Method for operating electric motor without rotation direction sensor

Abstract

A method for operating an electric motor without a direction-of-rotation sensor comprising a stator and a rotor, in which injected signals are used to determine the speed of rotation of the electric motor, characterized in that the direction of rotation of the electric motor is determined, and taking defined measures if an actual undesired direction of rotation is determined or if an erroneously determined undesired direction of rotation is determined.

Description

Technical Field

[0001] The invention relates to a method having the features of the preamble of claim 1 .

[0002] Fields of application of the invention are electric motor drives which are fixed in speed direction, such as pump drives, actuator drives or traction electric motors for hybrid or all-electric drives in vehicles. Background Art

[0003] When the electric motor is operated without a rotation direction sensor, the rotor position sensor which is usually used to determine the current angle of the rotor is omitted. The current sensor signal and the measured or estimated phase voltages are used to determine the rotor position and speed of the motor via a model.

[0004] In the case of a rotational speed threshold value below the absolute rotational speed, it is necessary to feed a so-called injection signal which supports the identification of the rotor position and speed within this rotational speed range.

[0005] Starting with a stationary rotor, the rotor position must be determined by an initialization routine. Using the injection method, the motor can be operated in a lower rotational speed range until, for example, the switch to a model-based sensorless algorithm is initiated.

[0006] For a certain number of points on the voltage circuit path, the initial rotor position can be determined by specifying an AC voltage excitation, a high-frequency oscillation in the d-voltage and the q-voltage, wherein the excitation voltage amplitude leads to a resultant current amplitude. Due to the dq coordinates, an ellipse must be formed in the dq plane in the case of a circular excitation in the current and in the voltage. The main axis of the ellipse corresponds to the d-direction. The direction of this main axis describes the initial value of the rotor position.

[0007] In the as yet unpublished German patent application DE 10 2022 110 304.8, it is proposed to find the longer main axis of the ellipse corresponding to the d-axis by means of an iterative controller method. By superimposing the injected signal on the voltage, the current can be measured. However, this is not converted into an imaginary d-direction, but into an imaginary d-45° direction and an imaginary d+45° direction (see Figure 1 , top, "Prior Art Signal"). This allows to achieve significantly larger amplitudes in the current compared to the evaluation of the current in the d-direction and in the q-direction, wherein the current in the q-direction disappears when the true d-axis is found. This makes the detection more robust to disturbances and in particular more robust to disturbances in dynamic situations. The amplitude of the injected signal is then determined using bandpass filtering and the two values ​​at + / -45° are compared. A correction is then made to the assumed angle so that the two amplitudes in the +45° and -45° directions become equal (see Figure 1, top, "Prior Art Signal"). The correction is chosen in such a way that the longer semi-axis, the d-axis, is found. If the signal is inverted during the correction, the algorithm finds the shorter semi-axis, the q-axis. With this approach, not only is the initial angle found, but the electric motor can and will operate with it.

[0008] The inductance Ld and Lq of the bonded magnet are more similar to each other than that of the buried magnet. Then the ellipse is less obvious and more like a circle.

[0009] In special cases, such as requesting an open terminal or an active short circuit, the actuator must be reinitialized, since no injected signal can be provided during this period. This situation may cause the so-called 180° error that was resolved during the initial initialization to reappear. It cannot be ruled out that the 180° error may be caused by external interference. If a 180° error occurs, the motor will start to rotate in the wrong direction. A further explanation of the 180° error can be found, for example, in the as yet unpublished German patent application DE 10 2022 103 221.3.

[0010] Sensorless operation of permanently excited synchronous machines must be performed at low absolute rotational speeds by means of injected signals. However, the injected signals can also be used over the entire operating range, as is shown, for example, in the as yet unpublished German patent application DE 10 2022 118 125.1. The anisotropy of the motor is evaluated, since the inductance in the q-direction and the d-direction is different (L_q is not equal to L_d). Especially in small motors, the magnets are often glued so that the difference in the inductance is small.

[0011] If the inductances are too similar at the operating points, or if special circumstances occur, such as the output stage being switched off for a short time (active short-circuit or open terminals), very rare and therefore rather spontaneous changes of orientation may occur in the system, because the electric motor actually or only apparently, i.e. not actually so unintentionally, rotates in the wrong direction due to an error in the determination of the direction of rotation caused by the special circumstances. Summary of the invention

[0012] The invention is based on the object that an undesired, unlikely but possible change of orientation in a system, i.e. an actual or simply assumed reversal of the direction of rotation of a system with a substantially fixed direction of rotation due to an unintentional actual or simply assumed rotation of an electric motor in the wrong direction, should be detected as quickly as possible by means of diagnostic methods so that defined suitable measures can be initiated.

[0013] This object is achieved by a method having the features according to claim 1 .

[0014] According to the method according to the invention for operating an electric motor without a rotational direction sensor having a stator and a rotor, in which an injected signal is used to determine the rotational speed of the electric motor, it is provided that the rotational direction of the electric motor is determined and that defined measures are taken if an actually existing undesired rotational direction is determined or if an undesired rotational direction is determined to be erroneously determined.

[0015] In a preferred embodiment, it is provided that the desired direction of rotation is detected when a certain positive rotational speed value is present.

[0016] In a further preferred embodiment, it is provided that an undesired direction of rotation is detected if a negative speed value is present during a detection phase of defined duration and if the rotation speed value falls below a defined negative speed threshold value during the detection phase.

[0017] In a further preferred embodiment, it is provided that the direction of rotation of the electric motor is determined immediately after the occurrence of a special situation.

[0018] In a further preferred embodiment, it is provided that special situations exist when the output stage of the electric motor is switched off or when anisotropy problems occur.

[0019] In a further preferred embodiment, it is provided that a special case exists when a short circuit occurs or when an active short circuit occurs or when an open-circuited terminal occurs.

[0020] In special cases, such as requesting an open terminal or an active short circuit, the electric motor must be reinitialized, since no injected signal is available during this period.

[0021] In a further preferred embodiment, it is provided that the defined measure is an active short-circuit.

[0022] In a further preferred embodiment, it is provided that the defined measure is a defined closing of a valve in the hydraulic system.

[0023] In this way, rotation of the electric motor in the wrong direction can be detected very quickly and appropriately defined measures can be initiated immediately before higher-level software strategies initiate measures that will or may have undesirable or even dangerous consequences. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further advantages and advantageous embodiments of the invention are the subject matter of the following figures and description of the invention.

[0025] In detail, in the accompanying drawings:

[0026] Figure 1Top: shows the prior art: by superimposing the injected signal on the voltage, the current can be measured. However, this is not converted to the imaginary d direction, but to the imaginary d-45° (line with long dash) direction and the imaginary d+45° (line without long dash) direction.

[0027] Middle: A method according to the invention for detecting a rotational direction error of an electrically operated pump motor in a hydraulic system is shown.

[0028] Bottom: shows the rotor angle of a rotation direction sensorless electric motor with a stator and rotor, the injected signal is used to determine the rotor angle. DETAILED DESCRIPTION

[0029] Figure 1 The middle shows a method according to the invention for detecting a rotational direction error, for example a 180° error, of an electrically operated pump motor in a hydraulic system.

[0030] In special systems, such as hydraulic pumps, the direction of rotation is always the same; the pump's electric motor is fixed in direction of rotation. The pressure generated is directed via valves to specific consumers.

[0031] Thus, observation of the direction of rotation can be evaluated as triggering the detection of a spontaneous, improbable change in the orientation of the hydraulic pump system.The direction of rotation is determined in the case of sensorless control and is usually evaluated in a higher-level rotational speed controller.

[0032] The situation is similar to the rotor of a hybrid traction electric motor, for example of a P1 hybrid vehicle, which is connected to the internal combustion engine in a rotationally fixed manner by means of a shaft. If the traction electric motor starts to move the internal combustion engine from a standstill in the wrong direction of rotation, this will be detected by the monitoring routines used to protect the internal combustion engine, and as a protective measure at least the traction electric motor will be stopped. However, these monitoring routines will only respond later than the method according to the invention, and therefore the electric motor will be stopped by the measures of the method according to the invention.

[0033] Two situations can occur:

[0034] When the electric motor starts to rotate, the electric motor, which is actually stable in speed, still rotates unintentionally in the wrong direction. In this case, the electric motor stops even before the software strategy designed as the invention for detecting the wrong direction of rotation can perform an evaluation, because monitoring routines are used to protect the system, which is inherently resistant to the direction of rotation, records this situation and at least stops the electric motor. If these monitoring routines are too slow or have failed, the electric motor is stopped by the measures of the method according to the invention. Therefore, the rotation speed is still low at this time and the pressure in the system will also be low.

[0035] The second situation is that the electric motor is still rotating in the correct direction at a certain point in time. However, short-term special circumstances (active short circuit, open terminals or anisotropy problems) may lead to the incorrect direction of rotation being suddenly detected when the device is switched on again or spontaneously. However, the motor itself is still rotating in the original correct direction. In this case, it is important that the detection according to the invention takes place so quickly that the superimposed rotation speed controller has not yet made any major control interventions. According to the invention, the incorrect direction of rotation should be detected before the motor can reverse and possible countermeasures, such as active short circuiting, should be initiated. Another measure would be to quickly close the valves in the consumption path in order to maintain the pressure in the hydraulic system for as long as possible.

[0036] Figure 1 The case of an electric motor starting from a standstill in a sensorless or controlled manner is shown. It can be clearly seen that the rotation speed is negative, although it may only be positive for the electric motor to operate correctly in the system. After the detection phase, countermeasures can be initiated. Figure 1 The sensorless method according to the invention and the angle of the speed direction sensor are shown. In a true sensorless system this is not possible as there is neither a transmitter nor a sensor to receive the signal from the transmitter.

[0037] After a very short time, the error can be detected by evaluating the rotational speed signal and the fault can be reported to higher-level software.

Claims

1. A method for operating an electric motor having a stator and a rotor without a rotation direction sensor, wherein: The injected signal is used to determine the rotational speed of the electric motor, characterized in that the rotational direction of the electric motor is determined and defined measures are taken if an actually existing undesired rotational direction is determined or if an erroneously determined undesired rotational direction is determined.

2. The method according to claim 1, characterized in that The desired direction of rotation is detected when a positive rotation speed value is determined.

3. The method according to any one of the preceding claims, characterized in that An undesired direction of rotation is detected if a negative speed value is present during a detection phase of defined duration and if during said detection phase said rotation speed value lies below a defined negative speed threshold.

4. The method according to any one of the preceding claims, characterized in that The direction of rotation of the electric motor is determined immediately after a special situation occurs.

5. The method according to any one of the preceding claims, characterized in that Special situations exist when the output stage of the electric motor is switched off or when anisotropy problems occur.

6. The method according to any one of the preceding claims, characterized in that Special conditions exist when a short circuit occurs or when an active short circuit occurs or when an open circuit terminal occurs.

7. The method according to any one of the preceding claims, characterized in that The defined measure is an active short-circuit.

8. The method according to any one of the preceding claims, characterized in that The defined measure is a defined closing of a valve in the hydraulic system.

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