the principles of the proposed methods, devices and systems exemplarily.

Claims

1. Apparatus (101, 300) for determining an estimated value (314, 315) of a measurement offset of a phase current sensor (115) for a phase current (112) of an electric machine (103); the apparatus (101, 300) being arranged to repeatedly determine, at each time point of a sequence of successive time points a measured value (215) of a control error of a current controller (200) for regulating the phase current (112) of the electric machine (103) at that time point; determine a modeled value (313) of the control error at that time point based on the estimated value (314, 315) of the measurement offset of the phase current sensor (115) at that time point by means of a model (302) depending on at least one stator inductance of the electric machine (103); and determine an estimated value (314, 315) of the measurement offset of the phase current sensor (115) at a time point subsequent to that time point based on the measured value (215) of the control error and based on the modeled value (313) of the control error by means of a filter unit (301).

2. The apparatus (101, 300) according to claim 1, wherein the filter unit (301) comprises a band-pass filter; and the apparatus (101, 300) is arranged to: determine the electrical frequency and / or the electrical speed of the electric machine (103) at that time point; and adjust the band-pass filter, in particular the passband of the band-pass filter, according to the electrical frequency and / or the electrical speed of the electric machine (103).

3. The device (101, 300) according to any one of the preceding claims, wherein, The apparatus (101, 300) is arranged to filter a signal depending on the measured value (215) of the control error at that time point and the modeled value (313) of the control error at that time point by means of the filter unit (301), in particular by means of the band-pass filter of the filter unit (301); and determine an estimated value (314, 315) of the measurement offset of the phase current sensor (115) at the next time point based on the filtered signal.

4. The device (101, 300) according to any one of the preceding claims, wherein, The apparatus (101, 300) is arranged to determine an input value (311) of the filter unit (301) based on the measured value (215) of the control error at that time point and based on the modeled value (313) of the control error at that time point, in particular based on the difference between the measured value (215) of the control error at that time point and the modeled value (313) of the control error at that time point; determine an estimated value (314, 315) of the measurement offset of the phase current sensor (115) at the next time point by means of the filter unit (301) based on the input value (311) of the filter unit (301).

5. The device (101, 300) according to claim 4, wherein, The filter unit (301) is arranged to adjust the estimated value (314, 315) of the measurement offset of the phase current sensor (115) along the sequence of time points such that the input value (311) is reduced.

6. The device (101, 300) according to any one of the preceding claims, wherein, The device (101, 300), in particular the filter unit (301), is configured to determine an estimate (314, 315) of the measurement offset of the phase current sensor (115) with respect to the electrical frequency of the electric machine (103) by means of a phase-locked loop; the electrical frequency depends on the electrical speed of the electric machine (103).

7. The device (101, 300) according to any one of the preceding claims, wherein, The device (101, 300) is configured to determine, for the d-axis and the q-axis of the dq coordinate system of the electric machine (103) respectively, a measured value (215) of the control error, a model value (313) of the control error, and an estimate (314) of the measurement offset of the phase current sensor (115); transform the estimate (314) of the measurement offset of the phase current sensor (115) from the dq coordinate system to the three-phase system by means of an inverse Park transformation (303) in order to determine an estimate (315) of the measurement offset of the first phase current sensor (115) for the first phase (121) of the electric machine (103) and an estimate (315) of the measurement offset of the second phase current sensor (115) for the second phase (122) of the electric machine.

8. The device (101, 300) according to any one of the preceding claims, wherein, The model (302) depends on L q stator inductance and Lx stator inductance; and the L q stator inductance and L d stator inductances are different.

9. The device (101, 300) according to any one of the preceding claims, wherein, The device (101, 300) is configured to determine the electrical speed of the electric machine (103) at this time point; and to adjust the model (302) according to the electrical speed.

10. The device (101, 300) according to any one of the preceding claims, wherein, The model (302) depends on and / or includes, in particular corresponds to where, i d_m and i q_m are the model values of the measured values of the d-axis and q-axis of the dq coordinate system of the phase current sensor (115) for the motor (103); are the target values of the phase currents for the d-axis and q-axis in the dq coordinate system; is the model value (313) of the control error; Δi d_off and Δi q_off are the estimated values (314) of the measurement offsets of the phase current sensor (115) for the d-axis and q-axis in the dq coordinate system; ω cc is the bandwidth of the current controller (200); R s is the resistance of the stator of the electric machine (103); L d and L q are the stator inductances for the d-axis and q-axis in the dq coordinate system; ω e is the electrical speed of the electric machine (103).

11. The device (101, 300) according to any one of the preceding claims, wherein, The device (101, 300) is configured to detect a measured value of the phase current (112) at the next time point by means of the phase current sensor (115); correct the measured value of the phase current (112) by means of an estimate (314, 315) of the measurement offset of the phase current sensor (115) at the next time point in order to determine a corrected measured value of the phase current (112) at the next time point; and in particular, regulate the phase current (112) in the range of current control according to the corrected measured value of the phase current (112), in particular to a target value of the phase current (112).

12. A method (400) for determining an estimate (314, 315) of the measurement offset of a phase current sensor (115) for a phase current (112) of an electric machine (103), the method (400) comprising repeatedly at each time point of a sequence of successive time points determining (401) a measured value (215) of the control error of a current controller (200) for regulating the phase current (112) of the electric machine (103) at this time point; determining (402) a model value (313) of the control error at this time point by means of a model (302) depending on the stator inductance of the electric machine (103) based on an estimate (314, 315) of the measurement offset of the phase current sensor (115) at this time point; and determining (403) an estimate (314, 315) of the measurement offset of the phase current sensor (115) at a time point after this time point by means of a filter unit (301) based on the measured value (215) of the control error at this time point and based on the model value (313) of the control error at this time point.

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