Method of controlling an electric motor

Abstract

The invention relates to a method and a system for controlling at least two electric machines, preferably electric motors, arranged in a vehicle; a first electric machine being controlled by means of a first pulse width modulation control signal having a first signal parameter outputted by a first inverter; at least one second electric machine being controlled by means of at least one second pulse width modulation control signal having a second signal parameter outputted by at least one second inverter; the first signal parameter being outputted from the first inverter to the at least one second inverter via an independent synchronization line; at least one third pulse width modulation control signal having a third signal parameter being modulated by means of the at least one second inverter; the third signal parameter being determined on the basis of the first signal parameter and a predeterminable synchronization parameter; the at least one third being outputted instead of the at least one second pulse width modulation control signal; the first and the at least one third pulse width modulation control signal having a phase relationship which can be predetermined by means of the predeterminable synchronization parameter.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for controlling at least two electric machines, preferably electric motors, arranged in a vehicle, and a system for carrying out such a method. BACKGROUND

[0002] Electric vehicles are known from the prior art, which have a single electric motor of any type as a drive device of the vehicle. Furthermore, solutions are also known in which a plurality of electric motors are arranged in an electric vehicle as drive devices at the same time. In particular, mention should be made in this connection of the arrangement of independent electric motors on the axles of an electric vehicle, the so-called axle drive, or of the arrangement of independent electric motors mounted in the wheels of an electric vehicle, the so-called hub motor.

[0003] Generally, the individual electric motors each have an independent inverter, which converts a DC voltage from a DC voltage source, such as a battery or a fuel cell, into an AC voltage for operating the electric motor. For example, a corresponding input from a driver of an upper engine controller is output as a power signal comprising data relating to the power to be provided by the electric motor to the individual inverters, which output control signals to the electric motors to be controlled in response thereto. It is known here that these control signals are output in the form of pulse width modulation signals (PWM signals).

[0004] The above-mentioned pulse width modulation control signals output by the inverters to the electric motors run freely in relation to one another or to one another on a time scale, wherein the (time) offset, also called phase shift, is variable and not controlled. This leads to a random congruence or phase shift of the individual control signals in relation to one another. In this case, high ripple currents (current ripple factor) can occur, in particular in the case of a high congruence or low phase shift of the PWM signals. High ripple currents are problematic in particular for the battery / fuel cell and the remainder of the on-board power supply system, since a power loss is generated via the equivalent series resistance (ESR), which is converted into heat. The entire system or individual components must therefore be designed so that they function under the occurring ripple voltage and remain functional over a longer period of time. SUMMARY

[0005] It is therefore an object of the present invention to provide a method and a corresponding system by means of which the above-mentioned disadvantages of the prior art can be eliminated.

[0006] The core idea of the present invention is a method for controlling at least two electric machines, preferably electric motors, arranged in a vehicle, comprising the following steps:

[0007] a) receiving a power signal output by an upper control device by means of a first inverter and at least one second inverter;

[0008] b) outputting a first pulse width modulation control signal having a first signal parameter to a first electric machine by means of a first inverter and at least one second pulse width modulation signal having a second signal parameter to at least one second electric machine by means of at least one second inverter, wherein the control signal is modulated on the basis of the power signal;

[0009] c) outputting at least one synchronization signal comprising a first signal parameter to at least one second inverter by means of a first inverter;

[0010] d) modulating at least one third pulse width modulation control signal having a third signal parameter by means of at least one second inverter, wherein the third signal parameter is determined on the basis of the first signal parameter and a predeterminable synchronization parameter;

[0011] e) outputting at least one third pulse width modulation control signal having a third signal parameter to at least one second electric machine by means of at least one second inverter, wherein the first pulse width modulation control signal and the at least one third pulse width modulation control signal have a phase relationship which is predeterminable by means of a predeterminable synchronization parameter.

[0012] The method serves for controlling at least two electric machines which are arranged in a vehicle, wherein the exact number is variable. The method is preferably used for controlling at least three electric machines, more preferably at least four electric machines, particularly preferably at least six electric machines. The electric machines are preferably electric motors. The same applies to the inverters, wherein at least three inverters are preferably provided, more preferably at least four inverters, particularly preferably at least six inverters. Preferably, the electric motors are designed as alternating current electric motors or three-phase electric motors, wherein particularly preferably synchronous electric motors or asynchronous electric motors are provided. Further preferably, the electric machines controlled by the method are arranged in a hybrid vehicle or an electric vehicle having an internal combustion engine and electric motors, wherein the vehicle can be, for example, a passenger car or a truck. Preferably, the electric machines represent the drive of the vehicle, and preferably each electric machine is mechanically connected to an axle of the vehicle (axle drive) or is mounted in a wheel of the vehicle (wheel hub motor). Preferably, each electric machine is controlled by means of an independent inverter or is at least connected in terms of signal technology to its own inverter, preferably in a power electronic manner.

[0013] The superordinate control device according to the application can be, for example, an engine controller which, among other things, takes over the control, regulation and monitoring of the engine function, or an inverter controller which exclusively controls the inverter. These can preferably be microprocessors or microcontrollers. Preferably, the superordinate control device receives inputs from the driver, such as the start-up or the required power, among other things, and passes these on to the electric machine or the inverter by means of a power signal, the electric machine or the inverter providing an AC voltage for operating the electric machine from a DC voltage of a DC voltage source, such as a battery or a fuel cell. This power signal sent by the superordinate control device to the inverter controlling / operating the electric machine usually comprises the data or parameters required by the inverter to output corresponding control signals to the electric machine, including, for example, an indication of the required power / load that the electric machine is to provide and that the inverter is to convert into control signals, or already parameters of the control signals, such as the frequency, the duty cycle, the period duration, etc. The first control signal and the at least one second control signal are thus modulated on the basis of the power signal or the data comprising the power signal, wherein this is known as pulse width modulation (see below).

[0014] The inverter according to the application is preferably connected to the electric machine, to the voltage source, preferably a DC voltage source, such as a battery or a fuel cell, at least in terms of signal technology, preferably in terms of power electronics, and to the superordinate control device at least in terms of signal technology. The connection in terms of power electronics is understood to mean a connection by means of which power is also transmitted to the signal or together with the signal. Preferably, the inverter is an inverter known from the prior art which is suitable for providing the DC voltage of the voltage source as an AC voltage for operating the electric machine.

[0015] The pulse width modulation control signal according to the present application is understood to mean a signal which is transmitted from an inverter to a motor, which inverter is connected to the motor at least in terms of signal technology, preferably in terms of power electronics, and is designed to control the motor, wherein the power generated by the motor is set or controlled via the pulse width modulation control signal. Pulse width modulation (PWM) is a type of modulation in which a voltage, current, etc. is varied between two fixed values at a fixed frequency. The information to be transmitted is contained in the duty cycle. The period of the pulse width modulation consists of a pulse and a pause. The degree of modulation is expressed in the duty cycle percentage of the pulse length to the cycle duration (pulse + pause). Usually, one of the two edges of the PWM signal is fixed, while the position of the other edge is variable by means of modulation. Thus, the PWM signal can be generated with modulation starting from the rest edge ("edge-aligned", e.g. left edge / rising edge or right edge / falling edge ("right-aligned")), or, starting from the center point of the signal, both edges are modulated ("center-aligned"). Thus, for pulse width modulation, at least one reference point must be known, wherein the reference point is preferably the time at which the corresponding edge or center point of the signal occurs. The generation and application of pulse width modulation signals are sufficiently known to the person skilled in the art of the prior art, which is why they are not discussed in more detail here.

[0016] In this case, the signal parameter is understood to mean a characteristic parameter of the associated pulse width modulation control signal. Preferably, the PWM signal is a voltage which is varied between two time values. Further preferably, the signal parameter can be the point in time at which an edge or center point of the PWM signal occurs (one could say the position of the edge or center point), the duty cycle / pulse duty factor, the cycle duration, the pulse duration, the pause duration, the voltage, the current and / or the frequency.

[0017] The predeterminable synchronization parameter according to the application reflects a phase shift, also referred to as phase difference or phase angle, to be present between the first pulse width modulation control signal and the at least one second pulse width modulation control signal. This is preferably a phase shift angle, a phase shift time, a phase shift length, etc. The third signal parameter of the third pulse width modulation control signal can thus preferably be determined or calculated on the basis of the first signal parameter of the first pulse width modulation control signal and the predeterminable synchronization parameter, and the at least one third pulse width modulation control signal, instead of the at least one second pulse width modulation control signal, can be output by the at least one second inverter, while the first inverter also outputs the first pulse width modulation control signal with the first signal parameter, so that the first pulse width modulation control signal and the at least one third pulse width modulation control signal have a predeterminable phase relationship. In this case, the synchronization parameter is predeterminable or adjustable and can preferably be changed as required, even during operation of the vehicle or the electric machine, as a result of which the desired phase shift between the first pulse width modulation control signal and the at least one second pulse width modulation control signal can be variably adjusted by the output of the at least one third control signal with the third signal parameter instead of the output of the at least one second control signal with the second signal parameter.

[0018] By means of the method according to the application, the phase shift or phase relationship between the pulse width modulation control signal output by the first inverter and the at least one pulse width modulation control signal output by the at least one second inverter can be adjusted, which is referred to as synchronization according to the application. This has the advantage that, as a result, the intermediate circuit current is distributed over the period of the PWM signals, resulting in a higher effective frequency of the accommodated intermediate circuit capacitor. This in turn results in the need for a lower intermediate circuit capacitance, preferably only half of the intermediate circuit capacitance, and a significantly reduced occurring ripple current compared to pulse width modulation control signals running freely relative to one another. As a result, the ripple load in the on-board electrical system and the demand on the capacitors are reduced, so that component costs can be saved.

[0019] The first inverter can thus be referred to as "master", which outputs its first signal parameter to the at least one second inverter, the so-called "slave". In this case, the master inverter can be set once, for example during production of the vehicle, or when the vehicle is started up, when the position of master or slave is redistributed. This can be achieved, for example, by the respective master signal being sent from one inverter to the other inverter present to the current master inverter. The slave inverter or at least one second inverter preferably follows the specifications of the master inverter or first inverter.

[0020] According to a preferred embodiment, the predeterminable synchronization parameter is present as stored information retrievable by the at least one second inverter. Preferably, the predeterminable synchronization parameter is output by the superordinated control device to the at least one second inverter. The inverter preferably comprises a storage unit or has access to a storage unit storing the synchronization parameter. The synchronization parameter is preferably variably settable and changeable. More preferably, the superordinated control device comprises a storage unit or has access to a storage unit storing the synchronization parameter and can transmit it to the at least one second inverter. The synchronization parameter is preferably variably settable. The synchronization parameter can preferably be provided as stored information to the at least one second inverter or can be output directly from the superordinated control device to the at least one second inverter (e.g. via a power signal which can comprise the synchronization parameter) or also indirectly via the first inverter which transmits the synchronization parameter to the at least one second inverter via the synchronization line by means of the synchronization signal. In this way, depending on the case, the phase relationship or the displacement can be adjusted by setting the synchronization parameter, so that the ripple current is correspondingly reduced.

[0021] According to a preferred embodiment, the plurality of synchronization parameters is present as retrievable stored information, wherein the synchronization parameter used for determining the third signal parameter is selected from the plurality of synchronization parameters depending on the power signal and / or the first pulse width modulation control signal and / or the second pulse width modulation control signal. Preferably, the second inverter, the first inverter and / or the superordinate control device can select from the plurality of stored synchronization parameters for determining the third signal parameter. Preferably, the synchronization parameter used for determining the third signal parameter is selected from the plurality of synchronization parameters depending on the power signal and / or the first pulse width modulation control signal and / or the second pulse width modulation control signal. Further preferably, the synchronization parameter used for determining the third signal parameter is selected from the plurality of synchronization parameters depending on the power or the load of the electric machine, wherein the power and the load of the electric machine are determined via the power signal and / or the pulse width modulation control signal. Further preferably, the synchronization parameter used for determining the third signal parameter from the plurality of synchronization parameters depends on the frequency, the duty cycle and / or the voltage specified by the power signal to the inverter and / or output from the inverter to the electric machine by the pulse width modulation control signal, which preferably determines the power of the electric machine. It has been found that for each power or load and the corresponding duty cycle, frequency and / or voltage, there is a synchronization parameter or a value of a synchronization parameter which leads to a ripple current which is caused. It is therefore conceivable that, preferably by experiment (for example on a test bench) and / or by simulation, for each power / load or each duty cycle, each frequency, each voltage and / or the corresponding range, a synchronization parameter is determined in advance which leads to a minimum ripple current in the power / load or the duty cycle, the frequency and / or the voltage, wherein these synchronization parameters are stored as retrievable for the second inverter, the first inverter and / or the superordinate control device. In this way, a plurality of stored synchronization parameters can be obtained, which can also be referred to as reference values, which can be selected depending on the power signal and / or the first pulse width modulation control signal and / or the second pulse width modulation control signal, wherein the selection of the synchronization parameter is preferably carried out depending on the duty cycle, the frequency and / or the voltage of the pulse width modulation control signal or the duty cycle, the frequency and / or the voltage provided for the pulse width modulation control signal. It can therefore advantageously be assumed that the predetermined synchronization parameters are assigned and / or will be assigned to each duty cycle, each frequency and / or each voltage or each predetermined range of the duty cycle, the frequency and / or the voltage. In this case, the selection of the synchronization parameter used for determining the third signal parameter from the plurality of synchronization parameters can preferably be understood as specifying the synchronization parameter.

[0022] According to a preferred embodiment, the signal parameters and the synchronization parameter represent time values, wherein the signal parameters each indicate a time of an edge or a center point of the respective pulse width modulation control signal, and wherein the synchronization parameter specifies a phase shift time or a phase shift angle. Preferably, the phase shift time and the phase shift angle can be converted into each other in a known manner (phase shift angle / 360° = phase shift time / period duration). Thus, the third signal parameters can be determined in a simple manner on the basis of the first signal parameters and the synchronization parameter.

[0023] Preferably, the determination of the third signal parameters is based on the first signal parameters and the pre-determinable synchronization parameter by means of adding the time points indicated by the first signal parameters and the phase shift time indicated by the synchronization parameter. It can be provided preferably that the phase shift angle reproducible by the synchronization parameter is first converted into a phase shift time.

[0024] According to a preferred embodiment, the value of the phase shift angle is in the range of ± 180° or the value is in the range of ± (90° to 120°). Furthermore, it is conceivable that the value of the phase shift angle is in the range of ± π (pi). Within said angle ranges of the phase shift angle of the synchronization parameter, the resulting ripple current can be effectively reduced. It has been shown that within these angle ranges a minimum of the resulting ripple current can be achieved.

[0025] According to a preferred embodiment, the phase shift time indicated by the synchronization parameter is divided into at least two phase shift time segments, wherein steps d) and e) of each of the at least two phase shift time segments are carried out individually one after the other to ensure a stepwise transition from the at least one second pulse width modulation control signal to the at least one third pulse width modulation control signal. The larger the phase shift time or the phase shift angle, the more phase shift time segments the latter is divided into to ensure a transition from the at least one second pulse width modulation control signal to the at least one third pulse width modulation control signal as smooth as possible and to prevent sudden signal changes and corresponding power changes of the at least one second machine.

[0026] According to a preferred embodiment, the first inverter and the at least one second inverter each have a clock generator, wherein the clock generator of the at least one second inverter is adjusted on the basis of the first signal parameters and the synchronization parameter before, during or after step d) to ensure a clock synchronization of the first inverter and the at least one second inverter for outputting the pulse width modulation control signals. Clock generators specify the working frequency of clock-dependent peripherals and processors and are known from the prior art. By adjusting the clock generator of the at least one second inverter on the basis of the first signal parameters and the synchronization parameter, its working frequency can be adjusted or synchronized to the working frequency of the first inverter or the clock generator of the first inverter.

[0027] According to a preferred embodiment, the synchronization signal is output from the first inverter to the at least one second inverter via an independent synchronization line, which connects the first inverter and the at least one second inverter in terms of signal technology. The independent synchronization line is preferably a push-pull line, a single-ended line or a radio link. It is particularly preferred that the synchronization line is a connection which enables communication between the first inverter and the at least one second inverter in the nanosecond range. It is further preferred that a bidirectional connection between the first inverter and the at least one second inverter is established via the independent synchronization line. In this way, signals can be transmitted from the first inverter to the at least one second inverter and vice versa, as a result of which, for example, a so-called handshake can be performed and the existing inverters recognize one another and possible defects on the synchronization line can be detected, error messages can be transmitted. It is also conceivable that the independent synchronization line is exclusively used for transmitting the synchronization signal.

[0028] It is preferred that the first inverter (master) is connected to the at least one second inverter (slave) or to each existing second inverter (slave) via an independent synchronization line at least in terms of signal technology, whereby the first inverter can output the synchronization signal to each provided second inverter via the respective synchronization line (direct synchronization signal transmission). As a result, the first inverter will thus be connected to each second inverter via an independent synchronization line at least in terms of signal technology, wherein the existing second inverters will not be connected to one another in terms of signal technology by means of a synchronization line. In this way, fast and simple signal transmission can be achieved. It is however also conceivable that the first inverter is connected to only one second inverter or to two second inverters in terms of signal technology by means of a synchronization line and the second inverters are connected to one another in terms of signal technology via an independent synchronization line by means of at least one, preferably at least two, more preferably exactly two further second inverters. Thus, the synchronization signal can be output from the first inverter to a second inverter which is connected to the first inverter in terms of signal technology by means of a synchronization line and via the second inverter to at least one further second inverter which is connected to the second inverter in terms of signal technology via a synchronization line (indirect synchronization signal transmission), wherein the synchronization signal comprises in each case a first signal parameter of the first pulse width modulation control signal. In this way, material and costs can be saved. It is furthermore also conceivable to design the synchronization line as a radio link, wherein each existing inverter has a respective transceiver unit by means of which the synchronization signal can be output and / or received.

[0029] Preferably, when the vehicle is started, preferably by means of the output of an initialization signal, a handshake between the existing (first and second) inverters can be carried out via the respectively provided synchronization lines, wherein, when it is determined that one inverter cannot handshake with the connected inverter, an error message is output to the superior control device, i.e. a handshake via the respective synchronization line is not possible and thus synchronization cannot take place. As a result, an error message from both inverters connected via the synchronization lines, i.e. a handshake is not possible or the transmission of the initialization signal is not possible, can lead to the conclusion that the respective synchronization line is defective. In the presence of a defective synchronization line, the transmission of the synchronization signal to the respective inverters can preferably be attempted via indirect synchronization signal transmission. Further preferably, a handshake or initialization signal transmission between the specified inverters takes place before or during step a).

[0030] According to a preferred embodiment, steps b) and c) are carried out simultaneously or one after the other immediately. In this way, it can be ensured that the first inverter and the at least one second inverter are converted into the synchronized state as quickly as possible or that the phase relationship between the first PWM control signal and the at least one third PWM control signal is set.

[0031] According to a preferred embodiment, the first inverter is operated at an adjustable switching frequency, which is detected by the at least one second inverter and adopted by the latter. In this way, on the one hand, the switching frequency of the first inverter or of the circuit breaker of the first inverter can be variably adjusted, wherein the switching frequency of the first inverter is detected by the at least one second inverter, preferably by means of a suitable sensor, and the detected or detected switching frequency of the first inverter itself or is switched over to the switching frequency of the first inverter is adopted. The variable adjustment of the switching frequency of the first inverter can preferably be carried out with a switching control strategy, wherein corresponding switching control strategies with variable frequency are known from the prior art. It is thus also possible to ensure frequency synchronization with regard to the control signals of the inverters.

[0032] Furthermore, the object is achieved by a system for carrying out the method, comprising a first electric machine and at least one second electric machine, a superior control device, a first inverter and at least one second inverter, wherein the first inverter and the at least one second inverter are connected via independent synchronization lines in terms of signal technology.

[0033] The above statements and features relating to the method according to the invention are also intended to apply by analogy to the system according to the invention and vice versa. BRIEF DESCRIPTION OF DRAWINGS

[0034] Further objects, advantages and facilities of the present invention can be found in the following description taken in conjunction with the accompanying drawings. The drawings show:

[0035] Figure 1System according to the preferred embodiment of the application;

[0036] Figure 2a d: various system parts according to the preferred embodiment of the application;

[0037] Figure 3 Flow chart of a method according to the preferred embodiment of the application. DETAILED DESCRIPTION

[0038] Figure 1 A system 1000 according to the preferred embodiment of the application is shown. The system 1000 is preferably arranged completely in a vehicle, wherein the vehicle and other components are not shown for reasons of clarity.

[0039] The system 1000 comprises a superior control device 1 which is connected at least in signal technology to a first inverter 2 and a second inverter 3. The first inverter 2 is further connected at least in power electronics to a first electric machine 4, the second inverter 3 is connected at least in power electronics to a second electric machine 5. According to the shown embodiment, two inverters 2, 3 and two electric machines 4, 5 are provided in each case, the two electric machines being connected in signal technology with the two inverters, wherein the number of inverters and inverters connected thereto at least in signal technology is variable.

[0040] The superior control device 1 is designed to output a power signal to the first inverter 2 and the second inverter 3, on the basis of which a first pulse width modulation control signal having a first signal parameter is modulated by the first inverter 2 and output to the first electric machine 4, a second pulse width modulation control signal having a second signal parameter is modulated by the second inverter 3 and output to the second electric machine 5.

[0041] Furthermore, the first inverter 2 and the second inverter 3 are connected at least in signal technology by a preferably bidirectional synchronization line 6. In this case, the first inverter is designed to transmit a synchronization signal comprising the first signal parameter of the first pulse width modulation control signal to the second inverter via the synchronization line 6. The synchronization line is preferably designed to ensure the transmission of the synchronization signal in the nanosecond (ns) range. For example, the synchronization line is designed as a push-pull line, a single-ended line or a radio link. According to this embodiment, the first inverter 2 is provided as master, the second inverter 3 is provided as slave, wherein the pulse width modulation control signal output by the second inverter 3 is synchronized with the first pulse width modulation control signal output by the first inverter 2 by means of the synchronization signal, or a phase relationship or a phase shift is set.

[0042] Furthermore, the second inverter 3 is designed to modulate a third pulse width modulation control signal having a third signal parameter on the basis of the received first signal parameter and a synchronization parameter and to output this third pulse width control signal instead of the second pulse width modulation control signal, while the first pulse width modulation control signal continues to be output by the first inverter. The synchronization parameter preferably specifies a predeterminable or adjustable phase shift angle or phase shift time, by means of which a desired phase relationship or phase shift between the first pulse width modulation control signal and the third pulse width modulation control signal can be set.

[0043] Figure 2a - d shows different preferred embodiments of an arrangement of inverters and electric machines which can be used in a system according to the application and which are suitable for implementing the method according to the application. Figure 1 The reference signs in Figure 2a - d are used analogously in Figure 1 The description of the system shown in Figure 2a - d is made with the necessary modifications for the system shown in

[0044] Figure 2a - d shows parts of the system, including the electric machines 4, 5, the inverters 2, 3 and the synchronization line 6, respectively.

[0045] In this case, Figure 2a A system with one first inverter 2 and one second inverter 3 is shown, wherein the first inverter 2 is connected power electronically to a first electric machine 4 and the second inverter 2 is connected power electronically to a second electric machine 5. The first inverter 2 and the second inverter 3 are connected at least in terms of signal technology by means of a synchronization line 6. The first inverter 2 and the second inverter 3 are arranged in separate housings and operate in separate intermediate circuits. It can thus be said to be two separate drives. This arrangement corresponds to the arrangement in Figure 1

[0046] Figure 2b A system with one first inverter 2 and one second inverter 3 is shown, wherein the first inverter 2 is connected power electronically to a first electric machine 4 and the second inverter 2 is connected power electronically to a second electric machine 5. The first inverter 2 and the second inverter 3 are connected at least in terms of signal technology by means of a synchronization line 6. The first inverter 2 and the second inverter 3 are arranged in separate housings and operate in separate intermediate circuits. It can thus be said to be two separate drives. This arrangement corresponds to the arrangement in

[0047] Figure 2c ​A first inverter 2 is shown, which is connected to a first electric machine 4 in a power electronic manner, and a second inverter 3, which is connected to a second electric machine 5 in a power electronic manner. The first inverter 2 and the second inverter 3 are connected at least in terms of signal technology by means of a synchronization line 6. The first inverter 2 and the second inverter 3 are each arranged in separate housings and operate in separate intermediate circuits. This can be two e-axes, front and rear axes, each with a separate drive.

[0048] Figure 2d A first inverter 2 is shown, which is connected to a first electric machine 4 in a power electronic manner, and three second inverters 3, each of which is connected to a second electric machine 5 in a power electronic manner. The first inverter 2 is connected to the three second inverters 3 in each case at least in terms of signal technology by means of a synchronization line 6. The first inverter 2 outputs a synchronization signal to each of the three second inverters 3. It is also envisaged that the second inverters 3 are likewise connected to one another by means of a synchronization line. This can be two e-axes, front and rear axes, each with two separate drives.

[0049] Figure 3 A flowchart of a method 100 for controlling at least two electric machines 4, 5 arranged in a vehicle according to a preferred embodiment of the application is shown.

[0050] In a step S1 corresponding to step a), the superordinate control device 1, preferably an engine controller, outputs a power signal, which is received by the first inverter 2 and the at least one second inverter 3.

[0051] In a subsequent step S2 corresponding to step b), a first pulse width modulation control signal having a first signal parameter is output by the first inverter 2 to the first electric machine 4 and a second pulse width modulation control signal having a second signal parameter is output by the at least one second inverter 3 to the second electric machine 5 on the basis of the power signal or data / parameters containing the power signal.

[0052] In a step S3 corresponding to step c), a synchronization signal comprising the first signal parameter is output from the first inverter 2 to the at least one second inverter 3 via the synchronization line 6 directly after step S2 or during step S2.

[0053] After step S3, according to step S4 corresponding to step d), at least one third pulse width modulation control signal having a third signal parameter, instead of the second pulse width modulation control signal, is modulated by the at least one second inverter and output by the at least one second inverter. In this case, the third signal parameter is determined on the basis of the first signal parameter and a synchronisation parameter which can be predetermined. The synchronisation parameter can preferably be used as stored information for the at least one second inverter, or can be output directly from the superior control device 1 to the at least one second inverter 3, for example via a power signal which can comprise the synchronisation parameter, or can also be output indirectly via the first inverter 2, which transmits the synchronisation parameter to the at least one second inverter 3 via the synchronisation line 6 by means of a synchronisation signal.

[0054] In a next step S5, according to step e), the at least one third pulse width modulation control signal having the third signal parameter, instead of the second pulse width modulation control signal having the second signal parameter, is output by the at least one second inverter 3 to the at least one second electric machine 5. By modulating the at least one third pulse width modulation control signal having the third signal parameter on the basis of the first signal parameter and the synchronisation parameter, it is possible to set or predetermine a phase relationship or phase shift between the first pulse width modulation control signal and the at least one third pulse width modulation control signal.

[0055] The various embodiments having all features can be combined and exchanged as desired.

[0056] All features disclosed in this application document are considered to be essential features of the invention, as long as they are novel, either individually or in combination, with respect to the prior art.

[0057] List of reference signs

[0058]

Claims

1. A method for controlling at least two electric machines (4, 5) arranged in a vehicle, comprising the following steps: a. receiving a power signal output by a superior control device (1) by a first inverter (2) and at least one second inverter (3); b. outputting a first pulse width modulation control signal with a first signal parameter by the first inverter (2) to a first electric machine (4) and at least one second pulse width modulation control signal with a second signal parameter by the at least one second inverter (3) to at least one second electric machine (5), wherein the control signals are modulated based on the power signal; c. outputting at least one synchronization signal comprising the first signal parameter by the first inverter (2) to the at least one second inverter (3); d. modulating at least one third pulse width modulation control signal with a third signal parameter by the at least one second inverter (3), wherein the third signal parameter is determined based on the first signal parameter and a pre-determinable synchronization parameter; e. outputting the at least one third pulse width modulation control signal with the third signal parameter by the at least one second inverter (3) to the at least one second electric machine (5), wherein the first pulse width modulation control signal and the at least one third pulse width modulation control signal have a phase relationship which is pre-determinable by the pre-determinable synchronization parameter, wherein the first signal parameter, the second signal parameter, the third signal parameter and the synchronization parameter represent time values, wherein the first signal parameter, the second signal parameter, the third signal parameter each indicate a time of an edge or a center point of the corresponding pulse width modulation control signal, and wherein the synchronization parameter specifies a phase shift time or a phase shift angle, wherein the phase shift time indicated by the synchronization parameter is divided into at least two phase shift time segments, wherein steps d) and e) are each individually performed for each of the at least two phase shift time segments to ensure a stepwise transition from the at least one second pulse width modulation control signal to the at least one third pulse width modulation control signal.

2. The method according to claim 1, characterized in that the pre-determinable synchronization parameter is present as retrievable stored information of the at least one second inverter (3) and / or the pre-determinable synchronization parameter is output by the superior control device (1) to the at least one second inverter (3).

3. The method according to claim 1, characterized in that a plurality of synchronization parameters is present as retrievable stored information, wherein the synchronization parameter for determining the third signal parameter is selected from the plurality of synchronization parameters depending on the power signal and / or the first pulse width modulation control signal and / or a second pulse width modulation control signal.

4. The method according to claim 1, characterized in that the phase shift angle has a value in the range of ± 180° or a value in the range of ± (90° to 120°).

5. The method according to any of the preceding claims 1 to 4, characterized in that ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The first inverter (2) and the at least one second inverter (3) each have a clock generator, wherein the clock generator of the at least one second inverter (3) is adjusted on the basis of the first signal parameter and a synchronization parameter before, during or after step d) to ensure clock synchronization of the first inverter (2) and the at least one second inverter (3) outputting pulse width modulation control signals.

6. The method according to any of the preceding claims 1 to 4, characterized in that The synchronization signal is output by the first inverter (2) to the at least one second inverter (3) via an independent synchronization line (6) which connects the first inverter (2) and the at least one second inverter (3) in terms of signal technology, wherein the independent synchronization line (6) is a push-pull line, a single-ended line or a radio link, and wherein a bidirectional connection is established between the first inverter (2) and the at least one second inverter (3) via the independent synchronization line (6).

7. The method according to any of the preceding claims 1 to 4, characterized in that Steps b) and c) are carried out simultaneously or immediately consecutively.

8. The method according to any of the preceding claims 1 to 4, characterized in that The first inverter (2) is operated with an adjustable switching frequency which is detected by the at least one second inverter (3) and adopted by the at least one second inverter (3).

9. A system for carrying out the method according to any of claims 1 to 8, comprising a first electric machine (4) and at least one second electric machine (5), a superordinate control device (1), a first inverter (2) and at least one second inverter (3), wherein the first inverter (2) and the at least one second inverter (3) are connected in terms of signal technology via an independent synchronization line (6).

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