Method for determining phase currents, control device, drive system and motor vehicle

Abstract

Method for determining phase currents (iu, iv, iw) for current control of an electric machine (4) of a drive system (1) for a motor vehicle, wherein measured waveforms (iu, iv, iw) of the phase currents supplied to at least three phases (u, v, w) of a phase set of the electric machine (4) and measured by at least three phase current sensors (Au, Av, Aw) of a phase current sensor set of the drive system (1) are received, and wherein zero crossings (Nu1, Nv1, Nw1, Nu2, Nv2, Nw2) in the at least three measured, phase current sensor-specific waveforms (iu, iv, iw) are detected, and a phase current value (Iu1(v), Iu2(v), Iu1(w)) is determined for at least one zero crossing (Nu1, Nv1, Nw1, Nu2, Nv2, Nw2) per measured waveform (iu, iv, iw) Iu2(w), Iv1(u), Iv2(u), Iv1(w), Iv2(w), Iw1(u), Iw2(u), Iw1(v), Iw2(v)) is determined based on the determined phase current values ​​(Iu1(v), Iu2(v), Iu1(w), Iu2(w),Iv1(u), Iv2(u), Iv1(w), Iv2(w), Iw1(u), Iw2(u), Iw1(v), Iw2(v)) for each phase current sensor (Au, Av, Aw), a characterization value describing the gain factor of the respective phase current sensor (Au, Av, Aw) is determined, and the phase currents (iu, iv, iw~) for current control are determined taking into account the characterization values ​​of the phase current sensors (Au, Av, Aw) by selecting, based on the characterization values, the two phase current sensors (Au, Av) that have the highest gain factors, whereby the two waveforms (iu, iv) measured by these two phase current sensors (Au, Av) and a third waveform (iw~) calculated from the two measured waveforms (iu, iv) are provided for current control.

Description

The invention relates to a method for determining phase currents for current control of an electric machine in a drive system for a motor vehicle. Measured phase current profiles, supplied to at least three phases of a phase set of the electric machine and measured by at least three phase current sensors of a phase current sensor set of the drive system, are received. The invention further relates to a control unit, a drive system, and a motor vehicle. The focus here is on drive systems for electrically powered motor vehicles, which include at least one electric machine. The electric machine is designed to provide a specific torque or drive torque for the motor vehicle and comprises a stator and a rotor rotatably mounted relative to the stator. The stator typically has at least one phase set with at least three phases. A multiphase current is supplied to the at least one phase set to generate a torque-specific rotating magnetic field in the stator. For this purpose, each phase is electrically connected to an inverter string of an inverter within the drive system, via which a phase current, in particular a sinusoidal one, is supplied to each phase. The three phase currents together constitute the multiphase current. To regulate the phase currents, the drive system incorporates a current controller that can specify target phase current profiles based on actual phase current profiles. A phase current sensor set is typically used to acquire these actual profiles, with one sensor for each phase, for example. The measured phase current profiles can deviate from the actual profiles due to differing gain factors of the phase current sensors. These differing gain factors can negatively impact the inverter's operation. The inverter has a specific operating range, which is extended by a tolerance range for peak phase current values. If peak currents exceed this tolerance range, the inverter is typically switched off. Peak currents can exceed the inverter's tolerance range, in particular, if at least one phase current sensor, due to an insufficient gain factor, outputs a measured phase current that is lower than the actual phase current. To prevent this, the phase current sensors are usually calibrated regularly. This involves adjusting both the offset values ​​and the gain factors of the phase current sensors. The offset value is adjusted with a safe zero current, i.e., when the drive system is switched off.The gain factor is usually determined indirectly during operation of the drive system using a phase-locked loop (PLL). This method for determining the gain factor has proven to be slow and inaccurate. JP 2005-162 462 A , JP 2010-110 067 A and JP 2016-178 797 A also show methods for amplification factor correction of phase current sensors of three-phase, inverter-fed three-phase motors. The object of the present invention is to provide a solution with which phase currents for current control of an electric machine of a drive system of a motor vehicle can be determined in a simple and accurate manner. This problem is solved according to the invention by a method, a control device, a drive system, and a motor vehicle with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures. A method according to the invention serves to determine phase currents for current control of an electric machine in a drive system for a motor vehicle. In this method, measured phase current profiles are received. These profiles are supplied to at least three phases of a phase set of the electric machine and are measured by at least three phase current sensors of a phase current sensor set in the drive system. Furthermore, zero crossings in the at least three measured, phase current sensor-specific profiles are detected, and for each profile, a phase current value of at least one other measured profile is determined. Based on the determined phase current values, a characterization value describing a gain factor of the respective phase current sensor is determined for each phase current sensor.The phase currents for current control are determined taking into account the characterization values ​​of the phase current sensors. The invention further relates to a control device for a motor vehicle's drive system, designed to carry out a method according to the invention. The invention also includes a drive system for a motor vehicle comprising at least one electric machine. The electric machine has at least one phase set with at least three phases. The drive system also includes a phase current sensor set with at least three phase current sensors for measuring the phase currents supplied to the phases, as well as a control device according to the invention. The electric machine, which has a stator and a rotor, can, for example, be a permanent magnet synchronous machine (PMSM) or a current-excited synchronous machine (CSM) and provide drive torque for the motor vehicle. The electric machine can, for example, be a three-phase machine and thus have a phase set with three (stator) phases.The electric machine can also be a six-phase machine and have two phase sets, each with three phases. At least one phase set is electrically connected to an inverter of the drive system, which converts the direct current supplied by an electrical energy storage device of the drive system into a multi-phase alternating current for the phase set. This multi-phase current consists, in particular, of three sinusoidal, phase-shifted phase currents, which are impressed into the phases of the electric machine. To control the multiphase current, the drive system also features a phase current sensor set for each phase set. Specifically, each phase sensor set includes a sensor that measures the phase current of the respective phase at the inverter output and machine input. Since these measured actual phase current waveforms form the basis for current control and depend on the gain factors of the phase current sensors, these gain factors are validated and taken into account when determining the phase currents. For this purpose, the zero crossings are determined from the measured, phase-specific current waveforms. During one fundamental frequency period, each phase experiences two zero crossings in the current waveform over time.Since the phase current sensors have already been calibrated at zero current (offset calibration), the current waveforms of the other two phases can be compared with respect to the gain factors of the corresponding phase current sensors. For this purpose, the phase current sensor-specific characterization value is determined based on the measured phase current value of at least one phase current sensor at the measured zero crossing of another phase current sensor. This characterization value, in turn, depends on the gain factor of that phase current sensor. Based on the phase current sensor-specific characterization values, and thus based on the gain factors of the phase current sensors, the phase currents used for current control can then be determined. The process involves determining the phase currents for current control based on the characterization values. This is done by selecting the two phase current sensors with the highest gain factors based on these values. The two waveforms measured by these two sensors are then used for current control, and a third waveform is calculated from the two measured waveforms and used for current control. Specifically, the two phase current sensors with the highest gain factors are selected by filtering out the sensor with the lowest gain factor based on its characterization values. In a star connection of the stator phases, the phase currents sum to zero at any given time, allowing the third phase current to be calculated from the two measured phase currents.Using this method, the phase current sensors with the highest gain can be selected based on their characterization values ​​and used to measure the phase current waveforms of two of the three phases for current control. The waveform of the third phase is not measured by the phase current sensor with the lowest gain, but rather calculated from the other two waveforms. Current control is therefore performed only using the phase current sensors with the highest gain. This avoids current spikes resulting from faulty current control due to an insufficient gain, thus advantageously increasing the inverter's tolerance range. In one embodiment of the method, the characterization value of a phase current sensor is determined as the phase current value of the waveform measured by that sensor at a zero crossing of another waveform. For example, at certain zero crossings of the waveforms, the corresponding phase current values ​​of the other waveforms, such as those on the rising edge, are determined as characterization values. In this way, at least one characterization value in the form of a phase current value is obtained for each phase current sensor, allowing the phase current values ​​of the phase current sensors to be compared. Ideally, with identical gain factors of the phase current sensors, the phase current values ​​of the different phases should be the same. If they differ, this may indicate different gain factors of the phase current sensors.However, this requires a constant fundamental wave amplitude of the current waveforms over a longer period of time. In a preferred embodiment of the method, for each zero crossing of a waveform, the corresponding phase current values ​​of the two other waveforms are determined. Based on these phase current values, a relative deviation of the gain factors of the two corresponding phase current sensors is determined, and the characterization values ​​are determined based on these relative deviations. In particular, the relative deviation of the gain factors of two phase current sensors is determined as the difference of the corresponding phase current values ​​relative to the arithmetic mean of the phase current values. Thus, for each zero crossing of a waveform, a phase pair can be determined from the phase current values ​​of the two other waveforms. This embodiment has the advantage of being robust to small changes in the fundamental frequency amplitudes, which are common even in steady-state operation. Preferably, two zero crossings are detected per fundamental wave period of a waveform, and at each zero crossing, the phase current values ​​of the other two waveforms are determined. Then, two relative deviations of the gain factors of the phase current sensors are determined per fundamental wave period, and the characterization values ​​are determined based on these six relative deviations. Preferably, the gain factors of the individual phase current sensors are determined as the characterization values ​​of the phase current sensors based on these relative deviations. Thus, two phases can be compared with each other per zero crossing. This comparison can be performed twice per fundamental wave period with all phase pairs. From these six comparisons, the gain factors of the phase current sensors can be determined and sorted in order of magnitude. In this way, the phase current sensors with the highest gain can be easily selected for current control. The invention also includes a motor vehicle with a drive system according to the invention. The motor vehicle is designed as an electrically powered motor vehicle. The embodiments and advantages presented with reference to the method according to the invention apply accordingly to the control device according to the invention, to the drive system according to the invention and to the motor vehicle according to the invention. Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified, but also in other combinations or on their own. The invention will now be explained in more detail with reference to a preferred embodiment and the drawings. Figure 1 shows a schematic representation of an embodiment of a drive system 1 for a motor vehicle; and Figure 2 shows a representation of current flow patterns. In the figures, identical and functionally equivalent elements are provided with the same reference symbols. Fig. 1 shows a drive system 1 for a motor vehicle with an electrical energy storage device 2, for example a high-voltage battery, an inverter 3 connected to the electrical energy storage device 2, and an electric machine 4 connected to the inverter 3. The electric machine 4 is a three-phase electric machine 4 and has a phase set with three phases u, v, w. To provide a specific torque, the electric machine 4 applies a phase current iu*, iv*, iw* to each of the phases u, w by the inverter 3. For torque control, these phase currents iu*, iv*, iw* are regulated by a current controller 5 of the drive system 1. For this purpose, the drive system 1 has a phase current sensor set for each phase set.The phase current sensor set comprises a first phase current sensor Au assigned to phase u, a second phase current sensor Av assigned to phase v, and a third phase current sensor Aw assigned to phase w. The phase current sensors Au, Av, and Aw measure the phase current waveforms iu, iv, and iw over time, which can deviate from the actual phase current waveforms iu*, iv*, and iw* due to their different gain factors. Actual waveforms iu*, iv*, and iw*, as well as the measured waveforms iu, iv, and iw that differ from them, are shown in Fig. 2. This figure illustrates that the measured waveform iu is higher than the actual waveform iu*, the measured waveform iv corresponds to the actual waveform iv*, and the measured waveform iw is lower than the actual waveform iw*. Therefore, the first phase current sensor Au has the highest gain factor, and the phase current sensor Aw has the lowest. In current control, the gain factors of the phase current sensors Au, Av, and Aw are taken into account. For this purpose, the current waveforms iu, iv, and iw measured by the phase current sensors Au, Av, and Aw are fed to a control unit 6 of the drive system 1. The control unit 6 can also be integrated into the current controller 5. The control unit 6 is designed to determine the phase currents for current control, taking the gain factors into account. To this end, the control unit 6 selects the phase current sensors Au and Av with the highest gain factors and feeds the phase currents iu and iv measured by these sensors to the current controller 5. The measured current waveform iw of the phase current sensor Aw with the lowest gain is not fed to the current controller 5; instead, the current waveform iw~ is calculated based on the measured phase currents iu and iv and fed to the current controller 5. To select the phase current sensors Au, Av with the highest gain factors, or to filter out the phase current sensor Aw with the lowest gain factor, the control unit 6 can determine the respective gain factor or a characterization value for each of the phase current sensors Au, Av, Aw. For this purpose, the control unit 6 determines zero crossings Nu1, Nv1, Nw1, Nu2, Nv2, Nw2 of the measured current waveforms iu, iv, iw, as shown in Fig. 2. For each fundamental waveform iu, iv, iw, there are two zero crossings Nu1, Nv1, Nw1, Nu2, Nv2, Nw2 for each fundamental waveform. For each zero crossing Nu1, Nv1, Nw1, Nu2, Nv2, Nw2 of a measured curve iu*, iv*, iw*, phase current values ​​Iu1(v), Iu2(v), Iu1(w), Iu2(w), Iv1(u), Iv2(u), Iv1(w), Iv2(w), Iw1(u), Iw2(u), Iw1(v), Iw2(v) of the other curves iu, iv, iw are then determined.For the first zero crossing Nu1 of the measured waveform iu, the phase current values ​​Iw1(u) of waveform iw and Iv1(u) of waveform iv are determined. For the second zero crossing Nu2 of the measured waveform iu, the phase current values ​​Iv2(u) of waveform iv and Iw2(u) of waveform iw are determined. For the first zero crossing Nw1 of the measured waveform iw, the phase current values ​​Iu1(w) of waveform iu and Iv1(w) of waveform iv are determined, and so on. From the pairs of values ​​Iu1(v), Iw1(v); Iu1(w), Iv1(w); Iv1(u), Iw1(u); Iu2(v), Iw2(v); Iu2(w), Iv2(w); Iv2(u), Iw2(u), the gain factors of the offset-calibrated phase current sensors Au, Av, Aw can then be calculated and compared. This comparison can be performed twice during one revolution, i.e., one fundamental wave period, with all phase pairs Iu1(v), Iw1(v); Iu1(w), Iv1(w); Iv1(u), Iw1(u); Iu2(v), Iw2(v); Iu2(w), Iv2(w); Iv2(u), Iw2(u).Ultimately, this results in a total gain and a differential gain between the phase current sensors Au, Av, and Aw. For simplicity, we can assume that the total gain is "1" and that the differential gains correspond to those of the individual phase current sensors Au, Av, and Aw. Based on these differential gains, the two phase current sensors Au and Av with the highest gain factors can then be identified.

Claims

Method for determining phase currents (iu, iv, iw) for current control of an electric machine (4) of a drive system (1) for a motor vehicle, wherein measured waveforms (iu, iv, iw) of the phase currents supplied to at least three phases (u, v, w) of a phase set of the electric machine (4) and measured by at least three phase current sensors (Au, Av, Aw) of a phase current sensor set of the drive system (1) are received, and wherein zero crossings (Nu1, Nv1, Nw1, Nu2, Nv2, Nw2) in the at least three measured, phase current sensor-specific waveforms (iu, iv, iw) are detected, and a phase current value (Iu1(v), Iu2(v), Iu1(w)) is determined for at least one zero crossing (Nu1, Nv1, Nw1, Nu2, Nv2, Nw2) per measured waveform (iu, iv, iw) Iu2(w), Iv1(u), Iv2(u), Iv1(w), Iv2(w), Iw1(u), Iw2(u), Iw1(v), Iw2(v)) is determined based on the determined phase current values ​​(Iu1(v), Iu2(v), Iu1(w), Iu2(w),Iv1(u), Iv2(u), Iv1(w), Iv2(w), Iw1(u), Iw2(u), Iw1(v), Iw2(v)) for each phase current sensor (Au, Av, Aw), a characterization value describing the gain factor of the respective phase current sensor (Au, Av, Aw) is determined, and the phase currents (iu, iv, iw~) for current control are determined taking into account the characterization values ​​of the phase current sensors (Au, Av, Aw) by selecting, based on the characterization values, the two phase current sensors (Au, Av) that have the highest gain factors, whereby the two waveforms (iu, iv) measured by these two phase current sensors (Au, Av) and a third waveform (iw~) calculated from the two measured waveforms (iu, iv) are provided for current control. Method according to claim 1, characterized in that the two phase current sensors (Au, Av) with the largest gain factors are selected for current control by filtering out the phase current sensor (Aw) with the smallest gain factor based on the characterization values. A method according to one of the preceding claims, characterized in that, for each zero crossing (Nu1, Nv1, Nw1, Nu2, Nv2, Nw2) of a waveform (iu, iv, iw), the associated phase current values ​​(Iu1(v), Iw1(v); Iu1(w), Iv1(w); Iv1(u), Iw1(u); Iu2(v), Iw2(v); Iu2(w), Iv2(w); Iv2(u), Iw2(u)) of the two other waveforms (iu, iv, iw) are determined, and a relative deviation of the gain factors of the two associated phase current sensors is determined based on the phase current values ​​(Iu1(v), Iw1(v); Iu1(w), Iv1(w); Iv1(u), Iw1(u); Iu2(v), Iw2(v); Iu2(w), Iv2(w); Iv2(u), Iw2(u)). (Au, Av, Aw) is determined and the characterization values ​​are determined based on the relative deviations. Method according to claim 3, characterized in that the relative deviation of the gain factors of two phase current sensors (Au, Av, Aw) is determined as the difference of the associated phase current values ​​(Iu1(v), Iw1(v); Iu1(w), Iv1(w); Iv1(u), Iw1(u); Iu2(v), Iw2(v); Iu2(w), Iv2(w); Iv2(u), Iw2(u)) based on the arithmetic mean of the phase current values ​​(Iu1(v), Iw1(v); Iu1(w), Iv1(w); Iv1(u), Iw1(u); Iu2(v), Iw2(v); Iu2(w), Iv2(w); Iv2(u), Iw2(u)). Method according to claim 3 or 4, characterized in that two zero crossings (Nu1, Nv1, Nw1, Nu2, Nv2, Nw2) are detected for each fundamental wave period of a waveform (iu, iv, iw), the phase current values ​​(Iu1(v), Iw1(v); Iu1(w), Iv1(w); Iv1(u), Iw1(u); Iu2(v), Iw2(v); Iu2(w), Iv2(w); Iv2(u), Iw2(u)) of the two other waveforms (iu, iv, iw) are determined at each zero crossing (Nu1, Nv1, Nw1, Nu2, Nv2, Nw2). Two relative deviations of the gain factors of the phase current sensors (Au, Av, Aw) per waveform (iu, iv, iw) are determined, and the characterization values ​​are determined on the basis of the six relative deviations. Method according to one of claims 3 to 5, characterized in that the amplification factors of the individual phase current sensors (Au, Av, Aw) are determined from the relative deviations as the characterization values ​​of the phase current sensors (Au, Av, Aw). Control device (6) for a drive system (1) of a motor vehicle, which is designed to perform a method according to one of the preceding claims. Drive system (1) for a motor vehicle comprising: - at least one electric machine (4) with at least one phase set comprising at least three phases (u, v, w), - a phase current sensor set comprising at least three phase current sensors (Au, Av, Aw) for measuring the phase currents (iu, iv, iw) supplied to the phases (u, v, w), and - a control device (6) according to claim 7. Motor vehicle with a drive system (1) according to claim 8 .

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