Method for sensorless determination of the position of a rotor of a rotating field machine

Abstract

Method for sensorless determination of the position of a rotor of an EC motor, with a system having at least three winding strands, comprising the steps a) Measuring the rate of current rise for each winding strand for at least two different space vector positions of an electrical quantity by means of an excitation of the respective winding strand, b) Determining the rotor position-dependent linked admittances for each winding strand, in which all different combinations of two winding strands of the at least three winding strands are alternately supplied with current in the two current directions, c) Determining the unlinked strand admittances from the linked admittances based on a network transformation, and d) Determining rotor position information based on the determined unlinked admittances.

Description

[0001] The invention relates to a method for sensorless determination of the position of a rotor of an EC motor with a system having at least two winding strands.

[0002] The invention further relates to a device for sensorless determination of the position of a rotor of an EC motor with a system having at least two winding strands.

[0003] Although the present invention is generally applicable to any rotating field machines, the present invention is explained using rotating field machines in the form of permanent magnet or reluctance EC motors.

[0004] To operate so-called electronically commutated motors, it is necessary to detect the instantaneous rotor position from standstill to maximum speed. This is required for the timing control of the motor currents via motor electronics. Regardless of the type of commutation / current control—block-commutated, sinusoidally controlled, or space-phasor modulated—the magnetic excitation field of the motor's stator must be controlled in such a way that a force is exerted on the motor's rotor, achieving a specific torque per unit current and / or maximum efficiency. This means that the rotating magnetic field of the stator must lead that of the rotor in the direction of rotation by an angle specified by the control electronics.

[0005] To detect the rotor position, it is common practice to use so-called angular position sensors, which are either permanently attached to the rotor axis or positioned at predetermined locations on the stator circumference. These sensors can include, for example, rotating segmented disks, resolvers (i.e., electromagnetic transmitters for converting the angular position of a rotor into an electrical value), or Hall effect sensors. Hall effect sensors, in particular, must be permanently installed during the motor's manufacturing process and may require adjustment or calibration. This results in additional costs and, furthermore, reduces system reliability due to the use of these components.

[0006] To reduce this complexity, so-called sensorless rotor position detection systems have become established. For evaluation, particularly in permanent magnet motors and reluctance motors, magnetic variations and the resulting inductance changes can be used. In reluctance motors, pronounced pole segments are present on the rotor for targeted flux guidance, creating a significant inductance difference between the d- and q-axes of the rotor. In permanent magnet motors, especially those with surface magnets, the dq difference is less pronounced, caused by the influence of the permanent rotor flux on the stator iron. In the direction of the main flux (d-axis), the stator iron becomes more saturated, according to the magnetization characteristic of iron, than in the q-axis, where the flux is lower.

[0007] These flux differences, which are coupled to the rotor position, lead to different inductances in the corresponding stator coils due to saturation effects. Therefore, it is possible to estimate the rotor's position by measuring the inductance at different spatial angles of the stator. The typically three-strand winding arrangement of EC motors results in 6 or 12 angular steps due to the excitation of the stator winding (solid angle), which must be evaluated with respect to their inductance.

[0008] Out of Fig. Figure 1 shows that in each of the 12 switching states, a winding combination of two or three winding strands can always be detected on the three motor leads. Therefore, with varying inductance influences due to the rotor position, only one line-to-line inductance can be measured. To determine the current rotor position with the flux-generating permanent magnets more precisely, an impedance or admittance measurement of the individual winding strands is required. It is known to implement the star point as the connection point of the winding strands in addition to the three winding starts of a three-phase winding system and to connect it to the measuring circuit. However, this represents an additional effort, since the connection of the star point is not required for the motor's power supply.

[0009] From EP 3 220 535 A1, a frequency converter and a method for determining the synchronous inductances of a salient-pole synchronous machine connected to a frequency converter with current measurement in the DC link are known. The method comprises supplying a voltage pulse of known magnitude for each phase of the salient-pole synchronous machine with the frequency converter, measuring the current in the DC link at the end of each voltage pulse, calculating the reciprocal of the inductance for each supplied voltage pulse as the measured current divided by the magnitude of the voltage and by the duration of the voltage pulse, and solving for the synchronous inductances from the calculated reciprocals of the inductances.

[0010] From DE 10 2015 217 986 A1, a method for identifying the magnetic anisotropy of an electric rotating field machine is known, comprising a rotor and a stator, wherein the rotating field machine is controlled by pulsed terminal voltages using pulse-width modulation. The method provides that during an injection interval, at least four voltage vectors are applied, which, in a space vector representation, all have the same magnitude after subtracting the common mean and are mutually orthogonal or antiparallel in pairs. A corresponding change in the current vector is determined in response to each of the four voltage vectors, and the anisotropy values ​​are deduced from the respective changes in the current vectors, taking the voltage vectors into account. Such a method offers the advantage of very low computational effort and is easy to implement.

[0011] Furthermore, a method for sensorless control of a three-phase machine is known from EP 2 026 461 A2. In this method, during the time of the inverter switch positions used for rotor position evaluation, the current is carried in two phases, and at least one of the phases is de-energized. The rotor or flux angle is determined based on two voltage equations valid during different inverter switch positions occurring in quick succession, where both inverter switch positions have the same de-energized phase.

[0012] One object of the present invention is therefore to provide a method and a device for sensorless determination of the position of a rotor of a rotating field machine with a system having at least two winding strands, which is simple and cost-effective to carry out or manufacture and enables a reliable determination of the position of a rotor with the fewest possible measurements.

[0013] In one embodiment, the present invention solves the above problem by means of a method for sensorless determination of the position of a rotor of an EC motor according to claim 1.

[0014] In a further embodiment, the present invention solves the aforementioned problem by means of a device for sensorless determination of the position of a rotor of an EC motor according to claim 11.

[0015] Using a network transformation based on the conformance principle, it is possible to determine the admittances measurable at the network ends. Based on these measured admittances, the individual strand admittances can then be determined. Once these are determined, the rotor position can be determined in a simple and reliable manner.

[0016] In other words, it is possible to determine the impedance values ​​of the individual motor windings and, via the impedance distribution of the motor windings, the rotor position with as few measurements as possible on the interconnected motor windings, for example, at the UVW terminals in a three-strand motor system. Based on the spatial admittance or impedance distribution, which resembles an ellipse, for example, it is possible to obtain or determine indications of variations in the motor parameters for qualitative motor testing or even indications of possible faults during motor operation.

[0017] The rotor position detection method presented here is based primarily on a current response, which can be generated in various ways, such as applying a high-frequency rotating space vector to the winding or injecting voltage pulses into the stator space vectors and measuring their admittance-dependent current rise rate. The voltage pulses can be provided, for example, as rectangular pulses with a predefined pulse-pause ratio. The pulse width is chosen to be sufficiently wide to obtain a usable current response. The pulse-pause ratio can vary but must be known. Current measurement is performed using appropriately arranged shunts or a comparable electronic circuit.

[0018] The current responses vary with the respective linked position-dependent strand admittances, which are necessary to determine the rotor position information. The magnitudes of the strand admittances change analogously to the rotor position.

[0019] The extraction of the individual phase inductances takes place after a network transformation. A conformity principle of the network transformation is used here, according to which the admittances measurable at the network ends are independent of the type of network. This applies in particular to the switching states of the winding system shown in the diagram. Fig. 1.

[0020] The invention utilizes the anisotropy caused by the permanent magnet-induced flux through the rotor magnets, which can easily lead to different inductances of the stator windings. These inductances are determined by measuring the current rise behavior when voltage pulses are applied to the connected winding terminals or by measuring high-frequency rotating fields with low voltage values ​​and their corresponding current responses. This measurement is achieved in particular by means of a current measurement integrated into an electronic circuit.

[0021] Further features, advantages and further embodiments of the invention are described below or are disclosed therein.

[0022] According to a beneficial further development, steps a)-d) are initially performed with the rotor stationary. This enables a particularly simple and reliable determination of rotor position information even when the rotor is at rest.

[0023] According to a further advantageous refinement, step c) is performed using a network transformation in the form of a triangle-star transformation. This enables a simple and efficient determination of the rotor position-dependent strand impedance and thus of rotor position information.

[0024] According to a further advantageous embodiment, excitation is achieved by means of voltage pulses. This allows for a particularly simple and efficient excitation of the respective winding strand.

[0025] Step b) is performed by alternately applying current to all different combinations of two winding strands of the at least three winding strands in each of the two current directions. This allows switching states to be provided in a particularly simple way using a winding combination of two winding strands, ultimately enabling the efficient determination of rotor position information.

[0026] According to a further advantageous refinement, step b) is performed in which the system is subjected to one current direction and to multiple current directions. In other words, all possible switching states of the system with at least three winding strands are used to determine the unlinked strand admittances, which further improves the accuracy with regard to the rotor position information.

[0027] According to a further advantageous refinement, the determined rotor position information is checked for plausibility. This increases the accuracy of the determined rotor position information. A plausibility check can be performed, for example, by ensuring that the sums of the currents measured in a single run and the sums of all current increases measured in that run each equal the value "0".

[0028] According to a further advantageous refinement, the initial rotor position is taken into account to determine rotor position information. Errors in rotor position detection can be minimized based on the initial rotor position.

[0029] According to a further advantageous embodiment, steps a)-d) are performed during the start-up of the EC motor, in particular with a slowly starting rotating field or via a forced-position method. In the forced-position method, a stator magnetic field is generated, depending on the rotor's initial position, such that it is aligned with the rotor's magnetic field (current flowing in the direction of the d-axis of the stationary rotor). With a now slowly starting rotating field and sufficient torque for the application, the rotor is driven into rotation.

[0030] According to a further advantageous refinement, changes in strand admittances and / or a mean strand admittance are evaluated based on the determined strand admittances. This allows, for example, the determination of air gap variations due to static or dynamic eccentricities or the like, which improves accuracy.

[0031] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the accompanying description of the figures based on the drawings.

[0032] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0033] Preferred embodiments and configurations of the present invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components or elements.

[0034] This is shown in schematic form Fig. 1 discrete current directions of a three-strand winding system; Fig. 2 a triangle-star transformation to determine admittances; Fig. 3 a schematic procedure for the extraction of rotor position-dependent strand impedances; Fig. 4 an admittance curve after evaluation of even-numbered space vector images according to an embodiment of the present invention; Fig. 5 a representation of a space vector for a three-strand winding system when current is applied according to an embodiment of the present invention; Fig. 6 a representation of a space vector for a three-strand winding system under current energization according to an embodiment of the present invention; and Fig. 7 an admittance curve according to evaluation of even-numbered space vector images according to an embodiment of the present invention.

[0035] Fig. Figure 1 shows discrete current directions of a three-strand winding system, Fig. 2. A triangle-star transformation to determine admittances and Fig. 3 a schematic procedure for the extraction of rotor position-dependent strand impedances.

[0036] In detail, in Fig. Figure 1 shows a total of twelve switching states No. 1-12, wherein the odd-numbered switching states No. 1, 3, 5, 7, 9, 11 are supplied with a total current that has only one component, whereas the even-numbered switching states No. 2, 4, 6, 8, 10 and 12 have a total current that has two components.

[0037] Fig. Figure 2 schematically illustrates a network transformation in the form of a triangle-star transformation. The network transformation is performed according to the following transformation laws: Z10=Z12⋅Z13Z123 Z¯20=Z¯12⋅Z¯23Z¯123 Z¯30=Z¯23⋅Z¯13Z¯123 and the rolling resistance: Z123=Z12+Z23+Z13.

[0038] This type of network conversion is particularly suitable for the in Fig. The odd-numbered network circuits listed in 1, Nos. 1, 3, 5, 7, 9 and 11, can alternatively or additionally be applied equally to the even-numbered switching states Nos. 2, 4, 6, 8, 10 and 12.

[0039] Preferably, the rotor position is determined in a first step via the odd-numbered switching states No. 1, 3, 5, 7, 9 and 11 according to Fig. 3 determined: The measured variables Z uv , Z uw , Z uw ( Fig. 3) can be considered under equivalence considerations of network transformations according to Fig. 2 as triangular elements in the associated star impedance Z u ,Z u ,Z w be converted.

[0040] This step is preferably applicable to determining the d- or q-axis of the rotor. The flux direction, used to distinguish the north-south direction of the rotor magnets, is then determined by test vectors, which are preferably applied to the non-moment-generating d-axis. For example, rectangular voltages can be used as test vectors, applied first in the positive and then in the negative d-direction.

[0041] In a further step, the even-numbered switching states No. 2, 4, 6, 8, 10, 12 can be evaluated. The total injected current is then divided into two components, which, comparable to the first step with the odd-numbered switching states No. 1, 3, 5, 7, 9, 11, are part of a network transformation, the delta-star conversion according to the Fig. 2 and Fig. 3, can be subjected to. By evaluating the displayed switching states according to Fig. 1. Twelve spatial magnetic flux vectors can be determined, whose admittance values ​​exhibit different characteristics depending on the rotor position. An expected admittance profile by evaluating the even-numbered switching states No. 2, 4, 6, 8, 10, 12 is, for example, in Fig. 4 shown. If the actual admittance curve deviates, as for example in Fig. 7, from the expected admittance curve according to Fig. From 4 onwards, air gap variances and eccentricities can be identified based on the corresponding differences.

[0042] The aforementioned procedure for determining the rotor position yields a list of extracted strand mitigations. According to the invention, these are subjected to a plausibility test to predict a rotor position based on the rotor's rest position and / or system- or ambient temperature-dependent influences. Regardless of the fact that different evaluation methods may determine a more or less erroneous rotor position, case distinctions can be made, which result, among other things, from the initial condition of the stationary rotor. Thus, the rotor's rest position can be located with an electrical angular resolution in the direction of one of the three winding strands u, v, w, or in the intermediate position between two strands (as in Fig. 5 and Fig. (as shown in Figure 6). In particular, by considering the most pronounced initial condition, the error in rotor position detection can be minimized. Different evaluation methods can be used, for example, by varying the sequence of the switching states according to... Fig. 1. A suitable, pronounced initial condition can be provided, for example, by determining the largest difference of the determined, chained admittances.

[0043] These exemplary representations of the first two of 12 possible space vectors of a three-strand winding system according to the Fig. 5 and Fig. The angles can be continued in 30° increments and describe the relationship between the current directions in the winding strands and the resulting magnetic flux vectors of a two-pole rotating field machine. In this case, the electrical and mechanical angles of the space vector are identical. For a 10-pole lathe, the electrical angle is divided by the number of pole pairs (5), resulting in a mechanical angle step of: 30° / 5 => 6° mechanically.

[0044] The magnetic flux pointer φPM points to the d-axis of the rotating dq coordinate system and, even when the stator is de-energized, causes a premagnetization of the flux paths of the associated magnetic circuit. With the rotor position according to Fig. 5 the stator strands U and V show and according to Fig.The winding U and, depending on their magnitudes, exhibit more or less pronounced saturation effects in the associated magnetic circuits. This, in turn, causes different flux magnitudes and thus different inductance values ​​between the coils of the individual winding strands, for example, according to the saturation behavior of iron. The higher the magnetic flux, the lower the inductance, or rather, the higher the admittance (the reciprocal of inductance). The individual winding strands exhibit different admittances depending on the rotor or permanent magnetic flux. The position-dependent admittance values ​​fluctuate around an average value.

[0045] The rotor position detection described above is initially performed with the rotor stationary. This also applies to the fault detection methods described below. For motor start-up, the described detection procedure can be continued in the lower speed range using a slowly starting rotating magnetic field, or a start can be achieved using the so-called forced-position method. The lower speed range is defined as the range with less than 5% of the motor's rated speed. In the latter case, a stator magnetic field is generated, depending on the rotor's initial position, such that it is aligned with the rotor's magnetic field (current flowing along the d-axis of the stationary rotor). As the speed increases, the rotor's torque requirement also increases, resulting in an increasing drag angle. The torque on the rotor also increases until a maximum torque is reached at a drag angle of 90° (current flowing only along the q-axis).When a sufficiently high rotational speed is reached and the resulting induced voltage is generated by the rotor magnets in the stator windings (EMF), it is possible, for example, to switch to so-called model-based fundamental wave methods, such as observer-based rotor position detection such as Luenberger observers, Kalman filters, or Model Reference Adaptive System (MRAS).

[0046] The described starting procedure can also be carried out without prior rotor position determination by admittance evaluations if, for example, disturbances such as changed motor parameters, air gap variations or demagnetization effects prevent a sufficiently accurate rotor position determination.

[0047] Similarly, the admittance analysis of the winding strands, using the described rotor position determination, can also be used to detect deviations and variances in the motor parameters. This allows valuable information to be obtained about operational reliability, aging behavior, and the current operating states of the motor.

[0048] In this respect, embodiments of the present invention offer the following advantages or provide the following features: • Extraction of strand admittances via an equivalent network transformation, in particular a triangle-star transformation, to increase the signal-to-noise ratio resulting from the measurement of the linked strand sizes, • A plausibility test with different test pulses to minimize fault influences depending on the rotor's rest position and / or system or ambient temperature, • Implementation of case distinctions at rotor rest position to improve start-up behavior with initial excitation by a current vector in the rotor d-axis. • Recording and evaluating mean strand admittances to determine air gap variances through static eccentricities, • Recording and evaluating admittance changes to determine air gap variances through dynamic eccentricities, • Recording and evaluation of admittance values ​​in conjunction with measured variables such as motor currents, voltages, speed values ​​and temperatures to determine temperature dependencies and batch variations of permanent magnets, • Recording and evaluation of admittance values ​​in conjunction with measured variables such as motor currents, voltages, speed values ​​and temperatures to determine operational malfunctions and motor malfunctions.

[0049] In summary, embodiments of the invention are based on a measurement of the current rise rates of the linked stator windings and a determination of the rotor position, the corner values ​​of which are determined by network transformations such as the delta-star conversion, a simple difference calculation of the space vector-oriented measured values ​​and / or matrix calculations or by solving linear systems of equations by methods such as the least squares method, the solutions of which are available in the form of simple arithmetic operations.

[0050] In other words, the rotor position-dependent magnetic anisotropy is amplified by the network transformations to improve the signal-to-noise ratio and subsequently converted from the three strand quantities into the Cartesian alpha / beta coordinate system by a coordinate transformation that is already available for vector control, thus obtaining the spatial location of the magnetic anisotropy.

[0051] Although the present invention has been described using preferred embodiments, it is not limited to these, but can be modified in many ways.

Claims

[1] Method for sensorless determination of the position of a rotor of an EC motor, with a system having at least three winding strands, comprising the steps a) Measuring the rate of current rise for each winding strand for at least two different space vector positions of an electrical quantity by means of an excitation of the respective winding strand, b) Determining the rotor position-dependent linked admittances for each winding strand, in which all different combinations of two winding strands of the at least three winding strands are alternately supplied with current in the two current directions, c) Determining the unlinked strand admittances from the linked admittances based on a network transformation, and d) Determining rotor position information based on the determined unlinked admittances. [2] Method according to claim 1, wherein steps a)-d) are first carried out with the rotor stationary. [3] Method according to one of claims 1-2, wherein step c) is performed by means of a network transformation in the form of a triangle-star transformation. [4] Method according to one of claims 1-3, wherein the excitation is carried out by means of voltage pulses. [5] Method according to one of claims 1-4, wherein step b) is carried out by subjecting the system to one current direction and to multiple current directions. [6] Method according to one of claims 1-5, wherein the determined rotor position information is checked for plausibility. [7] Method according to any one of claims 1-6, wherein the initial rotor position is taken into account to determine rotor position information. [8] Method according to one of claims 1-7, wherein steps a)-d) are carried out at the start of the rotating field machine, in particular with a slowly starting rotating field or via a forced-position method. [9] Method according to one of claims 1-8, wherein changes in strand admittances and / or an average strand admittance are evaluated based on the determined strand admittances. [10] Method according to one of claims 1-9, wherein steps a)-d) are only carried out up to a predetermined rotational speed of the rotating field machine. [11] Device for sensorless determination of the position of a rotor of an EC motor, comprising a system with at least three winding strands, comprising a measuring device for measuring a current rise rate for each winding strand for at least two different space vector positions of an electrical quantity by means of an excitation of the respective winding strand, an admittance determination device for determining the rotor position-dependent linked admittances for each winding strand and which is designed to alternately apply current to all different combinations of two winding strands of the at least three winding strands in the two current directions, a computing device for determining the unlinked strand admittances from the linked admittances based on a network transformation, and a rotor positioning device for determining rotor position information based on the determined unlinked admittances.

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