Control system for multi-phase brushless motor without position sensor

Abstract

The invention relates to a control system for a multiphase brushless motor without a position sensor, the multiphase brushless motor incorporating drive control electronics comprising:-switching means (20) provided with two-state switches (12 to 17) for varying the voltage applied to each of the phases; -an overload detection device (32) for detecting an overload of the motor; and-determination means (34) for determining the operating points, which determination means enable application of at least two operating points; -the control electronics are arranged to generate a sinusoidal waveform from the DC voltage using space vector modulation or vector modulation, and the control electronics are arranged to modify the operating point at least once in the event that the overload detection means (20) detects an overload.

Description

Technical Field

[0001] The present invention relates to the field of stepper motor gearboxes (multi-phase synchronous brushless DC motors controlled in stepping mode), and more specifically to gear motors controlled in microstepping mode.

[0002] The step control mode results in increments of rotor rotation called full steps, which for a three-phase (or two-phase) motor correspond, for example, to 6 (or 4) full steps per electrical cycle of the current present in each phase. In order to reduce this increment of rotation, for example in order to reduce operating noise and rotor vibrations, the full steps can be subdivided into microsteps. To achieve this, and in contrast to the full-step control mode, each motor phase must then be controlled with a current in substantially sinusoidal form according to the number of microsteps per step. For a three-phase motor, 6 transistors are required to simultaneously apply 3 substantially sinusoidal current waveforms, phase-shifted by 120°, to the 3 phases of the motor.

[0003] In stepper motor gearboxes, a common method for detecting locking or stalling uses a device for detecting the value of the voltage induced in the motor phases, in particular the state of the transistors controlling these phases (e.g. an off state capable of measuring the voltage induced in an unused phase without interference).

[0004] Thus, it can be seen that it is difficult to obtain this induced voltage measurement for a multi-phase motor controlled in microstep mode while using all power transistors. Prior art

[0005] In the prior art, patent application US2017126153 is known, which describes a method for detecting a locked rotor condition in a sensorless permanent magnet synchronous motor, the method comprising:

[0006] Determining an estimated rotor speed and a first back EMF voltage value BEMF in an estimated rotor-related reference frame using a BEMF observer;

[0007] Calculating a second estimated BEMF voltage value in a rotor-related reference frame based on at least the first motor constant and the estimated rotor speed

[0008] generating a BEMF error filter value (BEMFErrorFilt) based on a difference between the first estimated BEMF voltage value and the second estimated BEMF voltage value;

[0009] generating a BEMF error threshold (BEMFErrorThreshold) based on the estimated rotor speed (ω) subject to a minimum threshold BEMF value (BEMFErrorThresholdMin); and

[0010] Detecting a rotor locked condition in a sensorless permanent magnet synchronous motor based on at least a BEMF error filter value (BEMFErrorFilt) and a BEMF error threshold value (BEMFErrorThreshold).

[0011] Also known is patent application EP3826170, which describes a stall detector for detecting a stall of a brushless DC motor. The brushless DC motor is adapted to apply one or more drive signals so that a current through one or more coils of the brushless DC motor generates a flux for driving the motor. The stall detector comprises a processing device adapted to determine a direct angle between a back EMF voltage vector generated by the motor and a current vector representing the flux generated by the current through the one or more coils. The processing device is further adapted to determine that the motor is stalled when the direct angle exceeds a predetermined threshold at least once.

[0012] Patent EP2966772 provides a method for detecting stall of a two-phase or three-phase motor operating in microstep mode, the method comprising:

[0013] a) applying a plurality of phase-shifted microstep waveforms (6) to the phase windings (Lu, Lv, Lw) of the motor, whereby the phase shift is approximately 120° in the case of a three-phase motor and approximately 90° in the case of a two-phase motor;

[0014] b) determining a sum of currents flowing through phase windings of the motor and obtaining samples (Raw) from the sum of currents in synchronism with application of the microstep waveform;

[0015] c) in the case of a three-phase motor, calculating a moving average (MovAvg) or a moving sum of the samples over a plurality of samples of a microstep waveform corresponding to an even multiple of 120° or 60°, and in the case of a two-phase motor, calculating a moving average (MovAvg) or a moving sum of the samples over a plurality of samples of a microstep waveform corresponding to an even multiple of 180° or 90°;

[0016] d) calculating an adaptive threshold based on the sample (Raw);

[0017] e) When the moving average (MovAvg) or the moving sum is greater than the adaptive threshold, the stall of the motor is detected.

[0018] Patent application JP2005151678 provides an arrangement for sensorless control of an undamped permanent magnet synchronous motor (PM motor).

[0019] Disadvantages of Background Art Solutions

[0020] Some of the prior art solutions require one or more position or torque sensors, which increases manufacturing cost and complexity.

[0021] Other solutions require complex algorithmic processing, which involves the use of powerful processors and high power consumption.

[0022] Finally, these solutions also result in untimely stops, although not counted as locking, when the resistance to movement of the driven member increases and exceeds the resistive torque. This results in inappropriate positioning and may lead to inappropriate false reports.

[0023] The solution provided by the present invention

[0024] The object of the present invention is to remedy this drawback and, according to its most general recognition, relates to a control system for a multi-phase brushless motor having the technical features set out in claim 1 .

[0025] The motor has no position sensor and incorporates drive control electronics comprising:

[0026] a switching device having a two-state switch for varying the voltage applied to each phase,

[0027] A device for detecting motor overload,

[0028] means for determining an operating point, which means enable the application of at least two operating points,

[0029] • The control electronics is arranged to generate a sinusoidal waveform from the DC voltage using space vector modulation.

[0030] The control electronics are arranged to modify the operating point at least once if the overload detection means detects an overload.

[0031] Advantageously, the stall detection means comprises a circuit for measuring the total current consumed by the N phases of the motor.

[0032] In one embodiment, the stall detection means comprises a sampling resistor and means for measuring in said resistor an image of the total current drawn in the sum of the N phases of the multiphase motor.

[0033] In another embodiment, the stall detection device comprises:

[0034] means for measuring the sum of the currents flowing in each motor phase,

[0035] means for calculating a stop detection threshold associated with the evolution of the sum of said currents,

[0036] Means for processing the sampled current values ​​by mathematical or statistical operations, the stop detection threshold being determined with reference to the results of the processing.

[0037] Advantageously, in the event of an overload detection during X consecutive iterations, said overload detection means transmit a signal commanding a modification of the operating point and then a motor stop command in the event of a new stall being detected.

[0038] Furthermore, the means for determining the operating point comprises an interface for receiving signals from an external condition sensor.

[0039] For example, the external condition sensor is a temperature sensor.

[0040] Alternatively, an external condition sensor provides a measurement of the supply voltage to the switching device.

[0041] DETAILED DESCRIPTION OF A NON-LIMITING EXEMPLARY EMBODIMENT

[0042] Additional advantages of the present invention will be readily appreciated as they become better understood with reference to the following detailed description illustrated by the accompanying drawings, in which:

[0043] [ Figure 1 ][ Figure 1 ] shows a schematic diagram of a control circuit for driving a three-phase BLDC motor,

[0044] [ Figure 2 ][ Figure 2 ] shows a schematic diagram of a "space vector modulation" processing circuit for driving a three-phase BLDC motor,

[0045] [ Figure 3 ][ Figure 3 ] shows a timing diagram of signals used to implement the present invention,

[0046] [ Figure 4 ][ Figure 4 ] shows the timing diagrams for two types of operating points,

[0047] [ Figure 5 ][ Figure 5 ] shows an example of an action initiation sequence for updating the operating point when an overload is detected.

[0048] Basic principle of the invention

[0049] The proposed solution consists in implementing a space vector modulation (SVM) control mode, whose operating point can be adjusted according to the external load and / or external conditions (eg, temperature / voltage).

[0050] The principle of the invention is to provide control electronics which are arranged to detect an overload by means of an overload detection device (32) and to modify the operating point at least once if an overload is detected.

[0051] - by increasing current and / or voltage,

[0052] - and / or reduce the speed set point,

[0053] And in case of persistent overload detection (32) at the end of a loop of N iterations, N being greater than 1, the motor is commanded to stop in order to avoid constant calculation of new set points via the application of Clarke and Park transformations which require extensive digital processing.

[0054] The basic principle of the control circuit for driving a three-phase BLDC motor in star connection is described in [ Figure 1 ] is shown in the figure. The three-phase brushless DC motor consists of three motor windings (1 to 3) (designated as phases U, V, W) connected in a star network. One end (4 to 6) of each winding (1 to 3) is connected to a termination terminal (7 to 9) respectively. The other ends of the windings (1 to 3) are connected together through a termination terminal (10) to form a star connection. The control circuit includes a switching device (20), in this case a three-phase bridge. Each arm of the three-phase bridge includes a pair of switches (12 to 17) in the form of an upper transistor and a lower transistor connected in series between a power rail (18) and a ground line (19). The termination terminals (7, 8, 9) are electrically connected to the three-phase bridge between complementary switch pairs (12, 15; 13, 16; 14, 17), respectively. The switches (12 to 17) are switched on and off by a controller in a controlled manner to provide pulse width modulation of the potential applied to each of the terminations (7 to 9) so as to control the potential difference applied across each of the windings (1 to 3) and thereby also control the current flowing through the windings (1 to 3) and thereby control the strength and orientation of the magnetic field generated by the windings (1 to 3).

[0055] Notice,[ Figure 1 ] shows a three-phase bridge connected to a three-phase winding connected in star. However, this configuration is not a limitation of the invention and any other number of phases or winding connections known to a person skilled in the art are conceivable. For example, the invention includes a motor with 12 coils connected in parallel delta (each winding comprising 4 coils connected in parallel). It is also possible to use a full-bridge inverter with 2 times the arms, where each winding end is connected to an inverter arm. The use of a multi-level inverter with more than 2 switches per arm is also not excluded.

[0056] Detailed description of the "space vector modulation" control circuit

[0057] [ Figure 2] shows a schematic diagram of a “space vector modulation” processing circuit for driving a three-phase BLDC motor according to the present invention.

[0058] The SVM control is generated via subassembly (30). For this operation, a pre-programmed vector table can be used for subassembly (37), which does not require a lot of computing power by bypassing the conventional sinusoidal signal generator (35) and the transformation in the α, β plane performed by subassembly (36). Subassembly (38) generates the set point signal to the inverter (20) in the form of a PWM command. Subassemblies (35) to (37) can be combined into a single subassembly (39) via a pre-programmed vector switching table.

[0059] SVM control is a principle well known to those skilled in the art and makes it possible to generate sinusoidal phase currents from a DC supply voltage by controlling the activation time of each branch of the inverter. The feedback loop consists of a plurality of subcomponents, including current measurement means (31), overload detection means (32) and set point signal correction means (33). The feedback loop is conventionally formed by complex algorithms or sensors requiring the use of Clarke and Park transformations. Phase current / voltage measurements are made by subcomponent (31) and this data can be used by the overload detection means (32) for example for a stall detection algorithm. Based on the output signal of the overload detection algorithm, the means (33) for correcting the total set point signal for current and / or speed sends appropriate signals to the means (34) for determining the operating point. The means (34) for determining the operating point compiles all data from the feedback loop and possibly from external condition sensors (40, 41) (e.g. temperature or inverter supply voltage) in order to select the best operating point to be applied to the system.

[0060] Description of the operating point change algorithm

[0061] The operating principle of the algorithm is to dynamically adjust the operating point based on the detection of overload and optionally based on external condition data such as temperature, voltage, load or any other parameter or combination of these parameters.

[0062] This mode of operation avoids the need for computationally intensive digital processing of Clarke and Park transforms while closely resembling the behavior of the FOC (Field Oriented Control) control mode.

[0063] To achieve this, a stall detection algorithm is implemented to stop the motor before it stalls in case of a large external load so that a new operating point can be used. The algorithm may be for example the one described in patent EP1680862 or any other stall detection algorithm.

[0064] Stall detection algorithms are usually implemented to stop the motor before it stalls in case of large external loads. The present invention consists in not systematically commanding a motor stop, but in using this information temporarily to command a modification of the operating point (possibly in an incremental sequence) before actually commanding the motor to stop.

[0065] To this end, the microcontroller decides to restart the movement at an operating point providing more torque (by reducing speed and / or increasing current) before reporting a stall, after a predetermined time or movement, it is envisaged to return to the initial operating point.

[0066] If the second operating point is not sufficient, the user can be informed (via the ECU in the automotive field) that the actuator is stalled, or the movement can be retried with another operating point.

[0067] Depending on the responsiveness of the stall detection algorithm, one can choose whether to stall the motor for a change in operating point.

[0068] External conditions can also be used to evaluate the operating point to be applied to the motor. This external condition check can be done before initiating the move or during the move.

[0069] Example: An actuator is able to deliver 1.5Nm of dynamic torque at 4rpm over the entire temperature range, but only when the voltage is between 11V and 16V. If the measured voltage is between 9V and 11V, the actuator decides to reduce the speed to 2.25rpm to guarantee the 1.5Nm of torque.

[0070] Operation Example

[0071] Figure 3 A timing diagram of position command, position feedback, current and stall detection signals is shown. Position command pc is shown by curve (300), position feedback pm is shown by curve (310), current measurement c is shown by curve (320), and stall detection algorithm measurement sd is shown by curve (330). All curves are expressed in arbitrary units au.

[0072] During this sequence, a closing command (340) is sent to the actuator. During this closing movement, the actuator detects a stall (350).

[0073] A change in the operating point, for example by reducing the speed, is then performed without any errors being sent back to the ECU. This new operating point allows the movement to continue (360) and resolves the stall condition detected by the algorithm. Once the stuck point has been passed, another operating point can be set (370) to complete the movement until the controlled member reaches a known stop position at time (380). Since the final position is known, the algorithm does not adjust the operating point, but simply stops the movement.

[0074] Example of point adjustment in operation

[0075] Figure 4 A timing diagram showing the operating point adjustment according to the inverter supply voltage is shown. Curve (100) shows the variation of the inverter supply voltage v and curve (200) shows the variation of the set point speed s.

[0076] When the device is in use, the member connected to the actuator is driven at a nominal speed s = s1. The supply voltage of the inverter (now v = v M ) gives the nominal torque T1. If for any reason the supply voltage drops to the threshold voltage v=v at time (110) t=t0 n The voltage at the inverter terminals is then no longer sufficient to obtain the rated torque T1. The operating point can then be adjusted, for example by reducing the speed s to a level that enables a torque greater than v=v m The voltage of the rated torque T1 is obtained by s=s0. If at time (120) t=t1, the voltage rises again to the threshold value v=v n If the voltage drops to the threshold value v=v during the movement, the speed is adjusted back to its nominal value s=s1. m Following this, the speed is then adjusted again to ensure that the nominal torque T1 is achieved. If the voltage drops so that the nominal torque can no longer be achieved, the algorithm can decide to stop the movement.

[0077] Example of an operating point adjustment algorithm

[0078] In this context, Figure 5 ] shows an example of an action initiation sequence for updating the operating point when an overload is detected.

[0079] When the action is started, the algorithm leaves the initialization block (400) to perform an overload check, alternating via a loop through an overload detection monitoring block OL (401) and an action block MOVE (405). In the event of an overload, the algorithm leaves the loop to modify the operating point. The algorithm then joins a block (402) that controls the value of the increment variable i and, if the threshold X is not exceeded, continues to update the operating point via an UPDATE block (403) before returning to the loop to monitor the overload, before continuing to increment said variable i as described by block (404) in an attempt to pass this block without stopping the action. If the overload condition persists, the algorithm attempts to further increment the operating point, up to a limit of X attempts. If the overload persists after X operating point updates, the algorithm joins a block (406) and the motor is stopped.

[0080] This sequence is by no means a limitation of the invention and a person skilled in the art can envision other possibilities depending on the objectives to be achieved. For example, a sequence can be envisioned in which the operating point is not gradually increased to provide greater torque, but follows a binary regulation to optimize the final value.

Claims

1. A control system for a multi-phase brushless motor without a position sensor, the multi-phase brushless motor being combined with drive control electronics, the drive control electronics comprising: - a switching device (20) having two-state switches (12 to 17) for varying the voltage applied to each phase, - an overload detection device (32) for detecting an overload of the motor, - determination means (34) for determining an operating point, said determination means enabling the application of at least two operating points, Characterized in that the control electronics are arranged to modify the operating point at least once in the event of an overload detected by the overload detection device (20), in the event of an overload being detected during a plurality of consecutive iterations, the overload detection device (20) transmits a signal controlling the modification of the operating point and then transmits an instruction for stopping the motor in the event of a new stall being detected.

2. The control system for a sensorless multi-phase brushless motor according to claim 1, characterized in that: The control electronics is arranged to generate a sinusoidal waveform from the DC voltage using space vector modulation.

3. The control system for a sensorless multi-phase brushless motor according to claim 1, characterized in that: The overload detection device comprises a circuit for measuring the total current consumed by the N phases of the motor.

4. The control system for a sensorless multi-phase brushless motor according to claim 1, characterized in that: The overload detection means comprises a sampling resistor and means for measuring in said resistor an image of the total current drawn in the sum of said N phases of said multiphase motor.

5. The control system for a sensorless multi-phase brushless motor according to claim 1, characterized in that: The overload detection device comprises: - means for measuring the sum of the currents (I) flowing in each motor phase (A, B, C), - means for calculating a stop detection threshold (E) associated with the evolution of said sum of said currents (I), - means for processing the sampled current values ​​(I) by mathematical or statistical operations, said stop detection threshold (E) being determined with reference to the result of this processing.

6. The control system for a sensorless multi-phase brushless motor according to claim 1, characterized in that: The determining means (34) for determining the operating point comprises an interface for receiving signals supplied by external condition sensors (40, 41).

7. The control system for a sensorless multi-phase brushless motor according to claim 6, characterized in that: The external condition sensor (41) is a temperature sensor.

8. The control system for a sensorless multi-phase brushless motor according to claim 5, characterized in that: The external condition sensor (40) provides a measurement of the supply voltage to the switching device (32).

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