Fault diagnosis method based on position tube current variation in soft chopping mode

Abstract

The application provides a fault diagnosis method based on position observation current change in a soft chopping mode. For a motor system, the occurrence of faults is inevitable. Once a fault occurs or the motor stops running, the system will be affected, and even serious accidents will occur, which will endanger personal safety and cause huge economic losses. Therefore, the fault diagnosis research of the switched reluctance motor system is very important. The application is aimed at the soft chopping control mode, that is, the upper and lower main switch tubes are in different working modes. The application provides a fault diagnosis method based on position observation current change in the soft chopping mode of the main switch tube, which has simple judgment logic, small calculation amount and is easy to realize in the controller software.

Description

Technical Field

[0001] This invention relates to the field of switched reluctance motor power converters. Background Technology

[0002] Switched reluctance motor (SRM) drive systems have shown broad market prospects. However, due to the pulsating magnetic attraction between the stator and rotor of the SRM with its doubly salient poles, the generated electromagnetic torque is still pulsating, causing unstable rotor operation and problems such as output torque pulsation and high noise. On the other hand, because the main circuits of each phase of the SRD are independent, it is low-cost and highly efficient, making it safer and more reliable than traditional motors, suitable for harsh environments or applications with high reliability requirements. However, high reliability does not mean the absence of failures. In fact, in applications with high reliability requirements, if the SRD drive system fails or stops operating, it will not only affect the system but may even cause serious accidents, endangering personal safety and causing huge economic losses. Therefore, research on fault diagnosis of switched reluctance motor systems is extremely important. Summary of the Invention

[0003] This invention proposes a fault diagnosis method based on position tube current variation in soft chopper mode, as detailed below.

[0004] A fault diagnosis method based on position tube current variation in soft chopper mode, characterized by the following steps:

[0005] Step 1: Given a switched reluctance motor power converter, the power converter includes switching transistors and diodes, and the control method adopted is soft chopper control, that is, the switching transistors are divided into chopper transistors and position transistors.

[0006] Step 2: Place the current sensor on the chopper branch to ensure that current can be detected in the open range.

[0007] Step 3: Based on the winding voltage equation, the current change relationship under different switching states can be obtained.

[0008] Step 4: Therefore, we can work backwards to obtain the actual switching state through current changes. Since a fault in the switching transistor can be considered as a mismatch between the theoretical and actual signals (short circuit fault means the actual signal is always high, open circuit fault means the actual signal is always low), we can obtain the fault condition of the switching transistor by comparing it with the theoretical switching state.

[0009] Step 5: Since the current change needs to be obtained, the calculation is divided into two types: fixed frequency and random frequency. The advantages and disadvantages of each are analyzed.

[0010] The switching transistor type of the switched reluctance motor power converter mentioned in step 1 is one of the following: gate turn-off thyristor (GTO), bipolar junction transistor (BJT), power MOSFET, or insulated gate bipolar transistor (IGBT).

[0011] The current sensor in step 2 is placed in the position tube branch.

[0012] Step 4: Comparison of theoretical and actual switching states. Characteristic quantities include the theoretical switching state S. ae Actual switch state S al and the absolute value of the current change |Δi al |

[0013] The current change calculation in step 5 can be performed using either a fixed frequency or a random frequency.

[0014] In step 5, under different current change methods, there is a theoretical relationship between the sampling frequency and the chopping frequency in order to avoid false diagnosis.

[0015] This invention proposes a fault diagnosis method based on position transistor current variation in soft chopper mode. The fault of the switching transistor can be regarded as a mismatch between the theoretical signal and the actual signal of the switching transistor. Theoretically, the fault can be located by analyzing the current variation through the winding voltage and the fault characteristic value. Attached Figure Description

[0016] Figure 1 These are four circuits for soft chopper in switched reluctance motors.

[0017] Figure 2 These are the three basic operating modes of soft chopper for switched reluctance motors.

[0018] Figure 3 This indicates a short-circuit fault in the soft chopper of the switched reluctance motor.

[0019] Figure 4 This indicates an open-circuit fault in the soft chopper of the switched reluctance motor.

[0020] Figure 5 This is a topology of a switched reluctance motor power converter given in a specific embodiment of the present invention.

[0021] Figure 6 This is a flowchart of a fault diagnosis method given in a specific embodiment of the present invention.

[0022] Figure 7 This is a fixed sampling frequency waveform given in a specific embodiment of the present invention.

[0023] Figure 8 This refers to the random sampling frequency waveform given in a specific embodiment of the present invention. Detailed Implementation

[0024] According to step 1, in soft chopper mode, the switching transistors are divided into chopper transistors and position transistors. The main switch has two states: on and off. Based on the relationship between the switching transistor states and the drive signal, the switching transistor states are defined as follows: (1)

[0025] Taking phase A as an example, depending on the switching state, phase A may have four switching states: S1=S2=1 (ST1), S1=1, S2=0 (ST2), S1=0, S2=1 (ST3), and S1=S2=0 (ST4). Figure 1 As shown.

[0026] like Figure 2 As shown, the soft chopper mode is divided into three modes: excitation mode ST1, zero voltage freewheeling mode ST2, and negative voltage freewheeling mode ST4.

[0027] Taking phase A as an example, such as Figure 3 As shown, if the chopper tube experiences a short-circuit fault, the excitation state (ST1) remains unaffected, the zero-voltage freewheeling state (ST2) reverts to the excitation state (ST1), the current changes from a guaranteed decrease to a possible increase, the negative voltage freewheeling state (ST4) changes to the zero-voltage freewheeling state (ST3), and the current remains 0. If the position tube experiences a short-circuit fault, the excitation state (ST1) and the zero-voltage freewheeling state (ST2) remain unaffected, the negative voltage freewheeling state (ST4) reverts to the zero-voltage freewheeling state (ST2), and the current changes from 0 to a guaranteed decrease.

[0028] like Figure 4 As shown, if the chopper tube experiences an open-circuit fault, the zero-voltage freewheeling state (ST2) and the negative-voltage freewheeling state (ST4) remain unaffected. The excitation state (ST1) changes to the zero-voltage freewheeling state (ST2), and the current will continue to decrease until it reaches 0. If the position tube experiences an open-circuit fault, the negative-voltage freewheeling state (ST4) remains unaffected. The excitation mode changes to the zero-voltage freewheeling state (ST3), and the zero-voltage freewheeling state (ST2) will change to the negative-voltage freewheeling state (ST4), and the current will instantly become 0.

[0029] Figure 5 In the diagram, A, B, and C represent the windings of phases A, B, and C, respectively; ia, ib, and ic represent the currents of phases A, B, and C, respectively; S1 to S6 represent power transistors; D1 to D6 represent freewheeling diodes; iS1 to iS6 represent the current flowing through the corresponding power transistors; iD1 to iD6 represent the current flowing through the corresponding freewheeling diodes; C1 and C2 represent energy storage capacitors; and current sensors LEMA, LEMB, and LEMC measure the currents of choppers S2, S4, and S6 of each phase, respectively.

[0030] Define the switching state S of the theory ae This ensures that under normal conditions, the excitation mode is 1 (representing rising current), the sub-zero voltage freewheeling mode is 0 (representing falling current), and the negative voltage freewheeling mode is -1 (representing no current). (1)

[0031] First, we define the difference between the sensor current obtained from the k-th and (k-1)-th samplings as Δial, i.e. (2)

[0032] Secondly, the actual switching state is defined as follows: (3)

[0033] When the current instantaneously becomes 0, Δi al If the current changes instantaneously from a positive value to 0, it is considered a transient change, i.e., detected. (4)

[0034] Taking the A-phase bridge arm switch transistor as an example, the fault diagnosis flowchart is as follows: Figure 6 As shown. Under normal circumstances, the theoretical switching state Sae and the actual switching state Sal are the same, or the current is in the excitation mode, but because the current is large, the current decreases instead, i.e., Sae=1, Sal=0, and ial>0, or when just entering the turn-on range, zero-voltage freewheeling occurs first, i.e., Sae=0, Sal=-1, and ial=0. Otherwise, it can be determined that the switching transistor is faulty. When the current rises (Sal=1) in the sub-zero voltage freewheeling range (Sae=0), chopper S1 is short-circuited; when the current falls (Sal=0) in the negative voltage freewheeling range (Sae=-1), position transistor S2 is short-circuited; when the current drops to 0 (Sal: 0→-1) in the on-state range (Sae≥0) without a sudden change (|Δial|<ε), position transistor S2 is open-circuited; when the current suddenly drops to 0 (Sae=-1, and |Δial|>ε) in the on-state range, chopper S2 is open-circuited; when the current remains 0 (Sae: -1→-1, and |Δial|<ε) in the on-state range, that phase is open-circuited.

[0035] Table 1. Current and Fault Characteristic Quantities of Phase A Bridge Arm under Normal and Fault Conditions

[0036] The calculation of the current change Δial in step 6 can be performed using either a fixed frequency or a random frequency. Fixed frequency sampling means the time between two samplings is fixed. Due to the randomness of the sampling points, variations may occur, such as... Figure 5 In both cases, the theoretical switching state Sae and the actual switching state Sal are output after sampling and maintained until the next sampling period. When the sampling points are located in two different intervals, such as... Figure 7 (a) The boundary between the descending and ascending intervals, such as Figure 7 (b) At the boundary between the rising and falling points, ΔS appears in an interval that is not equal to 0, but the time is only one sampling period. Therefore, ΔS will be not equal to 0 for N consecutive periods before a fault diagnosis will occur. In addition, the sampling frequency must be greater than N times the chopping frequency. Therefore, under normal circumstances, a fault misdiagnosis will not occur. Here, we take N=3.

[0037] To prevent sampling points from appearing at both ends of the switch state change, random frequency sampling is only performed when the switch state changes or when the switch state remains unchanged for a long time. Figure 8 (a) Sampling occurs when the switch state changes. Figure 8 (b) Sampling is performed when the switch state remains unchanged for a long time. It can be seen that the theoretical switch state Sae and the actual switch state Sal are almost the same, so N can be set to 1 to avoid false diagnosis.

Claims

1. A fault diagnosis method based on position tube current variation in soft chopping mode, characterized by: The method includes the following steps: Step 1: Given a switched reluctance motor power converter, the power converter includes switching transistors and diodes, and the control method adopted is soft chopper control, that is, the switching transistors are divided into chopper transistors and position transistors; Step 2: Place the current sensor on the chopper branch to ensure that current can be detected in the open range; Step 3: Based on the winding voltage equation, the current variation relationship under different switching states can be obtained; Step 4: Establish the theoretical relationship of current change under different switching states based on the winding voltage equation; monitor the current value of the chopper branch in real time using a current sensor, and calculate the current change difference between adjacent sampling points; determine the actual switching state based on the current change difference and the absolute value of the current value: when the current value is zero, the actual switching state is determined to be -1; when the current change difference is negative, the actual switching state is determined to be 0; when the current change difference is positive, the actual switching state is determined to be 1; define the theoretical switching state. S ae As follows: When both the chopper and position transistor drive signals are low, S ae =-1; when the chopper drive signal is low and the position transistor drive signal is high. S ae =0; when both the chopper and position transistor drive signals are high. S ae =1; Step 5: When in the sub-zero voltage freewheeling range, the current increases. S al =1 indicates that chopper S1 is short-circuited; when in the negative voltage freewheeling range, the current decreases. S al If the current is 0, it can be determined that position transistor S2 is short-circuited; when in the on-state, the current drops to 0. S al If the current changes from 0 to -1 without any sudden change, it can be determined that the position transistor S2 is open-circuited; if the current changes to 0 when in the on-state, it can be determined that the chopper transistor S2 is open-circuited; if the current remains 0 when in the on-state, it can be determined that the phase is open-circuited. Step 6, Current change difference Δ i al The calculation can be performed using either a fixed frequency or a random frequency. Fixed frequency sampling means that the time between two samplings is fixed, while random frequency sampling only takes place when the switch state changes or when the switch state does not change for a long time.

2. The fault diagnosis method based on position tube current variation in soft chopper mode according to claim 1, characterized in that, The control method for the switched reluctance motor power converter described in step 1 can be current chopper control, voltage chopper control, or direct torque control, requiring only the presence of a chopper transistor and a position transistor.

3. The fault diagnosis method based on position tube current variation in soft chopper mode according to claim 1, characterized in that, The switching reluctance motor power converter control method described in step 1 adopts a soft chopper control method, which has excitation state, zero voltage freewheeling state and negative voltage freewheeling state.

4. The fault diagnosis method based on position tube current variation in soft chopper mode according to claim 1, characterized in that, The switching transistor type of the switched reluctance motor power converter mentioned in step 1 is one of the following: gate turn-off thyristor (GTO), bipolar junction transistor (BJT), power MOSFET, or insulated gate bipolar transistor (IGBT).

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