An air conditioner input voltage protection system and method based on a three-phase frequency converter

Abstract

The application discloses an air conditioner input voltage protection system and method based on a three-phase frequency converter, and relates to the technical field of frequency converters.The air conditioner input voltage protection method comprises the following steps: obtaining actual current by performing coordinate transformation on three-phase output current, obtaining actual rotating speed by combining instruction voltage and motor parameters, obtaining instruction current by combining the actual rotating speed and a set instruction rotating speed, and obtaining instruction voltage and output voltage by performing calculation on the actual current and the instruction current; obtaining output power according to the instruction voltage and the actual current in a synchronous rotating coordinate system; verifying the linear relationship between the output power and voltage difference, the existence of a constant coefficient, and the proportional relationship with bus voltage; calculating the voltage difference according to the linear relationship between the output power and the voltage difference, obtaining the voltage on the smoothing capacitor when the air conditioner is in use, and calculating the voltage of the air conditioner when the air conditioner is stopped, the power phase voltage and the input current by combining the constant coefficient.

Description

Technical Field

[0001] This invention relates to the field of frequency converter technology, specifically to an air conditioner input voltage protection system and method based on a three-phase frequency converter. Background Technology

[0002] In a household three-phase inverter air conditioner, the three-phase power supply provides three-phase AC power with a rated phase voltage of 220Vac / 50Hz. An AC reactor connected in series on each phase acts as a passive PFC (Power Factor Correction) circuit, improving the power factor and reducing current harmonics to meet the requirements of the national standard GB17625.1. The inductance of the AC reactor is very large, typically 20-30mH. This passive PFC solution has a simple circuit and low cost. The three-phase diode uncontrolled rectifier section is responsible for rectifying the input three-phase AC power into DC power, which is stored in the smoothing capacitor. The inverter is responsible for converting the DC power into AC power with adjustable magnitude and frequency to control the compressor's operation.

[0003] When air conditioners are installed in rural areas or peri-urban areas, the power grid is often found to be very unstable, with large fluctuations in phase voltage. The voltage can drop as low as 150V, causing the input current to increase significantly, leading to severe overheating of the AC reactor and potentially damage. Simultaneously, nearby wiring and other components exposed to high temperatures may also be damaged. The voltage can also rise to over 300V, and such drastic fluctuations can cause inverter malfunctions or even damage. The usual approach to overvoltage protection is to detect the power supply voltage and then determine the appropriate protection method based on the detection result. However, this method requires additional voltage detection devices, increasing the cost of the air conditioner. Summary of the Invention

[0004] The purpose of this invention is to provide an air conditioner input voltage protection system and method based on a three-phase frequency converter, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for protecting the input voltage of an air conditioner based on a three-phase frequency converter, the method comprising the following steps:

[0006] Step S100: The three-phase output current is transformed by coordinate transformation to obtain the actual current, and the actual speed is obtained by combining the command voltage and motor parameters;

[0007] Step S200: Combine the actual rotational speed and the set commanded rotational speed to obtain the commanded current, and calculate the commanded voltage and output voltage using the actual current and the commanded current;

[0008] Step S300: In the synchronous rotating coordinate system, obtain the output power based on the command voltage and the actual current;

[0009] Step S400: Based on the different voltages on the smoothing capacitor when the air conditioner is off and when it is in use, obtain a voltage difference and verify the linear relationship between the output power and the voltage difference; at the same time, when the power supply phase voltage and input power remain unchanged, verify that there is a constant coefficient that is proportional to the bus voltage.

[0010] Step S500: Calculate the voltage difference based on the linear relationship between output power and voltage difference, obtain the voltage on the smoothing capacitor when the air conditioner is in use, and calculate the voltage, power supply phase voltage and input current when the air conditioner is off by combining the constant coefficient.

[0011] Furthermore, step S100 includes the following steps:

[0012] Step S101: Detect the three-phase output current I a I b I c The actual current I is obtained through coordinate transformation in a synchronous rotating coordinate system. d I q ;

[0013] Step S102: The command voltage obtained by the voltage command generator is... Combined with motor parameters, the actual compressor speed f is estimated using the position estimation method based on extended back electromotive force. out .

[0014] Furthermore, the extended back EMF position estimation method in step S102 includes the following steps:

[0015] Step S102.1: Set up a real dq axis system; define an extended back electromotive force E of the motor. 0x According to the formula:

[0016] E 0x =ω e [K e +(L d -L q )i d ]+p(L q -L d )i q

[0017] Where, ω e K is the rotor electric angular velocity. e L is the electromotive force constant of the motor. d and L q For the inductance along the d and q axes of the stator, i d and i q Let E be the current along the d and q axes of the stator, and p be the differential operator; in the dq axis system, with respect to E... 0x The rotor position θ is obtained by estimation. rand velocity ω r ;

[0018] Step S102.2: Define a PMSM stator voltage equation:

[0019]

[0020] Among them, u d and u q R is the voltage across the d-axis and q-axis of the stator. s ω is the stator armature resistance. r Let ψ be the rotor's mechanical angular velocity. f For rotor permanent magnet flux linkage; E 0x Substituting into the PMSM stator voltage equation, according to the formula:

[0021]

[0022] Obtain the component form of the dq axis system;

[0023] Step S102.3: Set up a synchronously rotating dc-qc coordinate system, and use the Park transformation to transform the dq axis components into the dc-qc coordinate system. Let the transformation angle be Δθ, according to the formula:

[0024]

[0025] Among them, u dc and u qc For the voltages along the DC and QC axes of the stator, i dc and i qc For the stator DC and QC shaft currents; when the motor reaches steady state, pi dc pi qc The value of pΔθ is 0, E 0x The components on the dc-qc axis are represented as follows:

[0026]

[0027] command voltage Substitute u dc , Substitute u qc The actual current I d Substitute i dc I q Substitute i qc E 0xdc and E 0xqc Substituting into the PLL estimator, according to the formula:

[0028]

[0029] The actual synchronization speed ω was calculated.restim Therefore, the actual compressor speed f out =ω restim .

[0030] Furthermore, step S200 includes the following steps:

[0031] Step S201: Set a command speed on the control board. The calculated actual rotational speed f out and command speed The command current is obtained after the current command generator.

[0032] Step S202: Set the command current The command voltage is obtained through the voltage command generator. The three-phase voltage is obtained through coordinate transformation in a synchronous rotating coordinate system. and It is applied to the motor stator to drive the motor to rotate.

[0033] Furthermore, step S300 includes the following steps:

[0034] In a synchronous rotating coordinate system, based on the obtained command voltage and actual current, according to the formula:

[0035]

[0036] The output power P was calculated. out ,in, For command voltage, I d I q This represents the actual current.

[0037] Furthermore, step S400 includes the following steps:

[0038] Step S401: Let the voltage across the smoothing capacitor be Udc. When the air conditioner is in use, set the effective value of the power supply phase voltage to V. IN The line voltage is Line voltage amplitude is When the air conditioner is turned off, the current is 0, and the voltage across the smoothing capacitor reaches its maximum value Udc. MAX ,get

[0039] Step S402: Let the inductance of the AC reactor be L, and the current of the reactor be I. IN The power supply frequency is f, according to the formula:

[0040] V L =2π×f×L×I IN

[0041] Among them, VL The voltage across the reactor; set the voltage V before rectification of the AC reactor. I =V IN -V L The voltage of the smoothing capacitor Therefore, there exists a voltage difference ΔV, according to the formula:

[0042]

[0043] Obtain ΔV and V L They are linearly related, therefore ΔV and I IN It is also a linear relationship;

[0044] Step S403: Let the input power of the three-phase frequency converter be P. IN According to the formula:

[0045]

[0046] in, The input power factor is used to obtain the input power P. IN with I IN They are linearly related, therefore ΔV and P IN It is also a linear relationship;

[0047] Step S404: Let the output power of the three-phase frequency converter be P. out According to the formula:

[0048] P out =P IN ×η

[0049] Where η is the efficiency of the three-phase frequency converter's output power relative to its input power; the output power P is obtained. out With input power P IN They are linearly related, therefore ΔV and P out It is also a linear relationship;

[0050] Step S405: Set the DC-side power to Pdc and the DC-side current to Idc, where the DC-side power Pdc is equivalent to the output power P. out According to the formula:

[0051] pdc = Udc × Idc

[0052] get

[0053] Therefore, we get

[0054] When the power supply phase voltage V IN When the input power PIN remains constant, And η are constants, and the constant coefficients are set to k1, where, A proportional relationship was found between the constant coefficient k1 and the voltage Udc on the smoothing capacitor of the three-phase frequency converter.

[0055] Furthermore, step S500 includes the following steps:

[0056] Step S501: Based on ΔV and P out To establish a linear relationship, we obtain the voltage difference ΔV and the output power P. out Relationship:

[0057]

[0058] Where k and b are constant coefficients, P min The minimum power is set; the output power P is calculated accordingly. out Calculate the voltage difference ΔV;

[0059] Step S502: Calculate Udc based on the calculated voltage difference ΔV. MAX =Udc + ΔV; Calculate the phase voltage V of the power supply according to the formula. IN :

[0060]

[0061] To provide protection against excessive power supply voltage;

[0062] Step S502: Based on the proportional relationship between k1 and Udc, according to the formula:

[0063] k1=k ref +(Udc-U ref )×Δk

[0064] Where, k ref When Udc = U ref The scaling factor, U ref This is the reference value for Udc, and Δk is the scaling factor change per 1V. According to the formula:

[0065]

[0066] Where k1 is a constant coefficient, P out To calculate the output power, the input current I is obtained. IN .

[0067] Furthermore, to better implement the above method, an air conditioner input voltage protection system based on a three-phase frequency converter is proposed. This system includes a closed-loop feedback adjustment module, an output power calculation module, a verification module, and a power supply phase voltage calculation module.

[0068] The closed-loop feedback adjustment module is used to obtain the actual current from the three-phase output current through coordinate transformation, and to obtain the actual speed by combining the command voltage and motor parameters; to obtain the command current by combining the actual speed and the set command speed; and to obtain the command voltage and output voltage by calculating the actual current and the command current.

[0069] The output power calculation module is used to obtain the output power based on the command voltage and the actual current in a synchronous rotating coordinate system.

[0070] The verification module is used to obtain a voltage difference based on the different voltages on the smoothing capacitor when the air conditioner is off and when it is in use, and to verify the linear relationship between the output power and the voltage difference; at the same time, when the power supply phase voltage and input power remain unchanged, it verifies that there is a constant coefficient that is proportional to the bus voltage.

[0071] The voltage and current calculation module is used to calculate the voltage difference based on the linear relationship between the output power and the voltage difference, obtain the voltage on the smoothing capacitor when the air conditioner is in use, and calculate the voltage, power supply phase voltage and input current when the air conditioner is off by combining the constant coefficient.

[0072] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) In a three-phase variable frequency air conditioner with an AC reactor, the protection is usually carried out by directly detecting the power supply voltage and current; the present invention does not detect the power supply voltage and input current, but calculates the voltage difference ΔV based on the output power, and adds the bus voltage to calculate the power supply voltage and input current, thereby protecting the power supply voltage and input current. The algorithm is simple, does not increase any cost, and has high accuracy; (2) The present invention is calculated in a synchronous rotating coordinate system, and the voltage and current quantities are... I d I q All of these are direct current quantities, which remain constant under steady-state conditions. Furthermore, due to the use of vector closed-loop control, the compressor operates stably, further enhancing the stability of these quantities. Therefore, the results obtained by this method are more accurate. Attached Figure Description

[0073] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0074] Figure 1 This is a schematic diagram illustrating the steps of an air conditioner input voltage protection method based on a three-phase frequency converter.

[0075] Figure 2 This is a schematic diagram of an air conditioner input voltage protection system based on a three-phase frequency converter.

[0076] Figure 3This is a block diagram of the PLL estimator principle;

[0077] Figure 4 This is a schematic diagram of the conversion between three-phase output current and output voltage. Detailed Implementation

[0078] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0079] Please see Figures 1 to 4 The present invention provides a technical solution: a method for protecting the input voltage of an air conditioner based on a three-phase frequency converter, the method comprising the following steps:

[0080] Step S100: The three-phase output current is transformed by coordinate transformation to obtain the actual current, and the actual speed is obtained by combining the command voltage and motor parameters;

[0081] Step S100 includes the following steps:

[0082] Step S101: Detect the three-phase output current I a I b I c The actual current I is obtained through coordinate transformation in a synchronous rotating coordinate system. d I q ;

[0083] Step S102: The command voltage obtained by the voltage command generator is... Combined with motor parameters, the actual compressor speed f is estimated using the position estimation method based on extended back electromotive force. out ;

[0084] The extended back electromotive force position estimation method in step S102 includes the following steps:

[0085] Step S102.1: Set up a real dq axis system; define an extended back electromotive force E of the motor. 0x According to the formula:

[0086] E 0x =ω e [K e +(L d -L q )i d ]+p(L q -L d )i q

[0087] Where, ω e K is the rotor electric angular velocity. e L is the electromotive force constant of the motor. d and L q For the inductance along the d and q axes of the stator, i d and i q Let E be the current along the d and q axes of the stator, and p be the differential operator; in the dq axis system, with respect to E... 0x The rotor position θ is obtained by estimation. r and velocity ω r ;

[0088] Step S102.2: Define a PMSM stator voltage equation:

[0089]

[0090] Among them, u d and u q R is the voltage across the d-axis and q-axis of the stator. s ω is the stator armature resistance. r Let ψ be the rotor's mechanical angular velocity. f For rotor permanent magnet flux linkage; E 0x Substituting into the PMSM stator voltage equation, according to the formula:

[0091]

[0092] Obtain the component form of the dq axis system;

[0093] Step S102.3: Set up a synchronously rotating dc-qc coordinate system, and use the Park transformation to transform the dq axis components into the dc-qc coordinate system. Let the transformation angle be Δθ, according to the formula:

[0094]

[0095] Among them, u dc and u qc For the voltages along the DC and QC axes of the stator, i dc and i qc For the stator DC and QC shaft currents; when the motor reaches steady state, pi dc pi qc The value of pΔθ is 0, E 0x The components on the dc-qc axis are represented as follows:

[0096]

[0097] command voltage Substitute u dc , Substitute uqc The actual current I d Substitute i dc I q Substitute i qc E 0xdc and E 0xqc Substituting into the PLL estimator, according to the formula:

[0098]

[0099] The actual synchronization speed ω was calculated. restim Therefore, the actual compressor speed f out =ω restim .

[0100] Step S200: Combine the actual rotational speed and the set commanded rotational speed to obtain the commanded current, and calculate the commanded voltage and output voltage using the actual current and the commanded current;

[0101] Step S200 includes the following steps:

[0102] Step S201: Set a command speed on the control board. The calculated actual rotational speed f out and instruction transition The command current is obtained after the current command generator.

[0103] Step S202: Set the command current The command voltage is obtained through the voltage command generator. The three-phase voltage is obtained through coordinate transformation in a synchronous rotating coordinate system. and It is applied to the motor stator to drive the motor to rotate.

[0104] Step S300: In the synchronous rotating coordinate system, obtain the output power based on the command voltage and the actual current;

[0105] Step S300 includes the following steps:

[0106] In a synchronous rotating coordinate system, based on the obtained command voltage and actual current, according to the formula:

[0107]

[0108] The output power P was calculated. out ,in, For command voltage, I d I q This represents the actual current.

[0109] Step S400: Based on the different voltages on the smoothing capacitor when the air conditioner is off and when it is in use, obtain a voltage difference and verify the linear relationship between the output power and the voltage difference; at the same time, when the power supply phase voltage and input power remain unchanged, verify that there is a constant coefficient that is proportional to the bus voltage.

[0110] Step S400 includes the following steps:

[0111] Step S401: Let the voltage across the smoothing capacitor be Udc. When the air conditioner is in use, set the effective value of the power supply phase voltage to V. IN The line voltage is Line voltage amplitude is When the air conditioner is turned off, the current is 0, and the voltage across the smoothing capacitor reaches its maximum value Udc. MAX ,get

[0112] Step S402: Let the inductance of the AC reactor be L, and the current of the reactor be I. IN The power supply frequency is f, according to the formula:

[0113] V L =2π×f×L×I IN

[0114] Among them, V L The voltage across the reactor; set the voltage V before rectification of the AC reactor. I =V IN -V L The voltage of the smoothing capacitor Therefore, there exists a voltage difference ΔV, according to the formula:

[0115]

[0116] Obtain ΔV and V L They are linearly related, therefore ΔV and I IN It is also a linear relationship;

[0117] Step S403: Let the input power of the three-phase frequency converter be P. IN According to the formula:

[0118]

[0119] in, The input power factor is used to obtain the input power P. IN with I IN They are linearly related, therefore ΔV and P IN It is also a linear relationship;

[0120] Step S404: Let the output power of the three-phase frequency converter be P. outAccording to the formula:

[0121] P out =P IN ×η

[0122] Where η is the efficiency of the three-phase frequency converter's output power relative to its input power; the output power P is obtained. out With input power P IN They are linearly related, therefore ΔV and P out It is also a linear relationship;

[0123] Step S405: Set the DC-side power to Pdc and the DC-side current to Idc, where the DC-side power Pdc is equivalent to the output power P. out According to the formula:

[0124] pdc = Udc × Idc

[0125] get

[0126] Therefore, we get

[0127] When the power supply phase voltage V IN and input power P IN When kept constant, cosφ and η are constants, and the constant coefficients are set to k1, where, A proportional relationship was found between the constant coefficient k1 and the voltage Udc on the smoothing capacitor of the three-phase frequency converter.

[0128] Step S500: Calculate the voltage difference based on the linear relationship between output power and voltage difference, obtain the voltage on the smoothing capacitor when the air conditioner is in use, and calculate the voltage, power supply phase voltage and input current when the air conditioner is off by combining the constant coefficient.

[0129] Step S500 includes the following steps:

[0130] Step S501: Based on ΔV and P out To establish a linear relationship, we obtain the voltage difference ΔV and the output power P. out Relationship:

[0131]

[0132] Where k and b are constant coefficients, P min The minimum power is set; the output power P is calculated accordingly. out Calculate the voltage difference ΔV;

[0133] Step S502: Calculate Udc based on the calculated voltage difference ΔV. MAX =Udc + ΔV; Calculate the phase voltage V of the power supply according to the formula.IN :

[0134]

[0135] To provide protection against excessive power supply voltage;

[0136] Step S502: Based on the proportional relationship between k1 and Udc, according to the formula:

[0137] k1=k ref +(Udc-U ref )×Δk

[0138] Where, k ref When Udc = U ref The scaling factor, U ref This is the reference value for Udc, and Δk is the scaling factor change per 1V. According to the formula:

[0139]

[0140] Where k1 is a constant coefficient, P out To calculate the output power, the input current I is obtained. IN .

[0141] For a 5-horsepower air conditioner, it is desirable to implement protection when the power supply phase voltage reaches 275Vac, resulting in the following formula:

[0142]

[0143] According to the formula, when the power supply phase voltage is 275V, the data measured are shown in Table 1:

[0144] Table 1: Experimental Data on Voltage Difference and Output Power

[0145] ΔV(V) 31 37 45 53 62 71 <![CDATA[V IN (V)]]> 274 274 276 276 275 276 <![CDATA[P out (W)]]> 3517 4013 4468 5035 5452 5732 ΔV(V) 79 88 95 105 112 117 <![CDATA[V IN (V)]]> 275 274 274 274 275 276

[0146] Based on the test data, the calculated V IN It is very close to the actual power supply phase voltage of 275V, which can realize the protection against overvoltage.

[0147] For a 5-horsepower air conditioner, it is desirable to limit the input current to around 9.5A, which yields the following formula:

[0148] k1=0.8+(Udc-430)×0.0004 0.76≤k1≤0.84

[0149]

[0150] The experimental data obtained are shown in Table 2:

[0151] Table 2: Experimental data on power supply phase voltage, input power, and actual current.

[0152] Input power (W) 4203 5435 6830 6770 Actual current (A) 9.37 9.26 9.57 9.05 Calculated output power (W) 4038 5052 6053 6027 Bus voltage (V) 329 434 532 560 Calculated current (A) 9.3 9.3 9.6 9.0

[0153] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0154] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for protecting the input voltage of an air conditioner based on a three-phase frequency converter, characterized in that: The method includes the following steps: Step S100: The three-phase output current is transformed by coordinate transformation to obtain the actual current, and the actual speed is obtained by combining the command voltage and motor parameters; Step S200: Combine the actual rotational speed and the set commanded rotational speed to obtain the commanded current, and calculate the commanded voltage and output voltage using the actual current and the commanded current; Step S300: In the synchronous rotating coordinate system, obtain the output power based on the command voltage and the actual current; Step S400: Based on the different voltages on the smoothing capacitor when the air conditioner is off and when it is in use, obtain a voltage difference and verify the linear relationship between the output power and the voltage difference; at the same time, when the power supply phase voltage and input power remain unchanged, verify that there is a constant coefficient that is proportional to the bus voltage. Step S500: Calculate the voltage difference based on the linear relationship between output power and voltage difference, obtain the voltage on the smoothing capacitor when the air conditioner is in use, and calculate the voltage, power supply phase voltage and input current when the air conditioner is off by combining the constant coefficient.

2. The method for protecting the input voltage of an air conditioner based on a three-phase frequency converter according to claim 1, characterized in that: Step S100 includes the following steps: Step S101: Detect the three-phase output current I a I b I c The actual current I is obtained through coordinate transformation in a synchronous rotating coordinate system. d I q ; Step S102: The command voltage obtained by the voltage command generator is... Combined with motor parameters, the actual compressor speed f is estimated using the position estimation method based on extended back electromotive force. out .

3. The method for protecting the input voltage of an air conditioner based on a three-phase frequency converter according to claim 2, characterized in that: The extended back electromotive force position estimation method in step S102 includes the following steps: Step S102.1: Set up a real dq axis system; define an extended back electromotive force E of the motor. 0x According to the formula: E 0x =ω e [K e +(L d -L q )i d ]+p(L q -L d )i q Where, ω e K is the rotor electric angular velocity. e L is the electromotive force constant of the motor. d and L q For the inductance along the d and q axes of the stator, i d and i q Let E be the current along the d and q axes of the stator, and p be the differential operator; in the dq axis system, with respect to E... 0x The rotor position θ is obtained by estimation. r and velocity ω r ; Step S102.2: Define a PMSM stator voltage equation: Among them, u d and u q R is the voltage across the d-axis and q-axis of the stator. s ω is the stator armature resistance. r Let ψ be the rotor's mechanical angular velocity. f For rotor permanent magnet flux linkage; E 0x Substituting into the PMSM stator voltage equation, according to the formula: Obtain the component form of the dq axis system; Step S102.3: Set up a synchronously rotating dc-qc coordinate system, and use the Park transformation to transform the dq axis components into the dc-qc coordinate system. Let the transformation angle be Δθ, according to the formula: Among them, u dc and u qc For the voltages along the DC and QC axes of the stator, i dc and i qc For the stator DC and QC shaft currents; when the motor reaches steady state, pi dc pi qc The value of pΔθ is 0, E 0x The components on the dc-qc axis are represented as follows: command voltage Substitute u dc , Substitute u qc The actual current I d Substitute i dc I q Substitute i qc E 0xdc and E 0xqc Substituting into the PLL estimator, according to the formula: The actual synchronization speed ω was calculated. restim Therefore, the actual compressor speed f out =ω restim .

4. The method for protecting the input voltage of an air conditioner based on a three-phase frequency converter according to claim 2, characterized in that: Step S200 includes the following steps: Step S201: Set a command speed on the control board. The calculated actual rotational speed f out and command speed The command current is obtained after the current command generator. Step S202: Set the command current The command voltage is obtained through the voltage command generator. The three-phase voltage is obtained through coordinate transformation in a synchronous rotating coordinate system. and It is applied to the motor stator to drive the motor to rotate.

5. The method for protecting the input voltage of an air conditioner based on a three-phase frequency converter according to claim 1, characterized in that: Step S300 includes the following steps: In a synchronous rotating coordinate system, based on the obtained command voltage and actual current, according to the formula: The output power P was calculated. out ,in, For command voltage, I d I q This represents the actual current.

6. The method for protecting the input voltage of an air conditioner based on a three-phase frequency converter according to claim 5, characterized in that: Step S400 includes the following steps: Step S401: Let the voltage across the smoothing capacitor be Udc. When the air conditioner is in use, set the effective value of the power supply phase voltage to V. IN The line voltage is Line voltage amplitude is When the air conditioner is turned off, the current is 0, and the voltage across the smoothing capacitor reaches its maximum value Udc. MAX ,get Step S402: Let the inductance of the AC reactor be L, and the current of the reactor be I. IN The power supply frequency is f, according to the formula: In L =2π×f×L×I IN Among them, V L The voltage across the reactor; set the voltage V before rectification of the AC reactor. I =V IN -V L The voltage of the smoothing capacitor Therefore, there exists a voltage difference ΔV, according to the formula: Obtain ΔV and V L They are linearly related, therefore ΔV and I IN It is also a linear relationship; Step S403: Let the input power of the three-phase frequency converter be P. IN According to the formula: in, The input power factor is used to obtain the input power P. IN with I IN They are linearly related, therefore ΔV and P IN It is also a linear relationship; Step S404: Let the output power of the three-phase frequency converter be P. out According to the formula: P out =P IN ×η Where η is the efficiency of the three-phase frequency converter's output power relative to its input power; the output power P is obtained. out With input power P IN They are linearly related, therefore ΔV and P out It is also a linear relationship; Step S405: Set the DC-side power to Pdc and the DC-side current to Idc, where the DC-side power Pdc is equivalent to the output power P. out According to the formula: Pdc = Udc × Idc get Therefore, we get When the power supply phase voltage V IN and input power P IN When kept constant, cosφ and η are constants, and the constant coefficients are set to k1, where, A proportional relationship was found between the constant coefficient k1 and the voltage Udc on the smoothing capacitor of the three-phase frequency converter.

7. The method for protecting the input voltage of an air conditioner based on a three-phase frequency converter according to claim 6, characterized in that: Step S500 includes the following steps: Step S501: Based on ΔV and P out To establish a linear relationship, we obtain the voltage difference ΔV and the output power P. out Relationship: Where k and b are constant coefficients, P min The minimum power is set; the output power P is calculated accordingly. out Calculate the voltage difference ΔV; Step S502: Calculate Udc based on the calculated voltage difference ΔV. MAX =Udc + ΔV; Calculate the phase voltage V of the power supply according to the formula. IN : To provide protection against excessive power supply voltage; Step S502: Based on the proportional relationship between k1 and Udc, according to the formula: k1=k ref +(Udc-U ref )×Δk Where, k ref When Udc = U ref The scaling factor, U ref This is the reference value for Udc, and Δk is the scaling factor change per 1V; according to the formula: Where k1 is a constant coefficient, P out To calculate the output power, the input current I is obtained. IN .

8. An air conditioner input voltage protection system based on a three-phase frequency converter, applied to the air conditioner input voltage protection method based on a three-phase frequency converter as described in any one of claims 1-7, characterized in that: The air conditioner input voltage protection system includes a closed-loop feedback adjustment module, an output power calculation module, a verification module, and a voltage and current calculation module. The closed-loop feedback adjustment module is used to obtain the actual current from the three-phase output current through coordinate transformation, and to obtain the actual speed by combining the command voltage and motor parameters; to obtain the command current by combining the actual speed and the set command speed; and to obtain the command voltage and output voltage by calculating the actual current and the command current. The output power calculation module is used to obtain the output power based on the command voltage and the actual current in a synchronous rotating coordinate system. The verification module is used to obtain a voltage difference based on the different voltages on the smoothing capacitor when the air conditioner is off and when it is in use, and to verify the linear relationship between the output power and the voltage difference; at the same time, when the power supply phase voltage and input power remain unchanged, it verifies that there is a constant coefficient that is proportional to the bus voltage. The voltage and current calculation module is used to calculate the voltage difference based on the linear relationship between the output power and the voltage difference, obtain the voltage on the smoothing capacitor when the air conditioner is in use, and calculate the voltage, power supply phase voltage and input current when the air conditioner is off by combining the constant coefficient.

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