Method for determining an electrical resistance value of at least one phase winding of an electric machine, device for driving an electric machine, and electric drive system

Abstract

The invention relates to a method for determining a resistance value of at least one phase winding of an electric machine, comprising impressing a first current into the electric machine and impressing at least one second current into the electric machine, wherein a current intensity of the first current differs from that of the at least one second current; determining a first current value (I1) and a first voltage value (U1) with respect to the first impressed current, and determining a second current value (I2) and a second voltage value (U2) with respect to the at least one second impressed current; and determining the resistance value of the at least one phase winding as a function of the first current value (I1), the first voltage value (U1), the second current value (I2) and the second voltage value (U2).

Description

[0001] Description

[0002] Method for determining an electrical resistance value of at least one phase winding of an electrical machine, device for controlling an electrical machine and electrical drive system

[0003] The present invention relates to a method for determining an electrical resistance value of at least one phase winding of an electrical machine, a computing unit and a computer program for carrying out the method, as well as a device for controlling an electrical machine and an electrical drive system.

[0004] Background of the invention

[0005] Precise knowledge of the electrical winding resistance of one or more phase or stator windings of an electrical machine is usually required during initialization of the electrical machine at zero rotor speed and zero torque in order to initialize a control system, system diagnostics, and a thermal model as quickly and accurately as possible. The resistance of each phase winding is temperature-dependent and changes depending on the temperature of the stator winding during initialization.

[0006] For example, a temperature sensor can be used to measure the stator temperature to determine the winding resistance. The current winding resistance can be calculated based on a temperature dependence between the resistance and the stator temperature, depending on the measured current stator temperature and a reference resistance at a specific temperature. Disclosure of the Invention

[0007] According to the invention, a method for determining an electrical resistance value of at least one phase winding of an electrical machine, a computing unit and a computer program for implementing the method, as well as a device for controlling an electrical machine and an electrical drive system with the features of the independent patent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0008] The present invention provides an improved possibility for determining the current phase resistance of phase or stator windings, in particular during initialization of the electrical machine, in particular when the electrical machine is at a standstill with a rotor speed of zero and a torque of zero, particularly expediently without using a temperature sensor.

[0009] Within the scope of the method, a first current and at least one second current, each with different current intensities, are injected into the electrical machine or the phase windings. In particular, the at least one second current is injected shortly after or immediately after the first current. For example, only a single second current can be injected shortly after or immediately after the first current. Furthermore, in particular, a plurality of second currents can also be injected consecutively, each shortly after or immediately after.

[0010] Conveniently, a constant current is applied as the first current and as the at least one second current. The first and at least one second current are advantageously applied by means of field-oriented (current) control, in particular using a rotor-related dq coordinate system.

[0011] A first current value and a first voltage value are determined with respect to the first impressed current. A second current value and a second voltage value are determined with respect to the at least one second impressed current. In particular, a corresponding current and voltage value are determined for each impressed second current. The respective first or second voltage value can each correspond in particular to a voltage value applied to the phase winding as a manipulated variable for current impression. The respective first or second current value can each correspond in particular to the current value through the phase winding that arises at the respective applied voltage value and at the current resistance value. Provision can be made to measure the first and / or second voltage value and / or the first and / or second current value.

[0012] The resistance value of the at least one phase winding is determined based on the first current value, the first voltage value, the second current value, and the second voltage value. For example, the resistance value of a single phase winding can be determined. Furthermore, the respective resistance value of multiple phase windings, in particular of all phase windings of the electric machine, can also be determined.

[0013] The current resistance value is conveniently determined mathematically by means of the electrical relationship between voltage, resistance and current from the first and second voltage values ​​applied to the phase winding during the two current injections and from the first and second current values ​​established by the phase winding.

[0014] Within the scope of the present invention, a two- or multi-stage current injection and a resistance determination are carried out depending on the voltage values ​​and the current values ​​of these stages. In this way, a precise, as error-free as possible estimation of the current resistance value can be made possible across the entire temperature range, without the use of a temperature sensor and without knowledge of the current stator temperature. According to one embodiment, the resistance value is determined depending on a difference between the second voltage value U2 and the first voltage value Ui, as well as depending on a difference between the second current value I2 and the first current value h. In particular, the resistance value is determined as a quotient of the difference between the voltage value U2 and the first voltage value Ui divided by the difference between the second current value I2 and the first current value h, in particular according to the following equation:

[0015] By determining the resistance using the differences between the voltage values ​​and the current values ​​of the respective current injection stages, the linear offset error of the voltage can be determined and voltage errors can be reduced or minimized.

[0016] The two- or multi-stage current injection enables a determination of the resistance value that is particularly robust against errors compared to a single or single-stage current injection. In the course of such a single or single-stage current injection, for example, a single current injection can be performed along the d-axis, and the winding resistance can be determined, for example, from the corresponding manipulated variable or the corresponding voltage value Ud and from the corresponding current value Id according to equation (2). The current value Id can be calculated, for example, from measured phase currents and a rotor position or a rotor angle.

[0017] However, when determining resistance using single-stage current injection, an estimation error for the winding resistance can occur due to an operating point-dependent or temperature-dependent voltage error and an angle measurement error. Such an angle error can also distort the voltage and current vectors in the field-oriented control, leading to an undesirable component in the q-axis, and thus to unexpected torque and rotor movement.

[0018] The proposed resistance determination using two- or multi-stage current injection allows such errors to be avoided or eliminated. The present method particularly expediently enables resistance determination that is robust against voltage, current, and rotor angle errors. A linear voltage offset error can be determined or eliminated particularly effectively within the scope of the method. Furthermore, a voltage error and susceptibility to angle errors can be reduced or minimized. Furthermore, an undesirable parasitic torque and the resulting rotor movement during current injection can be reduced or minimized.

[0019] A voltage error can be assumed, in particular, in the form of an offset or voltage offset error Uoffset error, which remains constant at a certain temperature and over short time intervals, e.g., below 300 ms; see equations (3) and (4) below. This voltage offset can be reduced by differentially calculating the two- or multi-stage current injection, see equation (5) below.

[0020] This reduction in the voltage error is based on the fact that the resistance corresponds to the slope of the linear behavior between the voltage and the current and can therefore be determined by calculating the difference between voltage and current. In a corresponding manner, an offset error of the current can be minimized. According to one embodiment, a target value for the at least one second impressed current, in particular a target current value, is specified as a function of the determined first voltage value. The target value for each of the second current stages can expediently be adaptively adjusted depending on the determined voltage from the first current stage in order to reduce the voltage offset error as much as possible. Furthermore, the respective target value for the individual second stages can also be specified as a function of the voltage value of the respective previous second stage.

[0021] According to one embodiment, the first voltage value Ui and the second voltage value U2 are each determined or ascertained as the length Ü of an actual voltage vector in a rotor-related dq coordinate system during the field-oriented control. Accordingly, the first current value h and the second current value I2 are each determined or ascertained as the length I of an actual current vector in the dq coordinate system. The length Ü of the actual voltage vector is determined in particular as a function of a vector component Ud in the d-direction and of a vector component U q in the q-direction is determined or ascertained, in particular according to equation (6). Accordingly, the length I of the respective actual current vector is determined, in particular, depending on a vector component Id in the d-direction and on a vector component l q in the q-direction, in particular according to equation (7).

[0022] J — 1 / 2 i j2

[0023] 1 ~ Jd J q (7)

[0024] In this way, the resistance value can be determined independently of the angular error of the rotor angle or rotor position. This angular error can lead to a deviation from calculated voltages in the d- and q-axes in the rotor-related dq coordinate system. If the resistance value is determined from the voltage and current values ​​of only one axis, the accuracy of the calculated resistance can be indirectly influenced by the angular error. In particular, assuming that all phase resistances of the electrical machine are identical or at least essentially identical, the resistance value of the phase winding in the dq coordinate system can be considered as a scalar independent of the rotor position and determined using the length Ü, I of the voltage and current vectors, since the length of the respective vector does not change, especially despite the angular error, see equation (8) below.

[0025] According to one embodiment, the first voltage value Ui and the second voltage value U2 are each represented as a vector of individual phase voltages, e.g. [Ua, Ub, U c ] for a three-phase system or [U a , Uß], in a stator-related a-ß coordinate system. Accordingly, the first current value h and the second current value I2 are each determined as a vector of individual phase currents, e.g. [I a , lb, l c ] for a three-phase system or [I a , Iß], in the α-β coordinate system. In particular, all phase resistances, regardless of the angle, can be directly calculated from the voltage and current of each phase in the stator-related coordinate system. For example, the following equation (9) applies to a three-phase system, and equation (10) to the α-β system:

[0026] U a I a

[0027] = R (10) uß. ß.

[0028] According to one embodiment, the first current and the at least one second current are each impressed as a current in the positive direction of the d-axis in the dq coordinate system. In particular, for this purpose, a respective positive target current value is specified along the d-axis. By applying such a current in the positive direction of the d-axis, parasitic torque and thus unwanted rotor movement can be reduced.

[0029] Such an undesirable, parasitic torque can occur when an angle error in the current injection along the d-axis leads to a voltage and a current along the q-axis. The positive desired current injected along the d-axis can weaken an entire flux linkage, which in turn can reduce or minimize the torque despite a parasitic current along the q-axis.

[0030] The parasitic torque T can be expressed in particular according to the following equation (11):

[0031] Where N p the number of turns of the phase winding, l q the current component in q-direction and Id the current component in d-direction. pm denotes a first part of the flux linkage, especially with a positive sign. The difference (Ld-L q ) of the inductance components of the phase winding in the d- or q-direction has a negative sign in particular if the d-component is smaller than the q-component, Ld <L q . If the Id current component has a positive sign, the second part of the flux linkage, i.e. the product of the difference between the inductance components and the Id current component, has a negative sign, so that the entire flux linkage and thus the torque T can be reduced.

[0032] According to one embodiment, the injection of the first current and the at least one second current, as well as the determination of the resistance value, are carried out when the electric machine is at a standstill, during which standstill the electric machine does not generate any torque. In particular, the method can thus be carried out during the initialization of the electric machine, with a rotor speed and a torque of zero. The resistance value of the stator winding(s) can thus be estimated as precisely and error-free as possible during initialization in order, for example, to be able to initialize a control system, a system diagnosis, and a thermal model as quickly and accurately as possible. The invention is particularly suitable for application in the (power) vehicle sector, wherein the electric machine in a vehicle can be used, for example, to generate a drive torque and / or to recuperate kinetic energy into electrical energy.The invention enables the electrical machine to be operated safely and meets safety requirements in the (motor) vehicle sector, such as those specified in the ISO 26262 standard. Furthermore, the invention is also suitably suitable for other mobile or stationary applications of electrical machines.

[0033] The invention can be advantageously applied to a permanent magnet synchronous machine (PSM) or electrically excited synchronous machine (ESM) as an electrical machine, but also to other types of machines, such as asynchronous machines (ASM), etc.

[0034] A computing unit according to the invention, e.g. a control unit of a device for controlling an electrical machine, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0035] A device according to the invention for controlling an electrical machine comprises a power converter which is designed to be coupled to an electrical machine having a stator and a rotor and to provide an electrical voltage for controlling the stator of the electrical machine, and a computing unit according to the invention which is electrically coupled to the power converter and provides the control signals for the power converter.

[0036] An electric drive system according to the invention comprises a device according to the invention for controlling an electric machine and an electric machine with a stator and a rotor, which is electrically coupled to the power converter of the device for controlling the electric machine. The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for further tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as, for example,Hard drives, flash memory, EEPROMs, DVDs, and more. Downloading a program via computer networks (internet, intranet, etc.) is also possible. Such a download can be done via a wired connection or wirelessly (e.g., via a Wi-Fi network, a 3G, 4G, 5G, or 6G connection, etc.).

[0037] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0038] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

[0039] Short description of the drawings

[0040] Figure 1 shows a schematic representation of a block diagram of an electric drive system according to an embodiment.

[0041] Figure 2 schematically shows an embodiment of the method according to the invention as a block diagram.

[0042] Figure 3 schematically shows a diagram of a voltage versus a current, which can be determined in the course of one embodiment of the method according to the invention. Figure 4 schematically shows a diagram of a current versus time, which can be determined in the course of one embodiment of the method according to the invention.

[0043] Figure 5 shows schematically a diagram of a voltage in a dq diagram, which can be determined in the course of an embodiment of the method according to the invention.

[0044] Embodiment(s) of the invention

[0045] Figure 1 shows a schematic representation of a block diagram of an electric drive system 1 with a device 10 for controlling an electric machine 30. The electric drive system 1 comprises an electric machine 30 with a stator, which can be fed by a power converter 11 (so-called inverter), and a rotor. For this purpose, the power converter 11 can be fed, for example, by a DC voltage source such as a battery 20 or the like. The example of a three-phase electric machine 30 shown here serves only to improve understanding and does not represent a limitation of the present invention. Furthermore, any electric machines 30 with a number of electrical phases other than three are of course also possible. For example, it can also be a five- or six-phase electric machine 30 or an electric machine 30 with any other number of phases.

[0046] To control the stator of the electric machine 30, the power converter 11 can convert the DC voltage provided by the battery 20 into a suitable AC voltage. In the case of a three-phase electric machine 30, the power converter 11 can, for example, convert the DC voltage into a three-phase AC voltage. In particular, the amplitude of the AC voltage and / or the value of the output current from the power converter 11 to the stator windings (phases) of the electric machine 30 can be adjusted based on a predetermined setpoint S. For example, the power converter 11 can be a power converter with multiple half-bridges. In particular, the power converter 11 can comprise at least one half-bridge with two switching elements for each phase of the electric machine 30. For example, the power converter 11 for a three-phase electric machine 30 can have a B6 topology.The switching elements of the power converter 11 can be controlled by the control device 12 using suitable control signals, using the setpoint S. For example, the control device 12 can provide a control signal for each switching element of the power converter 11 to open or close the corresponding switching element. The control of an upper switching element of a half-bridge is complementary to the control of the corresponding lower switching element.

[0047] Figure 2 shows an embodiment of the method according to the invention as a schematic block diagram.

[0048] Within the scope of the method, for example, the temperature-dependent electrical resistance value of the stator or phase windings is to be determined during the initialization of an electrical machine in a motor vehicle. For this purpose, a control unit of the vehicle can be configured, in particular by programming, to carry out the embodiment of the method according to the invention. In addition to the (motor) vehicle sector, the method is also suitable for other mobile or stationary applications of electrical machines.

[0049] In the course of this, initialization of the electric machine begins in a step 110. The electric machine is at a standstill, with the rotor speed and torque of the electric machine both being zero.

[0050] In a step 120, a two-stage current injection takes place, wherein first a first current and then a second current are injected into the electrical machine or into the phase windings of the electrical machine, in particular shortly or directly one after the other. In particular, a constant current or a current with a constant current intensity is injected as the first current. Furthermore, in particular a current in the positive direction in a d-axis in a dq coordinate system is injected as the first current in the course of field-oriented (current) control. A constant current with a constant current intensity is also injected as the second current, furthermore in particular a current in the positive direction in the d-axis in the rotor-related dq coordinate system. A setpoint or setpoint current value for the second injected current is specified as a function of the determined first voltage value with respect to the first injected current.In particular, it is also possible to inject several second currents, each with different target current values, into the electrical machine shortly or immediately one after the other as several second stages.

[0051] In a step 130, a first current value h and a first voltage value Ui are determined with respect to the first impressed current. Furthermore, a second current value I2 and a second voltage value U2 are determined with respect to the second impressed current. If multiple second currents are impressed, a corresponding current and voltage value can be determined for each impressed current.

[0052] The first voltage value Ui and the second voltage value U2 can each correspond to a voltage value applied to the phase winding as a control variable for the respective current injection. The respective first current value h and the second current value I2 can each correspond to the current value through the phase winding that occurs at the respective applied voltage value and the current resistance value.

[0053] In a step 140, the resistance value of the phase windings is determined as a function of the first current value h, the first voltage value Ui, the second current value I2 and the second voltage value U2.

[0054] In a step 150, a control system, a system diagnostic, and a thermal model of the electric machine are initialized using the determined resistance value. The electric machine can now be started. By applying the current in two or more stages and determining the resistance value based on the current and voltage values ​​determined during this two or more stage, voltage and current errors can be reduced or minimized, as explained below with reference to Figure 3.

[0055] Figure 3 schematically shows a diagram 200 of a voltage U applied to the phase winding of the electrical machine as a function of a current I flowing through the phase winding.

[0056] The resistance value R of the phase winding corresponds to the slope of the linear behavior between the voltage and the current, i.e. the slope of the straight line 210. In particular, the resistance value can be determined as the ratio of the difference AU of the second voltage value U2 and the first voltage value Ui, designated 220 in Figure 3, divided by the difference AI, designated 230 in Figure 3, of the second current value I2 and the first current value h according to the equation (1) explained above.

[0057] For example, the voltage error can be in the form of an offset U O ffset_error can be assumed as expressed in equations (3) and (4) explained above. For example, the offset U Offset_error remains constant at a specific temperature and over a short time interval of, for example, less than 300 ms. This voltage offset can be reduced by differential calculation of the two- or multi-stage current injection, as can be seen from equation (5) above.

[0058] The reason for reducing the voltage error is that the resistance of the linear behavior between the voltage and current corresponds to the slope of the straight line 210 and can therefore be determined by calculating the difference between voltage and current. In a corresponding manner, an offset error of the current can be minimized. By specifying the setpoint for the second impressed current as a function of the determined first voltage value with respect to the first impressed current, in particular, an adaptive two-stage current injection can be implemented, as explained below with reference to Figure 4.

[0059] Figure 4 schematically shows a diagram 300 of the setpoint current Is as a function of time. Between times t0 and h, the first current is injected, for which a first setpoint Isi is specified. Between times h and t2, the second current is injected, for which a second setpoint Is2 is specified. The setpoint Is2 of the second current stage can be adaptively adjusted depending on the voltage determined from the first current stage in order to reduce the voltage offset error as much as possible.

[0060] Furthermore, the setpoint values ​​for the current injections can be specified in such a way, e.g. taking torque equations into account, that an undesired torque and the resulting rotor movement during the current injection can be reduced or minimized.

[0061] In order to avoid angular errors of a rotor angle or a rotor position, the individual voltage and current values ​​can each be determined as the length of a respective voltage vector in the rotor-related dq coordinate system of the field-oriented control, as explained below with reference to Figure 5.

[0062] Figure 5 schematically shows a diagram 400 of a voltage in a dq diagram.

[0063] Arrow 410 indicates a desired voltage or a desired voltage vector along the d-axis. This desired voltage vector 410 thus has only a component in the d-direction, but no component in the q-direction.

[0064] An angle error 450 can lead to an erroneous actual voltage or an erroneous actual voltage vector 420. This erroneous actual voltage vector 420 has a component 421 in the d-direction and a component 422 in the q-direction.

[0065] Since the desired voltage vector 410 has only one component in the d-direction, a length Ü d-soll the d-component of a length Ü so u of the desired voltage vector 410. As can be seen in Figure 5, a length U d -i St-error the component 421 of the actual voltage vector 420 in the d-direction from the length of the d-component of the desired voltage vector 410 d-actual-error ^d-desired)-

[0066] Since the target voltage vector 410 has no component in the q-direction, the length Ü q-soll the q-component of the target voltage vector 410 is zero. A length U q -i St-error However, the component 422 of the actual voltage vector 420 in the q-direction is different from zero and thus differs from the q-component of the desired voltage vector 410 U q-ist-error #= q-target

[0067] A length Ü ist-error However, the actual voltage vector 420 corresponds to the length Ü sou of the target voltage vector 410 voltage vector (Ü error #= U soll ).

[0068] The angular error of 45° thus leads to a deviation of the voltages along the d- and q-axes in the rotor-related dq coordinate system. If the resistance value were determined from the voltage and current along only one axis, the accuracy of the calculated resistance value could be indirectly influenced by the angular error of 45°.

[0069] In particular, assuming that the phase resistances of all phases of the electrical machine are identical or at least substantially identical, the phase resistance in the rotor coordinate system can be considered a scalar independent of the rotor position or the rotor angle and can be expressed by the length of the voltage and current vectors according to equation (8) above. This is because the length of the voltage vector, as shown in Figure 5, does not change despite the angular error 450. Therefore, it is particularly expedient to determine the first voltage value Ui and the second voltage value U2 each as the length Ü of a respective voltage vector in the dq coordinate system, and the first current value h and the second current value I2 each as the length I of a respective current vector in the dq coordinate system, in particular according to equations (6) and (7) above.

[0070] Furthermore, by applying the first current and the second current each as a current in the positive d-direction in the dq coordinate system, a parasitic torque and thus an undesired rotor movement can be reduced. Such an undesired parasitic torque can occur if the angular error 450 during the current application in the d-axis leads to a component of the actual voltage and the actual current in the q-axis. The positive desired current applied in the d-axis can weaken an entire flux linkage, as explained above with reference to equation (11), whereby the parasitic torque can be reduced or minimized despite a parasitic current in the q-axis.

[0071] The present invention thus provides a particularly useful way to precisely and reliably determine the resistance value of phase windings during the initialization of the electric machine across the entire temperature range. The proposed method is particularly robust against voltage errors, current errors, and angle errors. Furthermore, unwanted torque and the resulting rotor movement during current injection can be reduced or minimized.

Claims

Claims 1 . A method for determining an electrical resistance value of at least one phase winding of an electrical machine, comprising the following steps: Injecting (120) a first current into the electrical machine and injecting at least one second current into the electrical machine, wherein a current intensity of the first current differs from that of the at least one second current; Determining (130) a first current value (h) and a first voltage value (Ui) with respect to the first impressed current, and determining a second current value (I2) and a second voltage value (U2) with respect to the at least one second impressed current; and Determining (140) the resistance value of the at least one phase winding as a function of the first current value (h), the first voltage value (Ui), the second current value (I2) and the second voltage value (U2).

2. The method according to claim 1, wherein determining (140) the resistance value of the at least one phase winding comprises: Determining the resistance value depending on a difference (220) between the second voltage value (U2) and the first voltage value (Ui) and depending on a difference (230) between the second current value (I2) and the first current value (h).

3. The method according to claim 1 or 2, further comprising: Specifying a setpoint value for the at least one second impressed current depending on the determined first voltage value (Ui).

4. Method according to one of the preceding claims, further comprising: Determining the first voltage value (Ui) and the second voltage value (U2) each as the length of an actual voltage vector in a dq coordinate system; and Determining the first current value (h) and the second current value (I2) each as the length of an actual current vector in the dq coordinate system.

5. Method according to one of the preceding claims, further comprising: Determining the first voltage value (Ui) and the second voltage value (U2) each as a vector of individual phase voltages in an a-ß coordinate system; and Determining the first current value (h) and the second current value (I2) each as a vector of individual phase currents in the a-ß coordinate system.

6. The method according to any one of the preceding claims, wherein the impressing (120) of the first current and the impressing of the at least one second current each comprises: Impressing the respective current as a current in the positive direction of the d-axis in the dq coordinate system.

7. Method according to one of the preceding claims, wherein the impressing (120) of the first current and the at least one second current and the determining (140) of the resistance value are carried out when the electrical machine is at a standstill, in which standstill the electrical machine does not generate any torque.

8. Computing unit configured to carry out all method steps of a method according to one of the preceding claims.

9. Device (10) for controlling an electrical machine (30), comprising: a power converter (11) which is designed to be coupled to an electrical machine (30) having a stator and a rotor and to provide an electrical voltage for controlling the stator of the electrical machine (30); and a computing unit (12) according to claim 8, which is electrically coupled to the power converter (11) and provides the control signals for the power converter (11).

10. An electric drive system (1), comprising: a device (10) for controlling an electric machine (30) according to claim 9, and an electric machine (30) having a stator and a rotor, which is electrically coupled to the power converter (11) of the device (10) for controlling the electric machine (30).

11. A computer program which causes a computing unit to carry out all method steps of a method according to any one of claims 1 to 7 when executed on the computing unit.

12. A machine-readable storage medium having a computer program according to claim 11 stored thereon.

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