Starting-up motor disconnection detection method

Abstract

The invention relates to the technical field of motor detection, in particular to a power-on motor disconnection detection method, which comprises the following steps: when a motor is powered on and initialized, after the duty ratio of a grid control signal of each phase of upper MOS (Metal Oxide Semiconductor) tube of the motor is set to be more than a first numerical value, the grid control signals of all lower MOS tubes are closed at the moment; a current path is formed through a DS capacitor of a lower MOS tube and a body diode, a bootstrap capacitor of an upper tube of each phase is charged, the neutral-point voltage of the motor is detected after waiting for a preset time, and if the neutral-point voltage of any one of the three phases of the motor is lower than a set threshold value of a bus voltage, it is judged that the phase has a disconnection fault; according to the method, whether the motor is broken or not can be quickly and accurately judged by setting the specific duty ratio and sampling the three-phase midpoint voltage at the specific time point, and the detection accuracy and efficiency are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor detection, and more particularly to a method for detecting motor wire breakage at startup. Background Art

[0002] During the operation of a motor, motor wire breakage is a common fault, which will seriously affect the normal operation of the motor and the reliability of the equipment. If the motor wires are not properly connected before power-on or there is a wire breakage problem inside the motor itself, it is necessary to detect and find the fault point in advance. Existing motor wire breakage detection methods often require additional detection equipment or complex circuit structures, with high costs and cumbersome detection processes. In addition, some detection methods cannot detect wire breakage faults in time at the moment when the motor is powered on, resulting in the motor running in a fault state and increasing the risk of equipment damage.

[0003] A similar prior art Chinese patent application with the publication number CN104868804B discloses sensing the back electromotive force of a motor. The device includes a controller and a comparator. The controller generates a pulse width modulation (PWM) signal to drive the stator windings of a brushless direct current (BLDC) motor in a commutation sequence, such that one of the stator windings is open at a given time, and generates a tracking signal that is synchronized to the PWM signal and indicates the time when a leakage current exists in the open stator winding. The comparator senses when the back electromotive force of the open stator winding has an associated zero crossing. Although this solution selectively enables and disables sensing by the comparator through the tracking signal, it cannot determine wire breakage in the motor at startup.

[0004] Therefore, there is an urgent need for a method that can quickly and accurately detect wire breakage in a motor at startup to improve the stability and reliability of motor operation. Summary of the Invention

[0005] In order to better solve the above problems, the present invention provides a method for detecting motor wire breakage at startup, including the following steps: Step 1: When the motor is powered on and initialized, after setting the duty cycle of the gate control signal of each phase upper MOS tube of the motor to a value above a first value, at this time, the gate control signals of all lower MOS tubes are turned off; Step 2: Form a current path through the DS capacitor and body diode of the lower MOS tube to charge the bootstrap capacitors of each phase upper tube; Step 3: After waiting for a preset time, detect the midpoint voltage of the motor; Step 4: If the midpoint voltage of any one of the three phases of the motor is lower than the set threshold of the bus voltage, it is determined that there is a wire breakage fault in that phase; Step 5: After the detection is completed, adjust the duty cycle of the gate control signal of the upper MOS transistor of each phase to below 95%, and at this time, the gate control signal of the lower MOS transistor is turned on.

[0006] As a preferred technical solution of the present invention, in the step 1, the first values are different from each other, and the first values are all greater than 95%.

[0007] As a preferred technical solution of the present invention, in the step 2, the current path includes the DS capacitor charging stage and the body diode freewheeling stage of the lower MOS transistor, and the freewheeling current provides a charging circuit for the bootstrap capacitor.

[0008] As a preferred technical solution of the present invention, adjust the preset time based on the number of the upper MOS transistors and the lower MOS transistors and the capacitance of the bootstrap capacitor, and the value range of the preset time is 100 ms to 1000 ms.

[0009] As a preferred technical solution of the present invention, the set threshold of the bus voltage is 90%-100% of the bus voltage. If the midpoint voltage of any one of the three phases is lower than the set threshold, it is determined that the motor is disconnected.

[0010] As a preferred technical solution of the present invention, in the step 1, adjust the first value based on the PWM signal generator, and the PWM signal generator includes a clock source module, a counter module and a comparator module.

[0011] As a preferred technical solution of the present invention, after the first value is adjusted, the on state of the lower MOS transistor is realized by the reverse control of the duty cycle of the gate control signal of the MOS transistor.

[0012] As a preferred technical solution of the present invention, when the motor disconnection is detected, trigger an audible and visual alarm or send a fault signal to the controller.

[0013] As a preferred technical solution of the present invention, the preset time length is based on the number of the MOS transistors and the capacitance of the bootstrap capacitor of the MOS transistors.

[0014] As a preferred technical solution of the present invention, the preset time is 500 ms, and the calculation formula for the preset time of the bootstrap capacitor charging is: , where N represents the number of MOS transistors, represents the single-tube input capacitance, represents the bus voltage, represents the charging current.

[0015] Compared with the prior art, the beneficial effects of the present invention are at least as follows: The technical solution of the present invention can quickly and accurately determine whether there is a broken wire in the motor by setting a specific duty cycle and sampling the three-phase neutral point voltage at specific time points, greatly improving the accuracy and efficiency of detection. The detection time can be adjusted according to the number of MOS transistors and the size of the input capacitor, enhancing the adaptability and flexibility of the method, meeting the requirements of different motor systems. The entire detection process is simple and reliable, facilitating application and popularization in actual motor control systems, contributing to improving the stability of motor operation and the reliability of equipment, and reducing losses and maintenance costs caused by motor broken wire faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the provided drawings.

[0017] Figure 1 is a flowchart of the method for detecting motor broken wire at startup of the present invention; Figure 2 is a circuit diagram of the method for detecting motor broken wire at startup of the present invention; Figure 3 is a sampling schematic diagram of the method for detecting motor broken wire at startup of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] It can be understood that the terms "first", "second", etc. used in this application can be used herein to describe various elements, but unless otherwise specified, these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, the first xx script can be called the second xx script, and similarly, the second xx script can be called the first xx script.

[0020] In response to the above technical problems, the present invention proposes a method for detecting motor broken wire at startup as Figure 1 shown, and the method is implemented through the following steps: Step 1: When the motor is powered on and initialized at startup, after setting the duty cycle of the gate control signal of each upper MOS transistor of the motor to a value above the first value, the gate control signals of all lower MOS transistors are turned off at this time.

[0021] Furthermore, the first values are different from each other and all greater than 95%. Adjust the first values based on the PWM signal generator, which includes a clock source module, a counter module, and a comparator module.

[0022] Specifically, as Figure 2 shown, Figure 2 In the figure, Q1 - Q6 represent 6 MOS transistors, which are switching elements in the circuit. By controlling the voltage of their gates (G), the on - off state between the drains (D) and sources (S) can be controlled, thereby controlling the direction and magnitude of the current in the circuit to drive the motor (M). H1 - H3 and L1 - L3 represent the gate drive signal identifiers corresponding to Q1 - Q3 (upper - arm MOS transistors) and Q4 - Q6 (lower - arm MOS transistors), respectively, and are used to control the conduction and cut - off of the MOS transistors. At the moment of power - on, the motor control system sets different duty cycles for the three phases of U, V, and W. Among them, the duty cycle of U - GS is set to 95%, the duty cycle of V - GS is set to 96%, and the duty cycle of W - GS is set to 97%. Through this unique duty - cycle setting, the lower - transistor MOS transistors cannot conduct.

[0023] It should be noted that when the duty cycle of the upper - transistor MOS transistors approaches 100%, the time that the gate signal of the lower - transistor MOS transistors remains low in the PWM cycle is extremely short (for example, when the duty cycle is 95%, the turn - off time of the lower transistors corresponds to 5% of the cycle), resulting in the lower transistors being unable to conduct effectively. By setting the duty cycles of the three phases of U, V, and W to increase sequentially (95% → 97%), a small voltage difference is formed to drive the initial current while ensuring that the lower transistors are completely turned off.

[0024] In a three - phase motor with a rated voltage of 24V, set the duty cycles to 95%, 96%, and 97%, and sample after 500 ms. The results are as follows: Status U-phase voltage V-phase voltage W-phase voltage Normal 24.0V 24.0V 24.0V U-phase open circuit 12.1V 24.0V 24.0V Detection accuracy: 100% (50 repeated tests). At this time, due to the specific duty - cycle setting, the current path mainly passes through DS (where "DS" is the drain - source capacitance of the MOS transistor). The capacitor motor current is generated through the DS capacitance of the lower - transistor MOS at the moment of power - on. As the DS capacitance gradually fills up, and the motor generates a back - electromotive force during operation. The generated back - electromotive force of the motor will force the body diode of the lower transistor to conduct, thereby generating a free - wheeling current.

[0025] The setting of the duty cycle can be completed in the drive circuit of the motor control system through programming or hardware configuration. For example, in a microcontroller-based motor control system, the duty cycle of the three phases can be accurately set by writing a specific control program to configure the PWM output port of the microcontroller. In terms of hardware configuration, the duty cycle can be set by adjusting the parameters of components such as resistors and capacitors in the circuit, or by using a dedicated programmable logic device.

[0026] Step 2: Form a current path through the DS capacitor and body diode of the lower MOS transistor to charge the bootstrap capacitors of each phase's upper transistors.

[0027] Furthermore, the current path includes the charging stage of the DS capacitor of the lower MOS transistor and the freewheeling stage of the body diode. Among them, the freewheeling current provides a charging loop for the bootstrap capacitor. Since the gate control signal of the lower MOS transistor is turned off, the current charges through the DS capacitor of the lower MOS transistor. As the capacitor charging is completed, the back electromotive force generated by the motor forces the body diode of the lower transistor to conduct, forming freewheeling and charging the bootstrap capacitor of the upper transistor to ensure the normal operation of the upper transistor drive.

[0028] Specifically, at the moment of power-on, since the lower MOS transistor is cut off, the motor current starts to flow through the capacitor (DS capacitor) between the drain (D) and source (S) of the lower MOS transistor. The DS capacitor is an inherent parasitic capacitor of the MOS transistor structure. In this stage, it acts as a load and is charged by the current. As the charging process progresses, the voltage across the DS capacitor gradually increases. Taking a three-phase motor with a rated voltage of 24V as an example, the current starts from the positive pole of the power supply, passes through the upper MOS transistor (since the duty cycle of the upper transistor is high and it conducts most of the time), then through the DS capacitor of the lower MOS transistor, and finally returns to the negative pole of the power supply, forming a temporary current path.

[0029] When the DS capacitor is gradually filled, the motor generates a back electromotive force during operation. The back electromotive force is generated due to the electromagnetic induction phenomenon of the motor, and its direction is opposite to the direction of the power supply voltage. When the back electromotive force reaches a certain level, it forces the body diode of the lower MOS transistor to conduct. The body diode is a parasitic diode inside the MOS transistor, and its direction is from the source to the drain. Once the body diode conducts, a freewheeling current is formed. The path of the freewheeling current is from the motor winding, through the body diode of the lower MOS transistor, and then back to the negative pole of the power supply, and at the same time provides a necessary loop for charging the bootstrap capacitor of the upper transistor.

[0030] Step 3: After waiting for a preset time, detect the midpoint voltage of the motor (such as Figure 3As shown, the preset time is adjusted based on the number of MOS transistors and the capacitance value of the input capacitor. The value range of the preset time is from 100 ms to 1000 ms. The length of the preset time depends on the number of MOS transistors and the size of the input capacitance of the MOS transistors. When the number of MOS transistors is large or the capacitance value of the input capacitor of the MOS transistor is large, the interval time of the preset time can be reduced. The power-on preset time is 500 ms. The setting of the power-on preset time is based on the calculation of the bootstrap capacitor charging time constant. The formula is: , where N represents the number of MOS transistors, represents the input capacitance of a single transistor, represents the bus voltage, represents the charging current.

[0031] Specifically, after 500 ms of power-on (this time length is not fixed, but depends on the number of MOS and the size of the Ciss capacitance of the MOS. If the number of MOS is large or the Ciss capacitance value is large, this interval time can be appropriately reduced), at the midpoint of the drive, a dedicated voltage sampling circuit is used to sample the three-phase midpoint voltage simultaneously. The core function of this voltage sampling circuit is to convert the collected analog voltage signal into a digital signal and then transmit it to the microcontroller or other control units for subsequent analysis.

[0032] It should be noted that the setting of 500 ms is based on the calculation of the bootstrap capacitor charging time constant. The formula is: Among them: N represents the number of MOS transistors; represents the input capacitance of a single transistor; represents the bus voltage; represents the charging current (typical value 10 mA).

[0033] Example: When N = 3, = 1000 pF, = 48 V, = 10 mA, the calculated t = 432 ms, rounded to 500 ms.

[0034] To ensure the accuracy and stability of sampling, the voltage sampling circuit usually adopts a high-precision sampling chip and is equipped with corresponding circuit modules such as filtering and amplification. For example, in some application scenarios with high requirements for detection accuracy, an ADC sampling chip with 16-bit or even higher resolution can be selected to improve the accuracy of voltage sampling. At the same time, by adding a low-pass filter to the sampling circuit, high-frequency noise can be effectively filtered to ensure the purity of the sampling signal. The timing operation of 500 ms after power-on is completed by starting a timer. The timer can be the timer module built into the microcontroller in the motor control system or an external independent timer chip. Moreover, according to the actual number of MOS and the size of the Ciss capacitance, the timing can be flexibly adjusted. In software programming, the accurate control of the timing can be achieved by modifying parameters such as the initial count value and division factor of the timer.

[0035] Step 4: If the midpoint voltage of any one of the three phases of the motor is lower than the set threshold of the bus voltage, it is determined that there is a broken wire fault in the phase. The set threshold of the bus voltage is 90%-100% of the bus voltage. If the midpoint voltage of any one of the three phases is lower than the set threshold, it is determined that the motor has a broken wire. When any one of the three phases has a broken wire, the midpoint voltage of the phase is set to the divided voltage value of the DS capacitors of the upper and lower transistors, and the voltage division ratio is 1:1. When a certain phase of the motor has a broken wire, the circuit structure of that phase changes, and the bootstrap capacitor cannot be normally charged, resulting in a drop in the midpoint voltage. By comparing with the set threshold of the bus voltage, it is possible to accurately determine whether there is a broken wire fault in the motor. When a broken wire of the motor is detected, an audible and visual alarm is triggered or a fault signal is sent to the controller.

[0036] Specifically, the control unit judges the state of the motor wires according to the sampled midpoint voltages of the three phases. When the motor is running normally, the midpoint voltages of the three phases sampled after 500 ms should be the bus voltage of the BUS. When one or more motor wires are broken, the bootstrap capacitors on the corresponding lines cannot be normally charged, which in turn causes a significant change in the midpoint voltage on that line (there is a significant difference from the bus voltage of the BUS). Based on this voltage difference, the broken wire situation of the motor can be judged.

[0037] The specific judgment process is as follows: The control unit compares the collected three-phase neutral point voltage with the bus BUS voltage one by one. If the difference between the neutral point voltage of a certain phase and the bus BUS voltage exceeds the pre-set normal range (this normal range can be reasonably set according to factors such as the type of motor and the operating voltage), it is judged that there is a broken wire fault in the motor of this phase; if the three-phase neutral point voltages are all within the normal range and are equal to or close to the bus BUS voltage, it indicates that the motor circuit is normal. After completing the motor broken wire detection, in order to ensure the reliable conduction of the lower transistor and make the motor enter the normal drive control mode, the duty cycle of the upper transistor needs to be set below 95%, which is achieved through the PWM signal generator in the control circuit. By adjusting the duty cycle of the PWM signal, the conduction time of the upper transistor is changed to ensure that the lower transistor can work normally.

[0038] According to the actual situation, when the duty cycle of the upper transistor GS is set to 95%, the lower transistor GS cannot conduct. The size of this duty cycle depends on the MOS transistor conduction delay and frequency, which is not an absolute parameter and mainly depends on factors such as the MOS transistor conduction delay and frequency. In different motor systems, the MOS transistor conduction delay and operating frequency will be different, so the duty cycle value needs to be reasonably adjusted according to the actual situation.

[0039] Normal situation: According to the setting, the duty cycle of H-GS = 95%, the duty cycle of V-GS = 96%, and the duty cycle of W-GS = 97% are set to ensure that the lower transistor GS cannot conduct, and there is a voltage difference among the three in the motor. At the moment of power-on, the lower transistor GS cannot be turned on. The motor current is generated through the DS capacitor of the lower transistor MOS. When the DS capacitor is fully charged, the back electromotive force in the motor forces the body diode of the lower transistor to conduct and generate a freewheeling current.

[0040] This freewheeling current provides a loop for charging the three bootstrap capacitors driven by the three upper transistors, ensuring that the three upper transistor drives maintain a reliable drive voltage.

[0041] After 500 ms, the three-phase neutral point voltage is sampled as the bus BUS voltage at the midpoint of the drive.

[0042] Motor broken wire situation: When one or more motor windings are broken, the bootstrap capacitors on the corresponding lines cannot be charged normally, resulting in the neutral point voltage on that line being BUS / 2 (reason: the DS capacitors of the upper and lower transistors are voltage-divided). The motor broken wire situation is judged based on this voltage.

[0043] Step 5: After the detection is completed, adjust the duty cycle of the gate control signal of the upper MOS transistor of each phase to below 95%. At this time, the gate control signal of the lower MOS transistor is turned on. After the duty cycle is adjusted, the on-state of the lower MOS transistor is realized by the reverse control of the duty cycle of the gate control signal of the MOS transistor, so that the motor enters the normal drive control mode and ensures the stable operation of the motor.

[0044] Specifically, after the detection is completed, setting the duty cycle needs to ensure the reliable conduction of the lower transistor, that is, the duty cycle of the upper transistor needs to be set to below 95%.

[0045] Example: When the U-phase motor is open-circuited, the bootstrap capacitor of the U-phase cannot be normally charged, the upper transistor cannot be normally turned on, and the U-phase bridge arm voltage = the voltage division of the DS capacitor of the upper transistor + the DS capacitor of the lower transistor. Assuming that the capacitance values of both ends are the same, the midpoint voltage of the U-phase is BUS / 2. Explanation: 500 ms is an example time, and the length of this time depends on the number of MOS transistors and the Ciss capacitance value of the MOS transistors. If the number of MOS transistors is large (or the Ciss capacitance value is large), this interval time can be appropriately reduced. The purpose is to ensure that the electric charge in the bootstrap capacitor is fully consumed.

[0046] It should be understood that although the steps in the flowcharts of the embodiments of the present invention are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear indication in this article, the execution of these steps has no strict order limit, and these steps can be executed in other orders. Moreover, at least a part of the steps in each embodiment may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed alternately or alternately with at least a part of other steps or sub-steps or stages of other steps.

[0047] Those of ordinary skill in the art can understand that all or part of the processes of implementing the methods in the above embodiments can be completed by instructing relevant hardware through a computer program. The above program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memories. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and Rambus dynamic RAM (RDRAM), etc.

[0048] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0049] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent of the present invention should be subject to the appended claims.

[0050] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting a broken wire of a starting motor, characterized in that, The method includes the following steps: Step 1: When the motor is powered on and initialized, after setting the duty cycle of the gate control signal of each upper MOS transistor of the motor to a value above a first value, the gate control signals of all lower MOS transistors are turned off at this time; Step 2: A current path is formed through the DS capacitor and the body diode of the lower MOS transistor to charge the bootstrap capacitors of each upper transistor; Step 3: After waiting for a preset time, the neutral point voltage of the motor is detected; Step 4: If the neutral point voltage of any one of the three phases of the motor is lower than the set threshold of the bus voltage, it is determined that there is an open-circuit fault in that phase; Step 5: After the detection is completed, the duty cycle of the gate control signal of each upper MOS transistor is adjusted to below 95%, and at this time the gate control signals of the lower MOS transistors are turned on.

2. The method according to claim 1, wherein In the said Step 1, the first values are different from each other, and the first values are all greater than 95%.

3. The method according to claim 1, wherein In the said Step 2, the current path includes a charging stage of the DS capacitor of the lower MOS transistor and a freewheeling stage of the body diode, and the freewheeling current provides a charging circuit for the bootstrap capacitor.

4. The method according to claim 1, wherein The preset time is adjusted based on the number of the upper MOS transistors and the lower MOS transistors and the capacitance of the bootstrap capacitor, and the value range of the preset time is 100 ms to 1000 ms.

5. The method according to claim 1, wherein The set threshold of the bus voltage is 90% - 100% of the bus voltage. If the neutral point voltage of any one of the three phases is lower than the set threshold, it is determined that the motor is open-circuited.

6. The method according to claim 5, wherein In Step 1, the first value is adjusted based on a PWM signal generator, and the PWM signal generator includes a clock source module, a counter module, and a comparator module.

7. The method according to claim 1, characterized in that, After the first value is adjusted, the on-state of the lower MOS transistor is realized by the reverse control of the duty cycle of the gate control signal of the MOS transistor.

8. The method according to claim 1, wherein When the motor open-circuit is detected, an audible and visual alarm is triggered or a fault signal is sent to the controller.

9. The method according to claim 1, wherein The length of the preset time is based on the number of the MOS transistors and the capacitance of the bootstrap capacitor of the MOS transistor.

10. The method according to claim 1, wherein The preset time is 500 ms, and the calculation formula for the preset time of the bootstrap capacitor charging is: , where N represents the number of MOS transistors, represents the input capacitance of a single transistor, represents the bus voltage, represents the charging current.

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