REGULATION DEVICE AND METHOD FOR REDUCING THE COMMUTATION ANGLE ERROR IN AN EC MOTOR

Description

[0001] The invention relates to a control device and a method for reducing the commutation angle error in an EC motor.

[0002] For example, to control a permanently excited synchronous motor (PMSM) in a field-oriented manner, the position of the rotor relative to the stator must be known. This is referred to as an angular position within a magnetic period of the motor, or the so-called commutation angle. It is known to control EC motors by detecting the rotor position using a position measuring device. Given a known relative position between the actual rotor position and the rotor position detected by the position measuring device, a commutation offset or commutation angle error can be calculated and used to control a power unit supplying the motor, for example, a commutation device in the form of an inverter.

[0003] The commutation angle error, which is also referred to as commutation offset or electrical angle deviation, is therefore the deviation of the actual rotor rotational position from the determined rotor rotational position or rotor position.

[0004] The rotor position can be detected using either an absolute position measuring system, in which the rotor position is detected immediately after the EC motor is activated, or an incremental position measuring system, in which the absolute rotor position is only determined after one or more reference marks have been passed.

[0005] If the commutation offset, i.e., the phase deviation between the actual rotor position and the rotor position measured by the position measuring device, is known, the measured rotor position corrected for the commutation offset can be used as the basis for controlling the synchronous machine. A number of methods are known in the state of the art that address the topic of detecting the commutation offset and the question of how the offset can be appropriately taken into account in the control system during commutation.

[0006] In the following description, the terms "rotor" and "stator" refer only to the functional designation of the basic elements of an electric motor, which either change their position (rotate or shift) relative to an external coordinate system – the rotor – or are fixed relative to the external coordinate system – the stator. Especially when starting the EC motor, it is desirable to know the exact angular position or orientation of the rotor relative to the associated stator in order to be able to generate a suitable torque on the rotor. In known methods or devices, the angular position is obtained via absolute position measurement using sensors, incrementally, or alternatively using the solutions known in the state of the art for sensorless commutation.

[0007] Numerous other methods for determining the commutation angle are known from the state of the art. In addition to the numerous methods that determine the commutation angle by measuring electrical quantities such as inductance or magnetic saturation, there are also many methods that rely on applying current to the motor and detecting more or less significant rotor deflections.

[0008] From DE 10213375 A1, it is known to externally impose a movement on a synchronous motor under field-oriented control, while specifying a target current of zero in the control loop. The control loop therefore generates voltages that counteract the voltages induced in the motor by the movement. The commutation angle can be determined from the phase position of these voltages.

[0009] DE 4437793 A1 describes a two-stage method for determining the phase position of the rotor, in which the phase position is first determined coarsely and then finely. Small deflections of the initially stationary rotor, caused by the application of current vectors, are recorded, and from this, its phase position is determined. Another possibility for determining the commutation angle is to apply a torque-generating current to the synchronous motor in any chosen orientation. The rotor will then move and align itself parallel to this direction. This allows its position and commutation angle to be determined. Likewise, various methods for determining the commutation angle error are known in the prior art. For example, the commutation angle error can be determined from the starpoint difference voltage.

[0010] However, knowing both the commutation angle and the commutation angle error does not eliminate the influence of the commutation angle error. This commutation angle error can lead to instability in motor operation. However, the current state of the art solutions do not aim to prevent the commutation angle error, but rather to correct it through control engineering when controlling the motor. The commutation angle error arises from the phase shift of the starpoint differential voltage due to the field-weakening current (d-current component).

[0011] The phase shift of the star-point differential voltage refers to the phase shift of the third harmonic component of the star-point differential voltage relative to the fundamental and leads to the aforementioned commutation angle error. The phase shift is the shift between the fundamental of the rotor voltage and the current in a phase, or the function value of the arctangent of the ratio of the field-generating current (d-current) to the torque-generating current (q-current).

[0012] In EC motors where there is a pronounced phase shift in the starpoint voltage difference due to flux-generating and torque-generating current components, resulting in an error in the rotor rotational position determination, a corresponding commutation angle error will naturally occur without further countermeasures. A positive phase shift is detrimental in that it leads to a so-called positive feedback effect, which means that an increasing angle error in turn leads to an increasing current and current angle, both of which in turn lead to a further increasing angle error and, consequently, to motor failure. In the worst case, this positive feedback prevents the EC motor from operating as intended.

[0013] Furthermore, many of the correction methods known in the state of the art cannot be applied to EC motors with a current-dependent inductance.

[0014] Further printed prior art in the present technical field is disclosed in document EP 2 709 267 A1.

[0015] The invention is therefore based on the object not to reduce the consequences of the commutation angle error, but to fundamentally avoid or significantly reduce a current- or saturation-related commutation angle error.

[0016] This object is achieved by the feature combinations of independent claims 1 and 6, which define the invention.

[0017] A basic idea of ​​the present invention is to detect the rotor position by means of the star point potential and to impress a field-weakening current component (FSK) into the motor control system by means of a control device, in particular using a control loop.

[0018] The field-weakening current component is the current component that generates a magnetic field that counteracts the magnetic field of the permanent magnet of the EC motor. Such a field-weakening current component can be the field-weakening current (negative d-current) or a corresponding phase shift.

[0019] The central concept for reducing or avoiding a system-related angle error is the injection of a field-weakening current component (FSK).

[0020] A property of the field-weakening current component is the dependence on operating variables such as current, duty cycle or torque or a system variable related to an operating parameter, thus: a) current (such as torque-generating current component Iq, total current I, intermediate circuit current Izk, b) duty cycle A, c) speed n, d) torque M or e) also a combination thereof, such as a fan characteristic curve for a fan driven by the EC motor.

[0021] Another aspect concerns the functional definition of the field-weakening current component (FSK) in relation to one of the operating variables. The relationship between the field-weakening current component and the torque can be defined, for example, as a constant, a linear function, a function with an offset, or a higher-order polynomial. This definition can be freely chosen or can be made by specifying a maximum and minimum value that defines the limits.

[0022] Another aspect concerns the selection of a suitable value range. A reasonable value range for the field-weakening current component is limited by permissible boundary conditions, such as an accepted reduction in torque caused by the field-weakening current component FSK.

[0023] According to the invention, a control device is proposed which is specifically designed to reduce the commutation angle error ε of a three-phase EC motor connected via a star connection, the three phases of which are commutated via a motor control, comprising a rotor position detection in order to detect the relative angular position of the rotor by means of the star point potential at the star point of the star connection, and a control circuit which is designed to impress a field-weakening current component, as intended, on the motor control to reduce the commutation angle error ε.

[0024] In a further preferred embodiment of the invention, a signal processing device is provided which detects operating data of the EC motor which are dependent on the field-weakening current component (FSK) in order to supply these to a controller of the motor control for the control task.

[0025] A further aspect of the present invention relates, in addition to the device mentioned, to a method for reducing the commutation angle error ε of a three-phase EC motor connected via a star connection, the three phases of which are commutated via a motor control, preferably using a control device as defined above, wherein a rotor position detection takes place from the star point potential at the star point of the star connection of the motor phases and a field-weakening current component (FSK) is impressed on a commutation device for commutating the motor to reduce the commutation angle error.

[0026] In an advantageous embodiment of the method, the field-weakening current component is constant in magnitude. Alternatively, the field-weakening current component can be a linear or non-linear function, particularly dependent on an operating variable of the EC motor, more preferably dependent on the torque M or the current of the EC motor. However, other operating variables are also conceivable, such as the duty cycle, the speed, or the fan characteristic curve of a fan operated by the EC motor.

[0027] In a further advantageous embodiment of the method according to the invention, it is provided that the field-weakening current component is determined from the curve of the curve FSK = FSK ε Pi for a specific operating parameter Pi of the EC motor, whereby first the curve shape of the curve ε = ε (FSK) is determined, which indicates the relationship between the angular deviation ε and the field-weakening current component FSK and based on this, a constant current component for impression is determined from the intersection point of the curve FSK (ε, Pi) for which a maximum permissible angular deviation ε max is specified.

[0028] In a further embodiment of the invention, it is provided that the field-weakening current component is determined from the curve of the respective function FSK = FSK (ε, Pi) of at least two or more curve profiles of the respective curve for a different operating parameter, preferably for different torques of the EC motor, and from this the functional relationship between the said operating parameter and the field-weakening current component is obtained, whereby for this purpose the respective curve of the curve for different values ​​of a specific operating parameter (e.g. different torques): FSK = FSK ε Pi is determined, which indicates the relationship between the angular deviation ε and the field-weakening current component. Based on this, a current component for the impression is determined from the respective intersection points of the curves FSK (ε, Pi), at each of which a predetermined permissible angular deviation ε def is specified. This can be achieved, for example, by linear approximation or averaging the determined intersection values.

[0029] In a likewise advantageous embodiment of the invention, it is provided that first the curve profile of the curve ε = ε (FSK) is determined which indicates the relationship between the angular deviation ε and the field-weakening current component FSK and from this, first the angular deviation ε krit is determined from the curve profile at which the EC motor can no longer be commutated in a certain rotationally stable operating state by successively increasing the permissible angular deviation ε until the rotationally stable operating state of the EC motor changes into an unstable state, which is defined by the curve point ε krit at the tangential point of a tangent T with the gradient ST to the curve ε = ε (FSK), wherein the tangent T is shifted along the abscissa of the curve ε = ε (FSK) untiluntil the tangent T is tangential to a point on the curve ε (FSK) and the intersection point between the tangent T and the abscissa determines the value for the field-weakening current component.

[0030] Other advantageous developments of the invention are characterized in the subclaims or are presented in more detail below together with the description of the preferred embodiment of the invention with reference to the figures.

[0031] They show: Fig. 1 shows a diagram with a control loop according to the concept of the present invention; Fig. 2 shows a graphical explanation of the function definition; Fig. 3 shows a graphical explanation for setting the value range; Fig. 4 shows an exemplary embodiment for determining or setting a specific constant value for the field-weakening current component; Fig. 5 shows an exemplary embodiment for determining or setting a value for the field-weakening current component as a function of a varying operating parameter (here: the torque M); Fig. 6 shows an exemplary embodiment for determining or setting a specific value for the field-weakening current component at the transition to the unstable operating point of the EC motor; Fig. 7 shows an exemplary embodiment of an EC motor of a fan with a slow controller; Fig. 8 shows a graphical explanation of the value determination in % as a function of the phase shift λ; Fig. 9 shows a graphical explanation of the determination of intermediate values; Fig.10a functional representation of the field-weakening current component FSK as a function of the quotient of the intermediate circuit current and the nominal value of the intermediate circuit current and .

[0032] In the following, the invention is described with reference to the Figures 1 to 10 closer

[0033] described, whereby the same reference symbols or designations in the figures indicate the same structural and / or functional features or dimensions, unless otherwise stated in the figure description. Fig. 1shows a diagram with a control loop 10 according to the concept of the present invention, wherein a manipulated variable is controlled and transferred to the controller of the motor control unit 3. The motor control unit 3 controls the phase currents u, v, w of the EC motor (or generally of a PMSM machine). An exemplary topology of a motor control unit 3 includes a rotor position detector, a signal processing unit, the controller, a setpoint input (variable FSK input), a control unit, an acquisition unit (measuring unit with signal conditioning, possibly a filter, offset correction, current sensor for current detection, etc.), and the FSK calculation unit 11.

[0034] The acquisition unit processes the motor data and forwards it to the controller 6. In this way, the field-weakening current component FSK is impressed to reduce the commutation angle error ε.

[0035] The Fig. 2provides a graphical explanation of the function definition, which explains the relationship between the field weakening current component FSK for the reduction of the commutation angle error ε to a specific operating parameter. Fig. 2 The functional relationship between the field-weakening current component FSK and the torque M, which can be configured as a constant (curve a), a linear function (curve b), a function with an offset (curve c), or a polynomial function (curve d), particularly a higher-order polynomial, is shown as an example. The definition can be made by specifying minimum and maximum values ​​FSK min and FSK max, as shown in the example.

[0036] The Fig. 3 shows a graphical explanation of how to define the value range of the FSK using current as an example as an operating parameter.

[0037] The max value is set according to the following process: 1. Acceptable torque reduction: Reference a (typically between 10% - 25%); 2. Plot the line of equal current, e.g., the phase current amplitude, as the phase current, e.g., max. permissible constant current: Reference d; 3. Determine the intersection point of the torque reduction and the current line from step 2: Reference b; 4. Read out the maximum permissible field-weakening current component FSK: Reference c or e.

[0038] The typical maximum value for the phase shift λ determined in this way, rounded up to 5°, is 30° to 45°.

[0039] The procedure for setting the minimum value is, for example, by determining the FSK at which motor operation becomes unstable (i.e., the transition from a stable commutated state to an unstable state, in which, for example, the controller fails). A typical value for λ is -15° to 0°. For this example, the value range for λ would therefore be set between -15° and 45°.

[0040] The Fig. 4 shows an example for determining or setting a specific constant value for the field-weakening current component. 1. First, the angular error curve ε (FSK) is determined as a function of the FSK in the case of the largest deviation, here at maximum torque. The determination of ε 1 (FSK) can be carried out by calculation with FEM or by measurement. Then, the maximum permissible angular deviation ε max (reference G) is determined in the Figure 4 . From the intersection point of the curves G and ε 1 (FSK), the value for FSK, here F1, is determined. In addition, it is conceivable to provide a safety factor S, so that a different value for FSK results from the intersection point with the curve ε 1 (FSK), which in the Figure 4 designated with the reference F2.

[0041] The Fig. 5shows a further embodiment for determining or setting a value for the field-weakening current component FSK as a function of a varying operating parameter (here: the torque M for two different torque values). The process of determining the FSK described above is repeated for each of the two torque values, whereby the intersection points of the two curves ε (FSK) for the curve ε 1 and the curve ε 2 are determined. Consequently, two FSK values ​​are obtained (reference a and b in Figure 5 ). The two FSK values ​​now depend on the selected torque. For example, linear interpolation establishes a simple functional relationship between the torque M and the FSK.

[0042] The same procedure is used to obtain, for example, the functional relationship between the current or another operating parameter and the FSK.

[0043] The Fig. 6shows an exemplary embodiment for determining or specifying a specific value for the field-weakening current component at the transition to the unstable operating point of the EC motor. For this purpose, the curve ε = ε (FSK) is first determined, which indicates the relationship between the angular deviation ε and the field-weakening current component FSK. Such an exemplary curve is shown. From this, the critical angular deviation ε crit is determined from the curve as follows, at which the EC motor can no longer be commutated in a specific rotationally stable operating state. The corresponding point ε krit lies at the tangential point of a tangent T with the gradient ST (preferably ST < 1.5), which is applied tangentially to the curve ε = ε (FSK), whereby the tangent T is shifted along the abscissa of the curve ε = ε (FSK) until the tangent T lies tangentially at the said critical curve point of the curve ε (FSK).The intersection point between the tangent T and the abscissa FSK gives the value with the reference F in the . Figure 6 for the corresponding field-weakening current component.

[0044] The Fig. 7 shows an embodiment of an EC motor 2.2 of a fan with a slow-speed controller 13. The embodiment includes a mains connection 12, the converter 2.1 (rectifier 2.1.1 and the motor-side converter 2.1.2), which provides an intermediate circuit with measurement of the intermediate circuit current I* ZK. An EC motor 2.2 with an FSK controller 13 (with setpoint λ = FSK) is connected to this. The EC motor 2 drives a fan 2.3.

[0045] The FSK calculation unit with the reference number 11 is used to determine the field-weakening current component FSK and to limit it, in this embodiment according to the following calculation scheme: FSK = λ = k 1 ⋅ I ∗ ZK + k 2 wobei k 1 = 10 ∘ / 0 , 8 und k 2 = 3 , 75 ∘

[0046] The determination of the values ​​for the factors k 1 and k 2 for the calculation of FSK is carried out with reference to the Figures 8 to 10 explained. In the Figure 8 The error values ​​ε / ε max in % are determined as a function of the phase shift λ. The curve for ε / ε max = 1 is referenced to 1 in the Fig. 8 which thus defines the permissible error limit. By changing λ step by step or successively, the error values ​​ε / ε max are measured first at the lowest load condition (see reference 2 in the Figure 8 ). Determine the value λ below the specified error limit for this case. In this example, this results in: I* ZK,min ∼ 0.1, which corresponds to a phase angle of 2° (see reference 3 in the Fig. 8 ).

[0047] The same procedure is then carried out at the highest load condition. In this example, this results in: I* ZK,max ∼ 0.9, which corresponds to a phase angle of 11° (see reference 4 in the Fig. 8 ).

[0048] In a subsequent step, the values ​​for 5° and 15° are selected (see reference 5 in the Fig. 8 ).

[0049] In the Fig. 9 There is a graphical explanation of the determination of intermediate values ​​and the Fig. 10 shows a functional representation of the field-weakening current component FSK as a function of the quotient of the intermediate circuit current and the nominal value of the intermediate circuit current.

[0050] It is then necessary to determine the functional relationship to the FSK by measuring the intermediate values ​​between I* ZK,min and I* ZK,max which is described below with reference to the Figure 9 explained (see reference 1 in Fig.9 ).

[0051] The respective measurement for the intermediate values ​​is carried out according to the steps as in Fig. 8 for determining the min. and max. values ​​(ie concerning references 1 to 4 of the Fig. 8 ) The measured intermediate values ​​show in this example a nearly linear increase in the functional relationship between the FSK and the intermediate circuit current I* ZK , which in the Fig. 10 is evident (see reference 2 in the Fig. 10 ).

[0052] Now the values ​​for 5° and 15° are taken from the Fig. 8 adopted (these correspond to references 3 and 5 in the Figure 10 ), so that the gradient and the determined values ​​result in the above-mentioned functional relationship: FSK = λ = (10° / 0.8) · I* ZK + 3.75°.

[0053] Outside the measured range, the smallest FSK value is recorded for smaller current values ​​and for larger current values ​​the FSK values ​​are linearly extrapolated using the calculated function.

Claims

1. Control device (1) designed to reduce the commutation angle error ε of a three-phase (u,v,w) EC motor (2.2) connected via a star connection, the three phases (u,v,w) of which are commutated via a motor controller (3), having a rotor position detection (4) in order to detect the relative angular position of the rotor by means of the star point potential at the star point of the star connection, and a control circuit (10) which is designed to impress a field-weakening current component (FSK) into the motor controller (3) in order to reduce the commutation angle error ε.

2. Control device (1) according to claim 1, characterized in that an FSK calculation unit (11) is connected in terms of control technology to a measurement acquisition unit (9) and a setpoint specification (7) for inputting a variable field-weakening current component in order to impress a specific field-weakening current component on the motor control (3) for reducing the commutation angle error ε.

3. Control device (1) according to claim 2, characterized in that a signal processing device (5) is also provided to detect operating data of the EC motor (2.2), which are dependent on the field-weakening current component, and to supply them to a controller (6) of the motor control (3).

4. Control device (1) according to claim 1, 2 or 3, characterized in that the field-weakening current (negative d-current) or a certain phase angle value is used as the field-weakening current component.

5. Control device (1) according to any one of the preceding claims, characterized in that a current component is used to impress a field-weakening current component which is related as a function of operating variables, such as the current, the control level or the torque of the motor.

6. Method for reducing the commutation angle error ε of a three-phase (u, v, w) EC motor (2) connected via a star connection, the three phases (u, v, w) of which are commutated via a motor controller (3), preferably using a control device (1) according to one of claims 1 to 5, wherein a rotor position detection (4) takes place from the star point potential at the star point of the star connection of the motor phases (u, v, w) and a field-weakening current component (FSK) for reducing the commutation angle error ε is impressed on the motor controller (3) for commutating the EC motor (2.2).

7. Method according to claim 6, characterized in that the field-weakening current component is constant in magnitude.

8. Method according to claim 6, characterized in that the field-weakening current component is a linear or non-linear function, in particular as a function of an operating variable (Pi) of the EC motor (2.2), in particular as a function of the torque M or the current of the EC motor.

9. Method according to claim 6 or 7, characterized in that the field-weakening current component is detected from the curve of a curve FSK = FSK (ε, Pi) for a specific operating parameter (Pi), preferably a specific torque M of the EC motor (2.2), wherein for this purpose the curve ε = ε (FSK) is first determined, which indicates the relationship of the angular deviation ε to the field-weakening current component and based on this, a constant current component for impression is determined from the intersection point of the curve FSK (ε, Pi) at which a maximum permissible angular deviation εmax is specified.

10. Method according to one of claims 6, 7 or 8, characterized in that the field-weakening current component is determined from the curve of the respective function FSK (ε, Pi) of at least two or more curves of the respective curve FSK (ε, Pi) for a different operating parameter (Pi), preferably for different torques Mi of the EC motor (2.2), and the functional relationship between the operating parameter (Pi) and the field-weakening current component is obtained therefrom, wherein for this purpose the respective curve FSK (ε, Pi) is determined beforehand, which indicates the relationship between the angular deviation e and the field-weakening current component and based on this, a current component for impression is determined from the respective intersection points of the curves FSK (ε, Pi), for each of which a predetermined permissible angular deviation εdef is specified.

11. Method according to one of claims 6 to 8, wherein the curve ε = ε (FSK) is determined, which indicates the relationship between the angular deviation ε and the field-weakening current component, and from this the angular deviation εkrit is determined from the curve at which the EC motor (2.2) can no longer be commutated in a certain rotationally stable operating state, by successively increasing the permissible angular deviation ε until the rotationally stable operating state of the EC motor changes into an unstable state, which is defined by the curve point εkrit at the tangential point of a tangent T with the slope ST to the curve ε = ε (FSK), whereby the tangent T is shifted along the abscissa FSK until the tangent T is tangential to a curve point of the curve ε (FSK) and the intersection point between the tangent T and the abscissa determines the value for the field-weakening current component.