Defrosting control method and control system of heat pump system and heat pump system

Abstract

The invention relates to the technical field of air source heat pumps, in particular to a defrosting control method and system of a heat pump system and the heat pump system. The method comprises the steps that operation condition parameters of the compression mechanism are obtained; calculating a polytropic index under the current working condition; calculating an expected exhaust temperature; an exhaust superheat degree early warning threshold value is calculated; the real-time exhaust superheat degree is calculated; when the real-time exhaust superheat degree is reduced to be below a first threshold value, lasts for first preset time and is in a continuous low trend, an auxiliary heating mechanism is controlled to be started for defrosting; and when the real-time exhaust superheat degree rises to the second threshold value or above again and lasts for second preset time, and the change rate is smaller than the preset change rate threshold value, the auxiliary heating mechanism is controlled to stop defrosting. The defrosting judgment benchmark can be dynamically adjusted according to the real-time working condition, the defrosting time is accurately controlled, the efficient operation time of the heat pump is maximized on the premise that the safety of the compressor is guaranteed, and the overall energy efficiency of the system is improved.

Description

Technical Field

[0001] This invention relates to the field of air source heat pump technology, and in particular to a defrosting control method, control system, and heat pump system for a heat pump system. Background Technology

[0002] When a heat pump system is operating for heating, the outdoor heat exchanger acts as an evaporator, absorbing heat from the outdoor air. When the outdoor ambient temperature is low and humidity is high, frost easily forms on the surface of the outdoor heat exchanger. The presence of frost increases airflow resistance and reduces heat exchange efficiency, leading to a decrease in the system's heating capacity and energy efficiency. To ensure continuous and efficient system operation, timely defrosting of the outdoor heat exchanger is necessary. In existing technologies, the common defrosting method is reverse cycle defrosting, which involves switching the system from heating mode to cooling mode using a four-way valve, utilizing high-temperature refrigerant to melt the frost on the outdoor heat exchanger surface. However, during reverse cycle defrosting, the indoor heat exchanger absorbs heat from the indoor environment, causing indoor temperature fluctuations and affecting user comfort. Therefore, some heat pump systems are equipped with auxiliary heating mechanisms, such as hot gas bypass circuits or electric heating devices, to perform defrosting in a non-reverse cycle manner. This involves introducing an auxiliary heat source to heat and defrost the outdoor heat exchanger while maintaining the system's heating mode, thereby avoiding indoor temperature fluctuations.

[0003] In non-reverse cycle defrosting systems, accurately determining the timing of defrosting intervention and withdrawal is a critical technical challenge. If defrosting intervenes too early, the system frequently enters defrosting mode, increasing the energy consumption of the auxiliary heating mechanism and compressing the heat pump's efficient operating time, resulting in overall reduced energy efficiency. If defrosting intervenes too late, severe frost buildup on the outdoor heat exchanger significantly reduces heat exchange efficiency, also leading to reduced system energy efficiency. Insufficient heat exchange in the evaporator may even cause liquid slugging in the compressor's suction, resulting in liquid slugging and damage to the compressor. If defrosting withdraws too early, the frost layer has not completely melted, and the system will quickly re-frost, leading to repeated defrosting. If defrosting withdraws too late, the auxiliary heating mechanism continues to operate, wasting energy, and may cause control oscillations due to changes in system operating conditions during defrosting. In existing technologies, the determination of defrosting intervention and withdrawal typically relies on fixed temperature thresholds or time periods, making it difficult to adapt to changes in ambient temperature and operating conditions. This results in inaccurate defrosting control, failing to maximize the heat pump's efficient operating time while ensuring compressor safety. Summary of the Invention

[0004] This invention provides a defrosting control method, control system, and heat pump system for a heat pump system. The method can dynamically determine the defrosting judgment criteria based on the real-time operating conditions of the heat pump system, accurately identify defrosting needs, and promptly exit defrosting, thereby extending the effective operating time of the heat pump mode and improving the overall energy efficiency of the heat pump system while ensuring that the compressor does not experience liquid slugging.

[0005] The present invention provides a defrosting control method for a heat pump system, comprising:

[0006] The operating parameters of the compression mechanism are obtained, including exhaust temperature, exhaust pressure, intake pressure and rotational speed. The operating condition parameters are input into a preset thermodynamic characteristic model of the compression mechanism to calculate the polyvariance index of the compression mechanism under the current operating condition. Based on the intake pressure, the exhaust pressure, the polytropic index, and the preset compression chamber intake superheat threshold, the expected exhaust temperature corresponding to satisfying the compression chamber intake superheat threshold is calculated through thermodynamic back-calculation. Calculate the exhaust superheat warning threshold, wherein the exhaust superheat warning threshold is the difference between the expected exhaust temperature and the saturated condensation temperature corresponding to the exhaust pressure; Calculate the real-time exhaust superheat, where the real-time exhaust superheat is the difference between the exhaust temperature and the saturated condensation temperature; When the real-time exhaust superheat decreases below the first threshold, lasts for a first preset time, and shows a continuous downward trend, it is determined that the outdoor heat exchanger is frosted, and the auxiliary heating mechanism is controlled to start to perform non-reverse cycle defrosting on the outdoor heat exchanger. When the real-time exhaust superheat rises above the second threshold for a second preset time and the absolute value of the rate of change of the real-time exhaust superheat is less than the preset rate of change threshold, the auxiliary heating mechanism is controlled to stop to exit defrosting. Wherein, the first threshold is the product of the first coefficient and the exhaust superheat warning threshold mentioned before the defrost mode is started, the second threshold is the product of the second coefficient and the exhaust superheat warning threshold recalculated under the defrost mode, and the second coefficient is less than the first coefficient.

[0007] In one embodiment of the present invention, the thermodynamic characteristic model of the compression mechanism is a model obtained in advance by fitting the performance test data of the compression mechanism, which is used to describe the functional relationship between the polytropic index and the rotational speed, exhaust pressure and intake pressure.

[0008] In one embodiment of the present invention, the functional relationship model is represented as follows: , in, It is a variable index. For rotational speed, For exhaust pressure, Inhalation pressure, to These are the fitting coefficients. The exhaust pressure is the standard operating pressure. This is the intake pressure under the reference operating conditions.

[0009] In one embodiment of the present invention, the superheat threshold of the compression chamber is the minimum safe superheat value for preventing liquid slugging in the compression mechanism. This threshold is a preset constant value that does not change with the operating mode of the heat pump system. Meanwhile, during normal heating operation, the actual superheat of the compression chamber inlet is higher than the superheat threshold of the compression chamber. When the heat exchange performance of the outdoor heat exchanger is reduced due to frost, and the actual superheat of the compression chamber inlet decreases to this threshold, it indicates that the heat pump system has reached the critical state that requires defrosting.

[0010] In one embodiment of the present invention, the step of calculating the expected exhaust temperature corresponding to the compression chamber intake superheat threshold through thermodynamic back-calculation includes: Based on the suction pressure, the corresponding evaporation temperature is obtained by querying the pre-stored refrigerant property data table or calling the refrigerant property calculation function; Calculate the inlet temperature of the compression chamber, which is the sum of the evaporation temperature and the superheat threshold of the compression chamber intake. Calculate the compressor intake temperature, which is the compressor inlet temperature minus a preset temperature rise from the compressor intake to the compressor chamber. Based on the compressor intake temperature, the exhaust pressure, the intake pressure, and the polytropic index, the expected exhaust temperature is calculated using the thermodynamic formula for the compression process: , in, For the expected exhaust temperature, This refers to the compressor's suction port temperature. For exhaust pressure, Inhalation pressure, It is a highly variable index.

[0011] In one embodiment of the present invention, the first coefficient is determined in the following manner: The minimum allowable intake dryness of the compression mechanism is obtained, which is the minimum mass fraction of the gas phase in the wet vapor that the compressor is allowed to draw in. At the current suction pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the enthalpy value of the saturated liquid refrigerant and the enthalpy value of the saturated gaseous refrigerant corresponding to the suction pressure. Calculate the wet vapor enthalpy at the current inhalation pressure and the limiting minimum allowable inhalation dryness: ,in The saturated liquid enthalpy at the current intake pressure. The saturated gaseous enthalpy at the current inhalation pressure. This is the absolute minimum permissible inspiratory dryness. Calculate the enthalpy difference: ; Under the current exhaust pressure, the superheated vapor enthalpy value corresponding to the exhaust superheat warning threshold is obtained by querying the pre-stored refrigerant property data table or calling the refrigerant property calculation function. ,in The temperature at the current exhaust pressure is enthalpy value at time The saturated condensation temperature. The exhaust superheat warning threshold; Calculate the target enthalpy: ; Under the current exhaust pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to find the temperature Ta corresponding to the target enthalpy value Ha; Calculate the first coefficient: ,in This is the first coefficient.

[0012] In one embodiment of the present invention, the second coefficient is determined in the following manner: In defrost mode, the current intake pressure, exhaust pressure, and polytropic index of the compression mechanism are obtained; Based on the suction pressure in defrost mode, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the corresponding evaporation temperature; Calculate the sum of the current evaporation temperature and the superheat threshold of the compression chamber intake, and use it as the inlet temperature of the compression chamber in defrosting mode; The compressor intake temperature in defrost mode is calculated by subtracting the preset temperature rise from the compressor intake port to the compressor chamber from the compressor intake port temperature. Based on the compressor intake temperature, current discharge pressure, current intake pressure, and current polytropic index in defrost mode, the expected discharge temperature in defrost mode is calculated using the thermodynamic formulas for the compression process: ; in, This is the expected exhaust temperature in defrost mode. This refers to the compressor suction port temperature in defrost mode. This refers to the exhaust pressure in defrost mode. This refers to the suction pressure in defrost mode. The variable index under defrost mode; The difference between the expected exhaust temperature in defrost mode and the saturated condensation temperature corresponding to the current exhaust pressure is calculated and used as the exhaust superheat warning threshold in defrost mode. The second coefficient was calibrated through system dynamic response tests. During calibration Less than the first coefficient And select one that can make the exhaust superheat recover in real time during the defrosting process. The product of the exhaust superheat warning threshold in defrost mode and the value is greater than or equal to the threshold value without overshoot oscillation. value.

[0013] In one embodiment of the present invention, the auxiliary heating mechanism includes at least one of a hot gas bypass circuit, a triangular circulation circuit, a motor active heating device, and a PTC heater.

[0014] The present invention also provides a control system for a heat pump system, comprising: The parameter acquisition module is used to acquire the operating condition parameters of the compression mechanism, including exhaust temperature, exhaust pressure, intake pressure and rotational speed. The polytropic index calculation module is used to input the operating condition parameters into a preset thermodynamic characteristic model of the compression mechanism and calculate the polytropic index of the compression mechanism under the current operating condition. The threshold determination module is used to calculate the expected exhaust temperature corresponding to satisfying the intake superheat threshold of the compression chamber by thermodynamic back-calculation based on the intake pressure, the exhaust pressure, the polytropic index and the preset compression chamber intake superheat threshold; and to calculate the difference between the expected exhaust temperature and the saturated condensation temperature corresponding to the exhaust pressure as the exhaust superheat warning threshold. The defrosting control module is used to calculate the real-time exhaust superheat, which is the difference between the exhaust temperature and the saturated condensation temperature. And when the real-time exhaust superheat decreases to below the first threshold, continues for a first preset time and shows a continuous downward trend, it is determined that the outdoor heat exchanger is frosted, and the auxiliary heating mechanism is controlled to start to perform non-reverse cycle defrosting on the outdoor heat exchanger. When the real-time exhaust superheat rises above the second threshold for a second preset time and the absolute value of the rate of change of the real-time exhaust superheat is less than the preset rate of change threshold, the auxiliary heating mechanism is controlled to stop to exit defrosting. Wherein, the first threshold is the product of a first coefficient and the exhaust superheat warning threshold calculated by the threshold determination module before the defrost mode is started, the second threshold is the product of a second coefficient and the exhaust superheat warning threshold recalculated by the threshold determination module in the defrost mode, and the second coefficient is less than the first coefficient.

[0015] The present invention also provides a heat pump system, comprising: Compression mechanism, outdoor heat exchanger, indoor heat exchanger, auxiliary heating mechanism; and A controller, comprising a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the defrosting control method for a heat pump system as described in any one of claims 1 to 8.

[0016] The beneficial effects of this invention are as follows: This invention proposes a defrosting control method, control system, and heat pump system for a heat pump system. This method dynamically determines the exhaust superheat warning threshold based on the real-time operating conditions of the heat pump system. This threshold is adjusted in real-time according to changes in compressor speed, suction pressure, and exhaust pressure, thereby accurately reflecting the minimum exhaust superheat required for safe compressor operation under the current conditions. Based on this, a hysteresis control range is formed by setting a first coefficient and a second coefficient, combined with the real-time trend and stability judgment of exhaust superheat changes, to achieve accurate control of the timing of defrosting intervention and withdrawal. Compared with existing technologies, this invention avoids energy efficiency losses caused by premature or late defrosting intervention, and avoids repeated defrosting or energy waste caused by premature or late defrosting withdrawal. Simultaneously, by using the safe threshold of suction superheat in the compression chamber as a benchmark for reverse calculation, the safe operation of the compressor is simultaneously ensured during the defrosting control process, effectively preventing the risk of liquid slugging. Therefore, while ensuring reliability, it maximizes the effective operating time of the heat pump mode and improves the overall energy efficiency of the pump system. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0018] In the attached diagram: Figure 1 This is a flowchart of a defrosting control method for a heat pump system provided in an embodiment of the present invention; Figure 2 This is a structural block diagram of a defrosting control system for a heat pump system provided in an embodiment of the present invention; Detailed Implementation The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0019] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. The drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0020] In the following description, numerous details are explored to provide a more thorough explanation of embodiments of the invention. However, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring embodiments of the invention.

[0021] In this invention, the non-reverse cycle defrosting refers to a defrosting method in which the outdoor heat exchanger is heated by activating an auxiliary heating mechanism to melt the frost layer while keeping the heat pump system heating mode unchanged.

[0022] This invention aims to solve the problems of inaccurate timing of defrosting intervention and withdrawal in existing non-reverse cycle defrosting systems, making it difficult to maximize the efficient operation time of the heat pump while ensuring compressor safety. The invention will be described in detail below with reference to specific embodiments.

[0023] like Figure 1-2 As shown, the present invention provides a defrosting control method for a heat pump system, comprising the following steps: S1: Obtain the operating parameters of the compression mechanism, including exhaust temperature, exhaust pressure, intake pressure, and rotational speed. Specifically, the exhaust temperature is collected in real time by a temperature sensor installed on the compressor exhaust pipe, the exhaust pressure is collected in real time by a pressure sensor installed on the compressor exhaust pipe, the intake pressure is collected in real time by a pressure sensor installed on the compressor intake pipe, and the rotational speed is obtained either from within the compressor controller or through a rotational speed sensor. These four parameters together constitute the basic data reflecting the current operating status of the compressor and the system's thermodynamic conditions.

[0024] S2: Input the operating condition parameters into the preset thermodynamic characteristic model of the compression mechanism, and calculate the polytropic index of the compression mechanism under the current operating condition.

[0025] The thermodynamic characteristic model of the compression mechanism is a model obtained in advance by fitting performance test data of the compression mechanism, used to describe the functional relationship between the polytropic index and the rotational speed, exhaust pressure, and intake pressure. Specifically, by collecting performance test data of the compression mechanism under different rotational speeds, exhaust pressures, and intake pressures, including parameters such as input power, refrigerant flow rate, and exhaust temperature, the polytropic index values ​​under each operating condition are derived using thermodynamic principles, forming a set of test data points. Based on this, a nonlinear regression method is used to fit these data points to obtain a functional relationship model with rotational speed, exhaust pressure, and intake pressure as independent variables and the polytropic index as the dependent variable. In this way, the compression characteristics of the compression mechanism during actual operation can be accurately described, overcoming the errors caused by treating the polytropic index as a constant or using simple linear approximation, and providing reliable model support for subsequent accurate calculation of the expected exhaust temperature through thermodynamic back-calculation. The functional relationship model is expressed as: , in, It is a variable index. For rotational speed, For exhaust pressure, For the inhalation pressure, the polynomial part This describes the nonlinear relationship between the polytropic index and rotational speed. The introduction of cubic and quadratic terms allows the model to accurately fit the effect of rotational speed variations on the compression process. The pressure correction section includes an exhaust pressure correction term. and inhalation pressure correction item These are used to describe the impact of exhaust pressure and intake pressure deviating from the baseline operating condition on the polytropic index, respectively. and The exhaust pressure and intake pressure under the reference operating conditions are usually selected from the center operating point in the performance test data as the reference. to The fitting coefficients are obtained by substituting the collected performance test data into the model and solving it using the least squares method or other nonlinear regression algorithms, ensuring that the absolute value of the relative error between the model calculation results and the experimental data is controlled within 5%. This step involves real-time acquisition of... , , Substituting into the above model, the polytropic index n under the current operating condition can be calculated. This polytropic index describes the thermodynamic characteristics of the gas state changes during compression and is a key parameter connecting the compressor's intake and exhaust states. This functional model has a simple structure and low computational cost, making it suitable for real-time operation in the controller. Furthermore, its nonlinear characteristics ensure calculation accuracy under different operating conditions, providing an accurate polytropic index input for subsequent thermodynamic back-calculation.

[0026] S3: Based on the intake pressure, the exhaust pressure, the polytropic index, and the preset compression chamber intake superheat threshold, the expected exhaust temperature corresponding to satisfying the compression chamber intake superheat threshold is calculated through thermodynamic back-calculation.

[0027] The suction superheat of the compression chamber refers to the difference between the temperature of the refrigerant when it enters the compression chamber of the compression mechanism and the evaporation temperature corresponding to the current suction pressure. This value reflects the degree of superheat of the refrigerant before entering the compression chamber. When the suction superheat of the compression chamber is lower than a certain value, the refrigerant may contain liquid components, which can cause liquid slugging after entering the compression chamber, damaging the compression mechanism. Therefore, a suction superheat threshold is set as the minimum safety boundary to prevent liquid slugging. The specific value of this threshold is determined by the structural characteristics of the compression mechanism, lubrication requirements, and the physical properties of the refrigerant used, and is determined through bench testing during the system design phase.

[0028] The compression chamber suction superheat threshold is the minimum safe superheat value used to prevent liquid slugging in the compression mechanism. This threshold is a preset constant value that does not change with the operating mode of the heat pump system. During normal operation, the actual suction superheat at the compression chamber inlet is higher than this threshold. When the outdoor heat exchanger experiences heat exchange performance degradation due to frost, and the suction superheat at the compression chamber inlet gradually decreases to this threshold, it indicates that the system has reached a critical state requiring defrosting. Therefore, when the actual suction superheat of the compression chamber decreases to this threshold due to the evaporator's frost-induced drop in evaporation temperature, it not only signifies that the compression mechanism faces a risk of liquid slugging but also indicates that the evaporator frost has become severe enough to affect heat exchange efficiency, necessitating defrosting. By using this threshold simultaneously as a benchmark for both liquid slugging protection and frost assessment, a unification of safety and energy efficiency boundaries is achieved, providing a clear physical basis for defrosting control. In one specific implementation, this threshold is set to 5°C.

[0029] S31: The specific steps for calculating the expected exhaust temperature corresponding to the compression chamber intake superheat threshold through thermodynamic back-calculation include: S311: Based on the suction pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the corresponding evaporation temperature; the data table stores the saturation temperature values ​​of the refrigerant under different saturation pressures, and the corresponding evaporation temperature can be obtained by looking up the table using the suction pressure as an index when the system is running.

[0030] S312: Calculate the compression chamber inlet temperature, which is the sum of the evaporation temperature and the compression chamber suction superheat threshold. The suction superheat threshold is a preset, constant safety value used to prevent liquid slugging in the compressor; its specific value is determined by the compressor's structural characteristics and the refrigerant's properties. The compression chamber inlet temperature represents the temperature the refrigerant should reach when entering the compression chamber to ensure that the suction superheat of the compression chamber precisely meets the safety threshold.

[0031] S313: Calculate the compressor suction port temperature, which is the compressor cavity inlet temperature minus a preset temperature rise value from the compressor suction port to the compression cavity. During the process of refrigerant flowing from the compressor suction port to the compression cavity inlet, it absorbs heat from components such as the compressor housing and motor, resulting in a temperature rise. This temperature rise value is determined through prior testing and stored as a preset constant; for example, this temperature rise value is preset to 10℃. Subtracting this temperature rise value from the compression cavity inlet temperature yields the compressor suction port temperature, which is the starting point for reverse calculation.

[0032] S314: Based on the compressor intake temperature, the exhaust pressure, the intake pressure, and the polytropic index, calculate the expected exhaust temperature using the thermodynamic formula for the compression process: , in, For the expected exhaust temperature, This refers to the compressor's suction port temperature. For exhaust pressure, Inhalation pressure, The polytropic index is used to calculate the theoretically required system exhaust temperature under current operating conditions so that the intake superheat of the compression chamber exactly meets the safety threshold. Specifically, the compressor intake temperature is converted to Kelvin, and then the exhaust pressure, intake pressure, and polytropic index are substituted into the thermodynamic formula for the compression process to calculate the expected exhaust temperature in Kelvin, which is then converted back to Celsius. This reverse calculation process transforms the difficult-to-measure intake superheat of the compression chamber into a calculable and applicable expected exhaust temperature, providing a theoretical benchmark for subsequent dynamic threshold calculations.

[0033] S4: Calculate the exhaust superheat warning threshold, wherein the exhaust superheat warning threshold is the difference between the expected exhaust temperature and the saturated condensation temperature corresponding to the exhaust pressure; The saturated condensation temperature corresponding to the discharge pressure is obtained by querying a pre-stored refrigerant property data table or calling a refrigerant property calculation function. This discharge superheat warning threshold is a dynamic value that changes in real time with the compressor speed, suction pressure, and discharge pressure, reflecting the minimum discharge superheat required to ensure compressor safety under current operating conditions. The compression chamber suction superheat, a key parameter directly reflecting the risk of liquid slugging and evaporator frosting, cannot be directly measured by sensors. To solve this problem, this invention uses thermodynamic back-calculation, based on a preset compression chamber suction superheat threshold, combined with real-time operating parameters to calculate the expected discharge temperature, thereby transforming the difficult-to-measure compression chamber suction superheat into a measurable discharge superheat warning threshold.

[0034] S5: Calculate the real-time exhaust superheat, which is the difference between the exhaust temperature and the saturated condensation temperature. This real-time exhaust superheat reflects the current actual exhaust superheat state of the system.

[0035] S6: When the real-time exhaust superheat decreases below a first threshold for a first preset time and shows a continuous downward trend, it is determined that the outdoor heat exchanger has reached a level requiring defrosting. The auxiliary heating mechanism is then activated to perform non-reverse cycle defrosting on the outdoor heat exchanger. The first threshold is the product of a first coefficient and the exhaust superheat warning threshold before the defrosting mode is activated. The determination of a first preset time and a continuous downward trend avoids misjudgments caused by instantaneous fluctuations, ensuring the accuracy of defrosting intervention. In a specific implementation, the first preset time can be set to several consecutive sampling periods according to the system control cycle. The continuous downward trend can be determined by comparing the real-time exhaust superheat values ​​of multiple consecutive sampling points; for example, when the values ​​of three consecutive sampling points decrease sequentially, it is determined to show a continuous downward trend.

[0036] The first coefficient is determined in the following way: S61: Obtain the minimum permissible suction dryness of the compression mechanism. The minimum permissible suction dryness is the minimum mass fraction of the gas phase in the wet vapor that the compressor is allowed to inhale. This minimum permissible suction dryness is determined through compressor bench testing. This parameter is an inherent characteristic of the compressor and reflects the minimum mass fraction of the gas phase in the wet vapor that the compressor is allowed to inhale. Below this dryness, the compressor is at risk of liquid slugging. Each compressor unit needs to complete relevant anti-wet compression tests. The test parameters are determined and selected during the design and selection phase. The compressor supplier needs to provide the operating range of its compressors. Within this range, when the suction dryness is higher than the minimum permissible suction dryness, the compressor will not experience liquid slugging, overcurrent, or overheating protection. In other words, the exhaust overheat warning threshold... This corresponds to the exhaust superheat at which the intake superheat of the compression chamber is equal to the intake superheat threshold (i.e., the safety boundary) of the compression chamber. This corresponds to the exhaust superheat of the compressor when it operates at the allowable limit of suction dryness, where This is the first coefficient.

[0037] S62: At the current suction pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the enthalpy value of the saturated liquid refrigerant and the enthalpy value of the saturated gaseous refrigerant corresponding to the suction pressure; these data tables cover the thermodynamic properties of the refrigerant at different pressures.

[0038] S63: Calculate the wet vapor enthalpy at the current inhalation pressure and the ultimate permissible minimum inhalation dryness: ,in The saturated liquid enthalpy at the current intake pressure. The saturated gaseous enthalpy at the current inhalation pressure. This is the absolute minimum permissible inspiratory dryness. S64: Calculate the enthalpy difference: Enthalpy difference represents the difference between the enthalpy of saturated gas at the current suction pressure and the enthalpy of wet vapor at the limiting dryness. This difference reflects the minimum enthalpy margin required to ensure the safe operation of the compressor.

[0039] S65: Under the current exhaust pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the superheated vapor enthalpy value corresponding to the exhaust superheat warning threshold. ,in The temperature at the current exhaust pressure is The enthalpy value at that temperature That is, the expected exhaust temperature. The saturated condensation temperature. The exhaust superheat warning threshold; S66: Calculate the target enthalpy value: This value represents the enthalpy level that the exhaust side should reach after considering safety margins. S67: Under the current exhaust pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to find the temperature Ta corresponding to the target enthalpy value Ha. This temperature is the theoretical exhaust temperature after considering the safety margin.

[0040] S68: Calculate the first coefficient: ,in The first coefficient reflects the ratio of the safety margin to the warning threshold. It is used to scale the dynamic warning threshold to the actual defrosting intervention threshold, thereby accurately controlling the timing of defrosting intervention while ensuring the safety of the compressor.

[0041] In non-reverse cycle defrosting systems, the timing of defrosting termination directly affects defrosting effectiveness and system stability. If defrosting terminates too early, the frost layer hasn't completely melted, and the system will quickly re-frost, leading to repeated defrosting. If defrosting terminates too late, the auxiliary heating mechanism continues to operate, wasting energy and potentially causing control oscillations due to changes in system operating conditions during defrosting. Existing technologies typically rely on fixed thresholds for defrosting termination, which cannot adapt to changes in system operating conditions during defrosting. To address this issue, this invention recalculates the exhaust superheat warning threshold in defrosting mode and calibrates a second coefficient through system dynamic response tests to form a hysteresis control range, ensuring a smooth transition when exiting defrosting.

[0042] S7: In defrost mode, the exhaust superheat warning threshold is recalculated based on the real-time operating conditions during the defrost process to obtain the exhaust superheat warning threshold in defrost mode.

[0043] Specifically, after the system enters defrost mode, the auxiliary heating mechanism starts to heat the outdoor heat exchanger. At this time, the system operating conditions change significantly. The compressor speed usually increases, the suction pressure (low pressure) rises, the evaporation temperature rises, and the refrigerant flow rate increases. To accurately determine the exit timing, it is necessary to reacquire the real-time suction pressure, discharge pressure, and polytropic index in defrost mode. Therefore, S71: In defrost mode, acquire the current suction pressure, discharge pressure, and polytropic index of the compressor mechanism; S72: Based on the suction pressure in defrost mode, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the corresponding evaporation temperature; S73: Calculate the sum of the current evaporation temperature and the superheat threshold of the compression chamber intake air as the inlet temperature of the compression chamber in defrosting mode; the superheat threshold of the compression chamber intake air is a preset constant safety value, which is the same as the threshold in normal mode and generally does not change due to mode change.

[0044] S74: Calculate the compressor suction port temperature in defrost mode by subtracting the preset temperature rise value from the compressor suction port to the compressor chamber from the compressor suction port temperature; wherein, there is a temperature rise in the process of refrigerant flowing from the compressor suction port to the compressor chamber inlet, and this temperature rise value is a preset constant, determined by the compressor structural characteristics, and is the same as the temperature rise value in normal mode.

[0045] S75: Based on the compressor intake temperature, current exhaust pressure, current intake pressure, and current polytropic index in defrost mode, calculate the expected exhaust temperature in defrost mode using the thermodynamic formula for the compression process: ; in, This is the expected exhaust temperature in defrost mode. This refers to the compressor suction port temperature in defrost mode. This refers to the exhaust pressure in defrost mode. This refers to the suction pressure in defrost mode. The polytropic index is used in defrost mode. After converting the compressor intake temperature to Kelvin, the discharge pressure, intake pressure, and polytropic index in defrost mode are substituted into the thermodynamic formula of the compression process to calculate the Kelvin value of the expected discharge temperature in defrost mode, and then converted back to Celsius.

[0046] S76: Calculate the difference between the expected exhaust temperature and the saturated condensation temperature corresponding to the current exhaust pressure in defrost mode, and use it as the exhaust superheat warning threshold in defrost mode. This value reflects the minimum exhaust superheat required to ensure the safety of the compressor under defrost conditions.

[0047] S77: Compare the real-time exhaust superheat with a second threshold. When the real-time exhaust superheat rises above the second threshold and the absolute value of the rate of change of the real-time exhaust superheat is less than a preset rate of change threshold for a second preset time, it is determined that defrosting is complete, and the auxiliary heating mechanism is controlled to stop to exit defrosting. The second threshold is the product of a second coefficient and the exhaust superheat warning threshold recalculated in the defrosting mode, and the second coefficient is less than the first coefficient.

[0048] The second coefficient β is calibrated through system dynamic response tests. Specifically, tests are conducted in defrost mode with different β values. The system response is observed when the real-time exhaust superheat rises above the product of β and the exhaust superheat warning threshold in defrost mode, at which point defrost exits. A β value that allows the system to exit smoothly without overshoot oscillation is selected. β is less than the first coefficient α, making the exit threshold less than the intervention threshold, forming a hysteresis control range, thereby avoiding frequent switching of the system near the defrost exit critical point. In this way, the second coefficient is calibrated as a constant value matching the system's dynamic characteristics. This value, combined with the recalculated exhaust superheat warning threshold in defrost mode, forms a dynamic second threshold, used to accurately determine the timing of defrost exit and ensure a smooth transition back to heat pump mode. The determination that the second preset time and the rate of change are less than the preset rate of change threshold ensures the stability of the defrost completion state and avoids erroneous exit due to instantaneous fluctuations. In a specific implementation, the second preset time can be set to a continuous number of sampling periods according to the system control cycle, and the rate of change can be calculated by dividing the difference between adjacent sampling points by the sampling time interval.

[0049] In non-reverse cycle defrosting systems, the auxiliary heating mechanism is the executing component for defrosting, and its type and combination directly affect the system's hardware configuration and control logic. To adapt to the application requirements of different heat pump systems, the auxiliary heating mechanism can be implemented in various forms. Furthermore, to apply the aforementioned defrosting control method to actual products, it is necessary to construct a corresponding control system and heat pump system, achieving automated operation of the method through modular design and controller hardware.

[0050] In one optional embodiment of this case, the auxiliary heating mechanism includes at least one of a hot gas bypass circuit, a triangular circulation circuit, a motor active heating device, and a PTC heater.

[0051] A hot gas bypass circuit refers to a bypass pipe leading from the compressor discharge line, passing through a throttling device and connecting to the outdoor heat exchanger inlet or suction line. It utilizes the high-temperature refrigerant discharged from the compressor to directly heat and defrost the outdoor heat exchanger. A triangular circulation circuit involves setting up additional pipes and valves to create a circulation of refrigerant between the compressor, outdoor heat exchanger, and auxiliary heat exchanger, using the heat discharged from the compressor to heat the outdoor heat exchanger. An active motor heating device involves installing an electric heating element on the compressor housing or suction line. Heating the compressor housing allows heat to be conducted to the compressor's interior, thereby heating the refrigerant flowing through the compressor and increasing its temperature before entering the outdoor heat exchanger, thus achieving defrosting. A PTC heater is a positive temperature coefficient ceramic heating element installed on the surface of the outdoor heat exchanger, which directly heats the heat exchanger fins when energized. These auxiliary heating mechanisms can be used individually or in combination depending on system requirements and cost considerations. For example, a hot gas bypass circuit and a PTC heater can be configured simultaneously in a large-capacity heat pump system to provide a more sufficient defrosting heat source. By setting up an auxiliary heating mechanism, the system does not need to switch the four-way valve during defrosting, and can maintain continuous operation in heating mode to avoid indoor temperature fluctuations.

[0052] In one specific embodiment of the present invention, a scroll compressor using R134a refrigerant is used as an example to describe the defrosting control process in detail. This compressor has a displacement of 34cc and a maximum speed of 8000RPM.

[0053] First, the operating parameters of the compressor are obtained. Under a certain operating condition, the ambient temperature is -5℃, and the compressor's discharge temperature is collected by a sensor. Exhaust pressure Inhalation pressure and rotational speed Among them, inhalation pressure The pressure is 0.1779 MPa, corresponding to the evaporation temperature. -13℃; exhaust pressure The value is 1.4915 MPa, corresponding to the saturated condensation temperature. The temperature is 55℃; the compressor speed is... It is 5000 RPM.

[0054] Input the operating condition parameters into the preset thermodynamic characteristic model of the compression mechanism, and calculate the polyvariance index. The control error is kept within 5%. This model was obtained by fitting performance test data, the specific performance test data are shown in Table 1-2 below, and its expression is: Substitute =5000 RPM =1.4915MPa =0.1779MPa, calculated as follows =1.16888.

[0055] To prevent liquid slugging in the compressor, the preset superheat threshold for the compression chamber suction is 5°C. During the refrigerant flow from the compressor suction port to the compression chamber inlet, a temperature rise occurs due to the absorption of heat from inside the compressor; this minimum safe temperature rise is pre-determined to be 10°C. This is based on the suction pressure. =0.1779MPa, the evaporation temperature was found through the refrigerant property relationship. =-13℃. Therefore, the inlet temperature of the compression chamber is the sum of the evaporation temperature and the superheat threshold of the compression chamber intake, i.e., -13℃ + 5℃ = -8℃. The compressor intake temperature is the inlet temperature of the compression chamber minus the temperature rise, i.e., -8℃ - 10℃ = -18℃.

[0056] Substitute the above parameters into the thermodynamic formula for the compression process to calculate the expected exhaust temperature. : = =346.9K-273.15=73.75℃.

[0057] Then, calculate the exhaust superheat warning threshold. : The system calculates the real-time exhaust superheat. .when Continuously below the first threshold (i.e., the first coefficient) When the product of the exhaust superheat warning threshold T1 before defrosting mode and the value shows a continuously decreasing trend, it is determined that the outdoor heat exchanger is frosted, and the auxiliary heating mechanism is controlled to start non-reverse cycle defrosting. In this embodiment, the first coefficient is selected based on the compressor's wet compression capability. If the temperature reaches 40%, then the first threshold is 0.4 × 18.75 = 7.5℃. When... When the temperature remains below 7.5°C and continues to drop, the hot gas bypass circuit or auxiliary heating mechanism such as the PTC heater will intervene to defrost.

[0058] During defrosting, the system maintains the control positions of the compressor, outdoor heat exchanger, indoor heat exchanger, and electronic expansion valve, providing defrosting heat only through the auxiliary heating mechanism. At this time, the compressor speed increases to 7000 RPM, and the suction pressure... When the pressure is raised to 0.5 MPa, the corresponding evaporation temperature is... Approximately 15.73℃, exhaust pressure Maintain 1.4915 MPa, saturated condensation temperature The temperature remains at 55℃. The variability index under defrost mode is re-acquired. : .

[0059] In defrost mode, the system controls the compressor suction port superheat to reach 20°C (this value is the control target under this operating condition, and can be calibrated according to the system's dynamic response characteristics). Therefore, the compressor suction port temperature... The expected exhaust temperature under defrosting mode was recalculated using the thermodynamic formulas of the compression process. :

[0060] .

[0061] The exhaust superheat warning threshold in defrost mode .

[0062] When the real-time exhaust superheat Rebound to the second threshold (i.e., the second coefficient) The exhaust superheat warning threshold recalculated in defrost mode When the product of the two factors (a, b, c) is greater than or equal to the product of the two factors (a, b, c) and continues for a second preset time while the rate of change is less than a preset rate of change threshold, defrosting is determined to be complete, and the auxiliary heating mechanism is controlled to stop and exit defrosting. In this embodiment, the second coefficient is calibrated based on the system's dynamic response characteristics. If the temperature reaches 20%, then the second threshold is 0.2 × 18.75 = 3.75℃. When... When the temperature remains above 3.75℃ and the rate of change is less than the preset rate of change threshold, the auxiliary heat source is deactivated, and all components are orderly returned to the air source heat pump mode setting value, and the system resumes efficient operation.

[0063] in, The process for determining the value is as follows: In defrost mode, the compressor speed is increased to 7000 RPM, and the suction pressure... When the pressure is raised to 0.5 MPa, the corresponding evaporation temperature is... The temperature was 15.73℃. At this point, the exhaust superheat warning threshold under defrosting mode was recalculated. =18.75℃. Compared to the normal mode, the calculated compressor suction port temperature has increased from -18℃ (equivalent suction superheat of -5℃) to 35.73℃ (corresponding to suction superheat of 20℃), the refrigerant flow rate has increased significantly, the compressor no longer has the risk of liquid slugging, and the safety margin is sufficient. Referring to the principle for determining the first coefficient α, that is, based on the thermodynamic calculation of the compressor's limit allowable minimum suction dryness, combined with the operating condition where the safety margin increases significantly after the compressor speed and suction pressure are increased, β=20% is obtained through system dynamic response test calibration. Value less than This ensures that the second threshold for exiting defrost is lower than the intervention threshold, so that when the compressor speed and suction pressure decrease, the real-time exhaust superheat can recover smoothly, avoiding system overshoot oscillation after exiting defrost.

[0064] As can be seen from the above embodiments, the present invention can dynamically calculate the exhaust superheat warning threshold based on real-time operating conditions, and form a hysteresis control range by combining the first coefficient and the second coefficient, so as to accurately control the timing of defrosting intervention and withdrawal, thereby maximizing the efficient operation time of heat pump mode while ensuring the safety of the compressor.

[0065] Tables 1 and 2 below show the performance test data of the R134a refrigerant scroll compressor under different operating conditions, i.e., the different speeds shown in the tables. Exhaust pressure Inhalation pressure The performance data below was fitted to obtain to The coefficient.

[0066] Table 1

[0067] To establish a thermodynamic characteristic model of the compression mechanism, performance tests were conducted on a scroll compressor using R134a refrigerant. In the tests, Table 1 shows the evaporation temperature maintained at -10℃, with different condensing temperatures (40℃, 50℃, 60℃) and different speeds (2000RPM to 8000RPM). Table 2 shows the evaporation temperature maintained at -15℃, with different condensing temperatures (40℃, 50℃, 60℃) and different speeds (3000RPM to 8000RPM). Parameters such as suction pressure, suction superheat, discharge pressure, discharge temperature, mass flow rate, power consumption, heating capacity, COP, volumetric efficiency, and isentropic efficiency were recorded. Some experimental data are shown in Tables 1-2. Based on the above experimental data, a nonlinear regression method was used to fit a functional relationship model between the polytropic index and the speed, discharge pressure, and suction pressure, i.e., the thermodynamic characteristic model of the compression mechanism. This model can be generalized to the following form: ; Where n is the polytropic exponent, N is the engine speed, Po is the exhaust pressure, Pi is the intake pressure, and K1 to K6 are coefficients obtained through nonlinear fitting of experimental data. and These represent the reference exhaust pressure and reference intake pressure corresponding to the test conditions, respectively.

[0068] Table 2

[0069] The fitting process is as follows: using the reference exhaust pressure and reference intake pressure The corresponding experimental data is used as the training set to determine the fitting parameters K1 to K4. Experimental data under other pressure conditions are used as the validation and test sets. The fitting parameters K5 and K6 are optimized using the validation set, and the calculation error of the model interpolation is verified using the test set. Because this fitting result is non-linear, its interpolation accuracy is higher than that of the piecewise linearization method. This fitting method only requires standard compressor unit performance test data provided by the compressor supplier, without the need for additional experimental data, and can achieve high-precision generalization fitting with existing small datasets. Through the above method, the absolute value of the relative error between the model calculation results and the experimental data is controlled within 5%.

[0070] This invention provides a control system for a heat pump system, including a parameter acquisition module, a polytropic index calculation module, a threshold determination module, and a defrost control module. The parameter acquisition module acquires the operating parameters of the compression mechanism, including exhaust temperature, exhaust pressure, intake pressure, and rotational speed. The polytropic index calculation module inputs the operating parameters into a preset thermodynamic characteristic model of the compression mechanism to calculate the polytropic index of the compression mechanism under the current operating conditions. This module internally stores a functional relationship model pre-fitted from performance test data. Upon receiving the rotational speed, exhaust pressure, and intake pressure from the parameter acquisition module, it substitutes these values ​​into the model to calculate the polytropic index under the current operating conditions. The threshold determination module, based on the intake pressure, exhaust pressure, polytropic index, and a preset intake superheat threshold for the compression chamber, calculates the expected exhaust temperature corresponding to meeting the intake superheat threshold through thermodynamic back-calculation. It also calculates the difference between the expected exhaust temperature and the saturated condensation temperature corresponding to the exhaust pressure, using this difference as the exhaust superheat warning threshold. This module integrates a refrigerant property data table or a property calculation function call interface. It can look up the corresponding saturation temperature, saturation enthalpy, and other property parameters based on pressure parameters, and perform reverse calculations and early warning threshold calculations according to thermodynamic formulas. The defrost control module is used to calculate the real-time exhaust superheat, which is the difference between the exhaust temperature and the saturated condensation temperature. When the real-time exhaust superheat drops below a first threshold, persists for a first preset time, and shows a continuous downward trend, it determines that the outdoor heat exchanger is frosted and controls the auxiliary heating mechanism to start non-reverse cycle defrosting of the outdoor heat exchanger. When the real-time exhaust superheat rises above a second threshold, persists for a second preset time, and the rate of change is less than a preset rate of change threshold, it determines that defrosting is complete and controls the auxiliary heating mechanism to stop to exit defrosting. The first threshold is the product of a first coefficient and the exhaust superheat warning threshold before defrosting mode, and the second threshold is the product of a second coefficient and the exhaust superheat warning threshold recalculated in defrosting mode, with the second coefficient being less than the first coefficient. This module internally includes a timer and a counter for determining duration; a trend analysis unit for judging the downward trend of real-time exhaust superheat; and a rate of change calculation unit for calculating the rate of change of exhaust superheat. The functions of these modules can be implemented through software programs or hardware circuits such as dedicated integrated circuits or digital signal processors; this implementation does not limit this approach. Through modular design, the various functions of the defrosting control method are separated, facilitating system integration and debugging, while simultaneously improving the reliability and maintainability of the control system.

[0071] The parameter acquisition module is communicatively connected to the exhaust temperature sensor, exhaust pressure sensor, intake pressure sensor, and speed sensor installed on the compression mechanism, for receiving exhaust temperature, exhaust pressure, intake pressure, and speed signals collected by each sensor in real time. The output of the parameter acquisition module is connected to the input of the polytropic index calculation module, for transmitting the acquired operating condition parameters to the polytropic index calculation module. The output of the polytropic index calculation module is connected to the input of the threshold determination module, for transmitting the calculated polytropic index to the threshold determination module. The input of the threshold determination module is also connected to the output of the parameter acquisition module, for receiving intake pressure and exhaust pressure signals. The output of the threshold determination module is connected to the input of the defrost control module, for transmitting the calculated exhaust superheat warning threshold, the exhaust superheat warning threshold recalculated in defrost mode, and the first and second coefficients to the defrost control module. The input of the defrost control module is also connected to the output of the parameter acquisition module, for receiving exhaust temperature and saturated condensation temperature to calculate real-time exhaust superheat. The output of the defrosting control module is connected to the control terminal of the auxiliary heating mechanism, and is used to send start and stop control commands to the auxiliary heating mechanism. The connection between the above modules can be a physical wiring connection or a data communication method based on a bus or network; this embodiment does not limit this.

[0072] This invention provides a heat pump system, including a compressor, an outdoor heat exchanger, an indoor heat exchanger, an auxiliary heating mechanism, and a controller. The exhaust port of the compressor is connected to the first port of a four-way valve, the intake port of the compressor is connected to the outlet of a gas-liquid separator, and the inlet of the gas-liquid separator is connected to the second port of the four-way valve. The third port of the four-way valve is connected to one end of the outdoor heat exchanger, and the fourth port of the four-way valve is connected to one end of the indoor heat exchanger. The other end of the outdoor heat exchanger is connected to one end of an electronic expansion valve, and the other end of the electronic expansion valve is connected to the other end of the indoor heat exchanger. The auxiliary heating mechanism is connected in parallel between the exhaust port of the compressor and the inlet of the outdoor heat exchanger, or is disposed on the surface of the outdoor heat exchanger. In heating mode, the four-way valve switches to a state where the first and fourth ports are connected, and the second and third ports are connected. The refrigerant flows sequentially through the compressor, the indoor heat exchanger (condensation and heat release), the electronic expansion valve, the outdoor heat exchanger (evaporation and heat absorption), and the gas-liquid separator, returning to the compressor to form a heating cycle. In non-reverse cycle defrosting mode, the four-way valve remains in the heating mode position, the auxiliary heating mechanism is activated to provide a defrosting heat source for the outdoor heat exchanger, the electronic expansion valve remains at its original opening, and the control positions of other components such as the compression mechanism, outdoor heat exchanger, and indoor heat exchanger remain unchanged.

[0073] The controller is connected to the compression mechanism, auxiliary heating mechanism, four-way valve, electronic expansion valve, and exhaust temperature sensor, exhaust pressure sensor, intake pressure sensor, and speed sensor installed on the compression mechanism. The exhaust temperature sensor is installed on the pipeline between the exhaust port of the compression mechanism and the four-way valve to collect exhaust temperature data in real time. The exhaust pressure sensor is installed on the pipeline between the exhaust port of the compression mechanism and the four-way valve to collect exhaust pressure data in real time. The intake pressure sensor is installed on the pipeline between the inlet of the gas-liquid separator and the four-way valve to collect intake pressure data in real time. The speed sensor is integrated inside the compression mechanism or installed in the compression mechanism housing to collect speed data in real time. The controller's input terminals are connected to each sensor, and its output terminals are connected to the control terminals of the auxiliary heating mechanism, the four-way valve, and the electronic expansion valve.

[0074] The controller includes a memory and a processor. The memory stores a computer program containing instruction code for functions such as parameter acquisition, polytropic index calculation, threshold determination, and defrost control. When the processor executes the computer program, it implements the steps of the defrost control method for the heat pump system as described above. Specifically, the processor collects operating condition parameters through sensors, calculates the polytropic index, obtains the expected exhaust temperature through thermodynamic back-calculation, calculates the exhaust superheat warning threshold, calculates the real-time exhaust superheat, and controls the auxiliary heating mechanism to start when the defrost intervention conditions are met, and controls the auxiliary heating mechanism to stop when the defrost exit conditions are met, thereby achieving precise defrost control. The above signal connection can be wired or wireless, and this embodiment does not limit this. Through the above system structure, the present invention embeds the defrost control method into the controller, enabling the heat pump system to have adaptive defrost capability, dynamically adjusting the defrost judgment benchmark according to real-time operating conditions, and maximizing the high-efficiency operation time of the heat pump mode while ensuring the safety of the compression mechanism.

[0075] Through the above method, the present invention can dynamically determine the exhaust superheat warning threshold based on the real-time operating conditions of the system, combine the real-time exhaust superheat change trend and stability judgment, and achieve precise control of the defrosting intervention and withdrawal timing through the hysteresis control range formed by the first coefficient and the second coefficient, thereby maximizing the extension of the high-efficiency operation time of the heat pump mode and improving the overall energy efficiency of the system while ensuring the safe operation of the compressor.

[0076] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A defrosting control method for a heat pump system, characterized in that, include: The operating parameters of the compression mechanism are obtained, including exhaust temperature, exhaust pressure, intake pressure and rotational speed. The operating condition parameters are input into a preset thermodynamic characteristic model of the compression mechanism to calculate the polyvariance index of the compression mechanism under the current operating condition. Based on the intake pressure, the exhaust pressure, the polytropic index, and the preset compression chamber intake superheat threshold, calculate the expected exhaust temperature corresponding to the condition that the compression chamber intake superheat threshold is met. Calculate the exhaust superheat warning threshold, wherein the exhaust superheat warning threshold is the difference between the expected exhaust temperature and the saturated condensation temperature corresponding to the exhaust pressure; Calculate the real-time exhaust superheat, where the real-time exhaust superheat is the difference between the exhaust temperature and the saturated condensation temperature; When the real-time exhaust superheat decreases to below the first threshold, continues for a first preset time, and shows a continuous downward trend, the auxiliary heating mechanism is activated to perform non-reverse cycle defrosting on the outdoor heat exchanger. When the real-time exhaust superheat rises to above the second threshold, lasts for a second preset time, and the rate of change is less than the preset rate of change threshold, the auxiliary heating mechanism is controlled to stop to exit defrosting. Wherein, the first threshold is the product of the first coefficient and the exhaust superheat warning threshold mentioned before the defrost mode is started, the second threshold is the product of the second coefficient and the exhaust superheat warning threshold recalculated under the defrost mode, and the second coefficient is less than the first coefficient.

2. The defrosting control method for a heat pump system according to claim 1, characterized in that, The thermodynamic characteristic model of the compression mechanism is a model obtained in advance by fitting the performance test data of the compression mechanism, which is used to describe the functional relationship between the polytropic index and the rotational speed, exhaust pressure, and intake pressure.

3. The defrosting control method according to claim 2, characterized in that, The functional relationship model is represented as follows: ， in, It is a variable index. For rotational speed, For exhaust pressure, Inhalation pressure, to These are the fitting coefficients. The exhaust pressure is the standard operating condition. This is the intake pressure under the reference operating conditions.

4. The defrosting control method for a heat pump system according to claim 1, characterized in that, The superheat threshold of the compression chamber is the minimum safe superheat value to prevent liquid slugging in the compression mechanism. At the same time, during normal heating operation, the actual superheat of the compression chamber inlet is higher than the superheat threshold of the compression chamber. When the heat exchange performance of the outdoor heat exchanger is reduced due to frost, and the actual superheat of the compression chamber inlet drops to the threshold, it indicates that the heat pump system has reached the critical state that requires defrosting.

5. The defrosting control method for a heat pump system according to claim 1, characterized in that, The calculation of the expected exhaust temperature corresponding to the compression chamber intake superheat threshold, obtained through thermodynamic back-calculation, includes: Based on the suction pressure, the corresponding evaporation temperature is obtained by querying the pre-stored refrigerant property data table or calling the refrigerant property calculation function; Calculate the inlet temperature of the compression chamber, which is the sum of the evaporation temperature and the superheat threshold of the compression chamber intake. Calculate the compressor intake temperature, which is the compressor inlet temperature minus a preset temperature rise from the compressor intake to the compressor chamber. Based on the compressor intake temperature, the exhaust pressure, the intake pressure, and the polytropic index, the expected exhaust temperature is calculated using the thermodynamic formula for the compression process: ， in, For the expected exhaust temperature, This refers to the compressor's suction port temperature. For exhaust pressure, Inhalation pressure, It is a highly variable index.

6. The defrosting control method for a heat pump system according to claim 1, characterized in that, The first coefficient is determined in the following way: The minimum allowable intake dryness of the compression mechanism is obtained, which is the minimum mass fraction of the gas phase in the wet vapor that the compressor is allowed to draw in. At the current suction pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the enthalpy value of the saturated liquid refrigerant and the enthalpy value of the saturated gaseous refrigerant corresponding to the suction pressure. Calculate the wet vapor enthalpy at the current inhalation pressure and the limiting minimum allowable inhalation dryness: ,in The saturated liquid enthalpy at the current intake pressure. The saturated gaseous enthalpy at the current inhalation pressure. This is the minimum permissible inspiratory dryness. Calculate the enthalpy difference: ; Under the current exhaust pressure, the superheated vapor enthalpy value corresponding to the exhaust superheat warning threshold is obtained by querying the pre-stored refrigerant property data table or calling the refrigerant property calculation function. ,in The temperature at the current exhaust pressure is enthalpy value at time The saturated condensation temperature. The exhaust superheat warning threshold; Calculate the target enthalpy: ; Under the current exhaust pressure, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to find the temperature Ta corresponding to the target enthalpy value Ha; Calculate the first coefficient: ,in This is the first coefficient.

7. The defrosting control method for a heat pump system according to claim 1, characterized in that, The second coefficient is determined as follows: In defrost mode, the current intake pressure, exhaust pressure, and polytropic index of the compression mechanism are obtained; Based on the suction pressure in defrost mode, query the pre-stored refrigerant property data table or call the refrigerant property calculation function to obtain the corresponding evaporation temperature; Calculate the sum of the current evaporation temperature and the superheat threshold of the compression chamber intake, and use it as the inlet temperature of the compression chamber in defrosting mode; The compressor intake temperature in defrost mode is calculated by subtracting the preset temperature rise from the compressor intake port to the compressor chamber from the compressor intake port temperature. Based on the compressor intake temperature, current discharge pressure, current intake pressure, and current polytropic index in defrost mode, the expected discharge temperature in defrost mode is calculated using the thermodynamic formulas for the compression process: ； in, This is the expected exhaust temperature in defrost mode. This refers to the compressor suction port temperature in defrost mode. This refers to the exhaust pressure in defrost mode. This refers to the suction pressure in defrost mode. The variable index under defrost mode; The difference between the expected exhaust temperature in defrost mode and the saturated condensation temperature corresponding to the current exhaust pressure is calculated and used as the exhaust superheat warning threshold in defrost mode. The second coefficient was calibrated through system dynamic response tests. During calibration, β is made smaller than the first coefficient. And select one that can make the exhaust superheat recover in real time during the defrosting process. The product of the exhaust superheat warning threshold in defrost mode and the value is greater than or equal to the threshold value without overshoot oscillation. value.

8. The defrosting control method for a heat pump system according to claim 1, characterized in that, The auxiliary heating mechanism includes at least one of the following: a hot gas bypass circuit, a triangular circulation circuit, a motor active heating device, and a PTC heater.

9. A control system for a heat pump system, characterized in that, include: The parameter acquisition module is used to acquire the operating condition parameters of the compression mechanism, including exhaust temperature, exhaust pressure, intake pressure and rotational speed. The polytropic index calculation module is used to input the operating condition parameters into a preset thermodynamic characteristic model of the compression mechanism and calculate the polytropic index of the compression mechanism under the current operating condition. The threshold determination module is used to calculate the expected exhaust temperature corresponding to satisfying the compression chamber intake superheat threshold based on the intake pressure, the exhaust pressure, the polytropic index and the preset compression chamber intake superheat threshold. The difference between the expected exhaust temperature and the saturated condensation temperature corresponding to the exhaust pressure is calculated and used as the exhaust superheat warning threshold. The defrosting control module is used to calculate the real-time exhaust superheat, which is the difference between the exhaust temperature and the saturated condensation temperature. And when the real-time exhaust superheat decreases below the first threshold, lasts for a first preset time and shows a continuous downward trend, the auxiliary heating mechanism is activated to perform non-reverse cycle defrosting on the outdoor heat exchanger. When the real-time exhaust superheat rises to above the second threshold, lasts for a second preset time, and the rate of change is less than the preset rate of change threshold, the auxiliary heating mechanism is controlled to stop to exit defrosting. Wherein, the first threshold is the product of a first coefficient and the exhaust superheat warning threshold calculated by the threshold determination module before the defrost mode is started, the second threshold is the product of a second coefficient and the exhaust superheat warning threshold recalculated by the threshold determination module in the defrost mode, and the second coefficient is less than the first coefficient.

10. A heat pump system, characterized in that, include: Compression mechanism, outdoor heat exchanger, indoor heat exchanger, auxiliary heating mechanism; as well as A controller, comprising a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the defrosting control method for a heat pump system as described in any one of claims 1 to 8.

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