DE102016205462A1 - Method for determining a rotor position of a rotating, multi-phase, electrical machine fed by means of a PWM-controlled inverter - Google Patents

Abstract

The invention relates to a method for determining a rotor position of a means of a PWM-controlled inverter fed, rotating, multi-phase, electric machine. In this case, a change in current is achieved by repeatedly changing a predetermined voltage from a regulator (ucontrol). The current change is subsequently determined by determining a current profile of phase currents (ia, ib, ic) by measuring at least a first phase current (ia) and a second phase current (ib) several times and approximating them via model functions. From this detected current change, the rotor position is then determined.

Description

State of the art

The invention relates to a method for determining a rotor position of a means of a PWM-controlled inverter fed, rotating, multi-phase, electric machine.

Such a method is for example in the publication DE 10 2009 039 672 A1 disclosed. In this case, a sensorless control is disclosed, which tries to determine the rotor position without using a position sensor. At low speeds, so-called anisotropy-based methods are used, which determine the rotor position via the magnetic anisotropy of the machine. In the case of highly dynamic drives, an inverter with pulse width modulation (PWM) is generally used to generate the adjustable phase voltage of the electrical machines. The control signals of the inverter are calculated by means of a space vector modulation, which converts the voltage vector to be applied determined by the control into PWM duty cycles. In conventional anisotropy-based methods, a position-dependent current change is produced by targeted change of the voltage vector between two controller scanning steps, which is detected by current measurements at specific times. Depending on the current change, the rotor position is then determined.

Disclosure of the invention

• a. Mehrmaliges Verändern einer durch einen Regler zur Ansteuerung der elektrischen Maschine vorgegebenen Spannung zwischen einem ersten Reglerabtastschritt und einem zweiten Reglerabtastschritt, indem jeweils zusätzliche Spannungen mit unterschiedlicher Amplitude zusätzlich zur vorgegebenen Spannung eingespeist werden, um eine lageabhängige Stromänderung zu erzielen,
• b. Mehrmaliges PWM-synchrones Messen wenigstens eines ersten Phasenstroms und jeweils zeitgleich eines zweiten Phasenstroms zwischen dem ersten Reglerabtastschritt und dem zweiten Reglerabtastschritt, um einen Stromverlauf aller Phasenströme zu erhalten,
• c. Bestimmen der lageabhängigen Stromänderung, welche durch das Verändern der vorgegebenen Spannung entsteht, in Abhängigkeit des in Verfahrensschritt b erhaltenen Stromverlaufs der Phasenströme und den in Verfahrensschritt a zusätzlich eingespeisten Spannungen, wobei der Stromverlauf in einen ersten Strom, welcher ohne Veränderung der vorgegebenen Spannung fließen würde, und einen zweiten Strom, welcher durch die Veränderung der vorgegebenen Spannung erzeugt wird, unterteilt wird, und wobei der erste Strom mittels einer ersten Modellfunktion und der zweite Strom mittels einer zweiten Modellfunktion mit jeweils unbekannten Parametern angenähert wird,
• d. Bestimmen der Rotorlage in Abhängigkeit von der bestimmten, lageabhängigen Stromänderung,

wobei im Verfahrensschritt b mehr Messungen durchgeführt werden, als im Verfahrensschritt c unbekannte Parameter vorhanden sind. The invention relates to a method for determining a rotor position of a means of a PWM-controlled inverter fed, rotating, multi-phase, electric machine. The method comprises the method steps:

• a. Changing a voltage predetermined by a controller for driving the electrical machine a plurality of times between a first controller sampling step and a second controller sampling step by respectively supplying additional voltages of different amplitude in addition to the predetermined voltage to obtain a position-dependent current change;
• b. Repeated PWM synchronous measurement of at least a first phase current and at the same time a second phase current between the first controller sampling step and the second controller sampling step to obtain a current waveform of all phase currents,
• c. Determining the position-dependent current change, which arises by changing the predetermined voltage, as a function of the current waveform of the phase currents obtained in step b and the additionally fed in step a voltages, the current waveform in a first current, which would flow without changing the predetermined voltage, and a second current, which is generated by the change of the predetermined voltage, is divided, and wherein the first current is approximated by means of a first model function and the second current by means of a second model function, each with unknown parameters,
• d. Determining the rotor position as a function of the determined position-dependent current change,

wherein in the method step b more measurements are performed than in method step c unknown parameters are present.

In summary, it can thus be stated that the invention relates to a method for determining a rotor position of a rotating, multiphase, electrical machine fed by means of a PWM-controlled inverter. In this case, a change in current is achieved by repeatedly changing a predetermined voltage from a controller. The change in current is then determined by determining a current profile of phase currents by measuring at least a first phase current and a second phase current several times, at the same time, and approximating them via model functions. From this detected current change, the rotor position is then determined.

It is advantageous that the accuracy in determining the rotor position can be increased by the increased number of measurements compared to the number of unknown parameters. In addition, there is an improvement in the signal-to-noise ratio, whereby the noise is reduced, which is due to the rotor position determination. Furthermore, the method offers more opportunities to modify the predetermined voltage, whereby the additional voltages can be selected such that the noise is further reduced.

In an advantageous embodiment of the method according to the invention it is provided that the current change generated by changing the predetermined voltage has different frequencies. The advantage here is that this way the noise can be further optimized by, for example, the additional voltages are chosen such that the current change a high-frequency component, which generates a noise outside the audible range, and a low-frequency component, which generates a noise with a very small and thus produces inaudible amplitude.

According to an advantageous embodiment of the method according to the invention it is provided that the rotor position is determined by means of a linear combination of the current profile of the phase currents, taking into account all the different frequencies. The advantage here is that the linear combination provides a simple way of determining the rotor position and by taking into account all frequencies of the current change, the noise can be reduced accordingly.

According to a further advantageous embodiment of the method according to the invention it is provided that the frequencies between a Reglerabtastfrequenz, with which the controller scans, and a control frequency, with which the additional voltages are fed, are.

It is advantageous here that the current change in this frequency range can be detected optimally by means of the method according to the invention, in order thus to obtain a high signal-to-noise ratio in determining the rotor position.

In a further advantageous embodiment of the method according to the invention it is provided that the determination of the rotor position by means of the method of least squares takes place. The advantage here is that the determination of the rotor position as simple as possible and thus can be done quickly and without much computational effort.

According to a further advantageous embodiment of the method according to the invention, it is provided that the changing of the predetermined voltage in method step a and the PWM-synchronous measuring of the at least first phase current and the second phase current in method step b occur twice each in a PWM period. It is advantageous hereby that thereby the frequency range with which the change of the voltages can take place, and the number of current measured values for the evaluation are increased, without having to consider the influence of current ripple by the PWM clocking during the evaluation. A larger number of current readings improves the signal-to-noise ratio of the particular rotor position.

According to a further advantageous embodiment of the method according to the invention, it is provided that in step c, the current change is determined independently for each phase from the current waveform of the phase currents, and that in step d, the rotor position is determined as a function of the current change from all phases. The advantage here is that the computational effort for the determination of the rotor position is reduced by the separate determination of the current change for each phase current.

drawings

1 shows a first embodiment of a method according to the invention.

2 shows an exemplary voltage-time diagram, the additional injected voltage and the resulting phase current-time diagram

Description of exemplary embodiments

1 shows a first embodiment of a method according to the invention. The method determines a rotor position of a multiphase rotating machine fed by means of a PWM-controlled inverter. In this case, after start S in a method step a between a first controller sampling step t _{control, 1} and a second controller sampling step t _{control, 2} the voltage u _control preset by a controller for controlling the electric machine is changed several times, in addition to the predetermined voltage u _control Voltages u _{inj are} injected to achieve a position-dependent current change. In this case, the additional voltages u _{inj are added} to the predetermined voltage u _control and then converted into a PWM duty cycle for controlling the electrical machine. The additional voltages u _inj have different amplitudes, wherein the predetermined voltage u _{control should be changed} at least twice between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2} . The voltage injection takes place in a stator-fixed coordinate system, the angle φ _inj , which indicates in which direction the injection is kept constant, between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2} . It is also possible in this _case to select the additional voltages u _inj such that the sum of the additional voltages u _inj between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2} equals zero and thus the current change for the controller itself is not visible.

In a method step b, furthermore, at least one first phase current i _a and, at the same time, a second phase current i _b between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2 are} measured PWM synchronously in order to obtain a current profile of all phase currents. If, for example, only the first phase current i _a and the second phase current i _{b are} measured in a three-phase electrical machine, then a third phase current i _{c can be determined} by means of the first Kirchhoff law from the first phase current i _a and the second phase current i _b : i _c = -i _a -i _b

Alternatively, the third phase current i _{c can} also be measured. The sampling frequency of the current f _meas , with which the phase currents i _a, i _b or i _{c are} measured, should be at least twice the injection _frequency f _inj , with which the additional voltages u _{inj are} injected and which here the PWM frequency f corresponds to _PWM . In addition, the injection _frequency f _inj should be _at least half the regulator sampling frequency f _control . From this it can be concluded that between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2,} a number of n measurements of the phase currents i _a, i _b are made, this number being calculated as: n = f _meas / f _control

By way of example, the controller sampling frequency f _{control can be} 2 kHz, the PWM frequency f _PWM 16 kHz and the sampling frequency of the phase currents f _meas 32 kHz. Alternatively, it is also possible that the injection of additional voltages u _inj and the measurement of the phase _currents i _a , i _b or i _c takes place twice in a PWM period.

Subsequently, in a method step c, the current change is determined, which is produced by changing the predetermined voltage u _control in method step a. Here, _c and additionally fed in process step a voltages u _inj determining the current change takes place in dependence of the current waveform obtained in step b of the phase currents i _a, i _b, i. For this purpose, the current _waveform obtained in step b is divided into a first current i _control , which would flow without changing the predetermined voltage u _control , and a second current i _inj , which is generated by changing the voltage u _control , and the first current i _control by means of a first model function and the second current i _{inj approximated} by means of a second model function. The first and second model functions each have a certain number of unknown parameters. In this case, however, it is assumed that the number of unknown parameters is less than the number of measurements made in method step b of the phase currents i _a , i _b . Assuming that the voltage u _control given by the controller is constant in the rotor-fixed coordinate system between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2} , the first current i _control can be well approximated, for example, with a first or second order polynomial become. The second current i _inj can be approximated, for example, via a linear model. It is assumed here that a voltage drop at phase _resistances has no influence on the course of the second current i _inj . In addition, it is assumed that an inductance of the electric machine is constant between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2} . The first and second model functions can then be approximated, for example, by means of a least squares method, and the unknown parameters of the model functions can be determined therefrom. Alternatively, the current change can also be determined independently for each phase.

Thereafter, in a method step d, the rotor position of the electric machine is determined as a function of the current change determined in method step c, and the method is then terminated. If the current change in the method step is determined independently for each phase, the rotor position can subsequently be determined from a linear combination of the current change of all phases.

In an alternative, not illustrated embodiment, the method can be restarted regularly to continuously determine the rotor position of the electric machine.

2 shows an exemplary voltage-time diagram, an additional injected voltage and the resulting phase current-time diagram. Shown is the additional _injected voltage u _inj , which has a PWM curve and is fed between a first controller sampling step t _{control, 1} and a second controller sampling step t _{control, 2} . However, the amplitudes of the voltage u _inj are not always the same. _{By way of} example, the additional voltages u _{inj have} two different amplitudes. From the time interval between the first controller sampling step t _{control, 1} and the second controller sampling step t _{control, 2} , the controller sampling frequency f _control results: f _control = 1 / (t _{control, 2} -t _{control, 1} )

Furthermore, a time profile of the first phase current i _{a is} shown, which adjusts itself by the predetermined voltage u _control and the additional voltages u _inj . In addition, the duration of a PWM period is shown, which represents the reciprocal of the PWM frequency f _PWM . In addition, the distance between the respective measurements of the phase current i _{a is shown} as the inverse of the measuring frequency f _meas .

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009039672 A1 [0002]

Claims (7)

Method for determining a rotor position of a rotating, multiphase, electrical machine fed by means of a PWM-controlled inverter, comprising the method steps: a. Changing a voltage (u _contol ) predetermined by a controller for driving the electric machine a _{plurality of times} between a first controller sampling step (t _{control, 1} ) and a second controller sampling step (t _{control, 2} ) by adding additional voltages (u _inj ) having different amplitudes to the predetermined voltage (u _contol ) are fed to achieve a position-dependent current change, b. Repeated PWM synchronous measurement of at least a first phase current (i _a ) and at the same time a second phase current (i _b ) between the first controller sampling step (t _{control, 1} ) and the second controller sampling step (t _{control, 2} ) to a current waveform of all phase currents ( i _a , i _b , i _c ), c. Determining the current change, which is produced by changing the predetermined voltage (u _contol ), as a function of the current _{profile of} the phase currents (i _a , i _b , i _c ) obtained in method step b and the additionally _injected voltages (u _inj ) in method step a, wherein the current _{waveform is divided} into a first current (i _control ), which would flow without changing the predetermined voltage (u _contol ), and a second current (i _inj ), which is generated by changing the predetermined voltage (u _contol ) , and wherein the first current (i _control ) is approximated by means of a first model function and the second current (i _inj ) by means of a second model function, each with unknown parameters, d. Determining the rotor position as a function of the determined current change, wherein in the method step b more measurements are performed, as in method step c unknown parameters are present. A method according to claim 1, characterized in that the current change produced by changing the predetermined voltage (u _control ) has different frequencies (f). A method according to claim 2, characterized in that the rotor position by means of a linear combination of the current waveform of the phase currents (i _a , i _b , i _c ) is determined, all different frequencies (f) are taken into account. Method according to one of claims 2 or 3, characterized in that the frequencies (f) between a Reglerabtastfrequenz (f _control ), with which the controller samples, and an injection _frequency (f _inj ), with which the additional voltages (u _inj ) fed will, lie. Method according to one of the preceding claims, characterized in that the determination of the rotor position by means of the method of least squares takes place. Method according to one of the preceding claims, characterized in that the changing of the predetermined voltage (u _control ) in method step a and the PWM-synchronous measuring of the first phase current (i _a ) and the second phase current (i _b ) in step b in each case twice in a PWM period. Method according to one of the preceding claims, characterized in that in step c, the current change independently for each phase from the current waveform of the phase currents (i _a , i _b , i _c ) is determined, and that in step d, the rotor position as a function of the current change of all Phases is determined.

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