Determining a capacitively smoothed rotor current of an inductive transmitter of an externally excited electric machine

Abstract

The invention relates to a method (100) for determining a capacitively smoothed rotor current of an inductive transmitter (1) of an externally excited electric machine in order to thereby preferably control the capacitively smoothed rotor current to drive a rotor (40) of the externally excited electric machine. The method comprises: determining a capacitor voltage (110) of a secondary intermediate circuit capacitor (22) of the inductive transmitter (1) by means of a primary current of the inductive transmitter (1), an equivalent circuit diagram of a transformer (30) of the inductive transmitter (1) and a diode voltage of a first diode (21.1) of a rectifier circuit (21) of the inductive transmitter (1); determining a transmission power (120) of the inductive transmitter (1) by means of the primary current and a primary voltage of the inductive transmitter (1); determining a rotor resistance (130) by means of the capacitor voltage, the transmission power and detected interference signals of the rotor (40); and determining the rotor current (140) by means of the capacitor voltage, the rotor resistance and the interference signals.

Description

[0001]Description of a method for determining a capacitively smoothed rotor current of an inductive transformer of a separately excited electric machine. The present invention relates to a method for determining a capacitively smoothed rotor current of an inductive transformer of a separately excited electric machine, preferably to control the capacitively smoothed rotor current for driving a rotor of the separately excited electric machine. The invention also relates to a control unit and a vehicle with a separately excited electric machine and the control unit. It is known to estimate a rotor current of a separately excited electric machine using a current and a voltage across the inductive transformer. It is also known to estimate a rotor current of a separately excited electric machine using a primary current and a primary voltage across the inductive transformer.Furthermore, it is known to estimate the rotor current of a separately excited electric machine by means of a voltage induced in the stator of the machine. It is also known to determine the rotor current of a separately excited electric machine using sensors arranged on the machine. In this case, the rotor of separately excited electric machines is actively controlled or regulated based on the rotor current, with the regulation depending on the accuracy of the rotor current. Therefore, the accuracy of the determination or measurement of the rotor current directly affects the accuracy of the rotor current regulation. It is thus an object of the present invention to provide a technology that is more advanced than the prior art.In particular, the accuracy of determining the rotor current is to be improved compared to other methods using capacitive smoothing, in order to control the rotor current with greater accuracy. This objective is achieved by devices with the features according to the independent claims. Advantageous embodiments are the subject of the dependent claims. Disclosed is a method for determining a capacitively smoothed rotor current of an inductive transformer of a separately excited electrical machine, preferably for controlling or regulating the capacitively smoothed rotor current for driving a rotor of the separately excited electrical machine.The method comprises determining the capacitor voltage of a secondary DC link capacitor of the inductive transformer using the primary current of the inductive transformer, an equivalent circuit of a transformer of the inductive transformer, and the diode voltage of the first diode of a rectifier circuit of the inductive transformer. Furthermore, the method comprises determining the power transmission of the inductive transformer using the primary current and primary voltage of the inductive transformer. The method also comprises determining the rotor resistance using the capacitor voltage, the power transmission, and detected rotor interference signals, and determining the rotor current using the capacitor voltage, the rotor resistance, and the interference signals. The inductive transformer can, for example, have a primary side with a primary current and a secondary side with a secondary current.Furthermore, the transformer can transfer the primary current from the primary side to the secondary side as secondary current. The capacitively smoothed rotor current can also be referred to as rotor current, which is designed to supply the rotor with electrical current. The rotor current can be provided from the secondary side and may be at least partially dependent on the secondary current. The equivalent circuit can, for example, represent the actual behavior of the transformer, where the actual behavior is represented or modeled by means of at least one equivalent resistance and / or at least one equivalent inductance. The equivalent circuit can include at least data for a primary equivalent inductance, a secondary equivalent inductance, a primary equivalent resistance, and a secondary equivalent resistance. The disturbance signals can, for example, include the value of a voltage induced in the rotor.The induced voltage can, for example, be induced into the rotor by the stator of a separately excited electric machine. The value of the disturbance signals can be provided to the method. The method can, for example, calculate a freewheeling capacitor voltage using the primary current, the diode voltage, and the voltage and inductance data of the equivalent circuit. Furthermore, an active capacitor voltage can be calculated using a voltage supplied by the transformer, the primary current, the diode voltage, and the voltage and inductance data of the equivalent circuit. Similarly, a capacitor voltage can be calculated using the freewheeling capacitor voltage and the active capacitor voltage. Using the primary current to determine the capacitor voltage can increase the accuracy of the rotor current determination.Accuracy can be increased, in particular, by including the magnetization of the inductive transformer in the rotor current determination. Specifically, using the primary current to determine the rotor current allows influencing effects of a real transformer to be incorporated into the measurement. These influencing effects can include, for example, the magnetization of the transformer. Therefore, the rotor current and / or the rotor resistance can be used to generate control signals for setting a precise target value for the rotor current. Furthermore, the primary current and the primary voltage can be determined using oversampling. Oversampling allows the detection of the primary current's waveform, particularly its changes. Additionally, the primary current can be represented as a current gradient (di / dt), which can represent an instantaneous value of the primary current.Furthermore, the transmission power can be determined over a period TA of the capacitively smoothed rotor current. Preferably, the instantaneous value of the primary current can be acquired using oversampling, allowing the primary current flow to be represented with greater accuracy. This improved accuracy can be achieved, for example, compared to sampling at a required sampling rate. The sampling rate can, for instance, depend on the period TA. Furthermore, the transmission power can represent, for example, an average transmission power or energy quantity transmitted per period, such as a modulation period. The average transmission power p can be determined using the primary current ip and the primary voltage up, for example, based on the following formula: Furthermore, the transmission power can also be determined by measuring the power loss of the inductive transformer. This power loss can include, for example, the primary power loss of the inductive transformer, the secondary power loss of the inductive transformer, and / or the diode power loss of the first diode. Preferably, the power loss can be determined using all power losses. The power loss can vary depending on the external temperature of the inductive transformer, the component temperature of the inductive transformer, and the voltage of the first diode. Approximate formulas for the respective power losses to be determined can also be provided to the method for this purpose. Furthermore, the method can include determining the rotor temperature using the rotor resistance.For example, the rotor temperature can be determined using material constants of the rotor materials. In particular, information on a specific resistance, for example at 20 °C, and / or a temperature coefficient of a material used in the rotor can be provided to the method. Furthermore, information on the specific resistances and / or temperature coefficients of all materials used in the rotor can be provided to the method. Temperature models of the rotor can also be provided to the method. The method can also include providing a control signal for controlling the capacitively smoothed rotor current, which is determined using the rotor resistance and / or the rotor current and / or the rotor temperature. Preferably, the control signal can be determined using the rotor current and the rotor resistance.A control unit, configured and programmed to execute the disclosed method, is also disclosed. Furthermore, the control unit can control the capacitively smoothed rotor current using a control signal. For example, the rotor current and rotor resistance can be provided to the control unit, which can then generate the control signal to control the rotor current. "Control" can also refer to regulation or adjustment. A vehicle with a separately excited electric machine and the disclosed control unit is also disclosed. For example, the control unit can use the control signal to control the inductive transformer such that the inductive transformer provides a rotor current to drive the separately excited electric machine depending on the control signal. The controlled rotor current can then drive the rotor of the separately excited electric machine.The present invention is described in detail below with reference to the figures. Figure 1 shows an inductive transformer for providing a capacitively smoothed rotor current; and Figure 2 shows a process for determining a capacitively smoothed rotor current of an inductive transformer according to Figure 1 of a separately excited electrical machine, preferably to control the capacitively smoothed rotor current for driving a rotor of the separately excited electrical machine. The present invention is described below with reference to preferred embodiments and the figures. However, the description of the embodiments should not be considered exhaustive. Figure 1 shows an inductive transformer 1 for providing a capacitively smoothed rotor current iR. The inductive transformer 1 comprises a primary side 10 and a secondary side 20.The primary side 10 comprises a primary capacitor 11 and a bridge circuit 12. The secondary side 20 comprises a rectifier circuit 21 with a first diode 21.1 and a first secondary intermediate circuit capacitor 22. Furthermore, the inductive transformer 1 comprises a transformer 30, which is represented by an equivalent circuit diagram. The transformer 30 is configured to transfer a primary current iP of the primary side 10 via a first winding n1 to a second winding n2, resulting in a secondary current iS of the secondary side 20. The equivalent circuit diagram of the transformer 30 includes at least one primary equivalent resistance with a primary equivalent voltage uRP and one secondary equivalent resistance with a secondary equivalent voltage uRS. The equivalent circuit diagram also includes a primary equivalent inductance LP, a secondary equivalent inductance LS, and a load equivalent inductance LL.In this respect, the transformer 30 is further configured to transmit a primary voltage uP of the primary side 10 to a secondary voltage uS of the secondary side 10, wherein the secondary voltage uS depends on the transmission of the primary voltage uP to a primary equivalent voltage u'P of the primary side 10 and the electrical equivalent components of the equivalent circuit. The first diode 21.1 comprises a diode voltage UD, and the secondary intermediate circuit capacitor 22 a capacitor voltage u. Cand the secondary side 10 provides a rotor current iR. Furthermore, the secondary side 20 supplies the capacitively smoothed rotor current iR to a rotor 40 of a separately excited electric machine, the rotor 40 being represented by an equivalent electrical circuit. This equivalent electrical circuit of the rotor 40 comprises a voltage uind induced by a stator of the separately excited electric machine, an equivalent inductance with an equivalent inductance voltage uL, and an equivalent resistance with an equivalent voltage uw. The induced voltage uind can be assumed to be known. Fig. 2 shows a step of the method 100 for determining a capacitively smoothed rotor current iR of the inductive transformer 30 according to Fig. 1 of a separately excited electric machine, preferably to control the capacitively smoothed rotor current iR for driving the rotor 40 of a separately excited electric machine.Method 100 comprises determining the capacitor voltage uC 110 of the secondary DC link capacitor 22 of the inductive transformer 1 using the primary current iS of the inductive transformer 1, the equivalent circuit of the transformer 30 of the inductive transformer 1, and the diode voltage uD of the diode 21.1 of the rectifier circuit 21 of the inductive transformer 1. The method further comprises determining the power transfer rate pDC 120 of the inductive transformer 1 using the primary current iP and the primary voltage uP of the inductive transformer 1. The method also includes determining the rotor resistance RR 130 using the capacitor voltage uC, the power transfer rate pDC, and detected disturbance signals of the rotor 40. These disturbance signals include at least a voltage uind induced in the rotor 40 by a stator of the separately excited electrical machine. Furthermore, the method allows for the determination of the rotor current i. R140 using the capacitor voltage uC, the rotor resistance RR, and the interference signals. The capacitor voltage uC can also be determined or calculated, for example, using a freewheeling capacitor voltage uc-f and an active capacitor voltage uc-a. The freewheeling capacitor voltage uc-f can be calculated, in particular, based on the following formula: Furthermore, the active capacitor voltage uc-a can be calculated in particular based on the following formula: In particular, a current gradient di / dt of the primary current iP can be used. The power transfer pDC can, for example, be equal to the capacitor power pC of the secondary DC link capacitor 22. Preferably, an average power transfer pDC over a period TA of the rotor current iR can be determined using the primary voltage uP and the primary current iP 120. The power transfer pDC can then be calculated based on the following formula: The average transmission power pDC can preferably be determined over the period TA using the primary voltage uP, the primary current iP, and a power loss. The transmission power pDC can, for example, be calculated based on the following formula: The rotor resistance RR can preferably be determined using a formula for capacitor power pC and taking into account the induced voltage u130. The rotor resistance RR can, for example, be calculated based on a rearrangement of the following formula: The rotor current iR can preferably be determined as a quotient of the difference between the capacitor voltage uC and the induced voltage uund, and the rotor resistance RR. For example, the rotor current iR can be calculated based on the following formula: Furthermore, the method 100 in 130 can include determining a rotor temperature using the rotor resistance. The rotor temperature T can preferably also be determined using a formula for calculating the rotor resistance RR. The rotor temperature T can, for example, be calculated based on a rearrangement of the following formula: ^^^^ = ^^(^^20°) ∙ (1 + ^^ ∙ (^^ − ^^20°) In particular, a specific resistance ρ at a temperature of 20 °C of at least one material of the rotor 40 and a temperature coefficient α of at least one material of the rotor 40 can be used. After execution of the method, a control signal for controlling the capacitively smoothed rotor current can be output. The control signal can be determined using the rotor resistance and / or the rotor current and / or the rotor temperature. The method can be implemented in a control unit that is configured and programmed to execute the method.In particular, the control unit can control or regulate the capacitively smoothed rotor current using the provided control signal. The control unit can be installed and used in a vehicle with a separately excited electric machine. Reference list: 1 Circuit arrangement 10 Primary side 11 Primary capacitor 12 Bridge circuit 20 Secondary side 21 Rectifier circuit 21.1 First diode 22 Secondary DC link capacitor 30 Transformer 40 Rotor 100 Method for determining a capacitively smoothed rotor current 110 Determining capacitor voltage data 120 Determining transmission power data 130 Determining rotor resistance and rotor temperature data 140 Determining rotor voltage data 150 Determining rotor current data.

Claims

Claims 1. Method (100) for determining a capacitively smoothed rotor current of an inductive transformer (1) of a separately excited electrical machine, preferably to control the capacitively smoothed rotor current for driving a rotor (40) of the separately excited electrical machine, comprising: determining a capacitor voltage (110) of a secondary intermediate circuit capacitor (22) of the inductive transformer (1) by means of a primary current of the inductive transformer (1), an equivalent circuit of a transformer (30) of the inductive transformer (1) and a diode voltage of a first diode (21).1) a rectifier circuit (21) of the inductive transformer (1); determining a transmission power (120) of the inductive transformer (1) using the primary current and a primary voltage of the inductive transformer (1); determining a rotor resistance (130) using the capacitor voltage, the transmission power, and detected disturbance signals of the rotor (40); and determining the rotor current (140) using the capacitor voltage, the rotor resistance, and the disturbance signals.

2. Method according to claim 1, characterized in that the primary current and the primary voltage are determined using oversampling.

3. Method according to claim 1 or 2, characterized in that the primary current represents a current gradient di / dt.

4. Method according to any one of claims 1 to 3, characterized in that the transmission power is determined over a period of the capacitively smoothed rotor current. 5.Method according to one of claims 1 to 4, characterized in that the transmission power is further determined by means of a power loss of the inductive transformer (30).

6. A method according to any one of claims 1 to 5, characterized in that the method comprises determining a rotor temperature using the rotor resistance.

7. A method according to any one of claims 1 to 6, characterized in that the method further comprises providing a control signal for controlling the capacitively smoothed rotor current, which is determined using the rotor resistance and / or the rotor current and / or the rotor temperature.

8. A control unit configured and programmed to execute the method according to any one of claims 1 to 7.

9. A control unit according to claim 8, characterized in that the control unit controls the capacitively smoothed rotor current using the control signal.

10. A vehicle with a separately excited electric machine and the control unit according to claim 8 or 9.

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