A working method of a dual-shaft series four-stage compression magnetic levitation compressor

Abstract

This invention discloses a method for operating a dual-shaft, four-stage magnetic levitation compressor, comprising a low-temperature stage magnetic levitation two-stage compressor and a high-temperature stage magnetic levitation two-stage compressor. The method includes cooling mode control logic, heating mode temperature zone control logic, unit mode switching interlock logic, compressor switching interlock logic, start-stop timing logic, and multi-level protection logic. This invention features group control, temperature zone operation, dual PID independent closed-loop control, multi-level interlocking timing, hysteresis prevention of frequent switching, and graded protection logic. It allows for dual-compressor series operation, with the operating speed ratio of the high-temperature and low-temperature stage magnetic levitation two-stage compressors controlled within the range of 0.75-0.95. It also enables independent operation of each compressor, achieving stable operation of the unit under cooling and full-temperature-zone heating conditions, suppressing surge, pressure imbalance, and frequent start-stop faults, and improving adaptability to ultra-low temperature environments, operational safety, and overall energy efficiency.

Description

Technical Field

[0001] This invention relates to the field of magnetic levitation air source heat pumps, and in particular to a method for operating a magnetic levitation compressor with dual-shaft series four-stage compression. Background Technology

[0002] Currently, the patent with authorization announcement number "CN120252198B" discloses a dual-head, four-stage compression magnetic levitation air source heat pump chiller and hot water unit and its working method, including a low-temperature stage magnetic levitation two-stage compressor, a high-temperature stage magnetic levitation two-stage compressor, and several medium heat exchange components; the inlet end of the first one-way valve and the outlet end of the second one-way valve of each medium heat exchange component are connected to the outlet end of their corresponding condenser, the inlet end of the second one-way valve and the inlet end of the third one-way valve are connected to the outlet ends of their corresponding first main electronic expansion valve and the second main electronic expansion valve, the outlet end of the third one-way valve and the inlet end of the fourth one-way valve are connected to the inlet end of their corresponding finned evaporator, and the outlet ends of the first one-way valve and the fourth one-way valve are connected to the inlet ends of their corresponding first main electronic expansion valve and the second main electronic expansion valve.

[0003] Although it clearly explains the connection method of the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor, as well as the working method of the entire unit, it does not clearly point out the control logic and control method of the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor. Summary of the Invention

[0004] The purpose of this invention is to provide a working method for a dual-shaft series four-stage compression magnetic levitation compressor, which features dual compressor series operation, single compressor independent operation, group control, temperature zone operation, dual PID independent closed loop, multi-level interlocking timing, hysteresis to prevent frequent switching, and graded protection logic. This enables the unit to operate stably under cooling and full-temperature-zone heating conditions, suppresses surge, pressure imbalance, and frequent start-stop faults, and improves the adaptability to ultra-low temperature environments, operational safety, and overall energy efficiency.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A method for operating a dual-shaft series four-stage compression magnetic levitation compressor includes a low-temperature stage magnetic levitation two-stage compressor and a high-temperature stage magnetic levitation two-stage compressor. The low-temperature stage magnetic levitation two-stage compressor includes a first-stage compression unit and a second-stage compression unit, and the high-temperature stage magnetic levitation two-stage compressor includes a third-stage compression unit and a fourth-stage compression unit. It includes dual compressor series operation, single compressor independent operation, cooling mode control logic, heating mode temperature zone control logic, unit mode switching interlock logic, compressor start-stop interlock logic, start-stop timing logic, and multi-level protection logic.

[0006] The preferred option is as follows: Preferred: Cooling mode control logic, At any ambient temperature, the low-temperature stage magnetic levitation two-stage compressor implements a shutdown electrical interlock, and only the high-temperature stage magnetic levitation two-stage compressor operates by frequency conversion; The PLC control module collects the inlet and outlet water temperatures of the high-temperature magnetic levitation two-stage compressor and adjusts the start and stop of the high-temperature magnetic levitation two-stage compressor through PID calculation, thereby realizing closed-loop control of the inlet and outlet water temperatures of the high-temperature magnetic levitation two-stage compressor.

[0007] Preferred: Heating mode temperature zone control logic, divided into six temperature zones according to ambient temperature, with a 3℃ hysteresis set for all temperature zone switching; the operating speed ratio of the high-temperature stage magnetic levitation two-stage compressor and the low-temperature stage magnetic levitation two-stage compressor is set to be controlled in the range of 0.75-0.95; When the ambient temperature is >10℃, the low-temperature magnetic levitation two-stage compressor is shut down and locked, and only the high-temperature magnetic levitation two-stage compressor operates by frequency conversion. The high-temperature magnetic levitation two-stage compressor uses PID closed-loop speed regulation with the unit's heating inlet and outlet water temperatures as the target. When the ambient temperature is 0℃ < 10℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature corresponding to the interstage discharge pressure of 38℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperature of the unit as the control target for PID speed regulation. -10℃<Ambient temperature≤0℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the interstage discharge pressure corresponding to the temperature of 36℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the unit inlet and outlet water temperature as the control target for PID speed regulation. -20℃<Ambient temperature≤-10℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the interstage discharge pressure corresponding to the temperature of 33℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the unit inlet and outlet water temperature as the control target for PID speed regulation. -30℃≤Ambient temperature≤-20℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature of 30℃ corresponding to the interstage discharge pressure as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperature of the unit as the control target for PID speed regulation. When the ambient temperature is less than -30℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously using frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature corresponding to the interstage discharge pressure of 28℃ as the control target for PID speed regulation, while the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperatures of the unit as the control target for PID speed regulation.

[0008] Preferably, the unit mode switching interlock logic, i.e., the switching between heating mode and cooling mode, comprises the following steps: S1, the PLC control module controls the entire machine to reduce the load to the minimum speed; S2. After a 10-second delay, stop the currently running compressor unit; S3, maintain pressure balance for 5 seconds; S4. Switch the operating mode and start the compressor unit in the corresponding mode; S5. The entire process is protected by a double interlock to prevent the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor from being mistakenly put into operation at the same time.

[0009] Preferred: Compressor switching interlock logic, In heating mode, when the ambient temperature crosses the critical point of 10℃, the switching control of the low-temperature magnetic levitation two-stage compressor is as follows: the ratio of the operating speeds of the high-temperature magnetic levitation two-stage compressor and the low-temperature magnetic levitation two-stage compressor is controlled within the range of 0.75-0.95. When the ambient temperature drops from above 10℃ to 10℃ or below, the low-temperature magnetic levitation two-stage compressor needs to be started. First, open the auxiliary reflux valve, start the low-temperature magnetic levitation two-stage compressor after the pressure is balanced for 3 seconds, then gradually increase the speed of the low-temperature magnetic levitation two-stage compressor, then close the auxiliary reflux valve and match the interstage exhaust pressure to the corresponding temperature. When the ambient temperature rises from 10℃ or below to above 10℃, the low-temperature magnetic levitation two-stage compressor needs to be stopped. First, open the auxiliary reflux valve to control the low-temperature magnetic levitation two-stage compressor to gradually reduce its speed. After the speed reduction is completed, stop the machine and execute the electrical interlock. Close the auxiliary reflux valve and do not stop the machine under pressure differential.

[0010] Preferred start / stop timing logic for either the low-temperature magnetic levitation two-stage compressor or the high-temperature magnetic levitation two-stage compressor. S1, Pre-lubrication for 3 seconds; S2. The magnetic levitation bearing establishes a levitation state, which lasts for 5 seconds; S3. Gradually increase the speed to the operating speed; S4. Shutdown procedure: Control the compressor to gradually reduce speed; S5. Confirm that the magnetic levitation bearing has completely fallen back; S6. Stop lubrication operation.

[0011] Preferred: Multi-level protection logic, including high-pressure exhaust temperature protection, pressure protection, and surge protection. High-pressure exhaust temperature protection: when the high-pressure exhaust temperature is >95℃, load reduction protection is activated; when the temperature is >105℃, a fault shutdown is triggered. Interstage temperature protection: a warning signal is issued when the interstage temperature is >70℃, and load reduction protection is implemented when the interstage temperature is >78℃. Surge protection: If the compressor speed deviates from the anti-surge operating line, the speed is finely adjusted first, and at the same time, the auxiliary return valve is linked to control the flow and suppress the surge phenomenon.

[0012] Preferably, the rated speed range of the high-temperature magnetic levitation two-stage compressor is 15,000-36,000 rpm; The rated speed range of the low-temperature magnetic levitation two-stage compressor is 18,000-42,000 rpm.

[0013] In summary, the present invention has the following beneficial effects: 1. Strong wide temperature range adaptability. The heating mode is finely divided into six temperature zones according to the ambient temperature. The inter-stage temperature target is set for normal temperature, low temperature and ultra-low temperature environments to achieve stable heating in the entire range from -30℃ to normal temperature. 2. Flexible control logic and good anti-surge effect. It adopts dual PID independent closed-loop control, which is linked with the anti-surge control line and the auxiliary return valve to significantly reduce compressor surge and protect the magnetic levitation bearing. 3. Improved operational stability: All temperature zone switching is set with a 3℃ hysteresis to avoid frequent compressor switching and parameter oscillation at critical points; 4. The safety protection system is good, and a multi-dimensional graded protection mechanism for temperature, pressure and surge is constructed. Different protection levels are distinguished for early warning, load reduction and fault shutdown. Fault handling is carried out in a layered response to prevent small faults from escalating into equipment damage and improve the safety of unit operation. 5. Protection of magnetic levitation components: A special start-stop sequence is designed for magnetic levitation bearings, strictly distinguishing between pre-lubrication, levitation, deceleration, and descent steps, matching the operating characteristics of the magnetic levitation compressor, and reducing bearing wear; 6. Mode isolation: Cooling and heating modes employ dual hardware and software interlocks to prevent the two modes from operating simultaneously, reducing the risk of control system failure. Attached Figure Description

[0014] Figure 1 This is the control logic block diagram of Embodiment 2. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the accompanying drawings.

[0016] Example 1: A dual-shaft, four-stage magnetic levitation compressor, comprising a low-temperature stage magnetic levitation two-stage compressor and a high-temperature stage magnetic levitation two-stage compressor. The low-temperature stage magnetic levitation two-stage compressor includes a primary compression unit and a secondary compression unit, while the high-temperature stage magnetic levitation two-stage compressor includes a tertiary compression unit and a quaternary compression unit. The specific working principle is as follows: the low-temperature, low-pressure refrigerant from the evaporator flows to the primary compression unit, then to the secondary compression unit; the low-temperature stage magnetic levitation two-stage compressor completes the process, then the refrigerant reaches the interstage temperature and pressure measurement units, then the tertiary compression unit, and finally the quaternary compression unit; the high-temperature stage magnetic levitation two-stage compressor completes the process, then the refrigerant reaches the condenser at high temperature and high pressure. The entire process is divided into four progressively increasing pressure stages, i.e., standard four-stage compression, splitting the total compression ratio across four units to avoid problems such as excessively high single-stage compression ratios, excessive exhaust temperatures, and increased energy consumption.

[0017] The rated speed range of the high-temperature magnetic levitation two-stage compressor is 15,000-36,000 rpm; the rated speed range of the low-temperature magnetic levitation two-stage compressor is 18,000-42,000 rpm.

[0018] Example 2: A working method of a dual-shaft series four-stage compression magnetic levitation compressor, including cooling mode control logic, heating mode temperature zone control logic, unit mode switching interlock logic, compressor start-stop interlock logic, start-stop timing logic, and multi-level protection logic.

[0019] Cooling mode control logic, At any ambient temperature, the low-temperature stage magnetic levitation two-stage compressor implements a shutdown electrical interlock, and only the high-temperature stage magnetic levitation two-stage compressor operates by frequency conversion; The PLC control module collects the inlet and outlet water temperatures of the high-temperature magnetic levitation two-stage compressor and adjusts the start and stop of the high-temperature magnetic levitation two-stage compressor through PID calculation, thereby realizing closed-loop control of the inlet and outlet water temperatures of the high-temperature magnetic levitation two-stage compressor.

[0020] The heating mode is divided into six temperature zones according to the ambient temperature, and a 3℃ hysteresis is set for all temperature zone switching; the operating speed ratio of the high-temperature stage magnetic levitation two-stage compressor and the low-temperature stage magnetic levitation two-stage compressor is set to be controlled in the range of 0.75-0.95. When the ambient temperature is >10℃, the low-temperature magnetic levitation two-stage compressor is shut down and locked, and only the high-temperature magnetic levitation two-stage compressor operates by frequency conversion. The high-temperature magnetic levitation two-stage compressor uses PID closed-loop speed regulation with the unit's inlet and outlet water temperatures as the target. When the ambient temperature is 0℃ < 10℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature corresponding to the interstage discharge pressure of 38℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperature of the unit as the control target for PID speed regulation. -10℃<Ambient temperature≤0℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the interstage discharge pressure corresponding to the temperature of 36℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the unit inlet and outlet water temperature as the control target for PID speed regulation. -20℃<Ambient temperature≤-10℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the interstage discharge pressure corresponding to the temperature of 33℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the unit inlet and outlet water temperature as the control target for PID speed regulation. -30℃≤Ambient temperature≤-20℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature of 30℃ corresponding to the interstage discharge pressure as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperature of the unit as the control target for PID speed regulation. When the ambient temperature is less than -30℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously using frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature corresponding to the interstage discharge pressure of 28℃ as the control target for PID speed regulation, while the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperatures of the unit as the control target for PID speed regulation.

[0021] The unit mode switching interlock logic, i.e., the switching between heating mode and cooling mode, involves the following steps. S1, the PLC control module controls the entire machine to reduce the load to the minimum speed; S2. After a 10-second delay, stop the currently running compressor unit; S3, maintain pressure balance for 5 seconds; S4. Switch the operating mode and start the compressor unit in the corresponding mode; S5. The entire process is protected by a double interlock to prevent the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor from being mistakenly put into operation at the same time.

[0022] Compressor switching interlock logic, In heating mode, when the ambient temperature crosses the critical point of 10℃, the switching control of the low-temperature stage magnetic levitation two-stage compressor is as follows: When the ambient temperature drops from above 10℃ to 10℃ or below, the low-temperature magnetic levitation two-stage compressor needs to be started. First, open the auxiliary reflux valve, start the low-temperature magnetic levitation two-stage compressor after the pressure is balanced for 3 seconds, then gradually increase the speed of the low-temperature magnetic levitation two-stage compressor, then close the auxiliary reflux valve and match the interstage exhaust pressure to the corresponding temperature. When the ambient temperature rises from 10℃ or below to above 10℃, the low-temperature magnetic levitation two-stage compressor needs to be stopped. First, open the auxiliary reflux valve to control the low-temperature magnetic levitation two-stage compressor to gradually reduce its speed. After the speed reduction is completed, stop the machine and execute the electrical interlock. Then close the auxiliary reflux valve. Emergency stop with differential pressure is prohibited.

[0023] The start / stop timing logic for either the low-temperature stage magnetic levitation two-stage compressor or the high-temperature stage magnetic levitation two-stage compressor. S1, Pre-lubrication for 3 seconds; S2. The magnetic levitation bearing establishes a levitation state, which lasts for 5 seconds; S3. Gradually increase the speed to the operating speed; S4. Shutdown procedure: Control the compressor to gradually reduce speed; S5. Confirm that the magnetic levitation bearing has completely fallen back; S6. Stop lubrication operation.

[0024] Multi-level protection logic, including high-pressure exhaust temperature protection, pressure protection, and surge protection: High-pressure exhaust temperature protection: when the high-pressure exhaust temperature is >95℃, load reduction protection is activated; when the temperature is >105℃, a fault shutdown is triggered. Interstage temperature protection: a warning signal is issued when the interstage temperature is >70℃, and load reduction protection is implemented when the interstage temperature is >78℃. Surge protection: If the compressor speed deviates from the anti-surge operating line, the speed is finely adjusted first, and at the same time, the auxiliary return valve is linked to control the flow and suppress the surge phenomenon.

[0025] All temperature ranges in this invention patent can be adjusted according to actual conditions.

[0026] Example 3: On-site commissioning process; To ensure the stable operation of the unit after its deployment, this invention includes standardized commissioning procedures. S1. Individually debug the high-temperature magnetic levitation two-stage compressor, and test the cooling condition and the heating condition with an ambient temperature > 10℃ in sequence to verify the PID speed regulation of inlet and outlet water temperature, speed range, and basic protection functions. S2. Series mode debugging: simulate low temperature conditions, put the low temperature stage magnetic levitation two-stage compressor into operation step by step, observe the temperature, pressure and speed ratio between stages, and ensure that the speed ratio between the high temperature stage magnetic levitation two-stage compressor and the low temperature stage magnetic levitation two-stage compressor is stable in the optimal range of 0.75-0.95. S3, Temperature zone switching test, simulates the critical points of ±10℃, -20℃, and -30℃, and verifies the hysteresis effect at 3℃ and the smoothness of compressor switching. S4. Extreme operating condition test: Simulate ultra-low temperature operating conditions below -30℃ and check whether the exhaust temperature, surge protection, and pressure parameters are normal. S5. Linkage test: Conduct a comprehensive test of all alarm and shutdown protection logic to ensure accurate and reliable fault response.

[0027] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for operating a dual-shaft, four-stage magnetic levitation compressor, comprising a low-temperature stage magnetic levitation two-stage compressor and a high-temperature stage magnetic levitation two-stage compressor, characterized in that: The low-temperature magnetic levitation two-stage compressor includes a primary compression unit and a secondary compression unit, while the high-temperature magnetic levitation two-stage compressor includes a tertiary compression unit and a quaternary compression unit. It includes cooling mode control logic, heating mode temperature zone control logic, unit mode switching interlock logic, compressor start-stop interlock logic, start-stop timing logic, and multi-level protection logic.

2. The operating method of a dual-shaft series four-stage compression magnetic levitation compressor according to claim 1, characterized in that: Cooling mode control logic, At any ambient temperature, the low-temperature stage magnetic levitation two-stage compressor implements a shutdown electrical interlock, and only the high-temperature stage magnetic levitation two-stage compressor operates by frequency conversion; The PLC control module collects the inlet and outlet water temperatures of the high-temperature magnetic levitation two-stage compressor and adjusts the start and stop of the high-temperature magnetic levitation two-stage compressor through PID calculation, thereby realizing closed-loop control of the inlet and outlet water temperatures of the high-temperature magnetic levitation two-stage compressor.

3. The operating method of a magnetic levitation compressor with dual-shaft series four-stage compression according to claim 1, characterized in that: Two magnetic levitation compressors are connected in series to achieve four-stage compression. In heating mode, when the two compressors are connected in series, the temperature zone control logic is divided into six temperature zones according to the ambient temperature. All temperature zone switching is set with a 3℃ hysteresis. The operating speed ratio of the high-temperature stage magnetic levitation two-stage compressor and the low-temperature stage magnetic levitation two-stage compressor is set to be controlled in the range of 0.75-0.

95. When the ambient temperature is >10℃, the low-temperature magnetic levitation two-stage compressor is shut down and locked, and only the high-temperature magnetic levitation two-stage compressor operates by frequency conversion. The high-temperature magnetic levitation two-stage compressor uses PID closed-loop speed regulation with the unit's inlet and outlet water temperatures as the target. When the ambient temperature is 0℃ < 10℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature corresponding to the interstage discharge pressure of 38℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperature of the unit as the control target for PID speed regulation. -10℃<Ambient temperature≤0℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the interstage discharge pressure corresponding to the temperature of 36℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the unit inlet and outlet water temperature as the control target for PID speed regulation. -20℃<Ambient temperature≤-10℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the interstage discharge pressure corresponding to the temperature of 33℃ as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the unit inlet and outlet water temperature as the control target for PID speed regulation. -30℃≤Ambient temperature≤-20℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously by frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature of 30℃ corresponding to the interstage discharge pressure as the control target for PID speed regulation, and the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperature of the unit as the control target for PID speed regulation. When the ambient temperature is less than -30℃, the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor operate simultaneously using frequency conversion. The low-temperature magnetic levitation two-stage compressor uses the temperature corresponding to the interstage discharge pressure of 28℃ as the control target for PID speed regulation, while the high-temperature magnetic levitation two-stage compressor uses the inlet and outlet water temperatures of the unit as the control target for PID speed regulation.

4. The operating method of a magnetic levitation compressor with dual-shaft series four-stage compression according to claim 1, characterized in that: The unit mode switching interlock logic, i.e., the switching between heating mode and cooling mode, involves the following steps. S1, the PLC control module controls the entire machine to reduce the load to the minimum speed; S2. After a 10-second delay, stop the currently running compressor unit; S3, maintain pressure balance for 5 seconds; S4. Switch the operating mode and start the compressor unit in the corresponding mode; S5. The entire process is protected by a double interlock to prevent the low-temperature magnetic levitation two-stage compressor and the high-temperature magnetic levitation two-stage compressor from being mistakenly put into operation at the same time.

5. The operating method of a magnetic levitation compressor with dual-shaft series four-stage compression according to claim 3, characterized in that: Compressor switching interlock logic, In heating mode, when the ambient temperature crosses the critical point of 10℃, the switching control of the low-temperature magnetic levitation two-stage compressor is as follows: the ratio of the operating speeds of the high-temperature magnetic levitation two-stage compressor and the low-temperature magnetic levitation two-stage compressor is controlled within the range of 0.75-0.

95. When the ambient temperature drops from above 10℃ to 10℃ or below, the low-temperature magnetic levitation two-stage compressor needs to be started. First, open the auxiliary reflux valve, start the low-temperature magnetic levitation two-stage compressor after the pressure is balanced for 3 seconds, then gradually increase the speed of the low-temperature magnetic levitation two-stage compressor, and then close the auxiliary reflux valve to match the interstage exhaust pressure to the corresponding temperature. When the ambient temperature rises from 10℃ or below to above 10℃, the low-temperature magnetic levitation two-stage compressor needs to be stopped. First, open the auxiliary reflux valve to control the low-temperature magnetic levitation two-stage compressor to gradually reduce its speed. After the speed reduction is completed, stop the machine and execute the electrical interlock. Then close the auxiliary reflux valve. Emergency stop with differential pressure is prohibited.

6. The operating method of a dual-shaft series four-stage compression magnetic levitation compressor according to claim 1, characterized in that: The start / stop timing logic for either the low-temperature stage magnetic levitation two-stage compressor or the high-temperature stage magnetic levitation two-stage compressor. S1, Pre-lubrication for 3 seconds; S2. The magnetic levitation bearing establishes a levitation state, which lasts for 5 seconds; S3. Gradually increase the speed to the operating speed; S4. Shutdown procedure: Control the compressor to gradually reduce speed; S5. Confirm that the magnetic levitation bearing has completely fallen back; S6. Stop lubrication operation.

7. The operating method of a dual-shaft series four-stage compression magnetic levitation compressor according to claim 1, characterized in that: Multi-level protection logic, including high-pressure exhaust temperature protection, pressure protection, and surge protection: High-pressure exhaust temperature protection: when the high-pressure exhaust temperature is >95℃, load reduction protection is activated; when the temperature is >105℃, a fault shutdown is triggered. Interstage temperature protection: a warning signal is issued when the interstage temperature is >70℃, and load reduction protection is implemented when the interstage temperature is >78℃. Surge protection: If the compressor speed deviates from the anti-surge operating line, the speed is finely adjusted first, and at the same time, the auxiliary return valve is linked to control the flow and suppress the surge phenomenon.

8. The operating method of a magnetic levitation compressor with dual-shaft series four-stage compression according to claim 1, characterized in that: The rated speed range of the high-temperature magnetic levitation two-stage compressor is 15,000-36,000 rpm; The rated speed range of the low-temperature magnetic levitation two-stage compressor is 18,000-42,000 rpm.

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