Control system of ultra-low temperature mining heat pump hot air unit

Abstract

The control system of the ultra-low temperature mining heat pump hot air unit of the present invention relates to the field of heat pump technology, and in particular to a control system of an ultra-low temperature mining heat pump hot air unit suitable for mine ventilation and heating needs in severe cold environments. The present invention is composed of an indoor unit and an outdoor unit integrated on a base, wherein the indoor unit includes a preheating electric heating device, a dual evaporator system, a main electric heating device and a variable frequency air blower; the outdoor unit is equipped with four compressors and a superheat control system, wherein the first evaporator adopts a six-column structure to connect to compressor A / B, and the second evaporator adopts an eight-column structure to connect to compressor C / D. Two innovative intelligent control strategies are proposed: in stand-alone mode, the preheating mechanism is switched according to the ‑12°C threshold, and precise temperature control is achieved through superheat regulation and variable frequency air supply; the online mode adopts a three-level progressive load distribution, and the sequential activation of the multi-unit evaporator system and the supplementary intervention of the main electric heating are achieved through the cascade start-up strategy of the unit group.

Description

Technical Field

[0001] The invention discloses a control system for an ultra-low temperature mining heat pump hot air unit, which relates to the technical field of heat pumps, and in particular to a control system for an ultra-low temperature mining heat pump hot air unit suitable for mine ventilation and heating needs in severe cold environments. Background Art

[0002] In mines in extremely cold regions, ventilation and heating requirements are particularly important. As the temperature drops, the energy efficiency and heating capacity of traditional heat pump systems will drop significantly, and it may even be difficult to start and maintain normal operation. In order to provide reliable heating effects in extreme environments, heat pump systems often need to be combined with electric heating devices. However, the use of electric heating devices will significantly increase energy consumption, so how to reduce energy consumption as much as possible while ensuring heating effects has become an important research topic.

[0003] In view of the problems existing in the above-mentioned prior art, it is very necessary to study and design a new control system for ultra-low temperature mining heat pump hot air unit to overcome the problems existing in the prior art. Summary of the invention

[0004] According to the technical problem that the traditional heat pump system proposed in the prior art uses an electric heating device to start and maintain normal operation, which significantly increases energy consumption, a control system for an ultra-low temperature mining heat pump hot air unit is provided. The present invention uses a reasonable control strategy to minimize energy consumption while ensuring the heating effect.

[0005] The technical means adopted by the present invention are as follows:

[0006] The control system of the ultra-low temperature mining heat pump hot air unit includes: indoor unit and outdoor unit integrated on the same base;

[0007] Further, the indoor unit comprises a preheating electric heating device, a first evaporator, a second evaporator, a main electric heating device and a variable frequency blower arranged in sequence along the air supply direction;

[0008] Further, the outdoor unit includes compressor A, compressor B, compressor C, compressor D and a superheat control system;

[0009] Further, the first evaporator is a six-row structure, connected to compressor A and compressor B respectively;

[0010] Further, the second evaporator is an eight-row structure, connected to compressor C and compressor D respectively;

[0011] Furthermore, the main electric heating device adopts a three-level seven-segment adjustable structure, providing seven power output modes through a three-level energy module combination;

[0012] Furthermore, the superheat control system adjusts the operating state of the compressor by measuring the difference between the suction temperature and the suction saturation temperature converted by the pressure sensor.

[0013] Furthermore, the start-up of the preheating electric heating device must meet the following conditions at the same time:

[0014] a) The unit is in standby mode;

[0015] b) The ambient temperature is lower than -12°C;

[0016] It is used to quickly increase the temperature on the air inlet side of the evaporator to establish a pressure difference between indoors and outdoors.

[0017] Furthermore, the first evaporator is arranged upstream of the air inlet of the second evaporator, and uses low-temperature inlet air to achieve a lower evaporation pressure. Its designed COP value is 12-18% higher than that of the second evaporator.

[0018] Furthermore, the energy efficiency difference between the first evaporator and the second evaporator is due to the air flow design: the first evaporator processes the low-temperature inlet air Tin, and its evaporation pressure is P1; the second evaporator processes the air Tin+ΔK heated by the first evaporator, and its evaporation pressure P2 satisfies P2=1.15-1.25P1, resulting in a COP value reduction of 8-12%;

[0019] Further, ΔK is the temperature increase of the air after the second evaporator processes the air of the first evaporator.

[0020] Furthermore, the variable frequency blower adopts a progressive frequency increase control strategy in both stand-alone and online modes. During initial startup, the frequency is increased to the base frequency at a rate of 10-15Hz / s, and then the frequency is dynamically adjusted at a rate of 1-3Hz / s based on the deviation between the ambient temperature and the set temperature.

[0021] Furthermore, the superheat control system is regulated by the following steps:

[0022] The low-pressure side pressure is obtained through the pressure sensor and converted into the suction saturation temperature Tsat;

[0023] The actual intake air temperature Tact is obtained through the temperature sensor;

[0024] When the superheat ΔT=Tact-Tsat deviates from the set value by ±1.5℃, adjust the outdoor unit capacity output.

[0025] Furthermore, the three-level seven-segment adjustable structure of the main electric heating device is specifically as follows: the first-level module includes three sections of heating wire, the second-level module includes two sections of heating wire, and the third-level module includes two sections of heating wire, and seven kinds of stepped power output are formed through different combinations.

[0026] Furthermore, the activation priority of the three-level modules of the main electric heating device is: the first-level module is started first and the continuous operation time does not exceed 10 minutes, the second-level module is started after the temperature deviation lasts for 2 minutes, and the third-level module is only started when the deviation lasts for 5 minutes.

[0027] Furthermore, the control system of the ultra-low temperature mining heat pump hot air unit includes two intelligent control strategies, namely: single-machine control strategy and online control strategy;

[0028] Furthermore, the single machine control strategy includes the following steps:

[0029] S1. Receive the user set temperature and detect the ambient temperature T;

[0030] S2. If T≥-12℃, start the variable frequency blower to increase the frequency, activate the first evaporator and the second evaporator; if T<-12℃, force the preheating electric heating device to start and then execute step S2;

[0031] S3. Adjust the frequency of the variable frequency blower according to the real-time temperature deviation. Increase the frequency by 3-5Hz for every 2℃ increase in the deviation, and decrease the frequency by 3-5Hz for every 2℃ decrease in the deviation until the temperature stabilizes.

[0032] Furthermore, the online control strategy includes the following priority rules:

[0033] a) When multiple units are online, the first evaporators of each unit are activated in sequence. After all the first evaporators are started, the second evaporators of each unit are activated in the same sequence;

[0034] b) After all evaporators are started, if there is still a temperature deviation, activate their respective main electric heating devices in order of unit numbers;

[0035] c) After the main electric heating device of any unit is started, the main electric heating devices of the remaining units are allocated the number of starting stages according to the proportion of temperature deviation.

[0036] Furthermore, the start-up of the preheating electric heating device in the single-machine control strategy is a single-machine trigger type: when a unit detects that T is less than -12°C, only this unit starts the preheating electric heating device, and the other units independently determine whether to start according to their own ambient temperature.

[0037] Furthermore, a pressure protection mechanism is provided in the initial frequency increase stage of the variable frequency blower in the single-machine control strategy: when the pressure drop rate on the low-pressure side of the evaporator exceeds 0.3 MPa / s, the frequency increase rate is automatically reduced to 40%-60% of the set rate.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] 1. The control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention realizes reliable startup in an ultra-low temperature environment of -40℃ to -20℃ through linkage control of the preheating electric heating device and the compressor, and improves the low temperature adaptability by more than 35% compared with the traditional heat pump with the minimum operating threshold of -15℃.

[0040] 2. The control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention has a differentiated connection design of four compressors (A / B / C / D) and dual evaporators (six columns / eight columns), which can dynamically combine the operating modes according to load demand, so that the system energy efficiency ratio (COP) reaches above 2.3 under -20℃ conditions, which is 18-25% higher than the traditional single compressor system.

[0041] 3. In the control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention, the first evaporator preferentially processes the low-temperature air Tin≤-12°C, and uses a lower evaporation pressure to achieve high COP output; the second evaporator processes the air Tin+ΔK after primary heating, and realizes heat relay through a pressure compensation mechanism, thereby improving the overall system energy efficiency by 12-18%.

[0042] 4. The control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention adopts a progressive heat supplement strategy of "preheating device → primary evaporator → secondary evaporator → main electric heating", gives priority to the use of high COP heat sources, shortens the operating time of the electric heater, and significantly reduces the unit energy consumption cost.

[0043] 5. The control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention introduces a pressure change rate monitoring mechanism on the evaporator side. When the pressure drop rate is greater than 0.3MPa / s, the fan frequency increase rate is automatically limited to avoid low-pressure alarm failures caused by large air volume impact in traditional systems, thereby reducing the failure rate.

[0044] 6. The control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention calculates the real-time superheat of the suction saturation temperature based on the suction temperature and pressure conversion (ΔT=Tact-Tsat), controls the superheat fluctuation range within ±1.5°C, improves the control accuracy compared with the traditional post-valve temperature detection, reduces the influence of the ambient temperature on the post-valve temperature, and calculates the superheat more accurately.

[0045] 7. The control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention adopts the strategy of "activating each unit one by one + threshold triggering" when multiple units are running. Through the cascade startup sequence, it avoids multiple devices from running at full load at the same time, reduces the impact current of the power grid, and reduces the peak power demand.

[0046] 8. The control system of the ultra-low temperature mining heat pump hot air unit provided by the present invention forms a double backup circuit between the first evaporator and compressor A / B, and the second evaporator and compressor C / D. When a single compressor fails, it can still maintain 70% of the heating capacity, which is 50% more reliable than the traditional single-circuit system.

[0047] In summary, the technical solution of the present invention solves the problem that the traditional heat pump system in the prior art uses an electric heating device to start and maintain normal operation, which significantly increases energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0049] Figure 1 It is a schematic diagram of the structure of the present invention;

[0050] Figure 2 It is a logic flow chart of the single machine control strategy of the present invention;

[0051] Figure 3 This is a flow chart of the online control strategy of the present invention (taking 3 units as an example).

[0052] In the figure: 1. indoor unit; 2. variable frequency air blower; 3. main electric heating device; 4. first evaporator; 5. second evaporator; 6. preheating electric heating device; 7. compressor D; 8. compressor C; 9. compressor B; 10. compressor A; 11. superheat control system; 12. outdoor unit. DETAILED DESCRIPTION

[0053] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0054] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0056] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0057] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0058] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" may include both "above" and "below". The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0059] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0060] like Figure 1-3 As shown, the present invention provides a control system for an ultra-low temperature mining heat pump hot air unit, comprising: an indoor unit 1 and an outdoor unit 12 integrated on the same base;

[0061] The indoor unit 1 comprises a preheating electric heating device 6, a first evaporator 4, a second evaporator 5, a main electric heating device 3 and a variable frequency blower 2 which are sequentially arranged along the air supply direction;

[0062] The outdoor unit 12 includes a compressor A10, a compressor B9, a compressor C8, a compressor D7 and a superheat control system 11;

[0063] The first evaporator 4 is a six-row structure, connected to compressor A10 and compressor B9 respectively;

[0064] The second evaporator 5 is an eight-row structure, connected to compressor C8 and compressor D7 respectively;

[0065] The main electric heating device 3 adopts a three-level seven-segment adjustable structure, providing seven power output modes through a three-level energy module combination;

[0066] The superheat control system 11 adjusts the operating state of the compressor by measuring the difference between the suction temperature and the suction saturation temperature converted by the pressure sensor.

[0067] The start-up of the preheating electric heating device 6 must meet the following conditions at the same time:

[0068] a) The unit is in standby mode;

[0069] b) The ambient temperature is lower than -12°C;

[0070] It is used to quickly increase the temperature on the air inlet side of the evaporator to establish a pressure difference between indoors and outdoors.

[0071] The first evaporator 4 is arranged upstream of the air inlet of the second evaporator 5, and uses low-temperature inlet air to achieve a lower evaporation pressure. Its designed COP value is 12-18% higher than that of the second evaporator.

[0072] The energy efficiency difference between the first evaporator 4 and the second evaporator 5 is due to the air flow design: the first evaporator processes the low-temperature incoming air Tin, and its evaporation pressure is P1; the second evaporator processes the air Tin+ΔK heated by the first evaporator, and its evaporation pressure P2 satisfies P2=1.15-1.25P1, resulting in a COP value reduction of 8-12%; where ΔK is the air temperature increase after the second evaporator processes the first evaporator.

[0073] The variable frequency blower 2 adopts a gradual frequency increase control strategy in both stand-alone and online modes. During initial startup, the frequency is increased to the reference frequency at a rate of 10-15 Hz / s, and then the frequency is dynamically adjusted at a rate of 1-3 Hz / s according to the deviation between the ambient temperature and the set temperature.

[0074] The superheat control system achieves regulation through the following steps:

[0075] The low-pressure side pressure is obtained through the pressure sensor and converted into the suction saturation temperature Tsat;

[0076] The actual intake air temperature Tact is obtained through the temperature sensor;

[0077] When the superheat ΔT=Tact-Tsat deviates from the set value by ±1.5℃, adjust the outdoor unit capacity output.

[0078] The three-stage seven-section adjustable structure of the main electric heating device 3 is as follows: the first-stage module includes three sections of heating wire, the second-stage module includes two sections of heating wire, and the third-stage module includes two sections of heating wire, and seven kinds of stepped power output are formed through different combinations.

[0079] The activation priority of the three-level modules of the main electric heating device 3 is: the first-level module starts first and the continuous operation time does not exceed 10 minutes, the second-level module starts after the temperature deviation lasts for 2 minutes, and the third-level module starts only when the deviation lasts for 5 minutes.

[0080] The control system of ultra-low temperature mining heat pump hot air unit includes two intelligent control strategies: single machine control strategy and online control strategy;

[0081] The single machine control strategy includes the following steps:

[0082] S1. Receive the user set temperature and detect the ambient temperature T;

[0083] S2. If T≥-12°C, start the variable frequency blower 2 to increase the frequency, activate the first evaporator 4 and the second evaporator 5; if T<-12°C, force the preheating electric heating device 6 to start and then execute step S2;

[0084] S3. Adjust the frequency of variable frequency blower 2 according to the real-time temperature deviation. Increase the frequency by 3-5Hz for every 2℃ increase in the deviation, and decrease the frequency by 3-5Hz for every 2℃ decrease in the deviation until the temperature stabilizes.

[0085] Online control strategy, including the following priority rules:

[0086] a) When multiple units are online, the first evaporators 4 of each unit are activated in sequence. After all the first evaporators 4 are started, the second evaporators 5 of each unit are activated in the same sequence;

[0087] b) After all evaporators are started, if there is still a temperature deviation, activate the respective main electric heating devices 3 in the order of unit numbers;

[0088] c) After the main electric heating device 3 of any unit is started, the main electric heating devices 3 of the remaining units are allocated the number of starting stages according to the temperature deviation ratio.

[0089] The start-up of the preheating electric heating device 6 in the single-machine control strategy is a single-machine trigger type: when a unit detects that T is less than -12°C, only this unit starts the preheating electric heating device 6, and the other units independently determine whether to start according to their own ambient temperature.

[0090] In the single-machine control strategy, a pressure protection mechanism is provided in the initial frequency increase stage of the variable frequency blower 2: when the pressure drop rate on the low-pressure side of the evaporator exceeds 0.3 MPa / s, the frequency increase rate is automatically reduced to 40%-60% of the set rate.

[0091] Example 1

[0092] like Figure 2 As shown, the present invention provides a control system for an ultra-low temperature mining heat pump hot air unit, a single-machine control strategy (taking unit number K1 as an example), operating conditions: ambient temperature T=-18°C, set temperature Tset=25°C, control flow:

[0093] 1. Warm-up stage

[0094] The system detects T=-18℃. When the ambient temperature is lower than -12℃ and the unit is in standby mode, the preheating electric heating device (power 30kW) is activated and the variable frequency blower is started at a rate of 10Hz / s to a reference frequency of 35Hz.

[0095] The air inlet temperature of the evaporator is continuously monitored and the preheating device is turned off when it reaches -8°C (this takes 2 minutes and 15 seconds).

[0096] 2. Evaporator startup stage

[0097] Start compressor A to drive the first evaporator (six-row structure), the initial COP = 2.1, and the outlet air temperature rises to 5°C;

[0098] The superheat control system detects ΔT=+2.3°C and adjusts the speed of compressor A from 1800rpm to 2100rpm to stabilize ΔT within ±1.5°C.

[0099] 3. Load replenishment stage

[0100] When the temperature deviation (Tset-Tact) = 10°C, start compressor C to drive the second evaporator (eight-row structure), COP = 1.8, and the outlet air temperature rises to 18°C;

[0101] The frequency of the variable frequency blower increases to 45Hz according to the deviation value, and the air volume increases to 3200m³ / h.

[0102] 4. Electric heating intervention

[0103] After 10 minutes of operation, the temperature deviation still existed at 3°C, so the primary module of the main electric heating device (three-section heating wire, power 15kW) was activated, and the set temperature was finally reached within 5 minutes.

[0104] Example 2

[0105] like Figure 2 As shown, the present invention provides a control system for an ultra-low temperature mining heat pump hot air unit, an online control strategy (units K1 / K2 / K3 in parallel), operating conditions: ambient temperature T = -28 ° C, set temperature T set =28℃, control process:

[0106] 1. Warm-up stage (independent judgment)

[0107] K1 / K2 / K3 detect their own air inlet temperature respectively:

[0108] K1 detects T=-28℃ and triggers self-preheating;

[0109] K2 detects T=-25℃, standby;

[0110] K3 detects T=-27℃, standby.

[0111] 2. Full start of the first evaporator (mandatory sequence)

[0112] Stage triggering conditions: Any unit completes preheating or the ambient temperature is ≥ -12℃

[0113] Activation sequence: Start the first evaporator in sequence according to unit number K1 → K2 → K3:

[0114] K1: Start compressor A (six rows of the first evaporator);

[0115] K2: start compressor A (six columns of the first evaporator) with a delay of 30 seconds;

[0116] K3: Delay 60 seconds to start compressor A (first evaporator six columns).

[0117] Synchronous control: After the first evaporators of the three units are all running, the total heating capacity of the system reaches 215kW and the temperature rises to -5℃.

[0118] 3. Full start of the second evaporator (cascade supplement)

[0119] Stage triggering conditions: All units’ first evaporators are fully loaded and the temperature deviation is > 8°C

[0120] Activation sequence: K1 → K2 → K3 Start the second evaporator:

[0121] K1: Start compressor C (second evaporator row eight);

[0122] K2: start compressor C (second evaporator row eight) with a delay of 30 seconds;

[0123] K3: Delay 60 seconds to start compressor C (second evaporator column eight).

[0124] Effect: The total heating capacity is increased to 365kW and the temperature is raised to 15℃.

[0125] 4. Main electric heating starts on demand (priority allocation)

[0126] Trigger condition: Temperature deviation continues to be >3℃ for more than 5 minutes

[0127] Allocation logic:

[0128] a) K1: Activate the primary module (15kW), the deviation drops to 2°C;

[0129] b) K2: Activate the primary + secondary modules (15kW + 10kW), and the deviation returns to zero;

[0130] c) K3: Does not start because the temperature reaches the standard.

[0131] Constraint rule: During the electric heating operation of any unit, the other units are prohibited from starting a higher priority heat source (such as reverse activation of the evaporator).

[0132] 5. Abnormal handling (pressure protection)

[0133] When the pressure drop rate of the second evaporator K2 reaches 0.35MPa / s:

[0134] Reduce the frequency increase rate of K2 variable frequency blower to 8Hz / s (originally 12Hz / s);

[0135] Skipping the current phase is prohibited (while maintaining the second evaporator in operation).

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control system for an ultra-low temperature mining heat pump hot air unit, characterized in that: The control system of the ultra-low temperature mining heat pump hot air unit is integrated into an indoor unit (1) and an outdoor unit (12) on the same base; the indoor unit (1) comprises a preheating electric heating device (6), a first evaporator (4), a second evaporator (5), a main electric heating device (3) and a variable frequency air blower (2) arranged in sequence along the air supply direction; the outdoor unit (12) comprises a compressor A (10), a compressor B (9), a compressor C (8), a compressor D (7) and a superheat control system (11); the first evaporator (4) is a six-row structure, connected to the compressor A (10) and the compressor B (9) respectively; the second evaporator (5) is an eight-row structure, connected to the compressor C (8) and the compressor D (7) respectively; the main electric heating device (3) adopts a three-level seven-segment adjustable structure, and provides seven power output modes through a three-level energy module combination; the superheat control system (11) adjusts the compressor operation state by measuring the difference between the suction temperature and the suction saturation temperature converted by the pressure sensor.

2. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 1 is characterized in that: The activation of the preheating electric heating device (6) requires the following conditions to be met simultaneously: a) the unit is in standby mode; b) the ambient temperature is lower than -12°C; it is used to quickly increase the temperature of the air inlet side of the evaporator to establish an indoor and outdoor pressure difference.

3. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 1 is characterized by: The first evaporator (4) is arranged upstream of the air inlet of the second evaporator (5), and utilizes low-temperature inlet air to achieve a lower evaporation pressure. Its designed COP value is 12-18% higher than that of the second evaporator.

4. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 1 is characterized in that: The energy efficiency difference between the first evaporator (4) and the second evaporator (5) is due to the air flow design: the first evaporator processes the low-temperature inlet air Tin, and its evaporation pressure is P1; the second evaporator processes the air Tin+ΔK heated by the first evaporator, and its evaporation pressure P2 satisfies P2=1.15-1.25P1, resulting in a COP value reduction of 8-12%; The ΔK is the temperature rise of the air after the second evaporator processes the first evaporator.

5. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 1 is characterized in that: The variable frequency blower (2) adopts a gradual frequency increase control strategy in both stand-alone and online modes. During initial startup, the frequency is increased to a reference frequency at a rate of 10-15 Hz / s, and then the frequency is dynamically adjusted at a rate of 1-3 Hz / s according to the deviation between the ambient temperature and the set temperature.

6. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 1 is characterized in that: The superheat control system (11) is controlled by the following steps: The low-pressure side pressure is obtained through the pressure sensor and converted into the suction saturation temperature Tsat; The actual intake air temperature Tact is obtained through the temperature sensor; When the superheat ΔT=Tact-Tsat deviates from the set value by ±1.5℃, adjust the outdoor unit capacity output.

7. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 1 is characterized by: The three-stage seven-section adjustable structure of the main electric heating device (3) is specifically as follows: the first-stage module comprises three sections of electric heating wire, the second-stage module comprises two sections of electric heating wire, and the third-stage module comprises two sections of electric heating wire, and seven kinds of stepped power output are formed through different combinations; The activation priority of the three-level modules of the main electric heating device (3) is as follows: the first-level module is started first and the continuous operation time does not exceed 10 minutes, the second-level module is started after the temperature deviation lasts for 2 minutes, and the third-level module is started only when the deviation lasts for 5 minutes without being eliminated.

8. A control system for an ultra-low temperature mining heat pump hot air unit according to any one of claims 1 to 7, characterized in that: The control system of the ultra-low temperature mining heat pump hot air unit includes two intelligent control strategies: a single machine control strategy and an online control strategy; The single machine control strategy includes the following steps: S1. Receive the user set temperature and detect the ambient temperature T; S2. If T≥-12℃, start the variable frequency blower to increase the frequency, activate the first evaporator and the second evaporator; if T<-12℃, force the preheating electric heating device to start and then execute step S2; S3. Adjust the frequency of the variable frequency blower according to the real-time temperature deviation. For every 2°C increase in deviation, the frequency is increased by 3-5Hz, and for every 2°C decrease in deviation, the frequency is decreased by 3-5Hz until the temperature stabilizes. The online control strategy contains the following priority rules: a) When multiple units are online, the first evaporators of each unit are activated in sequence. After all the first evaporators are started, the second evaporators of each unit are activated in the same sequence; b) After all evaporators are started, if there is still temperature deviation, activate their respective main electric heating devices in order of unit numbers; c) After the main electric heating device of any unit is started, the main electric heating devices of the remaining units are allocated the number of starting stages according to the proportion of temperature deviation.

9. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 8 is characterized in that: The start-up of the preheating electric heating device (6) in the single-machine control strategy is a single-machine trigger type: when a unit detects that T is less than -12°C, only this unit starts the preheating electric heating device, and the other units independently determine whether to start according to their own ambient temperature.

10. The control system of the ultra-low temperature mining heat pump hot air unit according to claim 8, characterized in that: In the single-machine control strategy, a pressure protection mechanism is provided in the initial frequency increase stage of the variable frequency blower (2): when the pressure drop rate on the low-pressure side of the evaporator exceeds 0.3 MPa / s, the frequency increase rate is automatically reduced to 40%-60% of the set rate.

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