Anti-surge control method for energy storage heat management system of air flotation centrifugal compressor

Abstract

The invention relates to an anti-surge control method for an energy storage heat management system of an air-floating centrifugal compressor. The anti-surge control method comprises the following steps: customizing surge state judgment conditions of the air-floating centrifugal compressor; determining the current surge state of the air flotation centrifugal compressor according to the surge state judgment condition, wherein the surge state comprises a normal working area, a surge protection area and a surge area; a corresponding control strategy is adopted according to the surge state of the air flotation centrifugal compressor, and if the air flotation centrifugal compressor is located in the surge area, the compressor is closed; if the air flotation centrifugal compressor is in the surge protection area, the grade of triggering surge is further determined, if the grade of triggering surge is the first grade, the rotating speed of the fan, the rotating speed of the air flotation centrifugal compressor and the opening degree of the auxiliary throttling element are adjusted, and if the grade of triggering surge is the second grade, the rotating speed of the fan is adjusted. If yes, the rotating speed of the fan and the rotating speed of the air flotation centrifugal compressor are increased to the maximum value, and if the surge triggering grade is the third grade, the bypass valve is opened.

Description

Technical Field

[0001] The present invention relates to the technical field of heat management, and in particular to an anti-surge control method for an energy storage heat management system of an air-floating centrifugal compressor. Background Art

[0002] Thermal management is a rigid requirement for electrochemical energy storage, and has a significant impact on the performance, life, and safety of the energy storage system. The existing energy storage thermal management system uses a traditional positive displacement compressor, which has the following defects:

[0003] The low efficiency of traditional positive displacement compressors leads to low efficiency of the energy storage thermal management system. In order to meet the refrigeration needs of energy storage thermal management, high-power compressors or even two compressor systems are required.

[0004] The internal parts of traditional positive displacement compressors have friction during operation, and compressor oil is needed for lubrication and sealing, which reduces efficiency and reliability of system operation, and increases the cost of the compressor. Before starting at low temperature, the compressor needs to be heated to reduce the viscosity of the compressor oil. After the compressor oil enters the system, it dissolves with the refrigerant, affecting the heat exchange of the heat exchanger, which directly leads to a decrease in the cooling capacity of the system.

[0005] The traditional positive displacement compressors currently used in energy storage thermal management products cannot achieve the function of replenishing air and increasing enthalpy, and cannot further improve energy efficiency;

[0006] The compressor assembly has a large volume, which results in a larger overall volume of the integrated energy storage thermal management unit, thereby reducing the layout space of the energy storage battery.

[0007] Therefore, a thermal management system that uses air-floating centrifugal compressors instead of positive displacement compressors has emerged, but air-floating centrifugal compressors are prone to surge. The surge of fluid machinery will destroy the flow regularity of the medium inside the machine, generate mechanical noise, cause strong vibration of the working parts, accelerate the damage of bearings and seals, and once the surge causes resonance of the pipeline, machine and its foundation, it will also cause serious consequences.

[0008] At present, anti-surge control strategies are divided into the following two types:

[0009] Fixed limit flow anti-surge control strategy: The surge flow at the maximum speed and the highest temperature is used as the fixed limit flow, and the bypass valve is not opened when the suction flow is greater than the fixed limit flow. This strategy has a simple structure, low investment, and large capacity when the speed is changed. It is often used in occasions where the speed is constant, and its application range is not wide.

[0010] Variable limit flow anti-surge control strategy: The limit surge flow is calculated based on the anti-surge equation and the compressor, and the bypass valve is not opened when the suction flow is greater than the limit surge flow. This strategy and the fixed limit flow anti-surge control strategy both require the measurement of the refrigerant flow and the additional setting of a flow detection device, resulting in a high equipment cost for the thermal management system. Summary of the invention

[0011] In order to solve at least part of the above problems in the prior art, the present invention provides an anti-surge control method for an energy storage thermal management system of an air-floating centrifugal compressor, comprising:

[0012] Customize the surge state judgment conditions of the air-floating centrifugal compressor;

[0013] Determining a current surge state of the air-floating centrifugal compressor according to a surge state judgment condition, wherein the surge state includes being in a normal working area, being in a surge protection area, and being in a surge area; and

[0014] According to the surge state of the air-floating centrifugal compressor, the corresponding control strategy is adopted, among which:

[0015] If the air-floating centrifugal compressor is in the surge zone, shut down the compressor;

[0016] If the air-floating centrifugal compressor is in the surge protection zone, the level of surge triggering is further determined. If the level of surge triggering is level one, the fan speed, the air-floating centrifugal compressor speed and the auxiliary throttling element opening are adjusted. If the level of surge triggering is level two, the fan speed and the air-floating centrifugal compressor speed are increased to the maximum value. If the level of surge triggering is level three, the bypass valve is opened.

[0017] Furthermore, if the level of surge triggering is level one, the fan speed, the air-floating centrifugal compressor speed and the auxiliary throttling element opening are adjusted, including:

[0018] The cooling fan speed is increased to the base speed × safety factor;

[0019] If the auxiliary throttling element is in the closed state at this time, the auxiliary throttling element is forced to open;

[0020] The speed of the air-floating centrifugal compressor is increased over time at a fixed rate.

[0021] Furthermore, the self-defined surge state judgment condition of the air-floating centrifugal compressor includes selecting one or more of the compressor exhaust pressure fluctuation, the pressure ratio, and the compressor power fluctuation rate as the surge state judgment condition of the air-floating centrifugal compressor.

[0022] Furthermore, if only the compressor exhaust pressure fluctuation is used as the surge state judgment condition:

[0023] When the compressor exhaust pressure fluctuation Rp exceeds the surge exhaust pressure fluctuation Rp_max, it is determined that the air-floating centrifugal compressor has surged;

[0024] When the compressor exhaust pressure fluctuation Rp exceeds the critical exhaust pressure fluctuation Rp_max*A1 in the surge protection zone, that is, Rp_max*A 1≤Rp≤Rp_max, the air-floating centrifugal compressor is in the surge protection zone, where A1 is the surge protection coefficient of the exhaust pressure fluctuation;

[0025] When the compressor exhaust pressure fluctuation Rp<Rp_max*A1, the air-floating centrifugal compressor is in the normal working area.

[0026] Furthermore, if only the pressure ratio is used as the surge state judgment condition:

[0027] When the actual pressure ratio Pr exceeds the surge pressure ratio Pr_max, Pr>Pr_max, it is determined that the air-floating centrifugal compressor is in the surge zone;

[0028] When Pr_max*B1≤Pr≤Pr_max, the air-floating centrifugal compressor is in the surge protection zone, where B1 is the surge protection coefficient of the pressure ratio, and Pr_max*B1 is the critical pressure ratio of the surge protection zone;

[0029] When the actual pressure ratio Pr<Pr_max*B1, the air-floating centrifugal compressor is in the normal working area, where B1 is the surge protection coefficient of the pressure ratio.

[0030] Furthermore, if only the compressor power fluctuation rate is used as the surge state judgment condition:

[0031] When the compressor power fluctuation rate R exceeds the surge power fluctuation rate R_max, R>R_max, the air-floating centrifugal compressor is in the surge zone;

[0032] When R_max*C1≤R≤R_max, the air-floating centrifugal compressor enters the surge protection zone, C is the surge protection coefficient of the power fluctuation rate, and R_max*C1 is the critical power fluctuation rate of the surge protection zone;

[0033] When R<R_max*C1, the air-floating centrifugal compressor is in the normal working area.

[0034] Furthermore, the compressor exhaust pressure fluctuation, the pressure ratio, and the compressor power fluctuation rate are used as the surge state judgment conditions of the air-floating centrifugal compressor at the same time, wherein:

[0035] If the compressor exhaust pressure fluctuation Rp>Rp_max, and the pressure ratio Pr>Pr_max, and the compressor power fluctuation rate R>R_max, then it is determined that the air-floating centrifugal compressor is in the surge zone, Rp_max is the surge exhaust pressure fluctuation, Pr_max is the surge pressure ratio, and R_max is the surge power fluctuation rate;

[0036] When Rp_max*A1≤Rp≤Rp_max, and Pr_max*B1≤Pr≤Pr_max, and R_max*C1≤R≤R_max, the air-floating centrifugal compressor is in the surge protection zone, where A1 is the surge protection coefficient of the exhaust pressure fluctuation, Rp_max*A1 is the critical exhaust pressure fluctuation in the surge protection zone, B1 is the surge protection coefficient of the pressure ratio, Pr_max*B1 is the critical pressure ratio in the surge protection zone, C1 is the surge protection coefficient of the power fluctuation rate, and R_max*C1 is the critical power fluctuation rate in the surge protection zone.

[0037] Furthermore, when the air-floating centrifugal compressor is in the surge protection zone, the level of triggering surge is further determined, including:

[0038] When Rp_max*A1≤Rp<Rp_max*A2, and Pr_max*B1≤Pr<Pr_max*B2, and R_max*C1≤R<R_max*C2, it is determined that the level of triggering surge is level one;

[0039] When Rp_max*A2≤Rp<Rp_max*A3, and Pr_max*B2≤Pr<Pr_max*B3, and R_max*C2≤R<R_max*C3, it is determined that the level of triggering surge is level 2;

[0040] When Rp_max*A3≤Rp<Rp_max, and Pr_max*B3≤Pr<Pr_max, and R_max*C3≤R<R_max, the level of surge triggering is determined to be level three; among which A1<A2<A3, B1<B2<B3, C1<C2<C3, and the values ​​of A1, A2, A3, B1, B2, B3, C1, C2, and C3 are less than 1.

[0041] Furthermore, if the level of surge triggering is level one, adjusting the fan speed, the air-floating centrifugal compressor speed, and the auxiliary throttling element opening includes:

[0042] The cooling fan speed is increased to the base speed × safety factor;

[0043] If the auxiliary throttling element is in the closed state at this time, the auxiliary throttling element is forced to open;

[0044] Increase the speed of the air-floating centrifugal compressor at a fixed rate over time.

[0045] The present invention also provides an anti-surge control device for an air-floating centrifugal compressor energy storage thermal management system, comprising a controller configured to execute the anti-surge control method.

[0046] The present invention has at least the following beneficial effects: the present invention provides an anti-surge control method for an energy storage thermal management system of an air-floating centrifugal compressor, which uses the compressor exhaust pressure fluctuation, pressure ratio, and compressor power fluctuation to determine whether the compressor is surging, without the need to add a flow measurement device, thereby reducing costs; if the air-floating centrifugal compressor is surging, the air-floating centrifugal compressor is actively shut down; if the air-floating centrifugal compressor enters a surge protection zone, a series of measures are taken to make the air-floating centrifugal compressor leave the surge protection zone, thereby protecting the air-floating centrifugal compressor and extending the life of the air-floating centrifugal compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to further illustrate the above and other advantages and features of various embodiments of the present invention, a more specific description of various embodiments of the present invention will be presented with reference to the accompanying drawings. It will be understood that these drawings only depict typical embodiments of the present invention and are therefore not to be considered as limiting the scope thereof. In the accompanying drawings, for clarity, identical or corresponding parts will be represented by identical or similar reference numerals.

[0048] Figure 1 A schematic diagram of an air-floating centrifugal compressor energy storage thermal management system in one embodiment of the present invention is shown.

[0049] Figure 2 A flow chart for determining the minimum operating speed of a compressor in one embodiment of the present invention is shown.

[0050] Figure 3A and 3B A flow chart showing an anti-surge control method for an energy storage thermal management system for an air-floating centrifugal compressor in one embodiment of the present invention is shown.

[0051] Figures 4 to 6 The schematic diagrams of the structures of an air-floating centrifugal compressor according to an embodiment of the present invention are shown respectively.

[0052] Reference numerals: air-floating centrifugal compressor 1, exhaust temperature sensor 2, exhaust pressure sensor 3, bypass valve 4, condenser 5, ambient temperature sensor 6, fan 7, air supply pressure sensor 8, air supply temperature sensor 9, economizer 10, auxiliary throttling element 11, main throttling element 12, main line pressure sensor 13, main line temperature sensor 14, evaporator 15, suction pressure sensor 16, suction temperature sensor 17, water pump 18, water outlet temperature sensor 19, water outlet pressure sensor 20 , battery pack heat source 21, motor 100, air inlet 301, exhaust port 302, connecting pipe 303, rotor 101, stator 102, housing 103, air bearing 111, thrust plate 112, thrust bearing 113, first impeller 201, second impeller 202, first end cover 135, second end cover 136, first compression shell 131, second compression shell 132, first sealing ring 133, second sealing ring 134, air supply port 331, first locking nut 211, second locking nut 221. DETAILED DESCRIPTION

[0053] It should be noted that various components in the various drawings may be shown exaggeratedly for illustrative purposes and are not necessarily correct to scale.

[0054] In the present invention, each embodiment is only intended to illustrate the aspects of the present invention and should not be construed as limiting.

[0055] In the present invention, unless otherwise specified, the quantifiers "a", "an" and "an" do not exclude the presence of a plurality of elements.

[0056] It should also be pointed out that in the embodiments of the present invention, for the sake of clarity and simplicity, only a portion of the parts or components may be shown, but a person of ordinary skill in the art will understand that under the teachings of the present invention, required parts or components may be added as needed in specific scenarios.

[0057] It should also be pointed out that within the scope of the present invention, the terms "same", "equal", "equal to" and the like do not mean that the two values ​​are absolutely equal, but allow a certain reasonable error, that is, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0058] It should also be pointed out that in the description of the present invention, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than explicitly or implicitly indicating that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as explicitly or implicitly indicating relative importance.

[0059] In addition, the embodiments of the present invention describe the process steps in a specific order, but this is only for the convenience of distinguishing the steps, and does not limit the sequence of the steps. In different embodiments of the present invention, the sequence of the steps can be adjusted according to the adjustment of the process.

[0060] In view of the shortcomings of existing energy storage thermal management products, the present invention uses a high-speed air-floating centrifugal compressor as the power source of the refrigerant circuit, designs a high-efficiency energy storage thermal management system, and combines it with a unique control strategy to achieve the optimal energy storage thermal management solution.

[0061] Figure 1 A schematic diagram of an air-floating centrifugal compressor energy storage thermal management system in one embodiment of the present invention is shown.

[0062] like Figure 1 As shown, an air-floating centrifugal compressor energy storage thermal management system includes: a refrigeration circuit, which is configured to circulate a refrigerant; a heat exchange medium circuit, which is configured to circulate a heat exchange medium to cool a target device; a refrigeration system component, which is arranged on the refrigeration circuit. A heat exchange device, a part of the heat exchange device is connected to the refrigeration circuit, and the other part is connected to the heat exchange medium circuit. The heat exchange device is configured to transfer heat between the refrigeration circuit and the heat exchange medium circuit. The heat exchange device can be, for example, an evaporator 15. The evaporator 15 has a first fluid inlet, a first fluid outlet, a second fluid inlet, and a second fluid outlet. The target device is arranged on the heat exchange medium circuit, and the target device is a battery pack heat source 21.

[0063] The refrigeration system components include an air-floating centrifugal compressor 1, a bypass valve 4, a condenser 5, a fan 7, a main throttling element 12, an auxiliary throttling element 11, and an economizer 10. The throttling elements include an electronic expansion valve, a thermal expansion valve, a capillary tube, etc. The fan 7 is arranged on the condenser 5, and the fan 7 is used to ventilate and heat-exchange the high-temperature and high-pressure refrigerant to transfer the heat to the air. The two ends of the bypass valve 4 are respectively connected between the air inlet of the air-floating centrifugal compressor 1 and the first fluid outlet of the evaporator 15 and between the exhaust port of the air-floating centrifugal compressor 1 and the condenser 5. The input end of the bypass valve is connected to the evaporator 15, and the output end is connected to the condenser 5. The bypass valve 4 can be a solenoid valve.

[0064] The various components of the refrigeration system are connected by pipes (copper pipes), and the pipe diameter is matched according to the system flow, design pressure, and design temperature.

[0065] The refrigeration system components also include: an exhaust temperature sensor 2, an exhaust pressure sensor 3, an ambient temperature sensor 6, a make-up air pressure sensor 8, a make-up air temperature sensor 9, a main line pressure sensor 13, a main line temperature sensor 14, an intake pressure sensor 16, and an intake temperature sensor 17.

[0066] The exhaust temperature sensor 2 and the exhaust pressure sensor 3 are arranged at the exhaust port of the air-floating centrifugal compressor 1 .

[0067] The air supply pressure sensor 8 and the air supply temperature sensor 9 are arranged between the second output end of the economizer 10 and the air supply port of the air-floating centrifugal compressor 1 .

[0068] The main line pressure sensor 13 and the main line temperature sensor 14 are arranged between the output end of the main throttling element 12 and the first fluid inlet of the evaporator 15 .

[0069] A suction pressure sensor 16 and a suction temperature sensor 17 are disposed at the first fluid outlet of the evaporator 15 .

[0070] The ambient temperature sensor 6 is arranged at the air inlet of the fan 7. The ambient temperature sensor 6 is used to detect the temperature of the environment in which the thermal management system is located.

[0071] The above-mentioned thermal management system also includes a coolant system component, which is arranged in the heat exchange medium circuit and includes a water pump 18, a water outlet temperature sensor 19, and a water outlet pressure sensor 20.

[0072] The water outlet temperature sensor 19 and the water outlet pressure sensor 20 are arranged between the second fluid outlet of the evaporator 15 and the input end of the battery pack heat source 21 .

[0073] In the refrigeration circuit, the first fluid outlet of the evaporator 15 is connected to the air inlet of the air-floating centrifugal compressor 1 and the input end of the bypass valve 4 respectively; the exhaust port of the air-floating centrifugal compressor 1 is connected to the input end of the condenser 5, and the output end of the bypass valve 4 is connected to the input end of the condenser 5; the output end of the condenser 5 is connected to the first input end of the economizer 10, the first output end of the economizer 10 is connected to the input end of the main throttling element 12, and the output end of the main throttling element 12 is connected to the first fluid inlet of the evaporator 15; the first output end of the economizer 10 is also connected to the input end of the auxiliary throttling element 11, the output end of the auxiliary throttling element 11 is connected to the second input end of the economizer 10, and the second output end of the economizer 10 is connected to the air supply port of the air-floating centrifugal compressor 1; the second fluid outlet of the evaporator 15 is connected to the input end of the battery pack heat source 21, the output end of the battery pack heat source 21 is connected to the input end of the water pump 18, and the output end of the water pump 18 is connected to the second input end of the evaporator 15. The fan 7 is arranged on the condenser 5.

[0074] The air-floating centrifugal compressor 1 is used as the power source of the refrigerant in the system. The refrigerant is compressed by centrifugal means. The compressed high-temperature refrigerant reaches the condenser 5 through the pipeline. The fan 7 sucks the air at room temperature into the condenser fins. The condenser 5 exchanges the heat of the internal high-temperature refrigerant with the air. The condensed refrigerant reaches the main throttling element 12 and the auxiliary throttling element 11 through the pipeline. The main throttling element 12 and the auxiliary throttling element 11 throttle the refrigerant. The refrigerant throttled by the main throttling element 12 expands rapidly and enters the evaporator 15. In the evaporator 15, the throttled refrigerant absorbs heat from the heat exchange medium through the evaporator 15, so that the heat exchange medium is reduced to the expected temperature. The refrigerant after evaporation continues to reach the filter element through the pipeline. The filter element filters the impurities in the system, and the filtered refrigerant returns to the compressor again. Pressure and temperature sensors are installed on the outlet pipeline of the compressor and the outlet pipeline of the evaporator 15. The purpose of the sensor is to calculate the refrigeration demand of the system and protect the operation of the system.

[0075] When the unit is working, the refrigerant is discharged from the air-floating centrifugal compressor 1 as a high-temperature and high-pressure gas, condensed into a high-temperature and high-pressure liquid through the condenser 5, and then passed through the main throttling element 12 to become a low-temperature and low-pressure liquid, and then passed through the evaporator 15 to become a low-temperature and low-pressure gas and returned to the air-floating centrifugal compressor 1. In the air supply path, the refrigerant becomes a low-temperature and low-pressure liquid after passing through the auxiliary throttling element 11, and then becomes a low-temperature and low-pressure gas after passing through the evaporation side of the economizer 10 and is discharged into the air supply port of the air-floating centrifugal compressor 1. The bypass valve 4 directly connects the inlet and exhaust sides of the air-floating centrifugal compressor 1.

[0076] In the heat exchange medium circuit, the outlet of the water pump 18 is connected to the second fluid inlet of the evaporator 15, the second fluid outlet of the evaporator 15 is connected to the input end of the battery pack heat source 21, and the output end of the battery pack heat source is connected to the input end of the water pump. In the coolant circulation, the water pump 18 serves as the power source for the coolant circulation. The water pump is connected to the evaporator 15 through a water pipe, and sends the coolant into the evaporator 15 (in order to improve the heat exchange efficiency, in the evaporator 15, the coolant inflow direction is exactly opposite to the refrigerant inflow direction). After transferring the heat to the refrigerant, it enters the energy storage battery through the pipeline. In the energy storage battery, the heat generated by the battery cell is transferred to the coolant again, and the coolant returns to the water pump 18 again.

[0077] The energy storage thermal management system includes two parts: a refrigeration circuit and a heat exchange medium circuit. The two circuits exchange energy through a plate heat exchanger (evaporator 15), thereby achieving the purpose of cooling the coolant. The design of the refrigeration circuit and refrigeration system components is based on the characteristics of a small-capacity air-floating centrifugal compressor. The economizer is matched to replenish air to the compressor, increase the system's subcooling, reduce the power consumption of the compressor, and thus improve the overall energy efficiency. At the same time, considering that high-speed centrifugal compressors have surge phenomena, a bypass valve is added to bypass the compressor intake and exhaust, thereby achieving the purpose of preventing compressor surge.

[0078] Figures 4 to 6 The structural schematic diagrams of an air-floating centrifugal compressor according to an embodiment of the present invention are shown respectively. As shown in the figure, an air-floating centrifugal compressor comprises a motor 100, an impeller (201, 202), an air inlet 301, an exhaust port 302 and a connecting pipe 303.

[0079] The motor 100 includes a rotor 101, a stator 102 and a housing 103. The stator 102 is fixed inside the housing 103, and the central axis of the rotor 101 coincides with the central axis of the stator 102. Two radial air bearings 111 are provided on the rotor 101, and a thrust disk 112 is provided on the side close to the air inlet 301, and an air-floating thrust bearing 113 is provided on both sides of the thrust disk, respectively. The two thrust bearings are arranged opposite to each other to bear the axial thrust directed to the low-pressure side or the high-pressure side respectively.

[0080] As shown in the figure, the first chamber and the second chamber are respectively arranged at the two ends of the interior of the housing 103. The air inlet of the first chamber is connected to the air inlet 301 of the compressor, and it can also be understood that the air inlet 301 is the air inlet of the first chamber. The first impeller 201 is arranged in the first chamber, and the first impeller 201 is fixed to the first end of the rotor 101. A connecting pipe 303 is arranged between the first chamber and the second chamber. The gas compressed by the first impeller 201 flows out from the air outlet of the first chamber and enters the connecting pipe 303, and then enters the second chamber through the air inlet of the second chamber. The second chamber is provided with a second impeller 202, and the second impeller 202 is fixed to the second end of the rotor 101. Most of the gas compressed by the second impeller 202 flows out from the air outlet of the second chamber. The air outlet of the second chamber is connected to the exhaust port 302 of the compressor, and it can also be understood that the exhaust port 302 is the air outlet of the second chamber. As shown in the figure, in an embodiment of the present invention, the first chamber and the second chamber are respectively provided with a first end cover 135 and a second end cover 136 at the air outlet, and there is a gap between the first end cover 135 and the second end cover 136 and the rotor 101. At the same time, there is a certain gap between the first end cover 135 and the first impeller 201, and the gas flowing through the air bearing can return to the main gas path through this gap. There is also a certain gap between the second end cover 136 and the second impeller 202, and a part of the gas compressed by the second impeller 202 can enter the air bearing through this gap under the action of pressure. In one embodiment of the present invention, the first impeller 201 and the second impeller 202 are both closed impellers. Compared with the open impeller, the closed impeller can effectively eliminate the secondary flow from the pressure surface of the blade to the suction surface caused by the tip clearance, thereby effectively improving the aerodynamic efficiency of the compressor. In one embodiment of the present invention, as shown above, the first impeller 201 and the second impeller 202 are designed back to back, so that the axial thrusts of the first and second impellers are in opposite directions and cancel each other out, thereby effectively reducing the axial thrusts received by the thrust bearing. In one embodiment of the present invention, the first impeller 201 and the second impeller 202 are fixed to the rotor 101 by a first locking nut 211 and a second locking nut 221, respectively.

[0081] As shown in the figure, a first compression shell 131 and a second compression shell 132 are respectively provided on the outer sides of both ends of the motor, a first sealing ring 133 is provided between the first compression shell 131 and the first impeller 201, and a second sealing ring 134 is provided between the second compression shell 132 and the second impeller 202. The first and second sealing rings can significantly reduce the backflow effect from the outlet to the inlet of the first and second impellers, and can further improve the efficiency of the compressor.

[0082] In order to reduce the compression power consumption of the second impeller 202, in one embodiment of the present invention, an air supply port 331 is further provided on the connecting pipe 303 to receive the exhaust gas from the economizer to cool the gas compressed by the first impeller, thereby achieving the purpose of reducing the compression power consumption of the high-pressure impeller and improving the efficiency of the system.

[0083] In one embodiment of the present invention, the motor 100 adopts a high-speed permanent magnet synchronous motor, and its bearings are non-contact bearings when working, so it can withstand a higher speed than ordinary ball bearings. According to the Euler formula of the compressor Δh=U2Cu2-U1Cu1, it can be known that for compressors with the same functional capacity, the greater the speed, the smaller the radial size, so the use of a permanent magnet synchronous motor can improve the power density of the compressor.

[0084] The working principle of the air-floating centrifugal compressor as described above is that the gas compressed by the second impeller enters the second radial bearing on the high-pressure side through the gap between the second impeller and the second end cover, and the gap between the second end cover and the rotor, and then enters the first radial bearing on the low-pressure side through the air gap between the stator and the rotor, and then passes through the gap between the thrust plate and the motor housing and the gap between the thrust plate and the first end cover in sequence. Pass through the two thrust bearings, and finally pass through the gap between the first end cover and the rotor, and the gap between the first impeller and the first end cover in sequence to enter the first chamber, that is, the exhaust port of the first impeller, and return to the main gas path to achieve internal circulation. Compared with the static pressure air-floating bearing, the air-floating centrifugal compressor can omit the external air supply channel, simplify the system structure, and improve reliability. In the embodiment of the present invention, the term "main gas path" refers to the gas flow path where the gas enters the compressor along the air inlet and is compressed, and then is discharged through the exhaust port. The term "high-pressure side" refers to the side with higher air pressure inside the compressor, and the term "low-pressure side" refers to the side of the compressor relative to the high-pressure side. Under normal circumstances, the gas flows from the high-pressure side to the low-pressure side through the air-floating bearing and then returns to the main gas path.

[0085] The air-floating centrifugal compressor is small in size. Under the same cooling capacity, the ultra-high-speed air-floating centrifugal compressor has a volume reduction of about 50% and a weight reduction of about 90% compared to the scroll compressor. More energy storage batteries can be arranged in a container of the same size.

[0086] The air-floating centrifugal compressor uses air-floating bearings, which do not require oil lubrication. When the air-floating bearings are working, the rotating shaft does not contact the bearings, but relies on the air film to suspend the motor rotor, which can increase the system's operating life by more than 1 times and improve the reliability of the energy storage system.

[0087] The air-floating centrifugal compressor eliminates the need for oil return piping and electric heating, reducing the cost of the structure and the compressor.

[0088] The air-floating centrifugal compressor uses air-floating bearings and does not use compressor oil, which improves the heat exchange efficiency of the heat exchanger and thus increases the cooling capacity of the system.

[0089] The two-stage compression air-floating centrifugal compressor adopts the method of intermediate air replenishment, which improves the system subcooling, reduces the power consumption of the compressor, and thus improves the overall energy efficiency of the energy storage thermal management system.

[0090] The thermal management system of the present invention adopts an air-floating centrifugal compressor as the core component of the refrigeration system. Compared with the traditional electric scroll compressor, it is small in size, light in weight, does not require compressor oil, has high compressor and system reliability, and has a large system refrigeration capacity.

[0091] Figure 2 A flow chart for determining the minimum operating speed of a compressor in one embodiment of the present invention is shown.

[0092] like Figure 2 As shown, according to the ambient temperature, water outlet temperature, water pump speed, fan speed, and based on the compressor surge line, the minimum operating speed of the compressor is determined, and the compressor speed is ensured not to be lower than the minimum operating speed of the compressor during the operation of the compressor.

[0093] Calculation method for minimum operating speed: Calculate the minimum pressure ratio of the compressor based on the ambient temperature, fan speed, water outlet temperature, and water pump speed. Calculate the minimum operating speed based on the minimum pressure ratio and the compressor surge line equation.

[0094] Figure 3A and 3B A flow chart showing an anti-surge control method for an energy storage thermal management system for an air-floating centrifugal compressor in one embodiment of the present invention is shown.

[0095] Surge is a common problem that centrifugal compressors are prone to. The operating conditions of centrifugal compressors deviate from the design conditions, resulting in a decrease in inlet flow, which changes the direction of the airflow in the impeller, diffuser and other parts of the compressor, causing the airflow to rotate and detach on the non-working surface of the blade, making it impossible for the airflow in the impeller channel to pass. Under this condition, the compressor outlet pressure and the pressure of the pipeline network that works in conjunction with the compressor will fluctuate unstably, causing the compressor outlet gas to repeatedly flow back, which is the "surge" phenomenon.

[0096] The present invention provides an anti-surge control method for an energy storage thermal management system of an air-floating centrifugal compressor. It does not require the addition of a flow measurement device. It performs calculation analysis through signals such as compressor power, suction and exhaust pressure, and obtains compressor exhaust pressure fluctuations, pressure ratios, and compressor power fluctuations, thereby determining whether the compressor is surging. If the air-floating centrifugal compressor is surging, the air-floating centrifugal compressor is actively shut down. If the air-floating centrifugal compressor enters a surge protection zone, a series of measures are taken to make the air-floating centrifugal compressor leave the surge protection zone. The exhaust pressure can be detected by an exhaust pressure sensor, the pressure ratio can be calculated by the exhaust pressure and the suction pressure, the exhaust pressure and the suction pressure can be obtained using an exhaust pressure sensor and a suction pressure sensor, the compressor power can be calculated by the compressor voltage and current, and the surge determination only needs to be based on the sensors used in conventional thermal management systems, and no additional flow measurement device is required.

[0097] The anti-surge control method is described in detail below. Figure 3A As shown, an anti-surge control method for an air-floating centrifugal compressor energy storage thermal management system comprises the following steps:

[0098] Step 1: Customize the surge state judgment condition of the air-floating centrifugal compressor.

[0099] Step 2: determining the current surge state of the air-floating centrifugal compressor according to the surge state judgment condition, wherein the surge state includes being in a normal working area, in a surge protection area, and in a surge area.

[0100] Step 3, adopting a corresponding control strategy according to the surge state of the air-floating centrifugal compressor, wherein: if the air-floating centrifugal compressor is in the surge zone, shut down the compressor; if the air-floating centrifugal compressor is in the surge protection zone, further determine the level of triggering surge, if the level of triggering surge is level one, adjust the fan speed and the speed of the air-floating centrifugal compressor and the opening of the auxiliary throttling element; if the level of triggering surge is level two, increase the fan speed and the speed of the air-floating centrifugal compressor to the maximum value; if the level of triggering surge is level three, open the bypass valve.

[0101] The level of triggering surge is to classify the surge protection zone according to the distance from the surge zone. The farthest from the surge zone is level one, the closest is level three, and the middle is level two.

[0102] The above steps are described in detail below. First, the method of determining the surge state of the compressor is introduced.

[0103] 1. Compressor exhaust pressure fluctuation. Exhaust pressure fluctuation is the rate of change of exhaust pressure per unit time. When the air-floating centrifugal compressor is running under stable conditions, the exhaust pressure does not change much, and the fluctuation range is very small. When it approaches or enters surge conditions, the exhaust pressure will pulsate periodically and significantly.

[0104] When the compressor exhaust pressure fluctuation Rp exceeds the surge exhaust pressure fluctuation Rp_max, it can be determined that the air-floating centrifugal compressor has surged.

[0105] The critical exhaust pressure fluctuation in the surge protection zone is Rp_max*A1, where A1 is the surge protection coefficient of the exhaust pressure fluctuation. When Rp_max*A1≤Rp≤Rp_max, the air-floating centrifugal compressor is in the surge protection zone. When Rp<Rp_max*A1, the air-floating centrifugal compressor is in the normal working zone.

[0106] The protection factor A1 is obtained based on the compressor test data and is directly related to the compressor. The A1 value will vary for different compressors.

[0107] 2. Pressure ratio (exhaust pressure ÷ suction pressure). The surge pressure ratio Pr_max can be calculated based on the current air-floating centrifugal compressor speed, main valve opening, fan speed and suction and exhaust temperature. The surge pressure ratio is the surge line, and the required parameters are the compressor speed and suction and exhaust pressure (i.e., pressure ratio).

[0108] The actual pressure ratio Pr can be calculated based on the compressor inlet and outlet saturation pressures. The actual pressure ratio Pr is the absolute value of the exhaust pressure divided by the absolute value of the suction pressure. When the actual pressure ratio Pr exceeds the surge pressure ratio Pr_max, Pr>Pr_max, it is determined that the air-floating centrifugal compressor has surged. When Pr_max*B1≤Pr≤Pr_max (B1 is the surge protection coefficient of the pressure ratio, and Pr_max*B1 is the critical pressure ratio of the surge protection zone), the air-floating centrifugal compressor is in the surge protection zone. When Pr<Pr_max*B1, the air-floating centrifugal compressor is in the normal working area.

[0109] The protection factor B1 is obtained based on the compressor test data and is directly related to the compressor. The B1 value will vary for different compressors.

[0110] 3. Compressor power (or current) fluctuation rate: Compressor power fluctuation rate R = (maximum power - minimum power) / average power.

[0111] The surge power fluctuation rate is R_max. When the compressor power fluctuation rate R>R_max, the air-floating centrifugal compressor has surged. The compressor power (or current) can be obtained through detection. Generally, the compressor controller detects it internally and sends it to the controller through CAN, RS485 and other communications. The controller calculates the fluctuation based on the power (current). Fluctuation = 2*(maximum value-minimum value) / (maximum value+minimum value). The maximum and minimum values ​​are within the defined time and are related to the detection cycle.

[0112] When R_max*C1≤R≤R_max (C1 is the surge protection coefficient of power fluctuation rate, R_max*C1 is the critical power fluctuation rate of surge protection zone), the air-floating centrifugal compressor enters the surge protection zone. When R<R_max*C1, the air-floating centrifugal compressor is in the normal working zone.

[0113] The protection factor C1 is obtained based on the compressor test data and is directly related to the compressor. Different compressors will have different C1 values.

[0114] In order to prevent the air-floating centrifugal compressor from entering the surge zone and causing irreversible damage to the air-floating centrifugal compressor, the system operation is actively intervened when the air-floating centrifugal compressor enters the surge protection zone, and the air-floating centrifugal compressor is actively shut down after entering the surge zone.

[0115] The above three conditions for judging surge can be used as the judgment conditions of surge separately, or two or three of the compressor exhaust pressure fluctuation, pressure ratio, and compressor power (or current) fluctuation rate can be combined as the judgment conditions of surge. The selection is based on the complexity of the system working environment. If the system operating environment is more complex, more surge judgment conditions are required.

[0116] In order to prevent the air-floating centrifugal compressor from entering the surge state, when the compressor is about to enter the surge state and is in the surge protection zone, the compressor is kept away from the surge state by increasing the speed of the cooling fan, increasing the speed of the air-floating centrifugal compressor, intervening the opening of the auxiliary valve (auxiliary throttling element), opening the bypass valve, etc. The following is a specific strategy example, which determines the surge by the fluctuation rate of the compressor exhaust pressure, the pressure ratio, and the fluctuation rate of the compressor power (or current). Now it is explained in detail. There will be differences between the actual project and the example.

[0117] In one embodiment of the present invention, the compressor exhaust pressure fluctuation, the pressure ratio and the compressor power (or current) fluctuation rate are used as the judgment conditions of the surge state.

[0118] If Rp>Rp_max, and Pr>Pr_max, and R>R_max, it is determined that the air-floating centrifugal compressor enters the surge state. When the compressor is determined to enter the surge state, the compressor is stopped immediately to protect the long-term normal operation of the compressor.

[0119] like Figure 3BAs shown, when the fluctuation rate of the compressor exhaust pressure, pressure, and compressor power (or current) fluctuation rate are close to the surge point (in the surge protection zone), the system operation state is actively adjusted in a graded manner to keep the system away from the surge state. Through the parameters A1, A2, A3, B1, B2, B3, C1, C2, and C3, the level of triggering surge is divided into one, two, and three levels, among which A1<A2<A3, B1<B2<B3, and C1<C2<C3. The values ​​of A1, A2, A3, B1, B2, B3, C1, C2, and C3 are less than 1.

[0120] When Rp_max*A1≤Rp<Rp_max*A2, and Pr_max*B1≤Pr<Pr_max*B2, and R_max*C1≤R<R_max*C2, the level of surge triggering is determined to be level one, and the air-floating centrifugal compressor is freed from surge by simultaneously executing three methods: actively increasing the fan speed, intervening in the opening of the auxiliary throttling element, and increasing the compressor speed.

[0121] The cooling fan speed is increased to the base speed × safety factor, and the system is out of surge by improving the cooling heat exchange. The base speed refers to the fan speed when entering the surge protection zone, and the safety factor is 1 to 2.

[0122] Auxiliary throttling element opening intervention: If the auxiliary throttling element is in the closed state at this time, the auxiliary throttling element will be forced to open, and the exhaust temperature and pressure of the air-floating centrifugal compressor will be reduced by diverting part of the refrigerant to the first and second stage connecting pipes of the compressor, so that the air-floating centrifugal compressor can be out of surge. If the auxiliary throttling element is in the open state, the opening will be controlled by superheat to ensure that no liquid enters the compressor. Generally, the auxiliary throttling element opening is adjusted to control the air supply superheat in the range of 1 to 8k.

[0123] High speed can carry a larger load, allowing the air-floating centrifugal compressor to escape from surge. Generally, the speed increases over time at a fixed ratio. For example, within 1 second, the speed of the air-floating centrifugal compressor increases by 2%.

[0124] When Rp_max*A2≤Rp<Rp_max*A3, and Pr_max*B2≤Pr<Pr_max*B3, and R_max*C2≤R<R_max*C3, it is determined that the level of surge triggering is level 2, and the fan speed and the speed of the air-floating centrifugal compressor are directly increased to the maximum value.

[0125] When Rp_max*A3≤Rp<Rp_max, and Pr_max*B3≤Pr<Pr_max, and R_max*C3≤R<R_max, it is determined that the level of surge triggering is level three, and the bypass valve is opened to directly bypass the compressor suction and exhaust, so that the compressor is out of surge.

[0126] In other embodiments of the present invention, one or two of the compressor exhaust pressure fluctuation, pressure ratio and compressor power (or current) fluctuation rate are defined as conditions for judging the surge state. If the conditions are met, it is determined that the compressor enters the surge state. The specific definition is based on the degree of responsibility of the system working environment.

[0127] For the energy storage thermal management system of the centrifugal compressor, an anti-surge control strategy is formulated to ensure that the compressor operates stably within the controllable speed range. Through a series of actions, the unit is taken out of the surge working area to ensure the continuous and stable operation of the thermal management unit, avoiding damage to the thermal management unit and container due to surge;

[0128] The anti-surge strategy is implemented by monitoring and calculating the compressor voltage, current, inlet and outlet pressures, etc. to determine the compressor surge condition, without adding a flow test device to the thermal management unit.

[0129] The present invention also provides an anti-surge control device for an air-floating centrifugal compressor energy storage thermal management system, comprising: a controller configured to execute an anti-surge control method for the air-floating centrifugal compressor energy storage thermal management system.

[0130] Although some embodiments of the present invention have been described in this application document, it will be appreciated by those skilled in the art that these embodiments are merely shown as examples. Those skilled in the art may conceive of numerous variations, alternatives, and improvements under the teachings of the present invention without departing from the scope of the present invention. The appended claims are intended to define the scope of the present invention and to cover methods and structures within the scope of these claims themselves and their equivalents.

Claims

1. An anti-surge control method for an air-floating centrifugal compressor energy storage thermal management system, characterized in that: include: Customize the surge state judgment conditions of the air-floating centrifugal compressor; Determining the current surge state of the air-floating centrifugal compressor according to the surge state judgment condition, wherein the surge state includes being in a normal working area, being in a surge protection area, and being in a surge area; as well as According to the surge state of the air-floating centrifugal compressor, the corresponding control strategy is adopted, among which: If the air-floating centrifugal compressor is in the surge zone, shut down the compressor; If the air-floating centrifugal compressor is in the surge protection zone, the level of surge triggering is further determined. If the level of surge triggering is level one, the fan speed, the air-floating centrifugal compressor speed and the auxiliary throttling element opening are adjusted. If the level of surge triggering is level two, the fan speed and the air-floating centrifugal compressor speed are increased to the maximum value. If the level of surge triggering is level three, the bypass valve is opened.

2. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 1, characterized in that: If the level of surge triggering is level 1, adjust the fan speed, air-floating centrifugal compressor speed and auxiliary throttling element opening, including: The cooling fan speed is increased to the base speed × safety factor; If the auxiliary throttling element is in the closed state at this time, the auxiliary throttling element is forced to open; The speed of the air-floating centrifugal compressor is increased over time at a fixed rate.

3. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 1, characterized in that: The custom surge state judgment condition of the air-floating centrifugal compressor includes selecting one or more of the compressor exhaust pressure fluctuation, the pressure ratio, and the compressor power fluctuation rate as the surge state judgment condition of the air-floating centrifugal compressor.

4. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 3, characterized in that: If only the compressor exhaust pressure fluctuation is used as the surge state judgment condition: When the compressor exhaust pressure fluctuation Rp exceeds the surge exhaust pressure fluctuation Rp_max, it is determined that the air-floating centrifugal compressor has surged; When the compressor exhaust pressure fluctuation Rp exceeds the critical exhaust pressure fluctuation Rp_max*A1 in the surge protection zone, that is, Rp_max*A 1≤Rp≤Rp_max, the air-floating centrifugal compressor is in the surge protection zone, where A1 is the surge protection coefficient of the exhaust pressure fluctuation; When the compressor exhaust pressure fluctuation Rp<Rp_max*A1, the air-floating centrifugal compressor is in the normal working area.

5. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 3, characterized in that: If only the pressure ratio is used as the surge state judgment condition: When the actual pressure ratio Pr exceeds the surge pressure ratio Pr_max, Pr>Pr_max, it is determined that the air-floating centrifugal compressor is in the surge zone; When Pr_max*B1≤Pr≤Pr_max, the air-floating centrifugal compressor is in the surge protection zone, where B1 is the surge protection coefficient of the pressure ratio, and Pr_max*B1 is the critical pressure ratio of the surge protection zone; When the actual pressure ratio Pr<Pr_max*B1, the air-floating centrifugal compressor is in the normal working area, where B1 is the surge protection coefficient of the pressure ratio.

6. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 3, characterized in that: If only the compressor power fluctuation rate is used as the surge state judgment condition: When the compressor power fluctuation rate R exceeds the surge power fluctuation rate R_max, R>R_max, the air-floating centrifugal compressor is in the surge zone; When R_max*C1≤R≤R_max, the air-floating centrifugal compressor enters the surge protection zone, C1 is the surge protection coefficient of the power fluctuation rate, and R_max*C1 is the critical power fluctuation rate of the surge protection zone; When R<R_max*C1, the air-floating centrifugal compressor is in the normal working area.

7. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 3, characterized in that: At the same time, the compressor exhaust pressure fluctuation, pressure ratio, and compressor power fluctuation rate are used as the surge state judgment conditions of the air-floating centrifugal compressor, among which: If the compressor exhaust pressure fluctuation Rp>Rp_max, and the pressure ratio Pr>Pr_max, and the compressor power fluctuation rate R>R_max, then it is determined that the air-floating centrifugal compressor is in the surge zone, Rp_max is the surge exhaust pressure fluctuation, Pr_max is the surge pressure ratio, and R_max is the surge power fluctuation rate; When Rp_max*A1≤Rp≤Rp_max, and Pr_max*B1≤Pr≤Pr_max, and R_max*C1≤R≤R_max, the air-floating centrifugal compressor is in the surge protection zone, where A1 is the surge protection coefficient of the exhaust pressure fluctuation, Rp_max*A1 is the critical exhaust pressure fluctuation in the surge protection zone, B1 is the surge protection coefficient of the pressure ratio, Pr_max*B1 is the critical pressure ratio in the surge protection zone, C1 is the surge protection coefficient of the power fluctuation rate, and R_max*C1 is the critical power fluctuation rate in the surge protection zone.

8. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 7, characterized in that: When the air-floating centrifugal compressor is in the surge protection zone, the level of triggering surge is further determined, including: When Rp_max*A1≤Rp<Rp_max*A2, and Pr_max*B1≤Pr<Pr_max*B2, and R_max*C1≤R<R_max*C2, it is determined that the level of triggering surge is level one; When Rp_max*A2≤Rp<Rp_max*A3, and Pr_max*B2≤Pr<Pr_max*B3, and R_max*C2≤R<R_max*C3, it is determined that the level of triggering surge is level 2; When Rp_max*A3≤Rp<Rp_max, and Pr_max*B3≤Pr<Pr_max, and R_max*C3≤R<R_max, the level of surge triggering is determined to be level three; among which A1<A2<A3, B1<B2<B3, C1<C2<C3, and the values ​​of A1, A2, A3, B1, B2, B3, C1, C2, and C3 are less than 1.

9. The anti-surge control method of the air-floating centrifugal compressor energy storage thermal management system according to claim 8, characterized in that: If the level of surge triggering is level 1, the fan speed, air-floating centrifugal compressor speed and auxiliary throttling element opening are adjusted as follows: The cooling fan speed is increased to the base speed × safety factor; If the auxiliary throttling element is in the closed state at this time, the auxiliary throttling element is forced to open; The speed of the air-floating centrifugal compressor is increased over time at a fixed rate.

10. An anti-surge control device for an energy storage thermal management system of an air-floating centrifugal compressor, comprising a controller configured to execute the method according to claims 1 to 9.

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