Refrigeration method of fixed and variable frequency dual compressor

Abstract

The application relates to the technical field of refrigeration equipment, and particularly discloses a refrigeration method of a fixed-frequency and variable-frequency double-compressor, which comprises the following steps: switching between different control modes according to the operation parameters of a refrigerator, wherein the control modes comprise a quick-freezing mode, a temperature control mode and a state recognition mode; in the quick-freezing mode, the fixed-frequency compressor is turned off when the temperature in the refrigerator reaches a shutdown temperature, and the quick-freezing mode is returned to or the temperature control mode is switched to according to a fixed-frequency compressor starting signal; in the temperature control mode, the operating frequency of the variable-frequency compressor is adjusted by proportional integral control according to the temperature difference; and in the state recognition mode, the open-door state and the loading state are distinguished according to the open-door duration, and the quick-freezing mode or the temperature control mode is switched to according to the distinguishing result. The refrigeration method of the fixed-frequency and variable-frequency double-compressor solves the problem that the current refrigeration mode cannot reflect the complex refrigerator operation scene after loading and unloading through a single parameter, so that the refrigeration performance and energy consumption are difficult to balance.

Description

Technical Field

[0001] This invention relates to the field of refrigeration equipment technology, and more specifically, to a refrigeration method using a dual compressor with both fixed and variable frequency compressors. Background Technology

[0002] In commercial refrigerated display cases, the common refrigeration system design is either a fixed-frequency compressor combined with hot gas defrosting or a variable-frequency compressor combined with electric defrosting. However, these two systems have the following drawbacks: For the fixed-frequency compressor combined with hot gas defrosting, since the fixed-frequency compressor operates at a fixed speed, if a large-displacement fixed-frequency compressor is selected to meet high-load conditions, energy consumption and cost will be high. If a small-displacement fixed-frequency compressor is selected to save energy and cost, the refrigeration temperature will not meet the requirements. For the variable-frequency compressor combined with electric defrosting, if only a variable-frequency compressor is used, liquid will return to the pipes during defrosting, which can easily damage the variable-frequency compressor. Therefore, electric defrosting is used. Compared to hot gas defrosting, electric defrosting causes a larger temperature rise inside the cabinet during defrosting, which affects the quality of the goods inside the cabinet, and also has higher requirements in terms of electrical safety regulations.

[0003] Currently, a refrigeration method combining a fixed-frequency compressor and a variable-frequency compressor has emerged on the market, such as the Chinese invention patent "Refrigeration Control Method, Refrigeration Equipment and Computer-Readable Storage Medium" with application number 202410009344.2. This method uses refrigeration capacity as a parameter to coordinate the operation between the variable-frequency compressor and the fixed-frequency compressor. However, if the operation between the two compressors is coordinated solely by refrigeration capacity, it is difficult to reflect the complex operation scenario of the refrigerated display case after loading and unloading. As a result, the refrigeration method is difficult to adapt to the current operation of the refrigerated display case, making it difficult to achieve a balance between refrigeration performance and energy consumption. Summary of the Invention

[0004] In order to overcome the defects of the existing technology, the present invention provides a refrigeration method with a dual compressor of fixed and variable frequency, which aims to solve the problems in the above-mentioned existing technology.

[0005] The technical solution adopted by this invention to solve its technical problem is: a refrigeration method using a dual compressor with fixed and variable frequency drives, comprising:

[0006] Based on the operating parameters obtained from the freezer, the system switches between different control modes, including a quick-freezing mode where both the fixed-frequency compressor and the variable-frequency compressor run at full capacity, a temperature control mode where the fixed-frequency compressor is off and the variable-frequency compressor runs at variable frequency, and a status recognition mode.

[0007] The operating parameters include the temperature difference between the cabinet temperature and the set shutdown temperature, the door opening duration, and the fixed-frequency compressor start signal;

[0008] In the quick-freeze mode, when the temperature inside the cabinet reaches the set shutdown temperature, the fixed-frequency compressor is turned off, and then the system decides to return to the quick-freeze mode or switch to the temperature control mode based on the start signal of the fixed-frequency compressor.

[0009] In the temperature control mode, the operating frequency of the variable frequency compressor is adjusted according to the magnitude of the temperature difference using a proportional-integral control process.

[0010] In the state recognition mode, the door opening state and the loading state are distinguished according to the door opening duration, and the quick-freezing mode or the temperature control mode is switched according to the distinction result.

[0011] Preferably, it also includes: when a power-on signal is detected in the freezer, the quick-freezing mode is activated;

[0012] In the quick-freezing mode, the fixed-frequency compressor and the variable-frequency compressor are controlled to operate at full capacity; when the temperature inside the cabinet reaches the set shutdown temperature, the fixed-frequency compressor is turned off.

[0013] Within a preset first time window after the fixed-frequency compressor is turned off, if the fixed-frequency compressor receives the fixed-frequency compressor start signal, it returns to the quick-freeze mode; otherwise, it switches to the temperature control mode.

[0014] A fixed-frequency compressor start signal is generated when the preset temperature hysteresis value is less than the temperature difference between the cabinet temperature and the set shutdown temperature; otherwise, no fixed-frequency compressor start signal is generated.

[0015] Optionally, in the temperature control mode, the step of dynamically adjusting the operating frequency of the variable frequency compressor using a proportional-integral control process based on the magnitude of the temperature difference includes:

[0016] Obtain the temperature difference between the current cabinet temperature and the set shutdown temperature after the fixed-frequency compressor stops;

[0017] When the temperature difference is less than the first threshold, the variable frequency compressor is controlled to operate at a preset low frequency.

[0018] When the temperature difference is greater than or equal to the first threshold and less than the second threshold, the proportional and integral parameters of the proportional-integral control process are adjusted, and the operating frequency of the variable frequency compressor is adjusted using the adjusted proportional and integral parameters.

[0019] When the temperature difference is greater than the second threshold, the dynamic start-stop ratio protection logic is invoked based on the start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle to determine the adjustment method of the proportional and integral parameters. The operating frequency of the variable-frequency compressor is adjusted using the adjusted proportional and integral parameters. The start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle is the start-up time of the fixed-frequency compressor in the previous temperature control cycle divided by the time length of the previous temperature control cycle.

[0020] It is worth noting that the steps for invoking the dynamic start-stop ratio protection logic to determine the adjustment method of the proportional and integral parameters include:

[0021] Obtain the start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle;

[0022] If the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is less than or equal to the first preset ratio, the proportional parameter and integral parameter of the previous temperature control cycle will be used as the base values ​​of the proportional parameter and integral parameter to execute the small temperature difference refrigeration control mechanism.

[0023] If the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is greater than or equal to the first preset ratio, the proportional parameter and integral parameter of the previous temperature control cycle are used as the base values ​​of the proportional parameter and integral parameter to execute the large temperature difference refrigeration control mechanism.

[0024] Specifically, the small temperature difference refrigeration control mechanism includes: obtaining the basic values ​​of the proportional parameter and the basic values ​​of the integral parameter; multiplying the basic values ​​of the proportional parameter by a first small temperature difference coefficient to obtain the updated proportional parameter; multiplying the basic values ​​of the integral parameter by a second small temperature difference coefficient to obtain the updated integral parameter; and performing proportional-integral control of the operating frequency of the variable frequency compressor using the updated proportional parameter and the updated integral parameter.

[0025] Wherein, the first small temperature difference coefficient is greater than 1, and the second small temperature difference coefficient is greater than 0 and less than 1.

[0026] Optionally, the large temperature difference refrigeration control mechanism includes: obtaining the basic values ​​of the proportional parameter and the basic values ​​of the integral parameter; multiplying the basic values ​​of the proportional parameter by the first large temperature difference coefficient to obtain the updated proportional parameter; multiplying the basic values ​​of the integral parameter by the second large temperature difference coefficient to obtain the updated integral parameter; and performing proportional-integral control of the operating frequency of the variable frequency compressor using the updated proportional parameter and the updated integral parameter.

[0027] The first largest temperature difference coefficient is greater than 0 and less than 1, and the second largest temperature difference coefficient is greater than 1.

[0028] Preferably, in the large temperature difference refrigeration control mechanism, the current operating frequency of the variable frequency compressor output after proportional-integral control is obtained;

[0029] If the current operating frequency is in the optimal energy efficiency range, and the start-stop time ratio of the two most recent start-stop cycles of the fixed-frequency compressor is greater than or equal to the second preset ratio, then the current operating frequency is updated by adding a preset improvement coefficient to the current operating frequency, and then the variable-frequency compressor is operated according to the updated current operating frequency; otherwise, the variable-frequency compressor is maintained at the current operating frequency.

[0030] The start-stop time ratio of the two most recent start-stop cycles is the ratio of the previous start time length to the previous stop time length, and the ratio of the start time length before that to the stop time length before that.

[0031] It is worth noting that when a door open signal is generated, the door opening duration is obtained by statistically analyzing the duration of a single door open signal.

[0032] In the state recognition mode, when the distinction result is "door open", the mode is switched to temperature control mode; when the distinction result is "loading", the mode is switched to quick-freezing mode.

[0033] Preferably, in the state recognition mode, when the door opening duration is less than a preset time threshold, the distinction result of the door opening is the door opening state.

[0034] If the duration of the door opening is greater than or equal to a preset time threshold, the current door opening is determined as the initial loading state, and the distinction result of the current door opening is obtained through a secondary judgment mechanism.

[0035] Specifically, the secondary judgment mechanism includes: if a door opening signal is received within a preset second time window after the door closing signal is received, then the distinction result of the door opening at that time is the door opening state;

[0036] Otherwise, control the fixed-frequency compressor and the variable-frequency compressor to operate at full capacity, and shut down the fixed-frequency compressor when the temperature inside the cabinet reaches the set shutdown temperature;

[0037] Within a preset third time window after the fixed-frequency compressor is turned off, if the fixed-frequency compressor receives the start signal of the fixed-frequency compressor, the result of the door opening at that time is the loading state; otherwise, it is the door opening state.

[0038] The beneficial effects of this invention are as follows: The refrigeration method using dual fixed-frequency and variable-frequency compressors addresses the business problem of balancing operating efficiency and energy consumption in different usage scenarios for freezers. It integrates the logically related requirements of quick-freezing, temperature control, and status recognition, proposing a comprehensive control strategy. In quick-freezing mode, the start signal of the fixed-frequency compressor determines whether to maintain high-efficiency quick-freezing or switch to an energy-saving temperature control mode. In temperature control mode, the frequency of the variable-frequency compressor is dynamically adjusted using proportional-integral control based on the temperature difference inside the freezer, achieving precise temperature control and energy consumption optimization. In status recognition mode, the duration of door opening distinguishes between door opening and loading status, intelligently deciding whether to enter quick-freezing or temperature control mode to avoid unnecessary energy waste. This solution, through intelligent switching between multiple modes and dynamic parameter adjustment, significantly improves the operating efficiency and energy-saving effect of freezers in complex scenarios, achieving an ideal balance between refrigeration performance and energy consumption. Attached Figure Description

[0039] Figure 1 A flowchart of a refrigeration method using a dual compressor with fixed and variable frequency drives.

[0040] Figure 2 This is a flowchart of the state recognition mode. Detailed Implementation

[0041] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] Combination Figure 1 and Figure 2 The refrigeration method shown includes a dual compressor with fixed and variable frequency drives, comprising:

[0043] Based on the operating parameters obtained from the freezer, the system switches between different control modes, including a quick-freezing mode where both the fixed-frequency compressor and the variable-frequency compressor run at full capacity, a temperature control mode where the fixed-frequency compressor is off and the variable-frequency compressor runs at variable frequency, and a status recognition mode.

[0044] The operating parameters include the temperature difference between the cabinet temperature and the set shutdown temperature, the door opening duration, and the fixed-frequency compressor start signal;

[0045] In the quick-freeze mode, when the temperature inside the cabinet reaches the set shutdown temperature, the fixed-frequency compressor is turned off, and then the system decides to return to the quick-freeze mode or switch to the temperature control mode based on the start signal of the fixed-frequency compressor.

[0046] In the temperature control mode, the operating frequency of the variable frequency compressor is adjusted according to the magnitude of the temperature difference using a proportional-integral control process.

[0047] In the state recognition mode, the door opening state and the loading state are distinguished according to the door opening duration, and the quick-freezing mode or the temperature control mode is switched according to the distinction result.

[0048] The proposed dual-compressor refrigeration method, employing both fixed and variable frequency compressors, addresses the challenge of balancing operational efficiency and energy consumption in various usage scenarios for freezers. It integrates logically related requirements for quick-freezing, temperature control, and status recognition, proposing a comprehensive control strategy. In quick-freezing mode, the fixed-frequency compressor's start signal determines whether to maintain high-efficiency quick-freezing or switch to energy-saving temperature control mode. In temperature control mode, proportional-integral control dynamically adjusts the variable frequency compressor frequency based on the internal temperature difference, achieving precise temperature control and energy optimization. In status recognition mode, the duration of door opening distinguishes between door opening and loading status, intelligently determining whether to enter quick-freezing or temperature control mode to avoid unnecessary energy waste. This solution, through intelligent multi-mode switching and dynamic parameter adjustment, significantly improves the freezer's operational efficiency and energy-saving effect in complex scenarios, achieving an ideal balance between refrigeration performance and energy consumption.

[0049] It is worth noting that this also includes: running the quick-freeze mode when a power-on signal is detected in the freezer;

[0050] In the quick-freezing mode, the fixed-frequency compressor and the variable-frequency compressor are controlled to operate at full capacity; when the temperature inside the cabinet reaches the set shutdown temperature, the fixed-frequency compressor is turned off.

[0051] Within a preset first time window after the fixed-frequency compressor is turned off, if the fixed-frequency compressor receives the fixed-frequency compressor start signal, it returns to the quick-freeze mode; otherwise, it switches to the temperature control mode.

[0052] A fixed-frequency compressor start signal is generated when the preset temperature hysteresis value is less than the temperature difference between the cabinet temperature and the set shutdown temperature; otherwise, no fixed-frequency compressor start signal is generated.

[0053] In this embodiment, the freezer power-on signal is the freezer power-on signal. This signal is generated when the freezer is plugged in, causing it to enter quick-freeze mode. In quick-freeze mode, the fixed-frequency compressor and the variable-frequency compressor operate at full capacity, meaning the fixed-frequency compressor runs at its rated frequency and the variable-frequency compressor runs at its highest frequency, thus rapidly cooling the freezer. Specifically, the set stop temperature is set by a thermostat. Once the internal temperature reaches the set stop temperature, the thermostat stops the fixed-frequency compressor, leaving only the variable-frequency compressor running, thus saving energy. The preset first time window can be within 10 minutes. If the temperature has not reached the set temperature within 10 minutes, it indicates that the variable-frequency compressor's cooling capacity is insufficient, requiring the fixed-frequency compressor to start and assist in accelerating cooling. If the preset time is too long, it will affect temperature fluctuations inside the freezer; conversely, it cannot be set too short, as this will cause the fixed-frequency compressor to start frequently, affecting its lifespan. For example, after the fixed-frequency compressor is shut down due to the internal temperature reaching the set shutdown temperature, a timer will start. If the fixed-frequency compressor receives a start signal within 10 minutes, it indicates that the goods inside the freezer are not yet fully frozen and the internal temperature has risen. Therefore, the fixed-frequency compressor needs to be restarted, and the variable-frequency compressor will continue to operate at full capacity. Then, the internal temperature will continue to be monitored to see if it reaches the set shutdown temperature. Until the fixed-frequency compressor does not receive a start signal within 10 minutes, it indicates that the goods inside the freezer are fully frozen, and the temperature control mode will be entered. Specifically, during the process of determining whether a fixed-frequency compressor start signal is generated, the internal temperature is obtained through a temperature probe, and the temperature hysteresis value is preset by the temperature controller. The purpose is to control the shutdown point of the fixed-frequency compressor through the lowest temperature (set shutdown temperature) and the start point of the compressor through the highest temperature (set shutdown temperature + temperature hysteresis value). After the temperature controller obtains the temperature inside the cabinet, it subtracts the temperature it sets to stop and takes the absolute value to get the temperature difference. Then, it compares the temperature difference with the temperature hysteresis value to determine whether to generate a fixed-frequency compressor start signal.

[0054] Preferably, in the temperature control mode, the step of dynamically adjusting the operating frequency of the variable frequency compressor using a proportional-integral control process based on the magnitude of the temperature difference includes:

[0055] The temperature difference between the current temperature inside the freezer and the set shutdown temperature after the fixed-frequency compressor stops is obtained. When switching from quick-freezing mode to temperature control mode, the fixed-frequency compressor will stop, which will cause the temperature inside the freezer to rise slightly for a short time. Therefore, in temperature control mode, the operating frequency of the variable-frequency compressor will be adjusted to control the temperature inside the freezer.

[0056] When the temperature difference is less than the first threshold, the variable frequency compressor is controlled to operate at a preset low frequency. Specifically, the preset low frequency is a fixed value, which is set at the factory or manually set by the user. The low frequency of the variable frequency compressor is generally 1600 rpm. When the load temperature of the freezer is relatively stable, a large amount of cooling capacity is not needed to stabilize the temperature inside the freezer. The low frequency of the variable frequency compressor can be used to achieve the purpose of saving the most energy consumption.

[0057] When the temperature difference is greater than or equal to the first threshold and less than the second threshold, the proportional and integral parameters of the proportional-integral control process are adjusted, and the operating frequency of the variable frequency compressor is adjusted using the adjusted proportional and integral parameters to extend the response time of the variable frequency compressor and forcibly shut down the fixed frequency compressor.

[0058] When the temperature difference is greater than the second threshold, the dynamic start-stop ratio protection logic is invoked based on the start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle to determine the adjustment method of the proportional and integral parameters. The operating frequency of the variable-frequency compressor is adjusted using the adjusted proportional and integral parameters. The start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle is the start-up time of the fixed-frequency compressor in the previous temperature control cycle divided by the time length of the previous temperature control cycle.

[0059] For example, the first threshold could be 1°C, and the second threshold could be 3°C. Setting the first and second thresholds is primarily to determine the current temperature fluctuation range of the cabinet using these two data points. The design of 1°C or 3°C is determined based on current industry technology and relevant regulations and standards. When the temperature difference is less than 1°C, the temperature inside the cabinet is very close to the set shutdown temperature. This set shutdown temperature is based on the required freezing temperature of the goods inside the cabinet. Therefore, at this point, the temperature inside the cabinet is very close to the required freezing temperature of the goods, and the inverter compressor only needs to operate at a preset low frequency to achieve energy savings.

[0060] When the temperature difference is greater than or equal to 1℃ and less than 3℃, it indicates that there is some distance between the cabinet temperature and the set shutdown temperature. Therefore, it is necessary to adjust the proportional and integral parameters based on the initial proportional and integral parameters to perform proportional-integral control. In this embodiment, the formula for proportional-integral control is: Where u(t) is the operating frequency of the variable frequency compressor, Kp is the proportional parameter, which is the instantaneous correction of the current temperature difference ΔT. The larger the value of Kp, the faster the response of the variable frequency compressor and the shorter its frequency rise time. Ki is the integral coefficient, which is used to accumulate the temperature difference ΔT to eliminate steady-state error. The larger the value of Ki, the faster the steady-state error is eliminated and the shorter the response time of the variable frequency compressor. When the temperature difference is greater than or equal to 1℃ and less than 3℃, the initial proportional parameter is multiplied by the first initial adjustment parameter (such as 0.3 to 0.5) to reduce the value of the proportional parameter Kp, thereby reducing the sensitivity to small temperature differences and preventing high-frequency oscillations. The initial integral parameter is multiplied by the second initial adjustment parameter (such as 1.2 to 1.5) to increase the integral parameter Ki, strengthen the integral action to completely eliminate steady-state error, maintain temperature stability, and thus achieve stable temperature control, avoiding frequent start-stop or frequency conversion of the compressor. The initial proportional and integral parameters can be obtained using the critical proportional gain method: First, set the current integral parameter Ki0=0, retain only the proportional control, and gradually increase the proportional parameter Kp0 until the system exhibits continuous constant amplitude oscillation. Record the critical gain Ku0 and the oscillation period Pu at this point. Then, calculate the initial proportional parameter Kp_base=0.6×Ku and the initial integral parameter Ki_base=1.2×Ku / Pu.

[0061] Optionally, the steps for invoking the dynamic start-stop ratio protection logic to determine the adjustment method of the proportional and integral parameters include:

[0062] Obtain the start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle;

[0063] If the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is less than or equal to the first preset ratio, the proportional parameter and integral parameter of the previous temperature control cycle will be used as the base values ​​of the proportional parameter and integral parameter to execute the small temperature difference refrigeration control mechanism.

[0064] If the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is greater than or equal to the first preset ratio, the proportional parameter and integral parameter of the previous temperature control cycle are used as the base values ​​of the proportional parameter and integral parameter to execute the large temperature difference refrigeration control mechanism.

[0065] In this embodiment, the temperature control cycle is calculated from the moment the freezer door is opened until the next time it is opened. When the freezer is first powered on, an initial value, such as 50%, is assigned to the on / off ratio of the fixed-frequency compressor from the previous temperature control cycle. According to the operating characteristics of the fixed-frequency compressor, when the on / off ratio is less than 50%, the refrigeration system is relatively energy-efficient; when the on / off ratio is greater than 50%, it is more conducive to rapid cooling. Since 50% is the midpoint between 0 and 100%, this setting provides a suitable reference for subsequent adjustments. Simultaneously, the proportional and integral parameters from the previous temperature control cycle are also assigned as initial values ​​corresponding to the base values ​​of the proportional and integral parameters, specifically the initial proportional and initial integral parameters mentioned above. In this embodiment, the first preset ratio is preferably 50%. Based on the operating characteristics of the fixed-frequency compressor, when the on / off ratio is less than 50%, the refrigeration system is relatively energy-efficient; when the on / off ratio is greater than 50%, it is more conducive to rapid cooling; therefore, this value is set.

[0066] Preferably, the small temperature difference refrigeration control mechanism includes: obtaining the basic values ​​of the proportional parameter and the basic values ​​of the integral parameter; multiplying the basic values ​​of the proportional parameter by a first small temperature difference coefficient to obtain the updated proportional parameter; multiplying the basic values ​​of the integral parameter by a second small temperature difference coefficient to obtain the updated integral parameter; and performing proportional-integral control of the operating frequency of the variable frequency compressor using the updated proportional parameter and the updated integral parameter.

[0067] Wherein, the first small temperature difference coefficient is greater than 1, and the second small temperature difference coefficient is greater than 0 and less than 1.

[0068] Specifically, if the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is ≤50%, the current temperature control cycle enters small temperature difference refrigeration, and PI control is performed with reference to the proportional and integral parameters of the previous temperature control cycle to extend the response time of the variable-frequency compressor; wherein the value range of the first small temperature difference coefficient is 0.3 to 0.5 to reduce the sensitivity to small temperature differences and prevent high-frequency oscillation, and the value range of the second small temperature difference coefficient is 1.2 to 1.5 to strengthen the integral action to completely eliminate static difference and maintain temperature stability, thereby achieving stable temperature control and avoiding frequent start-stop or frequency conversion of the compressor.

[0069] It is worth noting that the large temperature difference refrigeration control mechanism includes: obtaining the basic values ​​of the proportional parameter and the basic values ​​of the integral parameter; multiplying the basic values ​​of the proportional parameter by the first large temperature difference coefficient to obtain the updated proportional parameter; multiplying the basic values ​​of the integral parameter by the second large temperature difference coefficient to obtain the updated integral parameter; and performing proportional-integral control of the operating frequency of the variable frequency compressor using the updated proportional parameter and the updated integral parameter.

[0070] The first largest temperature difference coefficient is greater than 0 and less than 1, and the second largest temperature difference coefficient is greater than 1.

[0071] If the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is ≥50%, the current temperature control cycle enters large temperature difference cooling. PI control is performed with reference to the proportional and integral parameters of the previous temperature control cycle to shorten the response time of the variable-frequency compressor. The first large temperature difference coefficient ranges from 1.5 to 2 to enhance instantaneous cooling output, and the second large temperature difference coefficient ranges from 0.3 to 0.5 to avoid excessive integral accumulation leading to subsequent overshoot. At the same time, integral limiting is activated to prevent integral saturation, thereby driving the variable-frequency compressor to quickly increase its frequency to a higher speed.

[0072] Optionally, in the large temperature difference refrigeration control mechanism, the current operating frequency of the variable frequency compressor output after proportional-integral control is obtained;

[0073] If the current operating frequency is in the optimal energy efficiency range, and the start-stop time ratio of the two most recent start-stop cycles of the fixed-frequency compressor is greater than or equal to the second preset ratio, then the current operating frequency is updated by adding a preset improvement coefficient to the current operating frequency, and then the variable-frequency compressor is operated according to the updated current operating frequency; otherwise, the variable-frequency compressor is maintained at the current operating frequency.

[0074] The start-stop time ratio of the two most recent start-stop cycles is the ratio of the previous start time length to the previous stop time length, and the ratio of the start time length before that to the stop time length before that.

[0075] In this embodiment, the optimal energy efficiency range is determined by pre-setting a COP limit value, where COP (Coefficient of Performance) is the energy efficiency index of a refrigeration system, defined as the ratio of cooling capacity to input power: COP = Cooling capacity ÷ Input power. The optimal energy efficiency range is defined as a continuous frequency range where the COP of the variable frequency compressor is greater than this COP limit value. The COP limit value is set between 1.63 and 1.72, where 1.63 is the COP limit value for the lowest speed, where power is lowest but cooling output is also low; 1.72 is the COP limit value for the optimal speed, where the power and cooling output of the variable frequency compressor are most balanced. The start-stop cycle is one cycle from the start of the fixed frequency compressor until the next start of the compressor. Therefore, the start-stop time ratio of the two most recent start-stop cycles means that, setting the current start-stop cycle as cycle N, the two most recent start-stop cycles are cycle N-1 and cycle N-2. The previous start time is the start time of the fixed-frequency compressor in cycle N-1, the previous stop time is the stop time of the fixed-frequency compressor in cycle N-1, the start time before that is the start time of the fixed-frequency compressor in cycle N-2, and the stop time before that is the stop time of the fixed-frequency compressor in cycle N-2. Within a single start-stop cycle, the sum of the start time and stop time of the fixed-frequency compressor is exactly the length of one start-stop cycle. When the freezer is first powered on, an initial value, such as 50%, is assigned to the start-stop time ratio of the two most recent start-stop cycles. According to the operating rules of fixed-frequency compressors, when the start-stop ratio is less than 50%, the refrigeration system is relatively energy-efficient; when the start-stop ratio is greater than 50%, it is more conducive to rapid cooling. Since 50% is the median of 0 to 100%, this setting provides a suitable reference for subsequent adjustments. For example, the second preset ratio could be 60%. As a stepped, progressive setting, the system's on / off ratio gradually increases but remains within a certain range, helping to maintain temperature stability without excessive energy consumption. The fixed-frequency compressor's operating rate should not exceed 60%, otherwise it will be detrimental to energy consumption.If the current operating frequency is within the optimal energy efficiency range, and the start-stop time ratio of the two most recent start-stop cycles of the fixed-frequency compressor is greater than or equal to 60%, then the current operating frequency is updated by adding a preset enhancement coefficient. This preset enhancement coefficient is obtained by querying a mapping table of enhancement coefficients and start-stop time ratios for the two most recent start-stop cycles of the fixed-frequency compressor. Each start-stop time interval in this mapping table corresponds to an enhancement coefficient. After updating the current operating frequency with this enhancement coefficient, the operating frequency of the variable-frequency compressor increases, increasing its cooling capacity and reducing the cooling capacity of the fixed-frequency compressor. This aims to lower the start-stop time ratio of the fixed-frequency compressor. Since the variable-frequency compressor is more energy-efficient than the fixed-frequency compressor, this ultimately saves energy. By incorporating the optimal energy efficiency range and the determination of the two most recent start-stop times of the fixed-frequency compressor, when the freezer is operating under conditions of large temperature differences, the temperature adjustment can be further tailored to the actual situation, avoiding the inaccurate temperature control problems caused by single-parameter control.

[0076] It is worth noting that when a door open signal is generated, the door opening duration is obtained by statistically analyzing the duration of a single door open signal. Specifically, a contact switch is installed on the freezer door. When the freezer door is opened, the contact switch pops up and the contacts close, forming a door open signal, thus starting the calculation of the door opening time. When the freezer door is closed, the contact switch is pressed down and the contacts open, forming a door close signal, thus ending the calculation of the door opening time. The duration from the start to the end of the calculation is the door opening duration.

[0077] In the state recognition mode, when the distinction result is "door open", the mode is switched to temperature control mode; when the distinction result is "loading", the mode is switched to quick-freezing mode.

[0078] In this embodiment, the open state refers to opening the freezer door to take out the goods from the freezer, while the loading state refers to opening the freezer door to put the goods into the freezer. The former will not cause large fluctuations in the temperature inside the freezer, while the latter will cause large fluctuations in the temperature inside the freezer.

[0079] Specifically, in the state recognition mode, when the door opening duration is less than a preset time threshold, the distinction result of the door opening at that time is the door opening state;

[0080] If the duration of the door opening is greater than or equal to a preset time threshold, the current door opening is determined as the initial loading state, and the distinction result of the current door opening is obtained through a secondary judgment mechanism.

[0081] For example, retrieving small items from a freezer typically takes no more than 3 minutes, so the preset time threshold can be set to 3 minutes. When the door is open for less than 3 minutes, the operation can be determined as retrieving small items from the freezer, and the result can be classified as an open state. When the door is open for 3 minutes or more, the operation may be retrieving large items from the freezer, placing items into the freezer, or retrieving multiple small items, thus requiring a secondary judgment mechanism for further determination.

[0082] Optionally, the secondary judgment mechanism includes: if a door open signal is received within a preset second time window after the door close signal is received, then the distinction result of the door opening at that time is the door open state;

[0083] Otherwise, control the fixed-frequency compressor and the variable-frequency compressor to operate at full capacity, and shut down the fixed-frequency compressor when the temperature inside the cabinet reaches the set shutdown temperature;

[0084] Within a preset third time window after the fixed-frequency compressor is turned off, if the fixed-frequency compressor receives the start signal of the fixed-frequency compressor, the result of the door opening at that time is the loading state; otherwise, it is the door opening state.

[0085] For example, a preset second time window can be set to 3 minutes, and a preset third time window can be set to 15 minutes. If a door open signal is received within 3 minutes after the door closes, it can be determined that multiple small items have been taken out, and the result is classified as an open state. Otherwise, it is considered that large items are being taken out of the cabinet, or that goods are being put into the freezer. Both of these operations require the cabinet door to be open for a long time, so some of the cooling capacity inside the cabinet will be lost. In this case, the fixed-frequency compressor and the variable-frequency compressor need to be controlled to operate at full capacity to make the temperature inside the cabinet reach the set shutdown temperature, and then the fixed-frequency compressor is turned off to achieve energy saving. After the fixed-frequency compressor is turned off, if the fixed-frequency compressor restarts within 15 minutes, it can be determined that goods are being put into the freezer, indicating that the newly added goods have not yet reached the rated cooling temperature, causing the temperature inside the cabinet to rise; otherwise, it is considered that large items are being taken out of the cabinet. In this state, because the removal of large items takes a long time, although some cooling capacity will be lost, the temperature inside the cabinet will not rise after the door is closed.

[0086] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A refrigeration method using a dual compressor with both fixed and variable frequency compressors, characterized in that, include: Based on the operating parameters obtained from the freezer, the system switches between different control modes, including a quick-freezing mode where both the fixed-frequency compressor and the variable-frequency compressor operate at full capacity, a temperature control mode where the fixed-frequency compressor is off and the variable-frequency compressor operates at variable frequency, and a status recognition mode. The operating parameters include the temperature difference between the cabinet temperature and the set shutdown temperature, the door opening duration, and the fixed-frequency compressor start signal; In the quick-freeze mode, when the temperature inside the cabinet reaches the set shutdown temperature, the fixed-frequency compressor is turned off, and then the system decides to return to the quick-freeze mode or switch to the temperature control mode based on the start signal of the fixed-frequency compressor. In the temperature control mode, the operating frequency of the variable frequency compressor is adjusted according to the magnitude of the temperature difference using a proportional-integral control process. In the state recognition mode, the door opening state and the loading state are distinguished according to the door opening duration, and the quick-freezing mode or the temperature control mode is switched according to the distinction result. When the power-on signal of the freezer is detected, the quick-freeze mode is activated; In the quick-freezing mode, the fixed-frequency compressor and the variable-frequency compressor are controlled to operate at full capacity. The fixed-frequency compressor is turned off when the temperature inside the cabinet reaches the set shutdown temperature. Within a preset first time window after the fixed-frequency compressor is turned off, if the fixed-frequency compressor receives the fixed-frequency compressor start signal, it returns to the quick-freeze mode; otherwise, it switches to the temperature control mode. A fixed-frequency compressor start signal is generated when the preset temperature hysteresis value is less than the temperature difference between the cabinet temperature and the set shutdown temperature; otherwise, no fixed-frequency compressor start signal is generated.

2. The refrigeration method of a dual compressor with fixed and variable frequency as described in claim 1, characterized in that: In the temperature control mode, the step of dynamically adjusting the operating frequency of the variable frequency compressor using a proportional-integral control process based on the magnitude of the temperature difference includes: Obtain the temperature difference between the current cabinet temperature and the set shutdown temperature after the fixed-frequency compressor stops; When the temperature difference is less than the first threshold, the variable frequency compressor is controlled to operate at a preset low frequency. When the temperature difference is greater than or equal to the first threshold and less than the second threshold, the proportional and integral parameters of the proportional-integral control process are adjusted, and the operating frequency of the variable frequency compressor is adjusted using the adjusted proportional and integral parameters. When the temperature difference is greater than the second threshold, the dynamic start-stop ratio protection logic is invoked based on the start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle to determine the adjustment method of the proportional and integral parameters. The operating frequency of the variable-frequency compressor is adjusted using the adjusted proportional and integral parameters. The start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle is the start-up time of the fixed-frequency compressor in the previous temperature control cycle divided by the time length of the previous temperature control cycle.

3. The refrigeration method of a dual compressor with fixed and variable frequency according to claim 2, characterized in that: The steps for invoking the dynamic start / stop ratio protection logic to determine the adjustment methods for proportional and integral parameters include: Obtain the start-stop ratio of the fixed-frequency compressor in the previous temperature control cycle; If the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is less than or equal to the first preset ratio, the proportional parameter and integral parameter of the previous temperature control cycle will be used as the base values ​​of the proportional parameter and integral parameter to execute the small temperature difference refrigeration control mechanism. If the on / off ratio of the fixed-frequency compressor in the previous temperature control cycle is greater than or equal to the first preset ratio, the proportional parameter and integral parameter of the previous temperature control cycle are used as the base values ​​of the proportional parameter and integral parameter to execute the large temperature difference refrigeration control mechanism.

4. The refrigeration method of a dual compressor with fixed and variable frequency as described in claim 3, characterized in that: The small temperature difference refrigeration control mechanism includes: obtaining the basic values ​​of proportional parameters and integral parameters; multiplying the basic values ​​of proportional parameters by a first small temperature difference coefficient to obtain updated proportional parameters; multiplying the basic values ​​of integral parameters by a second small temperature difference coefficient to obtain updated integral parameters; and performing proportional-integral control of the operating frequency of the variable frequency compressor using the updated proportional parameters and the updated integral parameters. Wherein, the first small temperature difference coefficient is greater than 1, and the second small temperature difference coefficient is greater than 0 and less than 1.

5. A refrigeration method using a dual-compressor system with both fixed and variable frequency compressors according to claim 3, characterized in that: The large temperature difference refrigeration control mechanism includes: obtaining the basic values ​​of proportional parameters and integral parameters; multiplying the basic values ​​of proportional parameters by the first large temperature difference coefficient to obtain the updated proportional parameters; multiplying the basic values ​​of integral parameters by the second large temperature difference coefficient to obtain the updated integral parameters; and performing proportional-integral control of the operating frequency of the variable frequency compressor using the updated proportional parameters and the updated integral parameters. Wherein, the first largest temperature difference coefficient is greater than 0 and less than 1, and the second largest temperature difference coefficient is greater than 1.

6. A refrigeration method using a dual compressor with fixed and variable frequency drives according to claim 5, characterized in that: In the large temperature difference refrigeration control mechanism, the current operating frequency of the variable frequency compressor output after proportional-integral control is obtained; If the current operating frequency is in the optimal energy efficiency range, and the start-stop time ratio of the two most recent start-stop cycles of the fixed-frequency compressor is greater than or equal to the second preset ratio, then the current operating frequency is updated by adding a preset improvement coefficient to the current operating frequency, and then the variable-frequency compressor is run according to the updated current operating frequency; otherwise, the variable-frequency compressor is maintained at the current operating frequency. The start-stop time ratio of the two most recent start-stop cycles is the ratio of the previous start time length to the previous stop time length, and the ratio of the start time length before that to the stop time length before that.

7. The refrigeration method of a dual compressor with fixed and variable frequency according to claim 1, characterized in that: When a door open signal is generated, the door opening duration is obtained by counting the duration of a single door open signal. In the state recognition mode, when the distinction result is "door open", the mode is switched to temperature control mode; when the distinction result is "loading", the mode is switched to quick-freezing mode.

8. The refrigeration method of a dual compressor with fixed and variable frequency according to claim 1, characterized in that: In the state recognition mode, when the duration of the door opening is less than a preset time threshold, the distinction result of the door opening at that time is the door opening state. If the duration of the door opening is greater than or equal to a preset time threshold, the current door opening is determined as the initial loading state, and the distinction result of the current door opening is obtained through a secondary judgment mechanism.

9. A refrigeration method using a dual-compressor system with fixed and variable frequency compressors according to claim 8, characterized in that: The secondary judgment mechanism includes: if a door opening signal is received within a preset second time window after the door closing signal is received, then the distinction result of the door opening at that time is the door opening state; Otherwise, control the fixed-frequency compressor and the variable-frequency compressor to operate at full capacity, and shut down the fixed-frequency compressor when the temperature inside the cabinet reaches the set shutdown temperature; Within a preset third time window after the fixed-frequency compressor is turned off, if the fixed-frequency compressor receives the start signal of the fixed-frequency compressor, the result of the door opening at that time is the loading state; otherwise, it is the door opening state.

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