Control method for transcritical CO2 air-conditioning heat pump system of high-altitude rail vehicle

Abstract

The present invention discloses a control method for a transcritical CO2 air-conditioning heat pump system of a plateau rail vehicle. For the plateau rail vehicle, the control method of the present invention includes adjusting the indoor air volume to match the cooling load and heating load that change with altitude, and finding the optimal air volume; adjusting the fresh air ratio to ensure that the oxygen concentration and carbon dioxide concentration in the carriage are within a safe range, and finding the minimum fresh air ratio; calculating the optimal exhaust pressure of the carbon dioxide cycle in real time. The system uses refrigerant carbon dioxide, which is energy-saving and environmentally friendly; the control method aims to reduce energy waste and effectively improve the energy efficiency of the system while meeting the normal functions of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of rail vehicle air - conditioning control, and particularly relates to a control method for a transcritical CO2 air - conditioning heat pump system of a high - altitude rail vehicle. Background Art

[0002] With the continuous improvement of environmental protection standards, the disadvantages of high GWP index and poor low - temperature heating performance of traditional HFCs refrigerants have become increasingly prominent. As a green and environmentally friendly natural refrigerant, the global warming potential index GWP of CO2 is only 1, and it has good low - temperature heating performance, which is the development direction of refrigerants for future rail transit.

[0003] Currently, the research and development of CO2 air - conditioning heat pump systems on rail vehicles mainly focuses on plain areas, that is, areas with conventional atmospheric pressure. At present, there are already multiple units running in high - altitude areas, and the Qinghai - Tibet Railway has also been in operation for a long time. The exploration of CO2 air - conditioning heat pump systems for high - altitude rail vehicles is almost blank. The highest altitude of high - altitude rail vehicles is nearly 5100m. As the altitude increases, the air density decreases and the heat transfer capacity drops. To ensure the system performance, it is necessary to adjust the air volume of indoor and outdoor fans. At the same time, generally, as the outdoor atmospheric pressure decreases and the environmental temperature drops, the cooling load of the air - conditioner during refrigeration decreases and the required air volume decreases, while the heat load of the heat pump during heating increases and the required air volume increases. In addition, an increase in air volume will lead to an increase in fan power consumption, and the overall system performance may decline. Therefore, the control of indoor air volume needs to comprehensively consider these factors. In addition to indoor air volume, the higher the fresh air volume, the greater the heat load, which will also affect the system performance. At the same time, the adjustment of fresh air volume is related to the adjustment of oxygen concentration and carbon dioxide. Finally, there is an optimal exhaust pressure in the CO2 cycle, and the system energy efficiency is the highest at this pressure. Therefore, it is necessary to find the optimal exhaust pressure applicable to the air - conditioning heat pump system of high - altitude trains to reduce the system energy consumption as much as possible.

[0004] In the prior art, the indoor air volume of high - altitude rail vehicles is generally divided into two gears, strong wind and weak wind, and no targeted control method has been proposed for the changing altitude environment, and the influence of fresh air volume on the system performance has not been considered. Summary of the Invention

[0005] The purpose of the present invention is to provide a control method for a transcritical CO2 air - conditioning heat pump system of a high - altitude rail vehicle for the above - mentioned technical problems of high - altitude rail vehicles. In the present invention, the indoor air volume and fresh air volume of high - altitude rail vehicles are adjusted to adapt to the changing outdoor atmospheric pressure, and the optimal exhaust pressure applicable to high - altitude operation is proposed, which can reduce the energy consumption of the transcritical CO2 air - conditioning heat pump system of high - altitude rail vehicles as much as possible.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A control method for a transcritical CO2 air-conditioning heat pump system of a high-altitude rail vehicle, characterized in that the transcritical CO2 air-conditioning heat pump system includes an air-conditioning heat pump system, and the method comprises the following steps:

[0008] S1. Determine the initial indoor air volume, adjust the indoor air volume of the high-altitude rail vehicle according to the change of the COP of the air-conditioning heat pump system to find the optimal indoor air volume, monitor whether the oxygen concentration and carbon dioxide concentration in the vehicle interior air are within the normal range. If the oxygen concentration and carbon dioxide concentration are within the normal range, do not adjust the opening degree of the fresh air valve in the air-conditioning heat pump system. If not, adjust the opening degree of the fresh air valve so that the oxygen concentration and carbon dioxide concentration are within the normal range. At the same time, calculate the optimal discharge pressure of the air-conditioning heat pump system in real time to ensure that the air-conditioning heat pump system is operated at the optimal discharge pressure in real time;

[0009] S2. After determining the indoor air volume, adjust the opening degree of the fresh air valve again to find the optimal opening degree of the fresh air valve under the current indoor air volume to improve the COP, and calculate the optimal discharge pressure at the same time;

[0010] S3. Adjust the indoor air volume again to find the optimal indoor air volume and calculate the optimal discharge pressure in real time. If the COP increases, the indoor air volume is the value of the air volume adjusted this time. If the COP decreases, the indoor air volume is the indoor air volume before this adjustment and the indoor air volume is no longer adjusted. Similarly, after adjusting the indoor air volume, adjust the opening degree of the fresh air valve again and calculate the optimal discharge pressure in real time. If the COP increases, the opening degree of the fresh air valve is the value adjusted this time. If the COP decreases, the fresh air valve is the opening degree value of the fresh air valve before this adjustment and the opening degree of the fresh air valve is no longer adjusted;

[0011] S4. Judge whether the number of adjustments reaches the preset number within a period of time. If so, keep the indoor air volume, the opening degree of the fresh air valve, and the discharge pressure unchanged. Otherwise, return to step S3.

[0012] Preferably:

[0013] COP = ρ×V×△h / (U c ×I c +U fin ×I fin +U fout ×I fout )

[0014] Where: ρ is the air density, V is the indoor air volume, △h is the enthalpy difference between the air inlet and air outlet of the indoor heat exchanger in the air-conditioning heat pump system, U c is the voltage of the compressor motor, I c is the current of the compressor motor, U fin is the voltage of the indoor fan motor, I fin is the current of the indoor fan motor, U fout is the voltage of the outdoor fan motor, Ifout is the current of the outdoor fan motor.

[0015] Preferably, the initial indoor air volume is determined according to the carriage volume, the outdoor atmospheric pressure and the ambient temperature. The specific processes of the initial indoor air volume and the indoor air volume adjustment include:

[0016] In the refrigeration operation mode, the initial indoor air volume Vc0 = fc(D, T amb , p0). If the carriage temperature T a reaches the set temperature Ts °C ± 0.5 °C, after calculating the COP, the indoor air volume is reduced by ΔVc, and ΔVc = fc(ΔT amb , Δp amb ). After a preset time, the COP is calculated again. If the COP increases, the indoor air volume is reduced by ΔV. If the COP decreases after reducing the indoor air volume, the indoor air volume is increased by ΔV until the COP is maximized and then the indoor air volume remains unchanged;

[0017] In the heating operation mode, the initial indoor air volume Vh0 = fh(D, T amb , p amb ). If the carriage temperature T a reaches the set temperature T s °C ± 0.5 °C, after calculating the COP, the indoor air volume is reduced by ΔVh, and ΔVh = fh(ΔT amb , Δp amb ). After a preset time, the COP is calculated again. If the COP increases, the indoor air volume continues to be reduced by ΔVh. If the COP decreases after reducing the indoor air volume, the indoor air volume is increased by ΔVh until the COP is maximized and then the indoor air volume remains unchanged;

[0018] wherein, D is the carriage volume, T amb is the ambient temperature, and p amb is the outdoor atmospheric pressure.

[0019] Preferably, the process of controlling the oxygen concentration and the carbon dioxide concentration by adjusting the opening of the fresh air valve includes the following steps:

[0020] Step 1: Set the lower limit of the oxygen concentration w O2 as zl O2 , the upper limit as zh O2 , and the upper limit of the carbon dioxide concentration w CO2 as z CO2 ;

[0021] Step 2: Monitor the indoor oxygen concentration w O2 and the carbon dioxide concentration w CO2 ;

[0022] Step 3: At the current indoor air volume, if it is monitored that w O2 ≥ zh O2, w CO2 ≥ z CO2 , then increase the fresh air ratio; if it is detected that w O2 ≤ zl O2 , w CO2 ≥ z CO2 , then increase the oxygen concentration and the fresh air ratio; if it is detected that w O2 ≤ zl O2 , w CO2 ≤ z CO2 , then decrease the fresh air ratio; if it is detected that w O2 ≥ zl O2 , w CO2 ≥ z CO2 , then increase the fresh air ratio; if it is detected that zl O2 < w O2 < zh O2 and w CO2 < z CO2 , then the fresh air ratio remains unchanged; when adjusting the fresh air ratio, convert the concentration difference into the change amount of the fresh air valve ΔR fresh = A × f(w O2 , w CO2 , zh O2 , zl O2 , z CO2 ), where A is the step adjustment coefficient;

[0023] Step 4. After determining the indoor air volume, calculate the system COP; first reduce the fresh air ratio ΔR. If the COP increases and the carbon dioxide concentration and the oxygen concentration are within the normal range, then continue to reduce the fresh air ratio ΔR(n) = B × |COP(n) - COP(n - 1)|, where B is the step adjustment coefficient, ΔR(n) is the change amount of the fresh air ratio this time, COP(n) is the COP at this adjustment, and COP(n - 1) is the COP at the previous adjustment. Calculate the COP again. If the COP increases and the carbon dioxide concentration and the oxygen concentration are within the normal range, then reduce the fresh air ratio until the COP is maximized. If the carbon dioxide concentration and the oxygen concentration are higher than their respective upper limits when reducing the fresh air ratio, then first ensure safety and increase the fresh air ratio; if reducing the fresh air ratio first results in a decrease in the COP, then increase the fresh air ratio. If the COP increases and the oxygen concentration is within the normal range, then continue to increase the fresh air ratio until the COP is maximized. If the oxygen concentration is lower than the normal range when increasing the fresh air ratio, then first ensure the oxygen concentration.

[0024] Preferably, the optimal exhaust pressure p op = f(T amb , R fresh , p amb , V), where T amb is the ambient temperature, R fresh is the fresh air ratio, p amb$P_{out}$ is the outdoor atmospheric pressure, $V$ is the indoor air volume, and the optimal exhaust pressure is obtained through experiments.

[0025] Preferably, the air-conditioning heat pump system includes a compressor, an electronic four-way valve, an outdoor heat exchanger, an expansion valve, an indoor heat exchanger, a gas-liquid separator, a regenerator, an outdoor fan, an indoor fan, a fresh air valve, an oxygen concentration probe, a carbon dioxide concentration probe, and a data acquisition and processing center. The compressor, the outdoor heat exchanger, the indoor heat exchanger, and the gas-liquid separator are respectively connected to different interfaces of the electronic four-way valve. One side of the outdoor fan is connected to the compressor and the outdoor heat exchanger, and the other side of the outdoor fan is connected to the indoor heat exchanger and the gas-liquid separator. An expansion valve is provided on the pipeline where the outdoor fan is connected to the indoor heat exchanger; the indoor heat exchanger is arranged on the fresh air passage. An indoor fan is provided upstream of the indoor heat exchanger on the fresh air passage. A fresh air valve is provided at the inlet of the fresh air passage. The outlet of the fresh air passage is communicated with the interior of the high-altitude rail vehicle. The oxygen concentration probe and the carbon dioxide concentration probe are both arranged in the interior of the high-altitude rail vehicle. The outdoor fan is arranged at the outdoor heat exchanger;

[0026] The data acquisition and processing center is used to collect signals and send control signals. The collected signals include: the voltage of the compressor motor, the current of the compressor motor, the voltage of the indoor fan motor, the current of the indoor fan motor, the voltage of the outdoor fan motor, the current of the outdoor fan motor, the indoor air density, the indoor air volume, the enthalpy difference between the air inlet and outlet of the indoor heat exchanger, the outdoor atmospheric pressure, the ambient temperature, the carriage temperature, the fresh air ratio, the oxygen concentration, and the carbon dioxide concentration; the control signals sent include the indoor air volume, the fresh air ratio, and the opening degree of the fresh air valve.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In the prior art, the indoor air volume of high-altitude rail vehicles is generally divided into two gears, strong wind and weak wind. There is no targeted control method for the changing altitude environment. Only two gears of air volume cannot cope with various working conditions of the train running on the plateau, which will cause shortages or surpluses of cooling capacity and heating capacity. Moreover, the fresh air ratio also has an important impact on the system performance. The existing high-altitude rail vehicle technology does not consider the impact of the fresh air ratio on the system performance; the present invention not only has a clean and efficient carbon dioxide circulation system, but also the control method takes into account the impact of the change of outdoor atmospheric pressure on the system performance, adjusts the indoor air volume and fresh air volume to adapt to the changing outdoor atmospheric pressure, improves the situation of system performance deterioration or system overproduction when the outdoor atmospheric pressure changes during the train running on the plateau, takes into account the indoor air quality, and at the same time proposes an optimal exhaust pressure for high-altitude rail vehicles for transcritical CO2 cycles, considering the influence of factors such as outdoor atmospheric pressure on the optimal exhaust pressure, saving the energy consumption of the air-conditioning heat pump system of high-altitude trains and improving the overall performance of the train. Description of the Drawings

[0029] Figure 1 It is a structural schematic diagram of a transcritical CO2 air-conditioning heat pump system for high-altitude rail vehicles.

[0030] In the figure, 1 is a compressor, 2 is an electronic four-way valve, 3 is an outdoor heat exchanger, 4 is an expansion valve, 5 is an indoor heat exchanger, 6 is a gas-liquid separator, 7 is a regenerator, 8 is an outdoor fan, 9 is an indoor fan, 10 is a fresh air valve, 11 is an oxygen concentration probe, 12 is a carbon dioxide concentration probe, and 13 is a data acquisition and processing center. Specific implementation mode

[0031] The present invention will be further described in detail below with reference to the accompanying drawings.

[0032] See the appendix Figure 1 , the transcritical CO2 air-conditioning heat pump system for high-altitude rail vehicles includes an air-conditioning heat pump system and a control system;

[0033] The air-conditioning heat pump system includes a compressor 1, an electronic four-way valve 2, an outdoor heat exchanger 3, an expansion valve 4, an indoor heat exchanger 5, a gas-liquid separator 6, a regenerator 7, an outdoor fan 8, an indoor fan 9, a fresh air valve 10, an oxygen concentration probe 11, a carbon dioxide concentration probe 12, and a data acquisition and processing center 13. The main working modes of the system are the summer cooling mode and the winter heating mode. In the cooling mode, the a port and the b port of the electronic four-way valve are connected, and the c port and the d port are connected; in the heating mode, the a port and the d port of the electronic four-way valve are connected, and the b port and the c port are connected. The selected expansion valve 4 is an adjustable expansion valve, the indoor fan 9 is a variable-frequency fan, and the fresh air valve 10 is an adjustable fresh air valve.

[0034] Signal acquisition, data calculation, and issuing control instructions are all carried out in the data acquisition and processing center 13. The signals that need to be collected include but are not limited to the motor voltage U c and current I c of the compressor 1, the voltage U fin and current I fin of the motor of the indoor fan 9, the voltage U fout and current I fout of the motor of the outdoor fan 8, the indoor air density ρ, the indoor air volume V, the enthalpy difference △h between the air inlet and outlet of the indoor-side heat exchanger 5, the outdoor atmospheric pressure P amb , the ambient temperature T amb , the car body temperature Ta, the fresh air ratio R fresh , the oxygen concentration w O2 , the carbon dioxide concentration w CO2 , and the signals that need to be issued for control include but are not limited to the indoor air volume, the fresh air ratio, and the opening degree of the fresh air valve.

[0035] A control system for controlling an air-conditioning heat pump system to adapt to a changing altitude environment, mainly including adjusting the indoor air volume and fresh air ratio, finding the optimal operating condition point of the system, and controlling the compressor discharge pressure according to the correlation formula, effectively improving the system energy efficiency. The control system needs to first determine the initial indoor air volume according to the outdoor atmospheric pressure and ambient temperature, then adjust the indoor air volume according to the change in the system COP and find the optimal indoor air volume. While adjusting the indoor air volume, the opening degree of the fresh air valve is adjusted to ensure the normal oxygen concentration and carbon dioxide concentration in the vehicle interior air. After determining the indoor air volume, the opening degree of the fresh air valve is adjusted again to improve the system energy efficiency, and at the same time, the optimal discharge pressure of the system is calculated in real time to ensure that the real-time control system operates at the optimal discharge pressure.

[0036] Specifically, the control method of the transcritical CO2 air-conditioning heat pump system for high-altitude rail vehicles of the present invention includes the following steps:

[0037] S1. Determine the initial indoor air volume according to the carriage volume, outdoor atmospheric pressure and ambient temperature, adjust the indoor air volume according to the change in the COP of the air-conditioning heat pump system and find the optimal indoor air volume, and monitor whether the oxygen concentration and carbon dioxide concentration in the vehicle interior air are within the normal range. If they are within the normal range, the opening degree of the fresh air valve is not adjusted. If they are not within the normal range, the opening degree of the fresh air valve needs to be adjusted to ensure that the oxygen concentration and carbon dioxide concentration are within the normal range. At the same time, calculate the optimal discharge pressure in real time to ensure that the air-conditioning heat pump system is operated at the optimal discharge pressure in real time;

[0038] S2. After determining the indoor air volume, adjust the opening degree of the fresh air valve again to find the optimal opening degree of the fresh air valve at the current indoor air volume to improve the COP, and at the same time calculate the optimal discharge pressure of the system;

[0039] S3. Adjust the indoor air volume again to find the optimal indoor air volume and calculate the optimal discharge pressure in real time. If the COP increases, the indoor air volume is the value of the air volume adjusted this time. If the COP decreases, the indoor air volume is the indoor air volume before this adjustment and the indoor air volume is no longer adjusted; Similarly, after adjusting the indoor air volume, adjust the opening degree of the fresh air valve again and calculate the optimal discharge pressure of the system in real time. If the COP increases, the opening degree of the fresh air valve is the value adjusted this time. If the COP decreases, the fresh air valve is the opening degree value of the fresh air valve before this adjustment and the opening degree of the fresh air valve is no longer adjusted;

[0040] S4. Judge whether the number of adjustments reaches K times within a period of time H. If it is satisfied, keep the indoor air volume, the opening degree of the fresh air valve, and the system discharge pressure unchanged, otherwise return to step S3;

[0041] Specifically, in the above solution of the present invention, the COP calculation formula of the air-conditioning heat pump system is as follows:

[0042] COP = W / (P c + P fin + Pf out) = ρ×V×△h / (U c ×I c +U fin ×I fin +U fout ×I fout )

[0043] Where: ρ is the air density, V is the indoor air volume, △h is the enthalpy difference between the air inlet and air outlet of the indoor heat exchanger in the air-conditioning heat pump system, U c is the voltage of the compressor motor, I c is the current of the compressor motor, U fin is the voltage of the indoor fan motor, I fin is the current of the indoor fan motor, U fout is the voltage of the outdoor fan motor, I fout is the current of the outdoor fan motor; P fin is the power consumption of the indoor fan, P fout is the power consumption of the outdoor fan, P c is the power consumption of the compressor, and W is the indoor heat exchange quantity.

[0044] Specifically, in the above solution of the present invention, the indoor air volume adjustment method includes the following process:

[0045] According to the carriage size D, ambient temperature T amb , outdoor atmospheric pressure p amb , select the initial indoor air volume according to the correlation formula. Specifically, the control relational formula is obtained through a finite number of experiments according to the quantitative relationship according to the following function;

[0046] In the refrigeration operation mode, the initial indoor air volume Vc0 = fc(D, T amb , p0). If the carriage temperature T a reaches the set temperature Ts℃ ± 0.5℃, after calculating the COP, the indoor air volume is reduced by △Vc. The air volume change △Vc is related to the ambient temperature change △T amb and the outdoor atmospheric pressure change △p amb , △Vc = fc(△T amb , △p amb ). After N minutes, calculate the COP again. If the COP increases, the indoor air volume continues to be reduced by △V. If the COP decreases after reducing the air volume, the indoor air volume is increased by △V until the COP value is the largest and then the indoor air volume remains unchanged.

[0047] In the heating operation mode, the initial indoor air volume Vh0 = fh(D, T amb , p amb) Since the required heating load of the heat pump air conditioner is smaller than the cooling load, even if the outdoor atmospheric pressure changes, the change in indoor air volume is smaller compared to the cooling mode change, and the change in heating load is smaller compared to the cooling mode change with the ambient temperature, so the air volume changes less with the ambient temperature. Therefore, a different correlation formula needs to be used for the change in air volume compared to the cooling operation mode. If the compartment temperature T a reaches the set temperature T s °C ± 0.5°C, after calculating the COP, the indoor air volume decreases by △Vh, and △Vh = fh(△T amb , △p amb ). After N minutes, calculate the COP again. If the COP increases, the indoor air volume continues to decrease by △Vh. If the COP decreases after reducing the air volume, the indoor air volume increases by △Vh until the COP value is maximized and the indoor air volume remains unchanged

[0048] Specifically, in the above solution of the present invention, the specific steps of the fresh air volume adjustment method are as follows:

[0049] Step 1: Set the lower limit of the O2 concentration as zl O2 and the upper limit as zh O2 , and the upper limit of the CO2 concentration as z CO2 ;

[0050] Step 2: Monitor the O2 concentration w O2 and the CO2 concentration w CO2

[0051] Step 3: At the current indoor air volume, if it is monitored that the O2 concentration reaches the upper limit concentration and the CO2 concentration reaches the upper limit concentration, that is, w O2 ≥zh O2 , w CO2 ≥z CO2 , then increase the fresh air ratio; if it is monitored that the O2 concentration reaches the lower limit concentration and the CO2 concentration reaches the upper limit concentration, that is, w O2 ≤zl O2 , w CO2 ≥z CO2 , then increase the oxygen production amount and increase the fresh air ratio; if it is monitored that the O2 concentration reaches the lower limit concentration and the CO2 concentration reaches the upper limit concentration, that is, w O2 ≤zl O2 , w CO2 ≤z CO2 , then decrease the fresh air ratio; if it is monitored that the O2 concentration reaches the lower limit concentration and the CO2 concentration reaches the upper limit concentration, that is, w O2 ≥zl O2 , w CO2 ≥z CO2 , then increase the fresh air volume, that is, increase the fresh air ratio; if it is monitored that the O2 concentration is between the lower limit and the upper limit concentration and the CO2 concentration is lower than the upper limit concentration, that is, zl O2 <wO2 <zh O2 and w CO2 <z CO2 , the fresh air ratio remains unchanged; when adjusting the fresh air ratio, the concentration difference is converted into the change amount ΔR of the fresh air valve fresh = A × f(w O2 , w CO2 , zh O2 , zl O2 , z CO2 ), where A is the step adjustment coefficient.

[0052] Step 4: After determining the indoor air volume, calculate the COP; first reduce the fresh air ratio ΔR. If the COP increases and the CO2 concentration and O2 concentration are within the normal range, continue to reduce the fresh air ratio ΔR(n) = B × |COP(n) - COP(n - 1)|, where B is the step adjustment coefficient, ΔR(n) is the change amount of the fresh air ratio for this time, COP(n) is the COP of the system during this adjustment, and COP(n - 1) is the COP of the system during the previous adjustment. Calculate the COP again. If the COP increases and the CO2 concentration and O2 concentration are within the normal range, reduce the fresh air ratio until the COP is maximized. If the CO2 concentration and O2 concentration are too high (i.e., higher than their respective upper limits) when reducing the fresh air ratio, ensure safety first and increase the fresh air ratio; if the fresh air ratio is reduced first and the system COP decreases, increase the fresh air ratio. If the system COP increases and the O2 concentration is within the normal range, continue to increase the fresh air ratio until the COP is maximized. If the O2 concentration is lower than the normal range when increasing the fresh air ratio, ensure the O2 concentration first;

[0053] Specifically, in the above solution of the present invention, the exhaust pressure adjustment method includes the following process:

[0054] The optimal exhaust pressure p of the transcritical carbon dioxide system op is related to the evaporation temperature and the outlet temperature of the gas cooler. The ambient temperature T amb , the fresh air ratio R fresh , the outdoor atmospheric pressure p amb , and the indoor air volume V have a greater impact on the evaporation temperature and the outlet temperature of the gas cooler. Therefore, the optimal exhaust pressure is related to the above factors, that is

[0055] The optimal exhaust pressure p op = f(T amb , R fresh , p amb , V)

[0056] The specific control relationship is obtained through a limited number of experiments according to the quantitative relationship according to the above function. After calculating the exhaust pressure, adjust the valve opening size to achieve the calculated optimal exhaust pressure. If the actual exhaust pressure is higher, increase the valve opening; if the actual exhaust pressure is lower, decrease the valve opening.

[0057] As is known by common technical knowledge, the present invention can be implemented by other embodiments that do not depart from its spiritual essence or essential features. Therefore, the above-disclosed embodiments are illustrative in all aspects and not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are encompassed by the present invention.

Claims

1. A control method for a transcritical CO2 air-conditioning heat pump system of a high-altitude rail vehicle, characterized in that, The transcritical CO2 air-conditioning heat pump system includes an air-conditioning heat pump system, and comprises the following steps: S1. Determine the initial indoor air volume, adjust the indoor air volume of the high-altitude rail vehicle according to the change of the COP of the air-conditioning heat pump system, and find the optimal indoor air volume. Monitor whether the oxygen concentration and carbon dioxide concentration in the vehicle air are within the normal range. If the oxygen concentration and carbon dioxide concentration are within the normal range, do not adjust the opening degree of the fresh air valve in the air-conditioning heat pump system. If not, adjust the opening degree of the fresh air valve so that the oxygen concentration and carbon dioxide concentration are within the normal range. At the same time, calculate the optimal exhaust pressure of the air-conditioning heat pump system in real time to ensure that the air-conditioning heat pump system operates at the optimal exhaust pressure in real time; S2. After determining the indoor air volume, adjust the opening degree of the fresh air valve again to find the optimal opening degree of the fresh air valve at the current indoor air volume to improve the COP, and calculate the optimal exhaust pressure at the same time; S3. Adjust the indoor air volume again to find the optimal indoor air volume and calculate the optimal exhaust pressure in real time. If the COP increases, the indoor air volume is the value of the air volume adjusted this time. If the COP decreases, the indoor air volume is the indoor air volume before this adjustment and the indoor air volume will not be adjusted anymore. Similarly, after adjusting the indoor air volume, adjust the opening degree of the fresh air valve again and calculate the optimal exhaust pressure in real time. If the COP increases, the opening degree of the fresh air valve is the value adjusted this time. If the COP decreases, the fresh air valve is the opening degree value of the fresh air valve before this adjustment and the opening degree of the fresh air valve will not be adjusted anymore; S4. Judge whether the number of adjustments reaches the preset number within a period of time. If it is satisfied, keep the indoor air volume, the opening degree of the fresh air valve, and the exhaust pressure unchanged. Otherwise, return to step S3.

2. A control method for a transcritical CO2 air-conditioning heat pump system of a high-altitude rail vehicle according to claim 1, characterized in that: COP = ρ×V×△h / (U c ×I c +U fin ×I fin +U fout ×I fout ) Among them: ρ is the air density, V is the indoor air volume, △h is the enthalpy difference between the air inlet and the air outlet of the indoor heat exchanger in the air-conditioning heat pump system, U c is the voltage of the compressor motor, I c is the current of the compressor motor, U fin is the voltage of the indoor fan motor, I fin is the current of the indoor fan motor, U fout is the voltage of the outdoor fan motor, I fout is the current of the outdoor fan motor.

3. The control method of a transcritical CO2 air-conditioning heat pump system for a high-altitude rail vehicle according to claim 1, wherein Determine the initial indoor air volume according to the carriage volume, outdoor atmospheric pressure and environmental temperature. The specific processes of the initial indoor air volume and the adjustment of the indoor air volume include: In the refrigeration operation mode, the initial indoor air volume Vc0 = fc(D, T amb , p0). If the temperature T of the carriage a reaches the set temperature Ts °C ± 0.5 °C, after calculating the COP, the indoor air volume is reduced by △Vc, and △Vc = fc(△T amb , △p amb ). After a preset time, the COP is calculated again. If the COP increases, the indoor air volume is reduced by △V. If the COP decreases after reducing the indoor air volume, the indoor air volume is increased by △V until the COP is maximized and then the indoor air volume remains unchanged; In the heating operation mode, the initial indoor air volume Vh0 = fh(D, T amb , p amb ). If the cabin temperature T a reaches the set temperature T s °C ± 0.5 °C, after calculating the COP, the indoor air volume is reduced by △Vh, △Vh = fh(△T amb , △p amb ). After a preset time, the COP is calculated again. If the COP increases, the indoor air volume continues to be reduced by △Vh. If the COP decreases after reducing the indoor air volume, the indoor air volume is increased by △Vh until the COP is maximized and then the indoor air volume remains unchanged; where D is the carriage volume, and T amb is the ambient temperature, and p amb is the outdoor atmospheric pressure.

4. A control method for a transcritical CO2 air-conditioning heat pump system of a high-altitude rail vehicle according to claim 1, characterized in that, The process of controlling the oxygen concentration and carbon dioxide concentration by adjusting the opening degree of the fresh air valve includes the following steps: Step 1. Set the lower limit of the oxygen concentration w O2 as zl O2 , and the upper limit as zh O2 . For the carbon dioxide concentration w CO2 , set the upper limit as z CO2 ; Step 2, monitor the indoor oxygen concentration w O2 and carbon dioxide concentration w CO2 ; Step 3: At the current indoor air volume, if it is monitored that w O2 ≥zh O2 、w CO2 ≥z CO2 , then increase the fresh air ratio; if it is monitored that w O2 ≤zl O2 、w CO2 ≥z CO2 , then increase the oxygen concentration and increase the fresh air ratio; if it is monitored that w O2 ≤zl O2 、w CO2 ≤z CO2 , then decrease the fresh air ratio; if it is monitored that w O2 ≥zl O2 、w CO2 ≥z CO2 , then increase the fresh air ratio; if it is monitored that zl O2 <w O2 <zh O2 and w CO2 <z CO2 , then the fresh air ratio remains unchanged; when adjusting the fresh air ratio, convert the concentration difference into the change amount of the fresh air valve ΔR fresh =A×f(w O2 , w CO2 , zh O2 , zl O2 , z CO2 ), where A is the step adjustment coefficient; Step 4. After determining the indoor air volume, calculate the system COP. First, reduce the fresh air ratio ΔR. If the COP increases and the carbon dioxide concentration and oxygen concentration are within the normal range, continue to reduce the fresh air ratio ΔR(n)=B×|COP(n)-COP(n - 1)|, where B is the step adjustment coefficient, ΔR(n) is the change amount of the fresh air ratio this time, COP(n) is the COP at this adjustment, and COP(n - 1) is the COP at the previous adjustment. Calculate the COP again. If the COP increases and the carbon dioxide concentration and oxygen concentration are within the normal range, reduce the fresh air ratio until the COP is the largest. If the carbon dioxide concentration and oxygen concentration are higher than their respective upper limits when reducing the fresh air ratio, first ensure safety and increase the fresh air ratio. If the COP decreases when first reducing the fresh air ratio, increase the fresh air ratio. If the COP increases and the oxygen concentration is within the normal range, continue to increase the fresh air ratio until the COP is the largest. If the oxygen concentration is lower than the normal range when increasing the fresh air ratio, first ensure the oxygen concentration.

5. A control method for a transcritical CO2 air-conditioning heat pump system of a high-altitude rail vehicle according to claim 1, characterized in that, Optimal exhaust pressure p op = f(T amb , R fresh , p amb , V), where T amb is the ambient temperature, R fresh is the fresh air ratio, p amb is the outdoor atmospheric pressure, and V is the indoor air volume. The optimal exhaust pressure is obtained through experiments.

6. A control method for a transcritical CO2 air-conditioning heat pump system of a high-altitude rail vehicle according to claim 1, characterized in that The air-conditioning heat pump system includes a compressor (1), an electronic four-way valve (2), an outdoor heat exchanger (3), an expansion valve (4), an indoor heat exchanger (5), a gas-liquid separator (6), a regenerator (7), an outdoor fan (8), an indoor fan (9), a fresh air valve (10), an oxygen concentration probe (11), a carbon dioxide concentration probe (12), and a data acquisition and processing center (13). The compressor (1), the outdoor heat exchanger (3), the indoor heat exchanger (5), and the gas-liquid separator (6) are respectively connected to different interfaces of the electronic four-way valve (2). One side of the outdoor fan (8) is connected to the compressor (1) and the outdoor heat exchanger (3), and the other side of the outdoor fan (8) is connected to the indoor heat exchanger (5) and the gas-liquid separator (6). An expansion valve (4) is provided on the pipeline where the outdoor fan (8) is connected to the indoor heat exchanger (5). The indoor heat exchanger (5) is arranged on the fresh air passage. An indoor fan (9) is provided upstream of the indoor heat exchanger (5) on the fresh air passage. A fresh air valve (10) is provided at the inlet of the fresh air passage. The outlet of the fresh air passage is communicated with the interior of the high-altitude rail vehicle. The oxygen concentration probe (11) and the carbon dioxide concentration probe (12) are both arranged in the interior of the high-altitude rail vehicle. The outdoor fan (8) is arranged at the outdoor heat exchanger (3). The data acquisition and processing center (13) is used for collecting signals and sending control signals. The collected signals include: compressor motor voltage, compressor motor current, voltage of the indoor fan motor, current of the indoor fan motor, voltage of the outdoor fan motor, current of the outdoor fan motor, indoor air density, indoor air volume, enthalpy difference between the air inlet and outlet of the indoor heat exchanger, outdoor atmospheric pressure, ambient temperature, car body temperature, fresh air ratio, oxygen concentration, and carbon dioxide concentration. The sent control signals include indoor air volume, fresh air ratio, and fresh air valve opening degree.

7. A control method for a transcritical CO2 air-conditioning heat pump system of a high-altitude rail vehicle according to claim 6, characterized in that, The expansion valve (4) adopts an adjustable expansion valve. The indoor fan (9) adopts a variable-frequency fan. The fresh air valve (10) adopts an adjustable fresh air valve.

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