Control system for a polyphase brushless motor without a position sensor.

Abstract

The present invention relates to a control system for a polyphase brushless motor without position sensors and incorporating drive control electronics, comprising: - switching means (20) with two-state switches (12-17) for varying the voltage applied to each of the phases; - means (32) for detecting an overload of the motor; - means (34) for determining an operating point, making at least two operating points applicable; - control electronics configured to generate a sinusoidal waveform from a DC voltage using space vector modulation or vector modulation, the control electronics being configured to change the operating point at least once if an overload is detected by the overload detection means (20).

Description

[Technical Field]

[0001] The present invention relates to the field of stepper motor gearboxes (polyphase synchronous brushless DC motors controlled in stepping mode), and more particularly to geared motors controlled in microstepping mode.

[0002] Stepper control mode produces rotor rotation increments called full steps, which, for example, in the case of a three-phase (two-phase each) motor, correspond to six full steps (four each) per electrical period of the current present in each phase. To reduce this rotation increment, for example to reduce operational noise and rotor vibration, the full steps can be subdivided into microsteps. To achieve this, and in contrast to full-step control mode, each motor phase must be controlled with a substantially sinusoidal current as a function of the number of microsteps per step. In the case of a three-phase motor, six transistors are required to simultaneously apply three substantially sinusoidal current waves, phase-shifted by 120°, to the three phases of the motor.

[0003] A common method for detecting lock or stall in a stepper motor gearbox uses means for detecting the value of the voltages induced in the motor phases, and in particular the state of the transistors controlling these phases (e.g., open state, which allows the voltages induced in unused phases to be measured without interference).

[0004] Therefore, in a polyphase motor controlled in microstepping mode, it proves difficult to access this induced voltage measurement using all the power transistors simultaneously. [Background technology]

[0005] prior art Known in the prior art is US Patent Application Publication No. 2017126153, which describes a method for detecting a locked rotor condition in a sensorless permanent magnet synchronous motor, comprising: determining an estimated rotor speed and a first back electromotive force (BEMF) voltage value in an estimated rotor-related reference frame using a BEMF observer; 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; 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; generating a BEMF error threshold (BEMFErrorThreshold) as a function of the estimated rotor speed (ω) according to a minimum threshold BEMF value (BEMFErrorThresholdMin); and Detecting a locked rotor condition in the sensorless permanent magnet synchronous motor based on at least a BEMF error filter value (BEMFErrorFilt) and a BEMF error threshold value (BEMFErrorThreshold).

[0006] Also known is European Patent No. 3826170, which describes a stall detector for detecting stall of a brushless DC motor. The brushless DC motor is adapted to apply one or more drive signals such that current through one or more coils of the brushless DC motor generates magnetic flux for driving the motor. The stall detector includes a processing device adapted to determine a direct angle between a voltage vector of a back EMF generated by the motor and a current vector representing the magnetic flux generated by the current through the one or more coils. The processing device is further adapted to determine that the motor is stalled if the direct angle exceeds a predetermined threshold at least once.

[0007] EP 2966772 provides a method for detecting stalls in a two-phase or three-phase motor operating in microstep mode, the method comprising: a) applying a plurality of phase-shifted microstep waveforms (6) to the phase windings (Lu, Lv, Lw) of the motor (the phase shift being approximately 120° for a three-phase motor and approximately 90° for a two-phase motor); b) determining the sum of the currents through the phase windings of the motor and taking a raw sample of the sum of the currents synchronously with the application of the microstep waveform; c) calculating a moving average (MovAvg) or moving sum of the samples over a number of samples corresponding to even multiples of 120° or 60° of the microstep waveform in the case of a three-phase motor, or even multiples of 180° or 90° of the microstep waveform in the case of a two-phase motor; d) calculating a fitness threshold based on the sample (Raw); e) detecting a motor stall when the moving average (MovAvg) or moving sum is greater than the adaptive threshold.

[0008] JP 2005151678 A provides a device for sensorless control of a damperless permanent magnet synchronous motor (PM (Permanent-Magnet) motor).

[0009] Drawbacks of the Background Art Solutions Some prior art solutions require one or more position or torque sensors, which increases manufacturing cost and complexity.

[0010] Other solutions require the use of powerful processors and complex algorithmic processing, which entails high power consumption.

[0011] Finally, these solutions increase resistance to movement of the driven member, resulting in premature stalling if the resisting torque is exceeded, which does not count as a lock, leading to improper positioning and potentially improper error reporting. Summary of the Invention

[0012] The object of the present invention is to remedy this drawback and relates to a control system for a polyphase brushless motor having the technical features set out in claim 1, as is most commonly accepted.

[0013] The motor does not have a position sensor and incorporates drive control electronics, which switching means having two-state switches for varying the voltage applied to each phase; means for detecting motor overload; means for determining an operating point, which allows the application of at least two operating points; The control electronics is configured to generate a sinusoidal waveform from a DC voltage using space vector modulation, and the control electronics is configured to change the operating point at least once if an overload is detected by the overload detection means.

[0014] Advantageously, the stall detection means includes circuitry for measuring the total current consumed by the N phases of the motor.

[0015] In one embodiment, the stall detection means includes a sampling resistor and means for measuring across the resistor an image of the total current flowing in a sum of N phases of a polyphase motor.

[0016] In another embodiment, the stall detection means comprises: means for measuring the sum of the currents flowing through each motor phase; means for calculating a stall detection threshold in relation to the change in said total current; means for processing the sampled current values ​​by mathematical or statistical operations, the stall detection threshold being determined with reference to the results of this processing.

[0017] Advantageously, said overload detection means issues a signal commanding a change of operating point if an overload is detected during X consecutive iterations, and then issues a motor stop command if a new stall is detected.

[0018] Additionally, the means for determining an operating point includes an interface for receiving a signal from an external condition sensor.

[0019] For example, the external condition sensor is a temperature sensor.

[0020] Alternatively, an external condition sensor provides a measurement of the supply voltage to the switching means. [Brief explanation of the drawings]

[0021] Further advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description, illustrated by the accompanying drawings, in which: [Figure 1] 1 shows a schematic diagram of a control circuit for driving a three-phase BLDC motor. [Figure 2] 1 shows a schematic diagram of a "space vector modulation" processing circuit for driving a three-phase BLDC motor. [Figure 3] 2 shows a timing diagram of signals used to implement the present invention; [Figure 4] Timing diagrams for two operating points are shown. [Figure 5] 10 illustrates an example of a start-up sequence in which the operating point is updated if an overload is detected. DETAILED DESCRIPTION OF THE INVENTION

[0022] General principles of the present invention The proposed solution consists of implementing a Space Vector Modulation (SVM) control mode, whose operating point can be adapted according to the external load and / or external conditions (e.g. temperature / voltage).

[0023] The principle of the present invention is to provide a control electronics device configured to detect an overload by means of an overload detection means (32), and if an overload is detected, to change the operating point at least once by increasing the current and / or voltage and / or reducing the speed set point, and if the overload detection (32) persists at the end of N repeated cycles (N greater than 1), to command the motor to stop in order to avoid constantly calculating new set points via application of Clarke and Park transforms, which requires intensive digital processing.

[0024] The general principle of a control circuit for driving a star-connected three-phase BLDC motor is shown in Figure 1. The three-phase brushless DC motor consists of three motor windings (1-3), designated Phase U, Phase V, and Phase W, connected in a star network. One end (4-6) of each winding (1-3) is connected to a termination (7-9), respectively. The other ends of the windings (1-3) are connected to each other by a termination (10) to form a star connection. The control circuit includes a switching means (20), in this case a three-phase bridge. Each arm of the three-phase bridge includes a pair of switches (12-17) in the form of upper and lower transistors connected in series between a supply rail (18) and a ground rail (19). The terminations (7, 8, 9) are electrically connected to the three-phase bridge between complementary pairs of switches (12, 15; 13, 16; 14, 17), respectively. The switches (12-17) are switched on and off in a controlled manner by the controller to provide pulse width modulation of the potential applied to each of the terminations (7-9) to control the potential difference applied to each of the windings (1-3), and therefore the current flowing through the windings (1-3), and consequently the strength and orientation of the magnetic field generated by the windings (1-3).

[0025] Note that Figure 1 shows a three-phase bridge connected to three star-connected windings. However, this configuration is not intended to limit the present invention, and any other number of phases or winding connections known to those skilled in the art are contemplated. For example, a motor with 12 coils connected in a parallel delta configuration, with each winding containing four coils connected in parallel, is within the scope of the present invention. It is also possible to use a full-bridge inverter with twice the number of arms, with each winding end connected to an inverter arm. The use of a multilevel inverter with more than two switches per arm is not excluded.

[0026] Detailed description of the "Space Vector Modulation" control circuit FIG. 2 shows a schematic diagram of a "space vector modulation" processing circuit for driving a three-phase BLDC motor in accordance with the present invention.

[0027] SVM control is generated via subassembly 30. For this operation, a pre-programmed vector table may be used for subassembly 37, which does not require significant computational power by bypassing the transformation in the α, β plane performed by conventional sinusoidal signal generator 35 and subassembly 36. Subassembly 38 generates a setpoint signal to inverter 20 in the form of a PWM command. Subassemblies 35-37 may be combined into a single subassembly 39 via a pre-programmed vector switching table.

[0028] SVM control, a principle well known to those skilled in the art, allows for the generation of sinusoidal phase currents from a DC supply voltage by controlling the operating time of each branch of the inverter. The feedback loop is composed of several subassemblies, including a current measurement means (31), an overload detection means (32), and a setpoint signal correction means (33). This feedback loop is traditionally formed by sensors or complex algorithms requiring the use of Clarke and Park transforms. Phase current / voltage measurements are performed via the subassembly (31), and this data can be used by the overload detection means (32), e.g., a stall detection algorithm. Depending on the output signal of the overload detection algorithm, the means for correcting the overall setpoint signal (33) for current and / or speed sends an appropriate signal to the means for determining the operating point (34). The means for determining the operating point (34) compiles all data from the feedback loop and, potentially, from external condition sensors (40, 41), e.g., temperature or inverter supply voltage, to select the optimal operating point to apply to the system.

[0029] Explanation of the operating point change algorithm The working principle of the algorithm is to dynamically adapt the operating point according to the detection of overload and, optionally, according to external condition data such as temperature, voltage, load or any other parameter or combination thereof.

[0030] This mode of operation avoids the need for computationally intensive digital processing of Clarke and Park transforms while approximating behavior similar to the FOC (Field Oriented Control) control mode.

[0031] To achieve this, a stall detection algorithm is implemented to stop the motor before it stalls in the case of a large external load, so that a new operating point can be used. This algorithm can be, for example, the algorithm described in EP 1 680 862 or any other stall detection algorithm.

[0032] Stall detection algorithms are typically implemented to stop the motor before it stalls when the external load is high. Rather than systematically commanding the motor to stop, the present invention uses this information temporarily to command operating point changes, possibly in increasing order, before actually commanding the motor to stop.

[0033] For this purpose, the microcontroller may be expected to decide to resume motion with an operating point that provides more torque (by reducing speed and / or increasing current) before reporting a stall, and then return to the initial operating point after a predetermined time or motion.

[0034] If the second operating point is not sufficient, it is possible to inform the user (via the ECU in the automotive industry) that the actuator is stalled, or to retry the movement at another operating point.

[0035] Depending on the responsiveness of the stall detection algorithm, it may be possible to choose whether or not to stall the motor for an operating point change.

[0036] It is also possible to use external conditions to evaluate the operating point applied to the motor, and this check of external conditions can be performed before starting a move or during a move.

[0037] Example: An actuator is capable of delivering 1.5 Nm of dynamic torque at 4 rpm over the entire temperature range only if the voltage is between 11 and 16 V. When the measured voltage is between 9 V and 11 V, the actuator decides to reduce the speed to 2.25 rpm to guarantee 1.5 Nm of torque.

[0038] Example of operation Figure 3 shows timing diagrams of the position command, position feedback, current, and stall detect signals. The position command pc is shown by curve (300), the position feedback pm is shown by curve (310), the current measurement c is shown by curve (320), and the stall detect algorithm measurement sd is shown by curve (330). All curves are expressed in arbitrary units au.

[0039] During this sequence, a termination command (340) is sent to the actuator. During this termination operation, the actuator detects a stall (350).

[0040] A change in the operating point, for example by decreasing the speed, is made without an error being sent back to the ECU. This new operating point allows the move to continue (360), resolving the stall condition detected by the algorithm. Once the sticking point is passed, another operating point (370) can be set to complete the move until the controlled member reaches a known stopping position at time (380). Since the final position is known, the algorithm does not adapt the operating point, but simply stops the move.

[0041] Examples of point matching in motion 4 shows a timing diagram illustrating the operating point adaptation as a function of the inverter supply voltage: curve (100) shows the change in inverter supply voltage v, and curve (200) shows the change in set point speed s.

[0042] When the device is in use, the member connected to the actuator is driven at a nominal speed s=s1, where v=v M The inverter supply voltage of t=t0 results in a nominal torque T1. If for some reason the supply voltage is below the threshold voltage v=v at time (110)t=t0, n The voltage at the inverter terminals is no longer sufficient to obtain the rated torque T1. Then, for example, the speed s is reduced to a value s=s0, and v=v m The operating point can be adapted by allowing the rated torque T1 to be obtained for a larger voltage. At time (120) t=t1, the voltage again reaches the threshold v=v n If the voltage rises above the threshold v=v during the movement, the speed is adjusted back to its nominal value s=s1. m If it falls below this value, the speed is adapted again to ensure that the nominal torque T1 is achieved. If the voltage drops so that the nominal torque is no longer achievable, the algorithm may decide to stop the movement.

[0043] Example of an operating point adaptation algorithm In this regard, FIG. 5 shows an example of a start-up sequence in which the operating point is updated if an overload is detected.

[0044] Upon starting operation, the algorithm exits initialization block (400) and performs an overload check, alternating through a loop between overload detection monitoring block OL (401) and motion block MOVE (405). In the event of an overload, the algorithm exits the loop and changes the operating point. The algorithm then enters block (402) which controls the value of increment variable i. If threshold X is not exceeded, an attempt is made to overcome this stall without stopping operation, proceeding to update the operating point via UPDATE block (403) and then incrementing variable i as indicated by block (404). The algorithm then returns to the overload monitoring loop. If the overload condition persists, the algorithm attempts further increments of the operating point, up to a limit of X attempts. If the overload persists after X operating point updates, the algorithm enters block (406) and stops the motor.

[0045] This sequence does not limit the invention in any way, and those skilled in the art can imagine other possibilities depending on the goal to be achieved, for example, it is possible to imagine a sequence in which the operating point is not gradually increased to provide more torque, but rather follows a dichotomous regulation to optimize the final value.

Claims

1. 1. A control system for a polyphase brushless motor without a position sensor, the control system incorporating drive control electronics, the drive control electronics comprising: - switching means (20) comprising two-state switches (12 to 17) for varying the voltage applied to each phase; - means (32) for detecting an overload of said motor; - means (34) for determining an operating point, allowing the application of at least two operating points; Including, the control electronics is adapted to change the operating point at least once if an overload is detected by the overload detection means (20); 1. A control system for a polyphase brushless motor without position sensors, characterized in that the overload detection means (20) issues a signal controlling the change of the operating point if an overload is detected during a number of successive iterations, and then issues a command to stop the motor if a new stall is detected.

2. 10. The control system for a sensorless polyphase brushless motor of claim 1, wherein the control electronics is configured to use space vector modulation to generate a sinusoidal waveform from a DC voltage.

3. 2. A control system for a sensorless polyphase brushless motor as defined in claim 1, wherein said overload detection means includes circuitry for measuring the total current drawn by the N phases of said motor.

4. The overload detection means a sampling resistor; means for measuring at said resistor an image of the total current flowing in the sum of the N phases of said polyphase motor; 2. The control system for a sensorless polyphase brushless motor of claim 1, comprising:

5. The overload detection means - 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) in relation to the change in the sum of said currents (I); means for processing the sampled current values ​​(I) by mathematical or statistical operations, the stoppage detection threshold (E) being determined with reference to the results of this processing; 2. The control system for a sensorless polyphase brushless motor of claim 1, comprising:

6. 2. A control system for a sensorless polyphase brushless motor according to claim 1, characterized in that the means (34) for determining the operating point includes an interface for receiving signals provided by external condition sensors (40, 41).

7. 7. The control system for a sensorless polyphase brushless motor according to claim 6, wherein the external condition sensor (41) is a temperature sensor.

8. 6. A control system for a sensorless polyphase brushless motor as claimed in claim 5, wherein said external condition sensor (40) provides a measurement of a supply voltage to said switching means (32).

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