ELECTRONICALLY COMMUTATED ELECTRIC MACHINE WITH SEVERAL SUB-MACHINES AND METHOD FOR OPERATING SUCH AN ELECTRIC MACHINE

Description

Technical field

[0001] The invention relates to electrical machines with multiple identical sub-machines in a redundant design, which are controlled separately and are galvanically isolated from each other. The invention further relates to methods for controlling the sub-machines in order to obtain homogeneous, identical torque contributions. Technical background

[0002] In safety-critical areas, such as steering drives in motor vehicles, electrical machines are often designed redundantly. The electrical machine incorporates sub-machines with galvanically isolated multi-phase stator windings. The multi-phase stator windings act on a rotor equipped with permanent magnets. The stator windings are controlled via separate, redundant control units for the sub-machines, so that the sub-machines, with the same control, provide a correspondingly identical torque contribution to the overall torque. However, due to various influences, the torque contributions of the sub-machines differ. This can lead to uncomfortable steering behavior.

[0003] US 2018 / 105201 A1 discloses a control device for a rotating machine, comprising a rotating machine having a rotor structure with first three-phase windings and second three-phase windings, a first current detector for detecting a first winding current flowing through each of the first three-phase windings, a second current detector for detecting a second winding current flowing through each of the second three-phase windings, a controller for calculating a first voltage command such that the first winding current detected by the first current detector matches a first current command, and for calculating a second voltage command such that the second winding current detected by the second current detector matches a second current command, a first power converter for applying a voltage to each phase of the first three-phase windings based on the first voltage command,a second power converter for applying a voltage to each phase of the second three-phase windings based on the second voltage command; a position estimation command generator for generating a first position estimation command at a first frequency and a second position estimation command at the first frequency; and a rotational position estimator for extracting an amplitude value of a component of the first frequency based on at least one of the first winding current and the second winding current, thereby estimating a rotational position of the AC rotary machine based on a magnitude of the amplitude value; wherein the controller superimposes the first position estimation command on the first voltage command and outputs a result of the superimposition to the first power converter; and superimposes the second position estimation command on the second voltage command and outputs a result of the superimposition to the second power converter.

[0004] From the document DE 10 2019 122 434 A1 a motor control system is known, comprising a first controller that calculates a first torque command using a first closed control loop, a second controller that calculates a second torque command using a second closed control loop, wherein both the first controller and the second controller calculate the respective first torque command and second torque command using a unified calculation in which a leakage integrator is used and an integrator state is calculated in the time domain, which is implemented by discretization in an electrical control unit, and a motor that receives a torque command for generating a corresponding torque amount based on the first torque command and the second torque command.

[0005] Document US2019 / 308664 A1 discloses a system comprising a position controller configured to receive an input shelf position command and a measured shelf position; and to calculate a speed command based on a difference between the input shelf position command and the measured shelf position, with a speed controller configured to receive the speed command and a measured motor speed and to calculate an input torque command based on a difference between the speed command and the measured motor speed; wherein the system adjusts a position of a rack by generating a torque amount corresponding to the application of the input torque command to a motor.

[0006] The document CN 108 107 734 discloses an electromechanical coupling modeling method for a feed system of a permanent magnet synchronous linear motor.

[0007] The publication ZHOU QIXUN ET AL: "Crossed-feedback control of dual-redundancy permanent magnetic brushless do servo system used in electro-hydrostatic actuator", ELECTRICAL MACHINES AND SYSTEMS, 2008. ICEMS 2008, pages 1237-1241 discloses a motor system with two galvanically isolated sub-motors that are controlled via a PID controller.

[0008] The publication KUANG XIAOLIN ET AL: "Research on a six-phase permanent magnet synchronous motor system at dual-redundant and fault tolerant modes in aviation application", CHINESE JOURNAL OF AERONAUTICS, Vol. 30, No. 4, June 14, 2017 (2017-06-14), pages 1548-1560 discloses a motor system with galvanically isolated control branches.

[0009] It is therefore an object of the present invention to control a motor system with an electric machine with several sub-machines in such a way that they provide torque contributions that are as equal as possible. Disclosure of the invention

[0010] This object is achieved by the motor system for controlling an electronically commutated electrical machine with a plurality of sub-machines according to claim 1 and a method for operating a motor system according to the independent claim.

[0011] Further embodiments are specified in the dependent claims.

[0012] According to a first aspect, an engine system is provided, comprising: an electrical machine and a plurality of sub-machines, each having a separate stator winding which is galvanically isolated from one another and serves to drive a common rotor with a respective torque contribution; a control branch for each of the stator windings, wherein each control branch is designed to operate the respective sub-machine with phase voltages in order to provide a desired torque contribution, wherein the control branches are electrically isolated from one another; one or more controllers in each of the control branches, which are designed to specify the phase voltages for controlling the associated stator winding as a function of a predetermined target value, wherein the one or more controllers are designed without dynamic components, i.e. without taking into account a time-dependent change in an actual value.

[0013] The multiple controls are provided as cascaded controls with a position control, which in particular includes a speed control and a current control.

[0014] In a redundant design of a motor system with an electric machine composed of several sub-machines, the sub-machines are controlled redundantly by separate control units. Each control unit incorporates a cascaded control structure.

[0015] A position control system is provided that is designed with only a proportional component. In particular, the position control can specify a target speed.

[0016] To adjust the target speed, a speed control can be provided, whereby the speed control can be designed with only a proportional component, a proportional and an integrator component (PI control), or a proportional, differential and an integrator component (PID control). Other speed control architectures can also be provided. Furthermore, the speed control can specify a target motor current that represents a torque contribution from the assigned The target motor currents specified by the control units via the respective speed control correspond to the desired torque contributions of the sub-machines, which together specify the total torque.

[0017] Current control can be provided to regulate the target motor current. The current control can be implemented with only a proportional component (P control), a proportional and an integrator component (PI control), or a proportional, derivative, and an integrator component (PID control). Other current control architectures can also be provided. Furthermore, the current control can specify phase voltages.

[0018] The target motor currents are converted into phase voltages to be set using current control and a Park and Clark transformation, which can be applied by a power driver to the phase strands of the respective stator winding.

[0019] The redundant design of the motor system with separate control units and stator windings is generally complete, meaning that both sub-machines are galvanically isolated from each other. The control units therefore operate asynchronously and provide pulse-width-modulated control signals as outputs for controlling the respective power driver. This means that the control signals each correspond to a cyclic pulsed signal, whose duty cycle specifies the phase voltage to be set. Even if the cycle frequencies are selected to be identical, deviations in the phase positions of the control signals may occur due to tolerances.

[0020] In addition, especially during dynamic operation, the asynchronous control of the sub-machines results in different torque contributions. The asynchronous operation of the control units means that the phase currents required to control a phase winding of each sub-machine are not calculated simultaneously, resulting in the target specifications of the controls deviating from one another. This results in different torque contributions provided by the sub-machines.

[0021] However, any synchronization of both control units to provide the partial engine torques evenly is disadvantageous, since with a redundant design of the engine system the galvanic isolation of the subsystems is eliminated, since the synchronization must be carried out using a synchronization channel, e.g. in the form of one or more electrical signal lines between the control units.

[0022] The above motor system, featuring an electric machine with multiple redundantly controlled sub-machines, follows a different approach. The sub-machines are controlled by specifying a target position, a target speed, or a target torque using position control, speed control, or torque control, respectively.

[0023] The position control comprises exclusively a P-controller, i.e., a control without dynamic components, which, instead of a PI or PID controller commonly used in the state of the art, is sufficiently accurate to control the position of the electric machine. Accordingly, the speed control and the torque control can be designed as simple P-controllers without a dynamic component if only speed control of the electric machine or torque control of the electric machine is required.

[0024] The provision of the corresponding control without dynamic control components avoids the situation that, due to the asynchronous operation of the control units, the differing actual values ​​of the position of the rotor, the speed and / or the motor current (actual variable) recorded at different times by an integrator (I component) or a differentiator (D component) of the control result in different control variables of the control for the individual sub-machines.

[0025] For example, different actual positions in conventional position controls designed for dynamic operation, particularly when an integrator is provided in the controls for the sub-machines, lead to rapidly differing target torques for the sub-machines, since differing actual positions lead to different integrator values. Providing a control with only a P component, i.e. without a dynamic component, therefore avoids deviations in the manipulated variables for the sub-machines due to phase shifts in the PWM cycle and asynchronous operation of the control units for the sub-machines. Omitting the integrator component of the position control avoids different states that can arise from the integration of control deviations, so that the control usually outputs the same manipulated variables for the sub-machines.

[0026] It can be provided that the phase voltages are specified as a duty cycle for a pulse width modulation and wherein a PWM block is provided in each control branch in order to generate control signals for a respective power driver for providing the phase voltages with a pulse width modulation depending on predetermined duty cycles and with a predetermined cycle frequency which specifies a period duration of the pulse width modulation.

[0027] According to a further aspect, a method is provided for operating an electrical machine with a plurality of sub-machines, each of which has a separate stator winding that is galvanically isolated from the other stator windings and serves to drive a common rotor with a respective torque contribution, wherein the sub-machines are each controlled with phase voltages via a separate control branch for each of the stator windings in order to provide a desired torque contribution, wherein the phase voltages are controlled as a function of a predetermined target value for controlling the associated stator winding with one or more cascaded control systems, wherein at least one of the one or more control systems is designed exclusively with a proportional component or without dynamic components. Brief description of the drawings

[0028] Embodiments are explained in more detail below with reference to the attached drawings. They show: Figure 1 shows a schematic representation of a motor system with an electric machine with two sub-machines that are controlled via redundant controls using two redundant control units; and Figure 2 shows a block diagram illustrating an exemplary control of one of the redundant control paths for one of the sub-machines. Description of embodiments

[0029] Figure 1 shows a motor system 1 with an electric machine 2, which is designed as an electronically commutated electric machine. The electric machine 2 has a stator 21 and a rotor 22. The stator 21 has two separate stator windings 23, each with three phase strands 24, so that two three-phase sub-machines 25 are formed.

[0030] Each of the stator windings 23 is controlled via a separate control branch 3. The control branches 3 are galvanically isolated from each other and provide phase voltages Uu, Uv, Uw for the sub-machines 25. The phase voltages Uu, Uv, Uw energize the stator windings 23, thus providing a torque contribution from the respective sub-machine 25.

[0031] The control branches 3 assigned to each sub-machine 25 each have a control unit 31 which provides control signals Tu, Tv, Tw for a three-phase power driver 32, which specify the phase voltages Uu, Uv, Uw for the respective phase strands 24 of the relevant stator winding 23.

[0032] The phase currents lu, Iv, Iw flowing through the respective phase strands of the respective stator winding 23 are measured using a respective phase current measuring unit 33, and a corresponding current indication for the phase currents lu, Iv, Iw is provided to the control unit 31. Furthermore, a rotor position of the rotor 22 is measured using a position sensor 5, and this is also provided to the control units 31 as the actual position Φ m (actual variable).

[0033] The control units 31 are designed, for example, to provide multi-stage control of the position of the electric machine 1 in hardware and / or software. For this purpose, a target position Φ ref is specified, from which, in conjunction with the actual position Φ m, a control deviation for position control can be determined.

[0034] The multi-stage control is shown as a block diagram in Figure 2 shown in more detail in the form of a position-controlled electrical machine 1.

[0035] The control deviation as the difference between the target position Φ ref and the actual position Φ ist is fed to a position controller 61 which is designed exclusively as a P control, ie has only a proportional component.

[0036] The manipulated variable of the position control corresponds to a setpoint speed ω ref . From the measured actual position Φ m , an actual speed ω ist can be derived by differentiation, so that a difference between the setpoint speed ω rer and the actual speed ω ist can be evaluated as a control deviation for a downstream speed control.

[0037] The speed control can be carried out using a speed controller 62, which can be configured, in particular, as a PI control or PID control. The speed control can therefore include a differential or integral component. The speed control provides a target motor current Iq_ref, which specifies a q-component of the motor current Iq in a rotor-fixed coordinate system.

[0038] A control deviation of the q-component Iq of the target motor current from a q-component of the actual motor current Iq is evaluated in a first current controller 63, which can preferably be configured as a P-control, PI-control, or PID-control, to output a q-component of a target voltage Uq_ref in the rotor-fixed coordinate system. Analogously, 0 is specified as the d-component Id of the target motor current.

[0039] The d-component of the target motor current can be set to zero, so that a 90° lead of the magnetic field caused by the motor current with respect to the direction of an excitation magnetic field of the rotor at the current rotor position can be achieved. A control deviation of the d-component Id of the target motor current from a d-component of the actual motor current Id is evaluated in a second current controller 64, which is preferably designed as a P-controller, in order to output a d-component of a target voltage Ud_ref in the rotor-fixed coordinate system.

[0040] By means of a corresponding transformation in a transformation block 65, the motor voltages Uq, Ud specified in the rotor-fixed coordinate system can be converted into the multi-phase phase voltages Uu, Uv, Uw using a Clarke and Park transformation, depending on an electrical rotor position Φ e , which can correspond to the actual position Φ m or can be derived therefrom.

[0041] The phase voltages Uu, Uv, Uw correspond to the target specifications for the phase voltages of the respective control branch and are converted into corresponding control signals Tu, Tv, Tw in a PWM block 66, which correspond to duty cycles for the control in the three-phase power driver 32.

[0042] The control deviation of the first and second current controllers 63, 64 of the current control results from an inverse transformation using a Clarke and Park transformation of the measured phase currents into the rotor-fixed coordinate system, so that the separate current controls for the q-component and d-component of the motor currents can be provided separately.

[0043] In a preferred embodiment, the position control is implemented as P control, the speed control, and the current control as Pi or PID control, in order to minimize the deviations in the control behavior due to the asynchronous operation of the control units 31 in both control branches 3. In this way, even with asynchronous operation of the two control units 31, essentially identical torque contributions can be realized in all control branches 3. List of reference symbols

[0044] 1Motor system 2Electric machine 21Stator 22Rotor 23Stator winding 24Phase phases 25Submachine 3Control branch 31Control unit 32Three-phase power driver Uu, Uv, UwPhase voltages Tu, Tv, TwControl signals lu, Iv, IwPhase currents 5Position sensor Φ ref Target position Φ m Actual position 61Position controller 62Speed ​​controller 63First current controller 64Second current controller 65Transformation block 66PWM block

Claims

1. Motor system (1) comprising: - an electrical machine (2) with a plurality of sub-machines (25), each having a separate stator winding (23), which windings serve to drive a common rotor (22) with a particular torque contribution; - a control branch (3) for each of the stator windings (23), each control branch (3) being designed to operate the particular sub-machine (25) with phase voltages (Uu, Uv, Uw) in order to provide a desired torque contribution; - one or more cascaded controls (61, 62, 63, 64) in each of the control branches (3), which are designed to specify the phase voltages (Uu, Uv, Uw) for controlling the associated stator winding (23) depending on a predetermined target value, the plurality of separate stator windings (23) being galvanically separated from the other stator windings (23), characterized in that the control branches (3) are electrically separated from one another and provide asynchronous control of the sub-machines, and in that at least one of the one or more controls (61, 62, 63, 64) is designed exclusively with a proportional component or without dynamic components, a position control (61) being provided which is designed only with a proportional component.

2. Motor system according to claim 1, wherein the plurality of controls (61, 62, 63, 64) comprise a speed control and a current control.

3. Motor system according to claim 1 or 2, wherein the phase voltages (Uu, Uv, Uw) are specified as a duty cycle for a pulse width modulation and wherein a PWM block (66) is provided in each control branch in order to generate control signals (Tu, Tv, Tw) for a particular power driver (32) for providing the phase voltages (Uu, Uv, Uw) with a pulse width modulation depending on predetermined duty cycles and with a predetermined cycle frequency which specifies a period duration of the pulse width modulation.

4. Motor system according to any of claims 1 to 3, wherein the position control (61) specifies a target speed, wherein a speed control (62) is provided in order to regulate the target speed, wherein the speed control is designed with an integral component.

5. Motor system according to claim 4, wherein the speed control (62) specifies a target motor current, wherein a current control (63, 64) is provided to regulate a target motor current, wherein the current control is designed with an integral component.

6. Method for operating an electrical machine (2) having a plurality of sub-machines (25), each of which has a separate stator winding (23) which is galvanically separated from the other stator windings (23), and drives a common rotor (22) with a particular torque contribution, wherein the sub-machines (25) are each controlled via a separate control branch (3) for each of the stator windings (23) with phase voltages (Uu, Uv, Uw) in order to provide a desired torque contribution, wherein the control branches (3) are electrically separated from one another and provide asynchronous control of the sub-machines, wherein the phase voltages (Uu, Uv, Uw) are regulated depending on a predetermined target value for controlling the associated stator winding (23) with one or more cascaded controls (61, 62, 63, 64), wherein at least one of the one or more controls (61, 62, 63, 64) is designed exclusively with a proportional component or without dynamic components, wherein a position control (61) is provided which is designed only with a proportional component.