A multi-mode cooperative control method of a condensing unit

Abstract

The application discloses a kind of multi-mode collaborative control methods of condensing unit, it is related to refrigeration system control technical field, to solve the problems of condensing unit control method in prior art in oil return reliability, dirty block identification accuracy, low temperature start success rate and fan control refinement, its technical points are: S1: system configuration: by the compressor module of parallel connection of variable frequency compressor and fixed frequency compressor, and by the condenser module of first heat exchange zone and second heat exchange zone divided by solenoid valve;S2: oil return safety judgment and capacity matching control: the average flow rate of refrigerant in condenser is calculated, when the average flow rate is lower than the preset oil return critical flow rate, through oil return safety judgment, multi-parameter dirty block identification, stage low temperature start, fan main standby rotation and soft start, intelligent mode switching and parameter self-optimization, comprehensively improve the oil return reliability of condensing unit, dirty block identification accuracy, low temperature start success rate and fan control refinement level.

Description

Technical Field

[0001] This invention relates to the field of refrigeration system control technology, specifically a multi-mode coordinated control method for condensing units. Background Technology

[0002] Condensing chillers are the core equipment of refrigeration systems, consisting of components such as compressors, condensers, condenser fans, and throttling devices. Their control strategies directly affect the system's operational reliability, energy efficiency, and maintenance costs. However, existing control methods for condensing chillers have the following problems: First, there are problems with compressor oil return under partial load conditions. During nighttime or low-load periods, the variable frequency compressor of the condensing unit usually operates at a lower frequency, and the refrigerant flow rate in the condenser pipeline decreases accordingly. When the flow rate is lower than a certain value, the lubricating oil dissolved in the refrigerant cannot be effectively carried back to the compressor and gradually deposits at the bottom of the condenser pipeline or at the bottom of the manifold. After long-term operation, the lubricating oil in the compressor will decrease, the oil level will drop, resulting in insufficient lubrication of moving parts. In severe cases, it will cause compressor wear, seizure, or even damage. Existing technology usually uses the method of periodically increasing the compressor frequency to return oil, but this method lacks accurate judgment of the oil return risk. The timing and duration of frequency increase are difficult to control precisely, which can easily lead to poor oil return effect and unnecessary increase in energy consumption. Second, the condenser is not accurate in identifying dirt blockage. When the condenser operates outdoors for a long time, dust, catkins, oil and other debris can easily adhere to the fins, leading to a decrease in heat exchange efficiency, an increase in condensing pressure and an increase in compressor power consumption. Current technology usually relies on the increase in condensing pressure to judge dirt blockage, but the increase in condensing pressure may also be caused by the increase in ambient temperature, excessive refrigerant charge, condenser fan failure and other reasons. Judging by a single parameter is very easy to produce misjudgment, leading to unnecessary cleaning and shutdown. Third, starting difficulties in low-temperature environments; in winter low-temperature environments, when starting a condensing unit, the refrigerant may migrate to the condenser and condense into liquid during shutdown. During startup, a large amount of liquid refrigerant enters the compressor, causing liquid slugging damage; in addition, the viscosity of lubricating oil increases and its fluidity decreases at low temperatures, making it difficult to establish sufficient oil pressure in the initial stage of startup; although the crankcase heater can preheat, the heating time is difficult to control precisely. Too short a time will cause starting difficulties, while too long a time will result in energy waste. Existing technology lacks a systematic low-temperature startup control scheme, resulting in a low startup success rate; Fourth, multiple condensing fans operate for different periods and have different lifespans. Large condensing units are usually equipped with multiple condensing fans. The existing control method is mostly staged start-stop, that is, the fans are turned on or off in stages according to the condensing pressure. This control method has two problems: First, the instantaneous current surge when the fans are turned on and off is large, which is detrimental to the power grid and the lifespan of the equipment; Second, the operating time of each fan is uneven, with some fans running for a long time and some fans being idle for a long time, causing the fans put into operation earlier to age prematurely and increasing maintenance costs. Summary of the Invention

[0003] The purpose of this invention is to provide a multi-mode collaborative control method for condensing units, so as to solve the problems of the condensing unit control methods proposed in the background art in terms of oil return reliability, dirt blockage identification accuracy, low temperature start-up success rate, and fan control refinement.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a multi-mode coordinated control method for condensing units, comprising the following steps: S1: System configuration: a compressor module consisting of a variable frequency compressor and a fixed frequency compressor connected in parallel, and a condenser module divided into a first heat exchange zone and a second heat exchange zone by solenoid valves; S2: Oil return safety judgment and capacity matching control: Calculate the average flow rate of refrigerant in the condenser. When the average flow rate is lower than the preset critical oil return flow rate, the effective heat exchange area of ​​the condenser is reduced by closing the solenoid valve of the second heat exchange zone, or the refrigerant flow rate is increased to above the critical oil return flow rate by increasing the compressor operating frequency. S3: Condenser blockage judgment: Calculate the difference between condensing pressure and saturated condensing pressure, the static pressure difference between the air inlet and outlet sides of the condenser, and the deviation between the measured value and the theoretical calculated value of the condenser outlet temperature. When any two of these parameters exceed the preset threshold, the condenser is judged to be blocked. S4: Low Temperature Start-up Control: When the ambient temperature is lower than the preset start-up temperature threshold, the preheating preparation stage, the low pressure difference establishment stage, and the load loading stage are executed sequentially. The preheating preparation stage, the low pressure difference establishment stage, and the load loading stage are executed sequentially. This includes preheating the lubricating oil to reduce oil viscosity, quickly establishing the pressure difference through the limited area operation of a single fixed-frequency compressor to promote oil circulation, gradually putting the variable-frequency compressor and the second heat exchange zone into operation, and monitoring the exhaust superheat to prevent liquid slugging. S5: Fan control steps, adopting a main and backup rotation mechanism for multiple condensing fans, and using frequency conversion soft start for fan start and stop; S6: Operating mode switching: Automatically switches the operating mode according to the ambient temperature and system load rate. The operating modes include dual-machine high-efficiency mode, single-machine energy-saving mode, oil return enhancement mode and low temperature start-up mode. In S2, when the risk of oil return is triggered, the system switches to the enhanced oil return mode. In S3, the result of the dirt blockage determination is used to trigger the self-cleaning operation. In S4, after the low temperature start-up is successful, the critical flow rate of oil return in S2 is recalibrated. In S5, the fan operating status serves as the basic input for the parameter calculation in S3. In S6, a comprehensive decision is made based on the output results from S2 to S5.

[0005] In a preferred embodiment, the present invention can be further configured as follows: In step S2, the determination of the critical oil return velocity includes, during the unit commissioning phase, gradually reducing the compressor operating frequency while observing the oil level changes in the compressor sight glass. When the oil level drops to the minimum allowable oil level, the refrigerant flow rate under the current operating condition is recorded as the critical oil return velocity. When reducing the effective heat exchange area of ​​the condenser, after closing the solenoid valve of the second heat exchange zone, the effective heat exchange area of ​​the condenser is reduced to a specified proportion of the initial area. This specified proportion is dynamically calculated based on the ratio of the current refrigerant flow rate to the critical oil return velocity. The method for increasing the compressor operating frequency includes: when the cooling demand allows, increasing the compressor frequency to above the safe oil return frequency; when the cooling demand does not allow, activating the intermittent oil return mode, periodically increasing the compressor frequency to the rated frequency and continuing for a preset oil return time.

[0006] In a preferred embodiment, the present invention can be further configured as follows: In step S3, when determining that the condenser is clogged, the compressor operating frequency in step S2 is also included as a fourth parameter in the determination. When the compressor operating frequency is lower than the oil return safety frequency, the clog determination threshold is lowered. After determining that the condenser is clogged, it is classified into mild clog and severe clog according to the degree of clog. When it is determined to be severe clog, the shutdown cleaning process is triggered to perform a reverse pulse purging self-cleaning operation. The start timing of the self-cleaning operation is linked with the operation mode switching in step S6: when the unit is in the dual-unit high-efficiency mode, the self-cleaning is delayed; when the unit is in the single-unit energy-saving mode, the self-cleaning is performed immediately.

[0007] In a preferred embodiment, the present invention can be further configured as follows: In S4, the preheating preparation stage includes turning on the compressor crankcase heater, turning off the condenser fan and the solenoid valve of the second heat exchange zone, and simultaneously monitoring the compressor casing temperature until the safe start-up temperature is reached. The low pressure difference establishment stage includes starting the fixed-frequency compressor to run at the lowest frequency, allowing the refrigerant to flow only through the first heat exchange zone, and monitoring the pressure difference between the condensing pressure and the evaporating pressure until it reaches the minimum pressure difference required for lubricating oil circulation before entering the next stage. The load loading stage includes starting the variable-frequency compressor, adjusting the frequency according to the cooling demand, gradually opening the solenoid valve of the second heat exchange zone to increase the effective heat exchange area of ​​the condenser, and continuously monitoring the compressor exhaust superheat during this period. When the superheat is lower than the safe threshold, the load increase is suspended.

[0008] In a preferred embodiment, the present invention can be further configured as follows: In S4, during the low pressure differential establishment stage, if the pressure differential still does not reach the minimum pressure differential required for lubricating oil circulation after the fixed-frequency compressor has been running for a preset time, a fault diagnosis is triggered, and it is determined that there is a refrigerant leak or the compressor exhaust valve plate is damaged. This fault diagnosis result serves as a prohibition condition for mode switching in S6, prohibiting switching to the dual-machine high-efficiency mode until the fault is eliminated.

[0009] In a preferred embodiment, the present invention can be further configured as follows: In S5, when the fan starts and stops using the variable frequency soft start method, the newly added fan uses a specified proportion of the rated speed as the initial speed, and gradually increases to the target speed with a specified speed change rate. The specified proportion and speed change rate are dynamically adjusted according to the degree of dirt and blockage in S3. When the degree of dirt and blockage is high, the initial speed proportion is reduced, and the fan adopts a gradual speed reduction method when reducing speed.

[0010] In a preferred embodiment, the present invention can be further configured as follows: in S6, the dual-machine high-efficiency mode is activated when the ambient temperature is higher than the set value and the system load rate is higher than the load rate increase switching threshold; the single-machine energy-saving mode is activated when the system load rate is lower than the load rate decrease switching threshold; the oil return enhancement mode is activated when the single-machine energy-saving mode has been running for more than a preset time or when it is determined in S2 that there is a risk of oil return; and the low-temperature start-up mode is activated when the ambient temperature is lower than the preset start-up temperature threshold.

[0011] In a preferred embodiment, the present invention can be further configured as follows: the switching between the dual-machine high-efficiency mode and the single-machine energy-saving mode adopts hysteresis comparison logic: the switching threshold for load rate increase is higher than the switching threshold for load rate decrease, and a switching dead zone is formed between the two thresholds. The range of the switching dead zone is dynamically adjusted according to the degree of dirt and blockage in S3. When the degree of dirt and blockage is high, the range of the switching dead zone is expanded.

[0012] In a preferred embodiment, the present invention can be further configured as follows: S7: Parameter self-optimization: Based on long-term operating data from S1 to S6, the preset parameters are optimized using mean-range control chart, exponential weighted moving average method, and multiple regression analysis. The optimized parameters include return oil critical flow rate, dirt blockage judgment threshold, low temperature start-up preheating time, fan rotation cycle, load rate increase switching threshold, and load rate decrease switching threshold. The parameter self-optimization is based on the duration ratio of the operating mode in S6 and the return oil risk trigger frequency in S2 as the optimization objective function, wherein the objective is set as: high proportion of high efficiency mode, reasonable proportion of energy-saving mode, low proportion of return oil mode, and low return oil risk trigger frequency.

[0013] In a preferred embodiment, the present invention can be further configured as follows: in S7, when the frequency of triggering the return oil risk is higher than the preset frequency threshold, the set value of the return oil critical flow rate is increased first; when the duration of the dual-machine high-efficiency mode is lower than the preset percentage threshold, the load rate increase switching threshold is reduced first.

[0014] Compared with the prior art, the beneficial effects of the present invention are: This invention, through S2's oil return safety judgment and capacity matching control, can calculate the average flow rate of refrigerant in the condenser in real time and accurately compare it with the preset critical oil return flow rate. When an oil return risk is detected, the system can intelligently choose to close the solenoid valve of the second heat exchange zone to reduce the effective heat exchange area of ​​the condenser, or flexibly increase the compressor operating frequency according to the cooling demand, including continuous frequency increase or intermittent oil return mode, thereby accurately controlling the refrigerant flow rate to rise to a safe level. This changes the traditional open-loop control method of timed forced oil return, realizes on-demand, precise, and low-energy oil return management, and completely solves the problems of lubricating oil deposition, compressor wear, and even damage under low load conditions, improving the operating reliability of the compressor and the service life of the whole machine.

[0015] This invention utilizes a multi-parameter fusion logic for determining clogging in S3, simultaneously calculating the difference between condensing pressure and saturated condensing pressure, the static pressure difference between the condenser's inlet and outlet sides, and the deviation between the measured and theoretically calculated condenser outlet temperature. It also incorporates the compressor's operating frequency as an auxiliary parameter. Clogging is only determined when any two parameters exceed preset thresholds. This multi-dimensional comprehensive judgment method effectively eliminates interference factors such as changes in ambient temperature, abnormal refrigerant charge, and condenser fan malfunctions, improving the accuracy of clogging identification. Furthermore, the system can differentiate between mild and severe clogging based on its severity and intelligently determine the timing of self-cleaning based on the current operating mode, avoiding unnecessary shutdowns or delayed cleaning and ensuring the condenser's heat exchange efficiency.

[0016] This invention systematically solves the problems caused by low-temperature startup through low-temperature startup control in the S4 preheating preparation stage, low pressure differential establishment stage, and load loading stage. In the preheating preparation stage, the crankcase heater raises the temperature of the lubricating oil and reduces its viscosity. In the low pressure differential establishment stage, the fixed-frequency compressor is started first and the refrigerant flow is restricted through the first heat exchange zone to quickly establish the minimum pressure differential required for lubricating oil circulation and ensure smooth oil passage. In the load loading stage, the variable-frequency compressor and the second heat exchange zone are gradually put into operation. At the same time, the exhaust superheat is continuously monitored to prevent liquid slugging. Through the phased and sequential control logic, the risk of liquid slugging and poor lubrication during low-temperature startup is solved, improving the startup success rate. It also has a built-in fault diagnosis mechanism that can accurately determine faults such as refrigerant leakage or exhaust valve plate damage when pressure building fails, and prohibit switching to dual-machine high-efficiency mode, enhancing the system's safety protection capabilities.

[0017] This invention achieves precise control of multiple condenser fans through the S5 primary / standby rotation mechanism and variable frequency soft start method. The primary / standby rotation mechanism records the cumulative running time of each fan and rotates its role periodically to ensure that the running time of all fans tends to be balanced, avoiding premature aging of some fans due to long-term operation and extending the overall service life of the fan group. The variable frequency soft start method allows new fans to start at a lower initial speed and gradually increase to the target speed according to the specified speed change rate. At the same time, it dynamically adjusts the initial speed ratio and change rate according to the degree of dirt and blockage, reducing the current impact on the power grid and fan motor at the moment of start-up and shutdown, protecting electrical equipment and condenser fins, and reducing maintenance costs.

[0018] This invention achieves optimal operating strategy under all operating conditions by automatically switching between dual-machine high-efficiency mode, single-machine energy-saving mode, oil return enhancement mode, and low-temperature start-up mode based on ambient temperature and system load rate through the operation mode switching in S6. The dual-machine high-efficiency mode and single-machine energy-saving mode adopt hysteresis comparison logic. By setting the switching threshold for load rate increase to be higher than the switching threshold for load rate decrease to form a switching dead zone, the frequent mode oscillation caused by small load fluctuations is effectively avoided. The range of the switching dead zone can also be dynamically adjusted according to the degree of dirt blockage in S3. When the degree of dirt blockage is high, the dead zone range is expanded to prevent false mode switching due to falsely high load rate caused by heat exchange efficiency decline. Through intelligent mode switching and comprehensive decision-making based on the output results of S2 to S5, a highly coordinated control system is formed.

[0019] This invention utilizes the parameter self-optimization step in S7 to continuously optimize various preset parameters based on long-term operating data using statistical analysis methods. These parameters include the critical return oil flow rate, the fouling judgment threshold, the low-temperature start-up preheating time, the fan rotation cycle, and the load rate switching threshold. The optimization process uses the duration percentage of the operating mode and the frequency of return oil risk triggering as objective functions. When the return oil risk frequency is too high, the critical return oil flow rate is increased first. When the proportion of dual-machine high-efficiency mode is too low, the load rate increase switching threshold is decreased first. Through a closed-loop learning mechanism, the system possesses self-learning and adaptive capabilities, enabling it to dynamically adjust the control boundaries according to the actual operating environment, equipment aging, and usage habits, always maintaining the unit in an optimal operating state, thus achieving intelligent control. Attached Figure Description

[0020] Figure 1 This is an overall flowchart of a multi-mode coordinated control method for a condensing unit according to the present invention; Figure 2 This is a flowchart of the return oil safety judgment and capacity matching control of the present invention; Figure 3 This is a logic block diagram for determining condenser blockage in this invention. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0022] In the description of this application, it should be noted that the terms "upper," "lower," "inner," "outer," "top / bottom," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installed," "equipped with," "sleeved / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] See Figure 1 The present invention provides an embodiment of a multi-mode coordinated control method for a condensing unit, comprising the following steps: S1: System Configuration. First, configure the system hardware, constructing a compressor module consisting of a variable-frequency compressor and a fixed-frequency compressor connected in parallel, and a condenser module divided into a first heat exchange zone and a second heat exchange zone by solenoid valves. The first and second heat exchange zones are connected in parallel. The variable-frequency compressor is responsible for continuous and efficient capacity adjustment according to load changes, while the fixed-frequency compressor is used to provide the base load in high-efficiency mode or to quickly establish a pressure differential during low-temperature startup. The parallel connection of the two can achieve a capacity adjustment range of 10% to 100% and improve overall part-load performance by more than 15%. The condenser's zoned design involves installing solenoid valves in the condenser piping to divide the originally complete heat exchange area into two independent zones. The system comprises two heat exchange zones, with the first zone serving as the basic heat exchange zone, accounting for 50% of the total heat exchange area. The second zone serves as an auxiliary heat exchange zone that can be switched on and off. By controlling the on / off state of the solenoid valve, the area of ​​the condenser participating in the heat exchange can be flexibly changed, thereby adjusting the refrigerant flow resistance and heat exchange capacity. Its working logic is as follows: the refrigerant flow rate is inversely proportional to the flow cross-sectional area; reducing the area can increase the flow rate while keeping the flow rate constant. At the same time, the heat exchange area is inversely proportional to the condensing pressure; reducing the area can increase the condensing pressure, thereby increasing the compressor power consumption and exhaust temperature, providing additional thermal power for oil return. This provides a flexible, efficient, and finely adjustable physical platform for the entire multi-mode collaborative control method, which is the foundation for realizing all subsequent advanced control logic.

[0025] See Figure 2 S2: Oil return safety judgment and capacity matching control. The system calculates the average flow rate of refrigerant in the condenser in real time. The formula for calculating the flow rate is: v=Qv / A, where Qv is the actual discharge volume flow rate of the compressor and A is the current effective heat exchange cross-sectional area of ​​the condenser. When the average flow rate is detected to be lower than a preset "critical oil return flow rate", it is determined that there is a risk of oil return. The method for determining the critical flow rate is: during the unit commissioning stage, gradually reduce the compressor operating frequency and observe the oil level change in the compressor through the oil sight glass. When the oil level drops to 1 / 3 of the sight glass height, the refrigerant flow rate under the current operating condition is recorded as the critical return flow rate under that condition. The critical flow rates under different ambient temperatures and condensing pressures will form a two-dimensional table, which is stored in the controller. After determining that there is a risk of oil return, the control strategy will be activated. The preferred solution is to close the second heat exchange zone by solenoid valve to reduce the effective heat exchange area of ​​the condenser. The physical principle is: when the refrigerant mass flow rate is constant, reducing the flow cross-sectional area will significantly increase the flow rate. According to the mass flow rate conservation in the continuity equation of fluid mechanics: when the refrigerant mass flow rate is constant and the density is approximately constant, the flow rate × flow cross-sectional area = constant. Therefore, when the cross-sectional area is reduced, the flow rate will inevitably increase, thereby enhancing the ability to carry lubricating oil back to the compressor. The effective heat exchange area of ​​the condenser is reduced to a specified proportion of the initial area. This proportion is dynamically calculated based on the ratio of "current refrigerant flow rate Vcurrent / critical return flow rate Vritical". For example, if Vcurrent = 0.8Vcritical, the target area proportion can be set to 0.8 to increase the flow rate above the critical value. The secondary option is to increase the compressor's operating frequency to improve the flow rate by increasing the refrigerant circulation volume. This can be achieved through two strategies: First, when the current evaporation temperature is not below the set lower limit and there is still a margin in the cooling load, the compressor frequency is increased to the pre-calibrated safe oil return frequency, i.e., 65% of the rated frequency, to continuously increase the flow rate. Second, when the storage temperature is close to the set point and increasing the frequency would lead to overcooling, an intermittent oil return mode is activated. This involves forcibly increasing the compressor frequency to the rated frequency every 30 minutes for a 2-minute oil return period. This brief period of high flow rate carries the deposited lubricating oil back to the compressor. The high pressure differential and high flow rate generated by the compressor's high-frequency operation create a "scouring airflow" that strips the oil film remaining at the bottom of the condenser and carries it back to the crankcase. Through precise flow rate judgment and intelligent capacity matching, on-demand oil return is achieved, reducing oil return-related energy consumption by 40% and improving the compressor's operational reliability and energy efficiency.

[0026] See Figure 3 S3: Condenser blockage detection. A multi-parameter fusion logic is used to accurately identify condenser blockage. The system calculates three key parameters in parallel: The difference between the condensing pressure Pc and the theoretical saturated condensing pressure Pc_sat under the current operating conditions is ΔPc=Pc−Pc_sat. An increase in this difference indicates that the actual heat exchange efficiency is lower than the theoretical value, which is caused by dirt blockage or fan failure. The static pressure difference between the air inlet and outlet sides of the condenser is ΔPstatic=Pin−Pout. An increase in this difference indicates that the airflow channel is blocked by dirt and debris, and the airflow resistance increases. The deviation ΔT = Tout_meas - Tout_calc between the measured value of the condenser outlet air temperature and the theoretical value Tout_calc calculated based on the current heat transfer model indicates a decrease in the air-side heat transfer coefficient, which also points to dirt blockage. When any two of the above three parameters exceed their respective preset thresholds, the system determines that the condenser is clogged. Each threshold is set at the factory based on cleanliness conditions; for example, the ΔPc threshold is 2 bar, the ΔPstatic threshold is 15 Pa, and the ΔT threshold is 5°C. To further improve the accuracy of the judgment, the compressor operating frequency fcomp in S2 is also included as a fourth parameter for auxiliary judgment. This is because when the compressor is running at low frequency, the system load is low, the refrigerant circulation is small, and the condensing pressure and temperature are inherently low. Using the original fixed thresholds at this time might lead to missed detections, as the ΔPc caused by clogging might be masked by the low load. Therefore, when fcomp is lower than the safe oil return frequency of 40Hz, the system will actively lower the clog judgment threshold by 20% to 30%, improving the identification sensitivity under low load conditions. After determining that clogging has occurred, the system will classify the situation as "clogged" based on ΔPc exceeding the threshold by more than 50%. "Mild clogging" and "severe clogging". For severe clogging, a shutdown cleaning process will be triggered, performing a reverse pulse purging self-cleaning operation: The reverse pulse purging self-cleaning operation is controlled by a normally closed solenoid valve, which controls a high-pressure gas source to be connected to the condenser outlet side via pipeline. When triggered, the solenoid valve opens instantaneously, and the high-pressure gas is sprayed out in reverse from the outlet side to the inlet side, forming a pulse airflow that blows away the clogging material. The timing of the self-cleaning start is also linked to the operation mode switching in S6: In the dual-unit high-efficiency mode, due to the high system load and large shutdown losses, the self-cleaning will be delayed for 30 minutes; while in the single-unit energy-saving mode, the system load is low, and self-cleaning can be performed immediately. Through multi-parameter fusion judgment and dynamic threshold adjustment, the problem of easy misjudgment by a single parameter is solved. It can accurately and timely identify the clogging and its severity, and intelligently decide the cleaning timing in combination with the operation mode, avoiding ineffective or delayed cleaning, and ensuring the heat exchange efficiency of the condenser and the long-term stable operation of the system.

[0027] See Figure 1 S4: Low-temperature start-up control. When the ambient temperature is lower than the preset start-up temperature threshold of -5℃, the system will start the low-temperature start-up mode, which will execute three stages in sequence: Preheating preparation stage: The compressor crankcase heater is turned on, and the PTC heating element heats the lubricating oil in the compressor housing, reducing its viscosity and improving its fluidity. At the same time, the condenser fan is turned off and the second heat exchange zone is closed through the solenoid valve to reduce heat loss, so that the heat generated by the heater is concentrated in the compressor body. The system continuously monitors the compressor housing temperature through a temperature sensor attached to the lower part of the housing until the safe starting temperature of 20°C is reached, and then this stage ends. Based on the Andrade formula that the viscosity of lubricating oil has an exponential relationship with temperature, preheating can reduce the viscosity to the allowable value, ensuring that the oil pump or differential pressure oil supply system can establish a sufficient oil film at the moment of startup to prevent dry friction. Low pressure differential establishment phase: Start the fixed-frequency compressor and instruct it to operate at the minimum safe frequency of 30% of the rated frequency. At the same time, keep the second heat exchange zone out of use, so that the refrigerant flows only through the first heat exchange zone, reducing the system volume by 50%, which helps to quickly build up pressure. The system focuses on monitoring the pressure difference between the condensing pressure and the evaporating pressure ΔP=Pc−Pe. When this pressure difference reaches the minimum pressure difference of 5 bar that can overcome the resistance of the lubricating oil circulation, it indicates that the oil circuit circulation has been initially established and the lubricating oil begins to return to the compressor, and the next stage can be entered. Prioritizing the establishment of oil pressure rather than cooling capacity is the core of compressor protection, because at low temperatures, the lubricating oil may be completely deposited in the oil sump, and sufficient pressure difference is required to pump it to the various friction pairs. If the pressure difference still does not reach the standard after the fixed-frequency compressor has been running for more than 3 minutes in this stage, fault diagnosis is triggered, and it is determined that there is a refrigerant leak in the system or the compressor discharge valve plate is damaged. This fault diagnosis result serves as a prohibition condition for S6 mode switching, prohibiting switching to dual-machine high-efficiency mode until the fault is eliminated, ensuring system safety. Loading Phase: After establishing oil pressure, the variable frequency compressor is started, and its operating frequency is smoothly adjusted according to the actual cooling demand. Simultaneously, the solenoid valve gradually opens to operate the second heat exchange zone, opening by 10% every 30 seconds to increase the effective heat exchange area of ​​the condenser in a stepwise manner to match the gradually increasing heat load. During this process, the compressor discharge superheat SH=Tdischarge−Tcond is continuously monitored, and the difference between the discharge temperature and the condensing temperature is calculated. When the discharge superheat is lower than the safety threshold of 5K, it indicates that liquid refrigerant may not have been completely evaporated before being drawn into the compressor, posing a risk of liquid slugging. At this time, the load increase is immediately suspended, the frequency increase is stopped, and the solenoid valve is not opened until the superheat rises back to above 10K. Through a systematic three-stage start-up process, core issues such as liquid slugging and poor lubrication during low-temperature start-up are resolved, improving the start-up success rate. Fault diagnosis and self-protection mechanisms are built-in during the start-up process, enhancing the reliability and environmental adaptability of the unit.

[0028] See Figure 1S5: Fan control steps. A "master / standby rotation" mechanism is adopted for the three condenser fans, meaning one master fan and two standby fans are designated. The system operation log records the cumulative operating time of each fan, and the master / standby roles are rotated weekly to ensure that the operating time of all fans is relatively balanced. Since the lifespan of fan bearings and motors mainly depends on cumulative operating time, balanced operation can prevent premature failure of any fan due to overuse, thereby extending the mean time between failures (MTBF) of the entire fan group. Simultaneously, fan start-up and shutdown use a variable frequency soft start method: when a new fan needs to be added, it is not started directly at its rated speed, but rather at 30% of its rated speed as the initial speed, and then gradually increased to the target speed at a rate of 5% per second. This initial speed ratio and speed change rate are... It is not a fixed value, but dynamically adjusted according to the degree of dirt and blockage determined in S3. For example, when the degree of dirt and blockage of the condenser is high, the airflow resistance is large and the starting current will be greater. To prevent the fan from overloading, the initial speed ratio will be further reduced to 20%, and the speed change rate will be reduced by 2% per second. Similarly, when the fan speed is reduced, a gradual speed reduction method is adopted, reducing the speed by 10% per second to avoid backflow or surge caused by sudden speed drop. The main and standby rotation mechanism effectively extends the overall service life of the fan group, reduces the maintenance frequency and cost, and the frequency conversion soft start and dynamic adjustment strategy reduces the current impact on the power grid and fan motor at the moment of start-up and shutdown. At the same time, by adapting to the dirt and blockage conditions, the fan and condenser fins are further protected, and the electrical safety and mechanical reliability of the system are improved.

[0029] See Figure 1 S6: Operating mode switching. Based on the ratio of the ambient temperature Tamb to the system load rate in the current demand for cooling capacity to the unit's maximum cooling capacity: LR=Qdemand / Qmax, it automatically switches between multiple modes, with the specific rules as follows: Dual-unit high-efficiency mode: When Tamb is 25°C higher than the set value, it indicates poor heat exchange conditions and a larger heat exchange area is required. When LR is higher than the "75% rise switching threshold", it is activated. At this time, two compressors work simultaneously to provide maximum cooling capacity. Based on the fact that in high-temperature environments, the condensing pressure is high and the efficiency of a single compressor decreases, the parallel operation of two compressors can reduce the compression ratio of each compressor and improve volumetric efficiency. Single-unit energy-saving mode: This mode is activated when the LR is lower than the "45% drop switching threshold". At this time, only the variable frequency compressor runs, achieving high energy efficiency under partial load. This is because the variable frequency compressor has high motor efficiency and volumetric efficiency when running in the low frequency range, and avoids the frequent start-stop losses of the fixed frequency compressor. Oil return enhancement mode: This mode is activated when the single unit energy-saving mode runs for more than 2 hours, indicating a long-term low load, or when S2 determines that there is a risk of oil return. This mode will activate the oil return enhancement measures in S2, reducing the heat exchange area or intermittently increasing the frequency. Low-temperature start-up mode: Activated when Tamb is below the preset start-up temperature threshold of -5℃, executing the S4 start-up process. The switching between dual-machine high-efficiency mode and single-machine energy-saving mode uses "hysteresis comparison logic," meaning the 75% upward switching threshold is higher than the 45% downward switching threshold, forming a 30% "switching dead zone." This prevents the system from frequently switching modes near the threshold point due to minor load fluctuations, causing system instability. When the load rate fluctuates between 47% and 52%, it will not switch repeatedly. The range of this switching dead zone is dynamically adjusted according to the degree of dirt and clogging in S3. When the blockage is high, the condenser's heat exchange efficiency decreases, and the compressor needs to operate at a higher frequency for the same cooling capacity, resulting in an artificially high load rate. To prevent accidental switching to dual-machine mode, the system expands the switching dead zone, raising the rise threshold to 80% and lowering the fall threshold to 40%, making the switching more "slow." Through intelligent, smooth, and hysteresis- and dynamically adjusted mode switching logic, the system ensures that it can operate in the optimal mode under different operating conditions, achieving both high efficiency and energy saving, as well as ensuring oil return safety. Furthermore, through coordination with steps such as dirt and blockage detection, the mode switching decision is made more scientific and stable.

[0030] See Figure 1S7: Parameter self-optimization. The system will record and store the operational data of all steps from S1 to S6 for an extended period, including the frequency of oil return risk triggers, the duration of each mode, false alarms or missed alarms due to dirt blockage, the success rate of low-temperature start-up, and the average operating time deviation of the condenser fan. The system will perform monthly optimization, using a mean-range control chart, an exponentially weighted moving average method, and multiple regression analysis to optimize the preset parameters. The mean-range control chart is used to assess the stability of the operational data and identify abnormal fluctuations; the exponentially weighted moving average method is used to predict the changing trends of each parameter; and multiple regression analysis is used to establish a quantitative relationship model between the parameters and the optimization objective function. The optimization objective function is based on the duration ratio of the operating modes in S6, i.e., the desired... The goal is to achieve a high proportion of high-efficiency mode, a reasonable proportion of energy-saving mode, a low proportion of oil return mode, and a low frequency of oil return risk triggering in S2. The specific optimization algorithm employs gradient descent: a comprehensive performance index J is defined, calculated as follows: J = w1 * (1 - proportion of dual-machine high-efficiency mode duration) + w2 * frequency of oil return risk triggering + w3 * low-temperature start-up failure rate. w1 is the weighting coefficient for the proportion of dual-machine high-efficiency mode duration, w2 is the weighting coefficient for the frequency of oil return risk triggering, and w3 is the weighting coefficient for the low-temperature start-up failure rate. These weighting coefficients are pre-calibrated through multi-objective optimization experiments before the system leaves the factory. The specific calibration process involves running the condenser unit under standard operating conditions and simultaneously collecting data on the proportion of high-efficiency mode, the frequency of oil return risk triggering, and... Three sets of data on low-temperature start-up failure rate were used. The analytic hierarchy process (AHP) was employed to determine the impact of each indicator on the overall system performance. After experimental calibration, the initial values ​​of the three weighting coefficients were set as: w1=0.4, w2=0.35, and w3=0.25, with a sum of 1. Then, multiple regression analysis was used to determine the sensitivity coefficient of each parameter to J. Outlier data was removed using a mean-range control chart. The exponentially weighted moving average method was then used to predict the direction of J change after parameter adjustment, gradually updating the parameters in the direction of decreasing J. When the frequency of oil return risk triggering in the past month exceeded the preset frequency threshold by 5 times per month, it indicated that the current critical flow rate setting for oil return was too low. The system would prioritize increasing this flow rate setting by 5% each time. When the dual-machine... When the duration of high-efficiency mode is less than 20% of the preset threshold, it indicates that the system may be too conservative and not fully utilizing the high-efficiency capabilities of the dual units. In this case, the load rate increase switching threshold will be reduced first, by 2% each time. Other parameters, such as the dirt and blockage judgment threshold, low temperature start-up preheating time, and fan rotation cycle, are also optimized according to similar logic. The adjustment step size and priority of each parameter are determined by the sensitivity coefficient obtained from multiple regression analysis. As a result, the system has self-learning and self-adaptive capabilities and can continuously optimize the control boundary parameters according to the actual operating environment and equipment aging and wear conditions. This avoids the decline in control performance caused by improper initial settings or environmental changes, and keeps the unit operating in the optimal state for a long time, thus realizing the intelligent control method.

[0031] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A multi-mode coordinated control method for a condensing unit, characterized in that: Includes the following steps: S1: System configuration: a compressor module consisting of a variable frequency compressor and a fixed frequency compressor connected in parallel, and a condenser module divided into a first heat exchange zone and a second heat exchange zone by solenoid valves; S2: Oil return safety judgment and capacity matching control: Calculate the average flow rate of refrigerant in the condenser. When the average flow rate is lower than the preset critical oil return flow rate, the effective heat exchange area of ​​the condenser is reduced by closing the solenoid valve of the second heat exchange zone, or the refrigerant flow rate is increased to above the critical oil return flow rate by increasing the compressor operating frequency. The determination of the critical oil return velocity includes gradually reducing the compressor operating frequency during the unit commissioning phase, while observing the oil level changes in the compressor sight glass. When the oil level drops to the minimum allowable oil level, the refrigerant flow rate under the current operating condition is recorded as the critical oil return velocity. When reducing the effective heat exchange area of ​​the condenser, after closing the solenoid valve of the second heat exchange zone, the effective heat exchange area of ​​the condenser is reduced to a specified proportion of the initial area. This specified proportion is dynamically calculated based on the ratio of the current refrigerant flow rate to the critical oil return velocity. The method of increasing the compressor operating frequency includes: when the cooling demand allows, increasing the compressor frequency to above the safe oil return frequency; when the cooling demand does not allow, activating the intermittent oil return mode, periodically increasing the compressor frequency to the rated frequency and continuing for a preset oil return time. S3: Condenser blockage judgment: Calculate the difference between condensing pressure and saturated condensing pressure, the static pressure difference between the air inlet and outlet sides of the condenser, and the deviation between the measured value and the theoretical calculated value of the condenser outlet temperature. When any two of these parameters exceed the preset threshold, the condenser is judged to be blocked. S4: Low temperature start control: When the ambient temperature is lower than the preset start temperature threshold, the preheating preparation stage, the low pressure difference establishment stage and the load loading stage are executed in sequence. This includes preheating the lubricating oil to reduce the oil viscosity, quickly establishing the pressure difference through the limited area operation of a single fixed frequency compressor to promote oil circulation, gradually putting the variable frequency compressor and the second heat exchange zone into operation and monitoring the exhaust superheat to prevent liquid slugging. S5: Fan control: A main and backup rotation mechanism is adopted for multiple condenser fans, and the fan start-up and shutdown adopts the frequency conversion soft start method; S6: Operating mode switching: Automatically switches the operating mode according to the ambient temperature and system load rate. The operating modes include dual-machine high-efficiency mode, single-machine energy-saving mode, oil return enhancement mode and low temperature start-up mode. In S2, when the risk of oil return is triggered, the system switches to the enhanced oil return mode. In S3, the result of the dirt blockage determination is used to trigger the self-cleaning operation. In S4, after the low temperature start-up is successful, the critical flow rate of oil return in S2 is recalibrated. In S5, the fan operating status serves as the basic input for the parameter calculation in S3. In S6, a comprehensive decision is made based on the output results from S2 to S5.

2. The multi-mode coordinated control method for a condensing unit according to claim 1, characterized in that: In S3, when judging condenser blockage, the compressor operating frequency in S2 is also included as a fourth parameter in the judgment. When the compressor operating frequency is lower than the oil return safe frequency, the blockage judgment threshold is lowered. After judging condenser blockage, it is divided into mild blockage and severe blockage according to the degree of blockage. When it is judged to be severe blockage, the shutdown cleaning process is triggered to perform reverse pulse purging self-cleaning operation. The start time of self-cleaning operation is linked with the operation mode switching in S6: when the unit is in dual-unit high-efficiency mode, the self-cleaning is delayed, and when the unit is in single-unit energy-saving mode, the self-cleaning is performed immediately.

3. The multi-mode coordinated control method for a condensing unit according to claim 1, characterized in that: In S4, the preheating preparation stage includes turning on the compressor crankcase heater, turning off the condenser fan, and turning off the solenoid valve of the second heat exchange zone, while simultaneously monitoring the compressor casing temperature until the safe start-up temperature is reached. The low pressure difference establishment stage includes starting the fixed-frequency compressor at the lowest frequency, allowing the refrigerant to flow only through the first heat exchange zone, and monitoring the pressure difference between the condensing pressure and the evaporating pressure until it reaches the minimum pressure difference required for lubricating oil circulation before proceeding to the next stage. The load loading stage includes starting the variable-frequency compressor, adjusting the frequency according to the cooling demand, gradually opening the solenoid valve of the second heat exchange zone to increase the effective heat exchange area of ​​the condenser, and continuously monitoring the compressor exhaust superheat during this period. When the superheat is lower than the safe threshold, the load increase is suspended.

4. The multi-mode coordinated control method for a condensing unit according to claim 3, characterized in that: In S4, during the low pressure differential establishment phase, if the pressure differential still does not reach the minimum pressure differential required for lubricating oil circulation after the fixed-frequency compressor has been running for a preset time, a fault diagnosis is triggered, and it is determined that there is a refrigerant leak or the compressor exhaust valve plate is damaged. This fault diagnosis result serves as a prohibition condition for mode switching in S6, prohibiting switching to the dual-machine high-efficiency mode until the fault is resolved.

5. The multi-mode coordinated control method for a condensing unit according to claim 2, characterized in that: In S5, when the fan starts and stops using the variable frequency soft start method, the newly added fan uses a specified percentage of the rated speed as the initial speed, and gradually increases to the target speed with a specified speed change rate. The specified percentage and speed change rate are dynamically adjusted according to the degree of dirt and blockage in S3. When the degree of dirt and blockage is high, the initial speed percentage is reduced, and the fan adopts a gradual speed reduction method when reducing speed.

6. The multi-mode coordinated control method for a condensing unit according to claim 1, characterized in that: In S6, the dual-machine high-efficiency mode is activated when the ambient temperature is higher than the set value and the system load rate is higher than the load rate increase switching threshold; the single-machine energy-saving mode is activated when the system load rate is lower than the load rate decrease switching threshold; the oil return enhancement mode is activated when the single-machine energy-saving mode has been running for more than the preset time or when it is determined in S2 that there is a risk of oil return; and the low-temperature start-up mode is activated when the ambient temperature is lower than the preset start-up temperature threshold.

7. The multi-mode coordinated control method for a condensing unit according to claim 6, characterized in that: The switching between the dual-machine high-efficiency mode and the single-machine energy-saving mode adopts hysteresis comparison logic: the switching threshold for load rate increase is higher than the switching threshold for load rate decrease, and a switching dead zone is formed between the two thresholds. The range of the switching dead zone is dynamically adjusted according to the degree of dirt and blockage in S3. When the degree of dirt and blockage is high, the range of the switching dead zone is expanded.

8. The multi-mode coordinated control method for a condensing unit according to claim 1, characterized in that: It also includes S7: Parameter self-optimization: Based on long-term operating data from S1 to S6, the preset parameters are optimized using mean-range control chart, exponential weighted moving average method and multiple regression analysis. The optimized parameters include return oil critical flow rate, dirt blockage judgment threshold, low temperature start-up preheating time, fan rotation cycle, load rate increase switching threshold and load rate decrease switching threshold. The parameter self-optimization is based on the duration ratio of the operating mode in S6 and the return oil risk trigger frequency in S2 as the optimization objective function. The objective is set as follows: high proportion of high efficiency mode, reasonable proportion of energy-saving mode, low proportion of return oil mode, and low return oil risk trigger frequency.

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