Stall detection of electronically commutated electric machines

Abstract

The invention relates to stall detection of an electronically commutated electric machine comprising one or more machine phases, with a phase inductance L and a phase resistance R for each machine phase. The driver (213, 230) is configured for driving (110) the electronically commutated electric machine (220) by applying a voltage or current vector to one or more motor phases of the electronically commutated electric machine (220) at a rotational speed omega of the voltage or current vector; the detector (212) is configured to obtain (120) an electrical angle between the applied voltage vector and the resulting current vector, or between the applied current vector and the resulting voltage vector; the processing device (211) is configured for determining a stall of the rotor if the absolute value of the electrical angle or a filtered version thereof crosses a stall threshold, where the stall threshold is arctan2 ([omega] L, R) plus or minus a predefined margin.

Description

Technical Field

[0001] The present invention relates to the field of stall detection of electronically commutated motors such as brushless direct current (BLDC) motors and stepper motors. More specifically, the present invention relates to a method or device for sensorless stall detection of a BLDC motor. Background Art

[0002] When operating a BLDC motor, it is important to know whether the motor suddenly stops running (stalls) by applying a voltage vector or a current vector to one or more motor phases of the BLDC motor. For example, this may be caused by an increase in mechanical load or the motor's inability to follow the applied current vector or voltage vector. When such a stall is not detected, energy will be wasted and the application driven by the motor will malfunction. When the stall is correctly detected, it can be safely disposed of (e.g., by restarting or stopping the application).

[0003] Conventional solutions for determining stall are to determine the position of the rotor of the motor by using a position sensor (e.g., a Hall sensor). The sudden stop of the rotor is clearly visible in the sensor data. This conventional method is very reliable but has the disadvantage of the additional cost of the sensor. Therefore, there is a need for sensorless stall detection methods and devices.

[0004] Other conventional solutions look at sudden current increases or back electromotive force (BEMF) drops. These methods do not require a position sensor but are only reliable at higher operating speeds.

[0005] Stepper motors are commonly used in thermal valves, HVAC systems, and consumer devices and operate based on discrete phase control. Different from BLDC motors typically driven by the continuous rotation of a voltage vector, stepper motors achieve rotation through incremental steps. These differences pose unique challenges in detecting stall conditions, especially in sensorless systems.

[0006] For a stepper motor, when the applied torque exceeds the holding torque, stall may occur due to loss of step. Conventional methods for detecting stall in a stepper motor typically rely on a position sensor or monitoring current spikes.

[0007] However, there is still a need for sensorless solutions that can reliably detect stall in both stepper motors and BLDC motors under various operating conditions including low speed and high load. Summary of the Invention

[0008] An object of embodiments of the present invention is to provide a good device and method for detecting stall of an electronically commutated motor.

[0009] The above object is achieved by the method and device according to the present invention.

[0010] In a first aspect, embodiments of the present invention relate to a method for detecting stall of a rotor of an electronically commutated motor. The electronically commutated motor includes one or more motor phases, each motor phase having an imaginary part ωL and a real part R. The method includes:

[0011] - Driving the electronically commutated motor by applying a voltage vector or a current vector to one or more motor phases of the electronically commutated motor for rotating the rotor,

[0012] - Obtaining an electrical angle between the applied voltage vector and the resulting current vector of one or more motor phases, or between the applied current vector and the resulting voltage vector of one or more motor phases,

[0013] - Indicating stall of the rotor when the absolute value of the electrical angle or a filtered version thereof is within a range defined by arctan2(ωL, R) plus or minus a predefined margin.

[0014] Advantages of embodiments of the present invention are that stall can be detected without using a position sensor. An advantage of embodiments of the present invention is that stall can be detected during low-speed operation compared to methods that use BEMF voltage to determine whether the rotor is stalled.

[0015] Advantages of embodiments of the present invention are that the applied vector for rotating the rotor can be such that it causes a constant speed, an accelerating speed, or a decelerating speed. In all these cases, the method according to embodiments of the present invention allows detection of stall of the rotor.

[0016] In an embodiment of the present invention, stall of the rotor is indicated when the absolute value of the electrical angle or a filtered version thereof becomes less than a stall threshold.

[0017] Advantages of embodiments of the present invention are that stall can be detected by a simple comparison of the electrical angle with the stall threshold.

[0018] In an embodiment of the present invention, the predefined margin is a positive value between 0 and 50% of arctan2(ωL, R).

[0019] Advantages of embodiments of the present invention are that the stall threshold can be adjusted to compensate for measurement noise, vibrations during stall, or motor variations.

[0020] In an embodiment of the present invention, the predefined margin can be, for example, a positive value between 0.1 and 50% of arctan2(ωL, R).

[0021] In an embodiment of the present invention, the motor is driven in an open-loop manner.

[0022] In an embodiment of the present invention, the electric machine is driven such that when the rotor rotates, the absolute value version of the electrical angle or its filtered version is greater than a stall threshold.

[0023] In an embodiment of the present invention, the method includes an enabling step when starting the electric machine. During this step, the absolute value of the electrical angle or its filtered version is compared with an enabling threshold. The indication of the stall of the rotor is enabled only when the absolute value of the electrical angle or its filtered version is greater than the enabling threshold. The enabling threshold is greater than the stall threshold.

[0024] Alternatively, in an embodiment of the present invention, the enabling step may enable stall detection when the drive speed ω exceeds a predefined threshold.

[0025] In an embodiment of the present invention, the method includes stopping the drive of the electronically commutated electric machine in case of indicating a stall.

[0026] In an embodiment of the present invention, a stall may be indicated to a higher-level system.

[0027] In an embodiment of the present invention, the method includes, in case of indicating a stall, applying a reduced voltage vector or a reduced current vector during a predefined duration.

[0028] An advantage of an embodiment of the present invention is that a stall can be handled by applying a reduced voltage vector or a reduced current vector. In an embodiment of the present invention, when a stall is indicated, the polarity of the voltage vector or the current vector applied during a predefined duration may even have a polarity opposite to the polarity used when driving the electronically commutated electric machine. An advantage of an embodiment of the present invention is that a stall can be handled by temporarily applying a voltage vector or a current vector with an opposite polarity.

[0029] In an embodiment of the present invention, the electronically commutated electric machine is a BLDC motor, a stepper motor, or a switched reluctance motor.

[0030] In a second aspect, an embodiment of the present invention relates to a stall detector for detecting a stall of an electronically commutated electric machine, the electronically commutated electric machine including one or more motor phases, each motor phase having an imaginary part ωL and a real part R.

[0031] The stall detector includes:

[0032] - A driver configured to drive the electronically commutated electric machine by applying a voltage vector or a current vector to one or more motor phases of the electronically commutated electric machine for rotating the rotor,

[0033] - A detector configured to obtain an electrical angle between an applied voltage vector and a resulting current vector of one or more motor phases, or between an applied current vector and a resulting voltage vector of one or more motor phases.

[0034] - A processing device configured to determine a stall of the rotor and indicate said stall when the absolute value of the electrical angle or a filtered version thereof is within a range defined by adding or subtracting a predefined margin from arctan2(ωL,R).

[0035] In an embodiment of the present invention, the processing device is configured to determine the stall of the rotor when the absolute value of the electrical angle or a filtered version of the electrical angle becomes less than a stall threshold.

[0036] In an embodiment of the present invention, the driver is configured to drive the motor in an open-loop manner.

[0037] In an embodiment of the present invention, the driver is configured to drive the motor such that when the rotor rotates, the absolute value of the electrical angle or a filtered version thereof is greater than the stall threshold.

[0038] In an embodiment of the present invention, when starting the motor, the stall of the rotor can be determined by the processing device. Thus, the processing device can be configured to compare the absolute value of the electrical angle or a filtered version thereof with an enabling threshold and enable the indication of the stall of the rotor when the absolute value of the electrical angle or a filtered version thereof is greater than the enabling threshold, where the enabling threshold is greater than the stall threshold.

[0039] Alternatively, in an embodiment of the present invention, the processing device is configured to enable the determination of the stall of the rotor when starting the motor and when the driving speed ω exceeds a predefined threshold.

[0040] A motor system according to an embodiment of the present invention includes a stall detector according to an embodiment of the present invention and an electronically commutated motor. The stall detector is connected to the electronically commutated motor for detecting the stall of the electronically commutated motor.

[0041] In an embodiment of the present invention, the electronically commutated motor is a BLDC motor. The BLDC motor can be, for example, a single-phase BLDC motor. It can also include multiple phases.

[0042] In an embodiment of the present invention, the electronically commutated motor is a stepper motor. The stepper motor can be, for example, a bipolar stepper motor having multiple phases (e.g., 2, 3, 5).

[0043] In an embodiment of the present invention, the electronically commutated motor is a multi-phase switched reluctance motor.

[0044] The specific and preferred aspects of the present invention are set forth in the appended independent and dependent claims. Features from the dependent claims may be combined appropriately with the features of the independent claims and with the features of other dependent claims, not only as explicitly set forth in the claims.

[0045] These and other aspects of the present invention will be apparent from and elucidated with reference to the (one or more) embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flowchart showing an exemplary method in accordance with an embodiment of the present invention is shown.

[0047] Figure 2 A block diagram showing an exemplary stall detector in accordance with an embodiment of the present invention, wherein the stall detector is connected to a BLDC motor, is shown.

[0048] Figure 3 A vector representation of the current, voltage, and BEMF of a three-phase motor driven in an optimal manner is shown.

[0049] Figure 4 The electrical angle of a motor operating at 200 electrical revolutions per minute (e-rpm) over time before and after stalling is shown.

[0050] Figure 5 The electrical angle of a motor operating at 1000 e-rpm over time before and after stalling is shown.

[0051] Figure 6 The electrical angle over time during ramp-up is shown.

[0052] Figure 7 The electrical angle over time during ramp-down is shown.

[0053] Figure 8 A block diagram showing an exemplary stall detector in accordance with an embodiment of the present invention, wherein the stall detector is connected to a stepper motor, is shown.

[0054] Any reference signs in the claims shall not be construed as limiting the scope.

[0055] In the different drawings, the same reference signs refer to the same or similar elements. DETAILED DESCRIPTION

[0056] The present invention will be described with respect to specific embodiments and with reference to specific drawings, but the present invention is not limited thereto and is only defined by the claims. The described drawings are merely illustrative and not restrictive. In the drawings, for illustrative purposes, the sizes of some of the elements may be enlarged and not drawn to scale. The dimensions and relative dimensions do not correspond to the actual reduction in the practice of the present invention.

[0057] The terms first, second, etc. in the description and claims are used to distinguish between similar elements and not necessarily to describe an order in time, space, rank or in any other way. It should be understood that the terms so used are interchangeable where appropriate, and that the embodiments of the present invention described herein can operate in an order different from the order described or illustrated herein.

[0058] In addition, the terms top, bottom, etc. in the description and claims are used for descriptive purposes and not necessarily to describe relative position. It should be understood that the terms so used are interchangeable where appropriate, and that the embodiments of the present invention described herein can operate in an orientation different from the orientation described or illustrated herein.

[0059] It should be noted that the term "comprising" used in the claims should not be construed as being limited to the means listed thereafter; it does not exclude other elements or steps. Thus, the term should be construed as specifying the presence of the stated features, integers, steps or components as mentioned, but not excluding the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "an apparatus comprising means A and B" should not be limited to an apparatus consisting only of components A and B. This means that for the present invention, the only relevant components of the apparatus are A and B.

[0060] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" throughout this specification are not necessarily all referring to the same embodiment, but may refer to different embodiments. In addition, in one or more embodiments, as will be apparent to those of ordinary skill in the art from this disclosure, the particular features, structures, or characteristics may be combined in any suitable manner.

[0061] Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than those expressly recited in each claim. On the contrary, as reflected in the appended claims, the inventive aspects lie in fewer features than all of the features of a single preceding disclosed embodiment. Thus, the claims appended to the specific embodiments are hereby expressly incorporated into the specific embodiments, with each claim itself representing a separate embodiment of the invention.

[0062] In addition, although some embodiments described herein include some features included in other embodiments but do not include other features included in other embodiments, as will be understood by those skilled in the art, the combination of features of different embodiments is intended to fall within the scope of the present invention and form different embodiments. For example, in the appended claims, any of the claimed embodiments may be used in any combination.

[0063] In the description provided herein, numerous specific details are set forth. However, it should be understood that embodiments of the present invention may be practiced without these specific details. In other instances, well-known methods, structures, and techniques are not shown in detail to avoid obscuring the understanding of this specification.

[0064] When referring to a voltage vector in embodiments of the invention, reference is made to a mathematical representation of the voltage applied to or measured from one or more coils of a motor as a single vector. By applying a voltage vector, the speed and position of the motor can be controlled.

[0065] When reference is made to a current vector in embodiments of the present invention, reference is made to a mathematical representation of the current passing through one or more coils of a motor as a single vector. By applying a current vector, the speed and position of the motor can be controlled.

[0066] The voltage vector or the current vector may be obtained, for example, by first applying a Clarke transformation and then applying a Cartesian to polar conversion.

[0067] For a three-phase motor with phases U, V, W (U, V, W can be, for example, voltages or currents on the phases), the Clarke transform that transforms the phases U, V, W to a two-dimensional reference system can be obtained as follows:

[0068] x=U

[0069]

[0070] After this, a Cartesian to polar conversion can be performed to obtain the magnitude and angle of the vector.

[0071]

[0072] Angle = atan2(y, x)

[0073] The result is a vector starting from the origin of the reference frame with the calculated magnitude and angle.

[0074] In a first aspect, embodiments of the present invention relate to a method 100 for detecting the stall of a rotor of an electronically commutated motor 220, and in a second aspect, embodiments of the present invention relate to a stall detector 210 for detecting the stall of an electronically commutated motor 220. Figure 1 A flowchart of an exemplary method according to an embodiment of the present invention is shown, and Figure 2 and Figure 8 A block diagram of a motor system 200 according to an embodiment of the present invention is shown, the motor system 200 including an electronically commutated motor 220 according to an embodiment of the present invention and an exemplary stall detector 210.

[0075] In an embodiment of the present invention, the electronically commutated motor 220 is a BLDC motor or a stepper motor. For example, in Figure 2 the electronically commutated motor 220 is a BLDC motor, and in Figure 8 the electronically commutated motor 220 is a stepper motor.

[0076] The electronically commutated motor includes a rotor and a stator. The electronically commutated motor 220 may include one or more phases on the stator. It may include, for example, one phase, two phases, three phases or even more phases, such as 4 or 6 phases for example. Each motor phase has a phase inductance L and a phase resistance R. Permanent magnets may be present on the rotor.

[0077] The method 100 according to an embodiment of the present invention includes driving 110 the electronically commutated motor 220 by applying a voltage vector or a current vector to one or more motor phases of the electronically commutated motor. The motor is driven such that the rotor rotates. The speed of the electrical voltage vector obtained by applying the voltage vector or the current vector is ω.

[0078] The method 100 includes obtaining 120 the electrical angle between the applied voltage vector and the resulting current vector of one or more phases, or between the applied current vector and the resulting voltage vector of one or more phases. This is done while the motor is being driven 110.

[0079] Furthermore, method 100 includes: comparing 130 the absolute value of the electrical angle or a filtered version thereof with a stall threshold, and indicating 140 a stall of the rotor if the absolute value of the electrical angle or a filtered version thereof is within a range defined by adding / subtracting a predefined margin to / from arctan2(ωL,R).

[0080] The predefined margin can be, for example, a positive value between 0 and 50% of arctan2(ωL,R), for example, between 0 and 40% of arctan2(ωL,R), for example, between 0 and 30% of arctan2(ωL,R), for example, between 0 and 20% of arctan2(ωL,R), for example, between 0 and 10% of arctan2(ωL,R).

[0081] The inventors considered the following for determining the stall threshold. Assume that the permanent magnets are removed from the electronically commutated motor, which simulates the rotor being completely stationary. In this case, only an RL series circuit remains on all stator phases. The transfer function of the system with voltage as the input and current as the output is equal to:

[0082]

[0083] This corresponds to the following phase shift:

[0084] ∠I - ∠V = -∠(R + jωL) = -artan2(ωL,R)

[0085] For simplicity, this is transformed into the following IV angle (i.e., electrical angle) without a negative result:

[0086] IV = ∠V - ∠I = artan2(ωL,R)

[0087] When the rotor is not moving and a rotating voltage vector is applied, the angle between the applied voltage vector and the measured current vector is approximately arctan2(ωL,R). This value (plus or minus the predefined margin) is the threshold used in embodiments according to the present invention.

[0088] In an embodiment of the present invention, the electronically commutated motor is driven in a non - optimal manner such that the electrical angle is greater than arctan2(ωL,R). The simplest non - optimal driving method is to apply a rotating voltage vector in open - loop. This voltage vector can be current - controlled, resulting in a constant current amplitude. The rotating voltage vector can be achieved by applying phase - shifted sinusoidal voltages on all phases of the electronically commutated motor. When the electronically commutated motor is driven non - optimally and the rotor stalls, the electrical angle or a filtered version thereof will become less than the stall threshold. In this case, if the absolute value of the electrical angle or a filtered version thereof becomes less than the stall threshold, a stall is indicated.

[0089] In an embodiment of the present invention, the electronically commutated motor can be driven in an optimal manner. During optimal operation, the current and BEMF vectors are aligned as Figure 3 shown. This figure shows the vector representation of the current, voltage, and BEMF of a three-phase motor. In this figure, Z y = ωL. The corresponding IV angle (i.e., electrical angle) can be calculated using the following formula:

[0090]

[0091] When the motor operates at a low speed ω, ωLI is small compared to BEMF + RI. Referring to Figure 3 and the above formula, this results in an IV angle close to 0. When the motor is driven optimally, the optimal IV angle is always less than the stall IV angle. Therefore, when an optimally driven motor stalls, the absolute value of the electrical angle or its filtered version will cross the stall threshold, where the stall threshold is arctan2(ωL, R) plus or minus a predefined margin.

[0092] On the other hand, non-optimal driving can be achieved by injecting more energy into the motor than required. Increasing the energy above the required energy will result in an increased IV angle. The higher the current is used, the higher the IV angle becomes. In an embodiment of the present invention, the energy can be increased such that when the rotor rotates, the IV angle is always greater than the stall threshold.

[0093] In an embodiment of the present invention, the motor can be driven optimally, and in this case, if the absolute value of the electrical angle becomes greater than the stall threshold, a stall is detected.

[0094] In an embodiment of the present invention, the motor can be driven non-optimally, and in this case, if the absolute value of the electrical angle becomes less than the stall threshold, a stall is detected.

[0095] In an embodiment, the motor can be driven by applying an accelerating voltage vector to the motor until the desired speed is obtained or the speed is high enough to transition to field-oriented control (FOC). During this part, the voltage amplitude can be current-controlled. For example, a constant current or an increasing current can be provided in an open-loop manner.

[0096] During driving, the electrical angle between the applied voltage vector and the resulting current vector, or between the applied current vector and the resulting voltage vector, is obtained.

[0097] In an embodiment of the present invention, when the difference between the electrical angle generated by non-optimal driving and the stall threshold becomes greater than the noise of the electrical angle measurement, the stall detection algorithm is enabled. For example, this may already be the case at 0.5% of the maximum motor speed. When the stall detection algorithm is active, it will indicate a stall of the rotor when the electrical angle or its filtered version crosses the stall threshold. The direct comparison of the electrical angle with the stall threshold results in fast stall detection with little loss of any position information, and filtering the electrical angle before the comparison results in more reliable stall detection at lower speeds.

[0098] In an embodiment of the present invention, a predefined margin may be added to or subtracted from the stall threshold arctan2(ωL,R). The margin may depend on the measurement noise, the vibration during stall, or motor variations.

[0099] In an embodiment of the present invention, if the obtained electrical angle or its filtered version is within the range defined by adding / subtracting a predefined margin to / from arctan2(ωL,R), a stall may be indicated. In these embodiments, the predefined margin is different from zero, for example, between 0.1 and 50% of arctan2(ωL,R).

[0100] In an embodiment of the present invention, if a stall is indicated 140, the driving 110 of the electronically commutated motor may be stopped. In an embodiment of the present invention, if a stall is indicated, a reduced voltage vector or a reduced current vector may be applied during a predefined duration. In an embodiment of the present invention, a voltage or current vector with an opposite polarity may be applied to remove the detected stall condition.

[0101] In an embodiment of the present invention, the current vector and / or voltage vector may be obtained by obtaining the voltage across the coils of the rotor, and / or by measuring the current through the coils of the rotor, and by projecting the current and / or voltage onto an axis system having at least two axes. In an embodiment of the present invention, the projection may be a Clarke transformation. It is also possible to represent the current and flux of each coil in a two-axis system by performing a projection, rather than representing the current and flux of each coil separately. Such a projection may be, for example, a Clarke transformation. When performing a Clarke transformation, different parameters may be written in vector representation. The Clarke transformation transforms phase U, V, W to a two-dimensional reference frame.

[0102] As previously discussed, in the case of three phases, the Clarke transformation can be performed using the following formula: x = U;

[0103] In the case of four phases, the Clarke transformation can be performed using the following formula: x = U – W; y = V - T..

[0104] In this example, all parameters can be described as vectors with reference to the stator.

[0105] The Clarke transformation transforms all three phases into an orthogonal reference frame. Thus, all parameters can be described, for example, as vectors with reference to the stator.

[0106] In Figure 2 and Figure 8 the block diagrams of, a motor system 200 according to an embodiment of the present invention is shown. The motor system 200 includes an electronically commutated motor 220, a full-bridge driver 230 for driving the BLDC motor, and a stall detector 210 according to an embodiment of the present invention for detecting a stall of the electronically commutated motor 220. In Figure 2 the electronically commutated motor is a three-phase BLDC motor, and in Figure 8 the electronically commutated motor is a two-phase stepper motor.

[0107] The stall detector 210 includes a pre-driver 213 configured to drive the electronically commutated motor 220 for rotating the rotor by applying a voltage vector or a current vector to one or more motor phases of the electronically commutated motor 220 (the brushless DC motor 220 in Figure 2 and the stepper motor 220 in Figure 8 ). In the exemplary embodiments in Figure 2 and Figure 8 the pre-driver 213 uses a drive signal to control the gates of the transistors of the full-bridge driver 230 for generating a current through the motor coils of the electronically commutated motor. The current can be generated by an average voltage difference across the motor coils generated by the full-bridge output driver 230. The drive signal can be a pulse-width modulation (PWM) signal or a linearly controlled signal. The resulting current through the coils is, for example, a sinusoidal current.

[0108] Furthermore, the stall detector 210 includes a detector 212 configured to obtain the electrical angle between the applied voltage vector and the resulting current vector of one or more motor phases, or between the applied current vector and the resulting voltage vector of one or more motor phases. In Figure 2 the detector is illustrated by rectangle 212. The voltage vector can be obtained from the supply voltage VSM that powers the motor. Based on the supply voltage and the known duty cycles on each phase ( Figure 2 U, V, W in Figure 2 ), the voltage applied to each phase can be calculated. The result can be multiplied by a constant factor that depends on the shape of the applied phase voltage (since the star point voltage may not be equal to zero). The supply voltage can be measured, or it can be obtained from a voltage source. Alternatively, as illustrated in Figure 8As shown in the figure, the phase monitoring PM of the phase voltage of the stepper motor 220 can also be completed by the detector 212. In an embodiment of the present invention, the measured voltage can be related to the supply of the ground or reference voltage level. The current vector can be determined, for example, by measuring the voltage across the summing resistor 231 connected between the full-bridge driver and the ground. Thus, a current vector can be obtained, and this voltage vector represents the flux generated by the current passing through one or more coils of the electronically commutated motor.

[0109] In an embodiment of the present invention, one or more ADC units can be used to measure the phase voltage of each phase to obtain a voltage vector, and to measure the voltage across the summing resistor 231 to obtain a current vector (see Figure 2 and Figure 8 ). If only one ADC is used, it can be multiplexed to different channels. In a preferred embodiment, the channels are sample-and-hold channels to ensure voltage measurements are made at the same time. If several ADCs are used, the ADC measurements of different channels can be synchronized.

[0110] Furthermore, the stall detector 210 includes a processing device 211 that is configured to determine the stall of the rotor when the absolute value of the electrical angle or its filtered version exceeds a stall threshold, and to indicate the stall, where the stall threshold is arctan2(ωL,R) plus or minus a predefined margin. Once a stall is detected, this can be indicated to the pre-driver 213, and the pre-driver 213 can stop the motor. The full-bridge output can be placed in a tri-state so that high current through the coil can be avoided. Alternatively, once a stall is detected, a reduced voltage vector or a reduced current vector can be applied during a predefined duration after receiving the stall indication. Alternatively, the low-side transistor can be turned on to draw all the current from the coil so that the motor is stopped. Alternatively, a sequence between a reduced voltage or current vector and an increased voltage or current vector can be applied to attempt to resolve the stall condition.

[0111] Figure 4 Shows the electrical angle (in electrical degrees) of a motor operating at 200 e-rpm before and after stall over time (in seconds). The stall threshold that can be used in this example is 2.66 electrical degrees (e-deg).

[0112] Figure 5 Shows the electrical angle (in electrical degrees) of a motor operating at 1000 e-rpm before and after stall over time (in seconds). The stall threshold that can be used in this example is 4.91 e-deg.

[0113] Figure 6Shows the electrical angle (in electrical degrees) varying with time (in seconds) during acceleration. In an embodiment of the present invention, the method or device is configured such that no stall is triggered during acceleration. The enabling function can be implemented in the processing device of the stall detector. For example, it can be used when starting the motor from zero speed and driving the motor in a non-optimal manner. Once the rotor has reached a certain minimum speed such that the difference between the IV angle and the stall threshold becomes greater than the measured noise, stall detection can be enabled for constant speed operation, acceleration, or deceleration.

[0114] Figure 7 Shows the electrical angle (in electrical degrees) varying with time (in seconds) during deceleration. In an embodiment of the present invention, the method or device is configured such that no stall is triggered during deceleration. The processing device of the stall detector can be configured to disable stall detection such that no stall is indicated during deceleration.

[0115] Figure 4 and Figure 5 The curves in show the electrical angle of a motor driven in a non-optimal manner. In these cases, the electrical angle will not be below the stall threshold and thus will not cause a stall to be triggered. When a change in torque does cause a stall to be triggered and it is not a true stall, then the change in torque causes the motor to operate very close to the optimal point, which means it is operating very close to the stability margin. Operating the motor in an open loop near this stability margin has a high risk of causing oscillations, which typically lead to a stall. Therefore, advantageously, in an embodiment of the present invention, when this occurs, the motor is stopped or restarted.

[0116] In an embodiment of the present invention, a stepper motor can be configured as a two-phase stepper motor. Other stepper motor configurations (such as, for example, three-phase and five-phase stepper motors) are also possible. The described stall detector or stall detection method according to an embodiment of the present invention can be applied, for example, to stepper motors used in: thermostatic expansion valves for HVAC systems (heat pumps, cooling circuits), smart valves in heating systems, and stepper motor drive assemblies in consumer appliances such as robotic vacuum cleaners and lawn mowers. These applications benefit from the sensorless stall detection described herein, which reduces system complexity and cost while improving reliability.

Claims

1. A method (100) for detecting stall of a rotor of an electronically commutated motor (220), the electronically commutated motor (220) comprising one or more motor phases, each motor phase having a phase inductance L and a phase resistance R, the method (100) comprising: driving (110) the electronically commutated motor (220) by applying the voltage vector or the current vector to the one or more motor phases of the electronically commutated motor (220) at a rotation speed ω of the voltage vector or the current vector for rotating the rotor, obtaining (120) an electrical angle between an applied voltage vector and a resulting current vector of the one or more motor phases, or between an applied current vector and a resulting voltage vector of the one or more motor phases, The absolute value of the electrical angle, or a filtered version thereof, is compared (130) to a stall threshold, wherein the stall threshold is arctan2(ωL,R) plus or minus a predefined margin, and if the absolute value of the electrical angle, or a filtered version thereof, is within a range defined by arctan2(ωL,R) plus / minus the predefined margin, stall of the rotor is indicated (140).

2. The method (100) according to claim 1, wherein: The predefined margin is a positive value between 0.1 and 50% of arctan2(ωL,R).

3. The method (100) according to claim 1, wherein: The motor is driven (110) in an open loop manner.

4. The method (100) according to claim 1, wherein: The motor (220) is driven (110) such that when the rotor rotates, the absolute value of the electrical angle or a filtered version thereof is greater than the stall threshold.

5. The method (100) according to claim 4, comprising an enabling step when starting the motor, wherein: The absolute value of the electrical angle, or a filtered version thereof, is compared to an enablement threshold, and an indication of a stall of the rotor is enabled only when the absolute value of the electrical angle, or a filtered version thereof, is greater than the enablement threshold, wherein the enablement threshold is greater than the stall threshold.

6. The method (100) according to claim 1, comprising: In the event of an indication (130) of a stall, the drive (110) of the electronically commutated motor is stopped.

7. The method (100) of claim 1, wherein: The electronically commutated motor (220) is a BLDC motor.

8. The method (100) of claim 1, wherein: The electronically commutated motor (220) is a stepper motor.

9. A stall detector (210) for detecting a stall of an electronically commutated motor (220), the electronically commutated motor (220) comprising one or more motor phases, each motor phase having a phase inductance L and a phase resistance R, the stall detector comprising: a driver (210, 230) configured to drive (110) the electronically commutated motor (220) by applying the voltage vector or the current vector to one or more motor phases of the electronically commutated motor (220) at a rotation speed ω of the voltage vector or the current vector for rotating the rotor, a detector (212) configured to obtain (120) an electrical angle between an applied voltage vector and a resulting current vector of the one or more motor phases, or between an applied current vector and a resulting voltage vector of the one or more motor phases, A processing device (211) configured to compare the absolute value of the electrical angle or a filtered version thereof with a stall threshold, wherein the stall threshold is arctan2(ωL,R) plus or minus a predefined margin, and to determine that the rotor is stalled if the absolute value of the electrical angle or a filtered version thereof is within a range defined by arctan2(ωL,R) plus / minus the predefined margin, and to indicate the stall.

10. The stall detector (210) according to claim 9, wherein: The driver (213, 230) is configured to drive the motor in an open loop manner.

11. The stall detector (210) according to claim 9, wherein: The driver (213, 230) is configured to drive the motor (220) so that when the rotor rotates, the absolute value of the electrical angle or a filtered version thereof is greater than the stall threshold.

12. A motor system (200), comprising the stall detector (210) according to claim 9, and an electronically commutated motor (220), wherein: The stall detector (210) is connected to the motor (220) to detect the stall of the electronically commutated motor (220).

13. The electric machine system (200) of claim 12, wherein: The electronically commutated motor (220) is a BLDC motor.

14. The electric machine system (200) of claim 12, wherein: The electronically commutated motor (220) is a stepper motor.

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