Permanent magnet brushless DC motor inverter with open circuit fault diagnosis and diagnosis method

Abstract

A permanent magnet brushless DC motor inverter with open circuit fault diagnosis and a diagnostic method, a three-phase full-bridge inverter circuit includes an A-phase switch branch, a B-phase switch branch and a C-phase switch-related branch respectively connected in parallel with a DC power supply voltage and formed by two switch components connected in series, each phase of the motor stator three-phase winding is formed by a winding inductance, the input end of the winding inductance in each phase of the motor stator three-phase winding is connected to the midpoint of the upper and lower switch components of the corresponding phase switch branch, the output ends of the winding inductance in the three-phase winding are connected together, a first set of linear current sensors are sleeved from the A and B phase upper bridge arm DC bus to the A phase switch branch and the B phase switch branch, and a second set of linear current sensors are sleeved from the B and C phase lower bridge arm DC bus to the B phase switch branch and the C phase switch-related branch. The present invention uses two current sensors to diagnose the open circuit fault of the inverter power switch device when the motor is in normal operation.

Description

Technical Field

[0001] The present invention relates to a permanent magnet brushless DC motor inverter open circuit fault diagnosis technology, and more particularly to a permanent magnet brushless DC motor inverter with open circuit fault diagnosis based on current difference and improved current sensor position and a diagnostic method. Background Art

[0002] With the development of industrial technology, permanent magnet brushless DC motors, as a high-efficiency drive device, have attracted people's attention in many industrial fields such as intelligent robots, home appliances, electric vehicles, etc. Compared with other motors, the control scheme they use is simpler and can achieve high efficiency and high torque operation.

[0003] In order to avoid major failures in motor control systems, which would cause large-scale damage to equipment and bring about cost and economic losses, motors in practical applications need to introduce fault diagnosis technology so that fault information can be obtained in a timely manner. However, offline fault diagnosis methods have a long detection cycle and poor real-time performance. With the urgent need for safe production and the development of artificial intelligence technology, technologies that can detect motor faults online and even provide early warning of faults have attracted the attention of the industry.

[0004] Common faults in motor control systems include inverter faults, sensor faults, and motor faults. Inverter faults are mainly caused by damage to the power switch components that constitute the inverter. During the operation of the motor, the motor needs to be commutated and the speed needs to be adjusted. The power switch tube needs to work in a high-frequency switching state for a long time, so it is often damaged due to heat, overcurrent, etc. It is estimated that 38% of the faults in motor control systems for industrial applications come from damage to power semiconductor switch components. If they are not diagnosed and eliminated in time, secondary faults will occur, eventually causing the system to shut down. In applications with high safety requirements, such as aerospace, robots, and automobiles, inverter failures may be fatal to the entire system.

[0005] The most common faults of inverters are short circuit and open circuit of power switch tubes. Short circuit faults occur in a short time, usually a few microseconds, and are not easy to detect. At the same time, a fast fuse is connected in series in each bridge arm of the inverter to convert the short circuit fault of the switch tube into an open circuit fault for diagnosis. Existing open circuit fault diagnosis is mainly divided into two categories: voltage method and current method. The voltage method requires an external voltage sensor or voltage acquisition circuit. Therefore, the current method accounts for a much larger proportion of the existing technology than the voltage method. However, most of the existing methods are suitable for permanent magnet synchronous motor vector control. There are few literatures on fault diagnosis under two-to-two conduction control of brushless DC motors, and it is still impossible to achieve rapid fault diagnosis, which requires further research and development. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a permanent magnet brushless DC motor inverter and a diagnostic method with open circuit fault diagnosis, which can realize real-time detection of inverter open circuit faults without affecting the normal operation of the motor in order to overcome the shortcomings of the prior art.

[0007] The technical solution adopted by the present invention is: a permanent magnet brushless DC motor inverter with an open circuit fault diagnosis function, which is composed of a three-phase full-bridge inverter circuit and a motor stator three-phase winding connected to the three-phase full-bridge inverter circuit, wherein the three-phase full-bridge inverter circuit includes an A-phase switch branch formed by a first switch component and a second switch component connected in series, a B-phase switch branch formed by a third switch component and a fourth switch component connected in series, and a C-phase switch branch formed by a fifth switch component and a sixth switch component connected in series, which are connected in parallel with a DC power supply voltage, wherein the first switch component, the second switch component, the third switch component, the fourth switch component, the fifth switch component and the sixth switch component are connected in series. The structures of the related components are the same, and are all composed of a power switch tube and a freewheeling diode in anti-parallel connection. Each phase of the three-phase winding of the motor stator is composed of a winding inductance. The input end of the winding inductance in each phase of the three-phase winding of the motor stator is connected to the midpoint of the upper and lower switch components of the corresponding phase switch branch. The output ends of the winding inductance in the three-phase winding are connected together. A first set of linear current sensors for detecting the current on the two branches are connected from the upper bridge arm DC bus of the A and B phases to the A phase switch branch and the B phase switch branch. A second set of linear current sensors for detecting the current on the two branches are connected from the lower bridge arm DC bus of the B and C phases to the B phase switch branch and the C phase switch branch.

[0008] A method for quickly diagnosing an open circuit fault of a permanent magnet brushless DC motor inverter with an open circuit fault diagnosis function comprises the following steps:

[0009] 1) Using a first set of linear current sensors to measure the current from the upper bridge arm DC bus of the inverter phases A and B to the A-phase switch branch and the B-phase switch branch, using a second set of linear current sensors to measure the current from the lower bridge arm DC bus of the inverter phases B and C to the B-phase switch branch and the C-phase switch branch, and then using the two sets of measured currents to reconstruct the three-phase phase currents, thereby controlling the operation of the permanent magnet brushless DC motor;

[0010] 2) Subtract the phase currents of two adjacent control cycles to determine whether the obtained difference satisfies the preset difference determination condition, thereby determining whether an open circuit fault occurs in the power switch device in the inverter and providing fault information;

[0011] 3) When fault information appears, the power switch tube where the fault occurs is located by using the difference in readings between the first set of linear current sensors and the second set of linear current sensors.

[0012] The difference determination condition described in step 2) is:

[0013] i k -i k+1 ≥g f ·i k

[0014] where i k is the phase current value of the kth control cycle, i k+1 is the phase current value of the k+1th control cycle, g f is the threshold coefficient, ranging from 0.5 to 1. When the phase current difference between two adjacent control cycles is greater than or equal to g f and i k When the product of is equal to or greater than , it is determined that an open circuit fault has occurred in the power switch device in the inverter, and then the control device issues a fault message.

[0015] Step 3) includes:

[0016] A permanent magnet brushless DC motor operation cycle is divided into six conduction phases, i m1 、i m2 Respectively represent the measurement values ​​of the first set of linear current sensors and the second set of linear current sensors, T1-T6 correspond to the first to sixth power switch tubes in the first switch component, the second switch component, the third switch component, the fourth switch component, the fifth switch component and the sixth switch component in the three-phase full-bridge inverter circuit of the inverter, and the difference in the readings of the first set of linear current sensors and the second set of linear current sensors is used to locate the specific power switch tube that has a fault, and the specific fault judgment is:

[0017] T1, T4 tube conduction stage: i m1 =0,i m2 >0, T1 fault, i m1 =0,i m2 =0 when T4 fails;

[0018] T1, T6 tube conduction stage: i m1 =0,i m2 >0, T1 fault, i m1 >0,i m2 =0 when T6 fails;

[0019] T3, T6 tube conduction stage: i m1 =0,i m2 =0 when T3 fails, i m1 >0,i m2 =0 when T6 fails;

[0020] T3, T2 tube conduction stage: i m1 =0,i m2 <0 when T3 fails, im1 =0,i m2 =0 when T2 fails;

[0021] T5, T2 tube conduction stage: i m1 =0,i m2 <0 when T5 fails, i m1 >0,i m2 =0 when T2 fails;

[0022] T5, T4 tube conduction stage: i m1 =0,i m2 =0 when T5 fails, i m1 >0,i m2 =0, T4 fault.

[0023] The permanent magnet brushless DC motor inverter with open circuit fault diagnosis and the diagnostic method of the present invention realize the diagnosis of the open circuit fault of the inverter power switch device by using only two current sensors while the motor maintains normal operation. The beneficial effects of the present invention are as follows:

[0024] 1. The present invention can diagnose the inverter open circuit fault by relying on only two current sensors, without adding additional current sensors or other types of signal acquisition devices, giving full play to the advantages of low cost and easy operation of the current method.

[0025] 2. The faulty tube can be diagnosed and located within two control cycles, avoiding the problem of mis-positioning due to long positioning time; it provides a guarantee for timely repair and fault removal, avoidance of secondary faults and stable operation of the motor.

[0026] 3. The present invention overcomes the defects of traditional off-line fault detection, realizes online fault detection without affecting the normal operation of the motor, and does not require shutdown, thus expanding the application scope of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the equivalent circuit diagram of the existing brushless DC motor control system;

[0028] Figure 2 This is a waveform diagram of the ON-PWM modulation strategy;

[0029] Figure 3 This is a circuit schematic diagram of a brushless DC motor control system after the position of the current sensor is changed in the present invention;

[0030] Figure 4 yes Figure 3 Schematic diagram of equivalent circuit;

[0031] Figure 5Schematic diagram of current flow after the T1 tube is open-circuited in the A+B- state in the embodiment of the present invention. DETAILED DESCRIPTION

[0032] The permanent magnet brushless DC motor inverter with open circuit fault diagnosis and the diagnosis method of the present invention are described in detail below in conjunction with the embodiments and the accompanying drawings.

[0033] The equivalent circuit diagram of the existing permanent magnet brushless DC motor control system is as follows: Figure 1 As shown, the three-phase stator windings are connected in star symmetry, T1-T6 are the six power switch tubes of the three-phase full-bridge inverter, D1-D6 are the anti-parallel diodes of the corresponding power switch tubes, Udc is the DC power supply voltage, m A 、m B 、m C is the current sensor, R is the winding resistance, L is the winding inductance, i A 、i B 、i C is the phase current, e A 、e B 、e C is the reverse electromotive force, and N is the neutral point of the motor's three-phase winding. Assuming that the motor magnetic circuit is not saturated, ignoring the influence of the switch tube voltage drop and its own structure, the voltage equation of the three-phase winding terminal of the brushless DC motor is:

[0034]

[0035] Among them, uA, uB, uC are the phase voltages of the three-phase windings of the motor; uN is the neutral point voltage of the motor.

[0036] Taking the commonly used two-by-two conduction mode of brushless DC motor and the commonly used ON-PWM modulation mode in unipolar symmetrical modulation as examples for analysis, the waveform of this modulation strategy is as follows Figure 2 As shown, under the two-by-two conduction control and ON-PWM modulation mode, one electrical cycle of the motor is divided into six states. Two switching tubes are turned on in each state. Each switching tube is continuously turned on for 120 degrees, with the first 60 degrees being chopped and the last 60 degrees being constantly on.

[0037] like Figure 3As shown, the permanent magnet brushless DC motor inverter with open circuit fault diagnosis function of the present invention is composed of a three-phase full-bridge inverter circuit and a three-phase winding of a motor stator connected to the three-phase full-bridge inverter circuit. The three-phase full-bridge inverter circuit includes an A-phase switch branch composed of a first switch component and a second switch component connected in series and connected in parallel with a DC power supply voltage Udc, a B-phase switch branch composed of a third switch component and a fourth switch component connected in series, and a C-phase switch branch composed of a fifth switch component and a sixth switch component connected in series. The first switch component, the second switch component, the third switch component, the fourth switch component, the fifth switch component and the sixth switch component have the same structure, and are all composed of a power switch tube T1, T2, T3, T4, T5, T6, and a freewheeling diode D1, D2, D3, D4, D5, D6. 6 is anti-parallel, each phase of the three-phase stator winding of the motor is composed of a winding inductance L, the input end of the winding inductance L in each phase of the three-phase stator winding of the motor is connected to the midpoint of the upper and lower switch components of the corresponding phase switch branch, the output ends of the winding inductance L in the three-phase winding are connected together, and a first set of linear current sensors m1 for detecting currents on the two branches are sleeved on the DC bus of the upper bridge arm of the A and B phases to the A phase switch branch and the B phase switch branch, and a second set of linear current sensors m2 for detecting currents on the two branches are sleeved on the DC bus of the lower bridge arm of the B and C phases to the B phase switch branch and the C phase switch branch.

[0038] The method for quickly diagnosing an open circuit fault of a permanent magnet brushless DC motor inverter with an open circuit fault diagnosis function of the present invention comprises the following steps:

[0039] 1) Using the first set of linear current sensors m1 to measure the current from the upper bridge arm DC bus of the inverter A and B phases to the A phase switch branch and the B phase switch branch, using the second set of linear current sensors m2 to measure the current from the lower bridge arm DC bus of the inverter B and C phases to the B phase switch branch and the C phase switch branch, and then using the two sets of measured currents to reconstruct the three-phase phase currents, so as to control the operation of the permanent magnet brushless DC motor;

[0040] Among the six states of one electrical cycle of the permanent magnet brushless DC motor, A+B- and C+B- can collect current under the effective vector (both working switch tubes are turned on), C+A- can collect current under the zero vector (the chopped switch tube is turned off, and the constant switch tube remains on), and A+C-, B+C-, and B+A- can all be collected under both the effective and zero vectors. Since the first set of linear current sensors m1 and the second set of linear current sensors m2 cannot directly measure the three-phase current after the positions are changed in the present invention, it is necessary to reconstruct the three-phase current based on the sampled current information.

[0041] According to the different sampling conditions of the first set of linear current sensors m1 and the second set of linear current sensors m2, the basis for phase current reconstruction shown in Table 1 can be obtained, where "√" indicates that current information can be collected under this condition.

[0042] Table 1

[0043]

[0044] According to Table 1, under the current sampling vector, the first set of linear current sensors m1 and the second set of linear current sensors m2 with corresponding conditions are used to reconstruct the three-phase current. In order to maximize the consistency of current sampling and reduce the sampling errors of the first set of linear current sensors m1 and the second set of linear current sensors m2, it is preferred to use the first set of linear current sensors m1 to reconstruct the phase current under the effective vector. For C+A- and C+B- that do not meet the condition, the current is sampled under the sampling conditions they meet to reconstruct the three-phase current. The specific reconstruction method is:

[0045] 1. Collect current once in one control cycle;

[0046] 2. Under the effective vector, the current value collected in one control cycle is divided by the duty cycle d to obtain the value of the phase current of the positive phase conduction; under the zero vector, the current value collected in one control cycle is divided by 1-d to obtain the value of the phase current of the positive phase conduction;

[0047] 3. The phase current value of the negative phase conduction is equal to the opposite number of the phase current value of the positive phase conduction. Thus, the three-phase phase current is reconstructed.

[0048] 2) After obtaining the three-phase currents, the phase currents of two adjacent control cycles are subtracted to determine whether the obtained difference satisfies the preset difference determination condition, thereby determining whether an open circuit fault occurs in the power switch device in the inverter and providing fault information; the difference determination condition is:

[0049] i k -i k+1 ≥g f ·i k

[0050] where i k is the phase current value of the kth control cycle, i k+1 is the phase current value of the k+1th control cycle, g f is the threshold coefficient, which is generally in the range of 0.5 to 1. When the phase current difference between two adjacent control cycles is greater than or equal to g f and i k When the product of kWhen , it is determined that the power switch device in the inverter has an open circuit fault, and then the control device sends a fault message. Taking A+B- conduction as an example, the positive phase conduction phase A is selected as the fault judgment variable. When the A phase upper bridge arm power switch tube or the B phase lower bridge arm power switch tube has an open circuit fault in the kth control cycle, the A phase current i a A sharp drop will occur. At this time, the control device determines that the current difference between the two control cycles satisfies the result of formula (1) and gives a fault indication signal.

[0051] 3) When fault information appears, the power switch tube where the fault occurs is located by using the difference in readings between the first set of linear current sensors m1 and the second set of linear current sensors m2; including:

[0052] After an open-circuit fault occurs in the inverter, the current will not decay to zero immediately due to the inductive characteristics of the motor winding. The current flow direction will change due to the open-circuit fault of the inverter, causing the readings of the two current sensors to change compared to before the fault. The readings of the two current sensors corresponding to the faults of different power switch tubes are different. Therefore, the measured values ​​of the two sheathed current sensors can be used to determine the specific power switch tube that has failed in the inverter. The operation cycle of a permanent magnet brushless DC motor is divided into six conduction stages, i m1 、i m2 Respectively represent the measurement values ​​of the first set of linear current sensors m1 and the second set of linear current sensors m2, T1-T6 correspond to the first to sixth power switch tubes in the first switch component, the second switch component, the third switch component, the fourth switch component, the fifth switch component and the sixth switch component in the three-phase full-bridge inverter circuit of the inverter, and the difference in the readings of the first set of linear current sensors m1 and the second set of linear current sensors m2 is used to locate the specific power switch tube that has a fault, and the specific fault judgment is:

[0053] T1, T4 tube conduction stage: i m1 =0,i m2 >0, T1 fault, i m1 =0,i m2 =0 when T4 fails;

[0054] T1, T6 tube conduction stage: i m1 =0,i m2 >0, T1 fault, i m1 >0,i m2 =0 when T6 fails;

[0055] T3, T6 tube conduction stage: i m1 =0,i m2 =0 when T3 fails, i m1 >0,i m2=0 when T6 fails;

[0056] T3, T2 tube conduction stage: i m1 =0,i m2 <0 when T3 fails, i m1 =0,i m2 =0 when T2 fails;

[0057] T5, T2 tube conduction stage: i m1 =0,i m2 <0 when T5 fails, i m1 >0,i m2 =0 when T2 fails;

[0058] T5, T4 tube conduction stage: i m1 =0,i m2 =0 when T5 fails, i m1 >0,i m2 =0, T4 fault.

[0059] Depend on Figure 4 As shown in the figure, when the A+B- is turned on, after the A phase upper bridge arm power switch tube T1 has an open circuit fault, T4 becomes a constant on state, and the current continues to flow through D2, T4 and the A and B phase windings. Due to the change in the current flow direction, the measured values ​​of the current sensors m1 and m2 will also change. When the T1 tube has an open circuit fault, Figure 4 It can be seen that m1=0, m2>0.

[0060] When the B-phase lower bridge arm power switch tube T4 has an open circuit fault, the current continues to flow through D3, T1 and the A and B phase windings, and at this time m1 = 0, m2 = 0. Therefore, the position sensor can be used to determine the two working switch tubes, and then the specific power switch tube with fault can be located through the magnitude relationship between the current sensors m1, m2 and zero. The fault location basis for the six power switch tubes with different working states is shown in Table 2.

[0061] Table 2

[0062]

[0063] It needs to be further explained that the present invention has a wide range of applications. The embodiments herein are only for detailed explanation. Some details may vary during actual use. All improvements, equivalent substitutions, etc. made within the spirit and principles of the present invention should fall within the scope of the present invention.

Claims

1. A permanent magnet brushless DC motor inverter with an open circuit fault diagnosis function, which is composed of a three-phase full-bridge inverter circuit and a motor stator three-phase winding connected to the three-phase full-bridge inverter circuit, wherein the three-phase full-bridge inverter circuit includes an A-phase switch branch connected in parallel with a DC power supply voltage (Udc) and formed by a first switch component and a second switch component connected in series, a B-phase switch branch connected in series with a third switch component and a fourth switch component, and a C-phase switch branch connected in series with a fifth switch component and a sixth switch component. The third switch assembly, the fourth switch assembly, the fifth switch assembly and the sixth switch assembly have the same structure, and are all composed of a power switch tube (T1, T2, T3, T4, T5, T6) and a freewheeling diode (D1, D2, D3, D4, D5, D6) connected in anti-parallel, each phase of the three-phase stator winding of the motor is composed of a winding inductance (L), the input end of the winding inductance (L) in each phase of the three-phase stator winding of the motor is connected to the midpoint of the upper and lower switch assemblies of the corresponding phase switch branch, and the output ends of the winding inductance (L) in the three-phase winding are connected together, characterized in that, A first set of linear current sensors (m1) for detecting currents on the two branches are sleeved between the upper bridge arm DC busbars of the A and B phases and the A phase switch branch and the B phase switch branch, and a second set of linear current sensors (m2) for detecting currents on the two branches are sleeved between the lower bridge arm DC busbars of the B and C phases and the B phase switch branch and the C phase switch branch.

2. A method for rapid open circuit fault diagnosis of a permanent magnet brushless DC motor inverter with open circuit fault diagnosis function as claimed in claim 1, characterized in that: The steps include: 1) Using a first set of linear current sensors (m1) to measure the current from the upper bridge arm DC busbars of the inverter phases A and B to the A-phase switch branch and the B-phase switch branch, using a second set of linear current sensors (m2) to measure the current from the lower bridge arm DC busbars of the inverter phases B and C to the B-phase switch branch and the C-phase switch branch, and then using the two sets of measured currents to reconstruct the three-phase phase currents, thereby controlling the operation of the permanent magnet brushless DC motor; 2) Subtract the phase currents of two adjacent control cycles to determine whether the obtained difference satisfies the preset difference determination condition, thereby determining whether an open circuit fault occurs in the power switch device in the inverter and providing fault information; 3) When fault information appears, the power switch tube where the fault occurs is located by using the difference in readings between the first set of linear current sensors (m1) and the second set of linear current sensors (m2).

3. The open circuit fault rapid diagnosis method according to claim 2, characterized in that: The difference determination condition described in step 2) is: i k -i k+1 ≥g f ·i k where i k is the phase current value of the kth control cycle, i k+1 is the phase current value of the k+1th control cycle, g f is the threshold coefficient, ranging from 0.5 to 1. When the phase current difference between two adjacent control cycles is greater than or equal to g f and i k When the product of is equal to or greater than , it is determined that an open circuit fault has occurred in the power switch device in the inverter, and then the control device issues a fault message.

4. The open circuit fault rapid diagnosis method according to claim 2, characterized in that: Step 3) includes: A permanent magnet brushless DC motor operation cycle is divided into six conduction phases, i m1 、i m2 Respectively represent the measurement values ​​of the first set of linear current sensors (m1) and the second set of linear current sensors (m2), T1-T6 correspond to the first to sixth power switch tubes in the first switch component, the second switch component, the third switch component, the fourth switch component, the fifth switch component and the sixth switch component in the three-phase full-bridge inverter circuit of the inverter, and the difference between the readings of the first set of linear current sensors (m1) and the second set of linear current sensors (m2) is used to locate the specific power switch tube that has a fault, and the specific fault judgment is: T1, T4 tube conduction stage: i m1 =0,i m2 >0, T1 fault, i m1 =0,i m2 =0 when T4 fails; T1, T6 tube conduction stage: i m1 =0,i m2 >0, T1 fault, i m1 >0,i m2 =0 when T6 fails; T3, T6 tube conduction stage: i m1 =0,i m2 =0 when T3 fails, i m1 >0,i m2 =0 when T6 fails; T3, T2 tube conduction stage: i m1 =0,i m2 <0 when T3 fails, i m1 =0,i m2 =0 when T2 fails; T5, T2 tube conduction stage: i m1 =0,i m2 <0 when T5 fails, i m1 >0,i m2 =0 when T2 fails; T5, T4 tube conduction stage: i m1 =0,i m2 =0 when T5 fails, i m1 >0,i m2 =0, T4 fault.

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