A method for detecting a broken wire of a starting motor

Abstract

The present application relates to motor detection technical field, more particularly to a kind of start motor wire break detection method, method includes: in the motor start power-on initialization, the duty cycle of the gate control signal of each phase upper MOS tube of the motor is set to first value or more, at this time, the gate control signal of all lower MOS tube is closed, current path is formed by the DS capacitor and body diode of lower MOS tube, and the bootstrap capacitor of each phase upper MOS tube is charged, after waiting for preset time, the midpoint voltage of motor is detected, if the midpoint voltage of any one phase of three-phase of motor is lower than the set threshold of bus voltage, then determine that phase exists wire break fault;The present application can quickly and accurately determine whether motor exists wire break condition by the way of specific duty cycle setting and sampling three-phase midpoint voltage at specific time point, greatly improve the accuracy and efficiency of detection.

Description

Technical Field

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

[0002] During motor operation, wire breakage is a common fault, severely impacting normal motor operation and equipment reliability. If the motor wires are not properly connected before power is applied, or a wire break occurs within the motor itself, early detection is necessary to identify the fault. Existing methods for detecting motor wire breakage often require additional testing equipment or complex circuit structures, resulting in high costs and a cumbersome detection process. Furthermore, some methods fail to detect wire breakages immediately upon motor power-up, causing the motor to operate in a faulty state and increasing the risk of equipment damage.

[0003] A similar prior art Chinese patent application with publication number CN104868804B discloses a device for 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 winding of a brushless DC (BLDC) motor in a commutation sequence so 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 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 scheme selectively enables and disables sensing by the comparator through the tracking signal, it cannot determine whether the motor is disconnected when it is turned on.

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

[0005] In order to better solve the above problems, the present invention provides a method for detecting a disconnection of a startup motor, comprising the following steps:

[0006] Step 1: When the motor is powered on and initialized, the duty cycle of the gate control signal of the upper MOS tube of each phase of the motor is set to be greater than a first value, and the gate control signals of all the lower MOS tubes are turned off;

[0007] Step 2: A current path is formed through the DS capacitor and body diode of the lower MOS tube to charge the bootstrap capacitor of each phase upper tube;

[0008] Step 3: After waiting for a preset time, detecting the midpoint voltage of the motor;

[0009] Step 4: If the midpoint voltage of any one of the three phases of the motor is lower than a set threshold value of the bus voltage, it is determined that a disconnection fault exists in the phase;

[0010] Step 5: After the detection is completed, adjust the duty cycle of the gate control signal of each phase upper MOS tube to below 95%, and then turn on the gate control signal of the lower MOS tube.

[0011] As a preferred technical solution of the present invention, in step 1, the first numerical values ​​are different from each other, and the first numerical values ​​are all greater than 95%.

[0012] As a preferred technical solution of the present invention, in step 2, the current path includes a DS capacitor charging stage of the lower MOS tube and a body diode freewheeling stage, and the freewheeling current provides a charging circuit for the bootstrap capacitor.

[0013] As a preferred technical solution of the present invention, the preset time is adjusted based on the number of the upper MOS tube and the lower MOS tube and the capacity of the bootstrap capacitor, and the value range of the preset time is 100ms to 1000ms.

[0014] As a preferred technical solution of the present invention, the set threshold value of the bus voltage is 90%-100% of the bus voltage. If the midpoint voltage of any phase in the three phases is lower than the set threshold value, it is determined that the motor is broken.

[0015] As a preferred technical solution of the present invention, in step 1, the first value is adjusted based on a PWM signal generator, wherein the PWM signal generator includes a clock source module, a counter module, and a comparator module.

[0016] As a preferred technical solution of the present invention, after the first value is adjusted, the on state of the lower MOS tube is achieved by reversely controlling the duty cycle of the gate control signal of the MOS tube.

[0017] As a preferred technical solution of the present invention, when the motor is detected to be disconnected, an audible and visual alarm is triggered or a fault signal is sent to a controller.

[0018] As a preferred technical solution of the present invention, the preset time length is based on the number of the MOS tubes and the capacity of the bootstrap capacitor of the MOS tube.

[0019] As a preferred technical solution of the present invention, the preset time is 500ms, and the calculation formula for the preset time of charging the bootstrap capacitor is: , where N represents the number of MOS tubes, Represents the input capacitance of a single tube, represents the bus voltage, Indicates the charging current.

[0020] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0021] The technical solution of the present invention can quickly and accurately determine whether a motor has a broken wire by setting a specific duty cycle and sampling the three-phase midpoint voltage at a specific time point, greatly improving the accuracy and efficiency of detection. The detection time can be adjusted according to the number of MOS tubes and the size of the input capacitor, enhancing the adaptability and flexibility of the method, and meeting the needs of different motor systems. The entire detection process is simple and reliable, and is easy to apply and promote in actual motor control systems. It helps to improve the stability of motor operation and the reliability of equipment, and reduce the losses and maintenance costs caused by motor broken wire failures. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0023] Figure 1 This is a flow chart of the method for detecting disconnection of a startup motor according to the present invention;

[0024] Figure 2 This is a circuit diagram of a method for detecting disconnection of a startup motor according to the present invention;

[0025] Figure 3 This is a sampling diagram of the startup motor disconnection detection method of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but unless otherwise specified, these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, a first xx script may be referred to as a second xx script, and similarly, a second xx script may be referred to as a first xx script without departing from the scope of this application.

[0028] In view of the above technical problems, the present invention proposes Figure 1 A method for detecting a disconnected motor when starting a machine is shown, and the method is implemented by the following steps:

[0029] Step 1: When the motor is powered on and initialized, the duty cycle of the gate control signal of the upper MOS tube of each phase of the motor is set to be greater than a first value, and the gate control signals of all the lower MOS tubes are turned off.

[0030] Furthermore, the first values ​​are different from each other and are all greater than 95%. The first values ​​are adjusted based on a PWM signal generator, and the PWM signal generator includes a clock source module, a counter module, and a comparator module.

[0031] Specifically, if Figure 2 As shown, Figure 2 In the figure, Q1 - Q6 represent six MOS tubes, which are switching elements in the circuit. By controlling the voltage of their gates (G), they control the on / off between the drain (D) and the source (S), 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 tubes) and Q4 - Q6 (lower-arm MOS tubes), which are used to control the conduction and cutoff of the MOS tubes. At the moment of power-on, the motor control system will set different duty cycles for the three phases 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-side MOS tube cannot be turned on.

[0032] It should be noted that when the duty cycle of the upper MOS tube is close to 100%, the gate signal of the lower MOS tube remains at a low level for a very short time during the PWM cycle (for example, a duty cycle of 95% corresponds to a lower tube off time of 5% cycle), resulting in the lower tube being unable to effectively turn on. By setting the duty cycles of the three phases U, V, and W to increase in sequence (95% → 97%), a small voltage difference is formed to drive the initial current while ensuring that the lower tube is completely turned off.

[0033] In a three-phase motor with a rated voltage of 24V, the duty cycle is set to 95%, 96%, and 97%, and sampling is performed after 500ms. The results are as follows:

[0034] state U phase voltage V-phase voltage W phase voltage normal 24.0V 24.0V 24.0V U phase disconnection 12.1V 24.0V 24.0V Detection accuracy: 100% (repeated test 50 times).

[0035] At this time, due to the specific duty cycle setting, the current path is mainly through DS ("DS" is the drain-source capacitance of the MOS tube). The capacitor motor current is generated through the DS capacitor of the lower tube MOS at the moment of power-on. As the DS capacitor is gradually filled, the back electromotive force generated by the motor during operation will force the lower tube body diode to turn on, thereby generating freewheeling current.

[0036] The duty cycle can be set in the drive circuit of the motor control system through programming or hardware configuration. For example, in a microcontroller-based motor control system, the PWM output port of the microcontroller can be configured by writing a specific control program to achieve precise setting of the three-phase duty cycle. 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 specialized programmable logic devices.

[0037] Step 2: A current path is formed through the DS capacitor and body diode of the lower MOS tube to charge the bootstrap capacitor of each phase upper tube.

[0038] Furthermore, the current path includes a DS capacitor charging stage of the lower MOS tube and a body diode freewheeling stage, wherein the freewheeling current provides a charging circuit for the bootstrap capacitor. Since the gate control signal of the lower MOS tube is turned off, the current charges the DS capacitor of the lower MOS tube. As the capacitor charging is completed, the back electromotive force generated by the motor forces the lower tube body diode to turn on, forming a freewheeling current, charging the bootstrap capacitor of the upper tube, and ensuring the normal operation of the upper tube drive.

[0039] Specifically, at the moment of power-on, since the lower MOS tube is cut off, the motor current begins to flow through the capacitor (DS capacitor) between the drain (D) and source (S) of the lower MOS tube. The DS capacitor is a parasitic capacitor inherent in the structure of the MOS tube itself. At this stage, it is equivalent to a load, and the current charges it. As the charging process proceeds, 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 tube (due to the high duty cycle of the upper tube, it is turned on most of the time), then passes through the DS capacitor of the lower MOS tube, and finally returns to the negative pole of the power supply, forming a temporary current path.

[0040] When the DS capacitor is gradually filled, the motor will generate back electromotive force during operation. The back electromotive force is generated by 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 will force the body diode of the lower MOS tube to turn on. The body diode is a parasitic diode inside the MOS tube, and its direction is from the source to the drain. Once the body diode is turned on, a freewheeling current is formed. The path of the freewheeling current is from the motor winding, through the body diode of the lower MOS tube, and then back to the negative pole of the power supply, while providing the necessary circuit for charging the bootstrap capacitor of the upper tube.

[0041] Step 3: After waiting for the preset time, detect the midpoint voltage of the motor (such as Figure 3As shown in the figure), the preset time is adjusted based on the number of MOS tubes and the input capacitance. The preset time ranges from 100ms to 1000ms. The length of the preset time depends on the number of MOS tubes and the size of the input capacitance of the MOS tubes. When the number of MOS tubes is large or the input capacitance of the MOS tube is large, the interval of the preset time can be shortened. The power-on preset time is 500ms. 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 tubes, Represents the input capacitance of a single tube, represents the bus voltage, Indicates the charging current.

[0042] Specifically, 500ms after power-on (this time length is not fixed, but depends on the number of MOS and the size of the MOS Ciss capacitance. If the number of MOS is large or the Ciss capacitance is large, the interval time can be appropriately shortened), at the driving midpoint, a dedicated voltage sampling circuit is used to simultaneously sample the three-phase midpoint voltage. The core function of this voltage sampling circuit is to convert the collected analog voltage signal into a digital signal, which is then transmitted to the microcontroller or other control unit for subsequent analysis.

[0043] It should be noted that the 500ms setting is based on the calculation of the bootstrap capacitor charging time constant, which is:

[0044]

[0045] in:

[0046] N represents the number of MOS tubes;

[0047] Represents the input capacitance of a single tube;

[0048] Indicates bus voltage;

[0049] Indicates the charging current (typical value 10mA).

[0050] Example: When N=3, =1000pF, =48V, =10mA, the calculated t=432ms, rounded to 500ms.

[0051] In order to ensure the accuracy and stability of sampling, the voltage sampling circuit usually adopts a high-precision sampling chip and is equipped with corresponding filtering, amplification and other circuit modules. For example, in some application scenarios with high requirements for detection accuracy, an ADC sampling chip with 16 bits 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 out to ensure the purity of the sampling signal. The 500ms timing work after power-on is completed by starting the timer. The timer can be a timer module inside the microcontroller in the motor control system or an external independent timer chip. In addition, the timing time can be flexibly adjusted according to the actual number of MOS and the size of the Ciss capacitor. In software programming, the timing time can be precisely controlled by modifying the timer's initial count value, division coefficient and other parameters.

[0052] Step 4: If the midpoint voltage of any of the three phases of the motor is lower than the set threshold of the bus voltage, it is determined that the phase has a broken line fault. The set threshold of the bus voltage is 90%-100% of the bus voltage. If the midpoint voltage of any of the three phases is lower than the set threshold, it is determined that the motor is broken. When any of the three phases is broken, the phase midpoint voltage is set to the voltage divider value of the upper and lower tube DS capacitors, and the voltage divider ratio is 1:1. When a phase of the motor is broken, the circuit structure of the phase changes, and the bootstrap capacitor cannot be charged normally, resulting in a drop in the midpoint voltage. By comparing with the set threshold of the bus voltage, it can be accurately determined whether the motor has a broken line fault. When a motor break is detected, an audible and visual alarm is triggered or a fault signal is sent to the controller.

[0053] Specifically, the control unit will determine the status of the motor line based on the sampled three-phase midpoint voltage. When the motor is operating normally, the three-phase midpoint voltage sampled after 500ms should be the bus voltage. When one or more motor lines are disconnected, the bootstrap capacitor on the corresponding line cannot be charged normally, which will cause the midpoint voltage on the line to change significantly (significantly different from the bus voltage). The motor disconnection can be determined based on this voltage difference.

[0054] The specific judgment process is as follows: the control unit compares the collected three-phase midpoint voltage with the bus voltage one by one. If the difference between the midpoint voltage of a phase and the bus voltage exceeds the preset normal range (this normal range can be reasonably set based on factors such as motor type and operating voltage), the motor in that phase is determined to have a broken wire fault. If the three-phase midpoint voltage is within the normal range and is equal to or close to the bus voltage, the motor circuit is normal. After the motor broken wire detection is completed, to ensure reliable conduction of the lower tube and enable the motor to enter normal drive control mode, the duty cycle of the upper tube needs to be set to below 95%. This 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 tube is changed, ensuring the normal operation of the lower tube.

[0055] In practice, when the upper GS transistor is set to a 95% duty cycle, the lower GS transistor will not conduct. This duty cycle depends on the MOS transistor's turn-on delay and frequency. It is not an absolute parameter, but mainly depends on factors such as the MOS transistor's turn-on delay and operating frequency. In different motor systems, the MOS transistor's turn-on delay and operating frequency will vary, so the duty cycle value needs to be adjusted appropriately based on the actual situation.

[0056] Normal situation:

[0057] According to the settings, the duty cycle of H-GS is 95%, the duty cycle of V-GS is 96%, and the duty cycle of W-GS is 97%. Ensure that the lower tube GS cannot be turned on. There is a voltage difference between the three in the motor.

[0058] At the moment of power-on, the lower tube GS cannot be turned on, and the motor current is generated through the DS capacitor of the lower tube MOS. When the DS capacitor is full, the back electromotive force in the motor forces the lower tube body diode to turn on, generating freewheeling current.

[0059] This freewheeling current provides a circuit for charging the three bootstrap capacitors of the three high-side tube drivers, ensuring that the three high-side tube drivers maintain a reliable driving voltage.

[0060] After 500ms, the three-phase midpoint voltage is sampled at the driving midpoint as the bus voltage.

[0061] Motor disconnection:

[0062] When one or more motor lines are disconnected, the bootstrap capacitors on the corresponding lines cannot be charged normally, causing the midpoint voltage on the line to be BUS / 2 (cause: voltage division by the DS capacitors of the upper and lower tubes). The motor disconnection status is determined based on this voltage.

[0063] Step 5: After the detection is completed, adjust the duty cycle of the gate control signal of each phase upper MOS tube to below 95%. At this time, the gate control signal of the lower MOS tube is turned on. After the duty cycle is adjusted, the on state of the lower MOS tube is achieved by reverse control of the duty cycle of the gate control signal of the MOS tube, so that the motor enters the normal drive control mode and ensures the stable operation of the motor.

[0064] Specifically, after the test is completed, the duty cycle must be set to ensure that the lower tube is reliably turned on, that is, the duty cycle of the upper tube must be set to less than 95%.

[0065] For example: When the U-phase motor is disconnected, the U-phase bootstrap capacitor cannot be charged normally, and the upper tube cannot be turned on normally. The U-phase bridge arm voltage = the upper tube DS capacitor + the lower tube DS capacitor voltage divider. Assuming that the capacitance at both ends is the same, the U-phase midpoint voltage is BUS / 2.

[0066] Note: 500ms is an example time. The length of this time depends on the number of MOS and the Ciss capacitance of the MOS. If there are many MOS (or a large Ciss capacitance), the interval time can be appropriately shortened to ensure that the power in the bootstrap capacitor is fully consumed.

[0067] It should be understood that, although the various steps in the flowcharts of the various embodiments of the present invention are shown in sequence as indicated by the arrows, these steps are not necessarily performed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps may be performed in other orders. Moreover, at least a portion of the steps in the various embodiments may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily performed at the same time, but may be performed at different times, and the execution order of these sub-steps or stages is not necessarily performed in sequence, but may be performed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0068] Those skilled in the art will appreciate that all or part of the processes in the above-described method embodiments can be implemented by instructing the relevant hardware through a computer program. The above-described program can be stored in a non-volatile computer-readable storage medium. When executed, the program can include the processes of the above-described method embodiments. Any reference to memory, storage, database, or other media used in the various embodiments provided herein may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may 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 (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct RAMbus dynamic RAM (DRDRAM), and RAMbus dynamic RAM (RDRAM).

[0069] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, 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, they should be considered to be within the scope of this specification.

[0070] The above embodiments merely represent several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the appended claims.

[0071] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting a disconnection of a startup motor, characterized in that: The method comprises the following steps: Step 1: When the motor is powered on and initialized, the duty cycle of the gate control signal of the upper MOS tube of each phase of the motor is set to be greater than a first value, and the gate control signals of all the lower MOS tubes are turned off; Step 2: A current path is formed through the DS capacitor and body diode of the lower MOS tube to charge the bootstrap capacitor of each phase upper tube; Step 3: After waiting for a preset time, detecting the midpoint voltage of the motor; The preset time is 500ms, and the calculation formula for the preset time of charging the bootstrap capacitor is: , where N represents the number of MOS tubes, Represents the input capacitance of a single tube, represents the bus voltage, Indicates charging current; Step 4: If the midpoint voltage of any one of the three phases of the motor is lower than a set threshold value of the bus voltage, it is determined that a disconnection fault exists in the phase; Step 5: After the detection is completed, adjust the duty cycle of the gate control signal of each phase upper MOS tube to below 95%, and then turn on the gate control signal of the lower MOS tube.

2. The method according to claim 1, characterized in that In 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, characterized in that In step 2, the current path includes a DS capacitor charging stage of the lower MOS tube and a body diode freewheeling stage, 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 tube and the lower MOS tube and the capacity of the bootstrap capacitor, and the value range of the preset time is 100ms to 1000ms.

5. The method according to claim 1, wherein The set threshold value of the bus voltage is 90%-100% of the bus voltage. If the midpoint voltage of any phase among the three phases is lower than the set threshold value, it is determined that the motor is disconnected.

6. The method according to claim 5, characterized in that In step 1, a first value is adjusted based on a PWM signal generator, wherein 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 tube is achieved by reversely controlling the duty cycle of the gate control signal of the MOS tube.

8. The method according to claim 1, characterized in that When the motor is detected to be disconnected, an audible and visual alarm is triggered or a fault signal is sent to the controller.

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

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