A two-stage methanol fuel supply bidirectional collaborative pressure stabilizing control method and system for a ship

Abstract

The application discloses a kind of ship methanol fuel two-stage supply bidirectional collaborative pressure stabilizing control method and system, belong to ship new energy power and fluid industrial control technical field.The method is aimed at two-stage methanol supply architecture in series, sequentially executes the serial start-up process of pre-position safety interlock start, low-pressure loop pressure building, high-pressure loop pressure building;After system normal operation, high-pressure return valve opening degree regulation fast ring and high-pressure pump frequency conversion regulation slow ring are synchronously operated, through flow feedforward pre-adjustment, adaptive dead zone double-loop decoupling, efficiency atlas optimization and opening-degree-frequency bidirectional constraint mechanism, high-precision pressure stabilization and pump set energy efficiency optimization under variable working condition are realized.The application can control high-pressure outlet pressure fluctuation within 0.5%, while eliminating pump set dry pumping and cavitation risk, reducing system operation energy consumption, suitable for various ship methanol fuel supply scenarios.

Description

Technical Field

[0001] This invention relates to the field of marine new energy power systems and fluid industry control technology, specifically to a two-stage, bidirectional, coordinated pressure stabilization control method and system for marine methanol fuel supply. Background Technology

[0002] Methanol, as a low-carbon and easily stored and transported alternative fuel for ships, is one of the important technological pathways for decarbonizing marine power systems. Existing ship methanol fuel supply systems generally adopt a two-stage pressurization structure: the low-pressure pump group draws room-temperature methanol from the methanol day tank and delivers it to the heat exchanger to be heated to the appropriate temperature; the high-pressure pump group draws the heated methanol from the heat exchanger for secondary pressurization and finally supplies it to the ship's main engine.

[0003] Affected by factors such as dynamic adjustments in ship speed, sea surface disturbances, and sudden load changes, the engine's real-time demand for methanol fuel exhibits a wide range and rapid fluctuation characteristic. Existing control schemes have three significant shortcomings in practical applications: First, most control strategies are single-variable adjustment modes, making it difficult to balance energy efficiency and reliability. Schemes that only adjust the pump speed via frequency converter result in extremely low pump speeds under low engine load and low flow demand conditions, deviating from the pump's optimal energy efficiency curve and easily leading to pump cavitation, overheating, and outlet pressure buildup. Schemes that only adjust the reflux valve opening keep the pump in a high-power operating state, with a large amount of power lost through reflux throttling, resulting in low system energy efficiency.

[0004] Second, the two-stage pressurization system lacks a standardized safe startup sequence. When the low-pressure and high-pressure systems are started in series, if there is residual air in the upstream pipeline or the valve action is delayed, it can easily lead to insufficient liquid level on the inlet side of the high-pressure pump. Blindly starting the high-pressure pump will cause dry pumping, resulting in equipment damage and fuel leakage safety hazards.

[0005] Third, insufficient pressure stability under varying operating conditions. Traditional single-loop PID control has limited response speed. When the supply and demand flow rates change abruptly, the pipeline network is prone to pressure oscillations and water hammer effects, which cannot meet the stringent requirements of the engine for feed pressure stability, thereby affecting combustion efficiency and operational safety.

[0006] Furthermore, the continuous roll and pitch changes during ship navigation cause severe periodic fluctuations in the methanol daily storage tank and pipelines. Methanol, with its low viscosity and high saturated vapor pressure, is highly susceptible to vaporization and pump cavity cavitation when the inlet level is insufficient or the inlet pressure head drops. Current technologies primarily mitigate these fluctuations by adding mechanical structures such as collection wells and stabilizing chambers, lacking proactive protective measures at the control logic and operational sequence levels to adapt to the swaying conditions. This fails to address the root causes of cavitation and dry-pumping risks. Summary of the Invention

[0007] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a two-stage, bidirectional, coordinated pressure stabilization control method and system for ship methanol fuel supply, thereby solving the technical problems of prominent contradictions between energy efficiency and reliability in existing two-stage methanol supply systems, high risk of dry pumping during startup, and large pressure oscillations under varying operating conditions, and achieving a coordinated unity of high pressure stabilization accuracy, high operational safety, and high energy efficiency under all operating conditions.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: On one hand, this invention provides a two-stage, bidirectional, coordinated pressure stabilization control method for ship methanol fuel supply, applied to a ship methanol fuel supply system consisting of a low-pressure supply circuit and a high-pressure supply circuit connected in series. The low-pressure supply circuit is connected between the methanol day tank and the heat exchanger, and the high-pressure supply circuit is connected between the heat exchanger and the methanol engine. The method includes the following steps: S1: After receiving the normal operation signal of the heat exchanger and the system start command, open the liquid inlet valve, and after the preset pre-filling liquid delay, detect the liquid level of the first stage before the pump; if the liquid level is lower than the safety threshold, terminate the start process and trigger the alarm; if the liquid level is normal, enter the two-stage serial pressure building process.

[0009] S2: Open the low-pressure return valve to the preset initial opening to establish a low-pressure side start-up bypass path; start the low-pressure supply pump group and use PID closed-loop regulation to make the low-pressure outlet pressure reach the first preset pressure; after confirming that the secondary liquid level before the high-pressure pump is normal, the low-pressure circuit pressure building is completed.

[0010] S3: Open the high-pressure reflux valve to the preset initial opening to establish a high-pressure side start-up bypass path; start the high-pressure supply pump group and use PID closed-loop regulation to make the high-pressure outlet pressure reach the target working pressure, while monitoring the methanol medium temperature in real time; if the pressure and temperature do not exceed the limits and reach the target value, the system enters normal operation.

[0011] S4: During normal system operation, the low-pressure loop uses PID constant pressure control of the low-pressure reflux valve to maintain the low-pressure outlet pressure at the first preset pressure, monitors the liquid level and pressure parameters on the low-pressure side in real time, and executes abnormal interlock protection; the high-pressure reflux valve opening adjustment fast loop and the high-pressure pump frequency conversion adjustment slow loop operate synchronously; within the slow loop, PID pressure stabilization adjustment has the highest priority, and efficiency graph optimization is paused when the pressure deviation exceeds the current dead zone threshold. Efficiency optimization is started after the pressure deviation remains within the dead zone for a set time. Through the coordinated action of four mechanisms—flow feedforward pre-adjustment, adaptive dead zone dual-loop decoupling, efficiency graph optimization, and opening-frequency bidirectional constraint—the pump unit continues to operate in the high-efficiency range while maintaining the high-pressure outlet pressure stability.

[0012] Furthermore, the specific process of flow feedforward pre-adjustment in step S4 is as follows: real-time acquisition of the instantaneous flow value of the methanol flow sensor, calculation of the rate of change of flow with time; when the absolute value of the flow rate of change is greater than the first threshold, the system is determined to enter the variable operating condition state, and feedforward compensation opening increment is applied to the high-pressure return valve according to the pre-stored flow rate of change - valve opening increment feedforward mapping relationship, and pre-adjustment is completed before the pressure deviation is formed.

[0013] Further, the specific process of adaptive dead-zone dual-loop decoupling in step S4 is as follows: Real-time calculation of the high-pressure outlet pressure deviation and the rate of change of the pressure deviation over time; dynamic updating of the fast loop dead-zone threshold based on the rate of change of the pressure deviation: when the absolute value of the rate of change of the pressure deviation is less than the second threshold, and it is determined to be a steady-state condition, the first wide dead-zone threshold is used; when the absolute value of the rate of change of the pressure deviation is greater than or equal to the second threshold, and it is determined to be a transient condition, the second narrow dead-zone threshold is used; when the absolute value of the pressure deviation is greater than the current dead-zone threshold, the fast loop takes priority action, adjusting the opening of the high-pressure return valve to smooth pressure fluctuations; when the absolute value of the pressure deviation is less than or equal to the current dead-zone threshold, the fast loop locks the current opening, and the slow loop adjusts the pump unit operating frequency.

[0014] Furthermore, the specific process of efficiency graph optimization in step S4 is as follows: pre-store the iso-efficiency surface data of the high-pressure supply pump group under the three-dimensional operating conditions of frequency, pressure, and flow; when the high-pressure outlet pressure deviation remains within the current dead zone for a set duration, efficiency graph optimization is initiated; the slow loop uses the current target pressure and measured flow as constraints to search for the optimal frequency that maximizes the pump group's operating efficiency within the preset allowable frequency range, driving the pump group's operating frequency to converge towards the optimal frequency in small steps, and verifying the pressure deviation after each frequency adjustment. If the pressure deviation exceeds the dead zone threshold, optimization is immediately paused, and the process switches back to PID pressure regulation.

[0015] Furthermore, the specific process of the opening-frequency bidirectional constraint in step S4 is as follows: real-time monitoring of the actual opening of the high-pressure return valve; if the actual opening deviates from the preset opening neutral range within a continuous first time period, a frequency migration request is sent to the slow loop to trigger the slow loop to re-execute efficiency optimization; if the actual opening of the high-pressure return valve returns to the neutral range, and the frequency change of the pump group operating frequency within a continuous second cycle is less than the third threshold, then the system is determined to enter the energy consumption optimal locking state, maintaining the current pump group frequency and valve opening combination operation.

[0016] On the other hand, the present invention provides a two-stage supply bidirectional coordinated pressure stabilization control system for ship methanol fuel, including a two-stage supply hardware loop and a control unit electrically connected to the hardware loop, wherein the control unit is configured to execute the control method described above.

[0017] The two-stage supply hardware circuit includes a methanol daily storage cabinet, an inlet valve, a primary level sensor, a low-pressure supply pump group, a low-pressure outlet pressure sensor, a heat exchanger, a secondary level sensor, a high-pressure supply pump group, a high-pressure outlet pressure sensor, a temperature sensor, a methanol flow sensor, and a methanol engine, connected in series via pipelines. A low-pressure reflux valve is connected in parallel between the outlet and inlet side pipelines of the low-pressure supply pump group, and a high-pressure reflux valve is connected in parallel between the outlet and inlet side pipelines of the high-pressure supply pump group.

[0018] Compared with the prior art, the present invention has the following significant beneficial technical effects: This invention adopts a two-stage serial pressure building combined with a bidirectional collaborative pressure stabilization architecture under varying operating conditions. It actively offsets flow disturbances through flow feedforward pre-adjustment and achieves fast and slow double-loop decoupling with adaptive dead zone, effectively suppressing pressure oscillations and water hammer effects caused by sudden changes in supply and demand flow. Under all operating conditions, the high-pressure outlet pressure fluctuation can be controlled within 0.5%, fully meeting the stringent requirements of ship engines for fuel supply pressure stability.

[0019] This invention sets up a pre-charge liquid delay and a two-stage liquid level interlocking judgment mechanism, which forcibly opens the return valve to a preset initial opening degree before pressure is built up, and constructs an anti-pump blockage bypass path. From the control logic level, it eliminates the risks of high-pressure pump dry running, pump cavity cavitation and start-up water hammer impact, effectively improves the system's operational reliability and extends the service life of the pump set.

[0020] This invention adopts a pump-valve dual-variable coordinated regulation mode, combined with efficiency spectrum optimization and bidirectional constraint convergence mechanism. It avoids the large throttling losses caused by pure valve regulation and solves the problem of inefficient operation of pure frequency conversion regulation under low load conditions. This enables the pump set to always be locked in the high-efficiency operating range under all sea conditions, achieving system-level energy saving and emission reduction effects. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process structure of the two-stage methanol fuel supply system for ships according to the present invention. Figure 2 This is the overall logic block diagram of the bidirectional collaborative voltage regulation control of the present invention; Figure 3 This is a schematic diagram illustrating the principle of the adaptive dead-zone dual-loop decoupling mechanism of the present invention; Figure 4 This is a schematic diagram illustrating the principle of efficiency graph optimization in this invention. Figure 5 This is a schematic diagram of the state transition of the fast-loop-slow-loop bidirectional constraint of the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] I. System Hardware Implementation Architecture Combination Figure 1 As shown, the two-stage, bidirectional, coordinated, and pressure-stabilized methanol fuel supply control system for ships described in this embodiment includes two-stage supply hardware loops and a control unit. The control unit adopts a marine industrial control PLC or an embedded controller. The two-stage supply hardware loops are arranged sequentially along the methanol delivery direction: Methanol day-use cabinet, used for storing room-temperature liquid methanol fuel; The liquid inlet valve PBV01 is an electrically operated switch valve located on the main outlet pipe of the methanol daily use tank and is used to control the opening and closing of the main liquid inlet passage of the system. The primary liquid level sensor LS01 is installed on the inlet pipe of the low-pressure supply pump unit to detect the liquid level status at the inlet side of the low-pressure pump in real time. The low-pressure supply pump set includes two low-pressure methanol supply pumps, P11 and P12, which serve as backups for each other. They are used to pressurize and deliver room-temperature methanol from the methanol day tank to the heat exchanger. The low-pressure reflux valve PRV01 is an electric proportional regulating valve connected in parallel between the outlet and inlet pipes of the low-pressure supply pump unit to regulate the reflux flow rate of the low-pressure circuit. The low-pressure outlet pressure sensor PT01 is installed on the outlet main pipe of the low-pressure supply pump unit and is used to collect the outlet pressure value of the low-pressure circuit. The heat exchanger is used to heat the methanol transported at low pressure to the required engine feed temperature. The secondary liquid level sensor LS02 is installed on the outlet pipe of the heat exchanger and the inlet side of the high-pressure supply pump group to detect the liquid level status at the inlet side of the high-pressure pump. The high-pressure supply pump set includes two high-pressure methanol supply pumps, P21 and P22, which serve as backups for each other. They are driven by frequency converters with a frequency adjustment range of 0-60Hz and are used to deliver the heated methanol to the engine after secondary pressurization. The high-pressure reflux valve PRV02 is an electric proportional regulating valve with an opening adjustment range of 0-100%. It is connected in parallel between the outlet and inlet pipelines of the high-pressure supply pump set and is used to regulate the reflux flow rate of the high-pressure circuit. The high-pressure outlet pressure sensor PT02 is installed on the outlet main pipe of the high-pressure supply pump set and is used to collect the outlet pressure value of the high-pressure circuit. Temperature sensor TE01 is installed on the high-pressure outlet pipeline to detect the temperature of the medium supplied with methanol in real time. The methanol flow sensor FM01 is located on the high-pressure outlet pipeline, in front of the engine feed end, and is used to detect the instantaneous flow rate of methanol supplied to the engine in real time. A methanol engine is the main propulsion combustion unit of a ship, which receives pressurized and heated methanol fuel.

[0024] The control unit is electrically connected to the inlet valve PBV01, the primary level sensor LS01, the low-pressure supply pump P11 / P12, the low-pressure reflux valve PRV01, the low-pressure outlet pressure sensor PT01, the secondary level sensor LS02, the high-pressure supply pump P21 / P22, the high-pressure reflux valve PRV02, the high-pressure outlet pressure sensor PT02, the temperature sensor TE01, and the methanol flow sensor FM01, respectively. It is used to collect the detection signals of each sensor, output control commands to each actuator, and execute the bidirectional collaborative pressure stabilization control method described in this invention.

[0025] II. Specific Implementation Steps of Control Methods The control method in this embodiment operates in the aforementioned control unit, and the overall control logic is as follows: Figure 2 As shown, the overall process is divided into four stages: pre-lock safety interlock activation, low-voltage circuit pressure building, high-voltage circuit pressure building, and bidirectional coordinated voltage stabilization under varying operating conditions. The specific implementation process is as follows: S1 front-mounted safety interlock start Once the ship's heat exchanger system has completed preheating and sent a normal operation signal to the control unit, the operator triggers a methanol supply system start command on the central control interface. After receiving the command, the control unit enters the system start-up process.

[0026] The control unit first outputs a switch command to open the inlet valve PBV01 and simultaneously starts the pre-filling delay timer. In this embodiment, the delay time is preferably 5 seconds. This delay is used to offset the lag in the mechanical action of the valve, ensuring that methanol is fully filled into the front-end pipeline and avoiding empty pipeline start-up.

[0027] After the delay ends, the control unit reads the detection signal from the primary liquid level sensor LS01: If LS01 triggers a low liquid level alarm, i.e. the liquid level is lower than the safe liquid level threshold at the inlet of the low-pressure pump, the control unit immediately terminates the startup process, outputs a low liquid level fault alarm signal before the low-pressure pump, and locks the startup circuit of the low-pressure supply pump set to prevent the pump set from being damaged by dry pumping. If there is no low liquid level alarm on LS01, it is determined that the system front-end filling is normal and meets the conditions for safe start-up, and enters the two-stage serial pressure building stage.

[0028] S2 low-voltage circuit pressure build-up After entering the pressure build-up phase, the control unit first performs the initial anti-stuck pump operation on the low-pressure side: it outputs an opening command to the low-pressure return valve PRV01, sets its initial opening value to 15%, and establishes a start-up bypass circuit to avoid pressure surge caused by no outlet passage at the moment the pump unit starts.

[0029] Subsequently, the control unit starts the low-pressure supply pump group. In this embodiment, P11 is started first, and P12 is in hot standby state. After the pump group is started, the control unit collects the pressure data of the low-pressure outlet pressure sensor PT01 in real time, and runs the PID closed-loop control algorithm with the first preset pressure of 7 bar as the set value. By adjusting the opening of the low-pressure return valve PRV01, the low-pressure outlet pressure gradually rises and stabilizes.

[0030] When the pressure value detected by PT01 remains within the range of 7 bar ± 0.2 bar for 3 consecutive seconds, the control unit determines that the low-pressure side pressure meets the standard and then checks the signal of the secondary liquid level sensor LS02: If LS02 triggers a low liquid level alarm, it indicates that the heat exchanger side is not filled with liquid. The control unit will immediately stop the low-pressure supply pump group and output a low liquid level fault alarm before the high-pressure pump. If there is no alarm in LS02, it is determined that the low-pressure cold system has completed pressure build-up and enters the high-pressure circuit pressure build-up stage.

[0031] S3 high-voltage circuit pressure build-up After the low-pressure build-up is completed, the control unit first performs the initial anti-blocking pump operation on the high-pressure side: it outputs an opening command to the high-pressure return valve PRV02, forcibly setting its initial opening to 15%, and constructing a high-pressure side start-up bypass circuit; then it starts the high-pressure supply pump group. In this embodiment, P21 is started first, and P22 is in hot standby state. The initial operating frequency of the pump group is set to 30Hz.

[0032] After the pump unit starts, the control unit collects the pressure data of the high pressure outlet pressure sensor PT02 and the temperature data of the temperature sensor TE01 in real time. With the target working pressure of 13 bar as the set value, the PID closed-loop control algorithm is run. By coordinating the adjustment of the opening degree of the high pressure return valve PRV02 and the operating frequency of the high pressure pump, the high pressure outlet pressure is gradually increased.

[0033] During the pressure build-up process, if the PT02 pressure exceeds the limit or the TE01 temperature exceeds the allowable feed temperature range of the engine (the normal feed temperature range in this embodiment is 30℃~65℃), the control unit will automatically perform adjustment and correction; if the limit is continuously exceeded, the fault protection logic will be triggered, the frequency will be reduced and the engine will be shut down and an alarm will be output.

[0034] When the high-pressure outlet pressure remains stable within the range of 13 bar ± 0.3 bar for 5 consecutive seconds and the medium temperature is within the normal range, the control unit outputs a methanol supply system start-up completion signal to the ship's main control system, illuminates the normal operation status indicator, and the system enters normal operation status.

[0035] S4 Variable Operating Condition Bidirectional Collaborative Voltage Stabilizer After the system enters normal operation, the low-pressure loop continuously employs PID closed-loop constant pressure control of the low-pressure return valve, adjusting the valve opening in real time with a setpoint of 7 bar to maintain stable low-pressure outlet pressure and provide a stable input pressure for the high-pressure loop. Simultaneously, the control unit activates the fast loop for high-pressure return valve opening adjustment and the slow loop for high-pressure pump frequency conversion adjustment. Through four mechanisms—flow feedforward pre-adjustment, adaptive dead-zone dual-loop decoupling, efficiency graph optimization, and opening-frequency bidirectional constraint—bidirectional coordinated control is achieved. Through the synergistic effect of these mechanisms, the fluctuation amplitude of the system's high-pressure outlet pressure can be controlled within 0.5%, as detailed below: S4-1 Flow Feedforward Pre-adjustment The control unit reads the instantaneous flow value F (unit: kg / s) of the methanol flow sensor FM01 in real time with a sampling period of 100ms, and calculates the flow rate change dF / dt through differential calculation.

[0036] The control unit is preset with a first threshold C1, which is preferably 0.5 kg / s in this embodiment. 2 It can be calibrated on-site according to the system pipeline capacity.

[0037] When the absolute value of the flow rate change rate is greater than the first threshold, it is determined that the engine fuel flow demand has changed abruptly, and the system enters a variable operating condition state. At this time, the control unit does not wait for the pressure deviation to be generated, but directly calls the pre-stored flow rate change rate-valve opening increment feedforward mapping relationship table, calculates the corresponding feedforward compensation opening increment, and adds it to the current opening command of the high-pressure return valve PRV02 to adjust the valve opening in advance and offset the influence of flow disturbance before the pressure peak is formed.

[0038] In this embodiment, the feedforward mapping relationship table of flow rate change rate and valve opening increment is obtained through previous operating condition calibration: when the flow rate change rate is positive and the flow demand increases rapidly, the reflux valve is closed to increase the outlet flow rate; when the flow rate change rate is negative and the flow demand decreases rapidly, the reflux valve is opened to release excess pressure.

[0039] S4-2 Adaptive Dead-Zone Dual-Loop Decoupling The principle of this decoupling mechanism is as follows: Figure 3 As shown, the control unit calculates the high-pressure outlet pressure deviation in real time, which is the set pressure minus the actual pressure, and also calculates the rate of change of the pressure deviation over time (unit: bar / s).

[0040] The control unit has a preset second threshold C2, which is preferably 0.1 bar / s in this embodiment, used to distinguish between steady-state and transient operating conditions. When the absolute value of the pressure deviation change rate is less than the second threshold, it is determined to be a steady-state condition, which corresponds to the scenario of stable ship navigation and small wind and waves. The fast loop dead zone threshold is set as the first wide dead zone, which is 0.2 bar in this embodiment. When the absolute value of the pressure deviation change rate is greater than or equal to the second threshold, it is determined to be a transient condition, corresponding to sudden speed change and large wind and waves. The fast loop dead zone threshold is set to the second narrow dead zone, which is 0.05 bar in this embodiment.

[0041] The difference in the fast and slow loop adjustment cycles is based on the hardware physical response characteristics: the high-pressure reflux valve is an electric proportional control valve with a full stroke action time of approximately 200ms to 500ms. The 100ms adjustment cycle matches the valve's mechanical response characteristics, ensuring that the valve completes an effective action after each adjustment command is output. After the frequency of the variable frequency pump is adjusted, there is a fluid inertial delay between the change in motor speed and the establishment of pipeline pressure. A 1s adjustment cycle is sufficient to complete an effective frequency adjustment and observe a complete pressure response, avoiding over-adjustment oscillation.

[0042] The double-ring action logic is as follows: When the absolute value of the pressure deviation is greater than the current dead zone threshold, the pressure deviation exceeds the allowable range. The fast loop responds first and adjusts the opening of the high-pressure return valve PRV02 with a 100ms adjustment cycle to quickly suppress the pressure spike. When the absolute value of the pressure deviation is less than or equal to the current dead zone threshold, the pressure deviation is within the allowable range. The fast loop enters the holding state and locks the current opening of PRV02. At this time, the slow loop starts and adjusts the operating frequency of the high-pressure pump smoothly with a 1-second adjustment cycle to gradually eliminate the steady-state pressure deviation.

[0043] The adaptive dead zone of this solution essentially resolves the core contradiction of dual-loop coupling: the fast loop has a fast response speed but poor steady-state accuracy and is prone to high-frequency oscillations, while the slow loop has high steady-state accuracy but a large response delay. If both loops use the same adjustment period or a fixed dead zone threshold, beat frequency oscillations will occur under transient conditions due to misaligned adjustment timing and reversed adjustment directions, which will exacerbate pressure fluctuations. This application dynamically switches the dead zone threshold by the pressure deviation change rate, realizing the dynamic allocation of the action priority of the fast and slow loops: under transient conditions, a narrow dead zone allows the fast loop to intervene as early as possible and undertake the function of rapid disturbance suppression; under steady-state conditions, a wide dead zone locks the opening of the fast loop, suppressing frequent valve actions, and the slow loop completes the steady-state accuracy correction, thus fundamentally avoiding the coupling conflict of dual-loop regulation.

[0044] Through an adaptive dead-time mechanism, the fast and slow dual loops are decoupled to avoid coupling oscillations caused by simultaneous adjustment, thus balancing response speed and operational stability.

[0045] S4-3 Efficiency Map Optimization The principle of this optimization mechanism is as follows: Figure 4 As shown, the storage module of the control unit pre-stores the efficiency spectrum data of the high-pressure supply pump set, which is an iso-efficiency surface data table under the three-dimensional operating conditions of frequency-pressure-flow rate. It is provided by the pump set manufacturer or obtained through on-site calibration, and records the pump set operating efficiency corresponding to different operating frequencies, outlet pressures, and delivery flow rates.

[0046] The slow loop executes a priority rule of "pressure stabilization first, steady-state optimization": when the high-pressure outlet pressure deviation exceeds the current dead zone threshold, the slow loop only runs PID pressure stabilization and pauses the efficiency graph optimization calculation to prioritize pressure control accuracy; when the pressure deviation remains within the current dead zone for a set duration (set to 5 seconds in this embodiment), the system is determined to have entered a steady state and efficiency graph optimization is initiated.

[0047] During the optimization process, the slow loop uses the current target pressure and measured flow rate as constraints to search for the maximum value of pump group efficiency within a preset allowable frequency range, and obtains the corresponding optimal frequency. In this embodiment, the lower limit of the allowable frequency range is set to 20Hz to prevent cavitation caused by low speed, and the upper limit is set to 55Hz to reserve overload margin.

[0048] After finding the optimal frequency, the slow loop gradually drives the pump unit's operating frequency to converge toward the optimal frequency with a small step size of no more than 0.5Hz per step. After each frequency adjustment, the high-pressure outlet pressure deviation is checked. If the pressure deviation exceeds the current dead zone threshold, the current optimization is terminated immediately, and the PID voltage regulation is switched back. The optimization is retried after the pressure returns to the dead zone and stabilizes. Under the premise of maintaining pressure stability, the pump unit continues to operate in the highest energy efficiency range.

[0049] S4-4 Opening-Frequency Bidirectional Constraints and Convergence Criteria The bidirectional constraint state transition logic is as follows: Figure 5 As shown, the control unit monitors the actual opening degree of the high-pressure return valve PRV02 in real time. A neutral operating range for the valve is preset. In this embodiment, the lower limit of the opening degree of the neutral range is 10% and the upper limit is 40%. This range is the operating range with the optimal linear adjustment characteristics and moderate throttling loss of the valve.

[0050] If the actual valve opening continuously deviates from the neutral range within the first time period (30 seconds in this embodiment), it indicates a mismatch between the current pump unit operating frequency and operating conditions: a consistently low valve opening indicates an excessively high pump frequency and significant throttling losses; a consistently high valve opening indicates an insufficient pump frequency and weak pressure support. At this point, the fast loop sends a frequency migration request to the slow loop. Upon receiving the request, the slow loop re-executes the efficiency graph optimization, adjusts the pump unit frequency, and pushes the valve opening back to the neutral range.

[0051] When the actual valve opening returns to the neutral range, and the frequency change of the pump unit is less than the third threshold (0.2Hz in this embodiment) for the second consecutive cycle (the second cycle is set to 10 adjustment cycles, totaling 10 seconds) in adjacent cycles, the control unit determines that the system has entered the energy consumption optimal locking state, maintains the stable operation of the current pump unit frequency and valve opening combination, and suspends the optimization calculation to reduce the system load.

[0052] When the rate of change of flow is detected to exceed the first threshold again, the lockout is released, and the system re-enters the collaborative adjustment and optimization process.

[0053] During normal operation, the low-pressure side synchronously implements full-time interlock protection: real-time acquisition of detection data from the primary liquid level sensor and the low-pressure outlet pressure sensor. If the primary liquid level is lower than the safety threshold, the control unit immediately interlocks and stops the low-pressure supply pump group and the high-pressure supply pump group, triggering a low liquid level fault alarm to prevent pump group dry running and cavitation faults. If the low-pressure outlet pressure exceeds the preset safety range (6bar~8bar), the pressure is preferentially corrected through PID adjustment of the low-pressure return valve. If it still exceeds the safety range for 10 consecutive seconds, the graded load reduction protection is triggered, gradually reducing the operating frequency of the high-pressure pump. If the pressure continues to exceed the limit, the fault shutdown procedure is executed. At the same time, the secondary liquid level status is monitored in real time. If the secondary liquid level is lower than the safety threshold, the operating frequency of the high-pressure pump is immediately reduced and the output capacity of the low-pressure circuit is increased. If the liquid level continues to drop, the high-pressure supply pump group is interlocked and stopped to avoid damage from high-pressure pump dry running.

[0054] III. Comparative Experiment Examples To verify the voltage stabilization performance and energy efficiency advantages of this solution, benchmark tests were conducted using three control modes under the same hardware platform and simulated sea state disturbance conditions. The test hardware adopted the two-stage methanol supply loop described in this embodiment, with the target operating pressure on the high-pressure side set at 13 bar, simulating a step disturbance in engine flow rate under sea state VI (flow rate change rate 0.8 kg / s). 2 Each test was repeated 5 times and the average value was taken. The test indicators included the high pressure outlet pressure fluctuation amplitude, the pressure convergence time after disturbance, and the pump set operating efficiency under rated conditions. The test results are as follows: 1. Pure PID valve control mode: The pump unit operates at a constant frequency through single-loop PID regulation only via the high-pressure return valve. The test results showed that the pressure fluctuation amplitude was ±3.1%, the time for the pressure to converge to steady state after the disturbance was 21.2s, and the pump unit operating efficiency under rated conditions was 62.3%.

[0055] 2. Conventional pump-valve coordination mode: Employs synchronous PID regulation of valves and pump unit, with no flow feedforward, no adaptive dead zone decoupling, and no fast / slow loop cycle difference design. Tests showed a pressure fluctuation amplitude of ±1.2%, a pressure convergence time of 8.7s after disturbance, and a pump unit operating efficiency of 71.5% under rated conditions.

[0056] 3. The bidirectional collaborative pressure stabilization control scheme of this application adopts a complete control architecture with flow feedforward pre-adjustment, adaptive dead zone double-loop decoupling, efficiency spectrum optimization, and bidirectional constraints of opening degree and frequency. The pressure fluctuation amplitude obtained by testing is ±0.42%, which meets the design target of ≤0.5%; the pressure convergence time after disturbance is 2.8s; and the pump set operating efficiency under rated conditions is 82.7%.

[0057] The test results show that, compared with the conventional pump and valve coordination scheme, this application reduces the pressure fluctuation amplitude by 65%, shortens the convergence time by 67.8%, and improves the pump group operating efficiency by 15.7% through the coordinated cooperation of multiple mechanisms, and all performance indicators have been significantly improved.

[0058] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A two-stage, bidirectional, coordinated pressure stabilization control method for ship methanol fuel supply, applied to a ship methanol fuel supply system consisting of a low-pressure supply circuit and a high-pressure supply circuit connected in series, wherein the low-pressure supply circuit is connected between the methanol day tank and the heat exchanger, and the high-pressure supply circuit is connected between the heat exchanger and the methanol engine, characterized in that... The method includes the following steps: S1: After receiving the normal operation signal of the heat exchanger and the system start command, the liquid inlet valve is opened. After the preset pre-filling liquid delay, the liquid level of the first stage before the pump is detected. If the liquid level is lower than the safety threshold, the start is terminated and an alarm is triggered. If the liquid level is normal, the two-stage serial pressure building process is entered. S2: Open the low-pressure reflux valve to the preset initial opening; start the low-pressure supply pump group and use PID closed-loop regulation to make the low-pressure outlet pressure reach the first preset pressure; after confirming that the secondary liquid level before the high-pressure pump is normal, the low-pressure circuit pressure building is completed. S3: Open the high-pressure reflux valve to the preset initial opening; start the high-pressure supply pump group, use PID closed-loop regulation to make the high-pressure outlet pressure reach the target working pressure, and monitor the medium temperature in real time; after the pressure and temperature do not exceed the limits and reach the target value, the system enters the normal operation state; S4: During normal operation of the system, the low-pressure circuit uses PID constant pressure control of the low-pressure reflux valve to maintain the low-pressure outlet pressure at the first preset pressure, monitors the liquid level and pressure parameters on the low-pressure side in real time and performs abnormal interlock protection; the high-pressure reflux valve opening adjustment fast loop and the high-pressure pump frequency conversion adjustment slow loop operate synchronously, and maintain the high-pressure outlet pressure through fast and slow loop coordinated control, and perform efficiency optimization under steady-state conditions to make the pump set operate in the high-efficiency range.

2. The control method according to claim 1, characterized in that, The primary liquid level detection point in step S1 is located at the inlet end of the low-pressure supply pump group, and the secondary liquid level detection point is located at the inlet end of the high-pressure supply pump group. When the liquid level is lower than the safety threshold, the start-up permission of the corresponding pump group is locked or the shutdown interlock protection is executed. During system operation, when the low-pressure outlet pressure exceeds the preset safety range, it is first adjusted and corrected by the low-pressure return valve. If it continues to exceed the limit, the load reduction or shutdown protection is triggered.

3. The control method according to claim 1, characterized in that, In step S4, the fast and slow loop coordinated control also includes flow feedforward pre-adjustment, specifically: real-time acquisition of the instantaneous flow value of the methanol flow sensor, calculation of the flow change rate; when the absolute value of the flow change rate is greater than the first threshold, the system is determined to enter the variable operating condition state, and according to the pre-stored flow change rate-valve opening increment feedforward mapping relationship, feedforward compensation opening increment is applied to the high-pressure return valve to pre-adjust the opening of the high-pressure return valve.

4. The control method according to claim 1, characterized in that, In step S4, the fast and slow loop coordinated control further includes adaptive dead-zone dual-loop decoupling, specifically: Real-time calculation of high-pressure outlet pressure deviation and pressure deviation change rate; The fast-loop dead zone threshold is dynamically updated based on the pressure deviation change rate: when the absolute value of the pressure deviation change rate is less than the second threshold, it is determined to be a steady-state condition, and the first wide dead zone threshold is used; when the absolute value of the pressure deviation change rate is greater than or equal to the second threshold, it is determined to be a transient condition, and the second narrow dead zone threshold is used. When the absolute value of the pressure deviation is greater than the current dead zone threshold, the fast loop takes priority and adjusts the opening of the high-pressure return valve; when the absolute value of the pressure deviation is less than or equal to the current dead zone threshold, the fast loop locks the current opening and the slow loop adjusts the pump unit operating frequency.

5. The control method according to claim 1, characterized in that, The efficiency optimization described in step S4 is as follows: pre-store the efficiency data of the high-pressure supply pump group under different operating conditions; when the high-pressure outlet pressure deviation remains within the current dead zone for a set duration, start efficiency optimization; using the current operating condition parameters as constraints, search for the optimal frequency that makes the pump group operate most efficiently within the preset allowable frequency range, drive the pump group operating frequency to converge towards the optimal frequency, and if the pressure deviation exceeds the dead zone threshold during the frequency adjustment process, pause optimization and switch back to PID voltage regulation.

6. The control method according to claim 1, characterized in that, In step S4, the fast-slow loop coordinated control also includes a two-way constraint of opening degree and frequency, specifically: The actual opening degree of the high-pressure return valve is monitored in real time. If the actual opening degree deviates from the preset opening degree neutral range within a continuous first time period, a frequency migration request is sent to the slow loop to trigger the slow loop to re-execute efficiency optimization. If the actual opening of the high-pressure return valve returns to the neutral range, and the frequency change of the pump unit operating frequency within the second consecutive cycle is less than the third threshold, then the system is determined to have entered the optimal energy consumption lockout state, maintaining the current combination of pump unit frequency and valve opening.

7. The control method according to claim 1, characterized in that, Under normal operating conditions, the pressure fluctuation amplitude at the high-pressure outlet is controlled within 0.5%.

8. A two-stage, bidirectional, coordinated, and pressure-stabilized control system for ship methanol fuel supply, comprising a two-stage supply hardware loop and a control unit electrically connected to the hardware loop, wherein the control unit is configured to execute the control method as described in any one of claims 1 to 7, characterized in that: The two-stage supply hardware circuit includes a methanol daily storage cabinet, an inlet valve, a primary liquid level sensor, a low-pressure supply pump set, a low-pressure outlet pressure sensor, a heat exchanger, a secondary liquid level sensor, a high-pressure supply pump set, a high-pressure outlet pressure sensor, a temperature sensor, a methanol flow sensor, and a methanol engine, which are connected in series via pipelines. A low-pressure reflux valve is connected in parallel between the outlet and inlet side pipelines of the low-pressure supply pump group, and a high-pressure reflux valve is connected in parallel between the outlet and inlet side pipelines of the high-pressure supply pump group.

9. The control system according to claim 8, characterized in that, Both the low-pressure supply pump group and the high-pressure supply pump group contain two supply pumps that serve as backups for each other; the high-pressure supply pump is a 0-60Hz variable frequency pump, and the high-pressure return valve is a 0-100% continuous regulating valve.

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