Motor drive circuit and system

Abstract

The present application provides a motor drive circuit and system, relating to the field of motor drive technology. The motor drive circuit includes a voltage regulator, a conversion module, a PLC, and a frequency converter. The voltage regulator, the conversion module, and the frequency converter are connected in sequence. The frequency converter is electrically connected to the voltage regulator, and the conversion module is also electrically connected to the PLC. The output end of the voltage regulator is used to connect to the generator and provide an excitation signal to the generator. The conversion module is used to convert the collected excitation signal into a DC signal and output the DC signal to the frequency converter based on the power frequency or intermediate frequency signal transmitted by the PLC. The power frequency signal and the intermediate frequency signal have different frequencies. The frequency converter is used to generate a feedback signal based on the DC signal and transmit the feedback signal to the voltage regulator to adjust the excitation signal. The motor drive circuit and system provided in the present application have the effect of ensuring the stability of the excitation signal output by the voltage regulator.

Description

Technical Field

[0001] The present application relates to the field of motor drive technology, and in particular to a motor drive circuit and system. Background Art

[0002] The voltage regulator (AVR) is specifically designed for AC brushless generators with fundamental and harmonic excitation, or with permanent magnet generator excitation. The voltage regulator automatically adjusts the generator's output voltage by controlling the excitation current of the generator's AC exciter. The generator voltage regulator can accommodate both standard 60 / 50Hz and 400Hz medium-frequency generators operating in single or parallel operation.

[0003] However, the voltage regulator in the prior art may not work properly, resulting in inaccurate excitation signals and ultimately abnormal voltage output by the generator. Furthermore, there is currently no detection device for the voltage regulator.

[0004] In summary, there is no detection device for the voltage regulator in the prior art, which results in the problem that when the voltage regulator is abnormal, the output voltage of the generator is affected. Summary of the Invention

[0005] The purpose of the present application is to provide a motor drive circuit and system to solve the problem in the prior art that there is no detection device for the voltage regulator, which affects the output voltage of the generator when the voltage regulator is abnormal.

[0006] In order to achieve the above objectives, the technical solutions adopted in the embodiments of the present application are as follows:

[0007] In a first aspect, an embodiment of the present application provides a motor drive circuit, the motor drive circuit comprising a voltage regulator, a conversion module, a PLC, and a frequency converter, wherein the voltage regulator, the conversion module, and the frequency converter are connected in sequence, the frequency converter is electrically connected to the voltage regulator, and the conversion module is also electrically connected to the PLC; wherein,

[0008] The output end of the voltage regulator is used to connect to the generator and provide an excitation signal for the generator;

[0009] The conversion module is used to convert the collected excitation signal into a DC signal, and to output the DC signal to the frequency converter according to the power frequency or intermediate frequency signal transmitted by the PLC, wherein the power frequency signal and the intermediate frequency signal have different frequencies;

[0010] The frequency converter is used to generate a feedback signal according to the DC signal, and transmit the feedback signal to the voltage regulator to adjust the excitation signal.

[0011] Used to receive the intermediate frequency or industrial frequency signal output by the PLC,

[0012] Optionally, the conversion module is integrated on a circuit board.

[0013] Optionally, the conversion module includes a sampling unit, an optical coupler, and an output unit, wherein the sampling unit, the optical coupler, and the output unit are electrically connected, the sampling unit is electrically connected to the output end of the voltage regulator, and the output unit is also electrically connected to the PLC and the frequency converter; wherein,

[0014] The sampling unit is used to collect the excitation signal output by the voltage regulator;

[0015] The optical coupler is used to convert the excitation signal into a DC signal;

[0016] The output unit is used to output the DC signal to the frequency converter according to the industrial frequency or intermediate frequency signal transmitted by the PLC.

[0017] Optionally, the output end of the voltage regulator includes a first circuit and a second circuit, the sampling unit includes a first resistor, the first input end of the optocoupler is connected to the first circuit through the first resistor, and the second input end of the optocoupler is connected to the second circuit, so that the first resistor is connected in parallel with the output end of the voltage regulator.

[0018] Optionally, the conversion module also includes a second resistor, the optocoupler includes a light-emitting diode and a light-receiving transistor, the light-emitting diode is electrically connected to the sampling unit, the collector of the light-receiving transistor is connected to a power supply, the emitter of the light-receiving transistor is grounded through the second resistor, and the emitter of the light-receiving transistor is also electrically connected to the output unit.

[0019] Optionally, the motor drive circuit also includes a voltage divider module, which includes a third resistor and a fourth resistor, one end of the third resistor and the fourth resistor connected in series is connected to the power supply, and the other end is grounded, and the collector of the light-receiving transistor is connected between the third resistor and the fourth resistor.

[0020] Optionally, the motor drive circuit further includes an indication module, which includes a fifth resistor and an indicator light, wherein one end of the fifth resistor and the indicator light connected in series is electrically connected to the power supply, and the other end is grounded.

[0021] Optionally, the output unit includes a relay, a first circuit and a second circuit, the relay is electrically connected to the conversion module, the PLC, the first circuit and the second circuit respectively, and the first circuit and the second circuit are both electrically connected to the frequency converter; wherein,

[0022] The relay is used to be in a first state or a second state according to the power frequency or intermediate frequency signal of the PLC;

[0023] When the relay is in the first state, the conversion module is connected to the frequency converter through the first loop;

[0024] When the relay is in the second state, the conversion module is connected to the inverter through the second circuit, and the resistance values ​​of the first circuit and the second circuit are different.

[0025] Optionally, the relay includes a coil, a normally open contact and a normally closed contact, one end of the coil is electrically connected to the PLC, and the other end is grounded, the normally open contact is electrically connected to the first circuit, and the normally closed contact is electrically connected to the second circuit.

[0026] On the other hand, an embodiment of the present application further provides a motor drive system, which includes a generator and the above-mentioned motor drive circuit, and the output end of the voltage regulator is electrically connected to the generator.

[0027] Compared with the prior art, this application has the following beneficial effects:

[0028] The present application provides a motor drive circuit and system, which includes a voltage regulator, a conversion module, a programmable logic controller (PLC), and a frequency converter. The voltage regulator, conversion module, and frequency converter are connected in sequence, the frequency converter is electrically connected to the voltage regulator, and the conversion module is also electrically connected to the PLC. The output end of the voltage regulator is used to connect to a generator and provide an excitation signal for the generator. The conversion module is used to convert the collected excitation signal into a DC signal and output the DC signal to the frequency converter based on a power frequency or intermediate frequency signal transmitted by the PLC. The power frequency signal and the intermediate frequency signal have different frequencies. The frequency converter is used to generate a feedback signal based on the DC signal and transmit the feedback signal to the voltage regulator to adjust the excitation signal. Since the motor drive circuit provided by the present application can use the conversion module to collect the excitation signal output by the voltage regulator, and the frequency converter can generate a feedback signal based on the converted signal and adjust the excitation signal, a feedback loop is formed using the regulator, conversion module, and frequency converter. Even if the voltage regulator malfunctions, the excitation signal can be adjusted using the feedback signal transmitted by the frequency converter, thereby not affecting the output voltage of the generator.

[0029] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 This is a schematic diagram of the first module of the motor drive circuit provided in an embodiment of the present application.

[0032] Figure 2 A second module schematic diagram of the motor drive circuit provided in an embodiment of the present application.

[0033] Figure 3 A schematic diagram of a conversion module according to an embodiment of the present application.

[0034] Figure 4 A circuit diagram of the conversion module provided in an embodiment of the present application.

[0035] Figure 5 A circuit diagram of the indicator module provided in an embodiment of the present application.

[0036] Figure 6 A circuit diagram of a relay provided in an embodiment of the present application.

[0037] In the figure: 100-motor drive circuit; 110-voltage regulator; 120-conversion module; 121-sampling unit; 122-optocoupler; 123-output unit; 130-frequency converter; 140-PLC; 150-power supply; 160-voltage divider module; R1-first resistor; R2-second resistor; R3-third resistor; R4-fourth resistor; R5-fifth resistor; R6-sixth resistor; R7-seventh resistor; R8-eighth resistor; R9-ninth resistor; C1-capacitor. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0039] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0040] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0041] It should be noted that, in this document, relational terms such as first and second, etc. are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0042] The following describes some embodiments of the present application in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features therein may be combined with each other.

[0043] As described in the background art, there is currently no detection device for the voltage regulator. When the voltage regulator fails to work properly, it may cause the output excitation signal to be inaccurate, thereby causing abnormal voltage output by the generator.

[0044] In view of this, in order to solve the above problems, the present application provides a motor drive circuit and system, which collects the excitation signal output by the voltage regulator, converts the excitation signal, and then uses the frequency converter to generate a feedback signal to adjust the excitation signal output by the voltage regulator in real time, thereby avoiding the problem of inaccurate excitation signal output by the voltage regulator.

[0045] The following is an exemplary description of the motor drive circuit provided in this application:

[0046] As an optional implementation, see Figure 1 The motor drive circuit 100 includes a voltage regulator 110, a conversion module 120, a PLC 140 (Programmable Logic Controller) and a frequency converter 130. The voltage regulator 110, the conversion module 120 and the frequency converter 130 are connected in sequence. The frequency converter 130 is electrically connected to the voltage regulator 110, and the conversion module 120 is also electrically connected to the PLC 140.

[0047] Among them, the output end of the voltage regulator 110 is used to connect to the generator and provide an excitation signal for the generator. The conversion module 120 is used to convert the collected excitation signal into a DC signal, and is used to output the DC signal to the frequency converter 130 based on the industrial frequency or intermediate frequency signal transmitted by the PLC140. The frequencies of the industrial frequency signal and the intermediate frequency signal are different. The frequency converter 130 is used to generate a feedback signal based on the DC signal and transmit the feedback signal to the voltage regulator 110 to adjust the excitation signal.

[0048] It is understandable that by providing the conversion module 120 and the frequency converter 130, the conversion module 120 can be used to collect the excitation signal output by the voltage regulator 110 and convert it into a DC signal. The frequency converter 130 then generates a feedback signal and transmits the feedback signal to the voltage regulator, thereby adjusting the output of the voltage regulator 110 through the feedback signal. Therefore, the voltage regulator 110, the conversion module 120, and the frequency converter 130 provided in this application form a feedback loop, which can adjust the excitation signal output by the voltage regulator 110 so that the output of the voltage regulator 110 will not malfunction.

[0049] At the same time, in order to be applicable to industrial frequency and medium frequency application scenarios, the conversion module 120 is connected to the PLC 140, and the different DC signals are transmitted to the inverter 130 through the signals transmitted by the PLC 140. Optionally, the medium frequency mentioned in this application refers to the voltage regulator 110 with a signal frequency of 400 Hz, and the industrial frequency refers to the voltage regulator 110 with a signal frequency of 50 / 60 Hz.

[0050] Alternatively, the conversion module 120 described herein may be integrated onto a circuit board to form a conversion board, thereby miniaturizing the entire electrode drive circuit. Of course, in another possible implementation, the voltage regulator 110, conversion module 120, PLC 140, and inverter 130 may all be integrated onto the same circuit board, which is not a limitation herein.

[0051] See also Figure 2 , shows another schematic diagram of the motor drive circuit provided in the present application. It can be understood that the motor drive circuit further includes a power supply 150, which is connected to the conversion module 120 and supplies power to the conversion module 120. For example, a 24V working power supply 150 can be used.

[0052] It should be noted that Figure 2The intermediate control signal refers to the industrial frequency or intermediate frequency signal output by PLC140. In one implementation, the industrial frequency signal and the intermediate frequency signal need to be set independently. For example, when the output is high, the conversion module 120 defaults to receiving the intermediate frequency signal and is in the first working state; when the output is low, the conversion module 120 defaults to receiving the industrial frequency signal and is in the second working state. As another implementation, the output of PLC140 can also be a switching signal between industrial frequency and intermediate frequency. For example, the conversion module 120 operates in the first working state, indicating that the conversion module 120 defaults to operating in the intermediate frequency signal mode. When the switching signal from PLC140 is received, the conversion module 120 switches from the first working state to the second working state, indicating that the conversion module 120 switches to the industrial frequency signal mode.

[0053] As an optional implementation, see Figure 3 The conversion module 120 includes a sampling unit 121, an optical coupler 122, and an output unit 123. The sampling unit 121, the optical coupler 122, and the output unit 123 are electrically connected. The sampling unit 121 is electrically connected to the output end of the voltage regulator 110, and the output unit 123 is also electrically connected to the PLC 140 and the inverter 130. The sampling unit 121 is used to collect the excitation signal output by the voltage regulator 110, the optical coupler 122 is used to convert the excitation signal into a DC signal, and the output unit 123 is used to output the DC signal to the inverter 130 based on the power frequency or intermediate frequency signal transmitted by the PLC 140.

[0054] Optionally, see Figure 4 The output end of the voltage regulator 110 includes a first circuit and a second circuit, which are respectively Figure 4 In E1 and E2, it can be understood that the voltage regulator 110 can be connected to the generator via the first line and the second line, thereby providing an excitation signal to the generator. Furthermore, the sampling unit 121 includes a first resistor R1. The first input end of the optocoupler 122 is connected to the first line via the first resistor R1, and the second input end of the optocoupler 122 is connected to the second line, so that the first resistor R1 is connected in parallel with the output end of the voltage regulator 110. For example, the first resistor R1 is a 30 ohm resistor. By connecting the first resistor R1 in parallel with the output end of the voltage regulator 110, when the voltage regulator 110 outputs an excitation signal, the voltage regulator 110 and the first resistor R1 also form a loop, thereby driving the optocoupler 122 to operate via the excitation signal.

[0055] The optocoupler 122 includes a light-emitting diode (LED) and a light-receiving transistor (BTR). The conversion module 120 also includes a second resistor R2. The LED is electrically connected to the sampling unit 121. Specifically, the anode of the LED is connected to the first circuit via the first resistor R1, and the cathode of the LED is connected to the second circuit. The collector of the BTR is connected to the power supply 150, and the emitter of the BTR is grounded via the second resistor R2. The emitter of the BTR is also electrically connected to the output unit 123.

[0056] It should be noted that the excitation signal is a pulse signal, and the optical coupler 122 converts the pulse signal into a DC signal.

[0057] Since the power supply 150 of the present application is powered by 24V and the optocoupler 122 is a low-power device, in order to prevent the light-receiving transistor from burning out when the power supply 150 is loaded on the optocoupler 122, the motor drive circuit provided in the present application also includes a voltage divider module 160. Specifically, the voltage divider module 160 includes a third resistor R3 and a fourth resistor R4, one end of the third resistor R3 and the fourth resistor R4 connected in series is connected to the power supply 150, and the other end is grounded. The collector of the light-receiving transistor is connected between the third resistor R3 and the fourth resistor R4.

[0058] By setting the voltage divider module 160, a fixed low DC voltage can be output. For example, the third resistor R3 is set to 300 ohms and the first resistor R1 is set to 100 ohms, then the collector terminal voltage of the light-receiving transistor is 6V. Of course, when the collector voltage of the light-receiving transistor needs to be changed, it is only necessary to change the resistance values ​​of the third resistor R3 and the fourth resistor R4, which will not be elaborated here.

[0059] At the same time, in order to ensure the normal operation of the power supply 150, the motor drive circuit also includes an indication module, see Figure 5 The indicator module includes a fifth resistor R5 and an indicator light. One end of the fifth resistor R5 and the indicator light connected in series is electrically connected to the power supply 150, and the other end is grounded. The indicator light can be an LED light. When the 24V working power supply 150 is normally supplied, the LED light is continuously on. When the 24V working power supply 150 fails, the LED light is off.

[0060] As an implementation, the output unit 123 includes a relay, a first circuit, and a second circuit. The relay is electrically connected to the conversion module 120, the PLC 140, the first circuit, and the second circuit, respectively. The first circuit and the second circuit are both electrically connected to the frequency converter 130. The relay is configured to switch between a first state and a second state based on the power frequency or intermediate frequency signal from the PLC 140. When the relay is in the first state, the conversion module 120 communicates with the frequency converter 130 via the first circuit. When the relay is in the second state, the conversion module 120 communicates with the frequency converter 130 via the second circuit, and the resistance values ​​of the first circuit and the second circuit are different.

[0061] Among them, the first loop includes a sixth resistor R6 and a seventh resistor R7, and the sixth resistor R6 and the seventh resistor R7 are connected in series. The second loop includes an eighth resistor R8 and a ninth resistor R9, and the eighth resistor R8 and the ninth resistor R9. In addition, the sum of the resistance values ​​of the sixth resistor R6 and the seventh resistor R7, the eighth resistor R8 and the ninth resistor R9, and the eighth resistor R8 and the ninth resistor R9 are not equal. For example, the resistance values ​​of the sixth resistor R6 and the eighth resistor R8 are not equal, and the resistance values ​​of the seventh resistor R7 and the ninth resistor R9 are also not equal; or, the resistance values ​​of the sixth resistor R6 and the eighth resistor R8 are equal, and the resistance values ​​of the seventh resistor R7 and the ninth resistor R9 are not equal, which is not limited here.

[0062] Furthermore, in order to make the output more stable, the output module further includes a first capacitor C1 , one end of the first capacitor C1 is electrically connected to both the first loop and the second loop, and the other end of the first capacitor C1 is grounded.

[0063] Optionally, see Figure 6 The relay includes a coil, a normally open contact and a normally closed contact. One end of the coil is electrically connected to PLC140 and the other end is grounded. The normally open contact is electrically connected to the first circuit and the normally closed contact is electrically connected to the second circuit.

[0064] During actual control, when no instruction from PLC140 is received, the DC signal output by the optocoupler 122 is transmitted to the inverter 130 through the second circuit, and the inverter 130 generates a feedback signal of the corresponding voltage based on the signal; and when a switching instruction from PLC140 is received, the normally open contact is closed and the normally closed contact is disconnected, and the DC signal output by the optocoupler 122 is transmitted to the inverter 130 through the second circuit, and the inverter 130 generates a feedback signal of the corresponding voltage based on the signal, and adjusts the excitation signal output by the voltage regulator 110 based on the feedback signal.

[0065] Based on the above implementation, an embodiment of the present application further provides a motor drive system, which includes a generator and the above motor drive circuit, and the output end of the voltage regulator 110 is electrically connected to the generator.

[0066] In summary, the embodiments of the present application provide a motor drive circuit and system, which includes a voltage regulator, a conversion module, a PLC, and a frequency converter. The voltage regulator, conversion module, and frequency converter are connected in sequence, the frequency converter is electrically connected to the voltage regulator, and the conversion module is also electrically connected to the PLC. The output end of the voltage regulator is used to connect to the generator and provide an excitation signal for the generator. The conversion module is used to convert the collected excitation signal into a DC signal and output the DC signal to the frequency converter based on the power frequency or intermediate frequency signal transmitted by the PLC, wherein the power frequency signal and the intermediate frequency signal have different frequencies. The frequency converter is used to generate a feedback signal based on the DC signal and transmit the feedback signal to the voltage regulator to adjust the excitation signal. Since the motor drive circuit provided by the present application can use the conversion module to collect the excitation signal output by the voltage regulator, and the frequency converter can generate a feedback signal based on the converted signal and adjust the excitation signal, a feedback loop is formed using the regulator, conversion module, and frequency converter. Even if the voltage regulator malfunctions, the excitation signal can be adjusted using the feedback signal transmitted by the frequency converter, thereby not affecting the output voltage of the generator.

[0067] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

[0068] It will be apparent to those skilled in the art that the present application is not limited to the details of the exemplary embodiments described above and that the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the present application is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A motor drive circuit, characterized in that: The motor drive circuit includes a voltage regulator, a conversion module, a PLC and a frequency converter, wherein the voltage regulator, the conversion module and the frequency converter are connected in sequence, the frequency converter is electrically connected to the voltage regulator, and the conversion module is also electrically connected to the PLC; wherein, The output end of the voltage regulator is used to connect to the generator and provide an excitation signal for the generator; The conversion module is used to convert the collected excitation signal into a DC signal, and to output the DC signal to the frequency converter according to the power frequency or intermediate frequency signal transmitted by the PLC, wherein the power frequency signal and the intermediate frequency signal have different frequencies; The frequency converter is used to generate a feedback signal according to the DC signal, and transmit the feedback signal to the voltage regulator to adjust the excitation signal; The conversion module is integrated on a circuit board; The conversion module includes a sampling unit, an optical coupler, and an output unit. The sampling unit, the optical coupler, and the output unit are electrically connected. The sampling unit is electrically connected to the output end of the voltage regulator. The output unit is also electrically connected to the PLC and the frequency converter. The sampling unit is used to collect the excitation signal output by the voltage regulator; The optical coupler is used to convert the excitation signal into a DC signal; The output unit is used to output the DC signal to the frequency converter according to the industrial frequency or intermediate frequency signal transmitted by the PLC.

2. The motor drive circuit according to claim 1, wherein: The output end of the voltage regulator includes a first circuit and a second circuit, the sampling unit includes a first resistor, the first input end of the optocoupler is connected to the first circuit through the first resistor, and the second input end of the optocoupler is connected to the second circuit, so that the first resistor is connected in parallel with the output end of the voltage regulator.

3. The motor drive circuit according to claim 1, wherein: The conversion module also includes a second resistor, the optocoupler includes a light-emitting diode and a light-receiving transistor, the light-emitting diode is electrically connected to the sampling unit, the collector of the light-receiving transistor is connected to a power supply, the emitter of the light-receiving transistor is grounded through the second resistor, and the emitter of the light-receiving transistor is also electrically connected to the output unit.

4. The motor drive circuit according to claim 3, wherein: The motor drive circuit also includes a voltage divider module, which includes a third resistor and a fourth resistor. One end of the third resistor and the fourth resistor connected in series is connected to a power supply, and the other end is grounded. The collector of the light-receiving transistor is connected between the third resistor and the fourth resistor.

5. The motor drive circuit according to claim 3 or 4, characterized in that: The motor drive circuit further includes an indication module, which includes a fifth resistor and an indicator light. One end of the fifth resistor and the indicator light connected in series is electrically connected to the power supply, and the other end is grounded.

6. The motor drive circuit according to claim 1, wherein: The output unit includes a relay, a first circuit and a second circuit, the relay is electrically connected to the conversion module, the PLC, the first circuit and the second circuit respectively, and the first circuit and the second circuit are both electrically connected to the inverter; wherein, The relay is used to be in a first state or a second state according to the power frequency or intermediate frequency signal of the PLC; When the relay is in the first state, the conversion module is connected to the frequency converter through the first loop; When the relay is in the second state, the conversion module is connected to the inverter through the second circuit, and the resistance values ​​of the first circuit and the second circuit are different.

7. The motor drive circuit according to claim 6, wherein: The relay includes a coil, a normally open contact and a normally closed contact. One end of the coil is electrically connected to the PLC, and the other end is grounded. The normally open contact is electrically connected to the first circuit, and the normally closed contact is electrically connected to the second circuit.

8. A motor drive system, characterized in that: The motor drive system includes a generator and the motor drive circuit according to any one of claims 1 to 7, and the output end of the voltage regulator is electrically connected to the generator.

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