SYSTEM AND METHOD FOR AN ELECTRICAL MACHINE

A computer system is provided, including processing circuitry configured to determine at least one electrical machine parameter during operation of an electrical machine based on an assumed resolver offset, to determine a residual from said at least one measured electrical machine parameter, and to determine if the assumed resolver offset is acceptable by comparing the residual with a predetermined reference value.

TECHNICAL FIELD

The disclosure relates generally to a system and method for an electrical machine. In particular aspects, the disclosure relates to a system and method for verifying resolver offset calibration for an electrical machine. The disclosure can be applied to heavy-duty vehicles, such as trucks, buses, and construction equipment, among other vehicle types. Although the disclosure may be described with respect to a particular vehicle, the disclosure is not restricted to any particular vehicle.

BACKGROUND

Electrical machines are used in a vast amount of applications. By applying position control of the electrical machine a number of benefits are obtained.

Especially in electrical vehicle applications, position control will allow for improved efficiency by enabling precise control of the speed and torque of the electrical machine. Hence, the electrical machine may operate at optimal efficiency for a given speed and load thereby extending the range of the vehicle and improving overall energy efficiency of the electrical vehicle.

Another benefit relates to improved performance and driving experience. Position control of the electrical machine will enable precise control of the position, speed, and torque of the electrical machine thereby allowing for faster acceleration, smoother operation, and better handling.

A further benefit of position control is related to reduction of wear and tear of the electrical machine, thereby prolonging the lifetime as the electrical machine can be driven at optimal efficiency.

Precise control of the moving parts of an electrical machine may be realized by a number of different devices, such as by encoders, Hall effect sensors, linear variable differential transformers, and laser displacement sensors. However, when considering factors such as accuracy, resolution, reliability, immunity to electromagnetic interference, size, and complexity a resolver is normally the first hand choice.

A resolver is a type of sensor that is used to determine the position and speed of a rotating shaft of an electrical machine. A resolver operates by converting the mechanical motion of the shaft into an electrical signal that is indicative of the position and speed of the electrical machine.

A resolver consists of a stator and a rotor. The stator has sets of coils which are typically positioned at specific angles. The rotor is a rotating component that also contains sets of coils, which are positioned around the rotor at specific angles to match the positions of the stator coils. While the stator is a stationary component, the rotor is connected to the rotating shaft of the electrical machine.

When the rotor rotates as the electrical machine is running, voltages will be induced in the stator coils that are proportional to the sine and cosine of the angle between the rotor and stator coils of the resolver. These voltages are then processed to determine the position and speed of the rotating shaft.

As is understood from the above background, correct positioning of the resolver is critical in order to benefit from precise position control.

Insufficient calibration of the resolver position may lead to decreased performance and may jeopardize the control of the electrical machine. Accurate calibration of the resolver, i.e. knowing any present resolver offset and compensating for this resolver offset, is consequently important to assure satisfying performance of the electrical machine, and specifically to assure the desired performance of the electrical vehicle when applicable.

Hence, there is a need for improvements with regards to the resolver calibration of an electrical machine, and especially there is a need for improved methods for determining if the resolver is calibrated accurately.

SUMMARY

According to a first aspect of the disclosure, a computer system comprising processing circuitry is provided. The processing circuitry is configured to: determine at least one electrical machine parameter during operation of the electrical machine based on an assumed resolver offset, determine a residual from said at least one measured electrical machine parameter, and determine if the assumed resolver offset is acceptable by comparing the residual with a predetermined reference value. The first aspect may seek to improve performance of the electrical machine. A technical benefit may include providing a simple technique for ensuring that the calibration of the resolver is sufficiently accurate. Typically, the assumed resolver offset is determined as being acceptable if the residual is less than the predetermined reference value. The term “acceptable” is thus to be interpreted as a quality criteria corresponding to a sufficiently good calibration of the resolver, meaning that the resolver will provide accurate signals within an acceptable limit.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to control the electrical machine to run in steady state when determining the at least one electrical machine parameter. A technical benefit may include improved accuracy of the determined residual, as effects caused by transient conditions may be eliminated.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to determine the at least one electrical machine parameter as at least one linear time-invariant parameter. A technical benefit may include improved consistency due to the constant behavior of the at least one electrical machine parameter.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to determine the at least one electrical machine parameter as a d-axis voltage, a stator resistance, a d-axis current, an electrical machine speed, a q-axis inductance, and a q-axis current. A technical benefit may include a more simple algorithm for determining the residual, since these parameters can be made readily available from associated control systems.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to determine the residual as RES=(Ud−Rs*Id+ω*Lq*Iq)/ω. A technical benefit may include a more versatile algorithm for determining the residual, in particular by allowing currents to be non-zero.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to determine a moving average of the residual, and to compare the predetermined reference value with the moving average of the residual. A technical benefit may include improved robustness, as a moving average will reduce noise and potential residual anomalies.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to low pass filter the residual to determine a low pass filtered residual, and to compare the predetermined reference value with the low pass filtered residual. A technical benefit may include improved robustness and reliability, as high frequency noise can be disregarded.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to determine the correct resolver offset from the residual. A technical benefit may include improved calibration of the resolver position.

Optionally in some examples, including in at least one preferred example, the processing circuitry is further configured to control the electrical machine to run in steady state when determining the at least one electrical machine parameter, determine the at least one electrical machine parameter as at least one linear time-invariant parameter, determine the residual as RES=(Ud−Rs*Id+ω*Lq*Iq)/ω, compare the predetermined reference value with a moving average of the residual, or with a low pass filtered residual, and determine the correct resolver offset from the residual.

According to a second aspect of the disclosure, a vehicle is provided. The vehicle comprises at least one electrical machine, and a computer system according to the first aspect.

Optionally in some examples, including in at least one preferred example, the electrical machine is a permanent magnet machine. A technical benefit may include improved simplicity, as no external components are needed for determining the residual in order to evaluate the resolver calibration.

According to a third aspect of the disclosure, a computer-implemented method is provided. The method comprises determining, by processing circuitry of a computer system, at least one electrical machine parameter during operation of the electrical machine based on an assumed resolver offset, determining, by the processing circuitry, a residual from said at least one measured electrical machine parameter, and determining, by the processing circuitry, if the assumed resolver offset is acceptable by comparing the residual with a predetermined reference value. A technical benefit may include providing a simple technique for ensuring that the calibration of the resolver is sufficiently accurate.

Optionally in some examples, including in at least one preferred example, the method further comprises controlling, by the processing circuitry, the electrical machine to run in steady state when determining the at least one electrical machine parameter. A technical benefit may include improved accuracy of the determined residual, as effects caused by transient conditions may be eliminated.

Optionally in some examples, including in at least one preferred example, the method further comprises determining, by the processing circuitry, the at least one electrical machine parameter as at least one linear time-invariant parameter. A technical benefit may include improved consistency due to the constant behavior of the at least one electrical machine parameter.

Optionally in some examples, including in at least one preferred example, the method further comprises determining, by the processing circuitry, the at least one electrical machine parameter as a d-axis voltage, a stator resistance, a d-axis current, an electrical machine speed, a q-axis inductance, and a q-axis current. A technical benefit may include a more simple algorithm for determining the residual, since these parameters can be made readily available from associated control systems.

Optionally in some examples, including in at least one preferred example, the method further comprises determining, by the processing circuitry, the residual as RES=(Ud−Rs*Id+ω*Lq*Iq)/ω. A technical benefit may include a more versatile algorithm for determining the residual, in particular by allowing currents to be non-zero.

Optionally in some examples, including in at least one preferred example, the method further comprises determining, by the processing circuitry, a moving average of the residual, or low pass filter the residual to determine a low pass filtered residual, and comparing, by the processing circuitry, the predetermined reference value with the moving average of the residual or with the low pass filtered residual. A technical benefit may include improved robustness and/or reliability, as high frequency noise can be disregarded.

Optionally in some examples, including in at least one preferred example, the method further comprises determining, by the processing circuitry, the correct resolver offset from the residual. A technical benefit may include improved calibration of the resolver position.

According to a fourth aspect of the disclosure, a computer program product is provided. The computer program product comprises program code for performing, when executed by the processing circuitry, the method according to the third aspect.

According to a fifth aspect, a non-transitory computer-readable storage medium is provided. The non-transitory computer-readable storage medium comprises instructions, which when executed by the processing circuitry, cause the processing circuitry to perform the method according to the third aspect.

There are also disclosed herein computer systems, control units, code modules, computer-implemented methods, computer readable media, and computer program products associated with the above discussed technical benefits.

DETAILED DESCRIPTION

Before describing specific details of the technology of this disclosure, some general comments on control of electrical machines will be given.

The dq frame is a mathematical tool used to simplify the analysis and control of electrical machines, such as electric motors or generators.

The dq frame is a coordinate system that rotates with the rotor of the electrical machine, with the d-axis aligned with the magnetic field from the permanent magnets in the rotor, i.e. the magnetization field, and the q-axis 90 degrees ahead of the d-axis. By transforming the three-phase electrical quantities of the machine (i.e. with regards to voltage and current) from the stationary orthogonal frame to the rotating dq frame, it is possible to represent the behavior of the electrical machine as a set of two variables, i.e. the direct-axis (d-axis) and the quadrature-axis (q-axis) components.

The d-axis and the q-axis components may represent any electrical or magnetic quantity (such as current, voltage, or flux) that changes in a three-phase system when the phases are shifted 120 degrees in space and time.

Using the dq frame, it is possible to control the behavior of the electrical machine with regards to speed and torque output by manipulating the d-axis and q-axis components of the voltage and current.

A commonly used way to control electrical machines is called field-oriented control (FOC). FOC involves adjusting the d-axis and q-axis components to control the machine's magnetic field. By adjusting these components in real-time, it is possible to maintain a desired speed or torque output from the machine.

FOC requires the position of the rotor as an input. For this purpose, a resolver may be arranged at the rotor shaft, providing resolver signals indicative of the position of the rotor. Nevertheless, a mechanical resolver offset may exist due to the imbalance of mechanical tolerance during the resolver assembly on the rotor shaft.

In order to minimize errors which may affect the control and efficiency of the electrical machine negatively, calibration of the resolver offset is needed. Calibration is normally performed by analyzing the actual resolver position, and applying corrective measures for compensating for the determined offset. Unless calibrated properly, the resolver offset will cause errors that may lead to an inaccurate determination of the rotor position.

In the following, solutions will be described which effectively determines if the calibration of the resolver offset is within acceptable limits.

FIG.1is an exemplary system diagram of a vehicle1according to an example. The vehicle1may be any type of vehicle, such as a heavy duty vehicle or a light duty vehicle. The vehicle1comprises an electrical machine arrangement5. The electrical machine arrangement5comprises an electrical machine10being provided with a resolver12, and a computer system100being configured to determine if a current calibration of the resolver offset of the electrical machine10is within acceptable limits, as will be further explained in the following. InFIG.1, the electrical machine arrangement5and its included components are shown schematically.

It should be emphasized that the computer system100described herein is not exclusively designed to operate with a vehicle1, but the computer system100may be used in any suitable application, such as moving or stationary applications, embedded or stand-alone applications, etc., as long as it is connected to an electrical machine10and forms part of an electrical machine arrangement5.

FIG.2is an exemplary system diagram of an electrical machine arrangement5. The electrical machine arrangement5comprises an electrical machine10. The electrical machine10is provided with a resolver12configured to transmit a resolver signal RS being indicative of the current position of a rotor14of the electrical machine10.

The electrical machine arrangement5further comprises a computer system100. The computer system100is programmed to determine if the calibration of the resolver offset of the resolver12is within acceptable limits. The computer system100is further configured to allow field-oriented control (FOC) of the electrical machine10. The computer system100comprises a transformation circuitry110configured to measure and transform the motor phase currents to the dq frame, resulting in measured dq frame currents Idand Iq. These transformed currents Idand Iqare compared to reference currents Idrefand Iqref(i.e. the flux reference and the torque reference) by regulators120a,120b, outputting reference voltages Udrefand Uqrefin the dq frame. An inverse transformation circuitry130is configured to invert the reference voltages Udrefand Uqrefto the voltage components Uαrefand Uβrefof the stator vector voltage in the stationary orthogonal reference frame. These reference voltages are inputs to a space vector pulse-width modulator140which is configured to provide drive signals to an inverter150.

Each of the transformation circuitry110and the inverse transformation circuitry130requires the rotor flux position θ, which depends on the position of the rotor. While the rotor flux position can be provided from the signals of the resolver12, any built-in error in the resolver12will cause control errors which may affect operation of the electrical machine10negatively.

For this purpose, the computer system100is configured to determine if these built-in errors of the resolver12are calibrated properly, according to a general principle which will be further explained in the following.

The computer system100comprises computing and/or processing circuitry160being configured to determine if the resolver offset is calibrated properly according to a method200generally described with reference toFIG.4.

It should be noted that the computing circuitry160, as well as any processing circuitry programmed to perform the method200, could be implemented as embedded software and/or hardware with a computer system100configured to control the operation of the electrical machine10. However, the computing circuitry160, as well as any processing circuitry programmed to perform the method200, could in other examples be implemented as a stand-alone application. Hence, evaluating the calibration of the offset of the resolver12could be performed as part of the normal operation control of the electrical machine10, or for example only once during production, preferably at the end of line of manufacturing.

The general idea is to perform measurements of at least one electrical machine10parameter based on an assumed resolver offset, and to determine a residual from said at least one electrical machine10parameter. This residual is then compared to a predetermined reference value; if the residual is greater than or equal to the predetermined reference value, calibration of the resolver offset is improper. For example, such conclusion may trigger a request for recalibration. On the other hand, if the residual is less than the predetermined reference value, calibration of the resolver offset is considered to be sufficiently accurate for continued operation of the electrical machine10.

Determining the residual is generally based on the assumption that the dq frame, as defined by the computer system100, is offset from the actual dq frame in the electrical machine10, where the permanent magnet flux is oriented along the d axis, by an angle α.

In this case, the d axis voltage of the assumed dq frame can be formulated by the following equation:

The above equation is valid only for small angles α, and when the electrical machine10is running in steady state. In the above equation, RSis the stator resistance, Ldand Lqare the d and q axis inductances, Idand Iqare the d and q axis currents in the control software frame, φmis the permanent magnet flux and ω is the electrical speed.

For no offset between the real and assumed dq frames, or for α=0, the equation reduces to the following equation:

If the assumed and actual dq frames were perfectly aligned and if RES=(Ud−Rs*Id+ω*Lq*Iq)/ω is evaluated, theoretically a value of RES=0 should be obtained during steady state operation. The value of Udcan be obtained from the transformation circuitry110and the d and q currents are obtained by transforming the three-phase measured currents to the dq frame as previously described. The speed ω is also available.

However, the same entity RES with a small offset a will not be perfectly 0. It can be calculated to be the following:

This value is not 0 and based on experiments, a suitable threshold T can be decided for this Udresidual to decide if the offset calibration is good or not.

A moving average or low pass filter may also added to the residual to filter out only the very low frequency component and that in turn is evaluated against a threshold to check if the offset is within acceptable limits.

According to some examples, the residual RES is only used to decide if the resolver offset is calibrated well or not. It does not provide any means to estimate α. However, some advanced estimation algorithms can be adopted to estimate α also, such as an RLS filter or a Kalman filter.

FIG.3schematically shows processing circuitry160according to one example. The processing circuitry160is configured to determine at least one electrical machine parameter during operation of the electrical machine based on an assumed resolver offset. In the shown example, the at least one electrical machine parameter comprises the q axis inductance Lq, the d and q axis currents Idand Iqof the assumed dq frame, the electrical speed ω, and the d axis voltage Udof the assumed dq frame.

The processing circuitry160is further configured to determine a residual RES from the at least one measured electrical machine parameter, and to determine if the assumed resolver offset is acceptable by comparing the residual RES with a predetermined reference value T.

Now turning toFIG.4, a method200for determining if a resolver offset is calibrated well or not, will be described. The method200operates by an initial control202of the electrical machine10, which preferably is a permanent magnet motor, to run in steady state.

The method200further assumes204a specific dq frame, and determines206at least one electrical machine parameter during steady state operation of the electrical machine10.

In the shown example, determining206at least one electrical machine parameter comprises determining208the q axis inductance Lq, determining210the d and q axis currents Idand Iqof the assumed dq frame, determining212the electrical speed ω of the electrical machine10, and determining214the d axis voltage Udof the assumed dq frame.

The method200further comprises determining216a residual RES based on the determined at least one electrical machine parameter. Preferably, the residual RES is determined as RES=(Ud− Rs*Id+ω*Lq*Iq)/ω.

The method200comprises accessing218, e.g. by fetching or receiving, a predetermined reference value T, and comparing226the determined residual RES with the predetermined reference value T. The predetermined reference value T may act as a threshold for a well-considered calibration, meaning that if the determined residual RES is less than the predetermined reference value T, the calibration of the resolver offset is deemed to be sufficient.

Optionally, the method200may operate to process220the residual RES before comparing it with the predetermined reference value T. Such processing220may e.g. comprise determining222a moving average of the residual RES. Processing220may also, alone or in combination, comprise filtering224the residual RES by applying a low pass filter to the residual RES.

Optionally, the method200may further operate by determining228a correct resolver offset based on the at least one electrical machine parameter.

The computer system300may comprise at least one computing device or electronic device capable of including firmware, hardware, and/or executing software instructions to implement the functionality described herein. The computer system300may include processing circuitry302(e.g., processing circuitry including one or more processor devices or control units), a memory304, and a system bus306. The computer system300may include at least one computing device having the processing circuitry302. The system bus306provides an interface for system components including, but not limited to, the memory304and the processing circuitry302. The processing circuitry302may include any number of hardware components for conducting data or signal processing or for executing computer code stored in memory304. The processing circuitry302may, for example, include a general-purpose processor, an application specific processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a circuit containing processing components, a group of distributed processing components, a group of distributed computers configured for processing, or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The processing circuitry302may further include computer executable code that controls operation of the programmable device.

The system bus306may be any of several types of bus structures that may further interconnect to a memory bus (with or without a memory controller), a peripheral bus, and/or a local bus using any of a variety of bus architectures. The memory304may be one or more devices for storing data and/or computer code for completing or facilitating methods described herein. The memory304may include database components, object code components, script components, or other types of information structure for supporting the various activities herein. Any distributed or local memory device may be utilized with the systems and methods of this description. The memory304may be communicably connected to the processing circuitry302(e.g., via a circuit or any other wired, wireless, or network connection) and may include computer code for executing one or more processes described herein. The memory304may include non-volatile memory308(e.g., read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), etc.), and volatile memory310(e.g., random-access memory (RAM)), or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a computer or other machine with processing circuitry302. A basic input/output system (BIOS)312may be stored in the non-volatile memory308and can include the basic routines that help to transfer information between elements within the computer system300.

Computer-code which is hard or soft coded may be provided in the form of one or more modules. The module(s) can be implemented as software and/or hard-coded in circuitry to implement the functionality described herein in whole or in part. The modules may be stored in the storage device314and/or in the volatile memory310, which may include an operating system316and/or one or more program modules318. All or a portion of the examples disclosed herein may be implemented as a computer program320stored on a transitory or non-transitory computer-usable or computer-readable storage medium (e.g., single medium or multiple media), such as the storage device314, which includes complex programming instructions (e.g., complex computer-readable program code) to cause the processing circuitry302to carry out actions described herein. Thus, the computer-readable program code of the computer program320can comprise software instructions for implementing the functionality of the examples described herein when executed by the processing circuitry302. In some examples, the storage device314may be a computer program product (e.g., readable storage medium) storing the computer program320thereon, where at least a portion of a computer program320may be loadable (e.g., into a processor) for implementing the functionality of the examples described herein when executed by the processing circuitry302. The processing circuitry302may serve as a controller or control system for the computer system300that is to implement the functionality described herein.

The computer system300may include an input device interface322configured to receive input and selections to be communicated to the computer system300when executing instructions, such as from a keyboard, mouse, touch-sensitive surface, etc. Such input devices may be connected to the processing circuitry302through the input device interface322coupled to the system bus306but can be connected through other interfaces, such as a parallel port, an Institute of Electrical and Electronic Engineers (IEEE) 1394 serial port, a Universal Serial Bus (USB) port, an IR interface, and the like. The computer system300may include an output device interface324configured to forward output, such as to a display, a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)). The computer system300may include a communications interface326suitable for communicating with a network as appropriate or desired.

The operational actions described in any of the exemplary aspects herein are described to provide examples and discussion. The actions may be performed by hardware components, may be embodied in machine-executable instructions to cause a processor to perform the actions, or may be performed by a combination of hardware and software. Although a specific order of method actions may be shown or described, the order of the actions may differ. In addition, two or more actions may be performed concurrently or with partial concurrence.

Example 1: A computer system (100) comprising processing circuitry (160,302) configured to determine (206) at least one electrical machine parameter during operation of an electrical machine (10) based on an assumed resolver (12) offset, determine (218) a residual (RES) from said at least one measured electrical machine parameter, and determine (226) if the assumed resolver (12) offset is acceptable by comparing the residual (RES) with a predetermined reference value (T).

Example 2: The computer system (100) of Example 1, wherein the processing circuitry (160,302) is further configured to: control (202) the electrical machine (10) to run in steady state when determining (206) the at least one electrical machine parameter.

Example 3: The computer system (100) of any of Examples 1-2, wherein the processing circuitry (160,302) is further configured to: determine (206) the at least one electrical machine parameter as at least one linear time-invariant parameter.

Example 4: The computer system (100) of any of Examples 1-3, wherein the processing circuitry (160,302) is further configured to: determine (206) the at least one electrical machine parameter as a d-axis voltage, a stator resistance, a d-axis current, an electrical machine speed, a q-axis inductance, and a q-axis current.

Example 5: The computer system (100) of Example 4, wherein the processing circuitry (160,302) is further configured to: determine (218) the residual (RES) as RES=(Ud−Rs*Id+ω*Lq*Iq)/ω.

Example 6: The computer system (100) of any of Examples 1-5, wherein the processing circuitry (160,302) is further configured to: determine (222) a moving average of the residual (RES), and compare the predetermined reference value (T) with the moving average of the residual (RES).

Example 7: The computer system (100) of any of Examples 1-6, wherein the processing circuitry (160,302) is further configured to: low pass filter (224) the residual (RES) to determine a low pass filtered residual, and compare the predetermined reference value (T) with the low pass filtered residual.

Example 8: The computer system (100) of any of Examples 1-7, wherein the processing circuitry (160,302) is further configured to: determine (228) a correct resolver offset from the residual (RES).

Example 9: The computer system (100) of Example 1, wherein the processing circuitry (160,302) is further configured to: control (202) the electrical machine (10) to run in steady state when determining (206) the at least one electrical machine parameter, determine (206) the at least one electrical machine parameter as at least one linear time-invariant parameter, determine (218) the residual (RES) as RES=(Ud− Rs*Id+ω*Lq*Iq)/ω, compare (226) the predetermined reference value (T) with a moving average of the residual (RES), or with a low pass filtered residual (RES), and determine (228) the correct resolver offset from the residual (RES).

Example 10: A vehicle (1) comprising the computer system (100) of any of Examples 1-9, and at least one electrical machine (10).

Example 11: The vehicle (1) of Example 10, wherein the electrical machine (10) is a permanent magnet machine.

Example 12: A computer-implemented method (200), comprising: determining (206), by processing circuitry (160,302) of a computer system (100), at least one electrical machine parameter during operation of an electrical machine (10) based on an assumed resolver offset, determining (218), by the processing circuitry (160,302), a residual (RES) from said at least one measured electrical machine parameter, and determining (226), by the processing circuitry (160,302), if the assumed resolver offset is acceptable by comparing the residual (RES) with a predetermined reference value (T).

Example 13: The method of Example 12, further comprising: controlling (202), by the processing circuitry (160,302), the electrical machine (10) to run in steady state when determining (206) the at least one electrical machine parameter.

Example 14: The method of any of Examples 12-13, further comprising: determining (206), by the processing circuitry (160,302), the at least one electrical machine parameter as at least one linear time-invariant parameter.

Example 15: The method of any of Examples 12-14, further comprising: determining (206), by the processing circuitry (160,302), the at least one electrical machine parameter as a d-axis voltage, a stator resistance, a d-axis current, an electrical machine speed, a q-axis inductance, and a q-axis current.

Example 16: The method of Example 15, further comprising: determining (218), by the processing circuitry (160,302), the residual as RES=(Ud−Rs*Id+ω*Lq*Iq)/ω.

Example 17: The method of any of Examples 12-16, further comprising: determining (222), by the processing circuitry (160,302), a moving average of the residual (RES), and/or low pass filter (224) the residual (RES) to determine a low pass filtered residual, and comparing (226), by the processing circuitry (160,302), the predetermined reference value (T) with the moving average of the residual (RES) or with the low pass filtered residual (RES).

Example 18: The method of any of Examples 12-17, further comprising: determining (228), by the processing circuitry (160,302), the correct resolver offset from the residual (RES).

Example 19: A computer program product comprising program code for performing, when executed by the processing circuitry (160,302), the method (200) of any of Examples 12-18.

Example 20: A non-transitory computer-readable storage medium comprising instructions, which when executed by the processing circuitry (160,302), cause the processing circuitry (160,302) to perform the method (200) of any of Examples 12-18.