Method for determining an initial rotor position of a rotor, computer program product, control unit, electric machine, inspection and / or test method and test stand

Abstract

The invention relates to a method for determining an initial rotor position of a rotor (1) of an electric machine (2), in particular a synchronous electric machine.

Description

[0001] Method for determining an initial rotor position of a rotor, computer program product, control unit, electrical machine, inspection and / or test method and test bench

[0002] The present invention relates to a method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine. The invention further relates to a computer program product, a control unit, an electrical machine, a testing and / or testing method for testing an electrical machine in a test bench, and a test bench for performing a testing and / or testing method for testing an electrical machine.

[0003] Electric motors are increasingly being used to power motor vehicles, creating alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday suitability of electric drives and also to provide users with the same level of driving comfort they are accustomed to.

[0004] In electric motors, the relative positioning of the parts through which the magnetic field flows is also very important. This applies both to the mechanical structure of the electric motor, which holds the parts and positions them precisely, and to precise knowledge of the angular position of the rotating parts. This is because the constantly changing position of the magnets integrated into the rotating rotor (angular position) relative to the magnet integrated into the stator as the motor rotates must always be precisely known in order to control the electric motor correctly. The changing angular position of the rotor must be precisely known at all times in order to determine the alignment of the rotor components (e.g., the rotor magnets, which are usually permanent magnets) relative to the stator components (e.g., the stator magnets, which are usually electromagnets) and to be able to adjust the motor control accordingly.

[0005] The control of such an electric motor is achieved by imposing a rotating field in the motor windings. Depending on the rotor position angle, the rotating field must be adjusted via a control system. Typically, the rotor position is measured using a rotor position sensor, and the determined rotor position angle is transmitted to the electric motor control system.

[0006] However, to save costs and space, sensorless control systems have also become known that do without a physical rotor position sensor. These systems rely solely on current sensors, which are indispensable for field-oriented control anyway. This control concept, which is particularly widespread in three-phase permanent-magnet synchronous machines, is based on transforming the three-phase alternating variables into a two-axis coordinate system that rotates synchronously with the machine's rotor flux. In such a coordinate system, commonly referred to as a d / q coordinate system, the three phase currents of the stator winding i_u, i_v, i_w, for example, are represented by a two-dimensional current vector with the components i_q and i_d.With an ideal sinusoidal rotor flux and ideal sinusoidal phase currents, the original alternating quantities i_u, i_v, i_w are mapped to equal quantities i_q, i_d as a result of the rotor flux-synchronous rotating coordinate system.

[0007] In field-oriented current control, the voltage or current values ​​of the phases of the synchronous machine's stator are transformed in a known manner into a two-dimensional coordinate system, whose mutually perpendicular axes are usually denoted by d ("direct") and q ("quadrature"). This coordinate system rotates relative to the synchronous machine's stator and is stationary relative to the synchronous machine's rotor. The transformation itself is called the Park transformation, and the two-dimensional coordinate system to which the transformation is performed is called the Park coordinate system. The Park transformation can be performed via the intermediate step of an equally well-known Clarke transformation, which transforms the voltage or current values ​​of the phases of the synchronous machine's stator into a two-dimensional, orthogonal coordinate system that is stationary relative to the stator.In sensorless operation of an electric motor, as mentioned above, the rotor position sensor, which is usually used to determine the current rotor angle, is omitted. Current sensor signals and measured or estimated phase voltages, for example, are used to infer the rotor position and speed of the motor using a model. Below a speed threshold of the absolute speed, it is necessary to feed in so-called injection signals, which support the identification of the rotor position and speed in this speed range. Starting with a stationary rotor, the rotor position must be determined using an initialization routine.

[0008] The initial rotor position can be determined by applying an alternating voltage excitation, a high-frequency oscillation in d- and q-voltage, for a specific number of points on a voltage circular path, where the exciting voltage amplitude results in a resulting current amplitude. Due to the d-q coordinates, an ellipse must be formed in the dq-plane for a circular excitation in the voltage and current. The major axis of the ellipse corresponds to the d-direction. This direction of the major axis thus describes the initial value of the rotor position.

[0009] One way to determine the initial rotor position is to move to several points on the circular path, which results in several points on an ellipse. From these points, the angular position of the semi-axes of the ellipse must then be deduced. If many points are selected, the result is more accurate, but it takes a certain amount of time, since each point must be approached and evaluated with a different amplitude in the d and q directions. If fewer points are selected, the process is accelerated, but the result may then be inaccurate because the angular position of the semi-axes cannot be determined as accurately from the few points. The measured data during evaluation is subject to a certain amount of noise, which ultimately distorts the result.

[0010] The object of the invention is therefore to provide an improved - in particular faster and more accurate - method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine. It is further the object of the invention to realize a computer program product for carrying out an improved method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine. It is also the object of the invention to develop a control unit for carrying out an improved method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine. Finally, it is also the object of the invention to provide an improved electrical machine.The object of the invention is also to realize an improved inspection and / or test method for checking an electrical machine in a test bench and an optimized test bench for carrying out an inspection and / or test method for checking an electrical machine.

[0011] This object is achieved by a method for determining an initial rotor position of a rotor of an electrical machine, in particular a synchronous electrical machine, comprising the following steps: a) Providing an electrical machine with a stationary rotor, b) Providing a starting value d_est, which represents a first angle of the rotor position, c) Generating a three-phase alternating voltage excitation in the electrical machine by specifying an alternating voltage in the d_est direction, d) Converting the three-phase current response to the alternating voltage excitation of the electrical machine for a first modified value d_est-45° into a first alternating current component i_[d_est-45°], e) Converting the three-phase current response to the alternating voltage excitation of the electrical machine for a second modified value d_est+45° into a second alternating current component i_[d_est+45°],f) Calculating the length of a first alternating current vector having d and q components for the first alternating current component i_[d_est-45°], g) Calculating the length of a second alternating current vector having d and q components for the second alternating current component i_[d_est+45°], h) Determining the difference in the absolute values ​​of the lengths between the first alternating current vector and the second alternating current vector according to delta_i = | i_d_est+45° | -| i_d_est-45° | , i) If the condition is met that the difference in the absolute values ​​of the lengths between the first alternating current vector and the second alternating current vector lies within a defined interval between and a defined error tolerance value FTW, according to delta_i=| i_d_est+45°|-|i_d_est-45°| =[0-FTW], Provision of the initial rotor angle for energizing the electric machine and termination of the process, j) If the condition is met,that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector is delta_i=|i_d_est+45°|-|i_d_est-45°| > 0, k) In the event that |i_d_est+45°|>|i_d_est-45°|, adjusting the starting value d_est such that the angle representing the rotor position is rotated clockwise by a predetermined amount, and l) In the event that |i_d_est+45°|<|i_d_est-45°|, adjusting the starting value d_est such that the angle representing the rotor position is rotated counterclockwise by a predetermined amount, m) repeating steps c)-l).

[0012] This has the advantage that the initial rotor position can be determined particularly quickly and reliably using an iterative method without a physical rotor position sensor. Furthermore, the method according to the invention can also prevent the electric machine from rotating in the wrong direction, even for a short time, during motor operation. At the beginning of the iterative solution algorithm, the first iteration is carried out using a randomly selected starting value for the angle. The three-phase current response to an AC voltage excitation of the system in the assumed d-direction is then converted into dq currents using the known methods. However, this conversion is not carried out using the assumed angle d_est as such, but rather with the modified angle d_est-45°, which corresponds to the assumed angle d_est minus 45°. This results in an AC current component i_(d_est-45°) in this direction.The corresponding currents in the dq plane are also calculated for the assumed angle plus 45°, yielding the alternating current component i_(d_est+45°). Using the difference in the length of the alternating current vector, which has d and q components, the direction of the supposedly "correct" d-axis is adjusted at the end of the iteration. After a few iterations, both vectors i_(d_est-45°) and i_(d_est+45°) are approximately the same length. The d-axis has then been determined, and the initial rotor angle can be read from this direction. This will be explained in more detail using the figures in the design descriptions.

[0013] First, the individual elements of the claimed subject matter of the invention are explained in the order in which they appear in the set of claims, and subsequently particularly preferred embodiments of the subject matter of the invention are described.

[0014] For the purposes of this application, motor vehicles are defined as land vehicles that are propelled by mechanical power without being tied to railway tracks. A motor vehicle can, for example, be selected from the group of passenger cars (PCs), trucks (HGVs), mopeds, light motor vehicles, motorcycles, buses (KOM), or tractors. A hybrid electric vehicle (HEV), also known as a hybrid electric vehicle (HEV), is an electric vehicle powered by at least one electric motor and another energy converter, and draws energy from both its electrical storage device (battery) and an additional fuel carried on board.

[0015] For the purposes of this application, the drive train of a

[0016] Motor vehicle refers to all components in the vehicle that generate the power for driving the vehicle and transmit it to the road via the vehicle wheels.

[0017] An electric machine serves to convert electrical energy into mechanical energy and / or vice versa. In the context of the invention, the electric machine of an axle drive train can be designed as a radial or axial flux machine. To create a particularly compact axle drive train, axial flux machines are preferred.

[0018] An electrical machine typically comprises a stationary part known as a stator, stator, or armature, and a part known as a rotor, which is movable relative to the stationary part. An electrical machine can be designed as a dry-running or wet-running machine.

[0019] The electric machine is intended in particular for use within an electrically operated drive train of a motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds greater than 50 km / h, preferably greater than 80 km / h, and in particular greater than 100 km / h can be achieved. The electric motor particularly preferably has an output greater than 30 kW, preferably greater than 50 kW, and in particular greater than 70 kW. It is further preferred that the electric machine provides rotational speeds greater than 5,000 rpm, particularly preferably greater than 10,000 rpm, and most particularly preferably greater than 12,500 rpm.

[0020] The rotor position sensor is preferably designed as an absolute or relative rotor position sensor for an electric machine. The rotor position sensor preferably provides a sensor signal representing the rotor position. Most preferably, the sensor signal is sent to a control unit for controlling the electric machine.

[0021] An electrical machine may further comprise a control unit. A control unit, as can be used in the present invention, serves in particular for the electronic control and / or regulation of one or more technical systems of the electrical machine. A control unit has, in particular, a wired or wireless signal input for receiving, in particular, electrical signals, such as sensor signals. Furthermore, a control unit preferably also has a wired or wireless signal output for transmitting, in particular, electrical signals.

[0022] Control and / or regulation operations can be performed within the control unit. It is particularly preferred that the control unit comprises hardware configured to execute software. The control unit preferably comprises at least two electronic processors for executing program sequences defined in a respective software. The two processors can also be structurally integrated into a processor as computer cores, with the corresponding computer cores then each representing a processor within the meaning of the invention.

[0023] The control unit may further comprise one or more electronic memories in which the data contained in the signals transmitted to the control unit can be stored and read again. Furthermore, the control unit may comprise one or more electronic memories in which data can be stored in a modifiable and / or non-modifiable manner.

[0024] A control unit can comprise a plurality of control units, which are arranged, in particular, spatially separated from one another in the motor vehicle. Control units are also referred to as Electronic Control Units (ECUs) or Electronic Control Modules (ECMs) and preferably have electronic microcontrollers for performing computing operations for processing data, particularly preferably using software. The control units can preferably be networked with one another, enabling wired and / or wireless data exchange between control units. In particular, it is also possible to network the control units with one another via bus systems present in the motor vehicle, such as the CAN bus or LIN bus.Most preferably, the control unit has at least one processor and at least one memory, which in particular contains a computer program code, wherein the memory and the computer program code are configured, with the processor, to cause the control unit to execute the computer program code.

[0025] The control unit can particularly preferably comprise power electronics for supplying current to the stator or rotor. Power electronics is preferably a combination of various components that control or regulate a current to the electrical machine, preferably including the peripheral components required for this purpose, such as cooling elements or power supplies. In particular, the power electronics contains one or more power electronic components that are designed to control or regulate a current. This particularly preferably involves one or more power switches, e.g.

[0026] Power transistors. The power electronics particularly preferably have more than two, particularly preferably three, separate phases or current paths, each with at least one dedicated power electronics component. The power electronics are preferably designed to control or regulate a power per phase with a peak power, preferably continuous power, of at least 10 W, preferably at least 100 W, particularly preferably at least 1000 W.

[0027] Advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined with one another in a technologically expedient manner and can define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, where further preferred embodiments of the invention are presented.

[0028] According to an advantageous embodiment of the invention, the starting value d_est can be randomly selected during the first run of the method. The object of the invention can also be achieved by a computer program product stored on a machine-readable medium or a computer data signal embodied by an electromagnetic wave, with program code suitable for implementing the method according to claims 1-2.

[0029] Furthermore, the object of the invention can also be achieved by a control unit for controlling and energizing an electrical machine, in particular a synchronous electrical machine, comprising a processor and a memory containing a computer program code, wherein the memory and the computer program code are configured, with the processor, to cause the control unit to carry out a method according to claims 1-2. According to a further particularly preferred embodiment of the invention, it can be provided that the control unit does not have a connection for a rotor position sensor for detecting the rotor position of the rotor, so that the control unit or the electrical machine controlled by it can manage without a physical rotor position sensor.

[0030] Finally, the object of the invention can also be achieved by an electrical machine, in particular a synchronous electrical machine, comprising a stator and a rotor rotatable relative to the stator, as well as a control unit for controlling and energizing the electrical machine, characterized in that the control unit is a control unit according to claim 4. In a likewise preferred embodiment of the invention, it can also be provided that the electrical machine does not have a rotor position sensor for detecting the rotor position of the rotor. It can also be advantageous to further develop the invention such that the electrical machine is configured for use in an electrically operated or hybrid drive train of a motor vehicle.

[0031] Furthermore, it may be particularly preferred to use the method according to the invention during a test and / or inspection cycle of the electric machine during its manufacture. During production, an electric machine is generally operated for various tests and inspections, for example in order to run through an acceptance profile for quality and functional control before delivery of the electric machine. In this state, the electric machine usually does not have its own rotor position sensor, since this rotor position sensor is generally only added during assembly in the vehicle. During acceptance, each electric motor to be tested is thus combined with a rotor position sensor permanently mounted on a corresponding test bench for the corresponding test. With this rotor position sensor, which is not optimally matched to this electric motor, the electric machine has previously been operated in the test bench in order to then complete a test and / or inspection cycle.Due to time constraints, the offset angle of the rotor position signal is generally not taught. The electric machine cannot operate optimally during these test and / or inspection cycles, as the rotor position angle offset cannot be adjusted during production. As a result, the electric machine may exhibit a significant rotor position angle error during a test and / or inspection cycle.

[0032] The inventive method for determining an initial rotor position of the rotor of an electric machine therefore proposes - as already explained above - finding the longer main axis of the ellipse, which corresponds to the d-axis, using an iterative controller approach. By imposing the injection signal on the voltage, a current can be measured. However, this current is not transformed into the imaginary d-direction, but rather into the imaginary d-45° direction and imaginary d+45° direction. This allows significantly larger current amplitudes to be achieved compared to an evaluation of the currents in the d- and q-directions, where the current in the q-direction disappears when the real d-axis is found. Detection thus becomes more robust against disturbances, especially in dynamic situations. The amplitude of the injection signal is then determined using bandpass filtering, and the two values ​​for +-45° are compared.The assumed angle is then corrected so that the two amplitudes in the +45° and -45° directions are equal. The sign of the correction is chosen so that the longer semi-axis, i.e., the d-axis, is found. If the sign is reversed during the correction, the algorithm finds the shorter semi-axis, i.e., the q-axis. This approach not only allows the initial angle to be determined, but also allows the electric machine to be operated with it, especially during a test cycle in the electric machine's production.

[0033] The production of the electrical machine also includes, in particular, the state of the electrical machine when not installed in a motor vehicle. In particular, this also includes operation of the electrical machine for inspection and testing purposes outside of a motor vehicle. This operation for inspection and testing purposes can preferably be carried out on a test bench for the electrical machine.

[0034] The object of the invention can thus also be achieved by a testing and / or test method for checking an electrical machine according to one of claims 6-8 in a test bench, wherein for operation of the electrical machine in the test bench the initial rotor position of the rotor of the electrical machine is determined by a method according to one of claims 1-2.

[0035] The object of the invention can further be achieved by a testing and / or test method for checking an electrical machine in a test bench, wherein the test bench for operating the electrical machine comprises a control unit according to claims 4-5 for controlling and energizing the electrical machine and the initial rotor position of the rotor of the electrical machine is determined by a method according to one of claims 1-2.

[0036] In contrast to back-EMF-based methods, the proposed method does not require any motor parameters; only the filters of the method need to be adjusted within a suitable range. Inaccuracies resulting from motor parameters thus become irrelevant.

[0037] Sensorless operation allows the test objects to be operated at the optimal angle for each application. This improves the measurement results and makes them more comparable. The torque and speed actually generated by the motor can be evaluated. In the variant with a non-learned rotor position sensor, the achievable torque and achieved speed are only of limited significance. The angle learned through sensorless operation can be compared with the permanently installed angle. This allows the sensorless angle to be validated, as it should always remain within a certain range relative to the measured fixed angle after a defined transient response, as part of a plausibility check.

[0038] The object of the invention can also be achieved by a test bench for carrying out a test and / or testing method for checking an electrical machine, comprising a holder for the electrical machine and a control unit according to claims 4-5 for controlling and energizing the electrical machine.

[0039] The electric motor can thus be operated and controlled without a rotor position sensor even during production. Sensorless operation using the method according to the invention for determining the initial rotor position of the electric motor's rotor can accurately determine the correct motor angle in the shortest possible time, thus enabling optimal operation for each motor in the corresponding test and / or inspection cycle.

[0040] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

[0041] It shows:

[0042] Figure 1 different positions of the d-axis in a d / q coordinate system,

[0043] Figure 2 electrical machine in a schematic representation,

[0044] Figure 3 Motor vehicles with one hybrid and one fully electric drive train in a schematic representation,

[0045] Figure 4 shows a first embodiment of a test bench in a schematic block diagram,

[0046] Figure 5 shows a second embodiment of a test bench in a schematic block diagram,

[0047] The method for determining an initial rotor position of a rotor 1 of an electrical machine 2, in particular an electrical synchronous machine, is explained in more detail below with reference to Figure 1.

[0048] First, an electrical machine 2 with a stationary rotor 1 is provided, as shown by way of example in Figure 2. By means of the control unit 3, a three-phase alternating voltage excitation is then generated in the electrical machine 2, which is also indicated in Figure 2 by the three parallel dashed lines between the control unit 3 and the energized stator 7.

[0049] First, a random starting value d_est is provided, which represents a first angle of the rotor position. Based on this starting value d_est, the alternating voltage excitation is applied in the d_est direction. The three-phase current is measured and transformed into the d_est-45° direction, and the modified value d_est-45° is calculated. A second modified value d_est+45° is calculated analogously, which corresponds to the starting value d_est plus 45°. Subsequently, the three-phase current response to the alternating voltage excitation of the electrical machine 2 for the first modified value d_est-45° is converted into a first alternating current component i_[d_est-45°], and the three-phase current response to the alternating voltage excitation of the electrical machine for the second modified value d_est+45° is converted into a second alternating current component i_[d_est+45°].

[0050] These two alternating current components are shown in figures a)-c) of Figure 1. Now, the length of a first alternating current vector comprising d and q components for the first alternating current component i_[d_est-45°] is calculated, as well as the length of a second alternating current vector comprising d and q components for the second alternating current component i_[d_est+45°].

[0051] Figure 1 schematically depicts corresponding ellipses in the real dq-plane. The "estimated" d-axis (d_est) is shown, which does not coincide with the direction of the d-axis of the dq-plane. The alternating current components i_(d_est+45°) and i_(d_est-45°) are shown, corresponding to the estimated direction of the d-axis.

[0052] Then the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector is determined according to delta_i=|i_d_est+45°|-|i_d_est-45°|.

[0053] If the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector delta_i=|i_d_est+45°|-|i_d_est-45°| >0, which can be seen in figures a) and b) of Figure 1, a distinction is made between two further alternatives.

[0054] For the first case, where |i_d_est+45°|>|i_d_est-45°|, the starting value d_est is adjusted in such a way that the angle representing the rotor position is rotated clockwise by a predetermined amount, as shown in figures a) and b). From figures a) and b) in Figure 1, it is clearly visible that the lengths of the alternating current components are different. Therefore, the "estimated" d-axis (d_est) must be rotated clockwise by a certain amount. This new "estimated" d-direction is then the new starting value for the next iteration. Figure b) in Figure 1 shows one of the next iterations. For the second case, where |i_d_est+45°|<|i_d_est-45°| is, an adjustment of the starting value d_est is made in such a way that the angle representing the rotor position is rotated counterclockwise by a predetermined amount, which is not shown in Figure 1.

[0055] These iterations are performed until the condition is met that the difference in the magnitudes of the lengths between the first alternating current vector and the second alternating current vector lies within a defined interval between 0 and a defined error tolerance value FTW, according to delta_i= | i_d_est+45° | -| i_d_est-45° | =[0-FTW] .

[0056] In other words, the process is repeated until the projections of the alternating current components, and thus the lengths of the absolute values ​​of the alternating current components, are equal. The initial rotor position angle can then be easily determined from the angle of the "estimated" d-axis. This can be seen in Figure 1 (c). Based on this, the initial rotor angle is then determined to energize the electric machine, thus completing the process.

[0057] After this initial angle determination, the d-axis is known, and electric motor 2 can be started in the desired direction of rotation. Even brief rotation of the electric motor in the wrong direction during motor operation can thus be prevented. A possible "180° error" must still be identified and eliminated using a suitable standard procedure, as is the case with the prior art method.

[0058] As shown in Figure 2, the control unit 3 for controlling and energizing the electric machine 2 comprises a processor 4 and a memory 5 containing a computer program code, wherein the memory 5 and the computer program code are configured, with the processor 4, to cause the control unit 3 to carry out the above method.

[0059] Unlike what is shown in Figure 2, the control unit 3 preferably does not have a connection for a rotor position sensor 6 for detecting the rotor position of the rotor 1 and can be controlled without a sensor. The electric machine 2 shown in Figure 2 has a current-carrying stator 7 and a rotor 1 rotatable relative to the stator 7, as well as the control unit 3 for controlling and supplying current to the electric machine 2 and the stator 7, respectively.

[0060] The electric machine 2 is configured in particular for use in an electrically operated or hybrid drive train 8 of a motor vehicle 9, as also outlined in Figure 3.

[0061] The described method can also be used within a test and / or inspection method for checking an electrical machine 2, as known from Figure 2, on a test bench 10. In this case, for the operation of the electrical machine 2 in the test bench 10, the initial rotor position of the rotor 1 of the electrical machine 2 is determined using the described method for determining the initial rotor position of the rotor 1 of the electrical machine 2. This structure of the test bench 10 is shown in Figure 4. The electrical machine 2 is already tested with its control unit 3 and is supplied with current via the control unit 3. However, it would also be conceivable for the test bench 10 to have a control unit 3 via which the electrical machine 2 is supplied with current, as outlined in Figure 5.

[0062] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority.

[0063] List of reference symbols

[0064] 1 rotor

[0065] 2 electric machine 3 control unit

[0066] 4 processors

[0067] 5 storage

[0068] 6 Rotor position sensor

[0069] 7 Stator 8 Drivetrain

[0070] 9 Motor vehicle

[0071] 10 Test bench

Claims

Claims: A method for determining an initial rotor position of a rotor (1) of an electric machine (2), in particular an electric synchronous machine, comprising the following steps: a) providing an electric machine with a stationary rotor, b) providing a starting value d_est, which represents a first angle of the rotor position, c) generating a three-phase AC voltage excitation in the electric machine by applying an AC voltage in the d_est direction, d) converting the three-phase current response to the AC voltage excitation of the electric machine for the first modified value d_est-45° into a first AC component i_[d_est-45°], e) converting the three-phase current response to the AC voltage excitation of the electric machine for the second modified value d_est+45° into a second AC component i_[d_est+45°],f) Calculation of the length of a first AC vector containing d and q components for the first AC component i_[d_est-45°], g) Calculation of the length of a second AC vector containing d and q components for the second AC component i_[d_est+45°], h) Determination of the difference in the magnitudes of the lengths between the first AC vector and the second AC vector according to delta_i=|i_d_est+45°|-|i_d_est-45°|, i) If the condition is met that the difference in the magnitudes of the lengths between the first AC vector and the second AC vector lies within a defined interval between and a defined error tolerance value FTW, according to delta_i=|i_d_est+45°|-|i_d_est-45°| =[0-FTW], provision of the initial, rotor angle for energizing the electric machine and termination of the procedure, j) If the condition is met that the difference in the magnitudes of the lengths between the first AC vector and the second AC vector is delta_i=|i_d_est+45°|-|i_d_est-45°| > 0, k) If |i_d_est+45°|>|i_d_est-45°|, adjust the initial value d_est such that the angle representing the rotor position is rotated clockwise by a predetermined amount, and l) If |i_d_est+45°|<|i_d_est-45°|, adjust the initial value d_est such that the angle representing the rotor position is rotated counterclockwise by a predetermined amount, m) Repeat steps c)-l). Method according to claim 1, characterized in that the starting value d_est is chosen randomly when the method is first run.Computer program product stored on a machine-readable medium, or computer data signal embodied by an electromagnetic wave, with program code suitable for carrying out the method according to claim 1-2.

4. Control unit (3) for controlling and energizing an electric machine (2), in particular an electric synchronous machine, comprising a processor (4) and a memory (5) containing a computer program code, wherein the memory and the computer program code are configured with the processor (4) to cause the control unit (3) to carry out a method according to claim 1-2.

5. Control unit (3) according to claim 4, characterized in that the control unit (3) does not have a connection for a rotor position sensor (6) for detecting the rotor position of the rotor (1).

6. Electric machine (2), in particular an electric synchronous machine, comprising a stator (7) and a rotor (1) rotatable relative to the stator (7) as well as a control unit (3) for controlling and energizing the electric machine (2), characterized in that the control unit (3) is a control unit (3) according to claim 4.

7. Electric machine (2) according to claim 6, characterized in that the electric machine (2) does not have a rotor position sensor (6) for detecting the rotor position of the rotor (1 ).

8. Electric machine according to claim 6 or 7, characterized in that the electric machine (2) is configured for use in an electrically operated or hybrid powertrain (8) of a motor vehicle (9). Testing and / or verification method for verifying an electric machine (2) according to any one of claims 6-8 in a test rig (10), characterized in that, for the operation of the electric machine (2) in the test rig (10), the initial rotor position of the rotor (1) of the electric machine (2) is determined by a method according to any one of claims 1-2. Testing and / or verification method for verifying an electric machine (2) in a test rig (10), characterized in that the test rig (10) for the operation of the electric machine (2) comprises a control unit (3) according to claims 4-5 for controlling and energizing the electric machine (2), and the initial rotor position of the rotor (1) of the electric machine (2) is determined by a method according to any one of claims 1-2.Test stand (10) for carrying out a test and / or verification procedure for checking an electrical machine (2) comprising a fixture for the electrical machine (2) and a control unit (3) according to claim 4-5 for controlling and energizing the electrical machine (2).

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