Control device for controlling an electric motor and method for compensating an interference signal in a control circuit for an electric motor

Abstract

Control device (1) for controlling an electric motor (3), comprising: a converter (14) configured to receive a setpoint value (M) and to output a control variable based on the received setpoint value (M); an output device (13) designed to convert an electrical voltage provided in the electrical network (10) into a further voltage; a measuring device (11) designed to detect measured values ​​in the electrical network (10); and a detector device (12) designed to - to determine an interference signal based on the recorded measured values, - to output a compensation signal based on the detected interference signal, and - to determine the compensation signal taking into account known system parameters of the electrical network (10) and the overall system, wherein the system parameters taken into account include parasitic inductances, capacitances, an intermediate circuit capacitance and an internal resistance of an energy storage device; wherein the output device (13) is designed to convert the electrical voltage in the electrical network (10) into a further voltage using the control variable output by the converter (14) and the compensation signal output by the detector device (12).

Description

The invention relates to a control device for controlling an electric motor and to a method for compensating an interference signal in a control circuit for an electric motor.Prior ArtDE 603 18 232 T2 describes an electric motor control device for generating compensation signals in order to reduce harmonic currents in an electric drive system. Frequency analyses, such as the FFT, are used to detect disturbances in the electrical network and to generate corresponding compensation signals. The compensation signals are used to suppress the disturbances by feedback into the network.Fully or partially electrically driven motor vehicles have an electrical energy store, such as a traction battery. The energy from this electrical energy store is supplied to one or more electric motors via a suitable control circuit, such as an inverter, for example. The electrical energy stores used in this case generally consist of a larger number of battery cells. FIG. 6 is a schematic diagram in which one battery includes two battery cells B 1 and B 2. Further, each of these battery cells B 1 and B 2 has a parasitic capacitance C 1 and C 2, respectively. Likewise, each of the battery cells B 1 and B 2 has a series inductance L 1 and L 2, respectively, as a result of the installed connection technology and the battery cells themselves. The internal resistances of the battery cells are further represented by series internal resistances R1 and R2, respectively. The entire battery system in turn likewise has a parasitic capacitance C 3 on account of the connection technique. The connection between the battery and the control electronics, that is to say usually the on-board power supply system of the vehicle, likewise has a parasitic series inductance which is represented by the inductances L 3 aand L 3 b. The control circuit, for example an inverter (inverter), furthermore has a physically implemented capacitance in the form of an intermediate circuit capacitor C 4.Such a construction described above is an oscillatory structure due to the multiple combination of inductances and capacitances, which can be excited to resonance. Due to the tendency of future system configurations, in which reduced intermediate circuit capacitances are to be expected, and which additionally preferably have battery systems with decreasing internal resistances, an increasing quality of the resonant circuit formed and a lower attenuation within the resonant circuit are also to be expected. This leads to increasingly pronounced resonance effects in modern systems.To mitigate or dampen these resonance effects, additional filter assemblies can be installed in the on-board electrical system of an electric vehicle, for example. The publication DE 199 08 124 C2 discloses, for example, an inverter with a suction circuit. This trap absorbs harmonics that occur. As a result of this absorption, the harmonics are converted into thermal energy.There is therefore a need for improved compensation of interference signals in an electrical network. In particular, there is a need for low-loss and efficient compensation of interference signals.Disclosure of the InventionThe present invention provides a control device for controlling an electric motor and a method for compensating an interference signal having the features of the independent patent claims. Further advantageous embodiments are the subject matter of the dependent claims.According to one aspect, the present invention provides a drive device for driving an electric motor, having a converter which is designed to receive a setpoint value and to output a control variable based on the received setpoint value; an output device which is designed to convert an electrical voltage provided in the electrical network into a further voltage; a measuring device which is designed to acquire measured values in the electrical network; and a detector device which is designed to ascertain an interference signal based on the acquired measured values and to output a compensation signal based on the ascertained interference signal; wherein the output device is designed to convert the electrical voltage in the electrical network into a further voltage using the control variable output by the converter and the compensation signal output by the detector device.According to a further aspect, the present invention provides a method for compensating an interference signal in a drive circuit for an electric motor, comprising the steps of capturing measurement values in the electrical network by means of a measurement device; determining an interference signal based on the captured measurement values by means of a detector device; determining a compensation signal based on the determined interference signal by means of the detector device; and driving an output device using the compensation signal determined by the detector device.It is an idea of the present invention to detect interference components, such as, for example, occurring resonances in the electrical network, that is to say in the on-board electrical system of an electrically driven vehicle, or of a similar system, and to compensate these interference components by active counter-steering. The interference components are determined by means of measurements of the current and / or voltage profile in the electrical network, that is to say in the power electronic region of the circuit, and subsequent analysis in the non-power electronic region, that is to say in the control electronics. Based on these determined interference components, a control variable for the actuation of the power electronics for the electric drive of the vehicle is then determined, which control variable makes it possible to actuate an electric motor with a predefined torque and at the same time actively compensate for the interference components on the power side of the on-board power supply system, that is to say in the electric network, of the vehicle.An advantage of the active counter-control is that the interference resonant frequencies do not have to be converted into thermal energy within an absorption circuit or the like due to the compensation of the interference signals according to the invention. Thus, no energy losses are produced by such a thermal conversion.A further advantage is that by eliminating additional modules which filter out the resonant frequencies, the circuit complexity can be reduced compared to compensation with suction circuits or the like.In addition, the continuous monitoring of the interference signals and the subsequent active compensation can react particularly flexibly to variable interference signals. A special adjustment of modules already at the beginning of the system design can thus be omitted.According to one embodiment, the drive device comprises a superposition device which is designed to superimpose the control variable provided by the converter with the compensation signal output by the detector device and to provide it to the output device.According to an embodiment, the output device is configured to convert the voltage provided in the network into a further voltage based on a predetermined clock rate. The predetermined clock rate can be greater than 18 kHz, preferably greater than 36 kHz. By means of an output clocked in this way, the output signal can be simulated in the desired manner by means of discretely sampled output values.According to an embodiment, the output device comprises an inverter.A further embodiment relates to an electrically driven vehicle having a control device according to the invention.According to one specific embodiment, the measuring device acquires the measured values in an on-board power supply system of the electrically driven vehicle.According to one specific embodiment, the step for determining the compensation signal ascertains a disturbance-free signal curve and ascertains the compensation signal on the basis of a comparison of the ascertained disturbance signal and the ascertained disturbance-free signal curve. In order to determine or calculate the interference-free signal profile, it is possible in this case to use, for example, the setpoint value received by the converter, the control variable output by the converter, the voltage provided in the network, the further voltage output by the output device or the output current and / or further known or measured variables within the drive circuit.The step for determining the compensation signal can determine the compensation signal as a function of the physical parameters, in particular parasitic and non-parasitic inductances and capacitances, of the connected electrical network. If sufficient parameters are already known during system design via the connected network, for example the on-board power supply system of an electrically driven vehicle, these can influence the system design in a helpful manner. For example, known values of parasitic inductance, capacitance, the size of an intermediate circuit capacitance, internal resistance of battery cells, etc., can also be used for determining a suitable compensation signal for compensating interference signals, in particular resonant interference signals.Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the attached drawings.Brief Description of the DrawingsThe following are shown: FIG. 1 : shows a schematic illustration of a control of an electric motor with a compensation device according to one embodiment of the present invention; FIG. 2 : shows a schematic illustration of a current / voltage time diagram of the base signal with a superimposed interference signal; FIG. 3 shows a schematic illustration of a current / voltage time diagram with a separate illustration of the base signal and the interference signal; FIG. 4 : shows a schematic illustration of a current / voltage time diagram from a base signal with superimposed interference signal, and a negative-phase control signal profile, illustrated here in a diagram, corresponding to the compensation signal according to one embodiment of the present invention; FIG. 5 is a schematic illustration of a method for compensating an interference signal according to an embodiment of the present invention; and FIG. 6 : shows a schematic illustration of an equivalent circuit diagram of an electrical energy store with parts of a connected inverter.The drawings depicted in the figures are, in part, schematic representations of elements that are not necessarily drawn to scale for reasons of clarity. Identical reference numerals generally denote identical or identically acting components.FIG. 1 shows a schematic illustration of a block diagram of a control device 1 for controlling an electric motor 3. The setpoint value for the torque M can be provided, for example, as an analog signal or as a digital signal, for example, via a bus system. This set value for the torque M is received by a converter 14. The converter 14 can then forward the received setpoint value for the torque M to an output device 13. If necessary, the received setpoint value for the torque can be adjusted in the converter 14, so that the control variable output by the converter 14 is provided in a form that can be further processed by the output device 13. Alternatively, it is also possible for the converter 14 to receive a setpoint value for a torque M and to convert this setpoint value for the torque M into a control variable for a current I.The control variable for the current I can then be provided from the converter 14 to the output device 13. This output device 13 is, for example, an inverter (inverter) or the like. The output device 13, based on the predefined control variable for the torque M or the current I, converts the DC voltage provided by the battery 2 into a desired single-phase or polyphase AC voltage and provides this AC voltage as an output signal in the form of a current or voltage profile to an electric motor 3. In place of the battery 2, any alternative electrical voltage source is also possible. The electrical voltage does not necessarily have to be provided as a constant DC voltage. Alternative machining sources are also possible. For example, an alternating voltage can also be provided as voltage. In particular, a direct voltage with a superimposed alternating voltage component is also possible.The electrical alternating current to be output can be either a single-phase or else a polyphase alternating current, for example a three-phase alternating current. The output device 13 can thus be a conventional inverter (inverter) which provides the desired output current on the basis of semiconductor switches or the like, for example.Due to the inductances and capacitances present in the on-board power supply system 10 of the electrically driven vehicle between the battery 2 and the output device 13, which inductances and capacitances are in part parasitic, oscillation processes can occur during the actuation of the electric motor 3. In this case, for example, resonance frequencies occur within the on-board power supply system 10, which can usually be between 1 and 10 kHz. Resonant frequencies in the range of approximately 5 kHz are very widespread in this case. However, resonant and interference frequencies in other frequency ranges are also possible.The measuring device 11 measures measured values for the current and / or voltage profile in the on-board power supply 10. For this purpose, the measuring device 11 can measure, for example, the voltage profile within the on-board power supply system 10 or additionally or alternatively also the current profile within the on-board power supply system 10. Based on the measured values obtained during the measurement of current and / or voltage, the detector device 12 can detect disturbances occurring in the on-board power supply system 10, in particular an disturbance signal, such as resonant oscillations, for example. For example, the detector device 12 can compare the measured values with a theoretical, interference-free current or voltage profile for this purpose, which can be calculated, for example, on the basis of a mathematical model. In order to determine or calculate the interference-free signal curve, it is possible in this case to use, for example, the setpoint value M received by the converter 14, the control variable output by the converter 14, the voltage provided in the network 10, the further voltage output by the output device 13 or the output current and / or further known or measured variables within the drive device 1. From this comparison between the theoretical and measured current or voltage curves, it is then possible to infer the faults within the on-board power supply system 10. Frequency analysis of the measured values is likewise possible.FIG. 2 shows an example of a schematic illustration of a current or voltage profile in the on-board electrical system 10. The amplitude of the interference-free current or voltage profile can be lower or greater than the amplitude of the higher-frequency interference component. For better understanding, the interference selected in the example illustrated has an amplitude which is lower than the amplitude of the interference-free current or voltage profile. Other amplitude ratios are also possible. In particular, non-sinusoidal current or machining profiles are also possible.FIG. 3 shows a decomposition of the measured current or voltage profile into a disturbance-free profile and higher-frequency disturbance component. For this purpose, the detector device 12 splits the current or voltage profile obtained on the basis of the measurement values of the measuring device 11 into a fault-free component and one or more superimposed fault components. The restriction to a single interference component, as is illustrated in FIG. 3, is likewise used only for better illustration. A plurality of interfering components of different frequencies that are superimposed are likewise possible in this case.After the detector device 12 in FIG. 1 has determined the interference component or components, i.e. the interference signal, from the measured signal profile of the measured values for the current or voltage profile, the detector device 12 then determines a suitable compensation signal which is capable of compensating the interference components of current or voltage within the on-board power supply system. For this purpose, the detector device 12 can ascertain, for example, a compensation signal which actuates the output device 13 in such a way that an additional current / voltage profile corresponding to the inverted interference component results in the electrical network, which current / voltage profile is superimposed on the disturbed signal profile and thus compensates for the original interference. This means that this inverts the sign of the interference components and a suitable compensation signal is determined therefrom. If required, this compensation signal can be varied in amplitude in a suitable manner in order to correspondingly amplify or attenuate the effect of compensating a resonance in the on-board power supply 10.After a suitable compensation signal has been determined by the detector device 12, the detector device 12 converts the determined compensation signal into a variable for the output device 13. The variable generated by the detector device 12 is suitable for causing a current or voltage profile in the on-board power supply system 10 when the output device 13 is controlled accordingly, which current or voltage profile is suitable for counteracting the interference component in the on-board power supply system. The variable output by the detector device 12 is superimposed on the control variable output by the converter 14 and fed as a control variable to the output device 13.If, for example, the converter 14 converts the received setpoint value for a torque M to be set at the electric motor 3 into a control variable for a current I to be set at the output device 13, the detector device 12 must also output a corresponding variable for a current as variable. If, on the other hand, a torque is transmitted from the converter 14 as a control variable to the output device 13, the detector device 12 must also output a corresponding variable for a setpoint value of a torque.FIG. 4 shows symbolically as a continuous line a current or voltage profile in the on-board power supply system 10, as is obtained from interference-free base signal with superimposed interference signal. The signal profile of a current or voltage profile in the on-board power supply system 10 is shown as a dashed line profile, as would result from the control of the output device 13 only with the variable output by the detector device 12 corresponding to the compensation signal.The current or voltage characteristic output by the output device 13 in FIG. 1 can be, for example, a current or voltage characteristic for driving the electric motor 3, as is obtained from a driving by superposition of the control variable corresponding to the predefined torque M from the converter 14 and the variable corresponding to the compensation signal from the detector device 12. For this purpose, the control variable output by the converter 14 can be superimposed, for example, in a superimposing device 15 on the variable output by the detector device 12 in order to obtain the manipulated variable for the output device 13. For example, the two quantities of converter 14 and detector device 12 can be added in superposition device 15. The manipulated variable obtained by superposition of the two variables can then be fed to the output device 13.Thus, with corresponding actuation of the output device 13 within the on-board power supply system 10, the originally occurring interference components, as would occur with the control variable output by the converter 14 alone, are minimized or, in the best case, completely compensated.When determining the variable output by the detector device 12 which is to be superimposed on the control variable output by the converter 14, the detector device 12 can take account of the known system parameters of the on-board power supply system 10 or of the overall system and also enter into the calculation process for the compensation signal. Thus, for example, known parasitic inductances, capacitances, but also parameters such as intermediate circuit capacitance or internal resistance of an energy store can also be included in the calculation process.Additionally or alternatively, the determination of a suitable compensation signal for the compensation of the disturbing components occurring can also be continuously adapted to the disturbing components according to the measured values from the measuring device 11 and in this way an adjustment can take place. By means of such an adaptation, it is possible at any point in time to detect interference components occurring in the on-board power supply system 10 promptly and to compensate the interference components directly by superimposing with suitable current or voltage profiles. For example, a compensation signal can be iteratively adapted for this purpose in order to successively adapt the current or voltage profile in the on-board power supply system 10 in such a way that it optimally counteracts the detected interference component. Other methods for flexibly adapting the compensation signal to the interference component are also possible.The voltage or current signal is output by the output device 13 usually at a predetermined clock rate. That is, the switching elements within the output device 13 are driven at this predetermined clock rate. In this way, pulse width modulation (PWM) based on the predetermined clock rate enables the output of a current or voltage value corresponding to the manipulated variable provided at the output device 13. Clock rates of approximately 10 kHz have been widely used up to now. For the most precise possible output of a current or voltage profile with a superimposed current or voltage profile for compensating interference components, this clock rate can be increased. In order to be able to compensate even sufficiently well for interference components in the range from 1 to 9 kHz, clock rates of 18 kHz or more, preferably 36 kHz or more, are therefore suitable. In any event, the sampling theory according to Shannon must be taken into account when selecting a suitable clock rate. Thus, the clock rate of the output device 13 must be more than twice as high as the frequency of the interference signal to be compensated.The compensation according to the invention of interference frequencies within the on-board power supply system 10 in the event of an energy flow from battery 2 to an electric motor 3 has been described above. In addition, it is also possible to operate a compensation according to the invention of interference signals with a reverse energy flow. In this case, the electric motor 3 functions as a generator, and the output device 13 functions as a rectifier in this case to charge the battery 2.FIG. 5 shows a method 100 for compensating an interference signal in a control device 1 for an electric motor 3. Subsequently, in step 120, interference signals are determined by means of a detector device 12 on the basis of the detected measurement values in the electrical network 10. The interference signals can be interference signals with a single interference frequency, or else interference signals which are composed of a plurality of frequency components.In step 130, a compensation signal is determined by means of the detector device 12 on the basis of the determined interference signal. Finally, in step 140, the output device 13 is driven using the compensation signal.In order to determine the interference signal in the electrical network 10, the step 110 for detecting the measured values can preferably detect a current signal and / or a voltage signal. Since the electrical networks, such as the on-board power supply system of a motor vehicle, already have current or voltage sensors, the required measurement values can be measured in this way without additional complexity.To determine the compensation signal in step 130, the determined interference signal may preferably be inverted, i.e., the sign of the determined interference signal is reversed. In this way, a signal profile for a compensation signal can be obtained particularly easily. This compensation signal is then superimposed on the desired interference-free ideal signal profile for the manipulated variable of the output device 13.To actuate the output device 13, the output signal of the output device 13 is usually output at a predefined clock rate. This clock rate is to be selected to be at least so high that the sampling theory for generating the compensation signal with the required frequency is fulfilled. For this purpose, clock rates of at least 18 kHz, preferably 36 kHz and more, are preferably to be selected.To determine the compensation signal in step 130, the method according to the invention can also take account of the properties of the connected electrical network 10 and also include them in the determination of the compensation signal. Alternatively or additionally, an adaptive or iterative determination of the compensation signal is also possible depending on the detected measured values and the interference signals determined therefrom.In order to determine the compensation signal, in step 130, a disturbance-free signal profile can first be determined or calculated in order to determine the compensation signal. The compensation signal can then be determined on the basis of a comparison of the determined interference signal and the calculated interference-free signal profile.In summary, the present invention relates to a control device for controlling an electric motor with an active compensation of interference signals within an electrical network, such as the on-board power supply system of an electrically driven vehicle. For this purpose, current or voltage profiles are measured and analyzed in a power section of the network in order to determine possible interference signals. Based on this analysis, the setpoint values for the control are adjusted in the power section of the network in order to achieve an active counter-control of the determined interference signals.

Claims

Control device (1) for controlling an electric motor (3), comprising: a converter (14) which is designed to receive a setpoint value (M) and to output a control variable based on the received setpoint value (M); an output device (13) which is designed to convert an electrical voltage provided in the electrical network (10) into a further voltage; a measuring device (11) which is designed to record measured values in the electrical network (10); A detector device (12) which is designed to - determine an interference signal based on the detected measurement values, - output a compensation signal based on the determined interference signal, and - determine the compensation signal taking account of known system parameters of the electrical network (10) and of the overall system, wherein the system parameters taken into account comprise parasitic inductances, capacitances, an intermediate circuit capacitance and an internal resistance of an energy store; wherein the output device (13) is designed to convert the electrical voltage in the electrical network (10) into a further voltage using the control variable output by the converter (14) and the compensation signal output by the detector device (12).Drive device (1) according to Claim 1, having a superposition device (15) which is designed to superimpose the control variable provided by the converter (14) with the compensation signal output by the detector device (12) and to provide it to the output device (13).The driving device (1) according to claim 1 or 2, wherein the output device (13) is configured to convert the voltage provided in the network (10) into a further voltage based on a predetermined clock rate.The driving device (1) according to claim 3, wherein the predetermined clock rate is greater than 18 kHz, preferably greater than 36 kHz.The driving device (1) according to any one of claims 1 to 4, wherein the output device (13) comprises an inverter.Electrically driven vehicle having a drive device (1) according to one of Claims 1 to 5.Electrically driven vehicle according to Claim 6, wherein the measuring device (11) records the measured values in an on-board power supply system (10) of the electrically driven vehicle.Method (100) for compensating an interference signal in a drive device (1) for an electric motor (3) according to one of Claims 1 to 7, having the steps: recording (110) measurement values in the electrical network (10) by means of the measurement device (11); recording (120) an interference signal on the basis of the recorded measurement values by means of the detector device (12); determining (130) a compensation signal on the basis of the recorded interference signal by means of the detector device (12), wherein the compensation signal is determined taking account of known system parameters of the electrical network (10) and of the overall system, and wherein the system parameters taken account comprise parasitic inductances, capacitances, an intermediate circuit capacitance and an internal resistance of an energy store; and driving (140) the output device (13) using the compensation signal determined by the detector device (12).Method according to Claim 8, wherein the step (130) of determining the compensation signal determines a disturbance-free signal profile and determines the compensation signal on the basis of a comparison of the determined disturbance signal and the determined disturbance-free signal profile.

Images