Heat pump system for concentration and evaporation and segmented control method of compressor of heat pump system

Abstract

The invention relates to the technical field of heat pump systems, and provides a compressor segmented control method of a heat pump system and a concentration and evaporation heat pump system. The method is applied to a heat pump system comprising a refrigerant loop and a concentration and evaporation loop, and the control process comprises the following stages which are executed in sequence or in a switchable mode: a starting stage: controlling a compressor to operate at an initial frequency and gradually increasing the initial frequency until the temperature of an outlet of a condenser or a heat supply medium reaches a first threshold value; in the earlier stage of evaporation, the target evaporation capacity serves as a set value, and the compressor frequency is subjected to closed-loop adjustment to enable the real-time evaporation capacity to approach the target; in the middle stage of evaporation, the evaporation capacity and the pressure ratio are monitored, and if the evaporation capacity is lower than a first flow threshold set in a progressively decreasing mode and the pressure ratio exceeds the first threshold, frequency reduction is conducted; and in the later evaporation stage, when the suction pressure is lower than the first pressure threshold value, the hot gas bypass valve is opened to maintain operation. According to the scheme, load change can be self-adapted, too low suction pressure, too large pressure ratio and pressure fluctuation are prevented, and the stability and energy efficiency of the system are improved.

Description

Technical Field

[0001] This application relates to the field of heat pump system technology, and more specifically, to a segmented control method for a heat pump system for concentration evaporation and its compressor. Background Technology

[0002] Heat pump evaporation technology, as a highly efficient and energy-saving method for concentration and separation, has been widely used in industries such as chemical, pharmaceutical, food, and environmental protection, especially for the volume reduction treatment of high-salt, high-concentration industrial wastewater. Its basic principle is to utilize a heat pump system (typically including a compressor, condenser, expansion valve, and evaporator) to recover the latent heat of the steam generated during evaporation, which is then used to heat the raw material liquid, thereby significantly reducing the system's consumption of external fresh steam and achieving energy savings.

[0003] During the waste liquid concentration and evaporation process, as water is continuously evaporated, the concentration of the raw liquid in the concentration tank continues to rise, leading to an increase in its boiling point, decreased fluidity, and a decrease in the heat transfer coefficient. The evaporation rate (load) of the entire system is not constant, but rather a dynamic process that changes from startup, ramp-up, stable operation to gradual decline. As the core power and heat-enhancing component of the system, the compressor's operating status directly affects the energy efficiency, stability, and processing capacity of the entire system.

[0004] Currently, research and practice in automatic control in this field are mostly focused on the automation of process flows, such as achieving automatic feeding, temperature and pressure monitoring, concentration compliance for discharge, and safety interlock protection. While these solutions improve the convenience and safety of system operation, their control core often revolves around logic or PID control of process parameters (such as liquid level, temperature, and pressure), without delving into refined control for the energy efficiency optimization of the compressor, a core energy-consuming device, under varying load conditions across all operating conditions.

[0005] In existing technologies, the common methods for controlling heat pump compressors are simple start-stop control or PID regulation based on a fixed target (such as evaporation temperature). However, these control methods have significant shortcomings in continuously changing load conditions such as concentration evaporation: during startup and low-load phases, the compressor is prone to triggering protective shutdown due to excessively low suction pressure; during the middle stage of evaporation, as the concentration of the feed liquid increases, if the compressor continues to operate at a high frequency, it will lead to an increase in discharge pressure (condensing pressure) and pressure ratio, causing the compressor to operate in an inefficient zone and significantly increasing energy consumption; in the later stage of evaporation, the evaporation rate is very low, and the compressor may be unable to maintain operation due to excessively low suction pressure, causing the evaporation process to be prematurely interrupted, affecting the final concentration effect. Furthermore, although magnetic levitation centrifugal compressors have great potential in such applications due to their oil-free, high-efficiency, and wide-frequency adjustable advantages, issues such as inverter heat dissipation and maintaining continuous system operation under low evaporation loads place higher demands on control strategies.

[0006] In summary, existing control strategies for evaporation heat pump systems fail to achieve adaptive matching between compressor operating frequency and dynamically changing evaporation process loads. This results in low overall energy efficiency throughout the system's operating cycle, and challenges to stability and reliability under conditions of drastic load changes. Therefore, there is an urgent need for an intelligent control method and system capable of adapting to load variations throughout the evaporation process and achieving efficient, stable, and adaptive compressor operation. Summary of the Invention

[0007] The purpose of this application is to provide a segmented control method for a heat pump system and its compressor used in concentration evaporation, which can adapt to the dynamic load changes of the heat pump system during the concentration evaporation process, effectively prevent the energy efficiency reduction caused by excessively low suction pressure during the start-up stage, excessively high pressure ratio during the middle stage of evaporation, and suction pressure fluctuations in the later stage of evaporation, and significantly improve the system's operational stability and energy utilization efficiency.

[0008] This application provides a segmented control method for the compressor of a heat pump system, the technical solution of which is as follows:

[0009] A compressor segment control method for a heat pump system, the heat pump system comprising a refrigerant circuit formed by a compressor, condenser, expansion valve, and evaporator connected by pipelines, and a condensing evaporation circuit that exchanges heat with the evaporator and condenser; the method includes the following control stages executed sequentially or switched according to operating conditions:

[0010] Start-up phase: Control the compressor to run at the initial frequency and gradually increase the operating frequency according to the preset cycle until the outlet temperature of the condenser or the temperature of the heating medium in the condensation evaporation circuit reaches the first temperature threshold.

[0011] Early stage of evaporation: Using the preset target evaporation rate as the set value, the operating frequency of the compressor is adjusted by a closed-loop control method to make the real-time evaporation rate approach the target evaporation rate;

[0012] Mid-stage evaporation: Monitor the real-time evaporation rate of the concentration evaporation circuit and the operating pressure ratio of the compressor;

[0013] When the real-time evaporation rate is lower than the first flow threshold set based on the decrease of the target evaporation rate, if the operating pressure ratio is higher than the corresponding first pressure ratio threshold, the operating frequency of the compressor is reduced.

[0014] Later stage of evaporation: When the compressor suction pressure is detected to be lower than the first pressure threshold, the hot gas bypass valve connected between the condenser and the evaporator is opened to bypass some of the high-temperature refrigerant to the evaporator inlet in order to maintain system operation.

[0015] Furthermore, this application also proposes that, during the mid-stage of evaporation, the target evaporation rate is defined as Q, the real-time evaporation rate as F, and the operating pressure ratio as R;

[0016] Set a series of traffic thresholds Fn = Q×(1 - n×k), where n is a positive integer starting from 1 and k is a preset decreasing percentage coefficient;

[0017] Set a series of pressure ratio thresholds Rn = R0 + n×m corresponding to the flow rate threshold Fn, where R0 is the preset base pressure ratio and m is the preset pressure ratio increment coefficient;

[0018] The following control logic is executed: when the real-time evaporation rate F is less than the currently determined flow threshold Fn, if the operating pressure ratio R is greater than the corresponding pressure ratio threshold Rn, the operating frequency of the compressor is reduced by a preset adjustment step.

[0019] Furthermore, this application also proposes that the decreasing percentage coefficient k is 1%, the pressure ratio increment coefficient m is 0.04, the reference pressure ratio R0 is 1.50, and the adjustment step size is 1.5% of the current operating frequency.

[0020] Furthermore, this application also proposes that, during the startup phase, the initial frequency is 30% of the compressor's rated frequency, the preset cycle is 30 seconds, and the frequency increase for each cycle is 5% of the rated frequency.

[0021] Furthermore, this application also proposes to include a frequency converter heat dissipation control stage:

[0022] Monitor the temperature of the frequency converter that powers the compressor;

[0023] When the inverter temperature exceeds the second temperature threshold, the refrigerant pump is started to draw liquid refrigerant from the condenser outlet and flow it through the heat dissipation channel set for the inverter to cool it.

[0024] Furthermore, this application also proposes that, during the startup phase, if the compressor's suction pressure is detected to be lower than the second pressure threshold during the frequency increase process, the hot gas bypass valve is opened until the suction pressure recovers to above the second pressure threshold.

[0025] Furthermore, this application also proposes that running the above method further includes:

[0026] Monitor real-time evaporation;

[0027] When the real-time evaporation rate exceeds the set value of the target evaporation rate, the split evaporation branch is opened, so that part of the gaseous working fluid is diverted to the split evaporator for auxiliary heat exchange. The liquid condensed by the split evaporator enters the distillation tank.

[0028] Furthermore, this application also proposes a heat pump system for concentration evaporation, used to implement the above method, comprising:

[0029] The refrigerant circuit connects the compressor, condenser, expansion valve, and evaporator in sequence to form a closed loop;

[0030] The concentration evaporation circuit includes a concentration tank, which is thermally coupled to an evaporator to absorb the heat of the gaseous working fluid generated by the evaporation of the liquid in the concentration tank. The concentration tank is also thermally coupled to a condenser to heat the liquid in the concentration tank through the condensation heat released by the condenser, so as to achieve its continuous evaporation.

[0031] A hot gas bypass pipeline is connected in the refrigerant circuit between the condenser and the evaporator to bypass the high-temperature refrigerant from the condenser to the inlet side of the evaporator. A hot gas bypass valve is provided on the pipeline.

[0032] The control system is connected to the compressor and the hot gas bypass valve via signals and is configured to execute the segmented control method described above.

[0033] Furthermore, this application also proposes that the compressor is a magnetically levitated centrifugal compressor.

[0034] Furthermore, this application also proposes to include a refrigerant cooling circuit, which includes a refrigerant pump and a heat dissipation channel. The inlet of the refrigerant pump is connected to the liquid refrigerant outlet of the condenser, and the outlet is connected to the heat dissipation channel, which is located at the inverter of the compressor for heat dissipation.

[0035] Furthermore, this application also proposes that the concentration evaporation circuit further includes a split evaporation branch, which includes a split evaporator and a connecting pipe. One end of the connecting pipe is connected to the gaseous working fluid output pipe of the concentration tank, and the other end is connected to the distillation tank via the split evaporator. The split evaporator is thermally coupled to the refrigerant circuit to condense the split gaseous working fluid, and a control valve is provided on the split evaporation branch. The control system is also signal-connected to the control valve and configured to open the control valve when the real-time evaporation rate is greater than the set value of the target evaporation rate.

[0036] Furthermore, this application also proposes that the concentration evaporation circuit further includes:

[0037] The raw material supply unit is used to supply the liquid to be treated to the concentration tank;

[0038] A distillation vessel is used to collect the distillate after it has been condensed by an evaporator and a split evaporator.

[0039] The concentrate discharge unit is used to discharge the concentrate when the liquid concentration in the concentration tank reaches a set value or the evaporation rate is lower than a set value.

[0040] As can be seen from the above, the segmented control method of the heat pump system and its compressor for concentration evaporation provided in this application effectively copes with the dynamic load changes in the concentration evaporation process by gradually increasing the frequency during the start-up stage, closed-loop regulation in the early stage of evaporation, dynamic frequency adjustment based on evaporation rate and pressure ratio during the middle stage of evaporation, and opening the bypass valve to maintain operation in the later stage of evaporation. This method prevents the energy efficiency reduction caused by excessively low suction pressure during the start-up stage, excessively high pressure ratio during the middle stage of evaporation, and suction pressure fluctuations in the later stage of evaporation. It has the advantages of significantly improving the system's operational stability and energy utilization efficiency. Attached Figure Description

[0041] Figure 1 This is a connection diagram of a heat pump system for concentration evaporation provided in this application. Detailed Implementation

[0042] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0043] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0044] Traditional heat pump evaporation systems face limitations in compressor control when handling dynamically changing loads. Existing control strategies fail to achieve adaptive matching between compressor operating frequency and process load, leading to system shutdowns due to excessively low suction pressure during startup and low-load phases. During the middle stages of evaporation, the compressor may operate in an inefficient region, increasing energy consumption. In the later stages of evaporation, low evaporation rates can easily cause system interruptions, affecting concentration efficiency. These issues result in overall system energy efficiency falling short of expectations, and pose challenges to operational stability and reliability under varying load conditions.

[0045] Example 1:

[0046] like Figure 1As shown, this application proposes a segmented compressor control method for a heat pump system. The heat pump system includes a refrigerant circuit formed by a compressor 1, condenser 2, expansion valve 3, and evaporator 4 connected by pipelines, and a concentration evaporation circuit that exchanges heat with the evaporator 4 and condenser 2. The method includes the following control stages executed sequentially or switched according to operating conditions: In the start-up stage, the compressor 1 is controlled to operate at an initial frequency, and the operating frequency is gradually increased according to a preset cycle until the outlet temperature of the condenser 2 or the heating medium temperature of the concentration evaporation circuit reaches a first temperature threshold; in the early evaporation stage, a preset target evaporation rate is used as the set value... A closed-loop control method is used to adjust the operating frequency of compressor 1, making the real-time evaporation rate approach the target evaporation rate. During the mid-evaporation phase, the real-time evaporation rate of the concentration evaporation circuit and the operating pressure ratio of compressor 1 are monitored. When the real-time evaporation rate is lower than a first flow rate threshold set based on the decrease from the target evaporation rate, if the operating pressure ratio is higher than the corresponding first pressure ratio threshold, the operating frequency of compressor 1 is reduced. In the late-stage evaporation phase, when the suction pressure of compressor 1 is detected to be lower than a first pressure threshold, the hot gas bypass valve connected between condenser 2 and evaporator 4 is opened to bypass some high-temperature refrigerant to the inlet of evaporator 4 to maintain system operation. This method solves the above problems by precisely segmenting the operation of compressor 1, thereby improving system energy efficiency, stability, and processing capacity.

[0047] For ease of understanding, the following explains some key terms in this embodiment:

[0048] A heat pump system is a device that uses a small amount of electricity to upgrade low-grade heat energy to high-grade heat energy. It achieves heat transfer through the phase change cycle of the refrigerant and is commonly used in heating, cooling, or evaporation and concentration processes.

[0049] The refrigerant circuit is the core cycle of a heat pump system. It consists of main components such as compressor 1, condenser 2, expansion valve 3, and evaporator 4 connected in sequence through pipelines. The refrigerant circulates in the circuit, completing heat transfer by absorbing and releasing heat.

[0050] The concentration evaporation loop is a process loop that exchanges heat with the evaporator 4 and condenser 2 of the heat pump system. It typically includes a liquid to be concentrated, which is evaporated by absorbing heat provided by the evaporator 4, and the liquid is preheated or directly heated by the heat released by the condenser 2 to achieve liquid concentration.

[0051] Compressor 1 is the power component in the refrigerant circuit, used to increase the pressure and temperature of the refrigerant so that it can transfer heat to the concentration and evaporation circuit.

[0052] Condenser 2 is a heat exchange component in the refrigerant circuit. High-temperature and high-pressure refrigerant vapor condenses and releases heat here, transferring the heat to the liquid in the concentration and evaporation circuit.

[0053] Expansion valve 3 is a throttling component in the refrigerant circuit, used to reduce the pressure and temperature of the refrigerant so that it can absorb heat when it enters evaporator 4.

[0054] Evaporator 4 is a heat exchange component in the refrigerant circuit. Low-temperature, low-pressure liquid refrigerant evaporates and absorbs heat here, absorbing heat from the concentration evaporation circuit, causing the liquid in the concentration tank 5 to evaporate.

[0055] The initial frequency refers to a low operating frequency set by compressor 1 at the start of the startup phase, which aims to achieve a smooth system start-up and avoid shocks.

[0056] The preset cycle refers to the time interval during the startup phase when the operating frequency of compressor 1 gradually increases, ensuring the stability and controllability of the frequency increase.

[0057] The first temperature threshold refers to a temperature reference value used to determine whether the system has reached a stable operating state during the startup phase. It can be the outlet temperature of condenser 2 or the temperature of the heating medium in the concentration evaporation circuit.

[0058] The target evaporation rate refers to the evaporation rate or evaporation load that the system expects to achieve in the early stage of evaporation, which is used as the setpoint for closed-loop control.

[0059] Real-time evaporation rate refers to the actual evaporation rate of the concentration evaporation loop as monitored in real time by sensors or computational models during system operation.

[0060] The operating pressure ratio refers to the ratio of the discharge pressure to the intake pressure of compressor 1, and is a key parameter for measuring the operating status and energy efficiency of compressor 1.

[0061] The first flow threshold is a reference value used to determine whether the real-time evaporation rate is too low during the middle of the evaporation process. It is set based on the decreasing target evaporation rate to adapt to load decay.

[0062] The first pressure ratio threshold refers to a pressure ratio reference value corresponding to the first flow rate threshold during the middle stage of evaporation, used to determine whether compressor 1 is operating in an inefficient or unstable region.

[0063] Suction pressure refers to the refrigerant pressure at the suction inlet of compressor 1, which is a key parameter reflecting the working status of evaporator 4 and system load.

[0064] The first pressure threshold is a reference value used to determine whether the suction pressure is too low in the later stage of evaporation. When the suction pressure is lower than this threshold, the system may face the risk of shutdown.

[0065] The hot gas bypass valve is a valve connected between the condenser 2 and the evaporator 4. It is used to bypass a portion of the high-temperature refrigerant to the inlet of the evaporator 4 under specific operating conditions to maintain system operation.

[0066] This method achieves precise management of the compressor 1 in a heat pump system through segmented control. The heat pump system includes a refrigerant circuit and a concentration-evaporation circuit. The refrigerant circuit typically consists of a compressor 1, condenser 2, expansion valve 3, and evaporator 4 connected by piping to form a closed loop, where the refrigerant undergoes a phase change to transfer heat. The concentration-evaporation circuit exchanges heat with the evaporator 4 and condenser 2. For example, the evaporator 4 absorbs the latent heat of vaporization from the concentration tank 5, and the condenser 2 releases the heat of condensation to the liquid in the concentration tank 5 to achieve continuous evaporation. The refrigerant circuit can use various refrigerants, such as R134a and R245fa. Its components can be selected according to the system scale and application scenario; for example, a screw compressor 1 and a plate heat exchanger can be used as the condenser 2 and evaporator 4. The concentration-evaporation circuit can be a simple concentration tank 5 or a system containing multiple components such as a preheater and flash tank. Heat exchange with the refrigerant circuit can be achieved through direct contact or indirect heat exchange.

[0067] During the startup phase, compressor 1 is controlled to operate at an initial frequency, and the operating frequency is gradually increased according to a preset cycle until the outlet temperature of condenser 2 or the temperature of the heating medium in the condensation evaporation circuit reaches the first temperature threshold. When starting compressor 1, a low initial frequency can be set, such as manually setting a fixed value or presetting an empirical value based on the ambient temperature. The increase in operating frequency can be controlled by a timer, increasing by a fixed frequency step at regular intervals, such as 5Hz per minute, or manually adjusted by the operator. The temperature threshold can be set to the refrigerant temperature at the outlet of condenser 2 or the temperature of the liquid to be heated in the condensation evaporation circuit. When this temperature is reached, the system is considered to have initially established stable operating conditions.

[0068] In the initial stage of evaporation, the operating frequency of compressor 1 is adjusted using a closed-loop control method with a preset target evaporation rate as the set value, so that the real-time evaporation rate approaches the target evaporation rate. The target evaporation rate can be set according to process requirements or empirical values, for example, by measuring the flow rate of the gaseous working fluid (such as water vapor) generated by the concentration tank using a flow meter, or by monitoring the rate of change of liquid level in the concentration tank 5 using a liquid level sensor. The closed-loop control can use a proportional-integral-derivative (PID) controller, which compares the real-time evaporation rate with the target evaporation rate and outputs control commands based on the deviation signal to adjust the operating frequency of compressor 1.

[0069] During the evaporation phase, the real-time evaporation rate of the concentration evaporation loop and the operating pressure ratio of compressor 1 are monitored. When the real-time evaporation rate is lower than a first flow rate threshold set based on a decrease from the target evaporation rate, if the operating pressure ratio is higher than the corresponding first pressure ratio threshold, the operating frequency of compressor 1 is reduced. Monitoring of the real-time evaporation rate and operating pressure ratio can be achieved through appropriate sensors and a control system. The first flow rate threshold can be set as a fixed percentage of the target evaporation rate or preset based on an empirical curve. The first pressure ratio threshold can be set as a fixed value, such as 1.5, or preset based on the performance curve of compressor 1. When both conditions are met simultaneously, the control system issues a command to reduce the operating frequency of compressor 1, for example, by reducing it by a fixed frequency value or a fixed percentage.

[0070] During the later stages of evaporation, when the suction pressure of compressor 1 is detected to be lower than a first pressure threshold, the hot gas bypass valve connected between condenser 2 and evaporator 4 is opened to bypass some high-temperature refrigerant to the inlet of evaporator 4, thereby maintaining system operation. The suction pressure can be detected in real time by a pressure sensor. The first pressure threshold can be set according to the minimum allowable suction pressure of compressor 1 or an empirical value for stable system operation, for example, set to 250 kPa. The hot gas bypass valve can be a solenoid valve or a pneumatic valve. When the suction pressure is detected to be lower than this threshold, the control system sends an opening signal to the bypass valve to bypass some high-temperature refrigerant to the inlet of evaporator 4, thereby maintaining system operation.

[0071] This method solves the operational problems of traditional systems under dynamic load changes by implementing segmented control throughout the concentration and evaporation process. The stable frequency increase during startup prevents compressor 1 from shutting down due to excessively low suction pressure; closed-loop control in the early stage of evaporation matches the operating frequency of compressor 1 with the target evaporation capacity, achieving energy optimization; pressure ratio and flow rate linkage adjustment in the middle stage of evaporation prevents compressor 1 from operating in inefficient regions; and hot gas bypass in the later stage of evaporation maintains the suction pressure, ensuring the continuity of the evaporation process. Therefore, the system achieves high operating efficiency and stable operation of compressor 1 during the concentration and evaporation process, thereby improving processing capacity.

[0072] In a specific implementation plan, during the mid-evaporation phase, a target evaporation rate Q, a real-time evaporation rate F, and an operating pressure ratio R of compressor 1 are defined. A series of flow thresholds Fn = Q × (1 - n × k) are set, where n is a positive integer increasing from 1, and k is a preset decreasing percentage coefficient. A series of pressure ratio thresholds Rn = R0 + n × m corresponding to the flow thresholds Fn are set, where R0 is a preset base pressure ratio, and m is a preset pressure ratio increment coefficient. The following control logic is executed: when the real-time evaporation rate F is less than the currently determined flow threshold Fn, if the operating pressure ratio R is greater than the corresponding pressure ratio threshold Rn, the operating frequency of compressor 1 is controlled to decrease by a preset adjustment step.

[0073] Specifically, the target evaporation rate Q refers to the ideal evaporation rate that the system expects to achieve during the concentration and evaporation process, which is the flow rate baseline. It is usually preset according to process requirements or system design capacity. The real-time evaporation rate F refers to the actual evaporation rate monitored in real time by sensors, such as by measuring the gaseous working fluid flow rate at the outlet of evaporator 4 or the liquid level change rate in concentration tank 5. The operating pressure ratio R is the ratio of the discharge pressure to the suction pressure of compressor 1, a key parameter for measuring the workload and energy efficiency of compressor 1, and can be calculated in real time by pressure sensors installed on the discharge and suction sides of compressor 1. The definition and real-time acquisition of these parameters are the foundation for achieving refined control.

[0074] A series of flow thresholds, Fn = Q × (1 - n × k), are set to provide multiple dynamically changing judgment points to adapt to the continuously decreasing trend of evaporation during the concentration evaporation process. Here, n is a positive integer starting from 1, representing the threshold number or level. As n increases, the flow threshold Fn gradually decreases, forming a decreasing sequence. k is a preset decreasing percentage coefficient used to control the decrease magnitude between each threshold. For example, k can be set to a small percentage value, such as 1%, to ensure a smooth transition in the threshold sequence. This multi-level decreasing flow threshold design allows the system to detect the decrease in evaporation load earlier and more precisely, avoiding the control lag that might be caused by a single fixed threshold.

[0075] A series of pressure ratio thresholds Rn = R0 + n×m, corresponding to the flow rate threshold Fn, are set to dynamically constrain the operating pressure ratio of compressor 1 as the evaporation rate decreases. Here, R0 is a preset reference pressure ratio, representing the system's reference pressure ratio under normal or higher load conditions. m is a preset pressure ratio increment coefficient, used to control the increment of the pressure ratio threshold. For example, m can be set to a positive value, so that as n increases, the pressure ratio threshold Rn gradually increases as well. This design takes into account that in the later stages of evaporation, as the concentrate concentration increases, the system resistance may increase, leading to a tendency for the pressure ratio of compressor 1 to increase at the same flow rate. By setting incremental pressure ratio thresholds, it is possible to more reasonably determine whether compressor 1 is in an overloaded or inefficient operating state.

[0076] The control logic is as follows: when the real-time evaporation rate F is less than the currently determined flow threshold Fn, and the operating pressure ratio R is greater than the corresponding pressure ratio threshold Rn, the operating frequency of compressor 1 is reduced by a preset adjustment step. This control logic is a dual-judgment mechanism; it not only considers whether the evaporation rate has dropped below a certain threshold, but also whether the operating pressure ratio of compressor 1 is too high. Only when both conditions are met is the reduction in compressor 1's frequency triggered. The preset adjustment step refers to the magnitude of each frequency reduction, for example, it can be set to a percentage of the current operating frequency to achieve a smooth and gradual frequency adjustment, avoiding drastic system fluctuations.

[0077] Through the above technical solution, this application introduces dynamic multi-level flow and pressure ratio thresholds during the evaporation process, achieving refined and adaptive control of the compressor 1's operating frequency. Compared to a single threshold control method, this solution can respond more accurately and promptly to continuous load changes during the concentration and evaporation process, especially under conditions where the evaporation rate gradually decreases and the concentrate concentration increases, potentially leading to an increase in the pressure ratio. When the real-time evaporation rate F is lower than a certain flow threshold Fn, and the operating pressure ratio R is simultaneously higher than the corresponding pressure ratio threshold Rn, the system will actively reduce the operating frequency of compressor 1. This effectively avoids compressor 1 operating in the inefficient zone of low load and high pressure ratio, thereby significantly reducing energy consumption and improving the overall energy efficiency of the system. Furthermore, this gradual frequency adjustment strategy also enhances the system's operational stability, reducing system oscillations or protective shutdowns caused by over-adjustment or delayed adjustment, ensuring the continuity and reliability of the concentration and evaporation process.

[0078] In the specific implementation plan, the decreasing percentage coefficient k is 1%, the pressure ratio increment coefficient m is 0.04, the reference pressure ratio R0 is 1.50, and the adjustment step size is 1.5% of the current operating frequency.

[0079] Specifically, the decreasing percentage coefficient k is used to define the decreasing step size of the flow threshold Fn. Setting k to 1% means that the flow threshold will gradually decrease in steps of 1% of the target evaporation rate Q. For example, it can be set to other values ​​such as 0.5% or 2% to adapt to different process requirements and system response characteristics. Precise setting of this parameter helps the system to trigger frequency adjustments in a timely and non-excessive manner as the evaporation rate gradually decreases, avoiding excessively high pressure ratios due to insensitivity to flow changes, or frequent frequency adjustments due to excessive sensitivity, which could affect system stability.

[0080] Meanwhile, the pressure ratio increment coefficient m is used to define the increment of the pressure ratio threshold Rn. When the real-time evaporation rate F is lower than a certain flow rate threshold Fn, the system will determine whether the operating pressure ratio R is higher than the corresponding pressure ratio threshold Rn. Setting m to 0.04 means that the pressure ratio threshold will gradually increase in increments of 0.04. For example, it can be set to other values ​​such as 0.02 or 0.05. The precise setting of this parameter ensures that the tolerance for the operating pressure ratio of compressor 1 can be appropriately increased when the system load decreases and the evaporation rate decreases. This ensures stable system operation while avoiding compressor 1 operating in an unnecessary inefficient zone or prematurely or lately triggering a reduction in frequency due to improper pressure ratio threshold setting.

[0081] Furthermore, the reference pressure ratio R0 serves as the starting point for the pressure ratio threshold Rn, providing an initial reference value for the entire pressure ratio adjustment logic. R0 is set to 1.50, or alternatively, to other values ​​such as 1.40 or 1.60, to match the typical pressure ratio range of different heat pump systems under normal operating conditions. This parameter setting ensures that the control logic can dynamically adjust from a reference point that matches the actual operating conditions of the system, thereby guaranteeing the applicability and consistency of the control strategy and avoiding control errors caused by reference point deviations.

[0082] Furthermore, the adjustment step size defines the adjustment range of the compressor 1's operating frequency when the frequency reduction condition is met. The adjustment step size is set to 1.5% of the current operating frequency; for example, it can be set to 1% or 2% of the current operating frequency, or other values, to balance the sensitivity and stability of the adjustment. This parameter setting aims to achieve a smooth frequency transition, avoiding system oscillation or instability caused by excessive frequency adjustment, while ensuring that the frequency can be effectively reduced when necessary, improving the compressor 1's operating pressure ratio, thereby improving the system's energy efficiency and operational stability.

[0083] By setting specific values ​​for the decreasing percentage coefficient k, pressure ratio increment coefficient m, reference pressure ratio R0, and adjustment step size, the operating frequency adjustment logic of compressor 1 during the evaporation phase is optimized. Specifically, a decreasing percentage coefficient k of 1% allows the flow threshold to decrease in precise steps, ensuring that the system can trigger frequency adjustment in a timely manner as the evaporation rate gradually decreases. This avoids both excessively high pressure ratios due to untimely adjustments, which would reduce energy efficiency, and overly frequent adjustments that would affect system stability. A pressure ratio increment coefficient m of 0.04 allows the pressure ratio threshold to increase reasonably as the flow rate decreases, allowing compressor 1 appropriate pressure ratio fluctuation space during load changes and preventing it from prematurely entering the inefficient operating zone. A reference pressure ratio R0 of 1.50 provides a starting point consistent with actual operating conditions for the entire control strategy, ensuring the effectiveness and adaptability of the control logic. Furthermore, setting the adjustment step size to 1.5% of the current operating frequency ensures the smoothness of compressor 1's frequency adjustment, avoiding the impact of large frequency fluctuations on system operation, thereby achieving efficient and stable operation of compressor 1 under dynamic load. This refined parameter setting enables the system to better adapt to continuous load changes during the concentration and evaporation process, significantly improving the overall energy efficiency and operational reliability of the heat pump system.

[0084] In the specific implementation plan, a flow base is set, that is, the target evaporation rate is Q = 900 kg / h.

[0085] When the flow rate is <900×(100%-1%): if the pressure ratio increases by more than 1.50+0.04, the frequency decreases by 1.5%; otherwise, the frequency remains unchanged.

[0086] When the flow rate is less than 900 × (100% - 2%), if the pressure ratio increases by more than 1.50 + 0.08, the frequency will continue to decrease by 1.5%; otherwise, the frequency will remain unchanged.

[0087] When the flow rate is less than 900 × (100% - 3%), if the pressure ratio increases by more than 1.50 + 0.12, the frequency will continue to decrease by 1.5%; otherwise, the frequency will not change.

[0088] And so on,

[0089] When the flow rate is <900×(100%-19%): if the pressure ratio increases by more than 1.50+0.78, the frequency will continue to decrease by 1.5%; otherwise, the frequency will not change.

[0090] When the flow rate is <900×(100%-20%): the frequency will no longer decrease at this point in order to maintain an appropriate concentration evaporation rate and meet the concentration requirements.

[0091] In summary, when the pressure ratio increases, appropriately reducing the frequency can improve the pressure ratio and increase the energy efficiency of compressor 1.

[0092] In a further preferred embodiment, during the startup phase, the initial frequency is 30% of the rated frequency of compressor 1, the preset cycle is 30 seconds, and the frequency increase in each cycle is 5% of the rated frequency. Specifically, the initial frequency of 30% of the rated frequency of compressor 1 means that when the heat pump system starts, compressor 1 does not directly operate at a high frequency, but first uses 30% of its rated operating frequency as the starting frequency. For example, if the rated frequency of compressor 1 is 50Hz, the initial frequency is set to 15Hz. This lower initial frequency helps to avoid the system from triggering a protective shutdown due to excessive load or a sudden drop in suction pressure at startup, providing a smooth starting point for subsequent frequency increases. In addition to setting it to 30% of the rated frequency, the initial frequency can also be set to 20% or 25% of the rated frequency, depending on factors such as the specific model of compressor 1, the type of refrigerant, and the ambient temperature, to adapt to different startup conditions.

[0093] The preset cycle of 30 seconds means that during the startup phase, the compressor 1's operating frequency increase is not continuous, but occurs at fixed time intervals. Each cycle lasts 30 seconds. During this period, compressor 1 maintains its current frequency and increases its frequency at the end of the cycle. This periodic frequency increase provides sufficient response time for the system, allowing the temperature and pressure of components such as condenser 2 and evaporator 4 to gradually establish and stabilize, avoiding system fluctuations caused by excessively rapid frequency changes. In addition to the 30-second preset cycle, the cycle can also be set to 20 seconds or 45 seconds, depending on factors such as system inertia and response speed, to achieve more precise or stable frequency adjustments.

[0094] The frequency increase per cycle is 5% of the rated frequency. This means that at the end of each preset cycle, the operating frequency of compressor 1 will increase by a fixed percentage based on its rated frequency. For example, if the rated frequency of compressor 1 is 50Hz, then the frequency will increase by 2.5Hz per cycle. This small-amplitude frequency increase strategy ensures a smooth increase in system load and avoids impacting compressor 1 and the entire refrigerant circuit. In addition to 5% of the rated frequency as the increase, the increase can also be set to 3% or 8% of the rated frequency, depending on the system's requirements for start-up speed and stability considerations, to achieve a balance between start-up speed and system stability.

[0095] Through the above technical solution, during the heat pump system startup phase, the initial operating frequency of compressor 1 is set to 30% of the rated frequency, effectively reducing the system load at startup and preventing protective shutdown triggered by excessively low suction pressure, thus ensuring a smooth startup of compressor 1. Simultaneously, by employing a preset 30-second cycle and a 5% increase in rated frequency per cycle, the operating frequency of compressor 1 can be gradually increased in a controlled manner. This refined frequency increase strategy not only provides sufficient buffer time for the temperature and pressure of various system components to establish themselves, effectively suppressing pressure fluctuations and shocks during startup, but also avoids energy efficiency losses caused by improper frequency changes. This allows the outlet temperature of condenser 2 or the heating medium temperature of the condensation evaporation circuit to rise steadily, ultimately reaching the preset first temperature threshold in a more stable and efficient manner, laying a solid foundation for the subsequent evaporation process.

[0096] Furthermore, this application proposes a frequency converter heat dissipation control stage, which includes: monitoring the temperature of the frequency converter supplying power to the compressor 1; when the frequency converter temperature exceeds a second temperature threshold, starting the refrigerant pump 9 to draw liquid refrigerant from the outlet of the condenser 2 and flow it through the heat dissipation channel provided for the frequency converter to cool it. Specifically, the frequency converter heat dissipation control stage refers to a specific control link that takes active cooling measures to address potential overheating issues of the frequency converter supplying power to the compressor 1 during the operation of the heat pump system. This stage aims to ensure that the frequency converter can maintain within a safe operating temperature range under long-term, high-load operation, especially under frequent frequency changes or high-frequency operation conditions caused by the segmented control method of the compressor 1, avoiding performance degradation, malfunctions, or even damage caused by overheating, thereby ensuring the stability and reliability of the entire heat pump system. This stage is typically triggered and executed by the control system based on real-time monitoring data, involving temperature sensors, a cooling medium circulation system, and corresponding control logic.

[0097] To effectively monitor the temperature of the frequency converter, temperature sensors such as thermistors and thermocouples can be installed on key heat-generating components inside the frequency converter (e.g., IGBT modules, heat sinks) or on their outer casing to transmit real-time temperature signals to the control system. Alternatively, infrared temperature measurement technology can be used to monitor the temperature distribution on the frequency converter surface non-contactly, and temperature data can be obtained through image processing or point-specific measurements.

[0098] When the monitored inverter temperature exceeds a preset second temperature threshold, the system will trigger a cooling action. This second temperature threshold serves as a safety upper limit and can be set according to the inverter's design specifications, manufacturer recommendations, and actual operating experience; for example, it can be 50°C, 60°C, or higher. This threshold can also be dynamically adjusted, for example, fine-tuned based on ambient temperature, compressor 1 operating frequency, or load conditions to achieve more precise control.

[0099] Once the inverter temperature exceeds the second temperature threshold, the control system will activate the refrigerant pump 9. The function of the refrigerant pump 9 is to provide power to drive the cooling medium (liquid refrigerant) to circulate in the heat dissipation circuit, thereby achieving active heat dissipation. The refrigerant pump 9 can be a DC brushless pump or an AC variable frequency pump, and it starts working through a start command issued by the control system. The refrigerant pump 9 can be started using a soft start method to avoid impacting the system, and its speed or flow rate can be adjusted according to the required cooling intensity. The refrigerant pump 9 draws liquid refrigerant from the outlet of the condenser 2. Utilizing the liquid refrigerant circulating within the heat pump system itself as the cooling medium eliminates the need for additional coolant, simplifying the system structure, reducing operating costs, and improving energy efficiency. The refrigerant at the outlet of the condenser 2 is typically in a subcooled liquid state, with a low temperature and high heat capacity, making it an ideal cooling medium. Specifically, a branch pipe can be installed on the outlet pipe of the condenser 2, connected to the suction port of the refrigerant pump 9. To prevent impurities from entering the refrigerant pump 9 and the heat dissipation channel, affecting its normal operation, a filter can be installed on the branch pipe. The extracted liquid refrigerant then flows through a heat dissipation channel designed for the inverter to cool it. The function of the heat dissipation channel is to guide the low-temperature liquid refrigerant directly to the heat-generating area of ​​the inverter, removing the heat generated by the inverter through heat exchange, thereby reducing its temperature. The heat dissipation channel can be designed as a microchannel structure embedded inside the inverter's heat sink, or a cold plate structure that directly contacts the inverter's heat-generating elements. Alternatively, the heat dissipation channel can also be a coil structure surrounding the inverter's casing or internal key components, cooling through forced convection heat transfer. The cooled refrigerant can return to the inlet of evaporator 4 or condenser 2 to rejoin the refrigerant cycle.

[0100] Through the above technical solution, this application can effectively solve the overheating problem that may occur in the inverter during the operation of the heat pump system. Under the segmented control method of compressor 1 (such as frequency increase during startup, frequency adjustment during the early and middle stages of evaporation), the workload of the inverter may be high, leading to an increase in its temperature. By monitoring the inverter temperature in real time and promptly starting the refrigerant pump 9 when it exceeds the preset second temperature threshold, the low-temperature liquid refrigerant in the system flows through a dedicated heat dissipation channel to cool the inverter, which can quickly and effectively remove heat. This not only ensures that the inverter can operate stably and reliably under various operating conditions, avoiding performance degradation or shutdown due to overheating, but also ensures the continuous and effective execution of the entire heat pump system, especially the segmented control method of compressor 1, improving the overall energy efficiency and service life of the system.

[0101] In addition, during the startup phase, if the suction pressure of compressor 1 is detected to be lower than the second pressure threshold during the frequency increase process, the hot gas bypass valve is opened until the suction pressure recovers to above the second pressure threshold.

[0102] Specifically, during the heat pump system startup phase, as compressor 1 begins operating at an initial frequency and gradually increases its operating frequency, the control system continuously monitors the suction pressure of compressor 1. This is achieved by installing a pressure sensor or pressure transmitter on the suction line of compressor 1. This sensor or transmitter converts the real-time pressure signal into an electrical signal and transmits it to the control system. The control system compares the received real-time suction pressure value with a preset second pressure threshold. This second pressure threshold is a critical low-pressure value determined based on the safe operating range of compressor 1, refrigerant characteristics, and system design requirements. It aims to prevent compressor 1 from experiencing surge, sudden efficiency drops, or triggering protective shutdown due to excessively low suction pressure. For example, this second pressure threshold can be set to 250 kPa.

[0103] When the control system determines that the real-time suction pressure is lower than the second pressure threshold, it immediately issues a command to open the hot gas bypass valve. This hot gas bypass valve is connected between the condenser 2 and the evaporator 4, and its function is to bypass a portion of the high-temperature refrigerant to the inlet of the evaporator 4. The hot gas bypass valve can be an electrically operated, pneumatically operated, or solenoid valve, and its opening degree or opening / closing state is precisely controlled by the control system. By introducing high-temperature, high-pressure gas, the pressure and temperature on the suction side can be rapidly increased, thereby preventing a continuous drop in suction pressure. After the hot gas bypass valve opens, the control system continues to monitor the suction pressure of the compressor 1 in real time. Once the suction pressure rises and exceeds the preset second pressure threshold, the control system will issue a command to close the hot gas bypass valve.

[0104] In a further embodiment, the above method also includes: monitoring the real-time evaporation rate; when the real-time evaporation rate is greater than the set value of the target evaporation rate, controlling the opening of the diversion evaporation branch, so that part of the gaseous working fluid is diverted to the diversion evaporator 11 for auxiliary heat exchange, and the liquid condensed by the diversion evaporator 11 enters the distillation tank 15.

[0105] Specifically, monitoring the real-time evaporation rate is the basis for the system's load judgment and control decisions, dynamically reflecting the actual load situation of the concentration and evaporation process. The real-time evaporation rate refers to the amount of gaseous working fluid produced by evaporation per unit time in the concentration and evaporation loop. This monitoring can be achieved in various ways. For example, a mass flow meter or volumetric flow meter can be installed on the gaseous working fluid outlet pipe of the concentration and evaporation loop to directly measure the flow rate of the gaseous working fluid, thereby obtaining the real-time evaporation rate. Alternatively, the real-time evaporation rate can be indirectly calculated by monitoring the rate of liquid level drop in the concentration tank 5, combined with the geometric dimensions and liquid density of the concentration tank 5. Furthermore, the heat absorbed by the evaporator 4 can be estimated by measuring the refrigerant superheat at the outlet of the evaporator 4 or the temperature difference across the evaporator 4, combined with the refrigerant flow rate and thermodynamic properties, thereby estimating the real-time evaporation rate.

[0106] When the real-time evaporation rate is detected to exceed the set value of the target evaporation rate (e.g., 930 kg / h), the system will control the opening of the split evaporation branch. The split evaporation branch is an auxiliary circuit connected in parallel with the main concentration evaporation circuit. Its function is to divert a portion of the gaseous working fluid for additional evaporation or condensation when the main system load is too high, thereby reducing the load on the main evaporator 4. This branch may include a pipeline connecting the gaseous outlet of the concentration tank 5 and the distillation tank 15, with a control valve 12 and a split evaporator 11 installed on the pipeline. Alternatively, it may be a pipeline connecting the gaseous outlet of the concentration tank 5 and a separate auxiliary condenser, which then sends the condensate to the distillation tank 15.

[0107] The split-flow evaporator 11 is the core component of the split-flow evaporation branch. Its function is to condense the split-flow gaseous working fluid and perform auxiliary heat exchange in the process. The split-flow evaporator 11 can be designed as a plate heat exchanger or a shell-and-tube heat exchanger, through which the refrigerant from the refrigerant circuit flows, condensing the gaseous working fluid through refrigerant evaporation. Auxiliary heat exchange refers to the heat transfer process between the split-flow evaporator 11 and the refrigerant circuit or other cooling media during the condensation of the gaseous working fluid. Its purpose is to effectively remove the latent heat of the gaseous working fluid, causing it to condense into a liquid. Auxiliary heat exchange can be achieved by thermally coupling the split-flow evaporator 11 with the refrigerant circuit, i.e., the refrigerant evaporates in the split-flow evaporator 11, absorbing the condensation heat of the gaseous working fluid. Alternatively, it can be achieved by introducing an independent cooling water circulation system, using cooling water to remove the condensation heat of the gaseous working fluid.

[0108] The liquid condensed by the split evaporator 11 enters the distillation tank 15. This clearly defines the treatment result of the split evaporation branch, ensuring that the distillate condensed by the auxiliary heat exchange can be effectively collected, maintaining the material balance and product purity of the system. This can be achieved by gravity flow or by using a small transfer pump to directly introduce the condensate from the outlet of the split evaporator 11 into the main distillation tank 15. Alternatively, the condensate can be introduced into a separate intermediate collection tank, and then periodically or continuously transported to the main distillation tank 15 from this intermediate collection tank.

[0109] Through the above technical solution, this application effectively solves the overload problem that the system may face when the real-time evaporation rate is too high. Continuous monitoring of the real-time evaporation rate allows the control system to grasp the actual load changes in the concentration and evaporation process in a timely and accurate manner, thereby identifying the operating conditions where the system load exceeds the expected target set value. When the real-time evaporation rate is detected to be greater than the target evaporation rate set value, it indicates that the main evaporator 4 may be operating under high load or even overload. If no intervention is taken, it will cause the compressor 1 to operate in the high pressure ratio and low efficiency region, and may even trigger a protective shutdown, affecting the system's energy efficiency and operational stability. At this time, the control system will intelligently open the diversion evaporation branch, so that part of the gaseous working fluid does not enter the main evaporator 4 completely, but is diverted to the diversion evaporator 11 for auxiliary heat exchange. This diversion operation effectively disperses the evaporation load of the main system and reduces the working pressure of the main evaporator 4 and the compressor 1. The diversion evaporator 11 condenses the diverted gaseous working fluid into a liquid through heat exchange with the refrigerant circuit or other cooling media, thereby removing the latent heat of this part of the working fluid. The liquid condensed by the distillation evaporator 11 is guided into the distillation tank 15, ensuring the effective collection and subsequent processing of all distillate and maintaining the system's material balance. Through this adaptive distillation mechanism, the system can effectively regulate dynamically changing evaporation loads, preventing compressor 1 from operating inefficiently under high loads for extended periods, reducing the operating pressure ratio and energy consumption of compressor 1, and improving the overall energy efficiency of the system. Simultaneously, it avoids system instability or even shutdown due to overload, enhancing the reliability and stability of the heat pump system under complex operating conditions, and ensuring the continuity and high efficiency of the concentration evaporation process.

[0110] Example 2:

[0111] like Figure 1As shown, this application proposes a heat pump system for concentration and evaporation, used to implement the method described in Example 1. The system includes a refrigerant circuit that sequentially connects a compressor 1, a condenser 2, an expansion valve 3, and an evaporator 4 to form a closed loop; a concentration and evaporation circuit that includes a concentration tank 5, which is thermally coupled to the evaporator 4 to absorb heat from the gaseous working fluid generated by the evaporation of the liquid in the concentration tank 5; the concentration tank 5 is also thermally coupled to the condenser 2 to heat the liquid in the concentration tank 5 through the condensation heat released by the condenser 2, thereby achieving continuous evaporation; a hot gas bypass pipeline connected between the condenser 2 and the evaporator 4, which bypasses a portion of the high-temperature refrigerant to the inlet of the evaporator 4, and a hot gas bypass valve is provided on the pipeline; and a control system that is signal-connected to the compressor 1 and the hot gas bypass valve, and is configured to execute a segmented control method.

[0112] Specifically, the refrigerant circuit achieves phase change of the refrigerant to transfer heat through a closed loop of compressor 1, condenser 2, expansion valve 3, and evaporator 4, laying the foundation for efficient heat recovery in the system. In the concentration-evaporation circuit, the thermal coupling between the concentration tank 5 and evaporator 4 allows the system to absorb the latent heat of vaporization, while the thermal coupling with condenser 2 utilizes the heat of condensation to heat the liquid. This bidirectional heat exchange design adapts to load fluctuations caused by increased concentration and promotes continuous evaporation of the liquid. A hot gas bypass line bypasses a portion of the high-temperature refrigerant to the inlet of evaporator 4 to maintain system operation. The control system adaptively adjusts the operating frequency of compressor 1 and the state of the hot gas bypass valve based on real-time operating parameters, including evaporation stage, evaporation rate, pressure ratio, and suction pressure, ensuring that compressor 1 always operates in the high-efficiency range.

[0113] During system operation, initially, during startup, the control system operates compressor 1 at an initial frequency and gradually increases the frequency according to a preset cycle until the outlet temperature of condenser 2 or the heating medium temperature of the concentration evaporation circuit reaches a first temperature threshold. Then, in the early stage of evaporation, the operating frequency of compressor 1 is adjusted using a closed-loop control method with a preset target evaporation rate as the setpoint, so that the real-time evaporation rate approaches the target evaporation rate. In the middle stage of evaporation, the real-time evaporation rate of the concentration evaporation circuit and the operating pressure ratio of compressor 1 are monitored. If the real-time evaporation rate is lower than a first flow rate threshold set based on a decreasing target evaporation rate and the operating pressure ratio is higher than the corresponding first pressure ratio threshold, the operating frequency of compressor 1 is reduced. Finally, in the later stage of evaporation, when the suction pressure of compressor 1 is detected to be lower than a first pressure threshold, the hot gas bypass valve is opened to maintain system operation. Through the above segmented control strategy, the system effectively solves the problems of low efficiency and poor stability caused by dynamic load changes.

[0114] Through the above technical solution, this application achieves precise matching between the operating frequency of compressor 1 and the evaporation process load, avoiding compressor 1 from operating in the inefficient zone and shutting down for protection, thereby significantly improving the overall energy efficiency, operational stability and processing capacity of the heat pump system.

[0115] In a further preferred embodiment, the compressor 1 in the heat pump system is a magnetically levitated centrifugal compressor.

[0116] A magnetic levitation centrifugal compressor is a device that uses magnetic force to levitate the rotor, avoiding mechanical contact friction, and uses a high-speed rotating impeller to centrifugally compress gas. Its core lies in using magnetic levitation bearings instead of traditional rolling or sliding bearings, thereby achieving oil-free, low-friction, and high-efficiency operation. By defining compressor 1 as a magnetic levitation centrifugal compressor, this application can effectively address the challenges posed by dynamic load changes during concentration evaporation. Due to its contactless and frictionless operation, the magnetic levitation centrifugal compressor significantly reduces mechanical losses and improves the operating efficiency and reliability of compressor 1. Its inherent wide-frequency regulation capability allows compressor 1 to accurately respond to the fine-grained frequency control requirements of the heat pump system during startup, early, middle, and late stages of evaporation. Especially during the middle and late stages of evaporation, when the evaporation rate and operating pressure ratio change significantly, the magnetic levitation centrifugal compressor can provide a wider and more stable frequency regulation range, thus avoiding the surge phenomenon that easily occurs in traditional compressor 1 under low-load or variable-load conditions, ensuring stable operation of the system under all operating conditions. In addition, the oil-free design of the magnetic levitation centrifugal compressor not only reduces the complexity and maintenance requirements of the lubrication system, but also provides a cleaner and more compatible operating environment for the subsequent introduction of inverter heat dissipation control (such as through the refrigerant cooling circuit), further improving the energy efficiency and long-term operational stability of the entire heat pump system.

[0117] In this regard, this application further proposes that the heat pump system for concentration evaporation also includes a refrigerant cooling circuit, which includes a refrigerant pump 9 and a heat dissipation channel. The inlet of the refrigerant pump 9 is connected to the liquid refrigerant outlet of the condenser 2, and the outlet is connected to the heat dissipation channel. The heat dissipation channel is located at the inverter of the compressor 1 for heat dissipation.

[0118] Specifically, the refrigerant cooling circuit is an independent circulation system designed to use refrigerant as a cooling medium to remove heat from the component requiring cooling (i.e., the inverter). This circuit can be a closed secondary loop or a branch partially connected to the main refrigerant circuit; its design should ensure effective flow of the cooling medium and heat transfer. The refrigerant pump 9 is a power device used to drive the refrigerant to circulate in the cooling circuit. For example, a micro DC pump, AC pump, or magnetic pump can be used, selected according to the required flow rate, head, and power consumption requirements. For example, a centrifugal refrigerant pump 9 or a positive displacement refrigerant pump 9 can be used. The heat dissipation channel is a channel structure designed to increase the heat exchange area and efficiency, through which the refrigerant flows and exchanges heat with the component being cooled. For example, the heat dissipation channel can be a metal block with internal fins, microchannels, or serpentine tubes, directly attached to or integrated onto the heat-generating component of the inverter. For example, a copper or aluminum microchannel radiator can be used, or a heat sink with an integrated cooling coil can be used. The inlet of the refrigerant pump 9 is connected to the liquid refrigerant pipeline discharged from the condenser 2 in the main refrigerant circuit via pipes and connectors. A three-way valve or a diverter port can be installed to utilize the cooled and liquefied refrigerant in the main refrigerant circuit as a cooling medium, eliminating the need for an additional cooling source and achieving resource recycling within the system. The outlet of the refrigerant pump 9 is connected to the inlet of the heat dissipation channel via a pipe, forming a refrigerant circulation path. This ensures that the refrigerant pumped by the refrigerant pump 9 can directly enter the heat dissipation channel to cool the inverter. The heat dissipation channel can be directly installed on the surface of the inverter's power module (such as IGBT) or main control chip, or integrated inside the inverter housing. It is in close contact with the heat-generating components through thermally conductive materials, ensuring that the heat dissipation channel can directly and effectively absorb the heat generated by the inverter, achieving near-source cooling. After absorbing heat from the inverter in the heat dissipation channel, the refrigerant carrying heat is returned to the main refrigerant circuit, thus achieving heat dissipation for the inverter.

[0119] Through the above technical solution, this application adds a refrigerant cooling circuit, specifically addressing the heat dissipation problem of the inverter in the magnetic levitation centrifugal compressor 1. The refrigerant pump 9 draws liquid refrigerant from the liquid refrigerant outlet of the condenser 2, utilizing the refrigerant circulating within the system as the cooling medium. This eliminates the need for external cooling resources, achieving a highly efficient and energy-saving heat source. The heat dissipation channel is directly located at the inverter, transferring heat from the inverter to the refrigerant through physical contact or thermal conduction, ensuring rapid heat absorption and removal. This design allows the heat generated by the inverter during wide-frequency adjustment to dissipate promptly, avoiding performance degradation or shutdown risks caused by overheating. This ensures the stable and continuous operation of the magnetic levitation centrifugal compressor 1 and the entire heat pump system, thereby improving the system's energy efficiency and reliability.

[0120] Furthermore, the concentration evaporation circuit also includes a split evaporation branch, which includes a split evaporator 11 and a connecting pipe. One end of the connecting pipe is connected to the gaseous working fluid output pipe of the concentration tank 5, and the other end is connected to the distillation tank 15 via the split evaporator 11. The split evaporator 11 is thermally coupled to the refrigerant circuit to condense the split gaseous working fluid, and a control valve 12 is provided on the split evaporation branch. The control system is also signal-connected to the control valve 12 and is configured to open the control valve 12 when the real-time evaporation amount is greater than the set value of the target evaporation amount.

[0121] Specifically, the branch evaporation system is an auxiliary piping system whose main function is to provide a backup path to handle a portion of the gaseous working fluid when the main evaporation process is overloaded. This branch typically consists of pipes, valves, and heat exchangers, designed to effectively divert and treat excess gaseous working fluid. This can be achieved by installing an independent bypass pipeline alongside the main evaporator 4, or by installing a branch pipeline at the gaseous outlet of the concentration tank 5. The branch evaporator 11 is the core heat exchange device in the branch evaporation system, used to condense the diverted gaseous working fluid. This evaporator can take various forms, such as plate heat exchangers, shell-and-tube heat exchangers, or spiral plate heat exchangers, with the selection depending on factors such as throughput, working fluid characteristics, and space constraints.

[0122] The connecting pipeline is responsible for guiding the gaseous working fluid from the concentrator 5 to the split evaporator 11 and transporting the condensed liquid to the collection unit. Its material and dimensions must meet the process fluid transport requirements. One end of the connecting pipeline is connected to the gaseous working fluid output pipeline of the concentrator 5, which is the main pipeline at the top of the concentrator 5 used to discharge the gaseous working fluid generated by evaporation. Connecting the connecting pipeline to this output pipeline ensures direct diversion from the source of the gaseous working fluid, preventing excessive accumulation of the gaseous working fluid in the main loop. This connection can be achieved through welding, flange connections, or threaded connections to ensure sealing and reliability. The other end of the connecting pipeline is connected to the distillation tank 15 via the split evaporator 11. The distillation tank 15 is used to collect the liquid distillate condensed by the split evaporator 11. The connecting pipeline connects the outlet of the split evaporator 11 to the collection unit, ensuring effective recovery of the condensed liquid. The distillation tank 15 can be a simple storage tank or a complex container with level control and discharge functions.

[0123] The split evaporator 11 is thermally coupled to the refrigerant circuit to condense the split gaseous working fluid. Thermal coupling refers to the establishment of a heat exchange relationship between the split evaporator 11 and the refrigerant circuit of the heat pump system. This means that the split evaporator 11 utilizes the cooling capacity provided by the refrigerant circuit to cool and condense the split gaseous working fluid. This thermal coupling can be achieved in various ways; for example, the split evaporator 11 can act as an auxiliary evaporator in the refrigerant circuit, or it can exchange heat with the low-temperature side of the refrigerant circuit through a separate heat exchanger. A control valve 12 is provided on the split evaporator branch. The control valve 12 is a flow control element installed on the split evaporator branch to precisely control or cut off the flow of the gaseous working fluid in the split branch. The control valve 12 can be an electric valve, a pneumatic valve, or a solenoid valve, and its type and size are selected according to the required control accuracy and flow range.

[0124] The control system is also connected to control valve 12 via signal. As the intelligent control core of the entire heat pump system, the control system is responsible for monitoring, analyzing, and issuing control commands. The signal connection to control valve 12 means that the control system establishes communication with control valve 12 through electrical signals or communication protocols, thereby enabling remote or automatic control of the opening, closing, or adjustment of control valve 12. This connection can be a hard-wired connection or a digital communication connection based on an industrial bus or Ethernet. The control system is configured to execute specific control logic, that is, when the monitored real-time evaporation exceeds the preset target evaporation, it automatically issues a command to open control valve 12 on the split evaporation branch. This configuration ensures that the system can adaptively activate the split mechanism according to changes in the actual operating load to maintain stable system operation. The real-time evaporation can be measured by a flow sensor, while the target evaporation is usually a parameter preset according to process requirements.

[0125] Through the above technical solution, when the real-time evaporation rate of the concentration evaporation circuit exceeds the set value of the target evaporation rate, the control system can respond promptly and control the opening of the control valve 12 on the split evaporation branch. At this time, some of the excess gaseous working fluid will be diverted to the split evaporator 11 through the connecting pipeline. The split evaporator 11 utilizes thermal coupling with the refrigerant circuit to effectively condense these diverted gaseous working fluids into liquid and transport them to the distillation tank 15. This mechanism effectively avoids system overload caused by excessive load in the main evaporation circuit, thereby preventing the compressor 1 from operating unstablely or experiencing reduced energy efficiency. At the same time, by condensing and recovering the diverted gaseous working fluid, not only is waste of the working fluid avoided, but the overall energy efficiency and economy of the system are further improved. This solution ensures that the heat pump system can maintain a highly efficient and stable operating state under dynamically changing evaporation loads, optimizes the working conditions of the compressor 1, and extends the service life of the equipment.

[0126] In a further embodiment, this application proposes that the concentration evaporation circuit also includes: a raw liquid supply unit 13, a distillation tank 15, and a concentrate discharge unit 16.

[0127] Specifically, the raw material supply unit 13 is used to supply the liquid to be processed to the concentration tank 5. This raw material supply unit 13 aims to ensure a continuous and stable material input during the concentration process, avoiding system downtime or efficiency fluctuations due to material interruptions. This can be achieved by including a storage tank, a transfer pump, and corresponding piping and valves, with the pump's start / stop and flow rate controlled by a level sensor or flow meter to achieve precise material supply. Alternatively, a gravity flow feeding system can be used, with automatic replenishment via a high-level tank and level control valves, or feeding can be achieved through a pressure vessel and differential pressure control.

[0128] The vacuum unit is connected to the concentration tank 5 to maintain its internal negative pressure environment. The function of this vacuum unit is to significantly lower the boiling point of the liquid under negative pressure, allowing evaporation to occur at lower temperatures, improving evaporation efficiency and reducing energy consumption. Maintaining a stable negative pressure environment also contributes to stable system operation. This vacuum unit may include a vacuum pump (e.g., a water ring vacuum pump, rotary vane vacuum pump, or Roots pump), a condenser (for condensing the extracted vapor, protecting the vacuum pump, and recovering the solvent), a buffer tank, and pressure sensors and control valves. Alternatively, a steam jet pump or a multi-stage vacuum pump assembly can be used, selected and configured according to the required vacuum level and throughput.

[0129] Distillation tank 15 is used to collect the distillate condensed by evaporator 4 and split evaporator 11. This collection unit aims to achieve effective recovery and utilization of the evaporation products, prevent mixing of the distillate and concentrate, and facilitate subsequent treatment or discharge. Distillation tank 15 may include one or more collection tanks, a level sensor, a transfer pump, and corresponding piping and valves. The pump's start and stop are controlled by the level to deliver the distillate to a designated location. Alternatively, a collection tank with automatic drainage function can be used to discharge the distillate by gravity or pressure difference, and a flow meter can be equipped for measurement.

[0130] The concentrate discharge unit 16 is used to discharge the concentrate in the concentration tank 5 when the liquid concentration reaches a set value or the evaporation rate is lower than a set value. This discharge unit ensures that the concentrate is removed at the optimal time, preventing over-concentration from causing scaling, blockage, or system instability, while maintaining the dynamic balance of the material in the concentration tank 5. The concentrate discharge unit 16 may include a discharge valve, a transfer pump (e.g., a screw pump or diaphragm pump, suitable for high-viscosity liquids), a concentrate storage tank, and corresponding piping and a concentration sensor or flow meter, triggering the discharge operation through a concentration or evaporation rate signal. Alternatively, a bottom discharge valve and gravity discharge may be used, or the concentrate may be pumped out by pressure difference, and an automatic cleaning function may be provided to prevent blockage.

[0131] Through the above technical solution, the concentration and evaporation loop of this application forms a complete and efficient closed-loop operating system by introducing a raw liquid supply unit 13, a vacuum unit, a distillation tank 15, and a concentrate discharge unit 16. The raw liquid supply unit 13 ensures the continuity and stability of the concentration process, avoiding efficiency decline due to material interruption. The vacuum unit, by maintaining a negative pressure environment within the concentration tank 5, significantly lowers the boiling point of the liquid, thereby achieving efficient evaporation at a lower temperature, improving the system's energy efficiency ratio, and reducing the load requirements on the heat pump system compressor 1. The distillation tank 15 effectively recovers the condensed pure distillate, realizing resource reuse or environmentally friendly discharge, avoiding waste. The concentrate discharge unit 16 intelligently discharges the concentrate according to its concentration or evaporation rate, preventing scaling, clogging, and other problems that may result from over-concentration, ensuring long-term stable operation and optimal concentration effect of the system. The coordinated work of these auxiliary units makes the entire concentration and evaporation process more automated, continuous, and efficient, significantly improving the overall operating efficiency and reliability of the system, and solving the problems of incomplete system operation and low efficiency.

[0132] The following example will provide a more detailed explanation of the above technical solution:

[0133] In an industrial concentration evaporation application scenario, a factory needs to concentrate a solution containing a specific solute. The factory employs a heat pump evaporation system, whose core components include a refrigerant circuit consisting of a magnetically levitated centrifugal compressor 1, a condenser 2, an expansion valve 3, and an evaporator 4, as well as a concentration evaporation circuit where a concentration tank 5 exchanges heat with the evaporator 4 and condenser 2. This system aims to achieve a highly efficient and energy-saving concentration process and address the dynamic load challenges posed by changes in solution concentration.

[0134] Upon system startup, the control system enters the startup phase. To prevent compressor 1 from triggering a protective shutdown due to low suction pressure under low load, the system initially controls compressor 1 to operate at an initial frequency of 30% of its rated frequency. Subsequently, the system gradually increases the operating frequency of compressor 1 in preset 30-second cycles, with each cycle increasing by 5% of the rated frequency. For example, from 30% to 35%, then to 40%, until the outlet temperature of condenser 2 or the heating medium temperature of the evaporation circuit reaches a preset first temperature threshold, such as 30°C. During this process, if the suction pressure of compressor 1 is detected to be lower than a second pressure threshold (e.g., 250 kPa), the system immediately opens the hot gas bypass valve connected between condenser 2 and evaporator 4 to stabilize the suction pressure, preventing compressor 1 from surging or shutting down, until the suction pressure recovers to above the second pressure threshold, ensuring a smooth system startup. This gradual startup strategy effectively avoids the problem of frequent shutdowns of compressor 1 due to startup shock or low-pressure protection under traditional control methods.

[0135] When the system enters the initial evaporation phase, the solution in the concentration tank 5 begins to evaporate rapidly. At this time, the control system uses a closed-loop control method to adjust the operating frequency of compressor 1, based on a preset target evaporation rate (e.g., 950 kg / hour). The system monitors the evaporation rate of the concentration evaporation loop in real time and precisely adjusts the frequency of compressor 1 according to the deviation between the real-time evaporation rate and the target evaporation rate, so that the real-time evaporation rate approaches the target evaporation rate. For example, if the real-time evaporation rate is lower than the target value, the frequency of compressor 1 is appropriately increased; if it is higher than the target value, the frequency is decreased. This ensures that the system can quickly and stably reach the preset evaporation load in the initial stage of evaporation, avoiding inefficiency caused by load fluctuations.

[0136] As the concentration process progresses, the solution concentration gradually increases, and the system enters the mid-evaporation stage. At this point, the boiling point of the solution rises, its fluidity decreases, and the heat transfer coefficient drops, leading to dynamic changes in the evaporation load. The control system continuously monitors the real-time evaporation rate of the concentration evaporation loop and the operating pressure ratio of compressor 1. To address the increased pressure ratio and decreased energy efficiency caused by the increased solution concentration, the system defines the target evaporation rate as Q, the real-time evaporation rate as F, and the operating pressure ratio as R. The system presets a series of flow rate thresholds Fn = Q × (1 - n × k), where n is a positive integer increasing from 1, and k is a decreasing percentage coefficient of 1%. Simultaneously, a series of pressure ratio thresholds Rn = R0 + n × m corresponding to the flow rate threshold Fn are set, where R0 is the base pressure ratio of 1.50, and m is the pressure ratio increment coefficient of 0.04. When the real-time evaporation rate F is lower than the currently determined flow threshold Fn (for example, when F is lower than Q×(1 - 1×1%) = 0.99Q), if the operating pressure ratio R is greater than the corresponding pressure ratio threshold Rn (for example, when R is greater than 1.50 + 1×0.04 = 1.54), the operating frequency of compressor 1 is reduced by a preset adjustment step, which is 1.5% of the current operating frequency. Through this refined segmented control logic, the system can dynamically adjust the frequency of compressor 1 according to the actual evaporation load and the operating efficiency of compressor 1, avoiding the problem of excessive pressure ratio and increased energy consumption caused by compressor 1 maintaining high frequency operation when the solution concentration is high and the heat transfer is poor, and significantly improving the energy efficiency of the system under variable load conditions. In addition, if the real-time evaporation rate is continuously greater than the target evaporation rate set value, the system will control the opening of the split evaporation branch, so that part of the gaseous working fluid is diverted to the split evaporator 11 for auxiliary heat exchange. The liquid condensed by the split evaporator 11 enters the distillation tank 15, thereby effectively handling the instantaneously high evaporation load and maintaining the stable operation of the system.

[0137] When the solution is concentrated to near its endpoint, the evaporation rate becomes very small, and the system enters the later stage of evaporation. At this point, the suction pressure of compressor 1 may drop sharply due to insufficient evaporation. To prevent compressor 1 from shutting down due to excessively low suction pressure, thus prematurely interrupting the concentration process, the control system continuously monitors the suction pressure of compressor 1. When the suction pressure falls below a preset first pressure threshold (e.g., 250 kPa), the system immediately opens the hot gas bypass valve connected between condenser 2 and evaporator 4. The opening of the hot gas bypass valve allows the high-temperature refrigerant from condenser 2 to bypass to the inlet side of evaporator 4, maintaining stable operation of compressor 1, extending the later stage of evaporation operation time, and ensuring the final concentration effect. This avoids the premature termination of the evaporation process due to low-pressure protection under traditional control.

[0138] In addition, to ensure the long-term stable operation of the frequency converter supporting the magnetic levitation centrifugal compressor 1, the system also includes a frequency converter heat dissipation control stage. The system monitors the temperature of the frequency converter that supplies power to the compressor 1 in real time. When the temperature of the frequency converter exceeds the second temperature threshold (e.g., 55 °C), the system starts the refrigerant pump 9 to extract the liquid refrigerant from the outlet of the condenser 2 and make it flow through the heat dissipation channel set for the frequency converter to cool it. This active cooling mechanism effectively solves the problem of insufficient heat dissipation of high-power frequency converters in high-temperature environments and ensures the reliable operation of the compressor 1.

[0139] The above are only the embodiments of the present application and are not used to limit the protection scope of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A segmented control method for a compressor in a heat pump system, characterized in that, The heat pump system includes a refrigerant circuit formed by a compressor (1), a condenser (2), an expansion valve (3), and an evaporator (4) connected by pipelines, and a condensing evaporation circuit that exchanges heat with the evaporator (4) and the condenser (2); the method includes the following control phases executed sequentially or switched according to operating conditions: Start-up phase: Control the compressor (1) to run at an initial frequency and gradually increase the operating frequency according to a preset cycle until the outlet temperature of the condenser (2) or the temperature of the heating medium of the concentration evaporation circuit reaches the first temperature threshold. Early stage of evaporation: Using the preset target evaporation amount as the set value, the operating frequency of the compressor (1) is adjusted by a closed-loop control method so that the real-time evaporation amount approaches the target evaporation amount; Mid-stage evaporation: Monitor the real-time evaporation rate of the concentration evaporation circuit and the operating pressure ratio of the compressor (1); When the real-time evaporation rate is lower than the first flow rate threshold set based on the decrease of the target evaporation rate, if the operating pressure ratio is higher than the corresponding first pressure ratio threshold, the operating frequency of the compressor (1) is reduced. Later stage of evaporation: When the suction pressure of the compressor (1) is detected to be lower than the first pressure threshold, the hot gas bypass valve connected between the condenser (2) and the evaporator (4) is opened to bypass part of the high-temperature refrigerant to the inlet of the evaporator (4) in order to maintain system operation.

2. The segmented control method for the compressor of the heat pump system according to claim 1, characterized in that, During the evaporation phase, the target evaporation rate is defined as Q, the real-time evaporation rate as F, and the operating pressure ratio as R. Set a series of traffic thresholds Fn = Q×(1 - n×k), where n is a positive integer starting from 1 and k is a preset decreasing percentage coefficient; Set a series of pressure ratio thresholds Rn = R0 + n×m corresponding to the flow rate threshold Fn, where R0 is a preset base pressure ratio and m is a preset pressure ratio increment coefficient; The following control logic is executed: when the real-time evaporation rate F is less than the currently determined flow threshold Fn, if the operating pressure ratio R is greater than the corresponding pressure ratio threshold Rn, the operating frequency of the compressor (1) is controlled to decrease by a preset adjustment step.

3. The method according to claim 2, characterized in that, The decreasing percentage coefficient k is 1%, the pressure ratio increment coefficient m is 0.04, the reference pressure ratio R0 is 1.50, and the adjustment step size is 1.5% of the current operating frequency.

4. The segmented control method for the compressor of the heat pump system according to claim 1, characterized in that, During the startup phase, the initial frequency is 30% of the rated frequency of the compressor (1), the preset cycle is 30 seconds, and the increase in the operating frequency in each cycle is 5% of the rated frequency.

5. The segmented control method for the compressor of the heat pump system according to claim 1, characterized in that, It also includes the inverter heat dissipation control stage: Monitor the temperature of the frequency converter that supplies power to the compressor (1); When the inverter temperature exceeds the second temperature threshold, the refrigerant pump (9) is started to draw liquid refrigerant from the outlet of the condenser (2) and flow through the heat dissipation channel provided for the inverter to cool it.

6. The segmented control method for the compressor of the heat pump system according to claim 1, characterized in that, During the startup phase, if the suction pressure of the compressor (1) is detected to be lower than the second pressure threshold during the frequency increase process, the hot gas bypass valve is opened until the suction pressure is restored to above the second pressure threshold.

7. The segmented control method for the compressor of the heat pump system according to any one of claims 1 to 6, characterized in that, Also includes: Monitor the real-time evaporation rate; When the real-time evaporation rate is greater than the set value of the target evaporation rate, the split evaporation branch is opened, so that part of the gaseous working fluid is diverted to the split evaporator (11) for auxiliary heat exchange, and the liquid condensed by the split evaporator (11) enters the distillation tank (15).

8. A heat pump system for concentration evaporation, used to implement the method as described in any one of claims 1 to 7, characterized in that, include: The refrigerant circuit is connected in sequence to the compressor (1), condenser (2), expansion valve (3) and evaporator (4) to form a closed loop; A concentration evaporation circuit includes a concentration tank (5) thermally coupled to an evaporator (4) to absorb heat from the gaseous working fluid generated by the evaporation of the liquid in the concentration tank (5) through the evaporator (4), and the concentration tank (5) is also thermally coupled to a condenser (2) to heat the liquid in the concentration tank (5) through the condensation heat released by the condenser (2) to achieve its continuous evaporation; A hot gas bypass pipeline is connected in the refrigerant circuit between the condenser (2) and the evaporator (4) to bypass the high-temperature refrigerant from the condenser (2) to the inlet side of the evaporator (4). A hot gas bypass valve is provided on the pipeline. The control system is signal-connected to the compressor (1) and the hot gas bypass valve and is configured to execute the segmented control method.

9. The heat pump system for concentration evaporation according to claim 8, characterized in that, The compressor (1) is a magnetic levitation centrifugal compressor.

10. The heat pump system for concentration evaporation according to claim 9, characterized in that, It also includes a refrigerant cooling circuit, which includes a refrigerant pump (9) and a heat dissipation channel. The inlet of the refrigerant pump (9) is connected to the liquid refrigerant outlet of the condenser (2), and the outlet is connected to the heat dissipation channel. The heat dissipation channel is located at the inverter of the compressor (1) for heat dissipation.

11. The heat pump system for concentration evaporation according to claim 8, characterized in that, The concentration evaporation circuit also includes a split evaporation branch, which includes a split evaporator (11) and a connecting pipe. One end of the connecting pipe is connected to the gas phase working fluid output pipe of the concentration tank (5), and the other end is connected to the distillation tank (15) via the split evaporator (11). The split evaporator (11) is thermally coupled to the refrigerant circuit to condense the split gas phase working fluid. A control valve (12) is provided on the split evaporation branch. The control system is also signal-connected to the control valve (12) and is configured to open the control valve (12) when the real-time evaporation amount is greater than the set value of the target evaporation amount.

12. The heat pump system for concentration evaporation according to claim 8, characterized in that, The concentration evaporation circuit also includes: The raw material supply unit (13) is used to supply the liquid to be processed to the concentration tank (5); A distillation vessel (15) is used to collect the distillate after it has been condensed by the evaporator (4) and the split evaporator (11); The concentrate discharge unit (16) is used to discharge the concentrate when the liquid concentration in the concentrate tank (5) reaches a set value or the evaporation rate is lower than a set value.

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