Sensorless determination of the rotor position of a brushless DC motor during a rotational movement of the rotor

Abstract

To determine the rotor position of a brushless DC motor (3) with a number of coils (12, 13) without sensors, a control signal (16a, 16b) is generated for each of the coils (12, 13), and the coil is supplied with electrical power according to the respective control signal (16a, 16b) to set the rotor (4) into rotation. A first subset of the coils (12, 13) is supplied with a test signal (14) during rotation. Depending on an electrical response signal (15) induced in a second subset of the coils (12, 13) in response, test data are determined, and the rotor position is determined by comparing the test data with predefined reference data (17).

Description

[0001] The present invention relates to a method for sensorless determination of the rotor position of a brushless DC motor (BLDC) during rotation of the rotor, wherein a rotor or stator of the brushless DC motor has a number of coils, and wherein a control signal is generated for each of the coils to control the coil, and the coil is supplied with electrical power according to the respective control signal to set the rotor into rotation. The invention further relates to a corresponding electronic circuit for sensorless determination of the rotor position of a rotor of a brushless DC motor, a motor device for an electrical appliance comprising such an electronic circuit, and an electrical appliance comprising such a motor device.

[0002] In BLDCs, the rotor's rotational motion can be mediated by an electronically commutated rotating magnetic field. Approaches for generating, regulating, and controlling rotating magnetic fields through electronic commutation are known. Crucial to the success of electronic commutation is, for example, the ability to precisely align the commutation, and thus the position of the magnetic field, with the rotor's current position, i.e., its rotation angle. Only when the generated magnetic fields are appropriately oriented to the rotor are they able to transmit optimal torque and thus efficiently transfer rotational energy. Two proven concepts have become established: commutation control based on measurements from Hall sensors and sensorless, predictive commutation control.

[0003] In approaches based on Hall sensors, Hall sensors are installed in the motor to determine the rotor position as precisely as possible. This allows the magnetic field generated by commutation to be optimally adjusted to the rotational position. A disadvantage of such approaches is that the positions of the Hall sensors are always subject to tolerances, as are other sensor components and the winding packages of the coils, whose magnetic fields induced by current also influence the measurement. Furthermore, Hall sensors are sensitive to shocks, other forces, and vibrations, all of which can potentially reduce accuracy. Measurements with Hall sensors can also be affected by temperature, which reduces the precision of the measurement, especially given the unclear and difficult-to-calibrate thermal effects associated with load and / or cooling airflow.Furthermore, the sensors incur additional costs.

[0004] Sensorless commutation approaches forgo direct measurement of the rotor's time-dependent rotation angle. When the motor is running and at sufficiently high speeds, the rotor position can be inferred based on electromagnetic feedback. However, at low speeds, i.e., during motor startup, these approaches are subject to considerable uncertainty. Pragmatic approaches involve essentially guiding the electronically commutated rotational field around the rotor during very slow motor startup. It is obvious that, due to inertia and potentially existing holding forces, only a very slow startup is possible, or the holding forces may not be overcome at all. Furthermore, the rotor may suddenly react to the stator field, i.e., start rotating abruptly and uncontrollably.Heuristic methods for overcoming these disadvantages are highly dependent on the design, layout and construction of the engine and drivetrain and are therefore not universally applicable.

[0005] It is an object of the present invention to provide a means for more reliable and / or more accurate sensorless determination of a rotor position of a brushless DC motor during a rotational movement of the rotor, in particular during a start-up phase of the rotor.

[0006] This problem is solved by the respective subject matter of the independent claims. Advantageous further developments and preferred embodiments are the subject matter of the dependent claims.

[0007] The invention is based on the idea of ​​feeding a test signal into at least one coil of the motor, which induces a response signal in at least one other coil of the motor, and determining the rotor position based on a comparison of test data that depend on the response signal with predetermined reference data.

[0008] According to one aspect of the invention, a method for the sensorless determination of the rotor position of a brushless DC motor (BLDC) during rotation is described. The rotor or stator of the brushless DC motor comprises a number of coils. A control signal is generated for each coil to actuate it, and the coil is supplied with electrical power according to the respective control signal, in particular with a defined current and / or a defined voltage, to set the rotor into rotation.

[0009] A first subset of coils (number of coils) is subjected to a test signal during rotation. This test signal corresponds to a voltage drop across the first subset of coils or a current flowing through them, or is generated based on the voltage or current. Test data is determined based on an electrical response signal induced in a second subset of coils (number of coils) in response to the test signal. The rotor position is determined by comparing the test data with predefined reference data.

[0010] The number of coils, which can also be called the set of coils or the plurality of coils, includes in particular two or more coils. A subset of this number, in particular the first subset and the second subset, each contains at least one coil of the number of coils. The first subset is not identical to the second subset. For example, the first subset and the second subset can be disjoint subsets of the number of coils. However, this is not necessarily the case, and whether the subsets are disjoint or not can also depend on the configuration of the number of coils.

[0011] If the first subset of coils contains two or more coils, these can, for example, be connected in series, so that the test signal is applied across the series connection of the first subset of coils. The same applies to the second subset of coils, so that the response signal, which could be, for example, an induced voltage or a resulting current, is applied across or flows through the series connection of the second subset of coils.

[0012] In principle, the method according to the invention is applicable regardless of the rotational speed. Limitations may arise in specific applications due to the metrological and temporal separation of the test signal, control signals, and response signal. However, the method according to the invention is particularly advantageous during the motor's start-up phase, i.e., when the rotor is moving at comparatively low to very low speeds, only slightly above standstill, which are significantly below the target rotor speed after the start-up phase is complete.

[0013] While the target speed is, for example, on the order of a few thousand or ten thousand rpm -1 The rotational movement during the execution of the method according to the invention, for example, has a rotational speed in the range of 0.1000 min⁻¹. -1 ], [1 min -1 , 1000 min -1 ], ] 0, 100 min -1 ] or [1 min-1 , 100 min -1 ] on.

[0014] The inventive method, as has been confirmed by numerous tests, makes it possible to reliably and accurately determine the rotor position even in this speed range without the use of corresponding magnetic sensors, i.e. sensorless.

[0015] In particular, at least one of the control signals can be modified or adjusted depending on the specific rotor position. This modification or adjustment can be carried out in a known manner to efficiently transmit torque to the rotor.

[0016] If the rotor has a certain number of coils, the stator can, for example, contain corresponding permanent magnets or coils that also serve as electromagnets. If the stator has a certain number of coils, the rotor can, for example, contain corresponding permanent magnets or coils that also serve as electromagnets.

[0017] For example, the first and second subsets of coils can be selected, or the application of the test signal can be timed, so that non-zero currents or voltages resulting from the test signal and the response signal do not overlap with non-zero currents or voltages resulting from the respective control signals. This largely eliminates the need for measurement-based separation of the individual components. However, it is also possible for such overlaps to occur, in which case the individual components of the currents or voltages must be measured separately to determine the response signal or the test data.

[0018] Depending on the embodiment of the method, the test data may include or be determined based on different properties or parameters of the response signal. In some embodiments, these properties or parameters can also be related to corresponding properties or parameters of the test signal to determine the test data. The reference data corresponds to the test data in this respect, except that the reference data has been determined in advance through calibration measurements for the specific BLDC or for a defined group of BLDCs, for example, BLDCs of the same type, and is stored and made available in a lookup table, a database, or in some other way.

[0019] The described steps of the method according to the invention can, for example, be repeated for different first and second subsets of coils in order to enable a more unambiguous or reliable determination of the rotor position. The test data can, in particular, depend on all response signals determined in this way, especially during a defined test period.

[0020] In a clear, though not necessarily limiting, example, the number of coils includes three coils: a first coil, a second coil, and a third coil, connected in a star configuration, specifically a star configuration without a neutral conductor. Each of the three coils has a first terminal and a second terminal, with the respective second terminals connected to the star point. The test signal could then be, for example, a voltage signal between the first terminal of the first coil and the first terminal of the second coil, or a corresponding current signal. The test signal induces, as a response signal, for example, a voltage in the third coil or a corresponding current. In this configuration, the first subset consists of the first coil and the second coil, and the second subset consists of the third coil.The described steps can then be repeated analogously, with the first subset consisting of the first coil and the third coil and the second subset consisting of the second coil, or with the first subset consisting of the second coil and the third coil and the second subset consisting of the first coil.

[0021] In another illustrative, though not necessarily limiting, example, the number of coils includes three coils: a first coil, a second coil, and a third coil, connected in a delta configuration. The test signal could then be, for example, a voltage signal between the first and second terminals of the first coil, or a corresponding current signal. The test signal, in turn, induces a voltage or a corresponding current in the second coil as a response signal. In this configuration, the first subset consists of the first coil, and the second subset consists of the second coil.The described steps can then be repeated analogously, with the first subset consisting of the second coil and the second subset consisting of the third coil, or with the first subset consisting of the third coil and the second subset consisting of the first coil.

[0022] According to at least one embodiment, for each coil of the number of coils, the respective control signal for controlling the respective coil includes a plurality of signal pulses, for example square pulses.

[0023] For example, this can be done using the principle of pulse width modulation (PWM). In other words, for each coil, the respective control signal for controlling that coil includes a pulse width modulation signal, which in particular contains the multitude of signal pulses.

[0024] In this way, the electrical energy converted into the rotor's rotational movement can be adjusted by modifying the pulse duration of the signal pulses or the pulse interval between them. Furthermore, controlling the coils based on the signal pulses is particularly well-suited for easily separating the test signal or response signal from the control signals.

[0025] The multitude of signal pulses can, in particular, be a pulse sequence with a predetermined period T, where each period contains exactly one of the signal pulses. A pulse duration S of the individual signal pulses is, for example, given by a duty cycle d = S / T, such that S = d*T. The pulse interval is then equal to (1-d)*T.

[0026] According to at least one embodiment, the test signal includes a test pulse.

[0027] The test pulse can be, for example, a rectangular test pulse. However, in other embodiments it can also have a different signal shape, such as a Gaussian pulse shape, a sinc pulse shape, a trapezoidal shape, a triangular shape, and so on.

[0028] If the control signal contains a multitude of signal pulses in the form of a pulse sequence, the test pulse will have a test pulse duration P that is shorter than the pulse interval. Accordingly, the test pulse can be placed between two consecutive signal pulses.

[0029] According to at least one embodiment, the at least one first subset of coils is supplied with the test signal in such a way that no signal pulse of the respective plurality of signal pulses for controlling the first subset of coils overlaps with the test pulse.

[0030] In other words, the test pulse for each coil of the first subset is located between two consecutive signal pulses of the respective control signal.

[0031] According to at least one embodiment, the test signal is generated by combining, in particular adding, the test pulse with one of the control signals, in particular the control signal of one of the coils of the first subset.

[0032] In this way, the first subset of coils can also be supplied with the test pulse even if the control signals are continuous, i.e., not defined by successive signal pulses separated by time intervals with a signal amplitude of 0. For example, the control signals in such cases can be sinusoidal.

[0033] According to at least one embodiment, the test pulse has a test pulse duration of less than 50µs or less than 20µs or less than 10µs or less than 5µs or less than 2µs.

[0034] For example, the test pulse duration is in the range [0.2 µs, 50 µs] or in the range [0.2 µs, 20 µs] in the range [0.2 µs, 10 µs] in the range [0.2 µs, 50 µs] in the range [0.2 µs, 2 µs].

[0035] Such short test pulse durations make it possible, firstly, to place the test pulse between successive signal pulses even in sequences of control signals with comparatively high duty cycles. Secondly, the steps of the inventive method can thus be repeated several times within a short period of time, for example, for different first and second subsets of coils, thereby increasing the accuracy of determining the rotor position.

[0036] According to at least one embodiment, the test data includes a maximum amplitude of the response signal or is determined at least partially depending on the maximum amplitude.

[0037] In particular, the comparison of the test data with the specified reference data includes a comparison of the maximum amplitude of the response signal with a specified reference amplitude as a function of the rotor position or depending on the rotor position.

[0038] The maximum amplitude is relatively easy to determine using measurement techniques and is also strongly influenced by the exact rotor position. Consequently, the reliability and accuracy of such designs are further increased.

[0039] According to at least one embodiment, the test data are determined at least partially depending on a signal shape of the response signal.

[0040] To determine the waveform of the response signal, the signal can be fitted to a predefined reference curve, for example, by varying one or more fit parameters. The resulting values ​​for the fit parameters specify the waveform, and the test data can either incorporate this waveform or be determined based on it.

[0041] In particular, the comparison of the test data with the specified reference data includes a comparison of the specified fit parameters with specified reference parameters as a function of the rotor position or depending on the rotor position.

[0042] The signal shape is influenced by the exact rotor position. Consequently, the reliability and accuracy of such designs are further increased.

[0043] According to at least one embodiment, the test data are determined at least partially depending on the decay behavior of the response signal.

[0044] The decay behavior can be specified, for example, by one or more characteristic time constants of the response signal. These one or more time constants can also be determined using fitting procedures. The resulting values ​​for the time constants specify the decay behavior, and the test data can either include these values ​​or be determined based on them.

[0045] In particular, the comparison of the test data with the specified reference data includes a comparison of the determined time constants with specified reference time constants as a function of the rotor position or depending on the rotor position.

[0046] According to at least one embodiment, the test data includes a relative temporal position or a relative phase position of the response signal with respect to the test signal, or is determined at least partially depending on the relative temporal position or the relative phase position.

[0047] In particular, the comparison of the test data with the specified reference data includes a comparison of the relative temporal position or relative phase position with a specified reference position as a function of the rotor position or depending on the rotor position.

[0048] The relative temporal position or relative phase position is relatively easy to determine using measurement techniques and is also strongly influenced by the exact rotor position. Consequently, the reliability and accuracy of such designs are further increased.

[0049] According to at least one embodiment, the test data are determined at least partially depending on a ratio of the maximum amplitude of the response signal to a maximum amplitude of the test signal, in particular the test pulse, or the test data are determined at least partially depending on a ratio of the maximum amplitude of the test signal, in particular the test pulse, to the maximum amplitude of the response signal.

[0050] This makes it possible to avoid, in particular, dependencies between the determination of the rotor position and the absolute value of the maximum amplitude of the response signal.

[0051] According to at least one embodiment, at least two distinct subsets of the number of coils are defined, wherein the at least two distinct subsets include the first subset. At least two further distinct subsets of the number of coils are defined, wherein the at least two further distinct subsets include the second subset.

[0052] Each subset of the at least two subsets is assigned at least one further subset of the at least two further subsets. For each subset of the at least two subsets and for each further subset assigned to the respective subset of coils, the following steps i) and ii) are performed: i) The respective subset of coils is subjected to a respective test signal, which corresponds to a voltage drop across the respective subset of coils or a current flowing through the respective subset of coils, or is generated depending on the voltage or current. ii) Depending on an electrical response signal induced in the respective further subset of coils in response to the application of the respective test signal, a test data set is determined.

[0053] The test data includes the test data sets, in particular all test data sets determined in this way.

[0054] In other words, in such embodiments, the steps performed above for the first and second subsets of coils are carried out successively for various, in particular all, combinations of suitable subsets of coils. This increases the reliability and accuracy of determining the rotor position.

[0055] According to a further aspect of the invention, an electronic circuit for sensorless determination of the rotor position of a brushless DC motor during rotation is provided. The rotor or stator of the BLDC motor has a number of coils. The electronic circuit includes a motor controller configured to generate a control signal for each coil and to supply electrical power to the corresponding coil according to the respective control signal in order to set the rotor into rotation.The electronic circuit includes a test circuit configured to apply a test signal to a first subset of coils (number of coils) during rotation. This test signal corresponds to, or is generated by, a voltage drop across or current flowing through the first subset of coils. The electronic circuit also includes at least one evaluation circuit configured to detect an electrical response signal induced in a second subset of coils (number of coils) in response to the test signal. Based on this response signal, the evaluation circuit determines test data and the rotor position by comparing the test data with predefined reference data.

[0056] The test circuit can be part of the motor control system or designed separately. The at least one evaluation circuit can be part of the motor control system or designed separately.

[0057] The motor control, the test circuit and / or the at least one evaluation circuit can be part of one or more data processing systems and / or include other electronic circuits.

[0058] The terms "data processing system" and "at least one data processing device" may be used interchangeably within the scope of this disclosure. In this disclosure, a data processing device may, for example, be understood as a device with processing circuits for processing data. A data processing device can thus perform arithmetic operations to process data. Indexed access to a data structure, such as a lookup table (LUT) or a database, may also be considered an arithmetic operation. Similarly, data processing that is partially or fully implemented in hardware may be considered an arithmetic operation.

[0059] A data processing device may, in particular, comprise one or more computers, one or more microcontrollers, and / or one or more integrated circuits, for example, one or more application-specific integrated circuits (ASICs), one or more field-programmable gate arrays (FPGAs), and / or one or more systems-on-a-chip (SoCs). A data processing device may also comprise one or more processors, for example, one or more microprocessors, one or more central processing units (CPUs), one or more graphics processing units (GPUs), and / or one or more signal processors, in particular one or more digital signal processors (DSPs). The data processing device may also comprise a physical or virtual cluster of computers or other devices of the aforementioned type.

[0060] A data processing device may also include one or more hardware and / or software interfaces, for example for receiving and / or providing data.

[0061] A data processing device may also include one or more storage devices. A storage device may be implemented as volatile memory, such as dynamic random access memory (DRAM) or static random access memory (SRAM), or as non-volatile data storage, such as read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory or flash EEPROM, ferroelectric random access memory (FRAM), magnetoresistive random access memory (MRAM), or phase-change random access memory (PCRAM).

[0062] Further embodiments of the electronic circuit according to the invention follow directly from the various configurations of the method according to the invention, and vice versa. In particular, individual features and corresponding explanations as well as advantages relating to the various configurations of the method according to the invention can be transferred analogously to corresponding configurations of the electronic circuit according to the invention. In particular, the electronic circuit according to the invention is configured or programmed to carry out a method according to the invention. In particular, the electronic circuit according to the invention carries out the method according to the invention.

[0063] According to a further aspect of the invention, a motor device for an electrical appliance, in particular a power tool, is provided. The motor device comprises a brushless DC motor and an electronic circuit according to the invention for sensorless determination of a rotor position of a rotor of the brushless DC motor.

[0064] According to another aspect of the invention, an electrical device, in particular a power tool, comprising a motor device according to the invention is specified.

[0065] According to at least one embodiment, the electrical device is an electrical device that can be operated with a battery pack.

[0066] In particular, the electrical device includes the battery pack. For example, the battery pack includes at least a part of the electronic circuit according to the invention, for example the test circuit and / or the at least one evaluation circuit.

[0067] The battery pack can be detachably, and in particular non-destructively, connected to the housing of the electrical device, for example via a snap-fit ​​connection, a plug connection, and / or a clamp connection. In particular, the mechanical connection of the battery pack to the housing of the electrical device can be designed as a positive-locking and / or force-locking connection without a material bond. In other words, the mechanical connection of the battery pack to the housing of the electrical device can be released without having to break a material bond. Preferably, the mechanical connection can be released manually as intended, without the use of any other tools.

[0068] In particular, the battery pack is designed as a replaceable battery pack, for example, a system battery pack. The housings of the battery pack and the electrical device can each have corresponding interfaces for electrical and mechanical connection. Specifically, the battery pack can be mechanically and electrically connected to the housing of the electrical device without the use of a cable between the battery pack and the housing of the electrical device. For example, the housing of the battery pack is immovable relative to the housing of the electrical device when the battery pack is attached to the housing of the electrical device, and this connection is not released by a corresponding mechanism.

[0069] An electrical connection between at least one battery cell and the electrical device, in particular a motor of the electrical device, can be made, for example, via one or more detachable electrical contacts, such as clamp contacts or plug contacts, in particular so-called tulip contacts or sword contacts. For example, compatible plugs or sockets or receptacles or the like can be provided at the interfaces of the corresponding housings to achieve the electrical connection of the battery pack to the electrical device.

[0070] In some designs, the battery pack can, for example, provide an output voltage in the range of 12V to 60V.

[0071] Further features of the invention are evident from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as those mentioned below in the description of the figures and / or illustrated in the figures, may be encompassed by the invention not only in the combinations specified, but also in other combinations. In particular, embodiments and combinations of features that do not include all the features of an originally formulated claim may also be encompassed by the invention. Furthermore, embodiments and combinations of features that go beyond or deviate from the combinations of features mentioned in the claims may also include the invention.

[0072] The invention is explained in more detail below with reference to specific exemplary embodiments and corresponding schematic drawings. Identical or functionally equivalent elements in the drawings may be provided with the same reference numerals. The description of identical or functionally equivalent elements is not necessarily repeated with respect to the different figures.

[0073] The figures show: Fig. 1 a schematic flowchart of an exemplary embodiment of a method according to the invention for sensorless determination of a rotor position of a BLDC; Fig. 2 a schematic circuit diagram of coils of a BLDC in an exemplary embodiment of an electronic circuit according to the invention for sensorless determination of the rotor position of the BLDC; Fig. 3 a schematic circuit diagram of coils of a BLDC in a further exemplary embodiment of an electronic circuit according to the invention for sensorless determination of the rotor position of the BLDC; Fig. 4 a schematic circuit diagram of an exemplary embodiment of a motor device according to the invention for an electrical appliance; Fig. 5 a schematic representation of signal pulses and a test pulse in a further exemplary embodiment of a method according to the invention; Fig. 6 a schematic representation of a test pulse and a response signal in a further exemplary embodiment of a method according to the invention; Fig. 7 a schematic representation of a test pulse and a response signal in a further exemplary embodiment of a method according to the invention; Fig. 8 a schematic representation of test data in a further exemplary embodiment of a method according to the invention; Fig. 9 a schematic representation of test data in a further exemplary embodiment of a method according to the invention; and Fig. 10 a schematic flowchart of a method for motor control with a further exemplary embodiment of a method according to the invention for sensorless determination of a rotor position of a BLDC.

[0074] Fig. Figure 1 shows a schematic flowchart of an exemplary embodiment of a method according to the invention for the sensorless determination of a rotor position of a BLDC 3 during a rotational movement of a rotor 4 of the BLDC 3. The rotor 4 or a stator 5 of the BLDC 3 has a number of coils 12, 13.

[0075] In step 100, a control signal 16a, 16b is generated for each of the coils 12, 13 to control the coil, and the respective coil is supplied with electrical power according to the respective control signal 16a, 16b to set the rotor 4 into rotation. In step 120, a first subset of coils 12, 13 is supplied with a test signal 14 during rotation. The test signal 14 corresponds to a voltage drop across the first subset of coils 12, 13 or a current flowing through the first subset of coils 12, 13, or is generated depending on the voltage or current.

[0076] In step 140, test data are determined for a second subset of coils 12, 13, depending on an electrical response signal 15 induced in reaction to the application of the test signal 14. In step 160, the rotor position is determined by comparing the test data with predefined reference data 17.

[0077] In various embodiments of the invention, electronic commutation is used to control the BLDC 3, as schematically shown in Fig. Figure 4 illustrates this process without the need for Hall sensors or other magnetic sensors, etc. Disadvantages of known sensorless commutation approaches are overcome, in particular, by an intrinsic measurement based on the test signal 14 and the response signal 15. In some embodiments, this is based specifically on exploiting the possibility of injecting very short voltage or current pulses as test signals 14 into the existing stator stacks used to generate the rotating commutation field. These test signals then lead to inductive responses in the other coils in the form of the response signal.

[0078] The rotor position, i.e. the current rotation angle of the rotor 4, influences the induced response and thus the response signal, for example via the coupling strength, as well as via the temporal behavior or resonance behavior, in particular the decay behavior of the response signal 15.

[0079] The method does not require highly localized magnetic field measurement and is therefore not subject to the strong dependencies of corresponding production tolerances. Nevertheless, the approach is based primarily on measurements and, in some embodiments, allows an electronically commutated field to be precisely aligned with a rotor position at any given time. This enables, in particular, a reliable and powerful start-up and thus also precise motor control, even during the start-up phase, universally applicable to various types of BLDCs or electrical devices in which such BLDCs are used.

[0080] The test signal 14 can be a current signal or a voltage signal. A regulated current source can be used for injecting current signals, while a voltage source is sufficient for injecting voltage signals.

[0081] The coil pairs of the BLDC 3 can be connected, for example, in a star configuration with or without a center conductor, as shown in Fig. 2 shown, will be executed.

[0082] The test signal 14 can always be applied here via two coils, in the example of the Fig. 2. The coil 12b and the coil 12c are fed with current. The induced response is also measured via two coils, which represent complementary coils, in the example of the Fig. These are coils 12a and 12b.

[0083] In a star connection without a neutral conductor, there are three ways to feed in the test signal 14 or to measure the response signal 15: 1) Power supply via coils 12b and 12c, measurement via coils 12a and 12b; 2) Power supply via coils 12a and 12b, measurement via coils 12b and 12c; 3) Power supply via coils 12a and 12c, measurement via coils 12b and 12c.

[0084] The coil pairs of the BLDC 3 can be configured, for example, according to a delta circuit, as shown in Fig. 3 shown, will be executed.

[0085] In a delta circuit, the test signal 14 is fed in via a coil, in the example of the Fig. 2 the coil 13c, and also measured via the complementary coils, in the example of the Fig. 2. Coils 13a and 13b. Here, there are also three power input and measurement options, two of which provide new information about the rotor position: 1) Power supply via coil 13a, measurement via coils 13b and 13c; 2) Power supply via coil 13b, measurement via coils 13a and 13c; 1) Power supply via coil 13c, measurement via coils 13a and 13b.

[0086] Different pulse shapes are possible for a test pulse of the test signal 14, with a rectangular pulse shape proving particularly easy to implement, as shown in Fig. Figure 5 on the left. In the case of a BLDC 3 controlled by PWM voltage, as shown in Fig. As shown in Figure 4, no additional electronic components are required for this; instead, the test signal 14 can be generated by appropriately controlling the bridge transistors 9a, 9b, 10a, 10b, 11a, 11b, for example, MOSFETs. The test pulse of the test signal 14 can then be injected, in particular, between successive PWM signal pulses 16a, 16b, as shown in Figure 4. Fig. 5 shown on the right. In the example of the Fig. 5 is the pulse duration of the test pulse of the test signal 14, denoted by P, the period of the PWM by T, and the corresponding duty cycle by d.

[0087] Fig. Figure 4 shows, in particular, a schematic circuit diagram of an exemplary embodiment of a motor device 1 according to the invention for an electrical appliance. The motor device 1 includes the BLDC 3 and an electronic circuit 2 according to the invention. The electronic circuit 2 has a motor controller 6 configured to generate the control signals 16a, 16b. The electronic circuit 2 has a test circuit 7 configured to apply the test signal 14 to the first subset of coils. The electronic circuit 2 has at least one evaluation circuit 8 configured to detect the response signal 15 and to determine the rotor position by comparing the test data with the reference data 17.

[0088] For example, it is possible to apply the test signal 14 to coils 12 and 13 in all states, such as when a coil is not carrying current or when it is. Since the pulse duration of the test pulse P can be less than one microsecond to a few microseconds in some embodiments, and therefore significantly shorter than T (for example, 50 µs at a PWM frequency of 20 kHz), the test signal 14 can be applied both in a voltage- and current-free state, as well as during PWM operation, and especially when the rotor 4 is rotating. In principle, a measurement on the complementary coils is also always possible, since they themselves are not supplied with voltage at the time the test signals 14 are applied.

[0089] It should be emphasized that the determination of the rotor position is possible not only when the rotor 4 is at a standstill, but also when the rotor 4 is rotating, especially when the rotor 4 is rotating slowly during the start-up phase.

[0090] The response signal 15 depends in particular on the rotor position and the test signal 14. Fig. 6 and Fig. Figure 7 shows measured induced voltages as response signals 15 for a BLDC 3 with a star connection and no neutral conductor. It should be noted that response signal 15 and test signal 14 are scaled differently. A denotes the maximum amplitude of response signal 15 and A0 denotes the maximum amplitude of test signal 14.

[0091] Fig. Figure 8 schematically shows the measured ratio A / A0 for different rotation angles α of the rotor 4. Fig. Figure 9 shows corresponding measurement results for two different feed-in and measurement configurations. Such measurements can be carried out, in particular, during a calibration phase and stored as reference data. The results of later measurements can then be compared with these to determine the rotor position precisely.

[0092] The rotor position potentially influences the response signal 15 in various ways. This is a consequence of the changing magnetic flux densities and field line lengths at different rotor positions relative to the coils 12, 13. For example, an air gap between magnetic elements can change its relative position to the coils 12, 13 with the rotation angle of the rotor 4.

[0093] The response signal 15 can be influenced by the rotor position, particularly in its amplitude, resonance pattern, decay behavior, and / or phase. Based on corresponding measured changes, the rotation angle of the rotor 4 can be deduced. Due to the continuous rotation, cyclically recurring measurement patterns are established, which can be used for calibration.

[0094] For example, consider the amplitude of the response signal 15 in relation to the amplitude of the applied test signal 14, which could be, for instance, a single rectangular pulse. The amplitudes of the response signals 15 change cyclically, particularly sinusoidally, as shown in Fig. 8 and Fig. Figure 9 illustrates this. Measuring the amplitude is therefore particularly advantageous and can also be used as a basis or as an auxiliary measurement in combination with other measurement parameters of the response signals 15. Practical implementation has shown that the rotor position can be determined with an accuracy of 3° in this way.

[0095] The cyclicity of the response signals 15 is generally faster than the 360° of the physical axis of the rotor 4. Depending on the number of magnetic pool pairs and coils, this so-called electrical axis may rotate many times faster than the physical axis. Therefore, the rotor position may not be uniquely determined with respect to the 360° of the physical axis. However, for the precise control of the BLDC 3 for the precise setting of the commutated fields, it is irrelevant in which rotation segment the rotor 4 is physically located.

[0096] It may also be impossible to uniquely determine the rotor position in a rotation segment with only one configuration of the first subset and the second subset. For example, if the BLDC 3 has five magnetic pool pairs and thus ten segments, the magnetic polarity of the pool pairs has no influence on the measured amplitude of the response signals 15. The periodicity of the amplitude of the response signals 15 is therefore 360° / 10 = 36°. In principle, two positions within a 36° segment can be assigned to a measured amplitude of the response signal 15. Therefore, the rotor position within the 36° segment cannot be uniquely determined with only one configuration. Consequently, the measurement can also be performed with a modified configuration to resolve the described degeneracy, as described in Fig. 9 shown.

[0097] With the slowly rotating rotor 4, it would also be possible to temporarily forgo commutation, that is, to briefly switch off the excitation of the coils by the control signals 16a, 16b in order to inject two test signals 14 with different configurations in quick succession. Since the duration of the test pulses of the test signals 14 is very short, for example, a few microseconds, this would not significantly disrupt operation. During this short period, any change in the angle of the rotor 4 would be very small, so errors in position determination would also be small.

[0098] For correct commutation, not only the position of the individual magnets is relevant, but also their polarity. In some embodiments, to determine the exact rotational position of the rotor 4 with respect to the polarity of the magnet pairs in the stationary state, it is possible, for example, to briefly change the rotor position by energizing a coil. Such a change, combined with the measurements described before and after the change in rotor position, then allows for a clear assignment of the magnetic polarity. In practice, such positional changes of the BLDC are possible due to the elasticity of the materials, especially the gear units, even when holding forces are applied.

[0099] With a slow-rotating BLDC motor, the change in rotor position is inherent anyway, therefore the described procedure is also feasible.

[0100] In some embodiments, a practical implementation based on an FPGA is possible. An FPGA possesses excellent real-time capabilities and therefore enables very precise timing control. For example, it is easy to generate a test pulse exactly 1 µs long and measure the response after exactly 1 µs. Furthermore, tests have confirmed that the method described here can be combined with other estimation methods. For instance, the method described here can be used at standstill and during startup, and a smooth switch to established methods is possible once a certain minimum speed is reached.

[0101] An exemplary procedure is shown schematically in Fig. 10 shown.

[0102] In step 1000, a test signal 14 with a 1 µs long test pulse is applied in a first configuration. Step 1100 corresponds to a delay of 10 µs. In step 1200, a test signal 14 with a 1 µs long test pulse is applied in a second configuration. In step 1300, the rotor position is determined while stationary. In step 1400, the rotor 4 is briefly rotated by a small angle. In step 1500, a test signal 14 with a 1 µs long test pulse is applied in the first configuration. Step 1600 corresponds to a delay of 10 µs. In step 1700, a test signal 14 with a 1 µs long test pulse is applied in the second configuration. In step 1800, the polarity is determined as described. In step 1900, the start-up phase begins, and the rotor position can be determined using a method according to the invention. REFERENCE MARK LIST: 1 Motor device 2 electronic circuit 3 brushless DC motors 4 Rotor 5 Stator 6 Motor control 7 Test circuit 8 Evaluation circuit 9a, 9b Bridge transistors 10a, 10b bridge transistors 11a, 11b Bridge transistors 12a, 12b, 12c coils 13a, 13b, 13c coils 14 Test signal 15 Response signal 16a, 16b Control signal 17 reference data 100th process step 120th process step 140 Procedure step 160 Process step 1000 process step 1100 Process step 1200 process step 1300 Process step 1400 process step 1500 process step 1600 process step 1700 process step 1800 process step 1900 process step

Claims

[1] Method for sensorless determination of a rotor position of a brushless DC motor (3) during a rotational movement of a rotor (4) of the brushless DC motor (3), wherein the rotor (4) or a stator (5) of the brushless DC motor (3) has a number of coils (12, 13) and wherein - for each of the coils (12, 13) a respective control signal (16a, 16b) is generated to control the coil and the coil is supplied with electrical power according to the respective control signal (16a, 16b) in order to set the rotor (4) into rotational motion; - a first subset of coils (12, 13) of the number of coils (12, 13) is subjected during the rotational movement to a test signal (14) which corresponds to a voltage drop across the first subset of coils (12, 13) or a current flowing through the first subset of coils (12, 13) or is generated depending on the voltage or current; - depending on an electrical response signal (15) induced in response to the application of the test signal (14) of a second subset of coils (12, 13) the number of coils (12, 13) test data are determined; and - the rotor position is determined by comparing the test data with predefined reference data (17). [2] Method according to claim 1, wherein the respective control signal (16a, 16b) for controlling the respective coil includes a plurality of signal pulses. [3] Method according to claim 2, wherein the respective control signal (16a, 16b) for controlling the respective coil is a pulse width modulation signal. [4] Method according to any of the preceding claims, wherein the test signal (14) includes a test pulse. [5] Method according to claim 4 and one of claims 2 or 3, wherein the at least one first subset of coils (12, 13) is supplied with the test signal (14) in such a way that no signal pulse of the respective plurality of signal pulses for controlling the first subset of coils (12, 13) overlaps with the test pulse. [6] Method according to one of claims 1 to 3, wherein the test signal (14) is generated by combining a test pulse with one of the control signals (16a, 16b). [7] Method according to any one of claims 4 to 6, wherein the test pulse has a test pulse duration of less than 50µs or less than 20µs or less than 10µs or less than 5µs or less than 2µs. [8] Method according to one of the preceding claims, wherein the rotational movement has a rotational speed in the range of 0, 1000 min -1 ] exhibits. [9] Method according to any of the preceding claims, wherein the test data - include a maximum amplitude of the response signal (15) or are at least partially determined depending on the maximum amplitude; and / or - are determined at least partially depending on a signal shape of the response signal (15); and / or - are determined at least partially depending on the decay behavior of the response signal (15); and / or - include a relative temporal position or a relative phase position of the response signal (15) with respect to the test signal (14) or are at least partially determined depending on the relative temporal position or the relative phase position. [10] Method according to any of the preceding claims, wherein the test data - are determined at least partially depending on a ratio of the maximum amplitude of the response signal (15) to a maximum amplitude of the test signal (14); or - can be determined at least partially depending on a ratio of the maximum amplitude of the test signal (14) to the maximum amplitude of the response signal (15). [11] Method according to any one of the preceding claims, wherein - at least two distinct subsets of the number of coils (12, 13) are defined, wherein the at least two distinct subsets include the first subset; - at least two different further subsets of the number of coils (12, 13) are defined, wherein the at least two different further subsets include the second subset; - each subset of at least two subsets is assigned at least one further subset of at least two further subsets; - for each subset of the at least two subsets and for each further subset assigned to the respective subset of coils (12, 13) i) the respective subset of coils (12, 13) is supplied with a respective test signal (14) which corresponds to a voltage drop across the respective subset of coils (12, 13) or a current flowing through the respective subset of coils (12, 13) or is generated depending on the voltage or current; and ii) depending on an electrical response signal (15) induced in the respective further subset of coils (12, 13) in response to the application of the respective test signal (14); a test data set is determined; and - the test data includes the test data sets. [12] Method according to one of the preceding claims, wherein at least one of the control signals (16a, 16b) is changed depending on the rotor position. [13] Electronic circuit (2) for sensorless determination of a rotor position of a rotor (4) of a brushless DC motor (3) during a rotational movement of the rotor (4), wherein the rotor (4) or a stator (5) of the brushless DC motor (3) has a number of coils (12, 13) and wherein - the electronic circuit (2) includes a motor control (6) which is configured to generate a respective control signal (16a, 16b) for each of the coils (12, 13) to control the coil and to supply the coil with electrical power according to the respective control signal (16a, 16b) in order to set the rotor (4) into rotational motion; - the electronic circuit (2) includes a test circuit (7) which is configured to apply a test signal (14) to a first subset of coils (12, 13) of the number of coils (12, 13) during rotational movement. The test signal corresponds to a voltage drop across the first subset of coils (12, 13) or a current flowing through the first subset of coils (12, 13), or is generated depending on the voltage or current. - the electronic circuit (2) has at least one evaluation circuit (8) which is configured to detect an electrical response signal (15) induced in response to the application of the test signal (14) of a second subset of coils (12, 13) of the number of coils (12, 13) and to determine test data depending on the response signal (15) and to determine the rotor position by comparing the test data with predefined reference data (17). [14] Motor device (1) for an electrical appliance comprising a brushless DC motor (3) and an electronic circuit (2) according to claim 13. [15] Electrical appliance comprising a motor device according to claim 14.

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