METHOD FOR DETERMINING THE ANGLE POSITION OF THE ROTOR OF A SYNCHRONOUS MOTOR FED BY AN INVERTER AND A DEVICE FOR CARRYING OUT THE METHOD

Description

[0001] The invention relates to a method for determining the angular position of the rotor of a synchronous motor and a device for carrying out the method.

[0002] It is common knowledge that an electric motor can be powered by an inverter.

[0003] The closest prior art from US 6 137 257 A is a method for monitoring the angular position of a switched reluctance motor (SLR).

[0004] A method for controlling a synchronous machine is known from US 2004 / 145334 A1.

[0005] From US 2008 / 129243 A1 a motor control method is known which controls the motor by using parameters of the associated magnetic flux.

[0006] US 2003 / 015987 A1 describes a method for speed control in an SLR engine.

[0007] From TURSINI M ET AL: "Sensorless control of an IPM synchronous motor for city scooter applications",CONFERENCE RECORD OF THE 2003 IEEE INDUSTRY APPLICATIONS CONFERENCE. 38TH. IAS ANNUAL MEETING. SALT LAKE CITY, UT, OCT 12 - 16, 2003; [CONFERENCE RECORD OF THE IEEE INDUSTRY APPLICATIONS CONFERENCE. IAS ANNUAL MEETING], NEW YORK, NY: IEEE, US, Vol. 3, October 12, 2003 (2003-10-12), pages 1472-1479, a sensorless control of a synchronous motor is known.

[0008] From LANDSMANN P ET AL: "Fundamental saliency based encoderless control for reluctance synchronous machines", ELECTRICAL MACHINES (ICEM), 2010 XIX INTERNATIONAL CONFERENCE ON, IEEE, PISCATAWAY, NJ, USA, 6 September 2010 (2010-09-06), pages 1-7, a sensorless control of a synchronous motor is also known.

[0009] The invention is therefore based on the object of developing a method for the improved determination of the angular position in a synchronous motor.

[0010] According to the invention, the object is achieved in the method for determining the angular position of the rotor of a synchronous motor according to the features specified in claim 1 and in the device for carrying out the method according to the features specified in claim 7.

[0011] The features of a further embodiment of the method are that it is intended to determine the angular position of the rotor of a synchronous motor fed by an inverter, wherein the inverter is controlled by signal electronics with a controller unit, in particular comprising a computer unit and memory, wherein the stator current is detected in particular by means of at least one current detection means, wherein the synchronous motor has a stator winding which is fed by a three-phase voltage, i.e. stator voltage, provided by the inverter in such a way that the detected stator current is regulated to a predetermined target stator current by the controller unit, wherein a target stator current is predetermined with a first setting angle related to the stator winding, in particular in the d-direction, wherein the stator flux is determined from the temporal profile of the stator voltage and the detected values ​​of the stator current.

[0012] An advantage of the invention is that the signal electronics supplies control signals for the inverter such that the inverter provides the motor, i.e. the stator winding of the motor, with a three-phase voltage such that the detected motor current is regulated to a respectively predetermined target stator current. A stator flux is determined from the detected stator current curve and motor voltage curve, which is then compared with the flux value dependency. This makes it possible to determine the angular position. For unambiguous determination, a further target stator current, preferably oriented perpendicular to the first-mentioned stator current, is specified and the stator flux is again determined, which is then compared with the flux value dependency. By evaluating the two determined angular positions, an unambiguous determination of the angular position can be carried out.

[0013] This makes it easy to determine the angular position without additional sensors. The current measurement device can be used for controlled operation of the synchronous motor.

[0014] The flux value dependency can be recorded by measurement for each stator current during manufacture or commissioning and is determined from support points which result in each case as the respective value of a flux component according to a characteristic curve as a function of the stator current.

[0015] The flux value dependence represents the stator flux as a function of the angle a of the rotor, whereby a target stator current is specified in the direction of a setting angle, for example in the d-direction, to which the stator current is controlled.

[0016] According to the invention, a target stator current is specified with a further setting angle related to the stator winding, in particular in the q-direction, wherein the stator flux is determined from the temporal progression of the stator voltage and the recorded values ​​of the stator current, wherein a further angle value, in particular a further angular position, is determined from the determined stator flux and a flux value dependency dependent on the stator current, in particular for the unambiguous determination of the further angle value. The advantage here is that the target stator current is first specified in a first direction and then in another direction. In this way, the angle can be determined twice, thus enabling an unambiguous determination. This is because the flux value dependency exhibits symmetries and the angle cannot therefore be unambiguously determined with a single determination of this type.

[0017] The flux value dependence associated with a stator current can be represented as an ellipse, so that the flux in the d-direction is smaller than in the q-direction. In an intermediate direction, i.e., in a direction with an angle α between the d-direction and the q-direction, the flux assumes a value between that in the q-direction and that in the d-direction, according to the shape of the ellipse.

[0018] The ellipse is a suitable interpolation function for approximately determining intermediate flux values. The major axis is determined by the sum of the flux values ​​in the d-direction and the direction opposite to the d-direction, while the minor axis of the ellipse is determined by twice the flux value in the q-direction.

[0019] To take higher orders into account, in particular to take a more precise course of the inductance into account, a higher order function must be used.

[0020] In an advantageous embodiment, the stator flux is determined from the temporal course of the stator voltage and the recorded values ​​of the stator current according to Y_a = ∫ U_S − R_S * I_S dt , where R_S is the stator resistance. The advantage of this approach is that the stator flux, which corresponds to the current angular position, can be determined from the measured electrical quantities, such as stator current and stator voltage. Thus, the flux can be determined as a model quantity, even if the angular position, i.e., the angular position of the rotor relative to the stator, is unknown.

[0021] In an advantageous embodiment, the flux value dependency is stored in a memory of the signal electronics, or characteristic curves are stored in a memory of the signal electronics, from which the flux value dependency is determined using respective interpolation functions, in particular those dependent on the stator current. This is advantageous because only a small amount of data needs to be stored; in particular, storing characteristic curves is sufficient, so that the flux value dependency associated with the respective stator current can be represented by interpolation.

[0022] According to the invention, the flux value dependency comprises a flux value as a function of the rotor angle and the stator current. This has the advantage that a comparison of the stator flux value determined by integration with the flux value dependency can be carried out easily, thus allowing the angular position of the rotor to be determined.

[0023] According to the invention, the function is an interpolation function that interpolates between support points. The advantage of this is that it requires only a small amount of memory while still allowing the flow value dependency to be taken into account.

[0024] According to the invention, a respective support point is determined from the stator current value using a respective characteristic curve. The advantage here is that the support point can be determined easily.

[0025] According to the invention, the respective characteristic curve represents a respective component of the flux as a function of the stator current, so that the respective support point displays the value of a respective component at the currently measured stator current. This has the advantage of enabling simple determination of the flux.

[0026] According to the invention, a first characteristic curve comprises the flux components in the d-direction, i.e., in a first direction of a rotor-based coordinate system. The advantage here is that an easily determinable characteristic curve is used.

[0027] According to the invention, a second characteristic curve exhibits the flux components opposite to the d-direction, i.e., opposite to the first direction of the rotor-based coordinate system. The advantage here is that an easily determinable characteristic curve is used.

[0028] According to the invention, a third characteristic curve shows the flux components in the q-direction, i.e., in the direction perpendicular to the first direction of the rotor-based coordinate system. The advantage here is that an easily determinable characteristic curve is used.

[0029] In an advantageous embodiment, the interpolation function is a second-order function and / or an ellipse. This is advantageous because higher orders do not need to be considered, yet a sufficiently accurate angular position determination can still be carried out.

[0030] In an advantageous embodiment, the angle value a is determined from Sin ∧ 2 a = Y_a ∧ 2 − Y_d ∧ 2 / Y_q ∧ 2 − Y_d ∧ 2 , wenn Y_d < Y_a < = Y_q , And from Sin ∧ 2 a − 90 ° = Y_a ∧ 2 − Y_q ∧ 2 / Y_ − d ∧ 2 − Y_q ∧ 2 , wenn Y_q < Y_a < = Y_ − d .

[0031] The advantage here is that it allows for easy identification.

[0032] Important features of the device for implementing the method include the connection of a current sensing device for detecting the motor current to the signal electronics. This allows for simple manufacturing.

[0033] Further advantages arise from the subclaims.

[0034] The invention will now be explained in more detail with the aid of illustrations: In the Figure 1The q-direction and the d-direction of the rotor of a synchronous machine are shown schematically, where the rotor is magnetized like a permanent magnet. Figure 2 The magnetization characteristic is shown schematically, where Y is the magnetic flux and I is the stator current. Figure 3 The flux characteristics are shown as a function of the stator current. Figure 4 The course of the flow determined from measured values, in particular the model value, is shown. In the Figure 5 the course of the stator flux magnitude is shown.

[0035] As in Figure 2 As shown, the permanent flux Y_PM caused by the permanent magnet corresponds to an offset magnetizing current I_d0 in the d-direction.

[0036] Based on this, a stator current causes a change in the stator flux, the component of which in the d-direction is denoted by Y_d, and the component opposite to the d-direction is denoted by Y_-d. Because of the offset, Y_d and Y_-d are different. The component of the stator flux in the q-direction is denoted by Y_q.

[0037] The dependence of the mentioned components Y_d, Y_-d and Y_q on the stator current are shown in Figure 3 shown schematically, with each component assigned a respective characteristic curve. These characteristic curves are measured during manufacture or before commissioning and stored in the memory of the signal electronics, which includes a computer unit. This then enables the computer unit to determine the values ​​of the components depending on the respective stator current value.

[0038] The synchronous motor has a rotor mounted so that it can rotate relative to a stator winding. The stator winding is designed as a three-phase rotating field winding. This allows the synchronous motor to be operated as a three-phase motor.

[0039] The motor is powered by an inverter comprising three half-bridges supplied from a unipolar voltage, particularly a DC link. Each of the half-bridges comprises a series connection of two controllable power semiconductor switches, particularly IGBTs or MOSFETs. The respective center tap of the series circuits represents one of the phase voltages for supplying the stator winding.

[0040] Signal electronics provide pulse-width-modulated control signals for controlling the circuit breakers. This allows the stator winding to be supplied with three-phase voltage of a predefined amplitude and frequency.

[0041] The unipolar voltage is measured using a voltage measurement device, and the current phase voltage can be determined by the computer unit from the pulse width modulation ratio of the control signals of the power switches of the respective half-bridge. The stator voltage space vector, in particular its magnitude and direction, can also be determined from the determined phase voltage values.

[0042] In addition, the motor current, i.e., the currents flowing in the three phases, is also determined. A corresponding single- or multi-part current measuring device is provided for this purpose. The stator current space vector, specifically its magnitude and direction, is determined from the currently measured current values.

[0043] Initially, a target current, i.e., a target stator current space vector, is specified to the controller located in the computer unit. This controller generates control signals for the inverter's power semiconductor switches such that the detected actual value, i.e., the stator current space vector determined from the current values ​​recorded by the current detection devices, is regulated to the target current by adjusting the motor voltage, i.e., the stator voltage space vector, accordingly. The actual value has a predetermined direction, i.e., a setting angle.

[0044] During this control process, i.e. the adjustment of the actual value to the target value, the corresponding flux is determined: By integrating the difference between the stator voltage U_S and the product of the stator resistance R_S and the stator current I_S, the stator flux Y_a is determined, i.e. according to: Y_a = ∫ U_S − R_S * I_S dt

[0045] The stator resistance R_S is a parameter determined during design, manufacture, or commissioning, which is stored in a memory of the signal unit and is thus known to the computer unit.

[0046] The rotation angle a of the rotor of the synchronous machine, related to the setting angle of the target stator current space vector, is initially unknown. To determine this rotation angle a, the values ​​of the components Y_d, Y_-d, and Y_q are first determined for the currently determined stator current using the characteristic curves.

[0047] An ellipse spanned by the three values ​​is then used for interpolation. To do this, a major axis of length Y_d + Y_-d is formed from the components Y_d and Y_-d, and the component Y_q is plotted perpendicular to it.

[0048] Then the angle a is determined at which the determined stator flux Y_a touches the ellipse, as in Figure 5 is shown.

[0049] The determination is made according to Sin ∧ 2 a = Y_a ∧ 2 − Y_d ∧ 2 / Y_q ∧ 2 − Y_d ∧ 2 , wenn Y_d < Y_a < = Y_q , And according to Sin ∧ 2 a − 90 ° = Y_a ∧ 2 − Y_q ∧ 2 / Y_ − d ∧ 2 − Y_q ∧ 2 , wenn Y_q < Y_a < = Y_ − d .

[0050] Since the ellipse is mirror-symmetrical to the main axis, the aforementioned process steps are repeated at a different time, preferably with the stator current I_S offset by essentially 90°. This avoids ambiguities.

[0051] Thus, by setting a target stator current space vector and determining the resulting model variable Y_a, the direction can be determined. This procedure is repeated two or more times with different setting angles of the target stator current space vector to eliminate ambiguities. Repeating this procedure multiple times can reduce the measurement error.

[0052] For the implementation of the invention, the synchronous motor should be designed as a fundamental wave motor. In such motors, two inductance values, such as the inductance in the q-direction and the inductance in the d-direction, are sufficient to fully describe the dependence of the inductance on the rotor angle. Higher-order deviations are not considered here.

[0053] The flux value dependence associated with a stator current can be represented as an ellipse, so that the flux in the d-direction is smaller than in the q-direction. In an intermediate direction, i.e., in a direction with an angle α between the d-direction and the q-direction, the flux assumes a value between that in the q-direction and that in the d-direction, according to the shape of the ellipse.

[0054] The ellipse is a suitable interpolation function for approximately determining intermediate flux values. The major axis is determined by the sum of the flux values ​​in the d-direction and the direction opposite to the d-direction, while the minor axis of the ellipse is determined by twice the flux value in the q-direction.

[0055] To take higher orders into account, in particular to take a more precise course of the inductance into account, a higher order function must be used.

[0056] The invention thus relates to a method for determining the angular position of the rotor of a synchronous motor. This involves determining interpolation points from stator current-dependent characteristic curves of stator flux components, through which interpolation points an interpolation function, preferably an ellipse, is placed. Thus, the stator flux, formed as a model variable from the detected motor current and motor voltage values, is compared with the interpolation function, and the angular position is determined from this. A clear determination of the angular position can be achieved by repeatedly performing the aforementioned steps, with the target stator current then being specified in different directions. List of reference symbols

[0057] q first direction d second direction N North pole S South pole Y Magnetic flux Y_q Component of the magnetic flux vector in q direction Y_d Component of the magnetic flux vector in d direction Y_-d Component of the magnetic flux vector opposite to d direction Y_PM Permanent flux Y_a Model value for the flux vector I_d0 Magnetizing current I_S Stator current I_Soll Setpoint of the stator current

Claims

1. Method for determining the angular position of the rotor of a synchronous motor, wherein interpolation points through which an interpolation function, in particular an ellipse, is placed are ascertained from stator current-dependent characteristic curves of components of the stator flux, after which the stator flux Y generated as a model variable from the detected motor current and motor voltage values is compared with the interpolation function, and the angular position is ascertained therefrom, wherein a stator current, I_S, is determined from the detected motor current, wherein the detected stator current, I_S, is controlled towards a predetermined target stator current, I_Soll, wherein a first of the characteristic curves representing the components Y_d of the stator flux in the d-direction, i.e. in a first direction of a rotor-based coordinate system, is ascertained, wherein a second of the characteristic curves representing the components Y_-d of the stator flux in the opposite direction to the d-direction, i.e. in the opposite direction to the first direction of the rotor-based coordinate system, is ascertained, wherein a third of the characteristic curves representing the components Y_q of the stator flux in the q-direction, i.e. in the direction perpendicular to the first direction of the rotor-based coordinate system, is ascertained, wherein the first, second and third stator current-dependent characteristic curves represent the components Y_d, Y_-d and Y_q of the stator flux Y, wherein the interpolation points through which the interpolation function is placed are ascertained as values of the components Y_d, Y_-d and Y_q at the currently determined stator current, I_S, by means of the first, second and third characteristic curves, wherein an angle value, a, of the angular position, at which angular value the determined stator flux Y touches the interpolation function, is determined.

2. Method according to claim 1, wherein the synchronous motor is fed by an inverter, wherein the inverter is actuated by signal electronics comprising a controller unit, in particular having a computer unit and a memory, wherein the stator current I_S is detected in particular by means of at least one current detection means, wherein the synchronous motor has a stator winding that is fed by a three-phase voltage, i.e. a stator voltage, that is provided by the inverter in such a way that the detected stator current I_S is controlled towards a predetermined target stator current I_Soll by the controller unit, wherein the target stator current I_Soll is predetermined by a first adjustment angle in relation to the stator winding, in particular in the d-direction, wherein each interpolation function is a second-order function and / or an ellipse.

3. Method according to claim 1 or claim 2, characterised in that a further target stator current I_Soll is predetermined by a further adjustment angle in relation to the stator winding, wherein the stator flux Y is determined from the time curve of the stator voltage and of the detected values of the stator current I_S, wherein a further angle value, in particular a further angular position, is determined from the determined stator flux Y and from a flux-value dependency that is dependent on the stator current, in particular in order to unambiguously determine the further angle value.

4. Method according to at least one of the preceding claims, characterised in that the stator flux Y is determined from the time curve of the stator voltage U_S and of the detected values of the stator current I_S in accordance with Y_a = ∫ U_S − R_S * I_S dt where R_S is the stator resistance and a is the angle value to be determined, where Y_a is the component of the magnetic flux vector in the direction belonging to the angle value a.

5. Method according to at least one of the preceding claims, characterised in that the flux-value dependency is stored in a memory of the signal electronics, or characteristic curves from which the flux-value dependency is ascertained by means of respective, in particular stator current-dependent, interpolation functions are stored in a memory of the signal electronics.

6. Method according to at least one of the preceding claims, characterised in that the angle value a is determined from Sin ∧ 2 a = Y _ a ∧ 2 − Y _ d ∧ 2 / Y _ q ∧ 2 − Y _ d ∧ 2 , when Y _ d < Y _ a < = Y _ q , and from Sin ∧ 2 a − 90 ° = Y _ a ∧ 2 − Y _ q ∧ 2 / Y _ − d ∧ 2 − Y _ q ∧ 2 , when Y _ q < Y _ a < = Y _ − d , where Y_q is the component of the magnetic flux vector in the q-direction, Y_d is the component of the magnetic flux vector in the d-direction, Y_-d is the component of the magnetic flux vector in the opposite direction to the d-direction, and a is the angle value to be determined, where Y_a is the component of the magnetic flux vector in the direction belonging to the angle value a.

7. Device for carrying out the method according to at least one of the preceding claims, wherein the device has a synchronous motor fed by an inverter, wherein the inverter is actuated by signal electronics comprising a controller unit, wherein a current detection means for detecting the motor current is connected to the signal electronics.