Neutral line missing detection circuit and air conditioner

Abstract

The utility model discloses a detection circuit for lack of neutral line and an air conditioner, wherein the detection circuit for lack of neutral line comprises: a line voltage detection circuit, respectively used for accessing any two-phase live wires in a three-phase power supply; a phase voltage detection circuit, respectively used for accessing one phase and a neutral wire in the two-phase live wires; a control chip, respectively connected to the output end of the phase voltage detection circuit and the output end of the line voltage detection circuit, the control chip is used for performing per-unit processing on the line voltage detection signal according to the phase voltage detection signal accessed, and outputting neutral line lack alarm information when the per-unit value of the line voltage after the per-unit processing is higher than a preset reference per-unit value; the technical scheme of the utility model aims to timely detect the lack of neutral line and reduce the difficulty of troubleshooting caused by the lack of neutral line.

Description

Technical Field

[0001] The utility model relates to the technical field of air conditioners, in particular to a detection circuit for lack of a neutral line and an air conditioner. Background Art

[0002] At present, three-phase four-wire power supply controllers are often used in high-power commercial air conditioners. During the power supply process, when the neutral line is accidentally lost, the single-phase power that should have been powered will lose power. Due to the presence of differential mode capacitors in the power supply controller, the leakage current of the differential mode capacitors will generate a voltage close to but less than the single-phase power on the single-phase line. This voltage can make the back-end switching power supply work, making the controller look normal, but unable to control the load to work normally, and unable to report the corresponding fault, making troubleshooting difficult. Utility Model Content

[0003] The main purpose of the utility model is to provide a detection circuit for lack of a neutral line and an air conditioner, aiming at timely detecting the lack of a neutral line and reducing the difficulty of troubleshooting caused by the lack of a neutral line.

[0004] To achieve the above object, the utility model provides a detection circuit for lack of neutral line, which is applied to a three-phase four-wire power supply controller. The detection circuit for lack of neutral line includes:

[0005] A line voltage detection circuit, wherein the two input terminals of the line voltage detection circuit are respectively used to connect to any two-phase live wires in a three-phase power supply, and the line voltage detection circuit is used to rectify and differentially process the input voltages of the two-phase live wires and output corresponding line voltage detection signals;

[0006] A phase voltage detection circuit, wherein the two input terminals of the phase voltage detection circuit are respectively used to connect to one phase of the two-phase live wire and the neutral wire, and the phase voltage detection circuit is used to rectify and differentially process the input voltage of the live wire and output a corresponding phase voltage detection signal;

[0007] The control chip is respectively connected to the output end of the phase voltage detection circuit and the output end of the line voltage detection circuit. The control chip is used to perform per-unit processing on the line voltage detection signal according to the connected phase voltage detection signal, and output neutral line missing alarm information when the per-unit value of the line voltage after per-unit processing is higher than a preset reference per-unit value.

[0008] In some embodiments, the line voltage detection circuit includes:

[0009] A first rectifier circuit, wherein two input ends of the first rectifier circuit are respectively used to connect to the two-phase live wires, and the first rectifier circuit is used to rectify the input voltages of the two-phase live wires and output two corresponding DC voltages;

[0010] A first differential circuit, wherein two input terminals of the first differential circuit are respectively connected to two output terminals of the first rectifier circuit in a one-to-one correspondence, and the first differential circuit is used to perform differential processing on two connected DC voltages and output corresponding line voltage detection signals.

[0011] In some embodiments, the phase voltage detection circuit includes:

[0012] a second rectifier circuit, wherein two input terminals of the second rectifier circuit are respectively used to connect to one phase of the two-phase live wire and the neutral wire, and the second rectifier circuit is used to rectify the input voltage of the live wire and the voltage of the neutral wire, and output a corresponding DC voltage;

[0013] The second differential circuit, the two input ends of the second differential circuit are respectively connected to the two output ends of the second rectifier circuit in a one-to-one correspondence, and the second differential circuit is used to perform differential processing on the two connected DC voltages and output corresponding phase voltage detection signals.

[0014] In some embodiments, the first differential circuit or the second differential circuit includes:

[0015] An operational amplifier having a non-inverting input terminal, an inverting input terminal and an output terminal;

[0016] a first resistor connected in parallel to two output ends of the first rectifier circuit or the second rectifier circuit;

[0017] a second resistor and a third resistor, wherein the first end of the second resistor is used to access a power supply and is connected to the first end of the first resistor, the second end of the second resistor is connected to the non-inverting input end, and the third resistor is connected in parallel between the second end of the first resistor and the inverting input end;

[0018] a fourth resistor, wherein a first end of the fourth resistor is connected to the output end of the operational amplifier, and a second end of the fourth resistor is connected to the control chip;

[0019] A fifth resistor is connected in parallel between the inverting input terminal of the operational amplifier and the output terminal of the operational amplifier.

[0020] In some embodiments, the phase voltage detection circuit or the line voltage detection circuit further includes:

[0021] The filter circuit is connected in parallel between the two input ends of the first differential circuit or the two input ends of the second differential circuit, and is used for filtering the connected DC voltage and then outputting it.

[0022] In some embodiments, the filtering circuit comprises:

[0023] The first capacitor is connected in parallel to both ends of the first resistor.

[0024] In some embodiments, the neutral line missing detection circuit further includes:

[0025] An alarm component, wherein a controlled end of the alarm component is electrically connected to the control chip;

[0026] The control chip is specifically used to control the warning component to work so as to output neutral line missing alarm information when the per-unit value of the line voltage after per-unit processing is higher than a preset reference per-unit value.

[0027] The utility model also proposes an air conditioner, including a three-phase four-wire power supply controller and the above-mentioned neutral line missing detection circuit, wherein the power supply end of the three-phase four-wire power supply controller is used to connect to the three-phase live wire and the neutral wire, and the power supply end of the neutral line missing detection circuit is used to connect to any two-phase live wire and the neutral wire.

[0028] In some embodiments, the three-phase four-wire power supply controller is used to rectify the line voltage between any two phase live wires connected thereto and output a corresponding first DC power supply;

[0029] The air conditioner also includes:

[0030] An inverter, wherein two input ends of the inverter are electrically connected to the three-phase four-wire power supply controller respectively, and the inverter is used to output an adjustable AC power after inverting the first DC power supply.

[0031] In some embodiments, the three-phase four-wire power supply controller is used to rectify the phase voltage between any phase live wire and the neutral wire connected, and output the corresponding second DC power supply;

[0032] The air conditioner also includes:

[0033] A switching power supply, wherein the two input terminals of the switching power supply are respectively electrically connected to the three-phase four-wire power supply controller, and the switching power supply is used to output a third DC power supply with an adjustable voltage value after performing multiple voltage conversion processes on the second DC power supply.

[0034] The technical solution of the utility model is to set a line voltage detection circuit and a phase voltage detection circuit, respectively collect the line voltage between any two phases of the three-phase live wires, and the phase voltage between any one phase of the two phases and the neutral line, and output the corresponding line voltage detection signal and phase voltage detection signal to the control chip, and then use the per-unit function and comparison function of the control chip to process the voltage value of the line voltage detection signal with the voltage value of the phase voltage detection signal, and output the zero line missing alarm information when the per-unit value of the line voltage after the per-unit processing is higher than the preset reference per-unit value. It avoids the influence of the differential mode capacitor in the filter of the three-phase four-wire power supply controller, when the neutral line is disconnected, the power supply connected to it makes the load unable to work normally, and because the corresponding fault cannot be reported, it causes difficulties in troubleshooting. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0036] Figure 1 It is a structural schematic diagram of an embodiment of a detection circuit for lack of neutral line of the utility model;

[0037] Figure 2 It is a structural schematic diagram of another embodiment of the detection circuit for lack of neutral line of the utility model;

[0038] Figure 3 It is a structural schematic diagram of another embodiment of the detection circuit for lack of neutral line of the utility model;

[0039] Figure 4 It is a structural schematic diagram of another embodiment of the detection circuit for lack of neutral line of the utility model;

[0040] Figure 5 A schematic diagram of a current loop of an embodiment of a three-phase four-wire power supply controller;

[0041] Figure 6 A current loop schematic diagram of another embodiment of a three-phase four-wire power supply controller;

[0042] Figure 7 A current loop schematic diagram of another embodiment of a three-phase four-wire power supply controller;

[0043] Figure 8 This is a comparison chart of the single-phase voltage value of a three-phase four-wire power supply when the neutral wire is missing and in a normal state.

[0044] Description of Figure Numbers:

[0045] Label name Label name 100 Line voltage detection circuit 500 Alert Components 110 The first rectifier circuit U1 Operational Amplifier 120 First differential circuit R1~R5 The first resistor to the fifth resistor 200 Phase voltage detection circuit C1 First capacitor 210 Second rectifier circuit Cy1~Cy8 Common mode capacitor 220 Second differential circuit Cx1~Cx6 Differential mode capacitance 300 Control chip RV1~RV6 Differential mode resistance 400 Filter circuit L1 Filter Inductor

[0046] The realization of the purpose, functional features and advantages of the utility model will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0048] In addition, in the present utility model, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present utility model.

[0049] The utility model provides a detection circuit for lack of a neutral line, which is applied to a three-phase four-wire power supply controller.

[0050] Reference Figure 1 In one embodiment, the detection circuit for lacking a neutral line comprises:

[0051] A line voltage detection circuit 100, wherein the two input terminals of the line voltage detection circuit 100 are respectively used to connect to any two-phase live wires in a three-phase power supply, and the line voltage detection circuit 100 is used to rectify and differentially process the input voltages of the two-phase live wires, and then output corresponding line voltage detection signals;

[0052] A phase voltage detection circuit 200, wherein the two input terminals of the phase voltage detection circuit 200 are respectively used to connect to one phase of the two-phase live wire and the neutral wire, and the phase voltage detection circuit 200 is used to rectify and differentially process the input voltage of the live wire and output a corresponding phase voltage detection signal;

[0053] The control chip 300 is connected to the output end of the phase voltage detection circuit 200 and the output end of the line voltage detection circuit 100 respectively. The control chip 300 is used to perform per-unit processing on the line voltage detection signal according to the connected phase voltage detection signal, and output a zero line missing alarm message when the per-unit value of the line voltage after per-unit processing is higher than a preset reference per-unit value.

[0054] It should be noted that the existing air conditioners usually use three-phase four-wire power supply controllers, which can reduce the current stress of the device on the one hand, and reduce the imbalance of the grid load on the other hand. In order to meet the national standard EMC (electromagnetic compatibility) requirements, the input current generally needs to add an EMI (electromagnetic interference) filter, that is, Figure 5 The input circuit shown in is composed of differential mode capacitors Cx1~Cx6, common mode capacitors Cy1~Cy8, common mode resistors RV1~RV6, filter inductor L1 and other devices.

[0055] In normal operation, the current loop connected to the three-phase four-wire power supply controller is as follows Figure 6 As shown, the live wire and the neutral wire form a current loop together, forming a voltage difference at both ends of the rectifier module. Therefore, when the neutral wire is disconnected, the live wire should not be able to form a current loop with the neutral wire, making the three-phase four-wire power supply controller unable to work.

[0056] However, when the differential mode capacitor in the input circuit leaks, the three-phase live wire will Figure 7 As shown, a current loop is formed through the leakage differential mode capacitor, so that the single-phase circuit generates voltage after flowing through the rectifier module. The voltage generated by the leakage of the differential mode capacitor increases with the increase of the differential mode capacitor capacity, and is close to and less than the single-phase power supply voltage, as shown in Figure 8 As shown in the figure, when the rated voltage is 220V, the voltage generated by the differential mode capacitor leakage is only 172V.

[0057] Therefore, in this embodiment, the magnitude relationship between the line voltage and the phase voltage is utilized to respectively set the line voltage detection circuit 100 and the phase voltage detection circuit 200, and the line voltage between any two phases of the three-phase live wires is detected by the line voltage, and the corresponding line voltage detection signal is output to the control chip 300, and the phase voltage detection circuit 200 detects the phase voltage between any one phase of the live wire and the neutral line in the above two phases of the live wires, and outputs the corresponding phase voltage detection signal. It can be understood that the mapping ratio of the voltage value of the phase voltage detection signal to the detected phase voltage value is consistent with the mapping ratio of the voltage value of the line voltage detection signal to the detected line voltage value. Therefore, after receiving the detection signals of two different voltage values, the control chip 300 can use the internal integrated per-unit module to perform per-unit processing on the voltage value of the line voltage detection signal with the voltage value of the phase voltage detection signal, and the output line voltage per-unit value is the effective value of the line voltage and the phase voltage.

[0058] Among them, although the voltage generated by the differential mode capacitor leakage is close to and less than the single-phase power supply voltage, since the phase voltage is a sinusoidal waveform, its voltage value is constantly changing even after rectification, and sometimes the voltage value suddenly increases due to noise interference and other reasons. If only the phase voltage is detected, it cannot ensure that the voltage generated by the differential mode capacitor leakage is accurately detected.

[0059] Therefore, the control chip 300 selects a CPU, MCU, etc. that integrates a per-unit module and a comparator, and outputs the processed line voltage per-unit value to the comparison circuit integrated in the control chip 300. Since under normal three-phase power supply conditions, the effective values ​​of the line voltage and the phase voltage are in a ratio of 1.732, the reference per-unit value can be set to a value close to the effective value ratio, such as 1.8 or 1.75. If, after comparison processing by the comparator, the output signal representing the line voltage per-unit value is greater than the reference per-unit value, it indicates that the neutral line is missing and the differential mode capacitor is leaking. If, after comparison processing by the comparator, the output signal representing the line voltage per-unit value is not greater than the reference per-unit value, it indicates that the neutral line is normal.

[0060] The technical solution of the utility model is to set a line voltage detection circuit 100 and a phase voltage detection circuit 200, respectively collect the line voltage between any two phases of the three-phase live wires, and the phase voltage between any one phase of the two phases and the neutral line, and output the corresponding line voltage detection signal and phase voltage detection signal to the control chip 300, and then use the per-unit function and comparison function of the control chip 300 to process the voltage value of the line voltage detection signal with the voltage value of the phase voltage detection signal, and output the zero line missing alarm information when the per-unit value of the line voltage after the per-unit processing is higher than the preset reference per-unit value. It avoids the influence of the differential mode capacitor in the filter of the three-phase four-wire power supply controller, when the neutral line is disconnected, the power supply connected to it makes the load unable to work normally, and because the corresponding fault cannot be reported, it causes difficulties in troubleshooting.

[0061] Reference Figure 1 and Figure 2 In one embodiment, the line voltage detection circuit 100 includes:

[0062] A first rectifier circuit 110, wherein two input terminals of the first rectifier circuit 110 are respectively used to connect to the two-phase live wires, and the first rectifier circuit 110 is used to rectify the input voltage between the two-phase live wires and output two corresponding DC voltages;

[0063] The first differential circuit 120, the two input terminals of the first differential circuit 120 are respectively connected to the two output terminals of the first rectifier circuit 110 in a one-to-one correspondence, and the first differential circuit 120 is used to perform differential processing on the two connected DC voltages and output the corresponding line voltage detection signal.

[0064] In this embodiment, the first rectifier circuit 110 is a full-bridge rectifier circuit. Taking the three-phase live wires of R phase, S phase and T phase as an example, when collecting the line voltage between the S phase and the T phase, the two input ends of the first rectifier circuit 110 are respectively connected to the S phase live wire and the T phase live wire, and after rectifying the connected S phase AC voltage and the T phase AC voltage, the corresponding S phase DC voltage and T phase DC voltage are output, and the two DC voltages are output to the first differential circuit 120. Through the differential processing of the first differential circuit 120, the corresponding line voltage VST, that is, the line voltage between the S phase and the T phase, is obtained.

[0065] Reference Figure 1 and Figure 2 In one embodiment, the phase voltage detection circuit 200 includes:

[0066] A second rectifier circuit 210, wherein two input terminals of the second rectifier circuit 210 are respectively used to connect to one phase of the two-phase live wire and the neutral wire, and the second rectifier circuit 210 is used to rectify the input voltage of the live wire and the voltage of the neutral wire, and output a corresponding DC voltage;

[0067] The second differential circuit 220, the two input terminals of the second differential circuit 220 are respectively connected to the two output terminals of the second rectifier circuit 210 in a one-to-one correspondence, and the second differential circuit 220 is used to perform differential processing on the two connected DC voltages and output corresponding phase voltage detection signals.

[0068] In this embodiment, the second rectifier circuit 210 is a full-bridge rectifier circuit. Taking the three-phase live wires of R phase, S phase and T phase as an example, when collecting the phase voltage of the T phase live wire, the two input ends of the second rectifier circuit 210 are respectively connected to the T phase live wire and the neutral line N, and after rectifying the connected T phase AC voltage and the AC voltage of the neutral line N, the corresponding T phase DC voltage and the neutral line N DC voltage are output, and the two DC voltages are output to the second differential circuit 220. Through the differential processing of the second differential circuit 220, the corresponding line voltage VTN, that is, the phase voltage between the T phase live wire and the neutral line N is obtained.

[0069] Reference Figure 1 , Figure 2 and Figure 4 In one embodiment, the first differential circuit 120 or the second differential circuit 220 includes:

[0070] An operational amplifier U1 having a non-inverting input terminal, an inverting input terminal and an output terminal;

[0071] A first resistor R1 is connected in parallel to two output ends of the first rectifier circuit 110 or the second rectifier circuit 210;

[0072] a second resistor R2 and a third resistor R3, wherein the first end of the second resistor R2 is used to access a power supply and is connected to the first end of the first resistor R1, the second end of the second resistor R2 is connected to the non-inverting input end, and the third resistor R3 is connected in parallel between the second end of the first resistor R1 and the inverting input end;

[0073] a fourth resistor R4, wherein a first end of the fourth resistor R4 is connected to the output end of the operational amplifier U1, and a second end of the fourth resistor R4 is connected to the control chip 300;

[0074] The fifth resistor R5 is connected in parallel between the inverting input terminal of the operational amplifier U1 and the output terminal of the operational amplifier U1.

[0075] In this embodiment, the first resistor R1 is used to shunt the output DC voltage, the second resistor R2 and the third resistor R3 are used to divide the input DC voltage, and the fifth resistor R5 is a feedback resistor of the operational amplifier U1.

[0076] Reference Figure 1 , Figure 2 and Figure 4 In one embodiment, the phase voltage detection circuit 200 or the line voltage detection circuit 100 further includes:

[0077] The filter circuit 400 is connected in parallel between the two input ends of the first differential circuit 120 or the two input ends of the second differential circuit 220 . The filter circuit 400 is used for filtering the input DC voltage and then outputting the filtered DC voltage.

[0078] In this embodiment, the filtering circuit 400 includes:

[0079] The first capacitor C1 is connected in parallel to the two ends of the first resistor R1, and is used to stabilize the connected DC voltage to prevent the clutter generated by noise interference from affecting the operation of the operational amplifier U1.

[0080] Reference Figure 1 and Figure 3 In one embodiment, the detection circuit for lacking a neutral line further comprises:

[0081] An alarm component 500, wherein a controlled end of the alarm component 500 is electrically connected to the control chip 300;

[0082] The control chip 300 is specifically used to control the alarm component 500 to work so as to output neutral line missing alarm information when the per-unit value of the line voltage after per-unit processing is higher than a preset reference per-unit value.

[0083] In this embodiment, when the control chip 300 detects that the neutral line of the connected three-phase four-wire power supply is disconnected according to the line voltage standard value, it will control the corresponding warning component 500 to output the corresponding neutral line missing alarm information. The neutral line missing alarm information can be freely defined by the research and development personnel according to the device selected by the warning component 500. The warning component 500 may include a display screen, an LED warning light, a buzzer or a voice broadcast component, etc. Correspondingly, the neutral line missing alarm information can be a "neutral line missing" subtitle displayed on the screen, a lit red warning light, a long buzzer sound, or a "neutral line missing" language prompt, etc.

[0084] The utility model also proposes an air conditioner, which includes a three-phase four-wire power supply controller and the above-mentioned neutral line missing detection circuit. The specific structure of the neutral line missing detection circuit refers to the above-mentioned embodiment. The power supply end of the three-phase four-wire power supply controller is used to connect to the three-phase live wire and the neutral wire, and the power supply end of the neutral line missing detection circuit is used to connect to any two-phase live wire and the neutral wire.

[0085] Since the air conditioner adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0086] It can be understood that the three-phase line is supplied to the three-phase inverter after passing through the three-phase rectifier bridge, and one phase plus the neutral line is supplied to the switching power supply after passing through the single-phase rectifier bridge, and the secondary single-phase can also be connected to other single-phase loads.

[0087] In one embodiment, the three-phase four-wire power supply controller is used to rectify the line voltage between any two phase live wires connected thereto and output a corresponding first DC power supply;

[0088] The air conditioner also includes:

[0089] An inverter, wherein two input ends of the inverter are electrically connected to the three-phase four-wire power supply controller respectively, and the inverter is used to output an adjustable AC power after inverting the first DC power supply.

[0090] In this embodiment, if Figures 5 to 7 As shown, the three-phase four-wire power supply controller includes a rectifier module 1 connected to the three-phase live wire, and the rectifier module rectifies the three-phase alternating current output by the three-phase live wire. The inverter is connected to the two output ends of the rectifier module, and inverts the rectified first direct current power supply. By adjusting the operating frequency of the inverter, AC power of different frequencies can be output.

[0091] In one embodiment, the three-phase four-wire power supply controller is used to rectify the phase voltage between any phase live wire and the neutral wire connected, and output the corresponding second DC power supply;

[0092] The air conditioner also includes:

[0093] A switching power supply, wherein the two input terminals of the switching power supply are respectively electrically connected to the three-phase four-wire power supply controller, and the switching power supply is used to output a third DC power supply with an adjustable voltage value after performing multiple voltage conversion processes on the second DC power supply.

[0094] In this embodiment, if Figures 5 to 7As shown, the three-phase four-wire power supply controller also includes a rectifier module 2 connected to any one-phase live wire and neutral wire, and the rectifier module rectifies the alternating current output by the single-phase live wire. The switching power supply is connected to the two output ends of the rectifier module, and the rectified second DC power supply is subjected to voltage conversion processing. By adjusting the operating frequency of the switching power supply, a third DC power supply with different frequencies can be output.

[0095] The above description is only an optional embodiment of the utility model, and does not limit the patent scope of the utility model. All equivalent structural changes made by using the contents of the utility model specification and drawings under the utility model concept, or directly / indirectly used in other related technical fields are included in the patent protection scope of the utility model.

Claims

1. A detection circuit for lack of neutral line, applied to a three-phase four-wire power supply controller, characterized in that: The detection circuit for lacking a neutral line comprises: A line voltage detection circuit, wherein the two input terminals of the line voltage detection circuit are respectively used to connect to any two-phase live wires in a three-phase power supply, and the line voltage detection circuit is used to rectify and differentially process the input voltages of the two-phase live wires and output corresponding line voltage detection signals; A phase voltage detection circuit, wherein the two input terminals of the phase voltage detection circuit are respectively used to connect to one phase of the two-phase live wire and the neutral wire, and the phase voltage detection circuit is used to rectify and differentially process the input voltage of the live wire and output a corresponding phase voltage detection signal; The control chip is respectively connected to the output end of the phase voltage detection circuit and the output end of the line voltage detection circuit. The control chip is used to perform per-unit processing on the line voltage detection signal according to the connected phase voltage detection signal, and output neutral line missing alarm information when the per-unit value of the line voltage after per-unit processing is higher than a preset reference per-unit value.

2. The detection circuit for missing neutral line according to claim 1, characterized in that: The line voltage detection circuit comprises: A first rectifier circuit, wherein two input ends of the first rectifier circuit are respectively used to connect to the two-phase live wires, and the first rectifier circuit is used to rectify the input voltages of the two-phase live wires and output two corresponding DC voltages; A first differential circuit, wherein two input terminals of the first differential circuit are respectively connected to two output terminals of the first rectifier circuit in a one-to-one correspondence, and the first differential circuit is used to perform differential processing on two connected DC voltages and output corresponding line voltage detection signals.

3. The detection circuit for lack of neutral line according to claim 1, characterized in that: The phase voltage detection circuit comprises: a second rectifier circuit, wherein two input terminals of the second rectifier circuit are respectively used to connect to one phase of the two-phase live wire and the neutral wire, and the second rectifier circuit is used to rectify the input voltage of the live wire and the voltage of the neutral wire, and output a corresponding DC voltage; The second differential circuit, the two input ends of the second differential circuit are respectively connected to the two output ends of the second rectifier circuit in a one-to-one correspondence, and the second differential circuit is used to perform differential processing on the two connected DC voltages and output corresponding phase voltage detection signals.

4. The detection circuit for lack of neutral line according to claim 3, characterized in that: The second differential circuit comprises: An operational amplifier having a non-inverting input terminal, an inverting input terminal and an output terminal; A first resistor connected in parallel to two output ends of the second rectifier circuit; a second resistor and a third resistor, wherein the first end of the second resistor is used to access a power supply and is connected to the first end of the first resistor, the second end of the second resistor is connected to the non-inverting input end, and the third resistor is connected in parallel between the second end of the first resistor and the inverting input end; a fourth resistor, wherein a first end of the fourth resistor is connected to the output end of the operational amplifier, and a second end of the fourth resistor is connected to the control chip; A fifth resistor is connected in parallel between the inverting input terminal of the operational amplifier and the output terminal of the operational amplifier.

5. The detection circuit for lack of neutral line according to claim 4, characterized in that: The phase voltage detection circuit or the line voltage detection circuit further includes: A filter circuit is connected in parallel between the two input terminals of the second differential circuit, and the filter circuit is used for filtering the input DC voltage and then outputting it.

6. The detection circuit for lack of neutral line according to claim 5, characterized in that: The filtering circuit comprises: The first capacitor is connected in parallel to both ends of the first resistor.

7. The detection circuit for lack of neutral line according to claim 1, characterized in that: The detection circuit for lacking a neutral line further comprises: An alarm component, wherein a controlled end of the alarm component is electrically connected to the control chip; The control chip is specifically used to control the warning component to work so as to output neutral line missing alarm information when the per-unit value of the line voltage after per-unit processing is higher than a preset reference per-unit value.

8. An air conditioner, characterized in that: It comprises a three-phase four-wire power supply controller and a neutral line missing detection circuit as described in any one of claims 1 to 7, wherein the power supply end of the three-phase four-wire power supply controller is used to connect to three-phase live wires and a neutral wire, and the power supply end of the neutral line missing detection circuit is used to connect to any two-phase live wires and a neutral wire.

9. The air conditioner according to claim 8, characterized in that: The three-phase four-wire power supply controller is used to rectify the line voltage between any two phase live wires connected to it and output the corresponding first DC power supply; The air conditioner also includes: An inverter, wherein two input ends of the inverter are electrically connected to the three-phase four-wire power supply controller respectively, and the inverter is used to output an adjustable AC power after inverting the first DC power supply.

10. The air conditioner according to claim 8, characterized in that: The three-phase four-wire power supply controller is used to rectify the phase voltage between any phase live wire and the neutral wire connected, and output the corresponding second DC power supply; The air conditioner also includes: A switching power supply, wherein the two input terminals of the switching power supply are respectively electrically connected to the three-phase four-wire power supply controller, and the switching power supply is used to output a third DC power supply with an adjustable voltage value after performing multiple voltage conversion processes on the second DC power supply.

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