A variable frequency motor loss modeling method suitable for energy control of air conditioning systems

Abstract

The present invention proposes a variable frequency motor loss modeling method suitable for energy control of air conditioning systems. The method provides a model basis for air conditioning energy-saving optimization strategies by modeling various losses of central air conditioning variable frequency motors. The efficiency value obtained by the regression analysis method is used as the initial value to calculate the various losses of the variable frequency motor, and then a new efficiency value is calculated. And when modeling the various losses of the variable frequency motor, the voltage, current, magnetic flux density and other electromagnetic quantities that are difficult to collect in large quantities are innovatively converted into calculable quantities such as motor speed and power based on physical relationships, so that the various losses of the variable frequency motor system are expressed in the form of speed and power, and then the various losses are associated with pump loads to optimize the central air conditioning system in a coordinated manner. Through simulation analysis, the model proposed by the present invention can provide a certain theoretical basis for the optimization and control of the central air conditioning system.

Description

Technical Field

[0001] The present invention belongs to the field of AC motor loss analysis and calculation, and specifically relates to a variable frequency motor loss modeling method suitable for energy control of air conditioning systems. Background Art

[0002] According to statistics, central air conditioning systems account for about 50% of the energy consumption in the global building sector. It is expected that energy consumption will further increase by 2050. At present, the rough operation mode makes buildings generally have a large space for energy saving. Under the premise of meeting the comfort of users, effectively reducing the operating energy consumption of air conditioning systems has become a current research hotspot.

[0003] During the operation of the central air-conditioning system, energy consumption can be effectively reduced by formulating appropriate optimization and control methods. The central air-conditioning system contains a large number of variable frequency drive induction motors. In the central air-conditioning optimization and control methods, the inverter loss and motor loss are usually ignored or simply approximated by the efficiency at rated operation. However, most of the motors in the central air-conditioning system are running under light load, so the conventional optimization algorithm has poor accuracy. In addition, a large number of traditional calculation models for variable frequency motor losses usually rely on electromagnetic quantities such as voltage, current, and magnetic flux collected by sensors for calculation. For the central air-conditioning system, there are many motors and the data acquisition and transmission system is not yet perfect. The traditional loss model calculated by voltage, current and other quantities is no longer applicable. In addition, the central air-conditioning system contains a large number of interrelated variable frequency motor drive systems, which are very complex. The traditional loss calculation method based on finite element and linear superposition is no longer applicable due to the slow calculation speed. A more concise and efficient loss calculation method needs to be proposed. Therefore, it is currently necessary to establish a motor loss model suitable for the energy-saving strategy of the central air-conditioning system for the multi-motor system of the central air-conditioning system. Summary of the invention

[0004] A variable frequency motor loss modeling method suitable for energy regulation of air-conditioning systems is proposed. This method provides a model basis for air-conditioning energy-saving optimization strategies by modeling various losses of variable frequency motors in central air-conditioning systems. The efficiency value obtained by regression analysis method is used as the initial value to calculate various losses of variable frequency motors. When modeling various losses of variable frequency motors, according to physical relationships, the voltage, current, magnetic flux density and other electromagnetic quantities that are difficult to collect in large quantities are innovatively converted into motor speed, power and other calculable quantities, so that the various losses of the variable frequency motor system are expressed in the form of speed and power, and then the various losses are associated with pump loads to optimize the central air-conditioning system in a coordinated manner; the variable frequency motor losses include copper loss, iron loss, inverter loss and mechanical loss, and the copper loss includes stator copper loss and rotor copper loss. The article verifies the effectiveness of the model through experiments, as well as the applicability of the model structure in real-time updating and optimization of the central air-conditioning system model. In order to achieve the above purpose, the present invention adopts the following technical solutions to achieve it:

[0005] Preferably, the modeling includes establishing an iron loss model, a motor mechanical loss model, and a frequency converter loss model.

[0006] The motor stator phase voltage will be replaced by the speed variable. Since variable frequency motors generally use a constant voltage-frequency ratio control method, the voltage can be expressed in terms of speed.

[0007] Below the fundamental frequency, is a constant, so we can get:

[0008]

[0009] When the speed is adjusted above the rated frequency, the voltage is limited by the insulation and weak magnetic control will be adopted to keep the voltage at the rated level unchanged, that is:

[0010] U1=U r (2)

[0011] The current is derived from the power as shown in formula (3):

[0012]

[0013]

[0014] In the formula, m is the number of phases, U1 is the phase voltage on the stator side, I1 is the phase current on the stator side, is the power factor; η motor is the efficiency of the motor, η pump is the efficiency of the pump, d1-d2 and g1-g3 are model coefficients, which can be obtained by polynomial, neural network or any other curve fitting; v is the speed ratio, which is expressed as the ratio of the current speed to the rated speed; M cIt is the flow rate of the water pump, in m3 / h (t / h).

[0015] 1) Speed ​​regulation below base frequency

[0016] Below the base frequency, the constant voltage-frequency ratio speed regulation mode is adopted, that is,

[0017]

[0018] Where, C = 4.44N1k w1 φ is a constant.

[0019] It can be seen from formula (7) that the air gap flux remains unchanged, and the reactive power mainly comes from the air gap magnetic field energy. Since the magnetic field energy remains unchanged, it can be approximately considered that the reactive power remains unchanged during the speed regulation process below the base frequency, and the rated reactive power can be used to represent the reactive power during the entire speed regulation process. The stator current can be expressed as:

[0020]

[0021] 2) Speed ​​regulation above base frequency

[0022] Above the base frequency, the weak magnetic control mode is adopted. From the electromotive force equation of the stator circuit, we can know that:

[0023] U1≈E φ =4.44f1N1k w1 φ (9)

[0024] Where U1 remains unchanged, the magnetic flux φ is inversely proportional to the frequency f1, which can be expressed as:

[0025]

[0026] Combined with the relationship between speed and frequency, the relationship between magnetic flux and speed can be obtained as follows:

[0027]

[0028] The air gap energy is proportional to the square of the magnetic flux, and hence, the reactive power is inversely proportional to the square of the speed. r When the corresponding rated reactive power is Q r . Then we know that:

[0029]

[0030] In the formula,

[0031] The stator current can be expressed as:

[0032]

[0033] It is concluded that the stator current expression in the entire speed regulation process is:

[0034]

[0035] According to the current solution method described above, the stator copper loss can be obtained according to Ohm's law:

[0036]

[0037] When establishing the iron loss model, it is also expressed as a function of the rotational speed.

[0038] The relationship between iron loss and speed is:

[0039]

[0040] The rotor copper loss is obtained by indirect method. The relationship between rotor copper loss and electromagnetic power can be expressed as:

[0041] P Cu2 =sP em =s(P ins -P Cu1 -P Fe ) (17)

[0042] Finally, the rotor copper loss can be further expressed as:

[0043]

[0044] The motor mechanical loss is also expressed as a function of the speed. The specific process of establishing the motor mechanical loss model is as follows:

[0045] When the motor parameters are stable, the mechanical loss P Mec is equivalent to:

[0046] p Mec =K L n 3 (19)

[0047] In the formula, K L is the mechanical loss coefficient of the motor.

[0048] The loss model of the inverter is still a function of the speed. The specific process of model establishment is as follows:

[0049] Because the on-state voltage drop of the switch tube is a constant value, the effective value of the switch tube current is:

[0050]

[0051] Then the relationship between the effective value of the switch tube current and the effective value of the phase current is:

[0052]

[0053] Then the conduction loss of the 6 switch tubes is:

[0054]

[0055] Where P PWM is the inverter loss. k is the PWM modulation ratio.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] (1) Developed a detailed calculation method for the losses of variable frequency motors used in central air conditioning systems

[0058] (2) The model is suitable for real-time optimization and control of air-conditioning systems

[0059] (3) The proposed model still has good versatility under non-rated conditions

[0060] (4) The proposed motor loss model can significantly improve the calculation accuracy of building energy consumption BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 Schematic diagram of frequency conversion motor system loss

[0062] Figure 2 The working characteristic curve of the variable frequency motor under pump load

[0063] Figure 3 It is a voltage type three-phase inverter circuit topology

[0064] Figure 4 The simulation results DETAILED DESCRIPTION

[0065] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0066] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0067] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0068] like Figure 1 As shown in the figure, the system loss of variable frequency motor includes: stator copper loss, rotor copper loss, basic iron loss, additional iron loss (surface additional loss, tooth pulsation loss), inverter loss, and motor mechanical loss. Based on the initialization of regression analysis method, this paper models the various losses of central air-conditioning variable frequency motor, providing a model basis for central air-conditioning energy-saving optimization strategy.

[0069] exist Figure 1 In, P PWM is the variable frequency drive loss, P Cu1 is the stator copper loss, P Fe is the iron loss, P Cu2 is the rotor copper loss, P Mec The copper loss and iron loss here include fundamental wave and harmonic wave losses.

[0070] When solving for current and voltage, power and rotational speed are used to solve them. By utilizing the relationship between the two, current and voltage are expressed as functions of rotational speed and power, which makes solving more convenient and eliminates the inconvenience of measurement.

[0071] For fans and pumps, in order to maintain a high power factor, their speed regulation method mostly adopts the constant voltage-frequency ratio method, that is, by adjusting the inverter output voltage and frequency, the magnetic flux in the core is kept basically unchanged. According to the constant voltage-frequency ratio speed regulation characteristics, the voltage U is replaced by variables in two cases: speed regulation below the base frequency and speed regulation above the base frequency.

[0072] 1) Speed ​​regulation below base frequency

[0073] When the speed is adjusted below the base frequency, the required solution is the stator side phase voltage U. From the constant voltage-frequency ratio speed regulation characteristics, it can be known that U / f=C is a constant. When the frequency is changed, the relationship between voltage and frequency satisfies the following relationship:

[0074]

[0075] The relationship between the speed and frequency of an asynchronous motor is:

[0076]

[0077] Where p is the number of pole pairs and s is the slip rate. When the slip rate is small enough, it can be ignored and the motor input frequency can be approximately calculated from the motor speed.

[0078] Under fan and pump loads, the variable frequency motor working characteristic curve is as shown in the attached figure. Figure 2 As shown, when the frequency changes, the speed of the motor (i.e., the pump) changes from n n When it changes to n, the torque T and the rated torque T n The relationship between

[0079] T / T n =(n / n n ) 2 (29)

[0080] When the frequency is modulated below the base frequency, f2 <f n , the variable frequency motor characteristic curve changes from ① to ②, the motor will change from point A on curve 3 to point A', triangle △n 01 An n With triangle △n 02 A'n2 is similar, and combined with formula (29), we can get

[0081] T2 / T n =(n 02 -n2) / (n 01 -n n )=(n2 / n n ) 2 (30)

[0082] According to the slip rate formula, we can get

[0083]

[0084] Transforming formula (31) we can get

[0085]

[0086] Expanding formula (32) yields

[0087]

[0088] When the induction motor is running at rated frequency, the slip is usually very small (0.01-0.06). However, from formula (33), when the frequency is adjusted below the base frequency, the motor slip is less than the slip during rated operation, so it can be ignored. From formula (28), when the slip does not change much, n is basically proportional to f1.

[0089] Therefore, when adjusting the speed below the base frequency, the slip rate can be ignored, that is,

[0090]

[0091] Therefore, the voltage can be expressed by the speed as

[0092]

[0093] 2) When speed regulation is above base frequency

[0094] When the speed is adjusted above the rated frequency, the motor is limited by the insulation withstand voltage and magnetic circuit saturation. In the variable voltage and variable frequency speed regulation mode, the voltage cannot increase with the increase of frequency. Generally, only the frequency is adjusted, and the maximum phase voltage on the stator side is equal to the rated voltage, that is: U = U r

[0095] The motor phase current is calculated as follows:

[0096] In the calculation, it is assumed that the output power (shaft power) of the pump is P out , we can approximately obtain the approximate input power of the power grid by formula (36).

[0097]

[0098]

[0099] In the formula, m is the number of phases, U1 is the phase voltage on the stator side, I1 is the phase current on the stator side, is the power factor; η motor is the efficiency of the motor, η pump is the efficiency of the pump, d1-d2 and g1-g3 are model coefficients, which can be obtained by polynomial, neural network or any other curve fitting; v is the speed ratio, which is expressed as the ratio of the current speed to the rated speed; M c It is the flow rate of the water pump, in m3 / h (t / h).

[0100] The power factor can be expressed as:

[0101]

[0102] In the formula, Q in is the reactive power.

[0103] The approximate input active power has been calculated previously, and now we need to solve the problem of reactive power.

[0104] When the frequency conversion speed is adjusted, the magnetic flux φ remains unchanged.

[0105] φ=BS (41)

[0106] Where S is the cross-sectional area of ​​the air gap and B is the magnetic induction intensity.

[0107] It can be seen that since the cross-sectional area S remains unchanged, the magnetic field intensity B remains unchanged, and the formula for the magnetic field energy density is:

[0108]

[0109] Where H is the magnetic field intensity; μ0 is the magnetic permeability; W is the magnetic field energy; V is the air gap volume.

[0110] The magnetic field energy can be obtained as:

[0111]

[0112] If the air gap volume V remains unchanged, the magnetic field energy remains unchanged, and the reactive power is a constant value. The rated reactive power value Q can be used. r Represents the reactive power value of the entire speed regulation process below the base frequency.

[0113]

[0114] In the formula, Q r is the rated reactive power; P r is the rated active power.

[0115] The stator current can be expressed as:

[0116]

[0117] 2) When f>f1

[0118] At this time, the quantity to be solved is still the stator side phase voltage U1, power factor

[0119] When the speed is adjusted above the rated frequency, the motor insulation withstand voltage and magnetic circuit saturation are limited. In the variable voltage and variable frequency speed regulation mode, the voltage cannot increase with the increase of frequency. Generally, only the frequency is adjusted, and the maximum phase voltage on the stator side is equal to the rated voltage, that is:

[0120] U1=U r (46)

[0121] Where U r is the rated voltage.

[0122] From the stator circuit electromotive force equation, we know that:

[0123] U1≈E φ =4.44f1N1k w1 φ (47)

[0124] Where U1 remains unchanged, the magnetic flux φ is inversely proportional to the frequency f1, which can be expressed as:

[0125]

[0126] Combined with the relationship between speed and frequency, the relationship between magnetic flux and speed can be obtained as follows:

[0127]

[0128] In the formula,

[0129] At this time, the magnetic field energy can be calculated as:

[0130]

[0131] Where l is the air gap length.

[0132] It can be seen that in this speed regulation situation, the reactive power is inversely proportional to the square of the speed. r When the corresponding rated reactive power is Q r . Then we know that:

[0133]

[0134] In the formula,

[0135] The stator current can be expressed as:

[0136]

[0137] The stator current expression in the entire speed regulation process is:

[0138]

[0139] According to the current solution method described above, the stator copper loss can be obtained according to Ohm's law:

[0140]

[0141] When establishing the iron loss model, it is also expressed as a function of the rotational speed.

[0142] The relationship between iron loss and speed is:

[0143]

[0144] The rotor copper loss is obtained by indirect method. The relationship between rotor copper loss and electromagnetic power can be expressed as:

[0145] P Cu2 =sP em =s(P ins -P Cu1 -P Fe ) (56)

[0146] Finally, the rotor copper loss can be further expressed as:

[0147]

[0148] Next, the inverter in the power system is further analyzed and modeled.

[0149] Assume that Figure 3 The typical voltage source three-phase inverter shown works in basic mode, that is:

[0150] a) Each bridge arm works in 180° conduction mode

[0151] b) The fundamental waves of each phase differ by 120°

[0152] c) Line voltage is 120 square wave

[0153] d) The conduction order of the switch tube is 561→612→123→234→345→456→561

[0154] Taking the switch Q1 as an example, it can be seen from the circuit topology that when the switch Q1 is turned on, the instantaneous current passing through the switch Q1 is equal to the instantaneous value of the phase current of phase A; and because the conduction time of the six switch combinations is equal, and there are three combinations that make the switch 1 turned on, therefore, within one cycle, Q1 is equivalently regarded as being turned on for only half a cycle.

[0155] The effective value of AC is defined as the heat generated by AC passing through a resistor in one cycle is equal to the heat generated by DC passing through the resistor in the same period of time. The value of this DC is the effective value of the AC. Based on the definition of the effective value of AC and the working mode of the switch tube, the following equation can be obtained:

[0156]

[0157] In the formula, T is one cycle, I m is the phase current amplitude, ΔU is the conduction voltage drop of the switch tube, i s is the effective value of the switch tube current.

[0158] Because the on-state voltage drop of the switch tube is a constant value, simplifying the above formula, the effective value of the switch tube current is:

[0159]

[0160] The effective value of the phase current is:

[0161]

[0162] Then the relationship between the effective value of the switch tube current and the effective value of the phase current is:

[0163]

[0164] Then the conduction loss of the 6 switch tubes is:

[0165]

[0166] Where P PWM is the inverter loss. k is the PWM modulation ratio.

[0167] Finally, mechanical losses in the power system are analyzed and modeled.

[0168] The mechanical loss of induction motors mainly includes bearing friction loss and ventilation loss. Bearing friction loss is related to the pressure on the friction surface, the friction coefficient and the relative speed between the friction surfaces. The friction coefficient has a greater impact on bearing friction loss. In most cases, the friction coefficient is difficult to determine accurately, but it can be reduced a lot by applying lubricating oil. For ventilation loss, its value is related to factors such as the structure of the motor, the type of fan, and the wind resistance in the ventilation system. In general, the ventilation loss in self-ventilated motors can be calculated using the following values:

[0169] p w =1.75q V v 2 (63)

[0170] In the formula, q v is the air volume flow rate through the motor; v is the circumferential speed of the motor blades.

[0171] In the above formula, since the air volume is proportional to the speed v, p w The motor bearing friction loss is introduced into the motor mechanical loss coefficient. When the motor mechanical parameters are stable, the mechanical loss P Mec is equivalent to:

[0172] p Mec =K L n 3 (64)

[0173] In the formula, K L is the mechanical loss coefficient of the motor.

[0174] Implementation Cases

[0175] This paper simulates four main types of loads in the central air-conditioning system, namely, chilled water pump, chiller, cooling water pump and cooling tower. The corresponding motors are simulated using standard specifications of induction motors.

[0176] Figure 4 It is the loss curve diagram of motors of various specifications obtained through simulation. Figure 4 The four sub-graphs show the loss values ​​corresponding to different speeds of the chilled water pump, chiller, cooling water pump and cooling tower when the air conditioning load changes. The output capacities of the corresponding motor equipment are 40.32, 169.42, 315.00 and 30.00kW respectively. Figure 4 It can be concluded that:

[0177] (1) Mechanical loss: Figure 4 As shown in (a), for fans and pumps, when they are in contact with fluids during work, a certain degree of energy loss will occur. As shown in the attached figure: for the same model of motor, taking 30kW as an example, when it is 300-1500r / min, the corresponding mechanical loss values ​​are: 40.52, 95.63, 185.42, 281.25 and 400.00W, which is approximately the cubic relationship with the speed. Under the same speed, the mechanical loss of the motors of different models corresponding to the four curves increases with the increase of the motor model.

[0178] (2) Iron loss: Figure 4 As shown in (b), for the same model of motor, the iron loss is slightly greater than the mechanical loss. For example, for 30kW, when the motor is 300-1500r / min, the corresponding iron loss is: 300.32, 640.45, 1012.39, 1570.21 and 2315.69W, which is approximately the cubic relationship with the speed. The larger the motor model, the higher the loss coefficient.

[0179] (3) Copper loss: Copper loss is related to the connected load. It includes stator copper loss and rotor copper loss. Generally speaking, the larger the motor grade, the smaller the resistance. When the speed is adjusted below the base frequency, the reactive power remains approximately unchanged. According to formula (27), when the load increases, the active power increases and the numerator becomes larger as a whole. But at the same time, the speed value also increases. Figure 4(c) As shown in the figure: For a specific motor, the rotor copper loss increases with the increase of load. The stator copper loss has the same trend as the total copper loss, showing an inverted U-shaped trend, because in the constant voltage-frequency ratio control method, when the load is small and the speed is small, the corresponding back electromotive force value is small, the power factor is low, and a larger current is caused. However, when the load is large, the speed increases accordingly. But the change trend of the numerator is greater than the denominator, so the stator current also increases. The copper loss is a function of the current, so it also presents a U-shape. When the speed is around 1000r / min, the total copper loss reaches a minimum.

[0180] (4) Inverter loss: Figure 4 As shown in (d): The value of the inverter loss is also a function of the current. Therefore, similar to the copper loss, the overall shape is U-shaped. Under the same motor grade, the value decreases first and then increases with the speed. When the rated power of the variable frequency motor is large, taking the 315kW motor as an example, at full load, the copper loss is 12892.0W, while the inverter loss is 14555.3W. The inverter loss is slightly larger than the copper loss, so it should not be ignored in the actual optimization process.

[0181] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A variable frequency motor loss modeling method suitable for energy control of air conditioning systems, characterized by: A variable frequency motor loss modeling method suitable for energy control of air conditioning systems is proposed. The method provides a model basis for the air conditioning energy-saving optimization strategy by modeling various losses of the central air-conditioning variable frequency motor; the efficiency value obtained by the regression analysis method is used as the initial value to calculate the various losses of the variable frequency motor, and then a new efficiency value is calculated; and when modeling various losses of the variable frequency motor, the voltage, current, and magnetic flux density are innovatively converted into quantities calculated by motor speed and power based on physical relationships, so that the various losses of the variable frequency motor system are expressed in the form of speed and power, and then the various losses are associated with pump loads to optimize the central air-conditioning system in a coordinated manner; the variable frequency motor loss includes copper loss, iron loss, inverter loss, and mechanical loss; the copper loss includes stator copper loss and rotor copper loss; In the process of establishing the copper loss and inverter loss model, the current is derived from the power, which is expressed as follows: In the formula, m is the number of phases, U1 is the phase voltage on the stator side, I1 is the phase current on the stator side, is the power factor; η motor is the efficiency of the motor, η pump is the efficiency of the pump, d1-d2 and g1-g3 are model coefficients, obtained by polynomial, neural network or curve fitting; v is the speed ratio, expressed as the ratio of the current speed to the rated speed; M c is the flow rate of the water pump, in m 3 / h(t / h); 1) Speed ​​regulation below base frequency Below the base frequency, the constant voltage-frequency ratio speed regulation mode is adopted, that is, Where, N1 is the number of series turns per phase; K w1 is the number of series turns per phase; Φ is the magnetic flux per pole; It can be seen from formula (7) that the air gap flux remains unchanged, and the reactive power mainly comes from the air gap magnetic field energy. Since the magnetic field energy remains unchanged, it can be approximately considered that the reactive power remains unchanged during the speed regulation process below the base frequency, and the rated reactive power represents the reactive power during the entire speed regulation process; the stator current can be expressed as: 2) Speed ​​regulation above base frequency Above the base frequency, the weak magnetic control mode is adopted. From the electromotive force equation of the stator circuit, we can know that: U1≈E φ =4.44f1N1k w1 f (9) Where U1 remains unchanged, the magnetic flux φ is inversely proportional to the frequency f1, which can be expressed as: Combined with the relationship between the speed and frequency of the asynchronous motor, the relationship between the magnetic flux and the speed is: The air gap energy is proportional to the square of the magnetic flux, and hence, the reactive power is inversely proportional to the square of the speed. r When the corresponding rated reactive power is Q r ; Then we can know: In the formula, The stator current is expressed as: It is concluded that the stator current expression in the entire speed regulation process is:

2. A variable frequency motor loss modeling method suitable for energy control of air conditioning systems according to claim 1, characterized in that: The modeling of various losses includes establishing a stator and rotor copper loss model, an iron loss model, a motor mechanical loss model, and a frequency converter loss model.

3. According to the method for modeling the loss of a variable frequency motor suitable for energy control of an air conditioning system as described in claim 1, the voltage parameters thereof are replaced by variables, characterized in that: Since the variable frequency motor adopts the constant voltage-frequency ratio control method, the voltage is expressed in terms of speed. Below the fundamental frequency, is a constant, so: When the speed is adjusted above the rated frequency, the voltage is limited by the insulation and weak magnetic control will be adopted to keep the voltage at the rated level unchanged, that is: U1=U r (2)。 4. A variable frequency motor loss modeling method suitable for energy control of air conditioning systems according to claim 1, characterized in that: According to Ohm's law, the stator copper loss is:

5. A variable frequency motor loss modeling method suitable for energy control of air conditioning systems according to claim 2, characterized in that: When establishing the iron loss model, it is expressed as a function of the rotational speed; The relationship between iron loss and speed is:

6. A variable frequency motor loss modeling method suitable for energy control of air conditioning systems according to claim 1, characterized in that; The rotor copper loss is obtained by indirect method; The relationship between rotor copper loss and electromagnetic power is expressed as: P Cu2 =sP em =s(P ins -P Cu1 -P Fe ) (17) The rotor copper loss is further expressed as:

7. A variable frequency motor loss modeling method suitable for energy control of air conditioning systems according to claim 2, characterized in that; The motor mechanical loss is expressed as a function of the speed. The specific process of establishing the motor mechanical loss model is as follows: When the motor parameters are stable, the mechanical loss P Mec is equivalent to: p Mec =K L n 3 (19) In the formula, K L is the mechanical loss coefficient of the motor.

8. A variable frequency motor loss modeling method suitable for energy control of air conditioning systems according to claim 2, characterized in that; The loss model of the inverter is still a function of the speed. The specific process of model establishment is as follows: Because the on-state voltage drop of the switch tube is constant, the effective value of the switch tube current is: Then the conduction loss of the 6 switch tubes is: Where P PWM is the loss of the inverter; k is the modulation ratio of PWM.

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