Sensorless locked-rotor detection system for brushless direct current motor

Abstract

The invention relates to the technical field of brushless direct current motor control, in particular to a sensorless locked-rotor detection system for a brushless direct current motor, which can accurately and quickly detect the locked-rotor condition of the brushless direct current motor, improve the running reliability and safety of the motor and improve the reliability and reliability of the motor. The device comprises a microcontroller, a pre-driving circuit, a three-phase inverter bridge, a sensing resistor, a comparator, a position detection module and a brushless direct current motor, after commutation of the brushless direct current motor, the guiding phase current of the three-phase inverter bridge is increased, the sensing voltage of the sensing resistor and the reference voltage are sent to the comparator for comparison, and the position detection module detects the position of the brushless direct current motor. And when the sensing voltage exceeds the reference voltage, entering a current limiting stage, counting the ratio S of the time of inputting the energy of the external load into the brushless direct current motor in the conduction phase period to the whole conduction time, and judging whether the motor is in a locked-rotor state or not according to the ratio S.

Description

Technical Field

[0001] The present invention relates to the technical field of brushless DC motor control, and in particular to a sensorless stall detection system for a brushless DC motor. Background Art

[0002] Brushless DC motors (BLDCs) are widely used in a variety of fields, including electric vehicles, aerospace, and industrial automation equipment, due to their high efficiency, long life, and low noise. During BLDC motor operation, stall is a critical abnormality requiring significant attention. Stall occurs when the motor rotor stops rotating due to mechanical failure (such as a stuck bearing or impeller obstruction) or sudden excessive load, while the stator winding remains energized.

[0003] Traditional sensored brushless DC motors use position sensors such as Hall sensors to detect the position and speed of the motor's rotor, making it easier to detect stalls. However, sensored solutions increase the motor's size, cost, and complexity, and can also affect sensor reliability in harsh environments. Consequently, sensorless brushless DC motor control solutions are gaining popularity.

[0004] Existing stall detection technologies in sensorless brushless DC motor control systems have limitations. Some methods rely on complex algorithms and precise motor parameters. This reduces detection accuracy and reliability when motor parameters fluctuate significantly or when external interference is present. Other solutions lack real-time detection capabilities, preventing them from promptly identifying stalls and implementing effective protective measures, potentially causing further damage to the motor and the entire system. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a sensorless stall detection system for a brushless DC motor, which can accurately and quickly detect the stall situation of the brushless DC motor and improve the reliability and safety of the motor operation.

[0006] The technical solution is as follows: a sensorless stall detection system for a brushless DC motor, characterized in that it includes a microcontroller, a pre-drive circuit, a three-phase inverter bridge, a sensing resistor and a comparator, a position detection module and a brushless DC motor. After the brushless DC motor is commutated, the pilot phase current of the three-phase inverter bridge increases, and the sensed voltage of the sensing resistor is sent to the comparator for comparison with the reference voltage. When the sensed voltage exceeds the reference voltage, the current limiting stage is entered. The ratio S of the time during the conduction phase that the energy of the external load is input into the brushless DC motor to the entire conduction time is calculated, and the ratio S is used to determine whether the motor is in a stalled state.

[0007] A further feature of the invention is that, in the current limiting stage, the microcontroller turns off the PWM signal provided to the three-phase inverter bridge in advance, entering the PWM OFF stage, and the current decreases; in the next PWM cycle, if the current is lower than the reference voltage in the PWM ON stage, the switch tube is controlled according to the normal PWM switching time; if the current still exceeds the reference voltage, the PWM OFF stage is continued in advance; The time accumulation of external load energy input is used to calculate the first calculated value T1, the three-phase inverter bridge conduction commutation duration, and the time interval between two adjacent back electromotive force zero crossing detections are calculated to obtain the second calculated value T2. The difference between T1 and T2 is used to obtain the third calculated value T3, S=T3 / T2.

[0008] After adopting the present invention, no additional sensors are required, which reduces system cost and installation complexity, and the motor load condition can be monitored and analyzed in real time; the detection is sensitive, and abnormal load can be discovered promptly and quickly, thereby improving the safety and stability of the motor; the motor speed is monitored in real time, and the system can further optimize the motor's working performance and improve the motor's operating efficiency through intelligent adjustment. It can be widely used in various occasions that require real-time monitoring and control of motor load or speed, and has good application prospects and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic diagram of the system of the present invention; Figure 2 It is a schematic diagram of periodic current control; Figure 3 This is the calculation flow chart of the stall index S value. DETAILED DESCRIPTION

[0010] See Figure 1 As shown, a sensorless stall detection system for a brushless DC motor is characterized in that it includes a microcontroller 10, a pre-drive circuit 20, a three-phase inverter bridge 30, a sensing resistor 40 and a comparator 60, a position detection module 70 and a brushless DC motor 50, and the sensing resistor 40 is used for current control.

[0011] The microcontroller 10 is an integrated circuit and may also include additional circuitry related to or unrelated to motor control. For example, the microcontroller 10 may include a microprocessor, microcomputer, system-on-chip (SOC), etc. Based on feedback from the position detection module 70, the microcontroller 10 calculates the rotor position and, based on the commutation logic for driving the brushless DC motor 50, performs corresponding commutation operations and outputs six PWM signals. The PWM signals are coupled to the pre-driver module 20, which amplifies the lower-voltage PWM control signals to the voltage level required to drive switching elements (such as IGBTs, MOSFETs, or transistors), ensuring sufficient drive power to drive the three-phase inverter bridge 30. The three-phase inverter bridge 30 controls the on and off states of power switching devices (such as IGBTs, MOSFETs, etc.) and, according to a specific pattern, divides the DC power supply into a series of pulse trains. This converts the input DC power into three-phase AC power with adjustable frequency and amplitude, providing appropriate power input to the brushless motor 50, generating a rotating magnetic field, and thus driving the rotor. The microcontroller 10 may include PWM signals configured to control the speed of the BLDC motor.

[0012] The microcontroller 10 can provide an initial set of three-phase PWM signals to the three-phase inverter bridge 30. The commutation circuit is configured to energize two of the three stator windings at any given time based on the three-phase PWM signals, while the third winding remains unenergized. For example, taking the AB phase as an example, during the PWM ON period, only S0 and S3 are turned on, so phase A is coupled to the power supply, phase B is coupled to ground, and phase C is floating. At this time, the AB phases in the motor are turned on, generating current in the coils, which interacts with the motor's rotor permanent magnets to drive the motor to rotate. During the PWM OFF period, S3 remains conductive, S0 is disconnected, and the corresponding lower arm switch S1 is also turned on. At this time, the current enters a decay phase. Due to the coil inductance characteristics, the current cannot suddenly change, and the coil current still interacts with the rotor permanent magnets to generate forward drive. The microcontroller 10 adjusts the speed of the brushless DC motor 50 by adjusting the ratio of the on and off time of S0.

[0013] The microcontroller 10 periodically applies power-on signals to the coil in a certain sequence (such as AB, AC, BC, BA, CA, CB) according to the real-time position of the rotor, and the motor will continue to rotate. The position detection device 70 is used to detect the real-time position signal of the rotor. The sensorless solution is usually based on a Hall-free back-electromotive force zero-crossing detection circuit. The duty cycle determines the speed of the rotor of the motor 30. The Hall-free back-electromotive force zero-crossing detection circuit is based on the fact that the back-electromotive force in the stator winding will change periodically as the position of the rotor changes. In the back-electromotive force change curve of each phase winding, there will be a zero-crossing point, that is, the moment when the back-electromotive force changes from positive to negative or from negative to positive. The back-electromotive force detection circuit detects these back-electromotive force zero-crossing points and then delays for a certain period of time to achieve phase switching. Similarly, when the rotor rotates through one electrical cycle, a zero-crossing signal appears every 60°. The position information of the rotor can be determined based on this signal. During the start-up and stall period of the brushless motor, such as when it is overloaded, the motor current increases rapidly. At this time, the current sensing resistor 40 located between the lower arm of the inverter bridge 30 and the ground can sense the abnormal current and convert it into a corresponding sensing voltage, which is coupled to the positive input terminal of the comparator 60. The comparator 60 compares the voltage with the preset reference voltage Vref coupled to the negative input terminal. When the sensing voltage is greater than the reference voltage Vref, the output level of the comparator 60 flips and is fed back to the microcontroller 10, thereby shutting down the PWM in advance and entering the PWM OFF stage. The current then begins to decrease, as shown in FIG. Figure 2 As shown in the dashed portion of the PWM control, in the next PWM cycle, if the current is lower than the reference voltage Vref during the PWM ON period, the switch is controlled according to the normal PWM switching time. If the current still exceeds the reference voltage Vref, the PWM OFF period is advanced. The control system 10 controls the current according to the above logic, maintaining the current at a level that does not exceed the preset value. This is cycle-by-cycle current control.

[0014] When the brushless motor is working normally, it needs to be commutated every 60 degrees. At the moment of commutation, the current of the conducting phase increases from zero. When the sensing voltage detected by the sensing resistor exceeds the reference voltage Vref, the current will enter Figure 2 In the current limiting stage shown, by counting the ratio S of the time of external energy input to the motor during the conduction phase to the entire conduction phase time, the size of the S value can be used to determine whether the motor is in a stalled state. When the load is large, the motor coil current increases rapidly. Due to the current limiting effect, the motor coil current will be limited to below the preset current. The comparator flip will cause the PWM to shut down early, and the energy input to the motor will also decrease accordingly, and the motor speed will also drop significantly. The input energy is the integral of the power over the action time period. This time period is the accumulation of the conduction phase connection time. From the time axis, it is the accumulation of several Tons, see Figure 2As shown, the calculation result is used as the first calculated value T1, that is, the accumulated value of the energy input time. The entire conduction commutation duration corresponds to the time of 60° angle. By obtaining the time interval detected by two adjacent back electromotive force zero crossing points in the zero-crossing monitoring circuit, it is used as the second calculated value T2. Then the difference between T1 and T2 is calculated as the third calculated value T3. Finally, the ratio of T3 to T2 is regarded as the stall index S. The process is shown in Figure 3 shown.

[0015] When the motor is unloaded, the rotor reaches its maximum speed, the average coil current is also very small, and the current does not enter the current limiting state. The corresponding S value reaches its minimum, which is related to the given duty cycle. When the external load increases slightly, the coil current also increases, but it is still less than the preset value corresponding to the reference voltage Vref. The speed remains at the maximum speed, and the corresponding S value remains unchanged. When the external load increases further, the motor coil current gradually enters the current limiting state, and the average coil current also gradually increases until it equals the preset value of the reference voltage Vref. At this time, the motor speed will also gradually decrease, and the corresponding S value will also gradually increase. When the external load is very large, the motor enters a completely blocked state, the speed is 0, S also reaches its maximum value, and is close to a fixed value of 1. The stall index S is directly related to the external load. The smaller the load, the smaller the S value, and the larger the load, the larger the S value. When the motor is operating normally, real-time monitoring of the first calculated value T1 and the second calculated value T2 can monitor the size of the external load in real time. If this indicator S value is sent to other controllers or a host computer for appropriate shutdown or other processing, precise closed-loop control of the motor speed can be achieved by changing the preset current value under external load fluctuations. It should be noted that in order to prevent the system from misinterpreting an excessively large S value at startup as a stall and triggering a stall shutdown, it is necessary to block the S value during the short initial startup period.

Claims

1. A sensorless stall detection system for a brushless DC motor, characterized in that: It includes a microcontroller, a pre-drive circuit, a three-phase inverter bridge, a sensing resistor and a comparator, a position detection module and a brushless DC motor. After the brushless DC motor is commutated, the pilot phase current of the three-phase inverter bridge increases, and the sensing voltage of the sensing resistor is sent to the comparator for comparison. When the sensing voltage exceeds the reference voltage, the current limiting stage is entered. The ratio S of the time of the energy input of the external load into the brushless DC motor during the conduction phase to the entire conduction time is calculated, and the ratio S is used to determine whether the motor is in a stalled state.

2. A sensorless stall detection system for a brushless DC motor according to claim 1, characterized in that: In the current limiting stage, the microcontroller turns off the PWM signal provided to the three-phase inverter bridge in advance, entering the PWM OFF stage, and the current decreases; in the next PWM cycle, if the current is lower than the reference voltage in the PWM ON stage, the switch tube is controlled according to the normal PWM switching time. If the current still exceeds the reference voltage, the PWM OFF stage is continued to be entered in advance.

3. The sensorless stall detection system for a brushless DC motor according to claim 1, characterized in that: The time accumulation of external load energy input is used to calculate the first calculated value T1, the three-phase inverter bridge conduction commutation duration, and the time interval between two adjacent back electromotive force zero crossing detections are calculated to obtain the second calculated value T2. The difference between T1 and T2 is used to obtain the third calculated value T3, S=T3 / T2.

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