CN211266457U - Protection circuit of motor drive system and air conditioning equipment - Google Patents

Abstract

The utility model discloses a motor drive system's protection circuit and air conditioning equipment. Wherein, this circuit includes: the circuit comprises: the three-phase rectifier bridge, the capacitor, the detection circuit and the switch circuit; the three-phase rectifier bridge is connected with a motor stator winding; the two ends of the capacitor are respectively connected with a first terminal and a second terminal of the direct current output end of the three-phase rectifier bridge and are used for storing electric energy and supplying power to the switch circuit; the input end of the detection circuit is connected with the two ends of the capacitor, the output end of the detection circuit is connected with the first end of the switch circuit, the second end of the switch circuit is connected with the first end of the capacitor, and the third end and the fourth end of the switch circuit are respectively connected with the first terminal and the second terminal of the direct current output end of the three-phase rectifier bridge. Through the utility model discloses, can make the counter electromotive force feedback that produces among the speed reduction process return motor stator winding to avoid it to fill to dc-to-ac converter and direct current bus-bar capacitance, improve the security.

Description

Protection circuit of motor drive system and air conditioning equipment

Technical Field

The utility model relates to an electronic circuit technical field particularly, relates to a motor drive system's protection circuit and air conditioning equipment.

Background

The permanent magnet synchronous motor has the advantages of high power density, good dynamic response and the like, and is widely applied to the air conditioning industry. In particular, in a variable frequency air conditioner, the motor is generally regulated by a driving plate, so that the purpose of frequency conversion is achieved. The circuit topology of the driving plate is generally an 'alternating current-direct current-alternating current' structure, the bus voltage of a direct current part is constant, and when the motor runs at a high speed and an overcurrent or other faults suddenly occur, the motor can be immediately protected to stop. During the process of the motor from high-speed operation to static operation, a large back electromotive force is generated. If not handling, then this counter electromotive force will fill to the direct current bus backward, in no energy storage capacitor actuating system, because the bus capacitance is the film capacitor that the capacitance value is very little, can't store a large amount of electric energy, counter electromotive force can lead to bus voltage to rise rapidly to cause components and parts such as dc-to-ac converter, bus capacitor to damage.

Aiming at the problem that the components of a driving system are easy to damage due to the fact that a large back electromotive force is generated in the process that a motor runs from a high speed to be static in the prior art, an effective solution is not provided at present.

SUMMERY OF THE UTILITY MODEL

The embodiment of the utility model provides an in provide a motor drive system's protection circuit and air conditioning equipment to solve among the prior art motor and produce great back electromotive force from high-speed operation to static in-process, easily cause the problem of actuating system component damage.

In order to solve the above technical problem, the utility model provides a motor drive system's protection circuit, wherein, this circuit includes: the three-phase rectifier bridge, the capacitor, the detection circuit and the switch circuit;

the three-phase rectifier bridge is connected with a motor stator winding;

the first end of the capacitor is connected with the first terminal of the direct current output end of the three-phase rectifier bridge, and the second end of the capacitor is connected with the second terminal of the direct current output end of the three-phase rectifier bridge, so that electric energy is stored and power is supplied to the switching circuit;

the input end of the detection circuit is connected with the two ends of the capacitor, and the output end of the detection circuit is connected with the first end of the switch circuit and is used for controlling the switch-on or switch-off of the switch circuit according to the running state of the motor;

and the second end of the switching circuit is connected with the first end of the capacitor, the third end of the switching circuit is connected with the first terminal of the direct current output end of the three-phase rectifier bridge, and the fourth end of the switching circuit is connected with the second terminal of the direct current output end of the three-phase rectifier bridge and is used for switching off when the motor is in a normal state and switching on when the motor is in a deceleration state.

Further, the detection circuit includes:

the first end of a first branch circuit formed by connecting a first resistor and a first voltage-regulator tube in series is connected with the first end of the capacitor, and the second end of the first branch circuit is connected with the second end of the capacitor;

the first end of a second branch circuit formed by connecting the second resistor and the third resistor in series is connected with the first end of the capacitor, and the second end of the second branch circuit is connected with the second end of the capacitor;

the comparator is used for outputting a high level signal when the voltage of the first input end is greater than that of the second input end, and outputting a low level signal when the voltage of the first input end is less than that of the second input end.

Further, the third resistor is a variable resistor.

Further, a third input end of the comparator is connected to the first end of the capacitor, and a fourth end of the comparator is connected to the second end of the capacitor, so that the capacitor supplies power to the comparator.

Further, the switching circuit includes:

the first pole of the first switch is connected with the first terminal of the direct current output end of the three-phase rectifier bridge, and the second pole of the first switch is connected with the second terminal of the direct current output end of the three-phase rectifier bridge and used for controlling the back electromotive force generated during the speed reduction of the motor to be fed back to the stator winding of the motor;

and a second switch, a first pole of which is connected with the output end of the comparator, a second pole of which is connected with the first end of the capacitor, and a third pole of which is connected with the third pole of the first switch, and is used for controlling the on or off of the first switch according to the low level signal or the high level signal output by the comparator.

Further, the first switch is a thyristor switch, and the second switch is a triode switch or an MOS transistor switch.

Further, the switching circuit further includes:

and the fourth resistor is arranged between the output end of the comparator and the first pole of the second switch and used for limiting the current input into the second switch.

Further, the circuit further comprises:

and the fifth resistor is arranged between the first end of the first branch circuit and the first end of the capacitor and used for limiting the charging current of the capacitor.

Further, the circuit further comprises:

and the second voltage-stabilizing tube is connected in parallel at two ends of the capacitor and is used for limiting the maximum voltage at two ends of the capacitor.

The utility model also provides an air conditioning equipment, including the motor, still include above-mentioned motor drive system's protection circuit.

Use the technical scheme of the utility model, state through detection circuitry detection motor is according to testing result output control signal, switching on or turn-off of control switch circuit, break down suddenly when the motor is when high-speed operation, when leading to the motor to slow down, control switch circuit switches on, the counter electromotive force who makes the in-process production of slowing down feeds back motor stator winding through the three-phase rectifier bridge, absorbed by motor stator winding, thereby avoid it to fill to dc-to-ac converter and direct current bus-bar capacitance backward, protect motor drive system's components and parts not damaged, the security is improved.

Drawings

Fig. 1 is a topology structure diagram of a conventional motor drive system;

fig. 2 is a block diagram of a protection circuit of a motor drive system according to an embodiment of the present invention;

fig. 3 is a block diagram of a protection circuit of a motor drive system according to another embodiment of the present invention;

fig. 4 is a connection diagram of the protection circuit and the motor driving system according to the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.

The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the embodiments of the present invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, and "a plurality" typically includes at least two.

It should be understood that the term "and/or" as used herein is merely one type of association that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.

It should be understood that although the terms first, second, etc. may be used to describe the switches in the embodiments of the present invention, the switches should not be limited to these terms. These terms are only used to distinguish between switches of different functions. For example, a first switch may also be referred to as a second switch, and similarly, a second switch may also be referred to as a first switch, without departing from the scope of embodiments of the present invention.

The words "if", as used herein, may be interpreted as "at … …" or "at … …" or "in response to a determination" or "in response to a detection", depending on the context. Similarly, the phrases "if determined" or "if detected (a stated condition or event)" may be interpreted as "when determined" or "in response to a determination" or "when detected (a stated condition or event)" or "in response to a detection (a stated condition or event)", depending on the context.

It is also noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in the article or device in which the element is included.

The following describes in detail alternative embodiments of the present invention with reference to the accompanying drawings.

Example 1

In a variable frequency air conditioner, the motor is generally regulated by a driving system to achieve the purpose of frequency conversion. Fig. 1 is a topological structure diagram of a conventional motor driving system, as shown in fig. 1, the driving circuit topological structure is generally an "ac-dc-ac" structure, that is, ac output by a power grid is converted into dc to be output to an inverter 2 through a rectifier 1, the dc output by the rectifier is converted into ac to be output to a motor 3 through the inverter 2, voltages of two dc buses between the rectifier 1 and the inverter 2 are constant, the two dc buses are connected in parallel with a dc bus capacitor C, an inductor L is further connected in series between one dc bus and one end of the capacitor C, when an overcurrent or other fault occurs suddenly during high-speed operation of the motor, the motor is immediately protected to stop, a large back electromotive force is generated during high-speed operation of the motor to a standstill, and if the fault is not processed, the back electromotive force is charged to the dc bus, in the drive system without the energy storage capacitor, because the direct-current bus capacitor C is a thin-film capacitor with a very small capacitance value, a large amount of electric energy cannot be stored, and the counter electromotive force can cause the bus voltage to rapidly rise, thereby causing the damage of components such as an inverter, a bus capacitor and the like.

In order to solve the above problem, this embodiment provides a protection circuit of a motor driving system, fig. 2 is a structural diagram of the protection circuit of the motor driving system according to the embodiment of the present invention, as shown in fig. 2, the protection circuit includes: the three-phase rectifier bridge 11 comprises three parallel branches, each branch comprises two diodes which are sequentially connected in series end to end, conducting wires between the diodes in each branch are respectively connected with U, V, W phase lines of the motor stator winding 14, and the motor stator winding 14 is connected with the driving system 15; a capacitor C1, a first end of the capacitor C1 is connected to a first terminal of the dc output end of the three-phase rectifier bridge 11, a second end of the capacitor C1 is connected to a second terminal of the dc output end of the three-phase rectifier bridge 11, and the capacitor C1 is used for storing electric energy output by the three-phase rectifier bridge and supplying power to the switching circuit 13; a detection circuit 12, an input end of which includes four connection ends, a first connection end and a second connection end are connected between a first end of a capacitor C1 and a first terminal of a dc output end of the three-phase rectifier bridge 11, a third connection end and a fourth connection end are connected between a second end of a capacitor C1 and a second terminal of the dc output end of the three-phase rectifier bridge 11, an output end of the detection circuit 12 is connected with a first end of the switching circuit 13, and since a reverse electromotive force is generated when the motor is decelerated, a voltage of a detection point between the second connection end and the fourth connection end of the input end of the detection circuit 12 is increased when the motor is decelerated, the detection circuit 12 can determine whether the motor is in a normal state or a decelerated state by the increase of the detected voltage, and control the switching circuit 13 to be turned on when the motor is in the decelerated state, and the motor is turned; the second end of the switch circuit 13 is connected with the first end of the capacitor C1, the third end is connected with the first terminal of the dc output end of the three-phase rectifier bridge 11, the fourth end is connected with the second terminal of the output end of the three-phase rectifier bridge 11, when the motor is in a normal state, the switch circuit is turned off, the switch circuit is not connected, when the motor stator winding 14 is in a deceleration state, the switch circuit is turned on, so that the inverter and the rectifier connected with the motor stator winding 14 are short-circuited, and the switch circuit is turned on between the three-phase rectifier bridge 11 and the motor stator winding 14, so as to control the anti-electromotive force generated when the motor decelerates to feed back to the motor stator winding 14 instead of reversely charging to the inverter, the.

In this embodiment, the state of the motor is detected by the detection circuit, and a control signal is output according to a detection result to control the on/off of the switch circuit, when the motor suddenly breaks down during high-speed operation, and the motor is decelerated, the switch circuit is controlled to be on, so that the counter electromotive force generated in the deceleration process is fed back to the motor stator winding through the three-phase rectifier bridge and absorbed by the motor stator winding, thereby preventing the counter electromotive force from being charged to the inverter, the direct-current bus capacitor or the rectifier, protecting components of the motor driving system from being damaged, and improving the safety.

Example 2

This embodiment provides another kind of motor drive system's protection circuit, and fig. 3 is according to the utility model discloses another embodiment's protection circuit's structure chart, voltage's increase when in order to further realize through detecting the motor speed reduction, and then control switching circuit switches on, as shown in fig. 3, detection circuitry 13 in this motor drive system's protection circuit includes: a first resistor R1 and a first voltage regulator tube D1, the first resistor R1 and the first voltage regulator tube D1 are connected in series, a first end of a first branch formed by the series connection is connected with a first end of the capacitor C1, and a second end of the first branch is connected with a second end of the capacitor C1; further comprising: a second resistor R2 and a third resistor R3, the second resistor R2 and the third resistor R3 are connected in series, a first end of a second branch formed by the series connection is connected with a first end of the capacitor C1, and a second end of the second branch is connected with a second end of the capacitor C1; the detection circuit 13 further comprises a comparator U1, a first input end of the comparator U1 is connected between the first resistor R1 and the first regulator D1, since the voltage at two ends of the first regulator D1 is kept unchanged, the voltage output from a connection point between the first resistor R1 and the first regulator D1 is kept unchanged, the voltage serves as the reference voltage Vr of the comparator U1, a second input end of the comparator U1 is connected between the second resistor R2 and the third resistor R3, when the motor decelerates, the voltage V1 output from a connection point between the second resistor R2 and the third resistor R3 is increased, so that the magnitude relation between the voltage V and the reference voltage Vr is also changed, and by configuring the resistance values of the first resistor R1, the second resistor R2 and the third resistor R3 and the voltage at two ends of the first regulator D1, the voltage V2 of the comparator U1 is smaller than the reference voltage Vr 1 when the motor normally operates, when the motor is decelerated, the voltage V1 rises to be higher than the reference voltage Vr, and the comparator U1 is caused to output a high level signal, and the comparator U1 is caused to output a low level signal.

In an embodiment, the resistance of the third resistor R3 is variable, and the proportional relationship between the voltage V1 and the actual back electromotive force can be changed by adjusting the resistance of the third resistor R3, so as to ensure that the first switch T1 in the protection circuit is immediately turned on to start the protection function when the back electromotive force increases to a certain value.

In order to ensure that the comparator U1 works normally, a stable power voltage needs to be supplied to the comparator U1, and therefore the comparator U1 further includes a third input terminal and a fourth input terminal, the third input terminal is connected to the first terminal of the capacitor C1, the fourth terminal is connected to the second terminal of the capacitor C1, and the comparator U1 is powered through the capacitor C1.

In order to realize the feedback of the back electromotive force generated during the motor deceleration to the motor stator winding 14, it is necessary to turn off the switch circuit 13 when the comparator U1 outputs a high level signal, and turn on the switch circuit 13 when the comparator U1 outputs a low level signal, and in order to realize this, as shown in fig. 3, the switch circuit 13 includes: a first switch T1, a first pole of which is connected to a first terminal of the dc output terminal of the three-phase rectifier bridge 11, and a second pole of which is connected to a second terminal of the output terminal of the three-phase rectifier bridge 11, for controlling the back electromotive force generated during the motor deceleration to be fed back to the motor stator winding 14; a second switch T2, a first pole of the second switch T2 is connected to the output terminal of the comparator U1, a second pole is connected to the first end of the capacitor C1, a third pole is connected to the third pole of the first switch T1, when the comparator U1 outputs a low level signal, the second switch T2 is turned on, and then the first end of the capacitor C1 is controlled to provide a high voltage to the first switch T1 to control the first switch T1 to be turned on, and when the comparator U1 outputs a high level signal, the second switch T2 is turned off to control the first switch T1 to be turned off. In a specific implementation, the first switch T1 may be a thyristor switch, and the second switch T2 may be a triode switch or a MOS transistor switch. If a transistor switch, preferably a PNP transistor switch, is used, it is turned on when a low signal is input to the base (i.e., the first terminal of the second switch T2) and turned off when a high signal is input to the base.

Since the second switch T2 is a triode switch or a MOS transistor switch, if the current flowing through the second switch T2 is too large, the device may not work normally, or even be damaged, and therefore, in order to control the working current of the second switch T2, as shown in fig. 3, the switch circuit 13 further includes: and the fourth resistor R4 and the fourth resistor R4 are arranged between the output end of the comparator U1 and the first pole of the second switch T2 and are used for limiting the current input into the second switch T2 to be less than the working current of the second switch T2, so that the second switch T2 works normally.

In the above embodiment, the capacitor C1 is charged through the three-phase rectifier bridge 11, so that the capacitor C1 charges the switching circuit and the detection circuit, and in order to avoid the charging current being too large during the charging process, which causes the capacitor C1 to be overcharged, as shown in fig. 3, the protection circuit of the motor driving system further includes: and the fifth resistor R5 is arranged between the first end of the first branch formed by connecting the first resistor R1 and the first voltage regulator tube D1 in series and the first end of the capacitor C1 and is used for limiting the charging current of the capacitor C1.

Since the capacitance of the capacitor C1 is constant, in order to limit the voltage across the capacitor C1 and prevent the capacitor C1 from breaking down, as shown in fig. 3, the protection circuit of the motor driving system further includes: and a second voltage regulator tube D2, wherein the second voltage regulator tube D2 is connected in parallel to two ends of the capacitor C1 and is used for limiting the maximum voltage of two ends of the capacitor C1.

Example 3

The embodiment provides another protection circuit of a motor driving system, which is used for protecting the driving system of a motor, in the small bus capacitor driving system, because the bus capacitor is small and the stored energy is limited, the counter electromotive force generated in the motor deceleration process is easy to back charge a direct current bus between a rectifier and an inverter to cause the voltage of the direct current bus to be increased, and the bus capacitor is broken down. Therefore, the overvoltage protection circuit of the small-bus capacitor motor driving system is provided, when the motor suddenly generates overcurrent or other faults when running at high speed, the back electromotive force generated in the speed reduction process is absorbed by the stator winding of the motor, so that the back charging to a direct-current bus is avoided, and components are protected from being damaged.

Fig. 4 is a connection relationship diagram of the protection circuit and the motor driving system according to the embodiment of the present invention, as shown in fig. 4, when the motor driving system works normally, the three-phase voltage inputted by the power grid obtains a stable dc bus voltage after passing through the rectifier 41 in the motor driving system 400 and filtering through the inductor L4 and the bus capacitor C4, and then controls the motor to operate through the inverter 42. The terminal voltage of the motor passes through the three-phase rectifier bridge 44 of the protection circuit, then the capacitor C41 is charged through the resistor R41, and the maximum voltage at the two ends of the capacitor C41 is limited through the voltage regulator tube D42. The thyristor switch T41 is normally in an off state, the protection circuit further includes a comparator U1, a first resistor R41, a second resistor R42, a third resistor R43, and a voltage regulator D41, and a voltage dividing structure formed by the first resistor R41 and the voltage regulator D41 is used for providing a stable reference voltage Vr for the comparator U41; a voltage division structure formed by the second resistor R42 and the third resistor R43 outputs a comparison voltage V1; under the condition that the motor normally works, the reference voltage Vr > the comparison voltage V1, the comparator U41 outputs high level, the protection circuit further comprises a triode T42 which is conducted when the comparator U41 outputs low level, in the embodiment, the third resistor R43 is a variable resistor, and the proportional relation between the comparison voltage V1 and the actual counter electromotive force can be changed by adjusting the resistance value of the resistor R43. Thereby ensuring that the thyristor switch T41 of the protection circuit is immediately turned on when the back emf increases to a certain extent and the protection function is turned on.

When the motor suddenly experiences overcurrent or other faults when running at high speed, the motor can be immediately decelerated. During the deceleration process, a large back electromotive force is generated, and at this time, the back electromotive force is divided by the second resistor R42 and the third resistor R43 in the protection circuit, so that the comparison voltage V1 is rapidly increased, and V1> Vr, so that the comparator U41 outputs a low level to turn on the transistor T42. Then the capacitor C1 gives a voltage signal to the thyristor T41 through the triode T42, so that the thyristor switch T41 is conducted;

after the thyristor switch T41 is turned on, the motor drive system 400, the first resistor R41, the second resistor R42, the third resistor R43, and the voltage regulator tube D41 are all short-circuited, the motor stator winding 43 is turned on with a loop formed by the three-phase rectifier bridge 44 of the overvoltage protection circuit and the thyristor switch T41, and the back electromotive force is consumed on the motor stator winding 43 to prevent the components from being damaged due to back charging to the dc bus.

The protection circuit further includes: the fourth resistor R44 is arranged between the output end of the comparator U41 and the first pole of the triode T42 and used for limiting the current input into the triode T42 to be not more than the working current of the triode T42, so that the triode T42 works normally;

the protection circuit further includes: and the fifth resistor R45 is arranged between the first end of the branch formed by connecting the first resistor R41 and the first voltage regulator tube D41 in series and the anode of the capacitor C41 and is used for limiting the charging current of the capacitor C41.

The motor driving system protection circuit of the embodiment completely performs overvoltage protection in a hardware mode, has very high response speed, and has great advantages compared with the existing software overvoltage protection mode.

Example 4

The embodiment provides an air conditioning equipment, which comprises a motor and a protection circuit of the motor driving system.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention in its corresponding aspects.

Claims (10)

1. A protection circuit for a motor drive system, the circuit comprising: the three-phase rectifier bridge, the capacitor, the detection circuit and the switch circuit;

the three-phase rectifier bridge is connected with a motor stator winding;

the first end of the capacitor is connected with the first terminal of the direct current output end of the three-phase rectifier bridge, and the second end of the capacitor is connected with the second terminal of the direct current output end of the three-phase rectifier bridge, so that electric energy is stored and power is supplied to the switching circuit;

the input end of the detection circuit is connected with the two ends of the capacitor, and the output end of the detection circuit is connected with the first end of the switch circuit and is used for controlling the switch-on or switch-off of the switch circuit according to the running state of the motor;

and the second end of the switching circuit is connected with the first end of the capacitor, the third end of the switching circuit is connected with the first terminal of the direct current output end of the three-phase rectifier bridge, and the fourth end of the switching circuit is connected with the second terminal of the direct current output end of the three-phase rectifier bridge, so that the switching circuit is switched off when the motor is in a normal state and switched on when the motor is in a deceleration state.

2. The circuit of claim 1, wherein the detection circuit comprises:

the first end of a first branch circuit formed by connecting a first resistor and a first voltage-regulator tube in series is connected with the first end of the capacitor, and the second end of the first branch circuit is connected with the second end of the capacitor;

the first end of a second branch circuit formed by connecting the second resistor and the third resistor in series is connected with the first end of the capacitor, and the second end of the second branch circuit is connected with the second end of the capacitor;

the comparator is used for outputting a high level signal when the voltage of the first input end is greater than that of the second input end, and outputting a low level signal when the voltage of the first input end is less than that of the second input end.

3. The circuit of claim 2, wherein the third resistor is a variable resistor.

4. The circuit of claim 2, wherein the third input terminal of the comparator is connected to the first terminal of the capacitor, and the fourth terminal is connected to the second terminal of the capacitor, so that the capacitor supplies power to the comparator.

5. The circuit of claim 2, wherein the switching circuit comprises:

a first switch, a first pole of which is connected with a first terminal of the DC output end of the three-phase rectifier bridge, a second pole of which is connected with a second terminal of the DC output end of the three-phase rectifier bridge, and the first switch is used for controlling the back electromotive force generated when the motor is decelerated to feed back to the stator winding of the motor;

and a second switch, a first pole of which is connected with the output end of the comparator, a second pole of which is connected with the first end of the capacitor, and a third pole of which is connected with the third pole of the first switch, and is used for controlling the on or off of the first switch according to the low level signal or the high level signal output by the comparator.

6. The circuit of claim 5, wherein the first switch is a thyristor switch and the second switch is a triode switch or a MOS transistor switch.

7. The circuit of claim 5, wherein the switching circuit further comprises:

and the fourth resistor is arranged between the output end of the comparator and the first pole of the second switch and used for limiting the current input into the second switch.

8. The circuit of claim 2, further comprising:

and the fifth resistor is arranged between the first end of the first branch circuit and the first end of the capacitor and used for limiting the charging current of the capacitor.

9. The circuit of claim 1, further comprising:

and the second voltage-stabilizing tube is connected in parallel at two ends of the capacitor and is used for limiting the maximum voltage at two ends of the capacitor.

10. An air conditioning apparatus including a motor, characterized by further comprising a protection circuit of the motor drive system of any one of claims 1 to 9.

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