Energy-saving modulation algorithm for inverters dedicated to air compressors

Abstract

The present invention proposes an energy-saving modulation algorithm for a special frequency converter for air compressors. First, the loss of the energy-saving modulation algorithm in different working modes is predicted, and then the mode with the least loss is output as the optimal loss mode. Then, it is determined whether the energy-saving modulation algorithm with the optimal loss belongs to one of the linear modulation area, the overmodulation I area, and the overmodulation II area, and the corresponding modulation wave is calculated in the corresponding area. The generated modulation wave is compared with the standard triangular carrier to obtain a PWM signal, which is injected into the inverter circuit to generate a new conduction current for iterative calculation to realize the energy-saving modulation algorithm. The present invention controls the algorithm switching in real time to ensure that the internal loss of the control system is minimized and realize energy-saving modulation.

Description

Technical Field

[0001] The invention relates to the field of special frequency converters for air compressors, and in particular to an energy-saving modulation algorithm for special frequency converters for air compressors. Background Art

[0002] An air compressor is a device that generates compressed air and is the main part of an air source device. As an important power device, it converts the mechanical energy of a prime mover, usually an electric motor, into gas pressure energy. It compresses the air in the atmosphere to increase its density and pressure, thereby enabling it to have more energy storage capacity. This way of storing energy can meet the demand for high-pressure gas in many industrial production processes and is widely used in various industries and fields.

[0003] At present, air compressor systems all use inverters for motor drive, so reducing the inverter loss will greatly improve the overall operating efficiency of the air compressor. The inverter loss mainly comes from switching loss, which mainly includes turn-on loss and turn-off loss. Turn-on loss refers to the power loss generated when the power tube changes from cut-off to conduction, while turn-off loss refers to the power loss generated when the power tube changes from conduction to cut-off. The optimization methods for the inverter air compressor switching loss include: optimizing the control method, using efficient switching devices, and reasonably designing circuits; among them, the optimization control method is the easiest to achieve and the most obvious improvement effect among all conditions. Nowadays, the air compressor control method for reducing switching loss is to select a minimum loss modulation algorithm for control, but because the air compressor system is in a constant change process, the error is large, and the algorithm cannot be guaranteed to be in the optimal loss state at any time. Therefore, it is very important to study an energy-saving modulation algorithm for an inverter dedicated to air compressors. Summary of the invention

[0004] To solve the above problems, the present invention proposes an energy-saving modulation algorithm for a dedicated frequency converter for air compressors. The algorithm unifies the calculations of different modulation algorithms to find the optimal loss algorithm, switches the control algorithms in real time, ensures that the internal loss of the control system is minimized, and realizes energy-saving modulation.

[0005] An energy-saving modulation algorithm for a frequency converter dedicated to an air compressor comprises the following steps:

[0006] Step S1, obtaining the coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system , , through 2s / 3s transformation , Convert to the three-phase stationary coordinate system to obtain its coordinate value , , ; Among them, the 2s / 3s transformation formula is:

[0007] ,

[0008] in, is the a-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the b-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the c-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the α-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, It is the β-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system.

[0009] Step S2, according to the coordinate values ​​in the two-phase stationary αβ coordinate system , Get the reference voltage vector magnitude , reference voltage vector magnitude The calculation formula is:

[0010] ,

[0011] in is the α-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, is the β-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, is the reference voltage vector magnitude.

[0012] According to the reference voltage vector magnitude , DC bus voltage The modulation ratio m is obtained; the calculation formula of the modulation ratio m is:

[0013] ,

[0014] Where m is the modulation ratio, is the circumference of a circle, is the reference voltage vector magnitude, is the DC bus voltage.

[0015] Step S3, by calculating the switching losses of the energy-saving modulation algorithms in different working modes, the algorithm with the minimum switching loss is regarded as the energy-saving modulation algorithm with the optimal loss;

[0016] The energy-saving modulation algorithm of the air compressor dedicated inverter has seven working modes, and different working modes correspond to different classes and phase angles. .

[0017] When the energy-saving modulation algorithm is in working mode 1, the category , phase angle ;

[0018] When the energy-saving modulation algorithm is in working mode 2, the category , phase angle ;

[0019] When the energy-saving modulation algorithm is in working mode 3, the category , phase angle ;

[0020] When the energy-saving modulation algorithm is in operating mode 4, the category , phase angle ;

[0021] When the energy-saving modulation algorithm is in working mode 5, the category , phase angle ;

[0022] When the energy-saving modulation algorithm is in working mode 6, the category , phase angle ;

[0023] When the energy-saving modulation algorithm is in working mode seven, the category , phase angle .

[0024] According to the IGBT voltage drop 、IGBT on-current The switching loss of a single switching cycle can be obtained:

[0025] ,

[0026] ,

[0027] in, is the turn-on loss, For the opening time, is the integral symbol, is the IGBT tube voltage drop, is the IGBT on-state current, t is the time, dt is the differential operator, is the turn-off loss, is the off time.

[0028] Among them, the IGBT tube voltage drop The calculation method is: Based on the output characteristic curves of the IGBT voltage drop and on-state current at 25°C, 150°C and 175°C provided in the data sheet, the IGBT voltage drop at the specified temperature and IGBT on-state current can be obtained through programming interpolation. At this time, the switching method between the original modulation algorithm and this modulation algorithm is: switching is performed when the current passes through the zero point.

[0029] The switching losses of the IGBT and the freewheeling diode FWD can be calculated through the switching losses of a single switching cycle.

[0030] When the working mode of the energy-saving modulation algorithm is working mode 1, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0031] When the working mode of the energy-saving modulation algorithm is working mode 2, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0032] When the working mode of the energy-saving modulation algorithm is working mode 3, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0033] When the working mode of the energy-saving modulation algorithm is working mode 4, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0034] When the working mode of the energy-saving modulation algorithm is working mode 5, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0035] When the working mode of the energy-saving modulation algorithm is working mode 6, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0036] When the working mode of the energy-saving modulation algorithm is working mode seven, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in .

[0037] Comparison of total switching losses in each operating mode of energy-saving modulation algorithms , , , , , , , we get the energy-saving modulation algorithm working mode with the minimum total switching loss, and the corresponding category of this working mode is called and phase angle , which corresponds to the energy-saving modulation algorithm with optimal loss.

[0038] Step S4, determining the region to which the energy-saving modulation algorithm with the best loss belongs, the regions including: linear modulation region, overmodulation I region, overmodulation II region;

[0039] The linear modulation range is: , when the m value range in step S2 satisfies When , the area of ​​the energy-saving modulation algorithm with the optimal loss belongs to the linear modulation area;

[0040] The range of overmodulation zone I is: , when the m value range in step S2 satisfies When , the area to which the energy-saving modulation algorithm with the optimal loss belongs is the overmodulation I area;

[0041] The range of overmodulation zone II is: , when the m value range in step S2 satisfies At this time, the area to which the energy-saving modulation algorithm with optimal loss belongs is the overmodulation II area.

[0042] Step S5: Select the category of the energy-saving modulation algorithm with the best loss and phase angle , the modulation wave is calculated by the area to which the algorithm belongs ;

[0043] (1) Linear modulation area: The three-phase modulation wave expression is obtained according to the zero-sequence component injection method. The zero-sequence component calculation expression is:

[0044] ,

[0045] ,

[0046] ,

[0047] ,

[0048] in, is the zero sequence component, k is the zero vector distribution coefficient, is the maximum value of the three-phase symmetrical sinusoidal signal, is the minimum value of the three-phase symmetrical sinusoidal signal, is a phase symmetrical sinusoidal signal, is a b-phase symmetrical sinusoidal signal, is a c-phase symmetrical sinusoidal signal.

[0049] When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles To perform translation, the translation signal is:

[0050] ,

[0051] Then determine the maximum value of the translation signal and minimum value , the sum of the maximum and minimum values ​​is positive, that is hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, .

[0052] When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles Shift is performed. At this time, the shifted signal is equal to the three-phase sinusoidal signal. Therefore, the maximum and minimum values ​​of the shifted signal are equal to the maximum and minimum values ​​of the three-phase sinusoidal signal. Then, the maximum and minimum values ​​of the shifted signal are determined, that is, the maximum and minimum values ​​of the three-phase sinusoidal signal are determined. The sum of the maximum and minimum values ​​is positive, that is, hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, .

[0053] When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles To perform translation, the translation signal is:

[0054] ,

[0055] Then determine the maximum value of the translation signal and minimum value , the sum of the maximum and minimum values ​​is positive, that is hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ;

[0056] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the maximum and minimum values ​​are obtained from the three-phase sinusoidal signal, when the sum of the maximum and minimum values ​​is positive, that is, hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ;

[0057] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ;

[0058] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ;

[0059] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is .

[0060] Injecting the zero-sequence component into the three-phase symmetrical sinusoidal signal generates a modulated wave ;

[0061] (2) Overmodulation I area: The modulation wave of the overmodulation I area is calculated by the weighted sum of the modulation waves of the maximum linear modulation area and the hexagonal edge part;

[0062] The modulation wave calculation formula in overmodulation zone I is:

[0063] ,

[0064] ,

[0065] in, is the modulated wave, is the overmodulation I zone ratio, is the modulation wave in the maximum linear modulation area, is the modulation wave of the edge of the hexagon, a is the a phase, b is the b phase, c is the c phase, and m is the modulation ratio;

[0066] in, The calculation formula is:

[0067] , , ,

[0068] in, is the modulation wave of phase a at the edge of the hexagon, is the modulation wave of phase b at the edge of the hexagon, is the modulation wave of phase c at the edge of the hexagon, is the angle of the reference voltage vector, is the pi, and cot is the tangent cosine function.

[0069] (3) Overmodulation II region: The modulation wave in the overmodulation II region is calculated by the weighted sum of the modulation waves of the hexagonal edge part and the six-beat wave part; the modulation wave calculation formula in the overmodulation II region is:

[0070] ,

[0071] ,

[0072] in, is the modulated wave, is the overmodulation II zone ratio, is the modulation wave of the hexagonal edge part, is the modulation wave of the six-beat wave part, a is the a phase, b is the b phase, c is the c phase, and m is the modulation ratio;

[0073] in, The calculation formula is:

[0074] , , ,

[0075] in, is the modulation wave of phase a of the six-beat wave part, is the modulation wave of phase b of the six-beat wave part, is the modulation wave of phase c of the six-beat wave part, is the angle of the reference voltage vector, is the pi, and cot is the tangent cosine function.

[0076] Step S6, the generated modulated wave By comparing with the standard triangular carrier, a PWM signal can be obtained and injected into the inverter circuit to generate a new conduction current and re-substitute it into step S3 for iterative calculation to realize the energy-saving modulation algorithm.

[0077] The technical effect of the present invention is that different modulation algorithms are uniformly calculated to find the optimal loss algorithm, and the algorithm is switched in real time to ensure that the internal loss of the control system is minimized, thereby achieving energy-saving modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 A flowchart of an energy-saving modulation algorithm for a dedicated frequency converter for an air compressor provided by the present invention;

[0079] Figure 2 A flow chart of the loss calculation module provided by the present invention;

[0080] Figure 3 A flow chart of the modulation algorithm module provided by the present invention;

[0081] Figure 4 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , Modulation algorithm simulation diagram;

[0082] Figure 5 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , Modulation algorithm simulation diagram;

[0083] Figure 6 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , Modulation algorithm simulation diagram;

[0084] Figure 7 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , Modulation algorithm simulation diagram;

[0085] Figure 8 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , Modulation algorithm simulation diagram;

[0086] Fig. 9 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , Modulation algorithm simulation diagram;

[0087] Fig.10 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , Modulation algorithm simulation diagram;

[0088] Fig.11 A comparison chart of switching losses between the energy-saving modulation algorithm with optimal loss provided by the present invention and other algorithms. DETAILED DESCRIPTION

[0089] The following is only a preferred embodiment of the present invention; the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can understand the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, all inventions and creations using the concept of the present invention are protected.

[0090] Figure 1 The energy-saving modulation algorithm flow chart of the inverter for air compressor provided by the present invention is as follows: Figure 1 As shown in the figure, the energy-saving modulation algorithm of the air compressor dedicated inverter includes the following steps:

[0091] Step S1, obtaining the coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system , , through 2s / 3s transformation , Convert to the three-phase stationary coordinate system to obtain its coordinate value , , ; Among them, the 2s / 3s transformation formula is:

[0092] ,

[0093] in, is the a-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the b-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the c-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the α-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, It is the β-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system.

[0094] Step S2, according to the coordinate values ​​in the two-phase stationary αβ coordinate system , Get the reference voltage vector magnitude , reference voltage vector magnitude The calculation formula is:

[0095] ,

[0096] in is the α-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, is the β-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, is the reference voltage vector magnitude.

[0097] According to the reference voltage vector magnitude , DC bus voltage The modulation ratio m is obtained; the calculation formula of the modulation ratio m is:

[0098] ,

[0099] Where m is the modulation ratio, is the circumference of a circle, is the reference voltage vector magnitude, is the DC bus voltage.

[0100] Step S3, by calculating the switching losses of the energy-saving modulation algorithms in different working modes, the algorithm with the minimum switching loss is regarded as the energy-saving modulation algorithm with the optimal loss;

[0101] The energy-saving modulation algorithm of the air compressor dedicated inverter has seven working modes, and different working modes correspond to different classes and phase angles. .

[0102] When the energy-saving modulation algorithm is in working mode 1, the category , phase angle ;

[0103] When the energy-saving modulation algorithm is in working mode 2, the category , phase angle ;

[0104] When the energy-saving modulation algorithm is in working mode 3, the category , phase angle ;

[0105] When the energy-saving modulation algorithm is in operating mode 4, the category , phase angle ;

[0106] When the energy-saving modulation algorithm is in working mode 5, the category , phase angle ;

[0107] When the energy-saving modulation algorithm is in working mode 6, the category , phase angle ;

[0108] When the energy-saving modulation algorithm is in working mode seven, the category , phase angle .

[0109] Figure 2 The flow chart of the loss calculation module provided by the present invention is as follows: Figure 2 As shown, according to the IGBT tube voltage drop 、IGBT on-current The switching loss of a single switching cycle can be obtained:

[0110] ,

[0111] ,

[0112] in, is the turn-on loss, For the opening time, is the integral symbol, is the IGBT tube voltage drop, is the IGBT on-state current, t is the time, dt is the differential operator, is the turn-off loss, is the off time.

[0113] Among them, the IGBT tube voltage drop The calculation method is: Based on the output characteristic curves of the IGBT voltage drop and on-state current at 25°C, 150°C and 175°C provided in the data sheet, the IGBT voltage drop at the specified temperature and IGBT on-state current can be obtained through programming interpolation. At this time, the switching method between the original modulation algorithm and this modulation algorithm is: switching is performed when the current passes through the zero point.

[0114] The switching losses of the IGBT and the freewheeling diode FWD can be calculated through the switching losses of a single switching cycle.

[0115] When the working mode of the energy-saving modulation algorithm is working mode 1, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0116] When the working mode of the energy-saving modulation algorithm is working mode 2, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0117] When the working mode of the energy-saving modulation algorithm is working mode 3, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0118] When the working mode of the energy-saving modulation algorithm is working mode 4, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0119] When the working mode of the energy-saving modulation algorithm is working mode 5, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0120] When the working mode of the energy-saving modulation algorithm is working mode 6, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ;

[0121] When the working mode of the energy-saving modulation algorithm is working mode seven, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in .

[0122] Comparison of total switching losses in each operating mode of energy-saving modulation algorithms , , , , , , , we get the energy-saving modulation algorithm working mode with the minimum total switching loss, and the corresponding category of this working mode is called and phase angle , which corresponds to the energy-saving modulation algorithm with optimal loss.

[0123] Figure 3 The modulation algorithm module flow chart provided by the present invention is as follows: Figure 3 As shown, the modulation ratio, three-phase sinusoidal signal, and the energy-saving modulation algorithm with the optimal loss selected by the loss calculation module are brought into the zero-sequence component calculation to obtain the final modulation wave.

[0124] Step S4, determining the region to which the energy-saving modulation algorithm with the best loss belongs, the regions including: linear modulation region, overmodulation I region, overmodulation II region;

[0125] The linear modulation range is: , when the m value range in step S2 satisfies When , the area of ​​the energy-saving modulation algorithm with the optimal loss belongs to the linear modulation area;

[0126] The range of overmodulation zone I is: , when the m value range in step S2 satisfies When , the area to which the energy-saving modulation algorithm with the optimal loss belongs is the overmodulation I area;

[0127] The range of overmodulation II area is: , when the m value range in step S2 satisfies At this time, the area to which the energy-saving modulation algorithm with optimal loss belongs is the overmodulation II area.

[0128] Step S5: Select the category of the energy-saving modulation algorithm with the best loss and phase angle , the modulation wave is calculated by the area to which the algorithm belongs ;

[0129] (1) Linear modulation area: The three-phase modulation wave expression is obtained according to the zero-sequence component injection method. The zero-sequence component calculation expression is:

[0130] ,

[0131] ,

[0132] ,

[0133] ,

[0134] in, is the zero sequence component, k is the zero vector distribution coefficient, is the maximum value of the three-phase symmetrical sinusoidal signal, is the minimum value of the three-phase symmetrical sinusoidal signal, is a phase symmetrical sinusoidal signal, is a b-phase symmetrical sinusoidal signal, is a c-phase symmetrical sinusoidal signal.

[0135] When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles To perform translation, the translation signal is:

[0136] ,

[0137] Then determine the maximum value of the translation signal and minimum value , the sum of the maximum and minimum values ​​is positive, that is hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, .

[0138] When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles Shift is performed. At this time, the shifted signal is equal to the three-phase sinusoidal signal. Therefore, the maximum and minimum values ​​of the shifted signal are equal to the maximum and minimum values ​​of the three-phase sinusoidal signal. Then, the maximum and minimum values ​​of the shifted signal are determined, that is, the maximum and minimum values ​​of the three-phase sinusoidal signal are determined. The sum of the maximum and minimum values ​​is positive, that is, hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, .

[0139] When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles To perform translation, the translation signal is:

[0140] ,

[0141] Then determine the maximum value of the translation signal and minimum value , the sum of the maximum and minimum values ​​is positive, that is hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ;

[0142] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the maximum and minimum values ​​are obtained from the three-phase sinusoidal signal, when the sum of the maximum and minimum values ​​is positive, that is, hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ;

[0143] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ;

[0144] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ;

[0145] When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ;

[0146] Injecting the zero-sequence component into the three-phase symmetrical sinusoidal signal generates a modulated wave ;

[0147] (2) Overmodulation I area: The modulation wave of the overmodulation I area is calculated by the weighted sum of the modulation waves of the maximum linear modulation area and the hexagonal edge part;

[0148] The modulation wave calculation formula in overmodulation zone I is:

[0149] ,

[0150] ,

[0151] in, is the modulated wave, is the overmodulation I zone ratio, is the modulation wave in the maximum linear modulation area, is the modulation wave of the edge of the hexagon, a is the a phase, b is the b phase, c is the c phase, and m is the modulation ratio;

[0152] in, The calculation formula is:

[0153] , , ,

[0154] in, is the modulation wave of phase a at the edge of the hexagon, is the modulation wave of phase b at the edge of the hexagon, is the modulation wave of phase c at the edge of the hexagon, is the angle of the reference voltage vector, is the pi, and cot is the tangent cosine function.

[0155] (3) Overmodulation II region: The modulation wave in the overmodulation II region is calculated by the weighted sum of the modulation waves of the hexagonal edge part and the six-beat wave part; the modulation wave calculation formula in the overmodulation II region is:

[0156] ,

[0157] ,

[0158] in, is the modulated wave, is the overmodulation II zone ratio, is the modulation wave of the hexagonal edge part, is the modulation wave of the six-beat wave part, a is the a phase, b is the b phase, c is the c phase, and m is the modulation ratio;

[0159] in, The calculation formula is:

[0160] , , ,

[0161] in, is the modulation wave of phase a of the six-beat wave part, is the modulation wave of phase b of the six-beat wave part, is the modulation wave of phase c of the six-beat wave part, is the angle of the reference voltage vector, is the pi, and cot is the tangent cosine function.

[0162] Step S6, the generated modulated wave By comparing with the standard triangular carrier, a PWM signal can be obtained and injected into the inverter circuit to generate a new conduction current and re-substitute it into step S3 for iterative calculation to realize the energy-saving modulation algorithm.

[0163] Figure 4 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , The modulation algorithm simulation diagram, Figure 5 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , The modulation algorithm simulation diagram, Figure 6 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , The modulation algorithm simulation diagram, Figure 7 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , The modulation algorithm simulation diagram, Figure 8 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , The modulation algorithm simulation diagram, Fig. 9 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , The modulation algorithm simulation diagram, Fig.10 The energy-saving modulation algorithm with the optimal loss provided by the present invention belongs to the linear modulation area and , The modulation algorithm simulation diagram. Figure 4-Figure 10 As shown, when the energy-saving modulation algorithm with optimal loss belongs to the linear modulation area, we can clearly see that the phase voltage peak error under this modulation wave control is lower than the specified value, and voltage control under optimal switching loss can be achieved.

[0164] Fig.11 The switching loss comparison diagram of the energy-saving modulation algorithm with the optimal loss provided by the present invention and other algorithms is as follows: Fig.11 As shown, the energy-saving modulation algorithm of the dedicated frequency converter for air compressors of the present invention is compared with other single algorithms, and can reduce the switching loss of the air compressor, switch the control algorithm at the right time, ensure that the internal loss of the control system is minimized, and realize energy-saving modulation.

[0165] Although the specific implementation methods of the invention have been described in detail in conjunction with the accompanying drawings, this should not be understood as a limitation on the scope of protection of this patent; within the scope described in the claims, various modifications and variations that can be made by technical personnel in this field without creative work still fall within the scope of protection of this patent.

Claims

1. An energy-saving modulation algorithm for a frequency converter dedicated to an air compressor, characterized in that: The following steps are involved: Step S1, obtaining the coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system , , through 2s / 3s transformation , Convert to the three-phase stationary coordinate system to obtain its coordinate value , , ; Step S2, according to the coordinate values ​​in the two-phase stationary αβ coordinate system , Get the reference voltage vector magnitude , reference voltage vector magnitude The calculation formula is: ， in is the α-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, is the β-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, is the reference voltage vector magnitude; According to the reference voltage vector magnitude , DC bus voltage The modulation ratio m is obtained; the calculation formula of the modulation ratio m is: ， Where m is the modulation ratio, is the circumference of a circle, is the reference voltage vector magnitude, is the DC bus voltage; Step S3, calculating the switching loss of the energy-saving modulation algorithm of the dedicated frequency converter for the air compressor under different working modes, and taking the working mode with the minimum switching loss as the optimal working mode of the energy-saving modulation algorithm of the dedicated frequency converter for the air compressor; The energy-saving modulation algorithm of the air compressor dedicated inverter has seven working modes, and different working modes correspond to different classes and phase angles. ; When the energy-saving modulation algorithm is in working mode 1, the category , phase angle ; When the energy-saving modulation algorithm is in working mode 2, the category , phase angle ; When the energy-saving modulation algorithm is in working mode 3, the category , phase angle ; When the energy-saving modulation algorithm is in operating mode 4, the category , phase angle ; When the energy-saving modulation algorithm is in working mode 5, the category , phase angle ; When the energy-saving modulation algorithm is in working mode 6, the category , phase angle ; When the energy-saving modulation algorithm is in working mode seven, the category , phase angle ; According to the IGBT voltage drop 、IGBT on-current The switching loss of a single switching cycle can be obtained: ， ， in, is the turn-on loss, For the opening time, is the integral symbol, is the IGBT tube voltage drop, is the IGBT on-state current, t is the time, dt is the differential operator, is the turn-off loss, is the off time; The switching loss of IGBT and freewheeling diode FWD can be calculated through the switching loss of a single switching cycle; When the working mode of the energy-saving modulation algorithm is working mode 1, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ; When the working mode of the energy-saving modulation algorithm is working mode 2, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ; When the working mode of the energy-saving modulation algorithm is working mode 3, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ; When the working mode of the energy-saving modulation algorithm is working mode 4, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ; When the working mode of the energy-saving modulation algorithm is working mode 5, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ; When the working mode of the energy-saving modulation algorithm is working mode 6, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ; When the working mode of the energy-saving modulation algorithm is working mode seven, that is, , When the switching loss of IGBT and freewheeling diode FWD is and , the total switching loss is ,in ; Comparison of total switching losses in each operating mode of energy-saving modulation algorithms , , , , , , , we get the energy-saving modulation algorithm working mode with the minimum total switching loss, and the corresponding category of this working mode is called and phase angle , which corresponds to the energy-saving modulation algorithm with optimal loss; Step S4, determining the region to which the energy-saving modulation algorithm with the best loss belongs, the regions including: linear modulation region, overmodulation I region, overmodulation II region; The value range of the modulation ratio m satisfies When the optimal loss energy-saving modulation algorithm belongs to the linear modulation area; the value range of the modulation ratio m satisfies When the optimal loss energy-saving modulation algorithm belongs to the overmodulation I area; the value range of the modulation ratio m satisfies When , the energy-saving modulation algorithm with the optimal loss belongs to the overmodulation II area; Step S5: Select the category of the energy-saving modulation algorithm with the best loss and phase angle , the modulation wave is calculated by the area to which the algorithm belongs ; (1) Linear modulation area: The three-phase modulation wave expression is obtained according to the zero-sequence component injection method. The zero-sequence component calculation expression is: ， ， ， ， in, is the zero sequence component, k is the zero vector distribution coefficient, is the maximum value of the three-phase symmetrical sinusoidal signal, is the minimum value of the three-phase symmetrical sinusoidal signal, is a phase symmetrical sinusoidal signal, is a b-phase symmetrical sinusoidal signal, is a c-phase symmetrical sinusoidal signal; When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles To perform translation, the translation signal is: ， Then determine the maximum value of the translation signal and minimum value , the sum of the maximum and minimum values ​​is positive, that is hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ; When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles Shift is performed. At this time, the shifted signal is equal to the three-phase sinusoidal signal. Therefore, the maximum and minimum values ​​of the shifted signal are equal to the maximum and minimum values ​​of the three-phase sinusoidal signal. Then, the maximum and minimum values ​​of the shifted signal are determined, that is, the maximum and minimum values ​​of the three-phase sinusoidal signal are determined. The sum of the maximum and minimum values ​​is positive, that is, hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ; When the optimal loss energy-saving modulation algorithm is used and phase angle for , By dividing the three-phase sinusoidal signal into phase angles To perform translation, the translation signal is: ， Then determine the maximum value of the translation signal and minimum value , the sum of the maximum and minimum values ​​is positive, that is hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ; When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the maximum and minimum values ​​are obtained from the three-phase sinusoidal signal, when the sum of the maximum and minimum values ​​is positive, that is, hour, , when the sum of the maximum and minimum values ​​is negative, that is hour, ; When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ; When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ; When the optimal loss energy-saving modulation algorithm is used and phase angle for , When the zero-sequence component calculation expression is ; Injecting the zero-sequence component into the three-phase symmetrical sinusoidal signal generates a modulated wave ; (2) Overmodulation I area: The modulation wave of the overmodulation I area is calculated by the weighted sum of the modulation waves of the maximum linear modulation area and the hexagonal edge part; The calculation formula for the modulation wave in the overmodulation I region is: ， ， in, is the modulated wave, is the overmodulation I zone ratio, is the modulation wave in the maximum linear modulation area, is the modulation wave of the edge of the hexagon, a is the a phase, b is the b phase, c is the c phase, and m is the modulation ratio; in, The calculation formula is: ， ， ， in, is the modulation wave of phase a at the edge of the hexagon, is the modulation wave of phase b at the edge of the hexagon, is the modulation wave of phase c at the edge of the hexagon, is the angle of the reference voltage vector, is pi, cot is tangent cosine function; (3) Overmodulation II region: The modulation wave in the overmodulation II region is calculated by the weighted sum of the modulation waves of the hexagonal edge part and the six-beat wave part; the modulation wave calculation formula in the overmodulation II region is: ， ， in, is the modulated wave, is the overmodulation II zone ratio, is the modulated wave at the edge of the hexagon, is the modulation wave of the six-beat wave part, a is the a phase, b is the b phase, c is the c phase, and m is the modulation ratio; in, The calculation formula is: ， ， ， in, is the modulation wave of phase a of the six-beat wave part, is the modulation wave of phase b of the six-beat wave part, is the modulation wave of phase c of the six-beat wave part, is the angle of the reference voltage vector, is pi, cot is tangent cosine function; Step S6, the generated modulated wave By comparing with the standard triangular carrier, a PWM signal can be obtained and injected into the inverter circuit to generate a new conduction current and re-substitute it into step S3 for iterative calculation to realize the energy-saving modulation algorithm.

2. The energy-saving modulation algorithm of a frequency converter for air compressor according to claim 1 is characterized in that: In step S1, the 2s / 3s conversion formula is: ， in, is the a-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the b-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the c-axis coordinate value of the reference voltage vector U in the three-phase stationary coordinate system, is the α-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system, It is the β-axis coordinate value of the reference voltage vector U in the two-phase stationary αβ coordinate system.

3. The energy-saving modulation algorithm of a frequency converter for air compressor according to claim 1 is characterized in that: In step S3, the IGBT voltage drop The calculation method is: Based on the output characteristic curves of the IGBT voltage drop and on-state current at 25°C, 150°C and 175°C provided in the data sheet, the IGBT voltage drop at the specified temperature and IGBT on-state current can be obtained through programming interpolation. At this time, the switching method between the original modulation algorithm and this modulation algorithm is: switching is performed when the current passes through the zero point.

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