Motor current detection circuit and method for switch cabinet

Abstract

The application relates to a motor current detection circuit and method, which comprises a control circuit, the control circuit comprising a MOS tube, one end of the MOS tube being connected with a motor, the other end of the motor being connected with a power supply; a current sampling circuit, the current sampling circuit comprising a sampling resistor R, one end of the sampling resistor R being connected with a source electrode of the MOS tube, the other end of the sampling resistor R being grounded; an MCU, a control output pin of the MCU being connected with an input end of the control circuit, used for controlling on-off of the MOS tube; and an input pin of the MCU being connected with an output end of the current sampling circuit, used for receiving a current size of the current sampling circuit. The application has the effect of reducing the cost of the motor current detection circuit while ensuring the accuracy of motor current collection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of switch cabinet, in particular to a motor current detection circuit and method of switch cabinet. BACKGROUND

[0002] In the switch cabinet, the electric operation controller requires not only to accurately and reliably pass through the motor operation energy storage and closing, but also to accurately collect the current waveform of the motor in the action process and record, and to communicate the current waveform data to the background synchronously. The background analyzes the state of the motor according to the current waveform, so as to judge the aging condition of the motor, and to give an early warning when the motor is close to the service life. When the motor runs abnormally, an alarm can be given in time, so as to improve the reliability of the whole control system of the switch cabinet.

[0003] The existing motor current collection is usually through a Hall current sensor and a high-precision amplifier to collect the current value of the motor loop, and to record the current waveform after calculation.

[0004] Although the above-mentioned motor current collection through the Hall current sensor and the high-precision amplifier has high precision, the cost is high, and therefore needs to be improved. SUMMARY

[0005] In order to reduce the cost of the motor current detection circuit, the present application provides a motor current detection circuit and method of switch cabinet.

[0006] In one aspect, the motor current detection circuit of the switch cabinet provided by the present application adopts the following technical scheme: a motor current detection circuit of a switch cabinet, comprising: a control circuit, the control circuit comprising a MOS tube, one end of the MOS tube being connected with a motor, and the other end of the motor being connected with a power supply;

[0007] a current sampling circuit, the current sampling circuit comprising a sampling resistor R, one end of the sampling resistor R being connected with the source electrode of the MOS tube, and the other end of the sampling resistor R being grounded;

[0008] an MCU, the control output pin of the MCU being connected with the input end of the control circuit, for controlling the on-off of the MOS tube; and the input pin of the MCU being connected with the output end of the current sampling circuit, for receiving the current size of the current sampling circuit.

[0009] By adopting the above technical scheme, the MCU outputs a signal to the control circuit, so that the MOS tube Q is turned on, so that the sampling resistor connected in series with the motor is powered, and the current value of the sampling resistor R is obtained, so that the current size of the motor is obtained. Compared with the Hall current sensor and the high-precision amplifier, the cost of the motor current detection circuit is greatly reduced.

[0010] Preferably, the current sampling circuit further comprises a first resistor R1, one end of the first resistor R1 is connected between the MOS tube Q and the sampling resistor R, and the other end of the first resistor R1 is connected with the MCU input pin.

[0011] By adopting the above technical solution, the first resistor R is connected with the MCU input pin, so that the voltage of the MCU input sampling resistor R can be stably given, and the current size can be calculated by the MCU, that is, the motor current size.

[0012] Preferably, the control circuit further comprises a power supply circuit and a driving circuit, the power supply circuit is connected with the direct current power supply, the control end of the power supply circuit is connected with the control pin of the MCU, the output end of the power supply circuit is connected with the driving circuit for supplying power to the driving circuit, the control end of the driving circuit is connected with the control pin of the MCU, and the output end of the driving circuit is connected with the gate of the MOS tube.

[0013] By adopting the above technical solution, the control end of the power supply circuit is controlled by the MCU to supply power to the driving circuit, so that the MCU can control the driving circuit to make the MOS tube conductive while the power supply circuit supplies power to the driving circuit, thereby reducing the power consumption of the control circuit.

[0014] Preferably, the driving circuit comprises a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a first triode Q1, a second triode Q2 and a third triode Q3, one end of the second resistor R2 is connected with one end of the third resistor R3 and the control pin of the MCU, the other end of the third resistor R3 is connected with the direct current power supply, the other end of the second resistor R2 is connected with the base of the first triode Q1, one end of the fourth resistor R4 is connected between the second resistor R2 and the first triode Q1, the other end of the fourth resistor R4 is grounded, the collector of the first triode Q1 is connected with one end of the fifth resistor R5, the emitter of the first triode Q1 is grounded, the other end of the fifth resistor R5 is connected with the output end of the power supply circuit, the base of the second triode Q2 is connected between the first triode Q1 and the fifth resistor R5, the collector of the second triode Q2 is connected with the output end of the power supply circuit, the emitter of the second triode Q2 is connected with the emitter of the third triode Q3, the base of the third triode Q3 is connected between the first triode Q1 and the second triode Q2, the collector of the third triode Q3 is grounded, one end of the sixth resistor R6 is connected between the second triode Q2 and the third triode Q3, the other end of the sixth resistor R6 is connected with the gate of the MOS tube Q, one end of the seventh resistor R7 is connected between the sixth resistor R6 and the MOS tube Q, and the other end of the seventh resistor R7 is grounded.

[0015] By adopting the technical scheme, the MCU outputs a control signal, the push-pull circuit composed of the first transistor Q1, the second transistor Q2 and the third transistor Q3 is turned on, so that the on-off of the MOS transistor can be stably controlled, and the sampling precision of the motor current can be improved.

[0016] Preferably, the power supply circuit comprises a fourth transistor Q4, an eighth resistor R8 and a ninth resistor R9, one end of the eighth resistor R8 is connected with the control pin of the MCU, the other end of the eighth resistor R8 is connected with the base of the fourth transistor Q4, the emitter of the fourth transistor Q4 is connected with the DC power supply, the collector of the fourth transistor Q4 is connected with the collector of the second transistor Q2, one end of the ninth resistor R9 is connected with the emitter of the fourth transistor Q4, and the other end of the ninth resistor R9 is connected with the base of the fourth transistor Q4.

[0017] By adopting the technical scheme, the MCU outputs a control signal to the power supply circuit, the fourth transistor Q4 is turned on, so that the DC power supply is supplied to the driving circuit, and the power consumption of the control circuit is reduced.

[0018] Preferably, the motor is connected in parallel with a diode D.

[0019] By adopting the technical scheme, the diode D connected in parallel with the motor can eliminate the reverse electromotive force of the motor, so that the service life of the motor is improved.

[0020] On the other hand, the motor current detection method of the switch cabinet provided by the application adopts the following technical scheme: a motor current detection method of a switch cabinet, applied to the motor current detection circuit of claim 1; the method comprises: setting a current sampling circuit and a PWM control circuit, connecting the sampling resistor in the current sampling circuit and the MOS transistor in the PWM control circuit in series with the motor, connecting the output end of the current sampling circuit with the MCU, and connecting the control end of the PWM control circuit with the MCU;

[0021] The MCU outputs a control signal, the PWM control circuit controls the on-off of the MOS transistor, and the current sampling circuit is used to make the MCU quickly and instantaneously acquire n continuous instantaneous current values of the sampling resistor;

[0022] The acquired n continuous instantaneous current values are weighted and averaged to obtain a current value at a time point;

[0023] The current values at each time point in the time period during which the motor operates form a current waveform, and the current waveform is stored in the MCU and then transmitted to the background.

[0024] By adopting the technical scheme, the current value of the motor is obtained through the sampling resistor connected in series with the motor, and the N connection instantaneous current values of the sampling resistor are obtained through the MCU control PWM control circuit controlling the conduction moment of the MOS tube, then the n continuous instantaneous current values obtained are weighted and averaged to obtain a current value at a time point; the current values at each time point in a time period during the operation of the motor form a current waveform, and the current waveform is stored and transmitted to the background, thereby greatly reducing the cost of motor current acquisition compared with the Hall current sensor and high-precision amplifier.

[0025] Preferably, when the PWM control circuit controls the MOS tube to be turned off, the relationship between the instantaneous value Ioff of the motor current and the instantaneous value Ion of the motor current when the MOS tube is turned on is:

[0026]

[0027] f is the frequency of the PWM control circuit, K1 is the instantaneous frequency f influence coefficient, L is the inductance value of the internal coil of the motor, K2 is the inductance L influence coefficient of the motor, P is the instantaneous load power of the motor, K3 is the instantaneous load power influence coefficient of the motor, D is the duty cycle of the PWM control circuit, and K4 is the duty cycle influence coefficient of the frequency.

[0028] By adopting the above technical scheme, during the process of the PWM control circuit controlling the motor, the sampling resistor and the actual current of the motor exist different, at the moment when the PWM control circuit controls the MOS tube to be turned off, the sampling resistor does not sample the current part of the motor freewheeling, therefore the current accuracy cannot meet the requirements, therefore the instantaneous freewheeling current of the motor is calculated through the relationship between the instantaneous value Ioff of the motor current and the instantaneous value Ion of the motor current when the MOS tube is turned on, the freewheeling current of the motor when the PWM is turned off is weighted and averaged or root mean square calculated with the current value sampled by the sampling resistor, and the actual current value of the motor at different times is obtained, thereby improving the accuracy of the motor current acquisition.

[0029] In summary, the present application includes at least one of the following beneficial technical effects:

[0030] 1. The MCU outputs a signal to the control circuit to make the MOS tube Q conduct, so that the sampling resistor connected in series with the motor is powered, and the current value of the sampling resistor R is obtained, thereby obtaining the current value of the motor; compared with the Hall current sensor and high-precision amplifier, the cost of the motor current detection circuit is greatly reduced;

[0031] 2. The motor instantaneous freewheeling current is calculated by the relationship between the instantaneous value Ioff of the motor current and the instantaneous value Ion of the motor current when the motor is turned on. The freewheeling current of the motor when the PWM is turned off is weighted and averaged or root mean squared calculated with the current value sampled by the sampling resistor to obtain the actual current value of the motor at different times, thereby improving the accuracy of the motor current acquisition. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A circuit schematic diagram of the detection circuit in the embodiment of the application is shown.

[0033] Figure 2 A circuit diagram of the detection circuit in the embodiment of the application is shown.

[0034] Figure 3 A principle block diagram of the detection method in the embodiment of the application is shown.

[0035] Marked for explanation: 1, control circuit; 2, current sampling circuit; 3, power supply circuit; 4, driving circuit. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings Figures 1-2 The application is further described in detail.

[0037] The embodiment of the application discloses a motor current detection circuit of a switch cabinet. Referring to Figure 1 , the motor current detection circuit comprises a control circuit 1, a current sampling circuit 2 and an MCU, wherein the control circuit 1 comprises a MOS tube, the drain of the MOS tube is connected with one end of the motor, and the other end of the motor is connected with a power supply. The MOS tube in the embodiment is an NMOS tube, and the use of the NMOS tube can isolate the interference of the control signal of the control circuit 1 on the current sampling circuit 2, thereby improving the precision of the current sampling circuit 2 in acquiring the working current of the motor.

[0038] The current sampling circuit 2 comprises a sampling resistor R, one end of the sampling resistor R is connected with the source of the MOS tube Q, and the other end of the sampling resistor R is grounded; the control output pin of the MCU is connected with the input end of the control circuit 1, for controlling the on-off of the MOS tube; and the input pin of the MCU is connected with the output end of the current sampling circuit 2, for receiving the current size of the current sampling circuit 2.

[0039] Specifically, the current sampling circuit 2 further comprises a first resistor R1, one end of the first resistor R1 is connected between the MOS tube Q and the sampling resistor R, and the other end of the first resistor R1 is connected with the input pin of the MCU. The first resistor R is connected with the input pin of the MCU, so as to stably give the voltage size of the sampling resistor R to the MCU, and the current size is calculated by the MCU, that is, the motor current size.

[0040] The control circuit 1 further comprises a power supply circuit 3 and a driving circuit 4, the power supply circuit 3 is connected with a direct current power supply, a control end of the power supply circuit 3 is connected with a control pin of the MCU, an output end of the power supply circuit 3 is connected with the driving circuit 4, for supplying power to the driving circuit 4; a control end of the driving circuit 4 is connected with the control pin of the MCU, and an output end of the driving circuit 4 is connected with a gate of the MOS tube. The control end of the power supply circuit 3 is controlled to supply power to the driving circuit 4 through the MCU, so that the MCU can control the driving circuit 4 to make the MOS tube conductive while the power supply circuit 3 supplies power to the driving circuit 4, thereby reducing the power consumption of the control circuit 1.

[0041] Specifically, the driving circuit 4 comprises a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a first triode Q1, a second triode Q2 and a third triode Q3, wherein the first triode Q1 and the second triode Q2 are NPN type triodes, and the third triode Q3 is a PNP type triode. One end of the second resistor R2 and one end of the third resistor R3 are connected with the control pin of the MCU, the other end of the third resistor R3 is connected with a 5V direct current power supply, the other end of the second resistor R2 is connected with a base of the first triode Q1, one end of the fourth resistor R4 is connected between the second resistor R2 and the first triode Q1, the other end of the fourth resistor R4 is grounded, a collector of the first triode Q1 is connected with one end of the fifth resistor R5, an emitter of the first triode Q1 is grounded, the other end of the fifth resistor R5 is connected with an output end of the power supply circuit 3, a base of the second triode Q2 is connected between the first triode Q1 and the fifth resistor R5, a collector of the second triode Q2 is connected with the output end of the power supply circuit 3, an emitter of the second triode Q2 is connected with an emitter of the third triode Q3, a base of the third triode Q3 is connected between the first triode Q1 and the second triode Q2, a collector of the third triode Q3 is grounded, one end of the sixth resistor R6 is connected between the second triode Q2 and the third triode Q3, the other end of the sixth resistor R6 is connected with a gate of the MOS tube Q, one end of the seventh resistor R7 is connected between the sixth resistor R6 and the MOS tube Q, and the other end of the seventh resistor R7 is grounded. The MCU outputs a control signal, which is conducted through a push-pull circuit composed of the first triode Q1, the second triode Q2 and the third triode Q3, so as to stably control the on-off of the MOS tube Q, thereby improving the sampling accuracy of the motor current.

[0042] The power supply circuit 3 comprises a fourth triode Q4, an eighth resistor R8 and a ninth resistor R9, wherein the fourth triode Q4 is a PNP triode. One end of the eighth resistor R8 is connected with the control pin of the MCU, the other end of the eighth resistor R8 is connected with the base of the fourth triode Q4, the emitter of the fourth triode Q4 is connected with the direct current power supply, the collector of the fourth triode Q4 is connected with the collector of the second triode Q2, one end of the ninth resistor R9 is connected with the emitter of the fourth triode Q4, and the other end of the ninth resistor R9 is connected with the base of the fourth triode Q4. The MCU outputs the control signal to the power supply circuit 3, so that the fourth triode Q4 is turned on, thereby the direct current power supply is supplied to the driving circuit 4 to reduce the power consumption of the control circuit 1.

[0043] The motor is connected in parallel with a diode D. The diode D connected in parallel with the motor can eliminate the reverse electromotive force generated when the motor stops working, thereby improving the service life of the motor.

[0044] The implementation principle of the motor current detection circuit of the switch cabinet according to the embodiment of the application is that the MCU outputs a signal to the control circuit to turn on the MOS tube Q, so that the sampling resistor R connected in series with the motor is powered, and the current value of the sampling resistor R is obtained, thereby obtaining the current value of the motor. Compared with the Hall current sensor and the high-precision amplifier, the cost of the motor current detection circuit is greatly reduced.

[0045] On the other hand, the application also provides a motor current detection method of a switch cabinet, which is applied to the motor current detection circuit of the switch cabinet.

[0046] Reference Figure 3 The detection method comprises the following steps:

[0047] 101. A current sampling circuit and a PWM control circuit are arranged, the sampling resistor in the current sampling circuit and the MOS tube in the PWM control circuit are connected in series with the motor, the output end of the current sampling circuit is connected with the MCU, and the control end of the PWM control circuit is connected with the MCU;

[0048] 102. The MCU outputs a control signal, the PWM control circuit controls the on-off of the MOS tube, and the current sampling circuit is used to make the MCU instantaneously acquire n continuous instantaneous current values of the sampling resistor.

[0049] The PWM control circuit controls the instantaneous on-off of the MOS tube by outputting a pulse signal through the MCU, the MCU instantaneously acquires the voltage value of the sampling resistor, and the MCU converts the voltage value of the sampling resistor into a current value.

[0050] 103. The acquired n continuous instantaneous current values are weighted and averaged to obtain a current value at a time point; wherein the current value can be filtered before being weighted and averaged.

[0051] Because the sampling resistor and the actual current of the motor are different during the process of the PWM control circuit controlling the motor through the pulse signal, at the moment when the PWM control circuit controls the MOS tube to be off, the current of the motor freewheeling is not sampled by the sampling resistor, and therefore it is necessary to compensate for the current of the motor existing during the period when the PWM control circuit controls the MOS tube to be off but the sampling resistor has no current.

[0052] When the PWM control circuit controls the MOS tube to be on, the motor current is Ion, and the current value is directly sampled and calculated by the sampling resistor; when the PWM control circuit controls the MOS tube to be off, the motor current is Ioff, and the instantaneous current value Ioff needs to be calculated by the instantaneous current value Ion, the frequency of the pulse signal of the PWM control circuit, the duty cycle, the instantaneous load power of the motor and other parameters.

[0053] The switch cabinet requires different running speeds of the motor at different times, and the load power of the motor also changes due to the changes of the spring compression and the speed change when the switch cabinet motor is in different running states; therefore, the MCU is required to control the motor to adopt different frequencies and duty cycles in different states.

[0054] The different running states of the motor include the motor starting, the motor running in the middle, the spring energy storage approaching to the position, the motor reversing unlocking and the motor locked-rotor protection, and the current changes in these different states need to be collected. Different switch cabinets require different rated powers of the motor, and the motor control is also different.

[0055] Specifically, when the PWM control circuit controls the MOS tube to be off, the relationship between the instantaneous value Ioff of the motor current and the instantaneous value Ion of the motor current when the MOS tube is on is as follows:

[0056]

[0057] f is the frequency of the pulse signal of the PWM control circuit, which changes according to different motor powers and working states; K1 is the instantaneous frequency f influence coefficient, and K1 also changes according to the frequency; L is the inductance value of the motor internal coil, K2 is the inductance L influence coefficient of the motor; P is the instantaneous load power of the motor, K3 is the instantaneous load power influence coefficient of the motor, D is the duty cycle of the pulse signal of the PWM control circuit, and K4 is the duty cycle influence coefficient of the frequency. The above corresponding frequency, motor power, duty cycle and corresponding influence coefficient corresponding to different running states of the motor are input into the MCU through the program.

[0058] 104、The current value of each time point in the time period during the operation of the motor constitutes a current waveform, and the current waveform is stored in the MCU and then transmitted to the background.

[0059] The background can determine the working condition of the motor through the fault recorder, and determine whether the motor exists short circuit or whether the coil of the motor exists aging condition.

[0060] Therefore, the freewheeling current of the motor is calculated by the relationship between the instantaneous value Ioff of the motor current and the instantaneous value Ion of the motor current when conducting, the freewheeling current of the motor when PWM is turned off is weighted and averaged or root mean square calculated with the current value sampled by the sampling resistor, and the actual current value of the motor at different times is obtained, so as to improve the precision of the motor current collection.

[0061] The above are preferred embodiments of the present application, and do not limit the protection scope of the present application, so: any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A method for detecting motor current in a switchgear, characterized in that, This is applied to motor current detection circuits, which include: The control circuit (1) includes a MOS transistor, a power supply circuit (3), and a drive circuit (4). The drain of the MOS transistor is connected to one end of the motor, and the other end of the motor is connected to the power supply. The power supply circuit (3) is connected to a DC power supply. The control terminal of the power supply circuit (3) is connected to the control pin of the MCU. The output terminal of the power supply circuit (3) is connected to the drive circuit (4) to supply power to the drive circuit (4). The control terminal of the drive circuit (4) is connected to the control pin of the MCU, and the output terminal of the drive circuit (4) is connected to the gate of the MOS transistor. The current sampling circuit (2) includes a sampling resistor R and a first resistor R1. One end of the sampling resistor R is connected to the source of the MOS transistor, and the other end of the sampling resistor R is grounded. One end of the first resistor R1 is connected between the MOS transistor Q and the sampling resistor R, and the other end of the first resistor R1 is connected to the MCU input pin. The MCU has its control output pin connected to the input terminal of the control circuit (1) for controlling the on / off state of the MOS transistor; the MCU's input pin is connected to the output terminal of the current sampling circuit (2) for receiving the current magnitude of the current sampling circuit (2). The method includes: Set up a current sampling circuit and a PWM control circuit. Connect the sampling resistor in the current sampling circuit and the MOSFET in the PWM control circuit in series with the motor. At the same time, connect the output terminal of the current sampling circuit to the MCU and the control terminal of the PWM control circuit to the MCU. The MCU outputs control signals, the PWM control circuit controls the switching on and off of the MOSFET, and the current sampling circuit enables the MCU to quickly and instantaneously acquire n consecutive instantaneous current values ​​of the sampling resistor; The current value at a given time point is obtained by performing a weighted average calculation on the n consecutive instantaneous current values. When the PWM control circuit turns on the MOSFET, the motor current is Ion, and the current value is directly sampled and calculated by the sampling resistor. When the PWM control circuit turns off the MOSFET, the motor current is Ioff. The instantaneous current value Ioff needs to be calculated from the instantaneous current value Ion, the frequency and duty cycle of the instantaneous pulse signal of the PWM control circuit, and the instantaneous load power parameters of the motor. The relationship between the instantaneous value of the motor current Ioff when the PWM control circuit controls the MOSFET to turn off and the instantaneous value of the motor current Ion when it is turned on is as follows: f is the frequency of the PWM control circuit, K1 is the influence coefficient of instantaneous frequency f, L is the inductance value of the internal coil of the motor, K2 is the influence coefficient of the inductance of the motor L, P is the instantaneous load power of the motor, K3 is the influence coefficient of the instantaneous load power of the motor, D is the duty cycle of the PWM control circuit, and K4 is the influence coefficient of the frequency duty cycle. The instantaneous freewheeling current of the motor is calculated by the relationship between the instantaneous value of the motor current Ioff and the instantaneous value of the motor current Ion when it is turned on. The freewheeling current of the motor when the PWM is turned off is weighted and averaged or calculated by the current value sampled by the sampling resistor to obtain the actual current value of the motor at different times. The current values ​​at various points in time during the motor's operation period form a current waveform, which is stored in the MCU and then transmitted to the backend.

2. The method for detecting motor current in a switchgear according to claim 1, characterized in that: The driving circuit (4) includes a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a first transistor Q1, a second transistor Q2, and a third transistor Q3. One end of the second resistor R2 and one end of the third resistor R3 are simultaneously connected to the control pin of the MCU. The other end of the third resistor R3 is connected to a DC power supply. The other end of the second resistor R2 is connected to the base of the first transistor Q1. One end of the fourth resistor R4 is connected between the second resistor R2 and the first transistor Q1, and the other end of the fourth resistor R4 is grounded. The collector of the first transistor Q1 is connected to one end of the fifth resistor R5, and the emitter of the first transistor Q1 is grounded. The other end of resistor R5 is connected to the output terminal of power supply circuit (3). The base of the second transistor Q2 is connected between the first transistor Q1 and the fifth resistor R5. The collector of the second transistor Q2 is connected to the output terminal of power supply circuit (3). The emitter of the second transistor Q2 is connected to the emitter of the third transistor Q3. The base of the third transistor Q3 is connected between the first transistor Q1 and the second transistor Q2. The collector of the third transistor Q3 is grounded. One end of the sixth resistor R6 is connected between the second transistor Q2 and the third transistor Q3. The other end of the sixth resistor R6 is connected to the gate of MOSFET Q. One end of the seventh resistor R7 is connected between the sixth resistor R6 and MOSFET Q. The other end of the seventh resistor R7 is grounded.

3. The method for detecting motor current in a switchgear according to claim 2, characterized in that: The power supply circuit (3) includes a fourth transistor Q4, an eighth resistor R8, and a ninth resistor R9. One end of the eighth resistor R8 is connected to the control pin of the MCU, and the other end of the eighth resistor R8 is connected to the base of the fourth transistor Q4. The emitter of the fourth transistor Q4 is connected to the DC power supply, and the collector of the fourth transistor Q4 is connected to the collector of the second transistor Q2. One end of the ninth resistor R9 is connected to the emitter of the fourth transistor Q4, and the other end of the ninth resistor R9 is connected to the base of the fourth transistor Q4.

4. The method for detecting motor current in a switchgear according to claim 1, characterized in that: The motor is connected in parallel with a diode D.

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