Detection system and method for motor current sensors

Abstract

A detection system and method for motor current sensor, four current sensors are arranged in a motor to detect three-phase current of the motor, the sum difference of the three-phase current and the difference of motor current parameters are calculated to detect the fault state of the four current sensors, the normal current sensor is selected to maintain the motor to continue to operate, and the abnormal current sensor is marked to issue a warning to improve production efficiency.

Description

Technical Field

[0001] The present invention relates to a motor current sensor, and more particularly to a detection system and method for detecting a motor current sensor failure and selecting a normal current sensor to maintain operation. Background Art

[0002] With the rapid development of robotics technology, factories are using robots to quickly and accurately perform processing, assembly, and manufacturing operations to improve factory production efficiency. However, the current control of robot motors seriously affects the robot's operating accuracy and safety.

[0003] like Figure 4 As shown, the background technology detects whether a motor is operating normally. Using a detection system, three current sensors S1, S2, and S3 are connected to the motor's A, B, and C current phases, respectively. The three current sensors S1, S2, and S3 detect the motor's A, B, and C currents one by one. The sum of the three currents detected by the three current sensors S1, S2, and S3 is then calculated to check whether the sum is zero, i.e., A+B+C=0. If the sum is zero, all three current sensors are operating normally. If the sum is not zero, one of the three current sensors is faulty. A faulty current sensor will produce an incorrect motor current signal. Using the motor current signal as a control signal can cause the robot to operate abnormally.

[0004] However, while the aforementioned prior art detection system can detect a current sensor failure after detecting an anomaly, the abnormal operation of the robot can severely impact its accuracy and safety, necessitating immediate shutdown of the robot for repair. This not only impacts factory production efficiency, but also prevents the system from determining which sensor failed, or even if the detection system itself has an error. Consequently, after the system is shut down, it takes time to locate the failed current sensor and perform repairs, increasing repair costs. Therefore, there are still urgent issues to be addressed regarding motor current sensor detection systems and methods. Summary of the Invention

[0005] The purpose of the present invention is to provide a detection system for a motor current sensor. By setting four current sensors on the motor to detect the three-phase current of the motor, a detection unit is used to detect and select two or three normal sensors for use, so as to maintain the normal and safe operation of the robot and improve production efficiency.

[0006] Another object of the present invention is to provide a method for detecting a motor current sensor. The method utilizes the difference between the sum of the three-phase currents and the difference between the motor current parameters to detect the operating status of the four current sensors. If a current sensor indicates an abnormality, an early warning is issued and the system is directly repaired after shutdown to maintain production efficiency.

[0007] Another object of the present application is to provide a motor current sensor detection method, when detecting two or more sensor abnormalities, unable to maintain safe operation, power off to stop the robot, to enhance safety.

[0008] To achieve the foregoing objects of the present application, the motor current sensor detection system of the present application, three current sensors are provided on the motor, respectively detecting the three-phase current of the motor, and an additional detection current sensor is provided to detect any phase current. The control system includes a receiving unit, a calculation unit and a detection unit, etc. The receiving unit receives the current signals detected by each phase current sensor of the motor. The calculation unit uses the current signals detected by each current sensor received by the receiving unit to check the operation state of each current sensor. The detection unit selects the normal current sensor for use according to the operation state of each current sensor detected by the calculation unit, and maintains the operation of the motor. The detection unit uses the calculation of the sum difference of the three-phase current of the motor detected by each current sensor and the motor current parameter difference to determine the normal or failure of each current sensor, and selects the normal current sensor for use.

[0009] The motor current sensor detection system of the present application, when the detection unit detects that four current sensors are operating normally, selects two or three normal current sensors for use, and uses the remaining normal current sensors as backup current sensors. When the detection unit detects that any of the current sensors in use is abnormal, the backup current sensor is replaced to allow the motor to continue to operate safely. The control system issues and displays a warning for the abnormal current sensor.

[0010] The motor current sensor detection method of the present application uses three current sensors to detect the first phase current A, the second phase current B, and the third phase current C of the motor, and uses an additional detection current sensor to detect the additional detection current C' of any phase of the motor. The current A, B, C and C' detected by each current sensor is read, the control angle θ of the motor is read, the first group sum = A+B+C and the second group sum = A+B+C' of the three-phase current of the motor are calculated, the absolute value of the first group sum is checked to be less than a preset threshold, and the absolute value of the second group sum is checked to be greater than a preset threshold, to determine that the detection additional detection current sensor is faulty, and the normal current sensor is used to allow the motor to continue to operate. A warning is issued for the failure of the additional detection current sensor. When the absolute value of the first group sum is less than the preset threshold and the absolute value of the second group sum is not greater than the preset threshold, it is determined that all four current sensors are normal, and the motor continues to operate.

[0011] The motor current sensor detection method of the present invention checks that the absolute value of the first group sum is not less than a preset threshold, and that the absolute value of the second group sum is less than the preset threshold. The current sensor detecting the third phase current is determined to be faulty. The current sensor detecting the first phase current A, the current sensor detecting the second phase current B, and the additional detection current sensor are used to allow the motor to continue operating and issue a warning of a fault in the current sensor detecting the third phase current C.

[0012] The detection method of the motor current sensor of the present invention checks that the absolute value of the first group sum is not less than a preset threshold, and the absolute value of the second group sum is not less than a preset threshold, and then uses the motor current conversion formula to calculate the first current parameter = I using the first phase current A and the second phase current B. β Cosθ-I α Sinθ, where I α =A,I β =(1 / 3 1 / 2 )*(A+2B), θ is the control angle of the motor, and the second current parameter is calculated by current-(B+C) and the second phase current B = I β Cosθ-I α Sinθ, where I α =-(B+C), I β =(1 / 3 1 / 2 )*(-(B+C)+2B), where θ is the motor control angle. When the first current parameter is greater than the second current parameter, and the absolute value of the first current parameter minus the second current parameter is greater than a preset threshold, the current sensor detecting first phase current A is determined to be faulty. The current sensor detecting second phase current B and the current sensor detecting third phase current C, or the current sensor detecting second phase current B and the additional detection current sensor, is used to maintain motor operation and issue a fault warning for the current sensor detecting first phase current A.

[0013] The detection method of the motor current sensor of the present invention checks that the first current parameter is not greater than the second current parameter, or that the absolute value of the first current parameter minus the second current parameter is not greater than a preset threshold. Then, if the first current parameter is less than the second current parameter and the absolute value of the second current parameter minus the first current parameter is greater than the preset threshold, it is determined that the current sensor detecting the second phase current B is faulty. The current sensor detecting the first phase current A and the current sensor detecting the third phase current C, or the current sensor detecting the first phase current A and the additional detection current sensor are used to allow the motor to continue operating while issuing a warning of a fault in the current sensor detecting the second phase current B.

[0014] The detection method of the motor current sensor of the present invention checks that a first current parameter is not greater than a second current parameter, or that the absolute value of the first current parameter minus the second current parameter is not greater than a preset threshold, and then checks that the first current parameter is not less than the second current parameter, or that the absolute value of the second current parameter minus the first current parameter is not greater than the preset threshold. In this case, it is determined that more than two current sensors have failed, the power supply is turned off, the motor operation is stopped, and a fault warning is issued. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the functional blocks of the motor current sensor detection system of the present invention.

[0016] Figure 2 This is a flow chart of the motor current sensor detection operation of the present invention.

[0017] Figure 3 This is the K-branch flow chart of the motor current sensor detection operation of the present invention.

[0018] Figure 4 Schematic diagram of a motor current sensor detection system in the background art.

[0019] Specific implementation

[0020] Regarding the technical means and effects adopted by the present invention to achieve the above-mentioned objectives, preferred embodiments are given and described below with reference to the accompanying drawings.

[0021] like Figure 1 FIG. 2 is a functional block diagram of the motor current sensor detection system of the present invention. Figure 1 In the detection system 1 of the present invention, three current sensors S1, S2, and S3 are respectively installed for the three phases A, B, and C of motor 2 to detect the three phase currents of motor 2. A fourth current sensor S4 is added to detect any phase current. For example, the first current sensor S1 detects the first phase current A of motor 2 and generates a first detection current signal. The second current sensor S2 detects the second phase current B of motor 2 and generates a second detection current signal. The third current sensor S3 detects the third phase current C of motor 2 and generates a third detection current signal. The fourth current sensor S4 is connected after the third current sensor S3 and similarly detects the third phase current C of motor 2. To distinguish it, it is represented as the fourth detection current signal C'. The sum of the three phase currents A, B, and C of motor 2 is zero under normal conditions, that is, A + B + C = 0. However, if a fault occurs in any of the four current sensors S1, S2, S3, and S4, the sum of the three phase currents A, B, and C of motor 2 will not be zero.

[0022] The detection system 1 of the present invention further includes a control system 3, which is provided with a receiving unit 4, a computing unit 5 and a detection unit 6, wherein the receiving unit 4 receives the detection current signals of the first current sensor S1, the second current sensor S2, the third current sensor S3 and the additional detection current sensor S4, and the computing unit 5 uses the detection current signals of each current sensor received by the receiving unit 4 to check the operating status of the four current sensors S1, S2, S3 and S4. The detection unit 6 uses the computing unit 5 to check the operating status of the four current sensors S1, S2, S3 and S4, and then determines whether the four current sensors S1, S2, S3 and S4 are normal or faulty. When the detection unit 6 detects that the four current sensors S1, S2, S3 and S4 are operating normally, two or three normal current sensors can be selected for use, and the remaining one or two normal current sensors can be used as backup current sensors. When the detection unit 6 detects that any of the normal current sensors in use is malfunctioning, it will immediately replace it with a spare current sensor, allowing the motor 2 to continue to maintain safe and normal operation. The control system 6 will issue and display a malfunctioning current sensor warning, so there is no need to stop the machine. After the work is completed, the malfunctioning current sensor can be directly repaired, thereby avoiding affecting production efficiency.

[0023] When the detection unit 6 of the detection system 1 of the present invention determines whether the four current sensors S1, S2, S3, and S4 are normal or faulty, the two current sensors S3 and S4 that detect the same-phase current of the motor 2 are used to distinguish the sums of the three-phase currents A, B, C and A, B, C' of the motor 2, i.e., the first sum D1 = A + B + C and the second sum D2 = A + B + C'. The difference calculation is performed to first check whether the third current sensor S3 and the additional detection current sensor S4 of the third phase current C and the additional detection current C' of the motor 2 are faulty. After checking that the two current sensors S3 and S4 are normal, the two-phase currents A and B of the motor 2 are used to calculate the first current parameter P1 of the motor 2 according to the conversion formula of the motor 2 current, i.e., P1 = I β Cosθ-I α Sinθ, where I α =A,I β =(1 / 31 / 2)*(A+2B), θ is the control angle of the motor. Since the sum of the three-phase current of the motor is zero, that is, A+B+C=0, A=-(B+C), that is, A can be replaced by -(B+C). Using -(B+C) and B, we can obtain the second current parameter P2=I β Cosθ-I α Sinθ, where I α =-(B+C), I β=(1 / 31 / 2)*(-(B+C)+2B), where θ is the control angle of the motor. The difference between the current parameters P1 and P2 of motor 2 is then calculated to detect whether the first current sensor S1 and the second current sensor S2 are faulty.

[0024] Please also refer to Figure 2 and Figure 3 , Figure 2 This is a flow chart of the motor current sensor detection operation of the present invention. Figure 3 This is the K-branch flow chart of the motor current sensor detection operation of the present invention. Figure 2 The detailed steps of the motor current sensor detection process of the present invention are as follows: Step T101: Detection begins. Three current sensors S1, S2, and S3 are used to detect the motor's three-phase currents A, B, and C, and one additional current sensor is used to detect the additional current C' of any motor phase. Step T102: The four detected currents A, B, C, and C' of the motor current sensors S1, S2, S3, and S4 are read. Step T103: The motor control angle θ is read. Step T104: The first sum D1 = A + B + C and the second sum D2 = A + B + C' of the motor's three-phase currents are calculated. Step T105: Whether the absolute value of the first sum D1 is less than a preset threshold Z. If the absolute value of the first sum D1 is less than the preset threshold Z, step T106: Whether the absolute value of the second sum D2 is greater than the preset threshold Z is checked. If the absolute value of the second group sum D2 is not greater than the preset threshold Z, then the process proceeds to step T107, indicating that the four current sensors S1, S2, S3, and S4 are all normal. Then, the process proceeds to step T108, allowing the motor to continue operating. If the absolute value of the second group sum D2 is greater than the preset threshold Z in step T106, the process proceeds to step T109, determining that the detected enhanced current C' is incorrect and that the corresponding enhanced current sensor S4 is faulty. Then, in step T110, the three motor current sensors S1, S2, and S3 are used to allow the motor to continue operating. Then, the process proceeds to step T111, issuing a warning indicating that the enhanced current sensor S4 is faulty.

[0025] In step T105, if the absolute value of the first sum D1 is not less than the preset threshold Z, the process proceeds to step T112 to check whether the absolute value of the second sum D2 is less than the preset threshold Z. If the absolute value of the second sum D2 is less than the preset threshold Z, the process proceeds to step T113, where it is determined that the third phase current C is incorrectly detected, indicating a fault in the third current sensor S3. Next, in step T114, the motor's first current sensor S1, second current sensor S2, and additional current sensor S4 are used to maintain motor operation. The process then proceeds to step T115, issuing a warning regarding a fault in the third current sensor S3. In step T112, if the absolute value of the second sum D2 is not less than the preset threshold Z1, the process proceeds to step T113, entering the K-branch process for the motor current sensor detection process.

[0026] Figure 3 After entering the K-branch process of the motor current sensor detection operation, in step T201, the motor current conversion formula is used to calculate the first current parameter P1 from the first phase current A and the second phase current B. The second current parameter P2 is calculated using the current -(B+C) and the second phase current B. In step T202, it is checked whether the first current parameter P1 is greater than the second current parameter P2. It is also checked whether the absolute value of the first current parameter P1 minus the second current parameter P2 is greater than a preset threshold Z. If the first current parameter P1 is greater than the second current parameter P2, and the absolute value of the first current parameter P1 minus the second current parameter P2 is greater than the preset threshold Z, the process proceeds to step T203, where it is determined that the first phase current A is detected incorrectly, indicating a failure of the corresponding first current sensor S1. Next, in step T204, the second current sensor S2 and the third current sensor S3 of the motor are used, using currents B, C, and -(B+C), or the second current sensor S2 and the additional detection current sensor S4 are used, using currents B, C', and -(B+C'), to allow the motor to continue operating. The process then proceeds to step T205, where a warning is issued indicating a failure of the first current sensor S1.

[0027] In step T202, if the first current parameter P1 is not greater than the second current parameter P2, or if the absolute value of the first current parameter P1 minus the second current parameter P2 is not greater than a preset threshold, the process proceeds to step T206. Furthermore, if the first current parameter P1 is less than the second current parameter P2, and the absolute value of the second current parameter P2 minus the first current parameter P1 is greater than a preset threshold Z, the process proceeds to step T207, where it is determined that the second phase current B is incorrectly detected, indicating that the second current sensor S2 is faulty. Subsequently, in step T208, the motor's first current sensor S1 and third current sensor S3 are used, utilizing currents A, C, and -(A+C), or the first current sensor S1 and the additional detection current sensor S4 are used, utilizing currents A, C', and -(A+C'), to allow the motor to continue operating. The process then proceeds to step T209, where a warning is issued indicating a fault in the second current sensor S2. In step T206, if the first current parameter P1 is not less than the second current parameter P2, or the absolute value of the second current parameter P2 minus the first current parameter P1 is not greater than the preset threshold Z, then step T210 is entered. If there are more than two faults in the motor's current sensors, the power supply is immediately turned off to stop the motor operation, and then step T211 is entered to issue a fault warning.

[0028] The aforementioned embodiment of the present invention configures the additional current sensor to detect the current of the third phase of the motor. Based on the aforementioned description, it can be inferred that configuring the additional current sensor to detect the current of the first or second phase of the motor can achieve the objectives of the present invention. Therefore, the present invention includes, but is not limited to, configuring the additional current sensor to detect the current of the third phase of the motor. Configuring the additional current sensor to detect the current of the first or second phase of the motor also falls within the scope of the present invention. Furthermore, the conversion formula for calculating motor current parameters can take many forms. The aforementioned embodiment of the present invention uses only one formula as an example, and the other formulas can be applied by analogy to achieve the objectives of the present invention. Similarly, the present invention includes, but is not limited to, the formulas used as examples.

[0029] Therefore, the detection system and method of the motor current sensor of the present invention can construct a detection system by setting four current sensors in the motor to detect the three-phase current of the motor, and use the difference between the total three-phase current and the difference between the motor current parameters to detect the fault status of the four current sensors, and issue an early warning if the abnormal current sensor is marked. After the machine is shut down, it is directly repaired and two or three normal sensors are selected for use to maintain the normal and safe operation of the robot. When more than two sensors are detected to be abnormal and safe operation cannot be maintained, the power is turned off and the robot is stopped, thereby achieving the invention purpose of improving production efficiency and enhancing safety.

[0030] The above description is only for the convenience of explaining the preferred embodiments of the present invention. The scope of the present invention is not limited to these preferred embodiments. Any changes made according to the present invention, without departing from the spirit of the present invention, are within the scope of the patent application of the present invention.

[0031]

Explanation of symbols

[0032] 1 Detection system

[0033] 2 motors

[0034] 3 Control System

[0035] 4 Receiving unit

[0036] 5 Computational Units

[0037] 6 Control System

[0038] 7 Detection unit

[0039] A, B, C three-phase current

[0040] S1, S2, S3 current sensors

[0041] S4 additional detection current sensor

Claims

1. A detection system for a motor current sensor, comprising: The motor is equipped with three current sensors to detect the three-phase current of the motor respectively, and an additional current sensor is also provided to detect the current of any phase; The control system includes a receiving unit, a computing unit, and a detecting unit. The receiving unit receives current signals detected by current sensors of each phase of the motor. The computing unit uses the current signals detected by each current sensor received by the receiving unit to check the operating status of each current sensor. The detecting unit selects a normal current sensor for use based on the operating status of each current sensor detected by the computing unit to maintain motor operation. in, The detection unit uses three current sensors to detect the first phase current A, second phase current B, and third phase current C of the motor, and uses one additional detection current sensor to detect the additional detection current C' of any phase of the motor. It determines whether the additional detection current sensor is normal or faulty, and selects the normal current sensor for use. Among them, using three current sensors to detect the first phase current A, second phase current B, and third phase current C of the motor and using one additional detection current sensor to detect the additional detection current C' of any phase of the motor to determine whether the additional detection current sensor is normal or faulty and select the normal current sensor for use includes: When the absolute value of the first sum of the three-phase current of the motor is not less than the preset threshold, and the absolute value of the second sum is not less than the preset threshold, the first current parameter = I is calculated using the motor current conversion formula using the first phase current A and the second phase current B. β Cosθ-I α Sinθ, where I α =A, I β =(1 / 3 1 / 2 )*(A+2B), θ is the control angle of the motor, and the second current parameter is calculated by current-(B+C) and the second phase current B = I β Cosθ-I α Sinθ, where I α =-(B+C), I β =(1 / 3 1 / 2 )*(-(B+C)+2B), θ is the control angle of the motor; and The normal or faulty current sensor is determined based on the comparison results among the first current parameter, the second current parameter and the preset threshold value, so as to select a normal current sensor for use or turn off the power to stop the motor operation, and issue a fault warning.

2. The motor current sensor detection system as claimed in claim 1, wherein when the detection unit detects that four current sensors are operating normally, two or three normal current sensors are selected for use, and the remaining normal current sensors are used as backup current sensors.

3. The motor current sensor detection system as claimed in claim 2, wherein when the detection unit detects that any of the current sensors in use is malfunctioning, a spare current sensor is used to replace it, allowing the motor to continue to operate safely.

4. The detection system of the motor current sensor as claimed in claim 3, wherein the control system issues and displays an abnormal current sensor warning.

5. A method for detecting a motor current sensor, comprising: Using three current sensors to detect the first phase current A, second phase current B, and third phase current C of the motor, and using one additional detection current sensor to detect the additional detection current C' of any phase of the motor; Read the currents A, B, C, and C' detected by each current sensor; Read the motor control angle θ; Calculate the first sum of the three-phase currents of the motor = A+B+C and the second sum = A+B+C'; Check that the absolute value of the first group's sum is less than a preset threshold; Checking that the absolute value of the second group sum is greater than a preset threshold; Determine and detect the fault of the additional detection current sensor; Use a normal current sensor to allow the motor to continue operating; Issue an early warning of additional current sensor failure. in, When the absolute value of the first sum of the three-phase current of the motor is not less than the preset threshold, and the absolute value of the second sum is not less than the preset threshold, the motor current conversion formula is used to calculate the first current parameter = I using the first phase current A and the second phase current B. β Cosθ-I α Sinθ, where I α =A,I β =(1 / 3 1 / 2 )*(A+2B), θ is the control angle of the motor, and the second current parameter is calculated by current-(B+C) and the second phase current B = I β Cosθ-I α Sinθ, where I α =-(B+C), I β =(1 / 3 1 / 2 )*(-(B+C)+2B), θ is the control angle of the motor; and based on the comparison results among the first current parameter, the second current parameter and the preset threshold value, it is judged whether the additional current sensor is normal or faulty, so as to select the normal current sensor to use or turn off the power to stop the motor operation, and issue a fault warning.

6. The motor current sensor detection method of claim 5 , wherein when the absolute value of the first set of sums is less than a preset threshold and the absolute value of the second set of sums is not greater than a preset threshold, it is determined that all four current sensors are normal and the motor can continue to operate.

7. The motor current sensor detection method of claim 5 , wherein when the absolute value of the first set of sums is not less than a preset threshold and the absolute value of the second set of sums is less than a preset threshold, the current sensor detecting the third phase current C is determined to be faulty, and the current sensor detecting the first phase current A, the current sensor detecting the second phase current B, and the additional detection current sensor are used to allow the motor to continue operating and issue a warning indicating a fault in the current sensor detecting the third phase current C.

8. The motor current sensor detection method of claim 5 , wherein when the first current parameter is greater than the second current parameter and the absolute value of the first current parameter minus the second current parameter is greater than a preset threshold, the current sensor detecting the first phase current A is determined to be faulty, and the current sensor detecting the second phase current B and the current sensor detecting the third phase current C, or the current sensor detecting the second phase current B and the additional detection current sensor, are used to allow the motor to continue operating and issue a warning indicating a fault in the current sensor detecting the first phase current A.

9. The motor current sensor detection method of claim 5, wherein if the first current parameter is not greater than the second current parameter, or if the absolute value of the first current parameter minus the second current parameter is not greater than a preset threshold, and if the first current parameter is less than the second current parameter, and the absolute value of the second current parameter minus the first current parameter is greater than the preset threshold, then the current sensor detecting the second phase current B is determined to be faulty, and the current sensor detecting the first phase current A and the current sensor detecting the third phase current C, or the current sensor detecting the first phase current A and the additional detection current sensor, are used to allow the motor to continue operating, while a warning is issued indicating a fault in the current sensor detecting the second phase current B.

10. The method for detecting a motor current sensor as claimed in claim 5, wherein when a first current parameter is checked to be not greater than a second current parameter, or when an absolute value of the first current parameter minus the second current parameter is checked to be not greater than a preset threshold, and then a check is made to see if the first current parameter is not less than the second current parameter, or when an absolute value of the second current parameter minus the first current parameter is not greater than a preset threshold, it is determined that two or more current sensors are faulty, the power is turned off to stop the motor operation, and a fault warning is issued.

11. A detection system for a motor current sensor, comprising: The motor is equipped with three current sensors to detect the three-phase current of the motor respectively, and an additional current sensor is provided to detect the current of any phase; The control system uses three current sensors to detect the first phase current A, second phase current B, and third phase current C of the motor, and uses an additional detection current sensor to detect the additional detection current C' of any phase of the motor. It determines whether the additional detection current sensor is normal or faulty, and selects the normal current sensor for use. in, Using three current sensors to detect the first phase current A, second phase current B, and third phase current C of the motor and using one additional current sensor to detect the additional current C' of any phase of the motor to determine whether the additional current sensor is normal or faulty and select the normal current sensor to use includes: When the absolute value of the first sum of the three-phase current of the motor is not less than the preset threshold, and the absolute value of the second sum is not less than the preset threshold, the first current parameter = I is calculated using the motor current conversion formula using the first phase current A and the second phase current B. β Cosθ-I α Sinθ, where I α =A, I β =(1 / 3 1 / 2 )*(A+2B), θ is the control angle of the motor, and the second current parameter is calculated by current-(B+C) and the second phase current B = I β Cosθ-I α Sinθ, where I α =-(B+C), I β =(1 / 3 1 / 2 )*(-(B+C)+2B), θ is the control angle of the motor; and The normal or faulty current sensor is determined based on the comparison results among the first current parameter, the second current parameter and the preset threshold value, so as to select a normal current sensor for use or turn off the power to stop the motor operation, and issue a fault warning.

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