Preheating control method for compressor of carbon dioxide asynchronous motor

Abstract

The invention discloses a preheating control method for a carbon dioxide asynchronous motor compressor, which comprises the following steps of: 1, connecting a U phase, a V phase and a W phase output by a frequency converter into a motor of the compressor, and simultaneously collecting the temperature of the compressor in real time; 2, acquiring an input signal; 3, judging whether the temperature of the compressor reaches the preheating temperature or not; 4, judging whether the compressor is in a shutdown state or not; 5, judging whether the shutdown time reaches the preheating shutdown switching time or not; 6, whether the preheating one-way duration time is reached or not is judged; 7, calculating actual target current according to the temperature of the IGBT module; 8, calculating a preheating output voltage through an IP controller of a current loop according to the actual target current, and generating a corresponding output current; and 9, calculating an alpha-axis voltage and a beta-axis voltage, and outputting an SVPWM signal. According to the invention, the preheating voltage can be accurately controlled, customized current control is realized, single-phase overheating is avoided through systematic phase switching, and a safety protection mechanism is provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of air conditioning systems, and particularly relates to a pre-heating control method for a carbon dioxide asynchronous motor compressor. BACKGROUND

[0002] In an air conditioning system, the compressor usually contains lubricating oil inside to reduce the friction and wear of the mechanical parts inside the compressor. However, when working in a low-temperature environment, the temperature of the lubricating oil is low, the viscosity increases, and it is difficult to effectively lubricate. At the same time, the refrigerant is easily dissolved in the lubricating oil. When the compressor starts, due to the change of temperature and pressure, the refrigerant dissolved in the lubricating oil quickly vaporizes, generating a large amount of foam, causing the liquid strike phenomenon, and seriously affecting the service life of the compressor.

[0003] In particular, for systems using carbon dioxide (CO2) as a refrigerant, the above problems become particularly serious. The working pressure of the CO2 refrigerant system is much higher than that of the traditional refrigerant (up to more than 10 MPa), and its pressure-temperature (P-T) curve is extremely steep, and a small temperature fluctuation can cause a sharp pressure change. This leads to an exponential increase in the destructive power of the liquid strike phenomenon during cold start, posing a fatal threat to the service life of the compressor. At the same time, inaccurate preheating can easily cause the local temperature of the lubricating oil to be too high, and the dissolved CO2 to vaporize in large quantities at once, not only generating foam, but also possibly forming a dangerous local high pressure inside the compressor. Therefore, the preheating control for CO2 compressors puts forward much more stringent requirements for the accuracy, uniformity and process safety of heating than traditional systems.

[0004] Chinese patent application CN109067303A discloses a motor heating method, which achieves heating by outputting high-frequency alternating current to the motor. This method mainly solves the problem of heating speed and is mainly applied to permanent magnet synchronous motors and direct current brushless motors. At the same time, using high-frequency alternating current has the risk of generating torque in the motor, and the high-frequency alternating heating process also produces high-frequency whistling sound.

[0005] Chinese patent application CN114623081A discloses a variable frequency compressor with adaptive control of heating power and an operating method thereof, which adaptively controls the heating power of the stator winding based on the rotor position or the stator winding phase resistance. This method can adjust the injected current or forcibly position the rotor according to the rotor position, but it is not optimized for the specific needs of CO2 compressors, and there is no systematic phase switching mechanism to prevent single-phase overheating. This patent application proposes an adaptive control method based on rotor position and winding phase resistance, but its control strategy is mainly for synchronous motor variable frequency compressors and does not consider the special needs of CO2 asynchronous motor compressors. In addition, this patent application focuses on positioning the rotor or measuring the phase resistance to adaptively control the heating power, and lacks a systematic phase switching mechanism and precise PI control strategy.

[0006] These prior arts have their own focuses on compressor preheating control, but have the following common deficiencies:

[0007] 1. Lack of special design for CO2 asynchronous motor compressor characteristics;

[0008] 2. Lack of mechanism for accurately controlling preheating current and voltage;

[0009] 3. No systematic solution to phase switching;

[0010] 4. Incomplete safety protection measures, especially IGBT temperature protection;

[0011] 5. The rotor may rotate during preheating, introducing refrigerant and affecting preheating effect.

[0012] Therefore, a preheating control method specifically for CO2 asynchronous motor compressor is needed, which can accurately control the preheating voltage, realize customized current control, avoid single-phase overheating through systematic phase switching, and provide a perfect safety protection mechanism. To this end, the applicant has found a method to solve the above problems through beneficial exploration and research, and the technical solution to be introduced below is produced in this background. SUMMARY

[0013] The technical problem to be solved by the present application is to provide a CO2 asynchronous motor compressor preheating control method that can accurately control the preheating voltage, realize customized current control, avoid single-phase overheating through systematic phase switching, and provide a perfect safety protection mechanism.

[0014] The technical problem to be solved by the present application can be solved by the following technical solution:

[0015] A CO2 asynchronous motor compressor preheating control method, comprising the following steps:

[0016] Step S101, connecting the U-phase, V-phase and W-phase output by the frequency converter to the motor of the compressor, and preheating the motor stator through the current of the U-phase, V-phase and W-phase, while collecting the temperature of the compressor in real time;

[0017] Step S102, obtaining the output phase current, output phase current set value, preheating shutdown switching time, preheating one-way duration, IGBT module temperature and bus voltage value, and setting the initial phase angle of the frequency converter to 0°;

[0018] Step S103, determining whether the temperature of the compressor reaches the preheating temperature, if yes, ending, otherwise entering step S104;

[0019] Step S104, determine whether the compressor is in a stop state, if yes, go to step S105, otherwise go to step S106;

[0020] Step S105, determine whether the stop time reaches the pre-heating stop switching time, if yes, set the output phase current to the target phase current, and go to step S107, otherwise, go to the stop state, set the output target phase current to 0, and then go to step S107;

[0021] Step S106, determine whether the pre-heating one-way duration is reached, if yes, go to the stop state, and set the phase angle of the frequency converter to the initial phase angle+120°, and set the output target phase current to 0, and then go to step S107;

[0022] Step S107, calculate the actual target current according to the IGBT module temperature;

[0023] Step S108, calculate the pre-heating output voltage according to the actual target current through the IP controller of the current loop, and generate the corresponding output current according to the pre-heating output voltage, so that the output current reaches the actual target current;

[0024] Step S109, calculate the voltage components of the α axis and the β axis through coordinate transformation according to the voltage calculated by the PI controller, and finally generate SVPWM signals to drive the IGBT module of the frequency converter to generate the required three-phase current, and then the program returns to step S103.

[0025] In a preferred embodiment of the application, the calculation formula of the PI controller of the current loop is as follows:

[0026] U=Kp*(I_ref-I_actual)+Ki*∫(I_ref-I_actual)dt

[0027] Where: U is the output voltage, Kp is the proportional coefficient, Ki is the integral coefficient, I_ref is the target current, which is determined according to the set value and IGBT temperature protection, and I_actual is the actual measured current.

[0028] In a preferred embodiment of the application, the actual target current of the current loop decreases with the increase of the IGBT module temperature, and the derating calculation formula is:

[0029] I_ref_actual=I_ref_setting*max(0,1-k*(T_IGBT-T_threshold)

[0030] Wherein: I_ref_actual is the actual target current, I_ref_setting is the set target current, k is the derating coefficient, T_IGBT is the current temperature of IGBT, and T_threshold is the temperature threshold.

[0031] Due to the adoption of the above technical solutions, the present application has the following advantages:

[0032] 1. Optimized for CO2 asynchronous motor compressors: specially designed for the characteristics of CO2 asynchronous motor compressors, especially suitable for carbon dioxide compressor preheating control, solving the demand of this type of compressor.

[0033] 2. Precise current control: through current loop PI control, precise control of preheating current is realized, avoiding the energy waste and inaccurate control problems in traditional preheating methods.

[0034] 3. Systematic phase switching: through timing commutation design, avoid motor and IGBT single-phase overheating, prolong the service life of the equipment.

[0035] 4. Effectively avoid rotor rotation: ensure that the rotor does not rotate during preheating, avoid the high and low pressure difference of the compressor and the refrigerant entering the pipeline, improve the preheating efficiency.

[0036] 5. Perfect safety protection: IGBT temperature protection mechanism ensures the safe operation of the system, prevents overheating damage to the equipment. This solves the problem of insufficient protection in the prior art.

[0037] 6. High configurability: provides multiple settable parameters, including current set value, shutdown switching time and single-phase duration, to meet different working condition requirements. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0039] Figure 1 is the flowchart of the present application.

[0040] Figure 2 is the preheating control hardware block diagram of the present application.

[0041] Figure 3 is the preheating control software block diagram of the present application.

[0042] Figure 4 is the direction relationship diagram of the stator current of the present application.

[0043] Figure 5 is a current versus phase relationship diagram of the present invention. DETAILED DESCRIPTION

[0044] In order to make the technical means, creative features, purposes and effects of the present invention easy to understand, the present invention is further described below in combination with specific drawings.

[0045] Referring to Figure 1 , a preheating control method for a carbon dioxide asynchronous motor compressor is shown in the figure, including the following steps:

[0046] Step S101, connect the U-phase, V-phase and W-phase output by the frequency converter 100 to the motor of the compressor 200, and preheat the motor stator through the current of the U-phase, V-phase and W-phase, thereby indirectly heating the lubricating oil in the stator outer oil circuit, and simultaneously collect the temperature of the compressor 200 in real time, i.e. connect the temperature sensor of the compressor 200 to the temperature collection interface 110 of the frequency converter 100, as shown in Figure 2 .

[0047] Referring to Figure 3 , the preheating module includes a preheating state machine, a current loop and a preheating phase calculation unit, the current loop is responsible for calculating the output voltage value, and the preheating state machine and the preheating phase calculation unit are responsible for judging the time point of stop switching. The input signals of the preheating module include the output phase current CLM_Is_Gc (unit: Arms), the output phase current set value RTE_PreHeatIsReq_Gc (unit: %), the preheating stop switching time RTE_PreHeatStopTime_Gc (unit: s), the preheating single-phase duration RTE_PhaseChangePeriod_Gc (unit: s), the IGBT module temperature ISM_TempIGBT_Gc (unit: degC) and the bus voltage value ISM_UdcLnk (unit: V); the output signals of the preheating module include the preheating request α-axis voltage ACT_PreHeatUa_Gc (unit: V), the preheating request β-axis voltage ACT_PreHeatUb_Gc (unit: V) and the preheating output voltage phase ACT_PreHeatAg_Gc (unit: Deg).

[0048] Step S102, obtain the output phase current, the output phase current set value, the preheating stop switching time, the preheating single-phase duration, the IGBT module temperature and the bus voltage value, and set the initial phase angle of the frequency converter to 0°;

[0049] Step S103, judge whether the temperature of the compressor reaches the preheating temperature, if yes, end, otherwise, go to step S104;

[0050] Step S104, determine whether the compressor is in a shutdown state, if yes, go to step S105, otherwise go to step S106;

[0051] Step S105, determine whether the shutdown time reaches the pre-heating shutdown switching time, if yes, set the output phase current to the target phase current, and go to step S107, otherwise, enter the shutdown state, set the output target phase current to 0, and then go to step S107;

[0052] Step S106, determine whether the pre-heating one-way duration is reached, if yes, enter the shutdown state, and set the phase angle of the frequency converter to the initial phase angle + 120°, and set the output target phase current to 0, and then go to step S107;

[0053] Step S107, calculate the actual target current according to the IGBT module temperature;

[0054] Step S108, calculate the pre-heating output voltage according to the actual target current through the IP controller of the current loop, and generate the corresponding output current according to the pre-heating output voltage, so that the output current reaches the actual target current;

[0055] Step S109, according to the voltage calculated by the PI controller, calculate the voltage components of the α axis and the β axis through coordinate transformation (Clarke transformation), and finally generate SVPWM (space vector pulse width modulation) signal to drive the IGBT module of the frequency converter to generate the required three-phase current; then return to step S103 and enter the next round of loop judgment.

[0056] In step S108, the current loop for pre-heating is realized based on a PI controller, and its main function is to calculate the output voltage to make the output current reach the set value. Unlike the prior art such as the invention patent application CN 114623081A which simply adjusts the current based on the rotor position or only adjusts the current according to the temperature difference, the present application adopts a more accurate closed-loop PI control strategy.

[0057] The calculation formula of the PI controller of the current loop is as follows:

[0058] U = Kp * (I_ref - I_actual) + Ki * ∫(I_ref - I_actual)dt

[0059] Where: U is the output voltage, Kp is the proportional coefficient, Ki is the integral coefficient, I_ref is the target current, which is determined according to the set value and IGBT temperature protection, and I_actual is the actual measured current.

[0060] Each time commutation occurs, the target current of the current loop is reset to 0A to ensure that commutation only occurs after shutdown. This mechanism effectively prevents the rotor from rotating during commutation, thus avoiding the introduction of refrigerant.

[0061] In step S107, to prevent the IGBT module from overheating, this invention designs a temperature protection mechanism. The actual target current of the current loop used for preheating is derating as the IGBT module temperature rises, and the derating calculation formula is as follows:

[0062] I_ref_actual=I_ref_setting*max(0,1-k*(T_IGBT-T_threshold))

[0063] Where: I_ref_actual is the actual target current, I_ref_setting is the set target current, k is the derating factor, T_IGBT is the current temperature of the IGBT, and T_threshold is the temperature threshold.

[0064] When the IGBT module temperature exceeds a certain value, the preheating function will automatically stop. This protection mechanism is an important supplement to the safety protection of existing preheating methods.

[0065] During the preheating process, the compressor operates similarly to a stall condition. To prevent excessive single-phase overheating of the compressor motor and IGBT module, this invention designs a systematic phase switching mechanism. Unlike the control method in invention patent application CN 114623081A, which is mainly based on rotor position, this invention achieves timed phase switching to ensure uniform heating of all three phases. The phase switching of this invention follows these rules:

[0066] 1. The initial phase of the voltage is 0°;

[0067] 2. The phase increases by 120° with each phase switch;

[0068] 3. The duration of a single phase is controlled by the RTE_PhaseChangePeriod_Gc parameter;

[0069] 4. The shutdown switching time is controlled by the RTE_PreHeatStopTime_Gc parameter.

[0070] Before phase switching, the target current of the current loop is reset to 0A to ensure that the motor is not powered during the switch. Then, the phase is changed, and preheating is restarted. This design ensures that the compressor motor and IGBT module single phases do not overheat, extending the service life of the equipment.

[0071] During preheating, all three phases carry current, but one phase always has a current value twice that of the other two, in opposite directions, to ensure the rotor does not rotate. (See also...) Figure 4When the phase changes, the maximum current changes accordingly:

[0072] The U-phase current is at its maximum at a phase angle of 1.0°.

[0073] 2.120° phase current is the maximum in phase V;

[0074] The W-phase current is at its maximum at a phase angle of 3.240°.

[0075] See Figure 5 This design ensures that the rotor does not rotate during the preheating process, avoiding potential problems such as high and low pressure differences in the compressor and the introduction of refrigerant into the pipeline.

[0076] The preheating control method for a carbon dioxide asynchronous motor compressor of the present invention has the following advantages:

[0077] 1. Current-loop PI controller: Calculates the output voltage to ensure the output current reaches the customer-set current value, and ensures precise control through feedback control. Unlike simple switching control or fixed current control in existing technologies, this invention achieves more precise current control through a PI controller, which can dynamically adjust the output voltage according to real-time conditions.

[0078] 2. State machine management: Determines the timing of shutdown and commutation, ensuring a complete shutdown before commutation to prevent refrigerant from being introduced during rotor rotation. This solves the problem of insufficient commutation control in existing technologies.

[0079] 3. Systematic phase switching: Responsible for changing the phase of the output voltage. The initial phase is 0°, and each switching increases the phase by 120°, effectively avoiding single-phase overheating.

[0080] 4. IGBT module temperature protection: The target current value of the preheating current loop automatically decreases as the IGBT temperature rises, ensuring safe system operation and preventing IGBT damage. This solves the problem of insufficient safety protection in existing technologies.

[0081] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A preheating control method for a carbon dioxide asynchronous motor compressor, characterized in that, Includes the following steps: Step S101: Connect the U-phase, V-phase, and W-phase outputs of the frequency converter to the compressor motor, and preheat the motor stator through the current of the U-phase, V-phase, and W-phase, while collecting the compressor temperature in real time. Step S102: Obtain the output phase current, output phase current set value, preheating shutdown switching time, preheating unidirectional duration, IGBT module temperature and bus voltage value, and set the initial phase angle of the inverter to 0°. Step S103: Determine whether the compressor temperature has reached the preheating temperature. If the determination is yes, the process ends; otherwise, proceed to step S104. Step S104: Determine whether the compressor is in a stopped state. If it is, proceed to step S105; otherwise, proceed to step S106. Step S105: Determine whether the shutdown time has reached the preheating shutdown switching time. If the determination is yes, set the output phase current to the target phase current and proceed to step S107. Otherwise, enter the shutdown state, set the output target phase current to 0, and then proceed to step S107. Step S106: Determine whether the preheating unidirectional duration has been reached. If the determination is yes, enter the shutdown state, set the phase angle of the frequency converter to the initial phase angle +120°, and set the output target phase current to 0, then proceed to step S107. Step S107: Calculate the actual target current based on the IGBT module temperature; Step S108: The IP controller of the current loop calculates the preheating output voltage based on the actual target current, and generates the corresponding output current based on the preheating output voltage, so that the output current reaches the actual target current. In step S109, based on the voltage calculated by the PI controller, the voltage components of the α-axis and β-axis are calculated through coordinate transformation, and finally an SVPWM signal is generated to drive the IGBT module of the frequency converter to generate the required three-phase current. Then the program returns to step S103.

2. The preheating control method for a carbon dioxide asynchronous motor compressor as described in claim 1, characterized in that, The calculation formula for the PI controller of the current loop is as follows: U=Kp*(I_ref-I_actual)+Ki*∫(I_ref-I_actual)dt Where: U is the output voltage, Kp is the proportional coefficient, Ki is the integral coefficient, I_ref is the target current, which is determined according to the set value and IGBT temperature protection, and I_actual is the actual measured current.

3. The preheating control method for a carbon dioxide asynchronous motor compressor as described in claim 1, characterized in that, The actual target current of the current loop is derating as the IGBT module temperature increases, and the derating calculation formula is as follows: I_ref_actual=I_ref_setting*max(0,1-k*(T_IGBT-T_threshold)) Where: I_ref_actual is the actual target current, I_ref_setting is the set target current, k is the derating factor, T_IGBT is the current temperature of the IGBT, and T_threshold is the temperature threshold.

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