Method for rotor current estimation

Abstract

The present invention relates to a method for estimating the rotor current of an electric machine (1), comprising the following: - a determination step (131) in which a current estimate is calculated in a PWM half-period, - an identification step (132) in which a first sampling center position (134) and a second sampling center position (136) are identified at zero voltage in a PWM / 2 interval in a corresponding PWM half-period of a voltage waveform (20); - a sampling step (133) in which current values ​​(140, 142) are taken at the sampling center positions (134, 136); - a correction step (139) in which the current estimate is corrected based on the current values ​​(140, 142); - an estimation step (144) in which a current value for the rotating part is estimated, taking into account a transformer transformation ratio in such a current value estimation.

Description

[0001] The present invention relates to the fields of electronics and electrical engineering, and in particular to the field of electrical machines.

[0002] Electric and hybrid vehicles can use electric motors to supply torque to the vehicle's wheels. The motor can be, for example, an electrically excited synchronous machine (EESM). The EESM is an alternative to permanent magnet synchronous machines, as the latter require the use of rare earth materials.

[0003] In an EESM (electrical energy storage system), energy must be transferred from a non-rotating part, i.e., the stator of the electric machine, to a rotating part, i.e., the rotor. Such power transfer can be either conductive or inductive.

[0004] In conductive power transmission, electrical contact is established by brushes on the non-rotating part pressing against slip rings on the rotating part. While the slip ring system of conductive power transmission allows for direct measurement of the rotor current, which is necessary for current and torque control, it causes both mechanical and electrical losses and requires regular maintenance.

[0005] In inductive power transfer, power is transmitted without contact and uses a rotating high-frequency transformer fed by a phase-shift full-bridge converter (PSFBC). A rectifier is connected between the transformer and the rotor winding of the electric machine. Inductive power transfer involves no mechanical losses and is maintenance-free. However, due to complexity and cost, placing a current sensor on the rotating part is highly undesirable, as this would require a sensor power supply at the rotating part of the machine and contactless signal transmission to the non-rotating part. Therefore, direct measurement of the rotor current is not feasible with current technology at a reasonable cost.

[0006] To accurately determine the rotor current required for efficient operation of the EESM, sensors can be used on the non-rotating part of the inductive power transfer system, and a predictive model is provided to estimate the rotor current. In other words, the sensors are positioned on a primary side of the non-rotating part to further estimate the current supplied on a secondary side, i.e., the rotating part.

[0007] For example, it is known to sample the primary-side transformer current at a time corresponding to the midpoint of a positive pulse in the transformer voltage and then apply a transformer transformation ratio. It is also known to use the input current, input voltage, and duty cycle of the converter and then apply a transformer transformation ratio.

[0008] Conventional methods based on sensors on the primary side of the non-rotating part usually work under steady-state conditions, but can be inaccurate under dynamic or transient conditions.

[0009] The present invention fits into this context by providing a method by which the output current at the rotating part of the electrical machine can be accurately estimated under both steady-state and transitional conditions, wherein this method is based on data acquired from the non-rotating part.

[0010] In this context, the present invention relates to a method for estimating the rotor current for a rotating part of an electric machine of an electric or hybrid vehicle, wherein the electric machine comprises a converter which is operated with phase shifts, wherein a duty cycle is associated with a phase shift, wherein the converter provides voltage to a transformer of the electric machine, wherein such voltage is provided to a primary side of the transformer.

[0011] According to the invention, the current estimation method comprises a determination step in which a current estimate is calculated in one half-period of pulse width modulation (PWM); an identification step in which a first sampling center position and a second sampling center position at zero voltage are identified in a corresponding PWM half-period of a voltage waveform generated by the converter in a PWM / 2 interval; a sampling step in which a first current value and a second current value, corresponding respectively to the first and second sampling center positions, are extracted from a primary transformer current waveform; and a correction step in which the current estimate calculated in the determination step is corrected based on the current values ​​extracted during the sampling step.and an estimation step in which a current value for the rotating part is estimated according to the corrected calculated current estimate from the correction step, taking into account a transformer transformation ratio in such a current value estimation.

[0012] The current estimation method according to the invention is intended to be used to determine the output current of a rotating part of an electrical machine, for example, a rotor of a motor in an electric or hybrid vehicle. More precisely, the electrical machine is an inductively electrically excited synchronous machine (iEESM). It comprises, among other things, a DC / AC converter, a transformer, and a rectifier. The converter is a phase-shift full-bridge converter (PSFBC) that operates with phase shifts to which a duty cycle is assigned. The converter provides bipolar square-wave voltages, which are applied to the transformer, specifically to the primary side of this transformer. This primary side of the transformer is located on a non-rotating part of the electrical machine, while a secondary side of the transformer is located on the rotating part of the electrical machine.

[0013] To estimate the rotor current, the current estimation method includes several steps that are performed sequentially, including a determination step, an identification step, a sampling step, a correction step, and an estimation step.

[0014] The determination step corresponds to calculating a current estimate using a power balance approach that is accurate under steady-state conditions.

[0015] Using a current estimation calculation during an identification step, instead of directly measuring the primary transformer current, is advantageous because it is more robust with respect to timing errors. During the identification step, sampling center positions for capturing the primary transformer current are identified in each pulse-width modulation (PWM) half-period based on the voltage waveform generated by the converter, specifically at zero-voltage points within the voltage waveform. In the sampling step, the primary transformer current corresponding to the sampling center positions from the identification step is sampled.

[0016] During this sampling step, at least one first sample value corresponding to the first sampling center position and one second sample value corresponding to the second sampling center position are taken.

[0017] In the correction step, the primary transformer current values ​​corresponding to the same PWM half-period as in the determination step are used to correct the calculated estimate of the primary transformer current from the determination step. In other words, the estimate of the primary transformer current in the determination step is corrected based on the current values ​​acquired during the sampling step, where these current values ​​themselves correspond to the sampling center positions identified during the identification step. The corrected current estimate thus obtained is then used in the estimation step to determine the rotor current.

[0018] Once all steps of the current estimation method are completed, the current value for the rotor is known, and this value can be used to control the torque delivered to the wheels of the electric or hybrid vehicle. Unlike other methods that use a primary transformer current, where parasitic elements can cause detrimental vibrational behavior, the present method is accurate under both steady-state and dynamic conditions.

[0019] According to an optional feature of the invention, during the determination step two successive primary transformer current values ​​are taken, each corresponding to a positive voltage pulse and a negative voltage pulse in the voltage waveform, and the correction step comprises a substep in which corrected successive current values ​​are calculated based on the current values ​​taken during the sampling step, and an additional averaging step in which the absolute values ​​of the corrected current values ​​are averaged.

[0020] The correction of the previously calculated current estimate is thus based either directly on the current values ​​corresponding to the sampling center positions at zero voltage, or it is based on a further calculation based on successive current values ​​corresponding to positive and negative pulses. During this further calculation, the current values ​​corresponding to the sampling center positions at zero voltage are used to determine the successive current values. According to an optional feature of the invention, the current values ​​taken during the sampling step correspond to a single value.

[0021] According to an optional feature of the invention, the current values ​​taken during the sampling step correspond to several values.

[0022] Using a single current value can be considered a single-shot sampling method, while using multiple values ​​can be considered an oversampling method. Single-shot sampling is easier to implement, while oversampling improves both accuracy and signal quality.

[0023] According to an optional feature of the invention, during the identification step the first scanning mean position is identified before a given positive or negative pulse and the second scanning mean position is identified after the given pulse.

[0024] In other words, the sampling center positions are chosen so that they surround a specific pulse of the voltage waveform.

[0025] According to an optional feature of the invention, the first scanning center position and the second scanning center position are identified at the beginning and at the end of the PWM half-period.

[0026] Such a selection of the sampling center positions at the beginning and end of the PWM half-period is performed in the case of a centrally aligned pulse generation. Alternatively, the sampling center positions can be shifted from the beginning and end of a given PWM half-period, as long as there is a difference of one PWM half-period between the first and second sampling center positions and both are identified in a zero-voltage phase.

[0027] According to an optional feature of the invention, during the determination step the current estimate, which corresponds to the PWM half-period, is calculated from an input power of the converter, the duty cycle and an input voltage of the converter.

[0028] The input power can be calculated from sensor values, for example the converter input current and the converter input voltage.

[0029] According to an optional feature of the invention, the input power of the converter is obtained from at least one input current of the converter, wherein an average value of the input current of a PWM half-period corresponds to the duty cycle of this PWM half-period.

[0030] According to an optional feature of the invention, the transformer transformation ratio is a relationship between the inductance and mutual inductance of the transformer.

[0031] Furthermore, it is possible to use a variable corresponding to an efficiency parameter, implemented, for example, through a lookup table depending on the relevant quantities. Adding such a variable improves the accuracy of the current estimation method. Alternatively, the transformer ratio is an effective transformation ratio. Such an effective transformation ratio is required when the inductance values ​​are not constant but current-dependent, for example, due to magnetic saturation.

[0032] According to an optional feature of the invention, the rotor current estimation method is combined with a machine model by embedding the machine model in an observer structure.

[0033] Combining the current estimation method with a machine model improves the accuracy of the rotor current estimation, especially under dynamic conditions. For example, the machine model can help reduce the deviations commonly encountered under dynamic conditions. The machine model can be driven by an output voltage estimation of the inductive power transfer system and by a stator shaft current derivation. The output voltage estimation of the inductive power transfer system corresponds to the voltage supplied to the rotor winding of the electric machine. The stator D-shaft current derivation can be used to further improve the estimation under dynamic conditions.

[0034] The observer structure is, for example, a Luenberger observer, an extended Luenberger observer, or a Kalman filter.

[0035] According to an optional feature of the invention, a correction value for the observer structure is calculated from an observer error signal based on the rotor current estimate from the estimation step.

[0036] In other words, the observer error signal can be calculated based on the results of the estimation step. Other rotor current calculation methods could also be used to calculate the observer error signal. If the observer error signal is calculated using a combination of several methods or implementations, weighting factors can be applied.

[0037] According to an optional feature of the invention, the correction value is set to zero if the observer error signal is unreliable.

[0038] For example, a duty cycle close to zero would make the observer error signal unreliable, as it would then be impossible to measure a primary transformer current that actually corresponds to the rotor current.

[0039] Further features, details and advantages of the invention will become clearer by reading the following description on the one hand and by several exemplary embodiments, which are given as an indication and without limitation, with reference to the accompanying schematic drawings on the other hand, the drawings showing: [ Fig. 1] is a schematic representation of an electric machine for an electric or hybrid vehicle, wherein the electric machine comprises a rotor, a stator and a transmitter which includes a rectifier and a transformer; [ Fig. 2] is another schematic representation of a part of the electrical machine made of Fig. 1, which further includes a converter; [ Fig. Figure 3] is a schematic representation of a first embodiment of a current estimation method, wherein such a method is used to determine a current value for the rotor of Fig. 1 to determine; [ Fig. Figure 4] is a schematic representation of a second embodiment of the current estimation method, which is used to determine the current value for the rotor of Fig. 1 is used; [ Fig. Figure 5] is a schematic representation of a third embodiment of the current estimation method, which is used to determine the current value for the rotor of Fig. 1 is used; [ Fig. Figure 6] is a schematic representation of a current estimation method according to the invention, wherein such a method is used to determine the current value for the rotor of Fig. 1 to determine; [ Fig. Figure 7] is a schematic representation of a combination of the current estimation method of Fig. 3 to 5 and the current estimation method according to the invention of Fig. 6 with a machine model.

[0040] The features, variants, and different ways of implementing the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention are conceivable that include only a selection of the features described below from the other described features, if this selection of features is sufficient to achieve a technical advantage and / or to differentiate the invention from the prior art.

[0041] In the drawings, identical numbers refer to identical elements.

[0042] Fig. 1 and Fig. Figure 2 shows schematic representations of an electric machine 1 or a part of the electric machine 1. The electric machine 1 is intended for installation in a vehicle, for example an electric or hybrid vehicle, where it can be used to provide torque to the vehicle's wheels. Here, the electric machine 1 is an inductively excited synchronous machine, also known by its abbreviation iEESM.

[0043] As in Fig. As can be seen in Figure 1, the electric machine 1 comprises a rotor 2 and a stator 4. In this example, the stator 4 is positioned around the rotor 2; however, in other embodiments, the rotor 2 could be positioned around the stator 4. In inductively excited synchronous machines like this electric machine 1, the power is transferred to a winding attached to the rotor 2 by means of a transformer 6. More precisely, the transformer 6 is a rotating high-frequency transformer. The transformer 6 comprises a primary side 8 and a secondary side 10, these two sides 8 and 10 differing in that the primary side 8 is located on a non-rotating part of the electric machine 1, i.e., the stator, while the secondary side 10 is located on a rotating part of the electric machine 1, i.e., the rotor. Fig. 1 is a separation between the non-rotating part and the rotating part, represented as a dashed line.

[0044] A rectifier 12 is associated with the transformer 6. The rectifier 12 is a rotating rectifier and, as such, is located on the secondary side 10 of the transformer 6, i.e., on the rotating part of the electric machine 1. The function of the rectifier 12 is to supply only positive voltage to the rotor 2. This rectifier 12 is implemented together with the transformer 6 in a transformer 14, in this case an inductive transformer.

[0045] As in Fig. As can be seen in Figure 2, a converter 16 is connected to the primary side 8 of the transformer 6. The converter 16 is a phase-shift full-bridge converter, or PSFBC. It operates with a variable pulse-width modulation frequency, or PWM frequency. The PWM frequency of the converter 16 can, in fact, vary over a wide range, for example from 5 to 100 kHz, depending on the design of the converter 16, the transformer 6, and the current required in the rotor 2.

[0046] The converter 16 includes an input capacitor 17. The converter 16 is controlled by an electronic control unit of the electric machine, such as a microcontroller, a field-programmable gate array (FPGA), or a digital signal processor (DSP), to convert direct current supplied by a vehicle battery into alternating current and thus apply a corresponding voltage to the primary side 8 of the transformer 6. As shown here, the converter 16 includes four transistors 18, with two upper transistors 18A and two lower transistors 18B. Each upper transistor 18A is associated with a lower transistor 18B, forming a respective half-bridge or phase branch. The upper 18A and the lower transistor 18B of each half-bridge are driven inversely. To prevent a short circuit at the converter input, an additional latching time is introduced in the command between the upper 18A and the lower 18B transistor of each phase branch.This additional locking time results in a delayed turn-on command for the upper transistor 18A or the lower transistor 18B of a half-bridge compared to the turn-off command for the upper transistor 18A or the lower transistor 18B of a half-bridge.

[0047] The converter 16 is operated by phase shifts, with each phase shift ranging from 0 to 180°. Additionally, each phase shift of the converter 16 is assigned a duty cycle, which ranges from 0 to 1. For example, a phase shift of 0° corresponds to a duty cycle of 0, a phase shift of 90° to a duty cycle of 0.5, and a phase shift of 180° to a duty cycle of 1.

[0048] The converter 16 generates a voltage waveform 20; this waveform 20 is in Fig. 3 to 5 visible. The voltage waveform 20 can be subdivided into a plurality of PWM periods 22, wherein in the waveform 20, for each PWM period 22, both a positive pulse 24 and a negative pulse 26 occur. With a duty cycle of 1, positive or negative voltages are applied successively during all given PWM periods, without zero voltage values, with each positive or negative voltage being applied for half the PWM period. Whereas with a duty cycle of, for example, 0.5, positive and negative voltages are applied for a shorter duration during the given PWM period, with zero voltage values ​​in between, with each positive or negative voltage being applied for half the time as is the case with a duty cycle of 1.

[0049] As mentioned previously, the electric machine 1 can be used to supply torque to the wheels of the hybrid or electric vehicle. To control the torque and, more generally, to ensure efficient operation of the electric machine 1, it is necessary to accurately determine the current of the rotor 4.

[0050] For this purpose, a rotor current estimation method can be used. A first current estimation method, comprising several embodiments, is now described with respect to Fig. 3 to 5 described. In Fig. 3, Fig. 4 and Fig. Figures 5, corresponding to a first, second, and third embodiment of the first current estimation method, show various waveforms. These waveforms correspond, from top to bottom, to the voltage waveform 20 generated by the converter 16, a corresponding primary transformer current waveform 28 generated in the transformer 6, and a corresponding rotor current waveform 30 generated in the rotor 4. "Corresponding" here means that the voltage waveform 20, the primary transformer current waveform 28, and the rotor current waveform 30 are observed in the same PWM period.

[0051] The first embodiment of the first current estimation method, which is also referred to below as method A, is described in Fig. Figure 3 illustrates this. In this first embodiment, i.e., in Method A, the current estimation method comprises an identification step 32 in which, for a given PWM period 22, sampling center positions for the primary transformer current are identified in the voltage waveform 20 such that they correspond to both the center of a positive pulse and the center of a negative pulse. In other words, a first sampling center position is identified at position 34, which is located in the center of a positive voltage pulse, and a second sampling center position is identified at position 36, which is located in the center of the following negative voltage pulse.

[0052] The first embodiment then comprises a sampling step 38 in which the primary transformer 6 is sampled in the primary transformer current waveform 28; such current values ​​are obtained from the first position S1. The sampling is performed with respect to the two sampling center positions 34 and 36, which are obtained in the identification step 32. In sampling step 38, the absolute value of the current value 40 is obtained, which corresponds to the first sampling center position 34 in the voltage waveform 20. This value corresponds to the average value of the primary transformer current within the positive voltage pulse 24. Similarly, within the negative voltage pulse 26, the absolute value of the current value 42 is taken corresponding to the sampling center position 36.

[0053] Once the absolute values ​​corresponding to the samples have been determined, the current estimation procedure for Method A includes an averaging step 37 in which the absolute value of the current value 40, corresponding to the positive voltage pulse 24, and the absolute value of the current value 42, corresponding to the negative voltage pulse 26, are averaged together. In other words, a first value 40, corresponding to the first sampling center position 34, is taken from the primary transformer current waveform 28, a second value 42, corresponding to the second sampling center position 36, is taken from the primary transformer current waveform 28, and then the absolute values ​​of the first value 40 and the second value 42 are added and divided by two to obtain an averaged absolute current value. The primary transformer current measurement that yields the values ​​40 and 42 is, for example, performed at the first location S1.It should be noted that such values ​​40, 42 can be acquired either by single-shot sampling, i.e., by sampling a single value, or by oversampling, i.e., by sampling a multitude of values ​​within the same pulse. More precisely, in the case of oversampling, the samples are taken such that their midpoint corresponds to the sampling center position 34 in the case of a positive voltage pulse 24, or to the sampling center position 36 in the case of a negative voltage pulse 26. The sampled values ​​obtained in the case of fast oversampling all lie within the positive or negative voltage pulse 24, 26. The specified PWM period 22 thus corresponds to one evaluation period.

[0054] After averaging step 37, method A includes an estimation step 44. In this estimation step 44, the averaged current value obtained in averaging step 38 is used to determine a corresponding value of the rotor current in the rotor current waveform 30. For this estimation step 44, a transformer transformation ratio is taken into account, which corresponds to a relationship between the inductance of transformer 6 and its mutual inductance. The value of the rotor current can then be estimated using the following formula: iF≈L11M12i1,avg, where: “i F “the rotor current value to be estimated; “L 11 “the inductance of transformer 6 is; "M 12 “the mutual inductance of transformer 6 is; and “i 1,avg “The averaged current value is obtained during averaging step 38.

[0055] Alternatively, the value of the rotor current can also be estimated using the following formula: i F ≈ xí 1,avg where x is an effective turns ratio that can be used instead of the transformer turns ratio when the inductance values ​​are current-dependent and not constant.

[0056] The rotor current estimate is marked as a star on rotor current waveform 30. As in Fig. As can be seen in Figure 3, the rotor current value obtained using the formula mentioned above is valid at a point corresponding to the midpoint between the first value 40 and the second value 42 in the primary transformer waveform 28. This also means it is valid at a point corresponding to the midpoint between the first sample value 36 and the second sample value 38 in the voltage waveform 20. Therefore, for every combination of a first value 40 and a second value 42, there is a valid rotor current value; that is, for every combination of a positive and a negative pulse, there is a valid rotor current value. There is one valid current value per PWM period 22.

[0057] The second embodiment of the first current estimation method, which is also referred to below as method B, is described in Fig. Figure 4 shows that it includes an identification step 32, a sampling step 38, a correction step 39, and an estimation step 44.

[0058] Identification step 32 is similar to the identification step of Method A, in which, for given PWM half-periods 23 and 25, sampling locations for the primary transformer current in the voltage waveform 20 are identified such that they correspond to both the center of a positive pulse 24 and the center of a negative pulse 26. In other words, a first sampling center position for a first PWM half-period 23 is identified at position 34, which is located in the center of a positive voltage pulse 24, and a second sampling center position for a second PWM half-period 25 is identified at position 36, which is located in the center of the following negative voltage pulse 26. Method B includes an additional identification step 46 in which two surrounding additional sampling center positions are identified in the zero-voltage phase before and after the corresponding active pulses 24 and 26.In the case of a positive voltage pulse 24, the additional scanning center positions 48 and 50 are identified. In the case of a negative voltage pulse 26, the additional scanning center positions 50 and 51 are identified.

[0059] Method B also includes a sampling step 38 and an additional sampling step 47, in which the sampling is performed within the primary transformer current waveform 28; such current values ​​are obtained from the first position S1. Similar to Method A, the sampling in sampling step 38 is performed more specifically with respect to the sampling center positions identified in identification step 32. In the case of the positive voltage pulse 24, the sample value 40 is obtained corresponding to the sampling center position 34 from the identification step. In the case of the negative voltage pulse 26, the sample value 42 is obtained corresponding to the sampling center position 36 from the identification step. The additional sampling step 47 performs samples corresponding to the additional sampling center positions identified in the additional identification step 46.In the case of a positive voltage pulse 24, samples 52 and 54 are taken in the primary transformer current, corresponding to the additional sampling center positions 48 and 50 from the additional identification step 46. In the case of a negative voltage pulse 26, samples 54 and 55 are taken in the primary transformer current, corresponding to the additional sampling center positions 50 and 51 from the additional identification step 46.

[0060] Unlike sample 34, which is located in the middle of the positive voltage pulse 24, and sample 36, which is located in the middle of the negative voltage pulse 26, the further samples 48 and 50 for a positive voltage pulse 24 and the further samples 50 and 51 for a negative voltage pulse 26 do not occur within an active pulse, but rather in the zero-voltage state, i.e., between two pulses. For example, the first additional sample 52 is taken before a specific positive pulse and the second additional sample 54 is taken after this positive pulse, or conversely, the first additional sample 54 is taken before a specific negative pulse and the second additional sample 55 is taken after the negative pulse.The two consecutive additional samples 52, 54 of the primary transformer current in the case of the first PWM half-period interval 23 or the two additional samples 54, 55 of the primary transformer current in the case of the second PWM half-period interval 25 are taken, for example, but not necessarily, at the beginning and at the end of a given PWM half-period.

[0061] During correction step 39, the current values ​​obtained during sampling step 38 and the additional sampling step 47 are processed. In the case of the first evaluation period 23, a correction value for the positive pulse is calculated from the average of the primary transformer current samples from locations 52 and 54. The correction value for the positive pulse obtained from samples 52 and 54 is then subtracted from sample 40 of the primary transformer current, resulting in a corrected value of the primary transformer current for the positive pulse, corresponding to the sampling center position 34. In the case of the second evaluation period 25, a correction value for the negative pulse is calculated from the average of the primary transformer current samples from locations 54 and 55.The correction value is then subtracted from the sampled value 42 of the primary transformer current, resulting in a corrected value of the primary transformer current for the negative pulse, corresponding to the sampling center position 36. Thus, a corrected transformer primary current value is obtained for each PWM half-period. The acquisition period in this case is therefore the PWM half-period.

[0062] Interestingly, the current values ​​40, 42 and the additional current values ​​52, 54, 55 of method B can be recorded similarly to method A using the single-shot sampling technique or the oversampling technique.

[0063] In estimation step 44, the rotor current is estimated using the result of subtracting the correction value from the corresponding current value. This estimate is determined using the following formula: iF≈L11M12i1,corr, where: “i F“the rotor current value to be estimated; “L n “the inductance of transformer 6 is; "M 12 “the mutual inductance of transformer 6 is; and “i 1,corr “The corrected current value is obtained during averaging step 38.

[0064] Alternatively, the value of the rotor current can also be estimated using the following formula: i F ≈ xi 1,corr , where x is an effective turns ratio that can be used instead of the transformer turns ratio when the inductance values ​​are current-dependent and not constant.

[0065] As in Fig. As shown in Figure 4, the rotor current value marked as a star is valid at a point on the rotor current waveform 30 that corresponds to each first value 40 and each second value 42 of the primary transformer current waveform 28. As a result, there is a valid rotor current value for each value 40, 42 taken from an active pulse. There are two valid current values ​​per PWM period 22.

[0066] In comparison to the first embodiment, method B offers a more accurate rotor current estimation with less delay under dynamic conditions.

[0067] The third embodiment of the first current estimation method, which combines elements from methods A and B, is hereinafter also referred to as method A+B. Method A+B is described in Fig. 5 shown.

[0068] In methods A+B, identification step 32 is performed as previously described, whereby the first scanning center position 34 and the second scanning center position 36 are identified based on the voltage waveform 20, more precisely based on one of their positive pulses and one of their negative pulses in the same PWM period. The third embodiment, method B, includes the additional identification step 46. In this additional identification step 46, the scanning center positions 48, 50, and 51 are identified for sampling in the zero-voltage phases, each around the first voltage pulse 24 and the second voltage pulse 26.In other words, a first additional sampling center position 48 is identified at zero voltage before the positive pulse 24, a second additional sampling center position 50 is identified at zero voltage after the positive pulse, and a third additional sampling center position 51 is identified at zero voltage after the negative pulse.

[0069] Once both identification step 32 and additional identification step 46 are completed, the third embodiment comprises a sampling step 38 and an additional sampling step 47, similar to those of Method B. Several current values ​​are extracted from the primary transformer current waveform 28, namely the first value 40, corresponding to the sampling center position 34; the second current value 42, corresponding to the second sampling center position 36; and a first additional current value 52 for the first additional sampling center position 48, a second additional current value 54 for the second sampling center position 50, and a third additional current value 55 for the third sampling center position 51. Similar to correction step 39 of Method B, the first additional current value 52 and the second additional current value 54, corresponding to each additional sampling center position 48 and 50, are averaged to obtain the first correction value.Furthermore, the second additional current value 54 and the second additional current value 55, corresponding to each additional sampling center position 50, 51, are averaged to obtain the second correction value. Subsequently, the first and second correction values ​​are subtracted from the corresponding current value 40, 42. As a result, a first corrected current value is obtained for the first current value 40, and a second corrected current value is obtained for the second current value 42.

[0070] Finally, an averaging step 37 is performed similarly to procedure A using the first and second corrected current values. The difference from procedure A is that the current values ​​40 and 42 are not used for the averaging step, but rather corrected values ​​corresponding to the same sampling center positions 34 and 36, namely the first and second corrected current values ​​obtained from the previous correction step. The first corrected value and the second corrected value are then averaged. Such an averaging is similar to the averaging step 37 performed in procedure A.

[0071] The average corrected value of methods A+B is then used in estimation step 44, which uses the following formula to determine the rotor current: iF≈L11M12i1,avgcorr, where: “i F “the rotor current value to be estimated; “L n“the inductance of transformer 6 is; "M 12 “the mutual inductance of transformer 6 is; and “i 1,avgcorr “The averaged corrected current value is obtained during averaging step 38.

[0072] Alternatively, the value of the rotor current can also be estimated using the following formula: i F ≈ xi 1,avgcorr , where x is an effective turns ratio that can be used instead of the transformer turns ratio when the inductance values ​​are current-dependent and not constant.

[0073] As in Fig. As can be seen in Figure 5, the rotor current value marked as a star in the rotor current waveform 30 is valid at a point corresponding to the midpoint between the first current value 40 and the second current value 42 in the primary transformer current waveform 28; in other words, it is valid at a point corresponding to the midpoint between the first sampling center position 36 and the second sampling center position 38 in the voltage waveform 20. Thus, in methods A+B, there is a valid rotor current value for every combination of a first current value 40 and a second current value 42, i.e., a valid rotor current value for every combination of a positive and a negative pulse. There is one valid current value per PWM period 22.

[0074] Compared to the first and second embodiments, method A+B offers an accurate rotor current estimation, even under dynamic conditions. The delay characteristics are the same as in method A.

[0075] It should be noted that while each of the first, second, and third embodiments has been described with respect to a acquisition period corresponding to either a given PWM period or a given PWM half-period, sampling step 32 could alternatively be performed in an acquisition period encompassing multiple PWM periods or multiple PWM half-periods. In this case, it is not necessary for sampling step 32 to be performed in every PWM period or in every PWM half-period. However, the samples from these longer acquisition periods would need to be averaged, for example, using a weighted averaging method.

[0076] While methods A, B and A+B are embodiments of the current estimation method according to the invention, in which the rotor current is estimated based on the waveform 28 of the primary transformer current, other current estimation methods can also be used to determine the rotor current.

[0077] A second current estimation method, this time a current estimation method according to the invention, is now used in relation to Fig. 6 described. The current estimation method according to the invention is hereinafter also referred to as method C.

[0078] The current estimation method according to the invention begins with a determination step 131. In this determination step 131, an estimate of the primary transformer current in a given PWM half-period is calculated.

[0079] For example, in the case of a positive voltage pulse half-period 23, a first position P1 in the waveform 28 of the primary transformer current can be estimated, or in the case of a negative voltage pulse half-period 25, a second position P2 can be estimated in this waveform 28. It should be noted that directly measuring the primary transformer current from the first position S1, as is the case in the previous methods A, B, and A+B, requires very precise timing and a very small variation in the sensor delay, whereas estimating a corresponding value, as in method C with the first position P1 for a positive voltage pulse or the second position P2 for a negative voltage pulse, is more robust with respect to timing errors.

[0080] The following formula is used to calculate the primary transformer current: i1pwrbalance=± η Pin,halfperiod,avg / dutyhalfperiod / UDC, where: “i 1pwrbalance “the estimated value of the primary transformer current is; “+-” corresponds to the sign of the expected transformer primary current, where + stands for positive voltage pulses and - for negative voltage pulses; “η” is an efficiency parameter used to account for the power losses occurring in the power converter 16; in general, this parameter is expected to depend on the operating point and can therefore be represented by a lookup table; "P in,halfperiod,avg “an average value of the input power of converter 16 in the evaluated half-period; "duty halfperiod “corresponds to the duty cycle that corresponds to the half-period to be evaluated; and “U DC “The input voltage of converter 16 is.”

[0081] It should be noted that “P in,halfperiod,avg “ can also be expressed as follows: Pin,halfperiod,avg=UDC,avg,halfperiodIDC,avg,halfperiod, where: “U DC,avg,halfperiod “corresponds to the input voltage in the evaluated PWM half-period, which can be measured at the input capacitor 17, and “I DC,avg,halfperiod “corresponds to the input current in the evaluated PWM half-period, which is connected to a in Fig. The second digit S2 shown in Figure 2 can be measured, with such a second digit S2 being located on the input side of the converter 16.

[0082] The input current is defined as follows: IDC,avg,halfperiod=∫tstarttStart+TPWM / 2iDC(τ)dτ

[0083] To implement such an integral, either fast oversampling using a delta-sigma analog-to-digital converter (DSADC) or fast acquisition and accumulation using a successive approximation register analog-to-digital converter (SAR-ADC) can be used. It is important to note that the acquisition rate must be as fast as possible to obtain a representative value of the DC input current over a PWM half-cycle corresponding to the sampling interval. Furthermore, it is necessary to synchronize the acquisition with the PWM generation to obtain the average DC current value corresponding to the duty cycle realized in a given PWM half-cycle.

[0084] Once the estimated primary transformer current has been determined, it must be corrected. For this purpose, an identification step 132 is performed. In this identification step 132, the sampling center positions during the zero-voltage phase in the voltage waveform 20 are identified. More precisely, a first sampling center position 134 and a second sampling center position 136 are identified, both at zero voltage. The first sampling center position 134 and the second sampling center position 136 are identified within a PWM / 2 interval. For example, the first sampling center position 134 is identified at the beginning of a given PWM half-period 23, and the second sampling center position 136 is identified at the end of the PWM half-period 23.

[0085] As in Fig. As can be seen in Figure 6, the first sampling center position 134 and the second sampling center position 136 are identified such that they surround voltage pulses, for example before a given positive pulse 124 and after this positive pulse 124 or alternatively before a given negative pulse 126 and after the negative pulse 126 in the case of the PWM half-period 25.

[0086] Following identification step 132, the current estimation method according to the invention comprises a sampling step 133. During sampling step 133, current values ​​corresponding to the sampling center positions 134 and 136 are captured in the primary current waveform 28, so that a first current value 140, corresponding to the first sampling center position 134, and a second current value 142, corresponding to the second sampling center position 136, are extracted. The primary current sampling values ​​of the transformer from the sampling step are then averaged in correction step 139. More precisely, the first current value 140 and the second current value 142 from sampling step 133 are averaged to obtain a correction value. The correction value is then subtracted from the estimate of the primary transformer current calculated during the previously performed determination step 131. The result is a corrected current estimate “i 1,pwrbalancecorr“ obtained. This corrected current estimate corresponds to either a positive or a negative voltage pulse.

[0087] According to the embodiment, the first current value 140 and the second current value 142 can be detected either by a single-shot sampling method or by an oversampling method; in other words, each of the first value 140 and the second value 142 corresponds to either a single value or multiple values.

[0088] Procedure C concludes with an estimation step 144, in which the rotor current is estimated based on the corrected current estimate from calculation step 133, the duty cycle, and a transformer transformation ratio, here a relationship between the inductance of transformer 6 and its mutual inductance. Consequently, the rotor current can be estimated using the following formula: iF≈L11M12i1,pwrbalancecorr, where: “i F“the rotor current value to be estimated; “L n “the inductance of transformer 6 is; "M 12 “the mutual inductance of transformer 6 is; and “i 1,pwrbalancecorr “The average corrected current value is the one obtained during calculation step 33.

[0089] Alternatively, the value of the rotor current can also be estimated using the following formula: i F ≈ x i,pwrbalancecorr , where x is an effective turns ratio that can be used instead of the transformer turns ratio when the inductance values ​​are current-dependent and not constant.

[0090] The rotor current value is shown as a star on rotor current curve 30. Fig. 6 is marked. This rotor current value is valid at a point on the rotor current waveform 30 that corresponds to the first position P1, and at a point that corresponds to the second position P2 in the primary transformer current waveform 28. This means that for each active pulse of the primary transformer current waveform 28, there is a valid rotor current value. There are two valid current values ​​per PWM period 22. Accordingly, there is one valid rotor current value per PWM half-period 23, 25.

[0091] An alternative to Method C can be implemented within the context of the invention. Method C was described above primarily with a determination step 131, in which a current estimate is calculated from a power balance for a given PWM half-period; an identification step 132, in which the sampling center positions 134, 136 for the additional primary transformer current samples are identified; a sampling step 133, in which the primary transformer current is sampled during zero-voltage phases; and a correction step 139 with current values ​​140, 142 resulting from the sampling step 133 with samples taken during the zero-voltage phase. In the same way as the averaging step 37 in Methods A and A+B described above, an averaging step 137 can be implemented, in which the current values ​​sampled during positive and negative pulses are taken into account.More precisely, during determination step 131, it is possible to use two consecutive samples of the rotor current estimate, each corresponding to a positive voltage pulse 24 and a negative voltage pulse 26. Subsequently, correction step 139 is applied, taking into account the current values ​​140 and 142 resulting from sampling step 133 to correct the two consecutive samples of the rotor current estimate. This yields the corrected current values ​​P1 and P2. Similar to averaging step 37 in methods A and A+B, averaging step 137 in method C calculates the mean of the absolute value of the corrected current value P1, corresponding to the first PWM half-period 23, and the absolute value of the corrected current value P2, corresponding to the second PWM half-period 25.Furthermore, it is also possible to use more than two consecutive PWM half-periods and weighted averages of these consecutive PWM half-periods to obtain an improved rotor current estimate.

[0092] The rotor current estimation method, be it Method A, Method B, Method A+B or Method C, can be combined with a machine model 56 to improve the accuracy of the rotor current estimation, as in Fig. Figure 7 shows the machine model 56 assigned to the electric machine 1, which corresponds to the following formula: uf=Rfif+Lffdifdt+32Mdfdiddt+32Mqfdiqdt, where: "u f “the voltage supplied to the rotor; “R f “ is a rotor resistance parameter that is temperature-dependent; “i f “the rotor current to be estimated is; “L ff“ is a rotor self-inductance parameter that depends on the rotor current, rotor position, stator D current and stator Q current; “i d “, „i f “Stator D current and stator Q current are; "M df “a parameter of the coupling inductance between the stator D-axis and the rotor winding, which depends on the rotor current, the rotor position, the stator D-current and the stator Q-current; and "M qf “ is a coupling inductance parameter between the stator Q-axis and the rotor winding, which depends on the rotor current, the rotor position, the stator D-current and the stator Q-current.

[0093] Fig. Figure 7 represents an observer structure 58 that uses the machine model 56 and possibly one or more of the above-mentioned current estimation methods, i.e., method A, method B, method A+B, or method C. This observer structure 58 is formed, for example, from a Luenberger observer such as the one described in Figure 7. Fig. 7, an extended Luenberger observer or a Kalman filter selected.

[0094] As in Fig. As can be seen in section 7, the derivation of the stator d-current is shown. diddt the voltage supplied to the rotor u F and the derivation of the stator Q current diqdt entered into machine model 56. The derivative of the stator D-current 7 is assigned to the coupling inductance of the stator D-axis to the rotor winding and the rotor self-inductance parameters, the voltage supplied to the rotor u. F is also associated with the rotor self-inductance, and the change in stator Q current diqdt is assigned to the coupling inductance of the stator q-axis to the rotor winding and the rotor self-inductance parameters to correspond to a differential equation 60 as follows: difdt=1Lff(uf−Rfif−32Mdfdiddt−32Mqfdiqdt)

[0095] Such a differential equation is implemented in an integrator 62 of the machine model 56, where it is integrated to provide the rotor current.

[0096] The machine model can be used for open-loop estimation by providing the necessary inputs u f , diddtunddiqdt The current values ​​can be entered. These can be obtained from sensor readings or by prediction. Furthermore, the actual rotor winding temperature, stator D current, stator Q current, and actual rotor current estimate must be used for parameter adjustment.

[0097] To improve the efficiency of machine model 56, it is combined, where possible, with at least one of the previously described current estimation methods or any other current estimation method. More precisely, one or more of methods A, B, A+B, C, or another current estimation method is used if it is reliable enough to correct the rotor current provided by the integrator 62.

[0098] In the embodiment of Fig.7 Both methods A+B and method C can be used to provide a rotor current estimate to a correction signal consolidation system 64. It should be noted that while only methods A+B and method C are used here, other embodiments may additionally or alternatively use method A, method B, or any other current estimation method. Here, the correction signal consolidation system 64 receives the rotor current estimate from method A+B and that from method C and, depending on reliability, can use either both, only one, or neither.

[0099] If both the rotor current estimate from methods A+B and the rotor current estimate from method C are unreliable, for example due to a duty cycle near zero or in the case of a pulse-off state of the converter 16, the current estimates are canceled by sending a corresponding negative value of the rotor current estimate to the correction signal consolidation system 64. For this purpose, the observer structure 58 includes a cancellation mechanism 66 to send the corresponding negative value back to the correction signal consolidation system 64. The compensation mechanism 66 is part of an observer correction mechanism 68. If both rotor current estimates are unreliable, a correction value 70 obtained by the observer correction mechanism 68 is thus set to zero.

[0100] If only one of the rotor current estimates from methods A+B and the rotor current estimate from method C is reliable, the correction signal consolidation system 64 isolates them and sends them to the observer correction mechanism 68.

[0101] If both the rotor current estimate from methods A+B and the rotor current estimate from method C are reliable, the correction signal consolidation system 64 can select only one of them to send to the observer correction mechanism 68, or alternatively, use both. If both estimates are used, the correction signal consolidation system 64 can perform a weighted average calculation. Furthermore, smooth blending can be implemented to ensure a seamless transition between the different current estimation methods.

[0102] In the observer correction mechanism 68, the reliable current estimate or the weighted reliable current estimates corresponding to an observer error signal are multiplied by an observer gain 72. Such an observer gain 72 can depend on the stator D current, the stator Q current, the estimated rotor current, the rotor position, and the rotor winding temperature. As a result of the multiplication by the observer gain 72, the observer correction mechanism 68 generates the correction value 70, which is then passed to equation 60 of the machine model 56 to correct it before it is integrated in the integrator 62.

[0103] If, as mentioned previously, no reliable rotor current estimate is sent to the correction signal consolidation system 64, the correction value 70 is set to zero. In this case, the machine model 56 can be used in an open-loop mode. Such an open-loop mode means that the observer structure 58 relies primarily on the change in the stator D current, the voltage supplied to the rotor 2, and the change in the stator Q current inputs to determine the rotor current.

[0104] The present invention thus comprises a current estimation method with which the output current at the rotating part of an electrical machine can be accurately estimated under both steady-state and dynamic conditions by sampling data from a non-rotating part of the electrical machine.

[0105] Many modifications and other embodiments of the invention presented herein will be obvious to a person skilled in the art who is familiar with the teachings presented in the preceding descriptions and the accompanying figures. It is therefore understood that the invention is not limited to the specific embodiments disclosed and that modifications and further embodiments are included within the scope of the appended claims. Although certain terms are used herein, they are used only in a general and descriptive sense, and not for the purpose of limitation.

Claims

[1] Method for estimating the rotor current for a rotating part of an electric machine (1) of an electric or hybrid vehicle, wherein the electric machine (1) comprises a converter (16) operated with phase shifts, wherein a duty cycle is associated with a phase shift, wherein the converter (16) supplies voltage to a transformer (6) of the electric machine (1), wherein such voltage is supplied to a primary side (8) of the transformer (6), wherein the converter (16) generates a voltage waveform (20) between the converter (16) and the transformer (6), wherein the current estimation method comprises: - a determination step (131) in which a current estimate is calculated in a PWM half-period, - an identification step (132) in which a first sampling center position (134) and a second sampling center position (136) are identified at zero voltage in a PWM / 2 interval in a corresponding PWM half-period of a voltage waveform (20) generated by the converter (16); - a sampling step (133) in which a first current value (140) and a second current value (142), corresponding respectively to the first sampling center position (134) and the second sampling center position (136), are recorded in a primary transformer current waveform (28); - a correction step (139) in which the current estimate calculated in the determination step (131) is corrected on the basis of the current values ​​(140, 142) recorded during the sampling step (133); and - an estimation step (144) in which a current value for the rotating part is estimated according to the corrected calculated current estimate from the correction step (139), taking into account a transformer transformation ratio in such a current value estimation. [2] A method for estimating rotor current according to the preceding claim, wherein during the determination step (131) two successive primary transformer current values ​​are taken, each corresponding to a positive voltage pulse (24) and a negative voltage pulse (26) in the voltage waveform (20), and wherein the correction step (139) comprises a substep in which corrected successive current values ​​(P1, P2) are calculated based on the current values ​​(140, 142) taken during the sampling step (133), and an additional averaging step (137) in which the absolute values ​​of the corrected current values ​​(P1, P2) are averaged. [3] Method for estimating rotor current according to the preceding claims, wherein the current value (140, 142) corresponds to a single value. [4] Method for estimating rotor current according to claim 1 and claim 2, wherein the current value (140, 142) corresponds to several values. [5] Method for rotor current estimation according to one of the preceding claims, wherein the first scanning center position (134) is identified before a given positive or negative pulse (124, 126) and the second scanning center position (136) is identified after the given pulse (124, 126). [6] Method for rotor current estimation according to one of the preceding claims, wherein the first scanning center position (134) and the second scanning center position (136) are identified at the beginning and at the end of the PWM half-period. [7] Method for rotor current estimation according to one of the preceding claims, wherein during the determination step (131) the current estimate corresponding to the PWM half-period is calculated from an input power of the converter (16), the duty cycle and an input voltage of the converter (16). [8] Method for estimating rotor current according to the preceding claim, wherein the input power of the converter (16) is obtained from at least one input current of the converter (16), wherein an average value of the input current of a PWM half-period corresponds to the duty cycle of this PWM half-period. [9] Method for estimating rotor current according to one of the preceding claims, wherein the transformer transformation ratio is a relationship between the inductance and mutual inductance of the transformer (6). [10] Method for rotor current estimation according to one of the preceding claims, which is combined with a machine model (56) by embedding the machine model (56) in an observer structure (58). [11] Method for rotor current estimation according to the preceding claim, wherein a correction value (70) for the observer structure (58) is calculated from an observer error signal based on the rotor current estimation from the estimation step (144). [12] Method for rotor current estimation according to the preceding claim, wherein the correction value (70) is set to zero if the observer error signal is unreliable.

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