Magnetic suspension ORC unit and control method

Abstract

The application discloses a kind of magnetic suspension ORC units and control method, it is related to low-temperature waste heat power generation technical field;The unit includes magnetic suspension motor, turbine, evaporator, preheater, condenser, liquid storage tank, working medium pump and control system;Magnetic suspension motor is coaxial direct connection with turbine, and constitutes oil-free integrated closed structure;Control system includes PLC controller, four-quadrant frequency converter, turbine inlet regulating valve, hot gas bypass valve and sensor assembly;PLC controller inside preset turbine performance curve and working medium property model, configured to: real-time calculation turbine import and export pressure ratio, query performance curve to determine the best speed target value, through adjusting turbine inlet regulating valve control magnetic suspension motor speed track the target value.The application solves the problems of large mechanical friction loss, high maintenance cost and low variable condition efficiency of existing ORC unit, and realizes efficient and stable operation of the unit under wide operating conditions through collaborative control strategy.

Description

Technical Field

[0001] This invention relates to the field of cryogenic power generation technology, and in particular to a magnetic levitation ORC generator unit and its control method. Background Technology

[0002] Organic Rankine cycle technology is an effective means of recovering low-grade heat energy. In existing organic Rankine cycle generator sets, the expander (turbine) is usually connected to the generator via a coupling and supported by traditional mechanical bearings.

[0003] Existing technologies suffer from the following drawbacks: First, system efficiency is limited. Mechanical bearings and gearboxes inevitably experience mechanical frictional power consumption, which is converted into heat dissipation, reducing the efficiency of waste heat to electrical energy conversion. Second, maintenance dependence is high. Traditional lubrication systems not only increase auxiliary machine power consumption but also require regular replacement of filters and oil. For industrial enterprises with continuous production, downtime for maintenance means significant economic losses. Third, dynamic adaptability is poor. Faced with unstable waste heat sources, traditional units struggle to maintain efficient operation across a wide range of operating conditions, and the lifespan of mechanical bearings deteriorates significantly under high-speed conditions, hindering the miniaturization and efficiency development of these units.

[0004] In addition, existing ORC control systems mostly use single-parameter control, such as adjusting the working fluid pump frequency only according to the evaporation pressure, or adjusting the valve only according to the load. They lack coordinated optimization control of turbine efficiency and system safety, making it difficult to ensure the unit's high efficiency and reliability at the same time when the heat source fluctuates.

[0005] Therefore, how to design an oil-free, high-efficiency magnetic levitation ORC unit with intelligent collaborative control capabilities is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a magnetic levitation ORC unit and control method, thereby solving the aforementioned problems existing in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In the first aspect, a magnetic levitation ORC unit includes a magnetic levitation motor, a turbine, an evaporator, a preheater, a condenser, a liquid storage tank, a working fluid pump, and a control system.

[0009] The magnetic levitation motor is coaxially and directly connected to the turbine, and is supported by magnetic levitation bearings, forming an integrated closed structure;

[0010] The evaporator, preheater, turbine, condenser, liquid storage tank and working fluid pump are connected in sequence through pipelines to form a closed organic Rankine loop.

[0011] The control system includes a PLC controller, a four-quadrant frequency converter, a turbine inlet regulating valve, a hot gas bypass valve, and sensor components.

[0012] The sensor assembly includes an intake pressure transmitter and an intake temperature sensor located at the turbine inlet, and an exhaust pressure transmitter and an exhaust temperature sensor located at the turbine outlet.

[0013] The PLC controller is connected to the four-quadrant frequency converter, turbine inlet regulating valve, hot gas bypass valve and sensor assembly respectively.

[0014] The PLC controller has a pre-set turbine performance curve, which represents the optimal speed corresponding to the highest turbine efficiency under different pressure ratios.

[0015] The PLC controller is configured to: calculate the current pressure ratio based on the turbine inlet and outlet pressures, determine the optimal speed target value under the current operating conditions based on the performance curve, and adjust the flow rate of the working fluid entering the turbine by controlling the opening of the turbine inlet regulating valve, thereby adjusting the speed of the magnetic levitation motor to track the optimal speed target value.

[0016] In some specific embodiments, the magnetic levitation motor is a permanent magnet synchronous magnetic levitation generator;

[0017] The permanent magnet synchronous magnetic levitation generator is connected to the power grid through the full-power converter component in the four-quadrant frequency converter;

[0018] The four-quadrant frequency converter is configured to drive the magnetic levitation motor to switch between motoring and generating states.

[0019] In some specific embodiments, the turbine inlet regulating valve is installed on the pipeline between the evaporator and the turbine;

[0020] The inlet end of the hot gas bypass valve is connected to the pipeline before the turbine inlet regulating valve, and the outlet end is connected to the pipeline after the turbine outlet.

[0021] The PLC controller is also configured to: gradually open the turbine inlet regulating valve and gradually close the hot gas bypass valve when the unit starts up; and close the turbine inlet regulating valve and open the hot gas bypass valve when the unit stops or the inlet pressure is higher than the preset protection value.

[0022] In some specific embodiments, a tank level gauge is installed on the storage tank, and the tank level gauge is connected to the PLC controller signal.

[0023] The PLC controller is also configured to provide net positive suction head (NPSH) protection and level interlock for the working fluid pump based on the signal from the tank level gauge.

[0024] Secondly, a control method for a magnetic levitation ORC unit includes the following steps:

[0025] S1: Real-time acquisition of turbine inlet and outlet pressures, and calculation of the current pressure ratio;

[0026] S2: Preset turbine performance curves in the PLC controller. The performance curves represent the optimal speed corresponding to the highest turbine efficiency under different pressure ratios.

[0027] S3: Query the performance curve based on the current pressure ratio to obtain the optimal target speed value under the current operating conditions;

[0028] S4: Compare the target speed with the current speed of the magnetic levitation motor, and adjust the opening of the turbine inlet regulating valve to change the flow rate of the working fluid entering the turbine, thereby adjusting the speed of the magnetic levitation motor to track the target speed.

[0029] S5: Calculate the superheat of the working fluid at the turbine inlet based on the turbine inlet pressure and temperature, combined with the organic working fluid saturated vapor pressure model pre-installed in the PLC controller.

[0030] S6: Compare the superheat with the set value, and adjust the frequency of the working fluid pump through PID to maintain the superheat within the set range.

[0031] In some specific embodiments, in step S2, the turbine performance curve is obtained through experimental calibration, CFD simulation or theoretical calculation, and is pre-set in the PLC controller in the form of a data table or function.

[0032] In some specific embodiments, in step S5, the saturated vapor pressure model of the organic working fluid is constructed based on the NIST physical property database or the REFPROP program, and stored in the PLC controller using polynomial fitting or table lookup method.

[0033] In some specific embodiments, start-stop and protection control steps are also included:

[0034] During the unit startup phase, the turbine inlet regulating valve is gradually opened and the hot gas bypass valve is gradually closed. Once the speed and superheat reach the safety threshold, the control steps S1 to S6 are activated.

[0035] During unit shutdown, quickly close the turbine inlet regulating valve, open the hot gas bypass valve, and reduce the working fluid pump frequency;

[0036] During operation, when the intake pressure exceeds the preset protection value, the hot gas bypass valve is opened to release pressure.

[0037] In some specific embodiments, step S4 further includes security restriction logic:

[0038] During the process of adjusting the speed of the magnetic levitation motor to track the optimal target speed value, the target speed of the magnetic levitation motor is always limited to be lower than its maximum allowable speed in real time.

[0039] The beneficial effects of this invention are:

[0040] 1. The use of magnetic levitation bearing technology enables oil-free direct connection between the motor and the turbine, eliminating mechanical friction loss, improving system efficiency, and avoiding downtime losses caused by lubrication maintenance.

[0041] 2. A pressure ratio-speed optimization control strategy based on turbine performance curves was constructed, which can adapt to heat source fluctuations and ensure that the turbine always operates in the high-efficiency range, significantly improving power generation efficiency under a wide range of operating conditions.

[0042] 3. It achieves the synergy of speed optimization and superheat control. While pursuing high efficiency, it ensures turbine safety through closed-loop superheat control and avoids the risk of liquid slugging.

[0043] 4. The application of four-quadrant frequency converters enables soft start and energy feedback of the unit, improving grid connection stability. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of the magnetic levitation ORC unit and control system in an embodiment of the present invention;

[0045] Figure 2 This is a flowchart of the magnetic levitation ORC unit control method in an embodiment of the present invention.

[0046] In the attached diagram, 1-magnetic levitation motor, 2-turbine, 3-condenser, 4-storage tank, 5-working fluid pump, 6-preheater, 7-evaporator, 8-four-quadrant frequency converter, 9-PLC controller, 10-turbine inlet regulating valve, 11-hot gas bypass valve, 12-inlet pressure transmitter, 13-inlet temperature sensor, 14-exhaust pressure transmitter, 15-exhaust temperature sensor, 16-storage tank level gauge. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] Firstly, referring to Figure 1 As shown, a magnetic levitation ORC unit includes a magnetic levitation motor, a turbine, an evaporator, a preheater, a condenser, a liquid storage tank, a working fluid pump, and a control system.

[0049] The magnetic levitation motor is coaxially and directly connected to the turbine, and is supported by magnetic levitation bearings, forming an integrated closed structure;

[0050] The evaporator, preheater, turbine, condenser, liquid storage tank and working fluid pump are connected in sequence through pipelines to form a closed organic Rankine loop.

[0051] The control system includes a PLC controller, a four-quadrant frequency converter, a turbine inlet regulating valve, a hot gas bypass valve, and sensor components.

[0052] The sensor assembly includes an intake pressure transmitter and an intake temperature sensor located at the turbine inlet, and an exhaust pressure transmitter and an exhaust temperature sensor located at the turbine outlet.

[0053] The PLC controller is connected to the four-quadrant frequency converter, turbine inlet regulating valve, hot gas bypass valve and sensor assembly respectively.

[0054] The PLC controller has a pre-set turbine performance curve, which represents the optimal speed corresponding to the highest turbine efficiency under different pressure ratios.

[0055] The PLC controller is configured to: calculate the current pressure ratio based on the turbine inlet and outlet pressures, determine the optimal speed target value under the current operating conditions based on the performance curve, and adjust the flow rate of the working fluid entering the turbine by controlling the opening of the turbine inlet regulating valve, thereby adjusting the speed of the magnetic levitation motor to track the optimal speed target value.

[0056] like Figure 1 As shown, the unit in this embodiment adopts a skid-mounted integrated design. The core power unit consists of a magnetic levitation motor 1 and a turbine 2. The magnetic levitation motor 1 is a high-speed permanent magnet synchronous motor, and its rotor is directly connected to the impeller of the turbine 2 on the same coaxial axis, that is, the two are fixed on the same main shaft without a gearbox or coupling in between. The main shaft is supported without contact by a magnetic levitation bearing system. The sensors integrated inside the motor and the bearing controller work together to achieve stable levitation of the rotor, completely eliminating mechanical friction and eliminating the need for a lubrication system.

[0057] The closed-loop organic Rankine cycle is constructed as follows: the outlet of the working fluid pump 5 is connected to the working fluid side inlet of the preheater 6 via a pressure pipe; the working fluid side outlet of the preheater 6 is connected to the working fluid side inlet of the evaporator 7; the working fluid side outlet of the evaporator 7 is connected to the air inlet of the turbine 2 via a pipe; the exhaust port of the turbine 2 is connected to the working fluid side inlet of the condenser 3 via a pipe; the working fluid side outlet of the condenser 3 is connected to the inlet of the liquid storage tank 4; and the outlet of the liquid storage tank 4 is connected to the inlet of the working fluid pump 5. The organic working fluid circulates in this loop.

[0058] The hardware configuration of the control system is as follows: PLC controller 9 serves as the core processing unit, and its signal input terminals are connected to the intake pressure transmitter 12, intake temperature sensor 13, and exhaust pressure transmitter 14 respectively via signal lines. The control output terminals of PLC controller 9 are connected to the actuator of turbine inlet regulating valve 10 via analog signal lines or industrial communication bus.

[0059] The PLC controller 9 has a pre-set turbine performance curve in its internal storage unit. This curve is stored in the form of a data table or function formula, and it represents the optimal speed value corresponding to the point where the turbine has the highest efficiency at different pressure ratios (the ratio of inlet pressure to outlet pressure).

[0060] The specific control process is as follows: PLC controller 9 reads the values ​​from inlet pressure transmitter 12 and exhaust pressure transmitter 14 in real time and calculates the current pressure ratio of turbine 2. PLC controller 9 calls the internally preset performance curve to find or calculate the optimal speed target value corresponding to this pressure ratio. Subsequently, PLC controller 9 compares the current speed of magnetic levitation motor 1, which is monitored in real time, with this target value. If the current speed is lower than the target value, PLC controller 9 outputs a control signal to increase the opening of turbine inlet regulating valve 10, increasing the steam flow into turbine 2, thereby increasing the turbine output torque and driving magnetic levitation motor 1 to accelerate; conversely, it decreases the valve opening to reduce speed. Through this closed-loop control, it ensures that turbine 2 always tracks the optimal efficiency point under different heat source conditions.

[0061] In some specific embodiments, the magnetic levitation motor is a permanent magnet synchronous magnetic levitation generator;

[0062] The permanent magnet synchronous magnetic levitation generator is connected to the power grid through the full-power converter component in the four-quadrant frequency converter;

[0063] The four-quadrant frequency converter is configured to drive the magnetic levitation motor to switch between motoring and generating states.

[0064] In this embodiment, the magnetic levitation motor 1 is a permanent magnet synchronous magnetic levitation generator. The stator winding of the motor is connected to the motor-side port of the four-quadrant frequency converter 8. The four-quadrant frequency converter 8 adopts a back-to-back dual PWM converter structure, including a motor-side converter and a grid-side converter.

[0065] The implementation process is divided into two phases:

[0066] Start-up phase: PLC controller 9 sends instructions to four-quadrant frequency converter 8. At this time, the frequency converter works in inverter mode, absorbs power from the grid, drives magnetic levitation motor 1 as a motor, drives turbine 2 to idle to the set speed, and establishes initial circulating pressure.

[0067] During power generation: When turbine 2 has sufficient power to drive the motor to generate electricity, the four-quadrant frequency converter 8 automatically switches control strategies. The motor-side converter operates in rectification mode, converting the variable frequency and variable voltage AC power generated by the motor into DC power; the grid-side converter operates in inverter mode, converting the DC power into AC power with the same voltage, frequency, and phase as the grid, and smoothly integrating it into the user's grid through the full-power converter components.

[0068] In some specific embodiments, the turbine inlet regulating valve is installed on the pipeline between the evaporator and the turbine;

[0069] The inlet end of the hot gas bypass valve is connected to the pipeline before the turbine inlet regulating valve, and the outlet end is connected to the pipeline after the turbine outlet.

[0070] The PLC controller is also configured to: gradually open the turbine inlet regulating valve and gradually close the hot gas bypass valve when the unit starts up; and close the turbine inlet regulating valve and open the hot gas bypass valve when the unit stops or the inlet pressure is higher than the preset protection value.

[0071] Turbine inlet regulating valve 10 is installed on the main steam pipeline from the outlet of evaporator 7 to the inlet of turbine 2. Hot gas bypass valve 11 is installed on the bypass pipeline, with its inlet end connected to the pipeline before turbine inlet regulating valve 10 and its outlet end connected to the pipeline after turbine 2 outlet, that is, hot gas bypass valve 11 is connected across both ends of turbine 2.

[0072] PLC controller 9 has a built-in start / stop control logic module:

[0073] Startup logic implementation: At the initial startup of the unit, PLC controller 9 controls the turbine inlet regulating valve 10 to be closed and the hot gas bypass valve 11 to be fully open. As steam is produced by evaporator 7, the steam directly enters condenser 3 through hot gas bypass valve 11, avoiding impact on turbine 2. Subsequently, PLC controller 9 gradually opens turbine inlet regulating valve 10 according to a preset rate, while simultaneously gradually closing hot gas bypass valve 11, achieving a smooth steam flow into turbine 2.

[0074] Shutdown / Overpressure Logic Implementation: When the PLC controller 9 receives a shutdown signal or detects that the value of the inlet pressure transmitter 12 is higher than the preset protection threshold, it immediately outputs a command to quickly close the turbine inlet regulating valve 10, cut off the steam source, and at the same time quickly opens the hot gas bypass valve 11 to release the high-pressure steam in the system to the condenser 3, ensuring system safety.

[0075] In some specific embodiments, a tank level gauge is installed on the storage tank, and the tank level gauge is connected to the PLC controller signal.

[0076] The PLC controller is also configured to provide net positive suction head (NPSH) protection and level interlock for the working fluid pump based on the signal from the tank level gauge.

[0077] The signal input terminal of the PLC controller 9 is also connected to the intake air temperature sensor 13. The storage unit of the PLC controller 9 contains a pre-set saturated vapor pressure model of the organic working fluid, which records the single-value correspondence between the working fluid pressure and the corresponding saturation temperature.

[0078] The control process is as follows: PLC controller 9 reads the value of the intake pressure transmitter 12 in real time, substitutes it into the saturated vapor pressure model to calculate the saturation temperature of the working fluid under the current pressure. PLC controller 9 subtracts the saturation temperature from the temperature value measured by intake temperature sensor 13 to calculate the actual superheat.

[0079] The PLC controller 9 compares the actual superheat with the internally set target superheat range. If the actual superheat is lower than the lower limit of the set range, it indicates a risk of liquid slugging at the turbine 2 inlet. The PLC controller 9 outputs an analog signal to reduce the output frequency of the working fluid pump 5 inverter, thereby reducing the working fluid circulation and increasing the superheat of the steam at the evaporator 7 outlet. This control logic operates independently and in parallel with the aforementioned speed control logic, without interfering with each other.

[0080] To further explain, a tank level gauge 16 is installed on the cylinder of the storage tank 4, and the signal output terminal of the level gauge is connected to the signal input terminal of the PLC controller 9.

[0081] The PLC controller 9 has an internally set liquid level safety threshold. During implementation, the PLC controller 9 monitors the value of the liquid level gauge 16 in the storage tank in real time. When the liquid level drops to the low liquid level warning value, the PLC controller 9 triggers an alarm or limits the speed of the working fluid pump 5 to prevent cavitation at the inlet of the working fluid pump 5. When the liquid level drops further to a dangerously low level, the PLC controller 9 triggers an interlocking shutdown logic, cutting off the power supply to the working fluid pump 5 to protect the equipment.

[0082] Secondly, referring to Figure 2 The control method of a magnetic levitation ORC unit shown includes the following steps:

[0083] S1: Real-time acquisition of turbine inlet and outlet pressures, and calculation of the current pressure ratio.

[0084] Specifically, during unit operation, the PLC controller 9 acquires current or voltage signals in real time from the inlet pressure transmitter 12 at the turbine inlet and the exhaust pressure transmitter 14 at the turbine outlet via its analog input module. The PLC controller 9's internal program first converts these electrical signals into physical pressure values, then performs a division operation, dividing the turbine inlet pressure value by the turbine outlet pressure value to calculate the actual turbine pressure ratio under the current operating conditions. This acquisition and calculation process is executed cyclically at millisecond intervals to ensure real-time data accuracy.

[0085] S2: Preset turbine performance curves in the PLC controller. The performance curves represent the optimal speed corresponding to the highest turbine efficiency under different pressure ratios.

[0086] This step specifically involves: before the unit is put into operation or during the program initialization phase, presetting the turbine performance curve in the non-volatile memory area of ​​PLC controller 9. Specifically, the optimal efficiency speed data of the turbine at different pressure ratios is written into the program block of PLC controller 9 in the form of a two-dimensional array table or a fitted polynomial. This curve establishes a mapping relationship, meaning that each turbine pressure ratio value corresponds to a unique optimal speed target value that maximizes turbine efficiency.

[0087] S3: Based on the current pressure ratio, query the performance curve to obtain the optimal target speed value under the current operating conditions.

[0088] Specifically, this step involves the PLC controller 9 executing a table lookup or function operation. After step S1 calculates the current pressure ratio, the PLC controller 9 uses this pressure ratio as an index to search through preset turbine performance curve data. If the current pressure ratio falls between discrete data points, the PLC controller 9 uses a linear interpolation algorithm to calculate the corresponding optimal target speed value. This target value represents the speed required for turbine 2 to achieve its highest operating efficiency under the current heat and cold source conditions.

[0089] S4: Compare the target speed with the current speed of the magnetic levitation motor. By adjusting the opening of the turbine inlet regulating valve, the flow rate of the working fluid entering the turbine is changed, thereby adjusting the speed of the magnetic levitation motor to track the target speed.

[0090] This step is specifically as follows: This step is the closed-loop speed adjustment process. The PLC controller 9 reads the current actual speed fed back by the encoder of the magnetic levitation motor 1 through the communication bus, and subtracts it from the optimal speed target value obtained in step S3 to obtain the speed deviation.

[0091] When the actual rotational speed is lower than the target optimal rotational speed, the PLC controller 9 outputs an increased control signal to the actuator of the turbine inlet regulating valve 10 through PID calculation. The turbine inlet regulating valve 10 responds to the signal by increasing its opening, thereby increasing the flow rate of the organic working fluid entering the turbine 2, increasing the turbine's working torque, and thus driving the magnetic levitation motor 1 to accelerate.

[0092] When the actual speed is higher than the target value of the optimal speed, the PLC controller 9 outputs a reduced control signal, the turbine inlet regulating valve 10 closes, the working fluid intake is reduced, the turbine work is reduced, and the magnetic levitation motor 1 decelerates.

[0093] Through the above feedback adjustment, the rotational speed of the magnetic levitation motor 1 is always dynamically tracked to the optimal rotational speed target value.

[0094] S5: Calculate the superheat of the working fluid at the turbine inlet based on the turbine inlet pressure and temperature, combined with the organic working fluid saturated vapor pressure model pre-installed in the PLC controller.

[0095] This step specifically involves the superheat calculation process. The PLC controller 9 reads the values ​​from the inlet pressure transmitter 12 and the inlet temperature sensor 13 in real time. The PLC controller 9 calls upon its internally stored organic working fluid saturated vapor pressure model (i.e., the functional relationship between pressure and saturation temperature), substitutes the currently collected inlet pressure value into the model, and calculates the saturation temperature of the working fluid at that pressure. Subsequently, the PLC controller 9 subtracts the calculated saturation temperature from the collected inlet temperature; the difference between the two is the actual superheat of the working fluid at the turbine inlet.

[0096] S6: Compare the superheat with the set value, and adjust the frequency of the working fluid pump through PID to maintain the superheat within the set range.

[0097] This step specifically involves a closed-loop superheat adjustment process. The PLC controller 9 compares the actual superheat calculated in step S5 with the preset superheat setpoint and calculates the deviation.

[0098] If the actual superheat is lower than the set value, it indicates a risk of liquid slugging at the turbine inlet. The PLC controller 9 outputs a command to reduce the frequency to the inverter of the working fluid pump 5 through a PID algorithm. The reduced speed of the working fluid pump 5 decreases the flow rate of the working fluid entering the evaporator 7, allowing the working fluid to absorb more heat and evaporate fully in the evaporator, thereby increasing the outlet superheat.

[0099] If the actual superheat is higher than the set value, it indicates that the evaporator's heat exchange capacity is not being fully utilized. The PLC controller 9 outputs a command to increase the frequency, thereby increasing the working fluid circulation and reducing the superheat. This adjustment stabilizes the superheat within the set range, ensuring turbine safety.

[0100] In some specific embodiments, in step S2, the turbine performance curve is obtained through experimental calibration, CFD simulation or theoretical calculation, and is pre-set in the PLC controller in the form of a data table or function.

[0101] In this embodiment, the performance curve of turbine 2 is not a simple linear relationship, but a multidimensional dataset. It is obtained as follows: during the turbine design and manufacturing stage, isentropic efficiency data of the turbine at different pressure ratios and rotational speeds are obtained through bench testing calibration or computational fluid dynamics (CFD) simulation calculations. The rotational speed values ​​corresponding to the highest efficiency points at each pressure ratio are extracted to form a "pressure ratio - optimal rotational speed" data pair.

[0102] During the implementation of the control system, these data pairs are written into the non-volatile memory of the PLC controller 9 in the form of a two-dimensional array table, or they are fitted into a polynomial function formula and written into the control program. After the PLC controller 9 calculates the current pressure ratio, it can output the corresponding optimal speed target value in real time through table lookup algorithm or function calculation.

[0103] In some specific embodiments, in step S5, the saturated vapor pressure model of the organic working fluid is constructed based on the NIST physical property database or the REFPROP program, and stored in the PLC controller using polynomial fitting or table lookup method.

[0104] Furthermore, to meet the rapid calculation requirements of the PLC controller 9, the saturated vapor pressure model is typically constructed using a polynomial fitting method. Specifically, this involves consulting the NIST property database or the REFPROP program to obtain multiple sets of discrete "pressure-saturation temperature" data points for the organic working fluid within its operating pressure range. Using the least squares method, these data points are curve-fitted to obtain a high-order polynomial formula, Tsat = f(P). In the control program, simply substituting the collected pressure value P into this polynomial formula allows for rapid calculation of the saturation temperature Tsat, avoiding complex real-time database queries and ensuring the real-time performance and accuracy of the superheat calculation.

[0105] In some specific embodiments, start-stop and protection control steps are also included:

[0106] During the unit startup phase, the turbine inlet regulating valve is gradually opened and the hot gas bypass valve is gradually closed. Once the speed and superheat reach the safety threshold, the control steps S1 to S6 are activated.

[0107] During unit shutdown, quickly close the turbine inlet regulating valve, open the hot gas bypass valve, and reduce the working fluid pump frequency;

[0108] During operation, when the intake pressure exceeds the preset protection value, the hot gas bypass valve is opened to release pressure.

[0109] During the unit startup phase, the PLC controller 9 executes the following steps: First, the working fluid pump 5 is turned on to establish a basic flow rate, while the turbine inlet regulating valve 10 is kept closed and the hot gas bypass valve 11 is opened, allowing the working fluid to circulate and heat in the bypass. When the outlet pressure and temperature of the evaporator 7 are detected to reach the preset threshold, and the speed of the magnetic levitation motor 1 stabilizes, the PLC controller 9 begins to execute the switching logic: gradually increasing the opening of the turbine inlet regulating valve 10 while decreasing the opening of the hot gas bypass valve 11, until the turbine inlet regulating valve 10 is fully open and the hot gas bypass valve 11 is fully closed, the unit enters normal operation, and the control logic described in claims 6 and 7 begins to intervene in the adjustment.

[0110] During the unit shutdown phase, PLC controller 9 prioritizes rapid unloading: immediately closes turbine inlet regulating valve 10, fully opens hot gas bypass valve 11, and simultaneously outputs a command to reduce the frequency of working fluid pump 5 to the minimum, ensuring that turbine 2 quickly leaves the working condition.

[0111] In some specific embodiments, step S4 further includes security restriction logic:

[0112] During the process of adjusting the speed of the magnetic levitation motor to track the optimal target speed value, the target speed of the magnetic levitation motor is always limited to be lower than its maximum allowable speed in real time.

[0113] During the control process, the PLC controller 9 adds a safety limiting step before outputting the speed adjustment command. The PLC controller 9 internally stores the maximum allowable speed parameter of the magnetic levitation motor 1, which is determined by the mechanical strength of the motor rotor.

[0114] The implementation process is as follows: The PLC controller 9 obtains the optimal target speed value from the performance curve based on the pressure ratio, and then compares this target value with the maximum permissible speed. If the target value is lower than the maximum permissible speed, the target value is used as the actual execution value to adjust the valve; if the target value is equal to or higher than the maximum permissible speed, the actual execution value is clamped at the maximum permissible speed, and the speed is no longer increased. This logic ensures that the unit pursues maximum efficiency without damaging the mechanical structure due to overspeed.

[0115] By adopting the above-disclosed technical solution of this invention, the following beneficial effects are obtained:

[0116] This invention provides a magnetic levitation ORC generator unit and its control method. It proposes the process flow, grid connection scheme, and unit control method of the magnetic levitation ORC system. Based on the control characteristics of the ORC waste heat generator unit based on the organic Rankine cycle system and permanent magnet synchronous magnetic levitation generator, the system utilizes internal valves, instruments, pressure transmitters, and temperature sensors to perform regulation, control, and interlock protection according to the control program, ensuring the stability and reliability of the ORC waste heat generator unit during start-up, shutdown, normal operation, and changes in operating conditions.

[0117] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A magnetic levitation ORC unit, characterized in that, It includes a magnetic levitation motor (1), a turbine (2), an evaporator (7), a preheater (6), a condenser (3), a liquid storage tank (4), a working fluid pump (5), and a control system; The magnetic levitation motor (1) is coaxially connected to the turbine (2) and supported by magnetic levitation bearings, forming an integrated closed structure; The evaporator (7), preheater (6), turbine (2), condenser (3), liquid storage tank (4) and working fluid pump (5) are connected in sequence through pipelines to form a closed organic Rankine loop. The control system includes a PLC controller (9), a four-quadrant frequency converter (8), a turbine inlet regulating valve (10), a hot gas bypass valve (11), and a sensor assembly; The sensor assembly includes an intake pressure transmitter (12) and an intake temperature sensor (13) disposed at the inlet of the turbine (2), and an exhaust pressure transmitter (14) and an exhaust temperature sensor (15) disposed at the outlet of the turbine (2). The PLC controller (9) is connected to the four-quadrant frequency converter (8), turbine inlet regulating valve (10), hot gas bypass valve (11) and sensor assembly respectively; The PLC controller (9) has a pre-set turbine (2) performance curve, which represents the optimal speed corresponding to the highest efficiency of the turbine (2) under different pressure ratios. The PLC controller (9) is configured to: calculate the current pressure ratio based on the inlet pressure and outlet pressure of the turbine (2), determine the optimal speed target value under the current operating conditions based on the performance curve, and adjust the working fluid flow rate into the turbine (2) by controlling the opening of the turbine inlet regulating valve (10), thereby adjusting the speed of the magnetic levitation motor (1) so that it tracks the optimal speed target value.

2. The magnetic levitation ORC unit according to claim 1, characterized in that, The magnetic levitation motor (1) is a permanent magnet synchronous magnetic levitation generator; The permanent magnet synchronous magnetic levitation generator is connected to the power grid through the full-power converter component in the four-quadrant frequency converter (8); The four-quadrant frequency converter (8) is configured to drive the magnetic levitation motor (1) to switch between electric and generator states.

3. The magnetic levitation ORC unit according to claim 1, characterized in that, The turbine inlet regulating valve (10) is installed on the pipeline between the evaporator (7) and the turbine (2); The inlet end of the hot gas bypass valve (11) is connected to the pipeline before the turbine inlet regulating valve (10), and the outlet end is connected to the pipeline after the turbine (2) outlet. The PLC controller (9) is also configured to: when the unit starts up, control the turbine inlet regulating valve (10) to open gradually, and at the same time control the hot gas bypass valve (11) to close gradually; when the unit stops or the inlet pressure is higher than the preset protection value, control the turbine inlet regulating valve (10) to close, and control the hot gas bypass valve (11) to open.

4. The magnetic levitation ORC unit according to claim 1, characterized in that, The storage tank (4) is equipped with a storage tank level gauge (16), and the storage tank level gauge (16) is connected to the PLC controller (9) via signal. The PLC controller (9) is also configured to provide net positive suction head (NPSH) protection and level interlock for the working fluid pump (5) based on the signal from the tank level gauge (16).

5. A control method for a magnetic levitation ORC unit as described in any one of claims 1-4, characterized in that, Includes the following steps: S1: Real-time acquisition of turbine (2) inlet and outlet pressures, and calculation of the current pressure ratio; S2: The turbine (2) performance curve is preset in the PLC controller (9). The performance curve represents the optimal speed corresponding to the highest efficiency of the turbine (2) under different pressure ratios. S3: Query the performance curve based on the current pressure ratio to obtain the optimal target speed value under the current operating conditions; S4: Compare the target value of the optimal speed with the current speed of the magnetic levitation motor (1), and change the flow rate of the working fluid entering the turbine (2) by adjusting the opening of the turbine inlet regulating valve (10), thereby adjusting the speed of the magnetic levitation motor (1) so that it tracks the target value of the optimal speed. S5: Based on the turbine (2) inlet pressure and temperature, combined with the organic working fluid saturated vapor pressure model pre-installed in the PLC controller (9), calculate the superheat of the turbine (2) inlet working fluid; S6: Compare the superheat with the set value, and adjust the frequency of the working fluid pump (5) by PID to maintain the superheat within the set range.

6. The control method according to claim 5, characterized in that, In step S2, the turbine (2) performance curve is obtained through experimental calibration, CFD simulation or theoretical calculation, and is pre-set in the PLC controller (9) in the form of a data table or function.

7. The control method according to claim 5, characterized in that, In step S5, the saturated vapor pressure model of the organic working fluid is constructed based on the NIST physical property database or the REFPROP program, and stored in the PLC controller (9) using polynomial fitting or table lookup method.

8. The control method according to claim 5, characterized in that, It also includes start-stop and protection control procedures: During the unit startup phase, the turbine inlet regulating valve (10) is gradually opened and the hot gas bypass valve (11) is gradually closed. After the speed and superheat reach the safety threshold, the control steps S1 to S6 are activated. During the unit shutdown phase, quickly close the turbine inlet regulating valve (10), open the hot gas bypass valve (11), and reduce the frequency of the working fluid pump (5); During operation, when the intake pressure is higher than the preset protection value, the hot gas bypass valve (11) is opened to release pressure.

9. The control method according to claim 5, characterized in that, Step S4 also includes security restriction logic: During the process of adjusting the speed of the magnetic levitation motor (1) to track the optimal speed target value, the target speed of the magnetic levitation motor (1) is always limited to be lower than its maximum allowable speed in real time.

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