Control system for a multiphase brushless motor without a position sensor

Abstract

The present invention relates to a control system for a multiphase brushless motor without a position sensor, incorporating drive control electronics, comprising: • - a switching means (20), provided with two-state switches (12 to 17), for varying the electrical voltage applied to each of the phases; • - a means for detecting overloading (32) of the motor; and • - a means for determining an operating point (34), allowing at least two operating points to be applied; • - the control electronics being arranged to use space vector modulation or vector modulation to generate a sinusoidal waveform from a DC voltage, and the control electronics being arranged to modify the operating point at least once if an overload is detected by the overload detection means (20).

Description

Control system for a polyphase brushless motor without a position sensor. Field of invention

[0001] The present invention relates to the field of stepper-type geared motors (brushless synchronous polyphase DC motors controlled in a stepper mode), and more particularly geared motors controlled in a micro-step mode.

[0002] The step-by-step control mode leads to rotation increments, at the rotor level, called whole steps, which correspond, for example, to 6 whole steps (respectively 4) per electrical period of the current present in each phase, for a three-phase (respectively two-phase) motor. To reduce this rotation increment, so as, for example, to reduce operating noise and vibrations generated at the rotor level, the whole steps can be subdivided into micro-steps. To do this, and unlike the whole-step control mode, each of the motor phases must then be controlled with a substantially sinusoidal current depending on the number of micro-steps per step. For this purpose, for a three-phase motor, 6 transistors will be necessary to simultaneously impose in the 3 phases of the motor 3 substantially sinusoidal current waves, phase-shifted by 120° electrical.

[0003] The usual methods for detecting stops, or stalling, of stepper geared motors use means for detecting the value of the voltage induced in the phases of the motor, in particular states of the control transistors of these phases (open state for example, allowing the voltage induced in the unused phase to be measured without interference).

[0004] We therefore see that for polyphase motors controlled in microstep mode, using all the power transistors simultaneously, it is difficult to have access to this induced voltage measurement. State of the art

[0005] Known in the prior art is patent application US2017126153 describing a method for detecting a rotor lock condition in a sensorless permanent magnet synchronous motor, comprising:determining an estimated rotor speed and a first back electromotive force voltage value, BEMF, in a reference frame associated with the rotor estimated by means of a BEMF observer;calculating a second estimated BEMF voltage value in a reference frame associated with the rotor at least on the basis of a first motor constant and the estimated rotor speed;generating a BEMF error filter value (BEMFErrorFilt) on the basis of a difference between the first and second estimated BEMF voltage values;generating a BEMF error threshold value (BEMFErrorThreshold) as a function of the estimated rotor speed (ω) subject to a minimum BEMF threshold value (BEMFErrorThresholdMin);anddetecting a locked rotor condition in the sensorless permanent magnet synchronous motor at least based on the BEMF error filter value (BEMFErrorFilt) and the BEMF error threshold value (BEMFErrorThreshold).;

[0006] Patent application EP3826170 is also known describing a stall detector for detecting the stalling of a brushless DC motor. The brushless DC motor is adapted to apply one or more control signals so that currents flowing through one or more coils of the brushless DC motor generate a flux for controlling 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 that represents the flux generated by the currents through one or more coils. The processing device is further adapted to determine that the motor is stalling when the direct angle exceeds a predefined threshold at least once.

[0007] Patent EP2966772 proposes a method for detecting stalling of a two-phase or three-phase motor operating in a micro-step mode, the method comprising:

[0008] a) applying a plurality of phase-shifted micro-stepping waveforms (6) to the phase windings (Lu, Lv, lw) of said motor, whereby the phase shift is about 120° in the case of a three-phase motor and about 90° in the case of a two-phase motor;

[0009] b) determining a sum of currents flowing through the phase windings of said motor, and taking samples (Raw) of said sum of currents synchronously with the application of said microstepping waveforms;

[0010] (c) calculating a moving average (MoAvg) or a moving sum of said samples over a number of samples corresponding to 120° or an even multiple of 60° of the microstepping waveform in the case of a three-phase motor and corresponding to 180° or an even multiple of 90° of the microstepping waveform in the case of a two-phase motor;

[0011] d) calculating an adaptive threshold based on said samples (Raw);

[0012] e) detecting engine stall when the moving average (MovAvg) or moving sum is greater than said adaptive threshold.

[0013] Patent application JP2005151678 proposes an apparatus for position sensorless control of a damper-free permanent magnet synchronous motor (PM motor). Disadvantages of prior art solutions

[0014] Some of the prior art solutions require one or more position or torque sensors, which increases manufacturing cost and complicates production.

[0015] Other solutions require complex algorithmic processing, involving the use of powerful processors and resulting in high power consumption.

[0016] Finally, these solutions lead to untimely stops when the resistance to the movement of the driven organ increases and exceeds a resistance torque without characterizing a blockage. This leads to inadequate positioning, and possibly inappropriate error reporting. Solution provided by the invention

[0017] The object of the present invention is to remedy this drawback and relates, in its most general acceptance, to a control system intended for a polyphase brushless motor having the technical characteristics set out in claim 1.

[0018] The motor has no position sensor and incorporates drive control electronics comprising a switching means, provided with two-state switches, intended to vary the electrical voltage applied to each of the phases, a means for detecting overload of the motor, a means for determining an operating point, allowing the application of at least two operating points, said control electronics being arranged to use space vector modulation or vector modulation in order to generate a sinusoidal waveform from a direct voltage.

[0019] Said control electronics are arranged to modify the operating point at least once in the event of detection of an overload by the overload detection means.

[0020] Advantageously, said blocking detection means comprises a circuit for measuring the total current consumed by the N phases of the motor.

[0021] In a variant, said blocking detection means comprises a sampling resistor and a measuring means in said resistor, an image of the total current consumed in the sum of the N phases of the polyphase motor.

[0022] In another variant, said blockage detection means comprises:

[0023] a means of measuring the sum of the currents flowing in each of the phases of the motor,

[0024] a means for calculating a stop detection threshold in relation to the evolution of the sum of said currents,

[0025] a means of processing the sampled current values ​​by a mathematical or statistical operation, the stop detection threshold being determined in relation to the result of this processing.

[0026] Advantageously, said overload detection means delivers a signal controlling the modification of the operating point in the event of overload detection for X consecutive iterations, then an instruction to stop the motor in the event of new blockage detection.

[0027] Furthermore, said means for determining an operating point comprises an interface for receiving a signal provided by an external conditions sensor.

[0028] For example, the external conditions sensor is a temperature sensor.

[0029] Alternatively, the external condition sensor provides a measurement of the supply voltage of the switching means.

[0030] Detailed description of a non-limiting example of embodiment

[0031] Other advantages of the present invention will be readily appreciated, as the same become better understood with reference to the following detailed description illustrated by the accompanying drawings in which:

[0032] It represents a schematic view of the control circuit for driving a three-phase BLDC motor,

[0033] The figure represents a schematic view of the “space vector modulation” processing circuit for controlling a three-phase BLDC motor,

[0034] Represents the timing diagrams of the signals used to implement the invention,

[0035] It represents the timing diagrams of two types of operating points,

[0036] This represents an example of a motion start sequence with operating point update upon overload detection. General principles of the invention

[0037] The proposed solution consists of creating a control mode using space vector modulation or commonly called "space vector modulation" (SVM) whose operating points can be adapted according to the external load and / or external conditions (example: temperature / voltage).

[0038] The principle of the invention consists in providing control electronics arranged to detect an overload by the overload detection means (32) and, in the event of detection of an overload, modify the operating point at least once by increasing the current and / or the voltage, and / or reducing the speed setpoint,

[0039] and in the event of permanent overload detection (32) at the end of a cycle of N iterations, to order the stopping of the motor, N being greater than 1, in order to avoid constantly calculating the new setpoint via the application of Park and Clark transforms requiring heavy digital processing.

[0040] The general principle of a control circuit for driving a star-connected three-phase BLDC motor is illustrated by the. A three-phase DC brushless motor comprises 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 (7 to 9) respectively. The other ends of the windings (1 to 3) are connected together by a termination (10) to obtain a star connection. The control circuit comprises a switching means (20), here a three-phase bridge. Each arm of the three-phase bridge comprises 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 the ground line (19). The terminations (7, 8, 9) are electrically connected to the three-phase bridge, respectively between a complementary pair of switches (12, 15; 13, 16; 14, 17).The switches (12 to 17) are switched on and off in a controlled manner by a controller to provide pulse width modulation of the potential applied to each of the terminations (7 to 9), this to control the potential difference applied across each of the windings (1 to 3) and therefore also the current flowing through the windings (1 to 3) and consequently the strength and orientation of the magnetic field produced by the windings (1 to 3).

[0041] Note that the diagram shows a three-phase bridge connected to a three-phase winding connected in star, however this configuration is not limiting of the invention and any other number of phases, or connection of the winding, known to those skilled in the art is envisaged. For example, a motor comprising 12 coils connected in parallel delta, each winding comprising 4 coils connected in parallel, is included in the invention. It is also possible to use a full-bridge inverter, comprising twice as many arms, for which each winding end is connected to an arm of the inverter. The use of multilevel inverters, comprising more than 2 switches per arm, is also not excluded.

[0042] Detailed description of the “spacevectormodulation” control circuit

[0043] The figure represents a schematic view of the “space vector modulation” processing circuit for controlling a three-phase BLDC motor according to the invention.

[0044] The generation of the SVM control is carried out via the sub-assembly (30). For this operation, a pre-programmed vector table can be used for the sub-assembly (37), which does not require significant computing power by bypassing the conventional sinusoidal signal generators (35) and the transformation in the α, β plane carried out by the sub-assembly (36). The sub-assembly (38) generates the setpoint signals to the inverter (20) in the form of a PWM command. The sub-assemblies (35) to (37) can be grouped within a single sub-assembly (39) via a pre-programmed vector switching table.

[0045] SVM control is a principle well known to those skilled in the art and makes it possible to generate a sinusoidal phase current from a DC supply voltage by controlling the activation time of each branch of the inverter. The feedback loop is made up of several sub-assemblies including in particular a current measurement means (31), an overload detection means (32) and a means for correcting the setpoint signal (33). This feedback loop is traditionally made up of sensors or complex algorithms requiring the use of Park, Clarke transformation. A measurement of the phase current / voltage is carried out through the sub-assembly (31), this data being able to be used by an overload detection means (32), for example a blocking detection algorithm.Depending on the output signal of the overload detection algorithm, the means for correcting the setpoint signal together (33) in current and / or speed transmits the appropriate signal to the means for determining an operating point (34). The means for determining an operating point (34) compiles all the data coming from the feedback loop and possibly from the external condition sensors (40, 41), for example the temperature or the supply voltage of the inverter, in order to select the optimal operating point to be applied to the system.

[0046] Description of the operating point change algorithm

[0047] The operating principle of the algorithm is to adapt the operating point dynamically based on the detection of an overload, and optionally, based on external condition data such as temperature, voltage, load, or any other parameter or one of these combinations.

[0048] This operating mode avoids the use of digital processing for calculating a Clarke and Park transform, requiring significant computing power, while approaching a behavior similar to the FOC (“Field Oriented Control”) control mode.

[0049] For this purpose, a blockage detection algorithm is implemented in order to stop the motor before it stalls in the event of a significant external load and to be able to use a new operating point. This algorithm may be, for example, the algorithm described in patent EP1680862 or any other blockage detection algorithm.

[0050] The stall detection algorithm is normally implemented to stop the motor before it stalls in the event of a significant external load. The invention consists of not systematically ordering the stopping of the motor, but of transiently using this information to order a modification of the operating point, possibly on an increasing sequence, before actually ordering the stopping of the motor.

[0051] To this end, the microcontroller decides before informing of the blockage to restart a movement with an operating point presenting more torque (by reducing the speed and / or increasing the current), after a predefined duration or movement, it can be considered to return to the initial operating point.

[0052] If the 2 ndoperating point is not sufficient, it is then possible to inform the user (via the ECU in the automotive field) of the actuator blocking or to retry the movement with another operating point.

[0053] Depending on the responsiveness of the stop detection algorithm, you can choose whether or not to stop the motor when changing the operating point.

[0054] It is also possible to use external conditions to evaluate the operating point to be applied to the motor. This verification of external conditions can be carried out before starting the movement or during the movement.

[0055] Example: The actuator is able to provide a dynamic torque of 1.5Nm at 4rpm over the entire temperature range but only if the voltage is between 11 and 16V. If the measured voltage is between 9V and 11V, the actuator decides to reduce the speed to 2.25rpm in order to guarantee a torque of 1.5Nm. Example of operation

[0056] Figure 3 shows the timing diagram of the position control, position feedback, current and jam detection signal signals. The position control, , is illustrated by curve (300), the position feedback, , is illustrated by curve (310), the current measurement, , is illustrated by curve (320), the measurement of the blocking detection algorithm, , is illustrated by curve (330). All these curves are represented in arbitrary units, .

[0057] During this sequence, a closing command (340) is transmitted to the actuator. During the execution of this closing movement, the actuator detects a blockage (350).

[0058] A change of operating point, by reducing the speed for example, is then carried out without reporting an error to the computer. This new operating point allows the movement to continue (360) and resolves the blocking condition detected by the algorithm. After passing the hard point, another operating point (370) can be established in order to complete the movement until the controlled member arrives at the known stop position, at time (380). Since the final position is known, the algorithm does not, in this case, adapt the operating point, but simply stops the movement. Example of point adaptation in operation

[0059] Figure 4 represents the timing diagram illustrating the adaptation of the operating point as a function of the inverter supply voltage. Curve (100) illustrates the evolution of the inverter supply voltage, , and curve (200) that of the set speed, .

[0060] When using the device, the member connected to the actuator is driven at a nominal speed . The inverter supply voltage, then worth , allows to obtain a nominal torque . If, for any reason, the supply voltage drops below the threshold voltage right now (110) The voltage at the inverter terminals is then no longer sufficient to obtain the nominal torque. The operating point can then be adapted, for example by lowering the speed. to a value allowing to obtain the nominal torque for a voltage greater than . If at the moment (120) the voltage rises above the threshold value the speed is adjusted again to return to its nominal value . If during the movement the voltage fell below the threshold , the speed would be adjusted again to ensure that the nominal torque was obtained . If the voltage drops so that it is no longer possible to obtain the nominal torque, then the algorithm can decide to stop the movement.

[0061] Example of operating point adaptation algorithm

[0062] In this context, it represents an example of a motion start sequence with operating point update upon overload detection.

[0063] When the movement is started, the algorithm leaves the initialization block (400) to perform an overload check is implemented, alternating the overload detection monitoring block OL (401) and the movement block MOVE (405) via a loop. In the event of an overload, the algorithm leaves said loop to modify the operating point. The algorithm then returns to the block (402) monitoring the value of the incremental variable i and, if the threshold X is not exceeded, proceeds to an update of the operating point to attempt to overcome this blockage, without stopping the movement, via the UPDATE block (403) before proceeding to the increment of said variable i described by the block (404) before returning to the loop monitoring the overload. If the overload condition persists, the algorithm attempts an additional increment of the operating point, up to a limit of X attempts.If the overload persists after X operating point updates, the algorithm returns to block (406) and the motor is stopped.

[0064] This sequence is in no way limiting of the invention and the person skilled in the art could imagine other possibilities depending on the goal to be achieved. For example, it is possible to imagine a sequence where the operating point is not gradually increased to provide more torque, but follows a dichotomy adjustment to optimize the final value.

Claims

Control system intended for a polyphase brushless motor without a position sensor integrating drive control electronics comprising a switching means (20), provided with two-state switches (12 to 17), intended to vary the electrical voltage applied to each of the phases, an overload detection means (32) of the motor, a means for determining an operating point (34), allowing the application of at least two operating points. characterized in that said control electronics is arranged to modify, in the event of detection of an overload by the overload detection means (20), at least once the operating point, said overload detection means (20) delivering a signal controlling the modification of the operating point in the event of overload detection during several consecutive iterations, then an instruction to stop the motor in the event of new blockage detection. Control system for a sensorless polyphase brushless motor according to claim 1 characterized in that said control electronics are arranged to use space vector modulation or vector modulation in order to generate a sinusoidal waveform from a DC voltage. Control system intended for a sensorless polyphase brushless motor according to claim 1 characterized in that said overload detection means comprises a circuit for measuring the total current consumed by the N phases of the motor. Control system for a sensorless polyphase brushless motor according to claim 1 characterized in that said overload detection means comprises a sampling resistor and a measuring means in said resistor, image of the total current consumed in the sum of the N phases of the polyphase motor. Control system intended for a sensorless polyphase brushless motor according to claim 1 characterized in that said overload detection means comprises: a means for measuring the sum of the currents (I) flowing in each of the phases (A, B, C) of the motor, a means for calculating a threshold (E) for detecting a stop relative to the evolution of the sum of said currents (I), a means for processing the sampled current values ​​(I) by a mathematical or statistical operation, the threshold (E) for detecting a stop being determined relative to the result of this processing. Control system for a sensorless polyphase brushless motor according to claim 1 characterized in that said means for determining an operating point (34) comprises an interface for receiving a signal provided by an external conditions sensor (40, 41). Control system for a sensorless polyphase brushless motor according to the preceding claim, characterized in that the external conditions sensor (41) is a temperature sensor. Control system for a sensorless polyphase brushless motor according to claim 5 characterized in that the external conditions sensor (40) provides a measurement of the supply voltage of the switching means (32).

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