Overcurrent protection circuit and air conditioner

Abstract

The utility model discloses an over-current protection circuit and an air conditioner, the over-current protection circuit is used for a driving loop of a variable frequency motor, and the driving loop comprises a driving controller; the driving circuit is used for receiving the control signal and outputting a PWM signal, the overcurrent protection circuit comprises an overcurrent detection circuit, the overcurrent detection circuit is used for outputting an overcurrent protection signal when detecting that the current output by the inverter circuit exceeds an overcurrent protection set value, the overcurrent protection signal is sent to the driving controller, and the driving controller controls the driving circuit to cut off the output of the PWM signal; the self-locking circuit receives the overcurrent protection signal and a self-locking reset signal output by the driving controller, when the self-locking reset signal is at a first level, the self-locking circuit receives the overcurrent protection signal and outputs a self-locking signal for enabling the driving circuit to cut off the output of the PWM signal, and when the self-locking reset signal is at a second level different from the first level, the self-locking circuit outputs the self-locking signal for enabling the driving circuit to cut off the output of the PWM signal. And resetting the self-locking circuit. According to the utility model, two-stage overcurrent protection of the driving loop can be realized.

Description

Technical Field

[0001] This utility model relates to the field of variable frequency motor protection technology, and in particular to an overcurrent protection circuit and an air conditioner. Background Technology

[0002] In the field of variable frequency motor drive technology, drive circuits need to use high-cost integrated chips (such as latches or comparators) to implement overcurrent protection design, or use discrete components to build overcurrent protection circuits, but cannot achieve the latching of protection signals. When the overcurrent signal changes at high frequency or the drive software is out of control, it will cause abnormal drive control and damage the drive circuit. Utility Model Content

[0003] In response to the problems mentioned in the background art, this application provides an overcurrent protection circuit. In the variable frequency motor drive circuit, the overcurrent protection signal is divided into two paths: one path is sent to the drive controller to control the cut-off of the PWM signal output, and the other path is sent to the self-locking circuit to output a self-locking signal to the drive circuit to cut off the PWM signal output, thereby realizing two-stage overcurrent protection of the drive circuit.

[0004] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0005] Some embodiments of this application relate to an overcurrent protection circuit for the drive circuit of the variable frequency motor, the drive circuit comprising:

[0006] A drive controller, which outputs control signals to drive the variable frequency motor.

[0007] The drive circuit receives the control signal and outputs a PWM signal to control the switching transistors in the inverter circuit. The overcurrent protection circuit includes:

[0008] An overcurrent detection circuit is used to detect when the current output by the inverter circuit exceeds the overcurrent protection setting value, and output an overcurrent protection signal. The overcurrent protection signal is sent to the drive controller, and the drive controller controls the drive circuit to cut off the output PWM signal.

[0009] The self-locking circuit receives the overcurrent protection signal and the self-locking reset signal output by the drive controller. When the self-locking reset signal is at a first level, the self-locking circuit receives the overcurrent protection signal and outputs a self-locking signal to cause the drive circuit to cut off the output PWM signal. When the self-locking reset signal is at a second level different from the first level, the self-locking circuit resets.

[0010] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0011] The overcurrent detection circuit detects that the current in the inverter circuit exceeds the overcurrent protection setting value and outputs an overcurrent protection signal. The overcurrent protection signal is sent to the drive controller to control the drive circuit to cut off the output PWM signal, forming the first level of overcurrent protection. On the other hand, the overcurrent protection signal is sent to the self-locking circuit, which outputs a self-locking signal to control the drive circuit to cut off the output PWM signal, forming the second level of overcurrent protection. The two levels of overcurrent protection ensure that the drive circuit stops working when there is an overcurrent, ensuring the safe and reliable operation of the variable frequency motor.

[0012] When the drive controller does not reset the self-locking circuit, the self-locking signal locks the self-locking circuit, continuously cutting off the output PWM signal to prevent abnormal drive control and damage to the drive circuit caused by abnormal states such as high-frequency changes in overcurrent signals and loss of control of drive software.

[0013] In some embodiments of this application, the overcurrent detection circuit includes:

[0014] The comparator has a first input terminal, a second input terminal, and an output terminal. The first input terminal receives a reference level, the second input terminal receives the current output by the inverter circuit through a resistor, and the output terminal outputs the overcurrent protection signal.

[0015] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0016] The overcurrent detection circuit adopts the form of a voltage comparator, which can set the overcurrent protection setting value through the voltage divider resistor and compare it to achieve the purpose of overcurrent detection.

[0017] In some embodiments of this application, the overcurrent detection circuit further includes:

[0018] The first filter circuit is located at the front end of the second input terminal and is used to filter the voltage signal input to the second input terminal.

[0019] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0020] The first filtering circuit filters the acquired current / voltage signals to ensure the reliability of the overcurrent comparison and improve the accuracy of overcurrent detection.

[0021] In some embodiments of this application, the overcurrent detection circuit further includes:

[0022] A charging and discharging circuit is located at the output terminal of the comparator, and the output terminal of the charging and discharging circuit outputs the overcurrent protection signal.

[0023] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0024] The charging and discharging circuit is used to set the duration of the overcurrent protection signal during overcurrent, ensuring that the drive controller can detect the overcurrent protection signal, improving detection reliability, and ensuring reliable completion of the first-level overcurrent protection.

[0025] In some embodiments of this application, the charging and discharging circuit includes a first power supply, a first resistor, a second resistor, and a first capacitor;

[0026] The first resistor and the first capacitor are connected in series between the first power supply and ground. One end of the second resistor is connected to the output terminal of the comparator and the other end is connected to the common connection position of the first resistor and the first capacitor. The overcurrent protection signal is output from the common connection position of the first resistor and the first capacitor.

[0027] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0028] By using discrete components such as resistors and capacitors to build a simple charging and discharging circuit, the overall structure of the variable frequency motor overcurrent protection circuit is simple, easy to implement, and also reduces cost.

[0029] In some embodiments of this application, the self-locking circuit includes:

[0030] The first switch control unit receives the self-locking reset signal at its control terminal and is grounded at its first terminal. The first switch control unit is a high-level conducting switch element.

[0031] The second switch control unit receives the overcurrent protection signal at its control terminal, its first terminal is grounded, and its second terminal is connected to the common connection position of the second terminal of the first switch control unit, the self-locking signal, and the pull-up resistor.

[0032] The third switch control unit has its control terminal connected to the common position of the second terminal of the first switch control unit, the second terminal of the second switch control unit, and the self-locking signal. The first terminal of the third switch control unit is grounded, and the second terminal of the third switch control unit is connected to the overcurrent protection signal.

[0033] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0034] The first switch control unit, which uses a high-level conducting switch element, ensures the unlocking and reset of the self-locking circuit. After the self-locking circuit is reset, it enters the overcurrent protection state.

[0035] After the self-locking circuit enters the overcurrent protection state, the second and third switch control elements are used to form a self-locking mechanism to ensure that the output self-locking signal is locked during overcurrent and is not affected by changes in the overcurrent signal.

[0036] In some embodiments of this application, the self-locking circuit further includes:

[0037] The second filtering circuit is located at the control terminal of the second switch control unit and is used to filter the voltage signal input to the control terminal of the second switch control unit.

[0038] The third filtering circuit is located at the control terminal of the third switch control unit and is used to filter the voltage signal input to the control terminal of the third switch control unit.

[0039] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0040] A second filtering circuit is used to filter the signal controlling the second switch control unit, and a third filtering circuit is used to filter the signal controlling the third switch control unit, so as to ensure reliable control of the second and third switch control units and realize reliable output of the self-locking signal.

[0041] In some embodiments of this application, the first switch control unit, the second switch control unit, and the third switch control unit are all NPN transistors, with the base of the NPN transistor being its control terminal, the emitter of the NPN transistor being its first terminal, and the collector of the NPN transistor being its second terminal.

[0042] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0043] Using ready-made NPN transistors makes it easy to implement a self-locking circuit.

[0044] Some embodiments of this application also relate to an air conditioner, including:

[0045] The refrigerant circulation loop allows the refrigerant to circulate within a loop consisting of the compressor, condenser, expansion valve, and evaporator.

[0046] A drive circuit for driving a variable frequency motor, wherein the variable frequency motor is a compressor motor, an outdoor fan motor, an indoor fan motor, and / or a drain pump motor in a drip tray, the drive circuit comprising:

[0047] A drive controller, which outputs control signals to drive the variable frequency motor.

[0048] A drive circuit, which receives the control signal and outputs a PWM signal to control the switching transistors in the inverter circuit;

[0049] An overcurrent detection circuit is used to detect when the current output by the inverter circuit exceeds the overcurrent protection setting value, and output an overcurrent protection signal. The overcurrent protection signal is sent to the drive controller, and the drive controller controls the drive circuit to cut off the output PWM signal.

[0050] The self-locking circuit receives the overcurrent protection signal and the self-locking reset signal output by the drive controller. When the self-locking reset signal is at a first level, the self-locking circuit receives the overcurrent protection signal and outputs a self-locking signal to cause the drive circuit to cut off the output PWM signal. When the self-locking reset signal is at a second level different from the first level, the self-locking circuit resets.

[0051] The technical solutions involved in the above embodiments have the following advantages or beneficial effects:

[0052] The overcurrent detection circuit detects that the current in the inverter circuit exceeds the overcurrent protection setting value and outputs an overcurrent protection signal. This overcurrent protection signal is sent to the drive controller, which controls the drive circuit to cut off the output PWM signal, forming the first level of overcurrent protection. On the other hand, the overcurrent protection signal is sent to the self-locking circuit, which outputs a self-locking signal to control the drive circuit to cut off the output PWM signal, forming the second level of overcurrent protection. The two levels of overcurrent protection ensure that the load motor stops working when there is an overcurrent, ensuring the safety and reliability of the air conditioner.

[0053] When the drive controller does not reset the self-locking circuit, the self-locking signal locks the self-locking circuit, continuously cutting off the output PWM signal to prevent abnormal drive control and damage to the drive circuit caused by abnormal states such as high-frequency changes in overcurrent signals and loss of control of drive software.

[0054] Other features and advantages of this utility model will become clearer after reading the detailed embodiments of this utility model in conjunction with the accompanying drawings. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 Here is a schematic diagram of an existing air conditioner.

[0057] Figure 2 This is a schematic diagram of the existing drive circuit.

[0058] Figure 3This is a circuit diagram showing the existing frequency converter topology for motors and the motor connections.

[0059] Figure 4 This is a schematic block diagram illustrating the application of the overcurrent protection circuit embodiment proposed in this application in a drive circuit.

[0060] Figure 5 This is a schematic block diagram of an embodiment of the overcurrent protection circuit proposed in this application;

[0061] Figure 6 This is a block diagram illustrating the principle of the self-locking circuit in an overcurrent protection circuit embodiment proposed in this application;

[0062] Figure 7 This is an implementation circuit for an overcurrent detection circuit in an overcurrent protection circuit embodiment according to the present application. Figure 1 ;

[0063] Figure 8 This is an implementation circuit for an overcurrent detection circuit in an overcurrent protection circuit embodiment according to the present application. Figure 2 ;

[0064] Figure 9 This is an implementation circuit for an overcurrent detection circuit in an overcurrent protection circuit embodiment according to the present application. Figure 3 ;

[0065] Figure 10 This is an implementation circuit for an overcurrent detection circuit in an overcurrent protection circuit embodiment according to the present application. Figure 4 ;

[0066] Figure label:

[0067] 10. Drive controller; 20. Drive circuit; 30. Variable frequency topology; 31. Rectifier circuit; 32. PFC circuit; 33. Inverter circuit; 40. Variable frequency motor; 50. Overcurrent detection circuit; 51. Comparator; 52. First voltage divider circuit; 53. Second voltage divider circuit; 60. Self-locking circuit; 61. First switch control unit; 62. Second switch control unit; 63. Third switch control unit; 70. Charging and discharging circuit. Detailed Implementation

[0068] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0069] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0070] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0071] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0072] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0073] The following disclosure provides many different embodiments or examples for implementing various structures of this invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the scope of the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0074] The basic working principle of an air conditioner is described below.

[0075] See Figure 1 An air conditioner executes a refrigeration cycle using a compressor, condenser, expansion valve, and evaporator. The refrigeration cycle involves a series of processes, including compression, condensation, expansion, and evaporation, to cool or heat an indoor space.

[0076] Low-temperature, low-pressure refrigerant enters the compressor, which compresses it into a high-temperature, high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0077] The expansion valve expands the high-temperature, high-pressure liquid refrigerant that condenses in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the expanded refrigerant in the expansion valve and returns the low-temperature, low-pressure refrigerant gas to the compressor. The evaporator achieves its cooling effect by utilizing the latent heat of refrigerant evaporation to exchange heat with the material being cooled. Throughout the cycle, the air conditioner regulates the temperature of the indoor space.

[0078] The outdoor unit of an air conditioner refers to the part of the refrigeration cycle that includes the compressor and the outdoor heat exchanger. The indoor unit of an air conditioner includes the indoor heat exchanger, and an expansion valve can be provided in either the indoor or outdoor unit.

[0079] The indoor and outdoor heat exchangers function as either condensers or evaporators. When the indoor heat exchanger is used as a condenser, the air conditioner functions as a heater in heating mode; when the indoor heat exchanger is used as an evaporator, the air conditioner functions as a cooler in cooling mode.

[0080] The variable frequency motor 40 is used in air conditioners and can be used as a motor for the compressor in the outdoor unit, a motor for the outdoor fan, a motor for the indoor fan, or a motor for the drain pump in the water tray in the indoor unit.

[0081] The operation of a variable frequency motor includes two aspects: drive and power supply. The drive is achieved through the drive circuit, and the power supply is achieved through the variable frequency topology 30.

[0082] In some embodiments of this application, see Figure 2 It shows the structure of the drive circuit, which includes a drive controller 10 and a drive circuit 20.

[0083] The drive controller 10 is the main control unit that drives the variable frequency motor 40. The drive controller 10 outputs a drive control signal to the drive circuit 20 to control the drive circuit 20 to output a PWM signal. The PWM signal is used for the switching transistor of the inverter circuit 33 in the variable frequency topology 30 to realize the on / off control of the switching transistor.

[0084] In some embodiments of this application, see Figure 2 and Figure 3 It shows a frequency conversion topology 30, which includes a rectifier circuit 31, a PFC circuit 32 and an inverter circuit 33 connected in sequence.

[0085] The input terminal of the rectifier circuit 31 is connected to a (single-phase or three-phase) AC power supply. The rectifier circuit 31 is used to rectify the AC power supplied by the AC power supply to obtain rectified pulsating waves.

[0086] In some embodiments of this application, the rectifier circuit 31 is a single-phase bridge rectifier bridge composed of four diodes, or a three-phase bridge rectifier bridge composed of six diodes.

[0087] See also Figure 3 The PFC circuit 32 is connected between the output terminal of the rectifier circuit 31 and the electrolytic capacitor E. The PFC circuit 32 is used to perform power factor correction on the power supply.

[0088] Electrolytic capacitor E is connected in parallel with variable frequency motor 40.

[0089] That is, after the AC power is rectified by the rectifier circuit 31, it passes through the PFC circuit 32 and then supplies power to the load through the inverter circuit 33.

[0090] In some embodiments of this application, the PFC circuit 32 includes an inductor L, a switching transistor Q1, and a diode D1. Its working principle is prior art and will not be described in detail here.

[0091] In some embodiments of this application, the inverter circuit 33 is a three-phase power inverter used to invert DC power and drive the variable frequency motor 40.

[0092] The three-phase power inverter consists of six switching transistors: T1 for the upper arm of phase U, T3 for the upper arm of phase V, T5 for the upper arm of phase W, T2 for the lower arm of phase U, T4 for the lower arm of phase V, and T6 for the lower arm of phase W.

[0093] The PWM signal output by the drive circuit 20 as described above is used to control the switching on and off of the switching transistor in the inverter circuit 33.

[0094] The control method used for the motor as described above is the mainstream field-oriented control (FOC), also known as vector control.

[0095] In some embodiments of this application, in order to realize overcurrent monitoring of the variable frequency motor 40 and avoid damage to the drive circuit or the variable frequency motor 40 due to excessive current in the drive circuit, an overcurrent protection circuit is provided to protect the drive circuit and the variable frequency motor 40 of the variable frequency appliance when an overcurrent occurs.

[0096] In some embodiments of this application, see Figure 4 The overcurrent protection circuit includes an overcurrent detection circuit 50 and a self-locking circuit 60.

[0097] The overcurrent detection circuit 50 is used to detect whether there is an overcurrent in the drive circuit, and outputs an overcurrent protection signal V when there is an overcurrent. FO .

[0098] The self-locking circuit 60 is used to detect the overcurrent protection signal V upon receipt. FO The PWM signal output of the drive circuit is cut off in time, so that the variable frequency motor 40 stops working and avoids damage to the variable frequency motor 40 due to abnormal operation of the drive circuit.

[0099] In some embodiments of this application, see Figure 4 Overcurrent protection signal V FO It split into two routes.

[0100] The signal is sent to the drive controller 10, which then controls the drive circuit 20 to cut off the output PWM signal. As a result, the variable frequency motor 40 stops working, thus forming the first stage of overcurrent protection.

[0101] The other signal is sent to the self-locking circuit 60, causing the self-locking circuit 60 to maintain the output of the self-locking signal V. DIS The signal is transmitted to the drive circuit 20, causing the drive circuit 20 to cut off the output PWM signal.

[0102] In this way, the variable frequency motor 40 stops working, thus forming a second-level overcurrent protection to avoid damage to the variable frequency motor 40 caused by abnormal control of the drive circuit, current fluctuations, etc.

[0103] In some embodiments of this application, see Figure 5 The overcurrent detection circuit 50 adopts the form of a comparator 51 to convert the detection of current into the detection of voltage. The comparator 51 includes a first input terminal, a second input terminal, and an output terminal.

[0104] In some embodiments of this application, the first input terminal is the positive input terminal of comparator 51, and the second input terminal is the negative input terminal of comparator 51. The first input terminal receives a reference level Vf, and the overcurrent protection setting value flows through the first voltage divider circuit 52, causing the first voltage divider circuit 52 to output the reference level. The second input terminal receives the divided voltage Vin output by the current output by the inverter circuit 33 through the second voltage divider circuit 53. By comparing the reference level Vf at the first input terminal with the divided voltage Vin at the second input terminal, an overcurrent protection signal V is output at the output terminal. FO .

[0105] See Figure 7 Resistors R7 and R8 are connected in series between the power supply VCC and ground to form the first voltage divider circuit 52 as described above. The reference level Vf of the first input terminal is VCC×R8 / (R7+R8), where VCC / (R7+R8) is the overcurrent protection setting value.

[0106] Therefore, by changing the resistance values ​​of resistors R7 and R8, the overcurrent protection setting value can be changed, and thus the reference level Vf will also change.

[0107] Resistors R9 and R10 are connected in series between the current terminal of the inverter circuit 33 and ground, forming the second voltage divider circuit 53 as described above, wherein the voltage corresponding to the current terminal is V. D， The voltage at the second input terminal is Vin = V D ×R9 / (R9+R10).

[0108] Overcurrent detection can be achieved by properly setting the resistance values ​​of resistors R7, R8, R9, and R10.

[0109] The output of inverter circuit 33 can output current through a current sensor or a resistor sampling circuit.

[0110] In some embodiments of this application, in order to improve the accuracy of the voltage input to the second input terminal of comparator 51 in real time, a first filter circuit (not shown) is further provided at the front end of the second input terminal to filter the voltage V. D Burrs, noise, etc.

[0111] In some embodiments of this application, the structure of the first filter circuit can be selected as a capacitor, a series-parallel capacitor, a capacitor and a resistor in parallel, etc.

[0112] See Figure 8The first filter circuit includes a capacitor C5 connected in parallel across resistor R9.

[0113] Under the initial normal state, the drive controller 10 outputs a self-locking reset signal V. reset When the signal is low, the self-locking signal V received by the drive circuit 20 is... DIS It is a low level.

[0114] In standby mode, the load current is 0, V D When the voltage is low (Vin < Vf), comparator 51 outputs a high level, i.e., the overcurrent protection signal V... FO It is a high level.

[0115] In some embodiments of this application, to ensure reliable operation of the frequency converter, the self-locking circuit 60 is reset before the frequency converter starts, that is, the self-locking reset signal V output by the drive controller 10 is reset. reset First, output a high level to unlock the self-locking circuit 60, then output V. reset Once the voltage level returns to low, the inverter enters overcurrent protection detection mode and can then operate normally.

[0116] When there is an overcurrent during the operation of the frequency converter, V D The voltage increase causes Vin > Vf, and the overcurrent protection signal V output by comparator 51... FO Low level; V FO The signal is detected by the drive controller 10, which controls the drive circuit 20 to cut off the output PWM signal, thereby achieving the first-level overcurrent protection.

[0117] In some embodiments of this application, in order to reliably enable the drive controller 10 to detect a low-level overcurrent protection signal V FO See Figure 9 A charging / discharging circuit 70 can be set at the output of comparator 51 to set V. FO The duration of the low level ensures that V FO When the level is low, it can be reliably detected by the drive controller 10, thereby ensuring the reliability of the first-stage overcurrent protection.

[0118] See Figure 9 The charging / discharging circuit 70 includes a first resistor R5, a first capacitor C3, a second resistor R6, and a power supply VCC. The first resistor R5 and the first capacitor C3 are connected in series between the power supply VCC and ground. One end of the second resistor R6 is connected to the output of the comparator 51, and the other end is connected to the common connection point of the first resistor R5 and the first capacitor C3. The common connection point of the first resistor R5 and the first capacitor C3 outputs an overcurrent protection signal V. FO .

[0119] In some embodiments of this application, referring back to 6, the self-locking circuit 60 includes a first switch control unit 61, a second switch control unit 62, and a third switch control unit 63.

[0120] The first switch control unit 61 is a high-level conducting switch element, and its control terminal receives a self-locking reset signal V. reset The first terminal is grounded, and the second terminal is connected to the second terminal of the second switch control unit 62 and the self-locking signal V. DIS .

[0121] In some embodiments of this application, see Figure 7 The first switch control unit 61 is selected as an NPN transistor Q1. The base of the NPN transistor Q1 is connected to the self-locking reset signal V through the current-limiting resistor R1. reset The emitter is grounded, and the collector is connected to the second terminal of the second switch control unit 62 and the self-locking signal V, respectively. DIS .

[0122] In V reset When the signal is high, NPN transistor Q1 is turned on, and the latching signal V... DIS It is pulled low to a low level.

[0123] In V reset When the signal is low, NPN transistor Q1 is cut off, and the latching signal V... DIS The on / off outputs of the second switch control unit 62 and the third switch control unit 63 are used to cut off the high-level signal of the output PWM signal.

[0124] In some embodiments of this application, the control terminal of the second switch control unit 62 receives an overcurrent protection signal V. FO The first terminal is grounded, and the second terminal is connected to the second terminal of the first switch control unit 61 and the self-locking signal V. DIS The common connection position of the pull-up resistor R2 and the control terminal of the third switch control unit 63.

[0125] The first terminal of the third switch control unit 63 is grounded, and the second terminal of the third switch control unit 63 is connected to the second terminal of the first switch control unit 61 and the self-locking signal V. DIS The common connection position of the pull-up resistor R2 and the control terminal of the third switch control unit 63.

[0126] In some embodiments of this application, the second switch control unit 62 and the third switch control unit 63 form a self-locking relationship during overcurrent and output a level signal that cuts off the output PWM signal.

[0127] In some embodiments of this application, see Figures 7 to 10The second switch control unit 62 is selected as NPN transistor Q2, and the third switch control unit 63 is also selected as NPN transistor Q3.

[0128] The base of NPN transistor Q2 is connected to the overcurrent protection signal V through current-limiting resistor R4. FO The emitter is grounded, and the collector is connected to the collector of NPN transistor Q1 and the latch-up signal V, respectively. DIS The common connection position of pull-up resistor R2 and base of NPN transistor Q3.

[0129] The emitter of NPN transistor Q3 is grounded, and its collector is connected to the common junction of the base of NPN transistor Q2 and current-limiting resistor R4.

[0130] In V reset When the voltage level is low, the self-locking circuit 60 enters the overcurrent protection detection state, at which time the NPN transistor Q1 is turned off.

[0131] When there is an overcurrent during the operation of the frequency converter, V D The voltage increase causes Vin > Vf, and the overcurrent protection signal V output by comparator 51... FO V is low level. FO The signal turns off NPN transistor Q2 and turns on NPN transistor Q3, locking the latching signal V. DIS It is a high level.

[0132] The drive circuit 20 receives a self-locking signal V DIS When the signal is high, the drive circuit 20 cuts off the drive signal and turns off the inverter circuit 33 to cut off the output PWM signal, thus achieving the second-level overcurrent protection.

[0133] In the self-locking signal V DIS After being locked to a high level, even if the overcurrent protection signal V... FO The signal continuously changes between high and low, and the self-locking signal V DIS It remains locked at a high level until the drive controller 10 sends a high-level self-locking reset signal V. reset Normal drive control can only be performed after the self-locking circuit 60 is reset, to prevent damage to the drive circuit and variable frequency motor 40 caused by abnormal drive control such as driver crash or runaway due to interference.

[0134] After completing the overcurrent protection, the drive controller 10 outputs a high-level self-locking reset signal V. reset Unlock the self-locking circuit 60, and then V reset Once the voltage level returns to low, the inverter enters overcurrent protection detection mode and can resume normal operation.

[0135] In some embodiments of this application, in order to reliably control the second switch control unit 62 and the third switch control unit 63, the self-locking circuit 60 further includes a second filter circuit (not shown) and a third filter circuit (not shown).

[0136] The second filtering circuit is located at the control terminal of the second switch control unit 62 and is used to filter the voltage signal input to the control terminal of the second switch control unit 62; the third filtering circuit is located at the control terminal of the third switch control unit 63 and is used to filter the voltage signal input to the control terminal of the third switch control unit 63.

[0137] In some embodiments of this application, see Figure 10 The second filter circuit includes a capacitor C2. One end of the capacitor C2 is connected to the common connection position of the base of the NPN transistor Q2 and the current limiting resistor R4, and the other end is grounded together with the emitter of the NPN transistor Q2.

[0138] In some embodiments of this application, the third filter circuit includes a resistor R3 and a capacitor C1 connected in parallel. One end of the parallel connection between capacitor C1 and resistor R3 is connected to the collector of NPN transistor Q2, the collector of NPN transistor Q1, pull-up resistor R2, and latch-up signal V. DIS The base of NPN transistor Q3 is connected in the same position as the base of NPN transistor Q3. The other end of capacitor C1 and resistor R3 connected in parallel is grounded together with the emitter of NPN transistor Q3.

[0139] This application utilizes simple discrete components to form an overcurrent protection circuit, which can achieve two-stage overcurrent protection and improve the reliability of overcurrent protection in the drive circuit.

[0140] In some embodiments of this application, the overcurrent protection circuit can be used in the drive circuit of a motor used in an air conditioner.

[0141] An air conditioner includes a refrigerant circulation loop that allows the refrigerant to circulate within a circuit consisting of a compressor, condenser, expansion valve, and evaporator.

[0142] When one of the outdoor and indoor heat exchangers is used as a condenser, the other is used as an evaporator.

[0143] The outdoor heat exchanger is used in conjunction with the outdoor fan, and the indoor heat exchanger is used in conjunction with the indoor fan.

[0144] The drain pump is a component of the indoor unit of an air conditioner. In the cooling mode of the air conditioner, when the airflow flows over the surface of the indoor heat exchanger, which acts as an evaporator, condensate will be generated on its surface. Generally, a drip tray is installed below the indoor heat exchanger to collect this condensate.

[0145] The drain pump is installed inside the drip tray and is used to draw the condensate in the drip tray to the outside of the air-conditioned indoor unit when the drain pump is started.

[0146] The overcurrent protection circuit described above can be used in the motor drive circuits of compressors, outdoor fans, indoor fans, and drain pumps to provide overcurrent protection for air conditioners.

[0147] In the description of the above embodiments, specific features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0148] The above are merely specific embodiments of this utility model, but the protection scope of this utility model is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the scope of the claims.

Claims

1. An overcurrent protection circuit for a drive circuit of a variable frequency motor, the drive circuit comprising: A drive controller, which outputs control signals to drive the variable frequency motor. A drive circuit, which receives the control signal and outputs a PWM signal to control the switching transistors in the inverter circuit, is characterized in that the overcurrent protection circuit includes: An overcurrent detection circuit is used to detect when the current output by the inverter circuit exceeds the overcurrent protection setting value, and output an overcurrent protection signal. The overcurrent protection signal is sent to the drive controller, and the drive controller controls the drive circuit to cut off the output PWM signal. The self-locking circuit receives the overcurrent protection signal and the self-locking reset signal output by the drive controller. When the self-locking reset signal is at a first level, the self-locking circuit receives the overcurrent protection signal and outputs a self-locking signal to cause the drive circuit to cut off the output PWM signal. When the self-locking reset signal is at a second level different from the first level, the self-locking circuit resets.

2. The overcurrent protection circuit according to claim 1, characterized in that, The overcurrent detection circuit includes: The comparator has a first input terminal, a second input terminal, and an output terminal. The first input terminal receives a reference level, the second input terminal receives the current output by the inverter circuit through a resistor, and the output terminal outputs the overcurrent protection signal.

3. The overcurrent protection circuit according to claim 2, characterized in that, The overcurrent detection circuit further includes: The first filter circuit is located at the front end of the second input terminal and is used to filter the voltage signal input to the second input terminal.

4. The overcurrent protection circuit according to claim 2, characterized in that, The overcurrent detection circuit further includes: A charging and discharging circuit is located at the output terminal of the comparator, and the output terminal of the charging and discharging circuit outputs the overcurrent protection signal.

5. The overcurrent protection circuit according to claim 4, characterized in that, The charging and discharging circuit includes a first power supply, a first resistor, a second resistor, and a first capacitor; The first resistor and the first capacitor are connected in series between the first power supply and ground. One end of the second resistor is connected to the output terminal of the comparator and the other end is connected to the common connection position of the first resistor and the first capacitor. The overcurrent protection signal is output from the common connection position of the first resistor and the first capacitor.

6. The overcurrent protection circuit according to claim 1, characterized in that, The self-locking circuit includes: The first switch control unit receives the self-locking reset signal at its control terminal and is grounded at its first terminal. The first switch control unit is a high-level conducting switch element. The second switch control unit receives the overcurrent protection signal at its control terminal, its first terminal is grounded, and its second terminal is connected to the common connection position of the second terminal of the first switch control unit, the self-locking signal, and the pull-up resistor. The third switch control unit has its control terminal connected to the common position of the second terminal of the first switch control unit, the second terminal of the second switch control unit, and the self-locking signal. The first terminal of the third switch control unit is grounded, and the second terminal of the third switch control unit is connected to the overcurrent protection signal.

7. The overcurrent protection circuit according to claim 6, characterized in that, The self-locking circuit also includes: The second filtering circuit is located at the control terminal of the second switch control unit and is used to filter the voltage signal input to the control terminal of the second switch control unit. The third filtering circuit is located at the control terminal of the third switch control unit and is used to filter the voltage signal input to the control terminal of the third switch control unit.

8. The overcurrent protection circuit according to claim 6, characterized in that, The first switch control unit, the second switch control unit, and the third switch control unit are all NPN transistors, with the base of the NPN transistor being its control terminal, the emitter of the NPN transistor being its first terminal, and the collector of the NPN transistor being its second terminal.

9. An air conditioner, characterized in that, include: The refrigerant circulation loop allows the refrigerant to circulate within a loop consisting of the compressor, condenser, expansion valve, and evaporator. A drive circuit for driving a variable frequency motor, wherein the variable frequency motor is a compressor motor, an outdoor fan motor, an indoor fan motor, and / or a drain pump motor in a drip tray, the drive circuit comprising: A drive controller, which outputs control signals to drive the variable frequency motor. A drive circuit, which receives the control signal and outputs a PWM signal to control the switching transistors in the inverter circuit; An overcurrent detection circuit is used to detect when the current output by the inverter circuit exceeds the overcurrent protection setting value, and output an overcurrent protection signal. The overcurrent protection signal is sent to the drive controller, and the drive controller controls the drive circuit to cut off the output PWM signal. The self-locking circuit receives the overcurrent protection signal and the self-locking reset signal output by the drive controller. When the self-locking reset signal is at a first level, the self-locking circuit receives the overcurrent protection signal and outputs a self-locking signal to cause the drive circuit to cut off the output PWM signal. When the self-locking reset signal is at a second level different from the first level, the self-locking circuit resets.

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