Circuit and method for sampling and self-adaptive grading variable range of motor insulation resistance

Abstract

The invention discloses a circuit and a method for adaptive stepping range variation of motor insulation resistance sampling, aiming at the requirement of automatic testing of stator insulation resistance of a shutdown alternating current motor, corresponding different sampling resistors are automatically switched according to different interval gears where the insulation resistance is located, so that the sampling voltage is adaptively maintained within a certain range, and the test accuracy is improved. According to the invention, sampling signals divided by sampling resistors in a wide range of insulation resistors can be reasonably amplified to an analog signal allowable range of a DSP ADC module with high precision, and high-precision calculation of the insulation resistors is realized in a DSP program according to the sampling signals and sampling resistance values. According to the technical scheme and the specific circuit and method provided by the invention, the circuit and method have the advantages that the structure is simple, the cost is low, and the circuit and method can meet the requirement of a shutdown AC motor wide-range insulation resistance high-precision test based on additional DC voltage.

Description

Technical Field

[0001] The invention relates to a circuit and a method for sampling an adaptive step-by-step variable range of motor insulation resistance, belonging to the technical field of motor insulation resistance detection. Background Art

[0002] At present, the insulation resistance measurement of AC motor stator winding can reflect the insulation treatment quality of its winding, as well as insulation moisture and surface pollution. Monitoring the insulation resistance of AC motor stator winding is one of the key technologies to improve its safe and stable operation level.

[0003] As a non-invasive monitoring method, the existing technology connects an additional DC voltage source to the series circuit of the main insulation and sampling resistor of the shut-down AC motor, and calculates the insulation resistance value of the AC motor according to the voltage divider value on the sampling resistor. This is a technology for realizing the stator insulation resistance test of the shut-down AC motor.

[0004] The decrease in the insulation resistance level of the AC motor stator is generally a long-term process. In the existing technology, when testing the insulation resistance of the stator winding of the AC motor that is out of service, a sampling resistor with a fixed resistance is used to sample the insulation resistance, which has the following problems:

[0005] 1. For motors whose stator insulation has not yet degraded, the insulation resistance is large, the voltage-dividing sampling signal of the sampling resistor is small, and noise interference will affect the conversion accuracy of the insulation resistance sampling signal.

[0006] 2. For motors with serious stator insulation degradation, the insulation resistance is small and the voltage-divided sampling signal of the sampling resistor is large. Not only is the output of the amplifier easily saturated, but the analog signal input to the DSP ADC module may also exceed the allowable range.

[0007] In view of these shortcomings, those skilled in the art urgently need to improve the existing motor insulation resistance sampling technology. Summary of the invention

[0008] Purpose: In order to overcome the difficulties in the prior art in high-precision testing of the stator insulation resistance of a shut-down AC motor mentioned in the background technology, the present invention provides a circuit and method for sampling the insulation resistance of a motor with an adaptive step-by-step variable range.

[0009] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

[0010] In the first aspect, a circuit for sampling the insulation resistance of a motor and adaptively stepping the variable range includes: a DC voltage source, n sampling resistor series branches with different resistance values, a first voltage comparator, a second voltage comparator, an AND gate, a controller, a first controllable potentiometer, a second controllable potentiometer, n-1 relays, where n is an integer, and an isolation and amplification circuit.

[0011] Wherein, the DC voltage source provides power for measuring insulation resistance.

[0012] The front end of the n sampling resistor series branches with different resistance values ​​is used to be connected to a DC voltage source through an insulation resistor, and the rear end of the n sampling resistor series branches with different resistance values ​​is grounded, wherein the resistance values ​​of the n sampling resistors increase in sequence, and the resistance value of each sampling resistor belongs to a different resistance value range of the insulation resistance.

[0013] The non-inverting input terminal of the first voltage comparator is connected to the moving contact of the first controllable potentiometer, and the inverting input terminal of the first voltage comparator is used to connect to the voltage sampling terminal of the insulation resistor.

[0014] The inverting input terminal of the second voltage comparator is connected to the moving contact of the second controllable potentiometer, and the non-inverting input terminal of the second voltage comparator is used to connect to the voltage sampling terminal of the insulation resistor.

[0015] The output end of the first voltage comparator is connected to the first input end of the AND gate, and the output end of the first voltage comparator is also connected to the first data end of the controller through the conversion circuit.

[0016] The output terminal of the second voltage comparator is connected to the second input terminal of the AND gate, and the output terminal of the second voltage comparator is also connected to the third data terminal of the controller through the conversion circuit.

[0017] The output end of the AND gate is connected to the second data end of the controller through a conversion circuit.

[0018] The first data output terminal of the controller is connected to the first relay through a driving circuit, the second data output terminal of the controller is connected to the second relay through a driving circuit, and so on, the n-1th data output terminal of the controller is connected to the n-1th relay through a driving circuit.

[0019] The normally open contacts of n-1 relays are all connected in parallel to the first sampling resistor.

[0020] The normally closed contact of the first relay is connected in parallel to the second sampling resistor, the normally closed contact of the second relay is connected in parallel to the third sampling resistor, and so on, the normally closed contact of the n-1th relay is connected in parallel to the nth sampling resistor.

[0021] The first input end of the isolation and amplification circuit is connected to the front end of the series branch of n sampling resistors with different resistance values, the second input end of the isolation and amplification circuit is connected to the rear end of the series branch of n sampling resistors with different resistance values, and the output end of the isolation and amplification circuit is connected to the fourth data end of the controller through the ADC.

[0022] As a preferred solution, the conversion circuit includes a coupler and a level conversion circuit, which is used to convert the output signal of the voltage comparator or the AND gate into a digital signal.

[0023] As a preferred solution, the coupler is isolated by a photoelectric coupler, and the level conversion circuit is isolated by a phototransistor.

[0024] As a preferred solution, the driving circuit includes: an inverter, a transistor, the data output end of the controller is connected to the input end of the inverter, the output end of the inverter is connected to the base of the transistor, the collector of the transistor is connected to the working power supply through a relay, and the emitter of the transistor is grounded.

[0025] As a preferred solution, the controller adopts DSP, and the DSP includes: an input / output multiplexer, and the input / output multiplexer includes three input pins and n-1 output pins.

[0026] As a preferred solution, the DSP includes: an ADC module, which is used to be connected to the output end of the isolation and amplification circuit.

[0027] In a second aspect, a method for measuring a circuit for sampling an insulation resistance of a motor with an adaptive step-by-step variable range is provided, specifically comprising:

[0028] The controller sets all n-1 data output terminals to 1, sets the sampling resistor mark f=0, and the n-1 relays are not powered. The first sampling resistor is connected to the test loop.

[0029] The moving contact of the first controllable potentiometer is set so that the voltage at the non-inverting input terminal of the first voltage comparator is the upper limit of the sampling voltage in the first interval.

[0030] The moving contact of the second controllable potentiometer is set so that the voltage at the inverting input terminal of the second voltage comparator is the lower limit of the sampling voltage in the first interval.

[0031] The collected sampling voltage of the insulation resistance is input into the inverting input terminal of the first voltage comparator and the non-inverting input terminal of the second voltage comparator respectively.

[0032] Read the level states of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the first interval, read the sampling signal of the first sampling resistor voltage division, calculate the insulation resistance, and return to the main program; if the first data terminal = 0, it indicates that the insulation resistance is less than the lower limit resistance value of the first interval, display the information and return to the main program. If the second data terminal = 0 and the first data terminal = 1, it indicates that the insulation resistance is greater than the upper limit resistance value of the first interval and is not in the first interval, the first data output terminal is set to 0, the first relay is energized, the first sampling resistor is cut off from the measurement circuit, the second sampling resistor is connected to the measurement circuit, and the sampling resistor flag f = 1 is set.

[0033] When the sampling resistor mark f=1:

[0034] The moving contact of the first controllable potentiometer is set so that the voltage at the non-inverting input terminal of the first voltage comparator is the upper limit of the sampling voltage in the second interval.

[0035] The moving contact of the second controllable potentiometer is set so that the voltage at the inverting input terminal of the second voltage comparator is the lower limit of the sampling voltage in the second interval.

[0036] Read the level states of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the second interval, read the sampling signal of the second sampling resistor voltage division, calculate the insulation resistance, and return to the main program; if the second data terminal = 0, it means that the insulation resistance is greater than the upper limit resistance value of the second interval and is not in the second interval, the second data output terminal is set to 0, the second relay is energized, the second sampling resistor is cut off from the measurement circuit, the third sampling resistor is connected to the measurement circuit, and the sampling resistor mark f=2 is set at the same time.

[0037] By analogy, when the sampling resistor mark f=n-1, the n-1th data output terminal is set to 0, the n-1th relay is energized, the n-1th sampling resistor is cut off from the measurement circuit, the nth sampling resistor is connected to the measurement circuit, and the sampling resistor mark f=n-1 is set at the same time.

[0038] Read the level status of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the nth interval, read the sampling signal of the nth sampling resistor voltage divider, calculate the insulation resistance, and return to the main program; if the third data terminal = 0, it means that the insulation resistance is greater than the upper limit resistance value of the nth interval, display this information and return to the main program.

[0039] As a preferred solution, when the sampling resistance mark is increased by 1, the delay time is t.

[0040] As a preferred solution, a sampling signal of sampling resistor voltage division is calculated based on a front-end signal of a sampling resistor series branch with n different resistance values ​​and a back-end signal of a sampling resistor series branch with n different resistance values.

[0041] As a preferred solution, the upper limit of the sampling voltage in the nth interval is , the calculation formula is as follows:

[0042]

[0043] in, represents the voltage of the DC voltage source, represents the resistance value of the nth resistor, Indicates the lower limit of resistance in the nth interval.

[0044] The lower limit of the sampling voltage in the nth interval , the calculation formula is as follows:

[0045]

[0046] in, Indicates the upper limit of the resistance in the nth interval.

[0047] Beneficial effect: The circuit and method for adaptive step-by-step variable range of motor insulation resistance sampling provided by the present invention adopt an additional DC voltage source to measure the insulation resistance of a shut-down AC motor, and adopt an adaptive step-by-step variable range circuit for insulation resistance sampling composed of a window voltage comparator composed of an integrated voltage comparator, a relay, a digital signal processor (DSP), etc. The method automatically switches the corresponding different sampling resistors according to the different intervals where the insulation resistance is located, thereby adaptively maintaining its divided voltage sampling voltage within a certain range, and obtains the sampling resistor divided voltage sampling signal and the sampling resistance value marking signal within the normal working range of the DSP digital / analog converter (ADC) module through isolation and amplification processing, thereby realizing high-precision calculation of the insulation resistance of the AC motor in the DSP program through the acquired sampling resistance value and its divided voltage sampling signal value.

[0048] The technical solution and its specific circuit and method proposed in the present invention have the advantages of simple structure, low cost, and adaptability to the high-precision testing of the insulation resistance of a wide range of out-of-service AC motors based on an additional DC voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The present invention is a schematic structural diagram of an embodiment of a circuit for sampling the insulation resistance of a motor and adaptively adjusting the variable range in steps.

[0050] Figure 2 The present invention is a flow chart of a measurement method of a circuit for sampling the insulation resistance of a motor with an adaptive step variable range. DETAILED DESCRIPTION

[0051] The following is a clear and complete description of the technical solutions in the examples of the present invention in conjunction with the accompanying drawings in the examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the protection scope of the present invention.

[0052] The present invention will be further described below in conjunction with specific embodiments.

[0053] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0054] Embodiment 1:

[0055] This embodiment introduces a circuit for sampling the insulation resistance of a motor with an adaptive step-by-step variable range, which specifically includes: a DC voltage source, n sampling resistors with different resistance values ​​connected in series, a first voltage comparator, a second voltage comparator, an AND gate, a controller, a first controllable potentiometer, a second controllable potentiometer, and n-1 relays, where n is an integer.

[0056] Wherein, the DC voltage source provides power for measuring insulation resistance.

[0057] The front end of the n sampling resistor series branches with different resistance values ​​is used to be connected to a DC voltage source through an insulation resistor, and the rear end of the n sampling resistor series branches with different resistance values ​​is grounded, wherein the resistance values ​​of the n sampling resistors increase in sequence, and the resistance value of each sampling resistor belongs to a different resistance value range of the insulation resistance.

[0058] The non-inverting input terminal of the first voltage comparator is connected to the moving contact of the first controllable potentiometer, and the inverting input terminal of the first voltage comparator is used to connect to the voltage sampling terminal of the insulation resistor.

[0059] The inverting input terminal of the second voltage comparator is connected to the moving contact of the second controllable potentiometer, and the non-inverting input terminal of the second voltage comparator is used to connect to the voltage sampling terminal of the insulation resistor.

[0060] The output end of the first voltage comparator is connected to the first input end of the AND gate, and the output end of the first voltage comparator is also connected to the first data end of the controller through the conversion circuit.

[0061] The output terminal of the second voltage comparator is connected to the second input terminal of the AND gate, and the output terminal of the second voltage comparator is also connected to the third data terminal of the controller through the conversion circuit.

[0062] The output end of the AND gate is connected to the second data end of the controller through a conversion circuit.

[0063] The first data output terminal of the controller is connected to the first relay through a driving circuit, the second data output terminal of the controller is connected to the second relay through a driving circuit, and so on, the n-1th data output terminal of the controller is connected to the n-1th relay through a driving circuit.

[0064] The normally open contacts of n-1 relays are all connected in parallel to the first sampling resistor.

[0065] The normally closed contact of the first relay is connected in parallel to the second sampling resistor, the normally closed contact of the second relay is connected in parallel to the third sampling resistor, and so on, the normally closed contact of the n-1th relay is connected in parallel to the nth sampling resistor.

[0066] It also includes: an isolation and amplification circuit, wherein the first input end of the isolation and amplification circuit is connected to the front end of a series branch of n sampling resistors with different resistance values, the second input end of the isolation and amplification circuit is connected to the rear end of the series branch of n sampling resistors with different resistance values, and the output end of the isolation and amplification circuit is connected to the fourth data end of the controller through the ADC.

[0067] Furthermore, the conversion circuit includes a coupler and a level conversion circuit, which are used to convert the output signal of the voltage comparator or the AND gate into a digital signal.

[0068] Furthermore, the coupler is isolated by a photoelectric coupler, and the level conversion circuit is isolated by a phototransistor.

[0069] Furthermore, the driving circuit includes: an inverter, a transistor, the data output end of the controller is connected to the input end of the inverter, the output end of the inverter is connected to the base of the transistor, the collector of the transistor is connected to the working power supply through a relay, and the emitter of the transistor is grounded.

[0070] Furthermore, the controller adopts a DSP (Digital Signal Processor), and the DSP includes: an input / output multiplexer (GPIO), and the input / output multiplexer includes three input pins and n-1 output pins.

[0071] Furthermore, the DSP includes: an ADC module, which is used to be connected to the output end of the isolation and amplification circuit.

[0072] Embodiment 2:

[0073] This embodiment introduces an embodiment of a circuit for sampling an insulation resistance of a motor and adaptively dividing the variable range, such as Figure 1As shown in the figure, five different insulation resistance intervals of the shut-down AC motor are preset, and five sampling resistors with different resistance values ​​are connected in series in the circuit of the additional DC voltage source to measure the insulation resistance of the motor. Among them, n=5 sampling resistors R0, R1, R2, R3, and R4 with different resistance values ​​are connected in series in the additional DC voltage source (+Vs) to measure the insulation resistance R of the AC motor. x In the circuit, and .

[0074] Adjust the moving contacts of the first potentiometer W1 and the second potentiometer W2 respectively, so that the voltage at the non-inverting input terminal of the first integrated voltage comparator is the set sampling voltage upper limit value V ref_H , so that the voltage at the inverting input terminal of the second integrated voltage comparator is the set sampling voltage lower limit value V ref_L .

[0075] R H , R L They are pull-up resistors of the first integrated voltage comparator and the second integrated voltage comparator respectively.

[0076] The output signals of the first integrated voltage comparator, the second integrated voltage comparator and the integrated AND gate are converted into signals within the normal working range of the DSP general input / output multiplexer (GPIO) through photoelectric coupler isolation and level conversion circuit and input to the three input pins I1, I2, and I3 of the GPIO. The four output pins O1, O2, O3, and O4 of the GPIO drive the contacts of the corresponding relays through inverters and transistor amplifier circuits respectively.

[0077] There are four DC relays J1, J2, J3, and J4, and the normally open contacts of the four DC relays J1, J2, J3, and J4 are connected in parallel to the sampling resistor R0, the normally closed contact of the DC relay J1 is connected in parallel to the sampling resistor R1, the normally closed contact of the DC relay J2 is connected in parallel to the sampling resistor R2, the normally closed contact of the DC relay J3 is connected in parallel to the sampling resistor R3, and the normally closed contact of the DC relay J4 is connected in parallel to the sampling resistor R4.

[0078] By setting the level of the corresponding GPIO output pin, driving and cutting off the corresponding relay, and adaptively selecting a sampling resistor in the corresponding interval through the corresponding normally open contacts and normally closed contacts of the n-1 DC relays, the DSP insulation resistance signal acquisition program reads the GPIO input pin level state, determines the interval where the insulation resistance is located, and cuts off the remaining n-1 sampling resistors, thereby adaptively maintaining the divided voltage sampling voltage of the sampling resistor within a certain range, and after isolation and amplification processing, obtains the sampling signal of the sampling resistor divided voltage within the normal working range of the DSP ADC module. The DSP calculates the insulation resistance of the AC motor through the sampling signal of the sampling resistor divided voltage.

[0079] Furthermore, the first integrated voltage comparator and the second integrated voltage comparator are both open collector voltage comparators.

[0080] Furthermore, the model of DSP is TMS320F28335.

[0081] Embodiment 3:

[0082] This embodiment introduces a measurement method of a circuit for sampling an insulation resistance of a motor with an adaptive step-by-step variable range according to Embodiment 1, which specifically includes:

[0083] The controller sets all n-1 data output terminals to 1, sets the sampling resistor mark f=0, and the n-1 relays are not powered. The first sampling resistor is connected to the test loop.

[0084] The moving contact of the first controllable potentiometer is set so that the voltage at the non-inverting input terminal of the first voltage comparator is the upper limit of the sampling voltage in the first interval.

[0085] The moving contact of the second controllable potentiometer is set so that the voltage at the inverting input terminal of the second voltage comparator is the lower limit of the sampling voltage in the first interval.

[0086] The collected sampling voltage of the insulation resistance is input into the inverting input terminal of the first voltage comparator and the non-inverting input terminal of the second voltage comparator respectively.

[0087] Read the level states of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the first interval, read the sampling signal of the first sampling resistor voltage division, calculate the insulation resistance, and return to the main program; if the first data terminal = 0, it indicates that the insulation resistance is less than the lower limit resistance value of the first interval, display the information and return to the main program. If the second data terminal = 0 and the first data terminal = 1, it indicates that the insulation resistance is greater than the upper limit resistance value of the first interval and is not in the first interval, the first data output terminal is set to 0, the first relay is energized, the first sampling resistor is cut off from the measurement circuit, the second sampling resistor is connected to the measurement circuit, and the sampling resistor flag f = 1 is set.

[0088] When the sampling resistor mark f=1:

[0089] The moving contact of the first controllable potentiometer is set so that the voltage at the non-inverting input terminal of the first voltage comparator is the upper limit of the sampling voltage in the second interval.

[0090] The moving contact of the second controllable potentiometer is set so that the voltage at the inverting input terminal of the second voltage comparator is the lower limit of the sampling voltage in the second interval.

[0091] Read the level states of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the second interval, read the sampling signal of the second sampling resistor voltage division, calculate the insulation resistance, and return to the main program; if the second data terminal = 0, it means that the insulation resistance is greater than the upper limit resistance value of the second interval and is not in the second interval, the second data output terminal is set to 0, the second relay is energized, the second sampling resistor is cut off from the measurement circuit, the third sampling resistor is connected to the measurement circuit, and the sampling resistor mark f=2 is set at the same time.

[0092] By analogy, when the sampling resistor mark f=n-1, the n-1th data output terminal is set to 0, the n-1th relay is energized, the n-1th sampling resistor is cut off from the measurement circuit, the nth sampling resistor is connected to the measurement circuit, and the sampling resistor mark f=n-1 is set at the same time.

[0093] Read the level status of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the nth interval, read the sampling signal of the nth sampling resistor voltage divider, calculate the insulation resistance, and return to the main program; if the third data terminal = 0, it means that the insulation resistance is greater than the upper limit resistance value of the nth interval, display this information and return to the main program.

[0094] Furthermore, when the sampling resistance flag is increased by 1, the delay time is t.

[0095] Furthermore, according to the front-end signal of the sampling resistor series branch with n different resistance values ​​and the back-end signal of the sampling resistor series branch with n different resistance values, the sampling signal of the sampling resistor voltage division is calculated.

[0096] Furthermore, the upper limit of the sampling voltage in the nth interval is , the calculation formula is as follows:

[0097]

[0098] in, represents the voltage of the DC voltage source, represents the resistance value of the nth resistor, Indicates the lower limit of resistance in the nth interval.

[0099] The lower limit of the sampling voltage in the nth interval , the calculation formula is as follows:

[0100]

[0101] in, Indicates the upper limit of the resistance in the nth interval.

[0102] Embodiment 4:

[0103] This embodiment introduces a measurement method of a circuit for sampling an adaptive variable range of motor insulation resistance according to Example 2, such as Figure 2 As shown, specifically including:

[0104] Initialization of the main program in DSP sets the four GPIO output pins O1, O2, O3, and O4 to 1, sets the sampling resistor flag f=0, transistors VT1, VT2, VT3, and VT4 are all cut off, relays J1, J2, J3, and J4 are not powered, and only the sampling resistor R0 is connected to the test circuit.

[0105] The moving contact of the first potentiometer W1 is set so that the voltage at the non-inverting input terminal of the first integrated voltage comparator is the upper limit of the sampling voltage in the first interval.

[0106] The moving contact of the second potentiometer W2 is set so that the voltage at the inverting input terminal of the second integrated voltage comparator is the lower limit of the sampling voltage in the first interval.

[0107] The collected insulation resistance The sampling voltage is respectively input into the inverting input terminal of the first integrated voltage comparator and the non-inverting input terminal of the second integrated voltage comparator.

[0108] Read the level status of the three GPIO input pins I1, I2, and I3. If I2=1, it means that the insulation resistance is in the first interval. Then read the sampling signal of the sampling resistor R0 voltage divider to calculate the insulation resistance. , return to the main program; if I1=0, it means the insulation resistance The resistance value is small, the voltage at the inverting input terminal of the first integrated voltage comparator is greater than the upper limit of the sampling voltage in the first interval, and since the voltage is inversely proportional to the resistance value, the insulation resistance The lower resistance value of the first interval corresponding to the upper limit of the sampling voltage of the first interval is less than , display this information and return to the main program. If I2=0 and I1=1, it means the insulation resistance The resistance value is greater than the upper limit resistance value of the first interval , not in the first interval, the GPIO output pin O1 is set to 0, the low-level output pin O1 signal will turn on the transistor VT1 through the inverter, the relay J1 is energized, and the normally open contacts connected in parallel at both ends of R0 are closed, thereby cutting off the sampling resistor R0 from the measurement circuit, and the normally closed contacts of the relay J1 connected in parallel at both ends of R1 are opened, connecting the sampling resistor R1 to the measurement circuit, and the program records the sampling resistor mark f=1.

[0109] The moving contact of the first potentiometer W1 is set so that the voltage at the non-inverting input terminal of the first integrated voltage comparator is the upper limit of the sampling voltage in the second interval.

[0110] The moving contact of the second potentiometer W2 is set so that the voltage at the inverting input terminal of the second integrated voltage comparator is the lower limit of the sampling voltage in the second interval.

[0111] After the sampling resistor R1 is connected to the measurement circuit and a delay period is set, the level status of the GPIO input pins I1, I2, and I3 is read again. If I2=1, it indicates that the insulation resistance is in the second interval, then the sampling signal of the sampling resistor voltage division is read, the insulation resistance is calculated, and the main program is returned; if I2=0, it indicates that the insulation resistance is not in the second interval, then the GPIO output pin O2 is set to 0, and the low-level O2 signal will turn on VT2 through the inverter, and the relay J2 is energized, and its normally open contacts connected in parallel at both ends of R0 are closed, thereby maintaining the sampling resistor R0 cut off from the measurement circuit, and the normally closed contacts of J2 connected in parallel at both ends of R2 are opened, thereby connecting the sampling resistor R2 to the measurement circuit, and the program records the sampling resistor mark f=2. After a delay period, O1 is set to 1, that is, the relay J1 is de-energized, and the sampling resistor R1 is cut off from the measurement circuit. After the sampling resistor R2 is connected to the measurement circuit, R1 is removed from the measurement circuit and a delay period is set, the level status of the GPIO input pins I1, I2, and I3 is read again. If I2=1, it indicates that the insulation resistance is in the third interval, then the sampling signal of the sampling resistor voltage division is read, the insulation resistance is calculated, and the main program is returned; if I2=0, it indicates that the insulation resistance is not in the third interval, then the GPIO output pin O3 is set to 0, the low-level O3 signal will turn on VT3 through the inverter, the relay J3 is energized, and its normally open contacts connected in parallel at both ends of R0 are closed, thereby maintaining the sampling resistor R0 removed from the measurement circuit, and the normally closed contacts of J3 connected in parallel at both ends of R3 are opened, thereby connecting the sampling resistor R3 to the measurement circuit, and the program records the sampling resistor mark f=3. After a delay period, O2 is set to 1, that is, the relay J2 is de-energized, and the sampling resistor R2 is removed from the measurement circuit. After the sampling resistor R3 is connected to the measurement circuit, R2 is removed from the measurement circuit and a delay period is set, the level status of the GPIO input pins I1, I2, and I3 is read again. If I2=1, it indicates that the insulation resistance is in the fourth interval, then the sampling signal of the sampling resistor voltage division is read, the insulation resistance is calculated, and the main program is returned; if I2=0, it indicates that the insulation resistance is not in the fourth interval, then the GPIO output pin O4 is set to 0, and the low-level O4 signal will turn on VT4 through the inverter, and the relay J4 is energized, and its normally open contacts connected in parallel at both ends of R0 are closed, thereby maintaining the sampling resistor R0 removed from the measurement circuit, and the normally closed contacts of J4 connected in parallel at both ends of R4 are opened, thereby connecting the sampling resistor R4 to the measurement circuit, and the program records the sampling resistor mark f=4. After a delay period, O3 is set to 1, that is, the relay J3 is de-energized, and the sampling resistor R3 is removed from the measurement circuit.After the sampling resistor R4 is connected to the measurement circuit and R3 is removed from the measurement circuit and a delay is set, the level status of the GPIO input pins I1, I2, and I3 are read again. If I2=1, it indicates that the insulation resistance is in the fifth interval. Then, the sampling signal of the sampling resistor voltage division is read, the insulation resistance is calculated, and the main program is returned. If I3=0, that is, the output of the integrated voltage comparator 2 is at a low level, indicating the insulation resistance. , then the message will be displayed and the program will return to the main program.

[0112] Furthermore, the sampling resistor R i The sampled voltage at both ends is

[0113]

[0114] When the insulation resistance R x In the maximum interval (fifth level interval)

[0115]

[0116] When the sampling resistor R4 is connected to the measurement circuit, the remaining sampling resistors are cut off. The corresponding sampling voltage is

[0117]

[0118] In the formula, The lower limit of the sampling voltage is set; The upper limit of the sampling voltage is set.

[0119] When the insulation resistance R x In the fourth level

[0120]

[0121] When the sampling resistor R3 is connected to the measurement circuit, the remaining sampling resistors are cut off, and the corresponding sampling voltage still meets

[0122]

[0123] Similarly, when the insulation resistance R x In the third level , Second level interval , first level interval When the sampling resistors R2, R1, and R0 are connected to the measurement circuit, the remaining sampling resistors are cut off, and the corresponding sampling voltages all meet

[0124]

[0125] The delay time t for entering the next resistance interval is set in the insulation resistance signal acquisition program. The delay time t needs to be reasonably set according to the relay action time.

[0126] When testing the stator insulation resistance of a shut-down AC motor, the DSP main program can call the insulation resistance signal acquisition program multiple times to calculate the insulation resistance, and then obtain the insulation resistance test result value.

[0127] It should be further explained that the above-mentioned five-level insulation resistance (n=5) and automatic switching of corresponding different sampling resistors are used as an example to illustrate the technical solution of the present invention. In actual projects, according to the actual needs of the insulation test of the shut-down AC motor, the number of insulation resistance levels can be less than five or more than five.

[0128] The purpose of the present invention is to provide a circuit and method for sampling an adaptive variable range of motor insulation resistance to solve the following problems:

[0129] In response to the need for automatic testing of the stator insulation resistance of a shut-down AC motor, different sampling resistors are automatically switched according to the different intervals of the insulation resistance, so as to adaptively maintain the sampling voltage within a certain range, ensuring that for insulation resistance within a wide range, the sampling signal of the sampling resistor voltage division can be reasonably amplified with high precision to the allowable range of the analog signal of the DSP ADC module, and the insulation resistance can be calculated with high precision based on the sampling signal and the sampling resistor value in the DSP program, which is of great significance for the development of high-performance digital AC motor insulation resistance test instruments.

[0130] Aiming at the need of automatic testing of the stator insulation resistance of a stopped AC motor, the present invention automatically switches the corresponding different sampling resistors according to the different intervals of the insulation resistance, thereby adaptively maintaining the sampling voltage within a certain range, ensuring that for the insulation resistance within a wide range, the sampling signal of the sampling resistor voltage division can be reasonably amplified with high precision to the analog signal allowable range of the DSP ADC module, and realizes high-precision calculation of the insulation resistance according to the sampling signal and the sampling resistance value in the DSP program.

[0131] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A circuit for sampling the insulation resistance of a motor in an adaptive step-by-step variable range, characterized in that: include: A DC voltage source, n sampling resistors with different resistance values ​​connected in series, a first voltage comparator, a second voltage comparator, an AND gate, a controller, a first controllable potentiometer, a second controllable potentiometer, n-1 relays, where n is an integer, and an isolation and amplification circuit; Wherein, the DC voltage source provides power for measuring insulation resistance; The front end of the n sampling resistor series branches with different resistance values ​​is used to be connected to a DC voltage source through an insulation resistor, and the rear end of the n sampling resistor series branches with different resistance values ​​is grounded, wherein the resistance values ​​of the n sampling resistors are increased in sequence, and the resistance value of each sampling resistor belongs to a different resistance value interval of the insulation resistance; The non-inverting input terminal of the first voltage comparator is connected to the moving contact of the first controllable potentiometer, and the inverting input terminal of the first voltage comparator is used to connect to the voltage sampling terminal of the insulation resistor; The inverting input terminal of the second voltage comparator is connected to the moving contact of the second controllable potentiometer, and the non-inverting input terminal of the second voltage comparator is used to connect the voltage sampling terminal of the insulation resistor; The output end of the first voltage comparator is connected to the first input end of the AND gate, and the output end of the first voltage comparator is also connected to the first data end of the controller through the conversion circuit; The output terminal of the second voltage comparator is connected to the second input terminal of the AND gate, and the output terminal of the second voltage comparator is also connected to the third data terminal of the controller through the conversion circuit; The output end of the AND gate is connected to the second data end of the controller through a conversion circuit; The first data output terminal of the controller is connected to the first relay through a driving circuit, the second data output terminal of the controller is connected to the second relay through a driving circuit, and so on, the n-1th data output terminal of the controller is connected to the n-1th relay through a driving circuit; The normally open contacts of n-1 relays are all connected in parallel to the first sampling resistor; The normally closed contact of the first relay is connected in parallel to the second sampling resistor, the normally closed contact of the second relay is connected in parallel to the third sampling resistor, and so on, the normally closed contact of the n-1th relay is connected in parallel to the nth sampling resistor; The first input end of the isolation and amplification circuit is connected to the front end of the series branch of n sampling resistors with different resistance values, the second input end of the isolation and amplification circuit is connected to the rear end of the series branch of n sampling resistors with different resistance values, and the output end of the isolation and amplification circuit is connected to the fourth data end of the controller through the ADC.

2. The circuit for sampling the motor insulation resistance and adaptively varying the range according to claim 1 is characterized in that: The conversion circuit includes a coupler and a level conversion circuit, and is used to convert the output signal of the voltage comparator or the AND gate into a digital signal.

3. The circuit for sampling the motor insulation resistance and adaptively varying the range according to claim 2 is characterized in that: The coupler is isolated by a photoelectric coupler, and the level conversion circuit is isolated by a photoelectric transistor.

4. The circuit for sampling the motor insulation resistance and adaptively varying the range according to claim 1 is characterized in that: The driving circuit comprises an inverter and a transistor. The data output end of the controller is connected to the input end of the inverter, the output end of the inverter is connected to the base of the transistor, the collector of the transistor is connected to the working power supply through a relay, and the emitter of the transistor is grounded.

5. The circuit for sampling the motor insulation resistance and adaptively varying the range according to claim 1 is characterized in that: The controller adopts DSP, and the DSP includes: an input / output multiplexer, and the input / output multiplexer includes three input pins and n-1 output pins.

6. The circuit for sampling the motor insulation resistance and adaptively varying the range according to claim 5 is characterized in that: The DSP comprises: an ADC module, which is used to be connected with the output end of the isolation and amplification circuit.

7. The measuring method of the circuit for sampling the motor insulation resistance and adaptively varying the range according to any one of claims 1 to 6, characterized in that: Specifically include: The controller sets all n-1 data output terminals to 1, sets the sampling resistor flag f=0, and the n-1 relays are not powered. The first sampling resistor is connected to the test circuit; Setting the moving contact of the first controllable potentiometer so that the voltage at the non-inverting input terminal of the first voltage comparator is the upper limit of the sampling voltage in the first interval; Setting the moving contact of the second controllable potentiometer so that the voltage at the inverting input terminal of the second voltage comparator is the lower limit of the sampling voltage in the first interval; Input the collected sampling voltage of the insulation resistance into the inverting input terminal of the first voltage comparator and the non-inverting input terminal of the second voltage comparator respectively; Read the level states of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the first interval. Read the sampling signal of the first sampling resistor voltage division, calculate the insulation resistance, and return to the main program. If the first data terminal = 0, it means that the insulation resistance is less than the lower limit resistance value of the first interval, and the message is displayed and then the main program is returned; If the second data terminal = 0, and the first data terminal = 1, it means that the insulation resistance is greater than the upper limit resistance value of the first interval and is not in the first interval, the first data output terminal is set to 0, the first relay is energized, the first sampling resistor is cut off from the measurement circuit, the second sampling resistor is connected to the measurement circuit, and the sampling resistor flag f = 1 is set at the same time; When the sampling resistor mark f=1: Setting the moving contact of the first controllable potentiometer so that the voltage at the non-inverting input terminal of the first voltage comparator is the upper limit of the sampling voltage in the second interval; Setting the moving contact of the second controllable potentiometer so that the voltage at the inverting input terminal of the second voltage comparator is the lower limit of the sampling voltage in the second interval; Read the level states of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the second interval. Read the sampling signal of the second sampling resistor voltage division, calculate the insulation resistance, and return to the main program. If the second data terminal = 0, it means that the insulation resistance is greater than the upper limit resistance value of the second interval and is not in the second interval, the second data output terminal is set to 0, the second relay is energized, the second sampling resistor is cut off from the measurement circuit, the third sampling resistor is connected to the measurement circuit, and the sampling resistor flag f = 2 is set; Similarly, when the sampling resistor mark f=n-1, the n-1th data output terminal is set to 0, the n-1th relay is energized, the n-1th sampling resistor is removed from the measurement circuit, the nth sampling resistor is connected to the measurement circuit, and the sampling resistor mark f=n-1 is set at the same time; Read the level states of the first data terminal, the second data terminal and the third data terminal of the controller. If the second data terminal = 1, it indicates that the insulation resistance is in the nth interval, read the sampling signal of the nth sampling resistor voltage division, calculate the insulation resistance, and return to the main program; If the third data terminal = 0, it means that the insulation resistance is greater than the upper limit resistance value of the nth interval, and the main program is returned after displaying this information.

8. The measuring method according to claim 7, characterized in that: When the sampling resistor mark increases by 1, the delay time is t.

9. The measuring method according to claim 7, characterized in that: According to the front-end signal of the sampling resistor series branch with n different resistance values ​​and the back-end signal of the sampling resistor series branch with n different resistance values, the sampling signal of the sampling resistor voltage division is calculated.

10. The measuring method according to claim 7, characterized in that: The upper limit of the sampling voltage in the nth interval , the calculation formula is as follows: ； in, represents the voltage of the DC voltage source, represents the resistance value of the nth resistor, Indicates the lower limit of resistance in the nth interval; The lower limit of the sampling voltage in the nth interval , the calculation formula is as follows: ； in, Indicates the upper limit of the resistance in the nth interval.

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