Four-quadrant variable frequency differential pressure power generation system and control method suitable for steelmaking steam

Abstract

The application discloses a four-quadrant variable-frequency differential pressure power generation system and a control method suitable for steelmaking steam, relates to the technical field of industrial waste heat and pressure recovery power generation, and realizes the dynamic adjustment of the turbine speed along with the steam pressure difference through the introduction of a four-quadrant frequency converter and a variable speed self-adaptive control technology, so that the unit always operates at an optimal aerodynamic working condition point, the variable working condition adaptability and power generation efficiency of the system are significantly improved, meanwhile, the four-quadrant frequency converter is adopted as a grid-connected core equipment, the decoupling control of the generator speed and the grid frequency is realized, the smoothness and non-impact of the grid-connected process are ensured, and the stability and operation convenience of the power grid are improved, in addition, the system also has the advantages of wide load continuous operation capacity and low maintenance cost and the like, and provides powerful support for the efficient recovery and utilization of the steelmaking steam waste heat and pressure for a steel enterprise.

Description

Technical Field

[0001] This invention relates to the field of industrial waste heat and pressure recovery power generation technology, specifically a four-quadrant variable frequency differential pressure power generation system and control method adapted to steelmaking steam. Background Technology

[0002] In the steel production process, the steelmaking stage generates a large amount of high-temperature, high-pressure saturated steam. This steam contains abundant thermal energy, and its effective recovery and utilization can significantly improve the energy efficiency of steel enterprises, reduce production costs, and minimize environmental impact. Traditionally, this steam has been used for domestic and industrial steam consumption or directly released into the atmosphere, resulting in enormous energy waste. With the advancement of energy conservation and emission reduction policies and rising energy prices, how to efficiently recover and utilize the waste heat and pressure generated during steelmaking has become a crucial issue that steel enterprises urgently need to address.

[0003] Traditional steelmaking steam power generation technology suffers from several shortcomings: First, it cannot adapt to fluctuations in steam parameters. The steam pressure and flow rate generated during steelmaking fluctuate significantly with the production cycle. Fixed-speed units struggle to adjust their operating status promptly to these changes, leading to stalling and surge issues under varying operating conditions, impacting safe and stable operation. Second, it experiences significant grid connection impact and low reliability. Traditional units rely on automatic synchronizing devices for grid connection. The minute phase deviation at the moment of closing generates substantial inrush current and torque, damaging both the unit and the grid, and potentially causing unstable operation. Third, it has a narrow operating load range. Traditional units struggle to operate stably under low load conditions. During steelmaking breaks, when steam volume is low, frequent start-stop cycles prevent continuous online operation, reducing overall system efficiency and reliability. Finally, maintenance costs are high. Traditional units often employ mechanical transmission components such as reduction gearboxes, increasing system complexity, potential failure points, and maintenance costs and difficulties.

[0004] In view of the problems of traditional steelmaking steam power generation technology, such as inability to adapt to steam parameter fluctuations, large grid connection impact, narrow operating load range and high maintenance costs, this invention proposes a four-quadrant variable frequency differential pressure power generation system and control method adapted to steelmaking steam, which is of particular importance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a four-quadrant variable frequency differential pressure power generation system and control method adapted to steelmaking steam. By introducing a four-quadrant frequency converter and variable speed adaptive control technology, it achieves dynamic adjustment of turbine speed according to steam pressure difference, ensuring that the unit always operates at the optimal aerodynamic operating point, significantly improving the system's adaptability to changing operating conditions and power generation efficiency. At the same time, by using a four-quadrant frequency converter as the core grid-connected equipment, it achieves decoupled control of generator speed and grid frequency, ensuring a smooth and shock-free grid connection process, improving grid stability and ease of operation. In addition, the system also has the advantages of wide-load continuous operation capability and low maintenance costs, providing strong support for steel enterprises to efficiently recover and utilize waste heat and pressure from steelmaking steam.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In one aspect, a four-quadrant variable frequency differential pressure power generation system adapted to steelmaking steam, the system comprising the following components: The main steam passage module includes, in sequence, a steam inlet pipeline and isolation valve group, a steam-water separator, a unit regulating valve, a turbine expander, and a steam outlet pipeline and isolation valve group, which are used to transport and process steelmaking saturated steam and provide energy carriers for the system. The rotary power generation module includes a coaxially connected turbine expander and a high-speed permanent magnet synchronous generator. The output shaft of the turbine expander is rigidly connected to the rotor shaft of the high-speed permanent magnet synchronous generator. It has no reduction gearbox structure and is used to convert the thermal energy of steam into mechanical energy, and then into variable frequency and variable voltage alternating current. The four-quadrant frequency converter grid-connected module includes a generator output contactor, rectifier, DC bus, inverter, filter unit, and grid-connected cabinet connected in sequence. The DC bus is connected in parallel with an energy-saving braking unit. The rectifier and inverter are back-to-back dual PWM converter structures to achieve four-quadrant operation. The input terminal of the four-quadrant frequency converter grid-connected module is electrically connected to the output terminal of the high-speed permanent magnet synchronous generator, and the output terminal is electrically connected to the power grid of the plant area. It is used to convert the frequency-converted AC power output by the generator into power frequency AC power with the same frequency and phase as the power grid, so as to achieve impact-free flexible grid connection. At the same time, it can realize reverse power supply from the grid side to the generator side to drive the generator to run as a motor. The parameter monitoring module includes a flow meter, an inlet pressure sensor, an inlet temperature sensor, an intermediate pressure sensor, an intermediate temperature sensor, an outlet pressure sensor, and an outlet temperature sensor installed in the main steam passage, as well as a speed sensor installed in the rotating power generation module. All sensors are electrically connected to the control system to collect system operating parameters in real time and transmit them to the control system. The auxiliary system modules include steam pipeline steam traps, turbine steam traps, oil coolers, and shaft seal coolers, which are used to ensure the safe and stable operation of the system.

[0007] Furthermore, the main steam passage module is also equipped with a pre-processing linkage control unit electrically connected to the steam-water separator, the unit regulating valve, and the parameter monitoring module. Its control steps are as follows: First, during the start-up and warm-up phase, the control unit receives data from the inlet temperature and pressure sensors to determine the steam dryness. When the dryness is below 95%, it controls the steam-water separator drain valve to be fully open and the unit regulating valve to be fully closed until the dryness stabilizes above 98% before opening the regulating valve for preheating with a slight opening. Second, during the normal variable operating condition phase, the control unit collects steam flow data in real time. When it detects a flow fluctuation exceeding 20% ​​within 10 seconds, it triggers the secondary drainage of the steam-water separator and simultaneously limits the rate of change of the unit regulating valve opening to avoid sudden changes in turbine intake parameters. Third, during the shutdown or standby phase, the control unit first fully closes the unit regulating valve and then closes the steam-water separator drain valve after a 30-second delay to ensure that residual condensate in the pipeline is completely discharged.

[0008] Furthermore, the parameter monitoring module incorporates a real-time correction calculation unit for the dryness of steelmaking saturated steam, and its core correction formula is: ,in The corrected real-time dryness of the steam; The theoretical dryness fraction of saturated steam is obtained by interpolation from the steam thermodynamic property table based on the inlet pressure P1 and temperature T1. The weight for adjusting the flow rate fluctuation is set to 0.0012, which is derived from the linear fitting test data of converter steam flow rate fluctuation and dryness deviation in 12 steel plants in China. This is the absolute value of the difference between the current time and the average steam flow rate of the previous 10 seconds, expressed in t / h. The weight for adjusting the warm-up time is set to 0.008, which is derived from the measured data of the rate of condensate precipitation from the pipe wall during the warm-up process. This is the difference between the warm-up time and the standard warm-up time; if the warm-up meets the standard, it is taken as 0. The weight for correcting the condensate drainage state is set to 0.035, which is derived from the measured data of the effect of water retention in the pipeline on dryness when the condensate drain valve is closed. The state coefficient of the steam trap is 0 when steam is draining normally and 1 when it is closed for more than 60 seconds. This dryness correction calculation unit can accurately match the intermittent fluctuation characteristics of steelmaking steam. The error of the corrected dryness data does not exceed 0.5%. It provides accurate basic data support for the opening control of the unit's regulating valve and the anti-surge control of the turbine, avoiding the inaccuracy of control strategy due to dryness calculation deviation. It fundamentally solves the defect that the traditional dryness calculation method cannot adapt to the changing working conditions of steelmaking.

[0009] Furthermore, the turbine expander and high-speed permanent magnet synchronous generator of the rotary power generation module adopt an integrated rigid coaxial direct connection structure, equipped with a full-condition vibration suppression control unit. Its structure and control steps are as follows: First, the turbine output shaft and the generator rotor shaft are connected by an integrally forged rigid coupling. The coupling is equipped with a centering calibration reference surface and is calibrated using a dual dial indicator method. The radial runout deviation is ≤0.02mm, and the end face runout deviation is ≤0.01mm, eliminating the additional vibration caused by coaxiality deviation. Second, both the turbine and the generator are supported by tilting pad sliding bearings. The bearing lubrication oil circuit is equipped with an independent throttling orifice to form a stable dynamic pressure oil film across the entire speed range. The bearing is equipped with a temperature sensor. When the bearing temperature exceeds 65℃, the cooling water regulating valve of the oil cooler is triggered to open wider to enhance cooling. Third, the vibration suppression control unit collects speed and bearing housing vibration data in real time. When the detected vibration value exceeds 2.8mm / s, the generator torque is finely adjusted through the four-quadrant frequency converter module to suppress vibration. At the same time, the opening of the regulating valve is finely adjusted to keep the turbine away from the surge boundary range.

[0010] Furthermore, the control system incorporates an adaptive calculation unit for the turbine's variable speed target value, and its core adaptive calculation formula is as follows: ,in The real-time target speed of the turbine; This refers to the rated speed of the turbine. This refers to the real-time differential pressure of the steam. The unit is designed with a rated differential pressure. This refers to the real-time mass flow rate of steam. Design the rated steam flow rate for the unit; Real-time steam outlet pressure; Set pressure for the downstream pipeline network; This is the differential pressure weighting coefficient, with a value of 0.65. This is the traffic weighting coefficient, with a value of 0.30. The back pressure correction weighting coefficient is set to 0.05, and the sum of the three weighting coefficients is 1. This value is derived from orthogonal experimental data of 1500 sets of turbine optimal aerodynamic efficiency points under varying steam conditions in steelmaking, and is optimized using the response surface methodology. This ensures that the turbine operates within its highest aerodynamic efficiency range under any steam condition. When the calculated... When the speed is lower than the minimum anti-surge speed, the minimum anti-surge speed is taken as the target speed. When the speed is higher than the rated speed, the rated speed is taken as the target speed. This adaptive calculation unit can perfectly match the intermittent fluctuation characteristics of steelmaking steam, so that the turbine can always maintain the best aerodynamic conditions in the full fluctuation range of steam pressure from 2.0 to 3.5 MPa. This fundamentally avoids the stall and surge problems caused by constant speed operation, while maximizing the efficiency of steam energy recovery, improving power generation efficiency by more than 20% compared with the traditional constant speed control method.

[0011] Furthermore, the four-quadrant frequency converter grid-connected module incorporates a hierarchical synchronous flexible grid-connected control unit. Its control steps are as follows: First, in the pre-synchronization preparation stage, before the unit starts operation, the control unit collects grid voltage, frequency, and phase data through the grid-connected cabinet voltage transformer to complete benchmark calibration. Simultaneously, it pre-charges the inverter output filter unit to eliminate initial harmonic impacts during grid connection. Second, in the no-load synchronization stage, when the generator speed reaches 30% of the rated speed, the rectifier starts and maintains a stable DC bus voltage, the inverter starts in no-load mode, and the control unit locks in the phase-locked loop. The first step involves tracking the grid phase and frequency, correcting the phase deviation every 20ms, and maintaining synchronization for 30 seconds when the phase deviation is ≤0.5°, the frequency deviation is ≤0.05Hz, and the voltage amplitude deviation is ≤1%. The second step is the grid connection closing stage, where the control unit first closes the grid-side isolating switch and then gradually adjusts the inverter output power to ensure a smooth rise in the grid connection current, with the closing inrush current ≤5% of the rated current. The third step is the post-grid connection power adjustment stage, where the control unit gradually increases the inverter output power to the optimal power generation capacity under the current operating conditions based on changes in steam parameters.

[0012] Furthermore, the auxiliary system module incorporates a built-in all-condition condensate drain and shaft seal adaptive linkage control unit, which is electrically connected to the steam pipeline drain valve, turbine drain valve, shaft seal cooler, and parameter monitoring module. Its control steps are as follows: First, during the cold start warm-up phase, the control unit fully opens all pipeline drain valves and turbine drain valves, fully opens the shaft seal cooler cooling water regulating valve, and maintains a slight positive pressure by supplying sealing steam to the shaft seal system. Once the inlet steam temperature exceeds the saturation temperature by 5°C and the temperature difference between the upper and lower cylinders of the turbine block is ≤30°C, the control unit gradually closes the valves. The first step is to keep the pipeline steam trap open continuously. The second step is to close the turbine body steam trap during rated load operation. The control unit adjusts the steam trap's drainage cycle to a short-term drainage every 10 minutes according to the steam parameters. At the same time, the cooling water volume is adjusted according to the shaft seal exhaust temperature to control the exhaust temperature at 40~60℃. The third step is to reopen the turbine body steam trap during low load or standby operation. The control unit keeps the pipeline steam trap fully open and increases the cooling water volume of the shaft seal cooler to prevent steam from carrying water and damaging the bearing lubricating oil.

[0013] Furthermore, the control system incorporates a built-in fully automatic switching control unit for negative power standby mode. Its control steps are as follows: First, in the standby mode trigger judgment stage, the control unit collects steam flow data in real time. When it detects that the flow rate is continuously lower than the minimum power generation flow threshold for 30 seconds and the inlet pressure difference is lower than 30% of the rated pressure difference, it triggers standby prediction, sends a warning signal to the plant's DCS system, and preemptively opens the high and low pressure steam bypasses. Second, in the power generation to standby switching stage, the control unit gradually closes the unit's regulating valve to reduce the intake air flow, while simultaneously controlling the frequency converter module to gradually reduce the power generation to 0, and then switches to reverse electric mode. The first step is to maintain the minimum anti-surge speed of the generator unit by drawing power from the grid, and the switching process is completed within 60 seconds. The second step is to monitor the steam parameters in real time during the standby stable operation phase, maintain the minimum anti-surge speed of the unit, continuously monitor the condensate status, and control the power drawn from the grid to be within 10% of the rated power. The third step is to switch from standby to power generation. When the steam flow rate is detected to be higher than the minimum power generation threshold for 10 consecutive seconds and the inlet pressure difference is restored to more than 30% of the rated pressure difference, the control unit gradually opens the regulating valve and simultaneously reduces the reverse electric power. When the turbine output torque exceeds the electric torque, it automatically switches back to the power generation mode and completes the power increase within 8 seconds.

[0014] Furthermore, the control system incorporates a comprehensive fault protection linkage control unit that classifies faults into three levels: early warning, general, and severe. The control steps are as follows: First, early warning level fault protection: When early warning faults such as low steam dryness, slightly excessive bearing temperature, minor fluctuations in grid voltage, or vibration values ​​approaching the threshold are detected, an early warning signal is sent to the plant's DCS system, simultaneously triggering fine-tuning control of corresponding components to eliminate potential faults without reducing load. Second, general fault level protection: When sudden changes in steam parameters exceeding the adjustment range or excessive grid harmonics are detected... In the event of a common fault such as a continuous rise in bearing temperature, the regulating valve is gradually closed to reduce the unit load to 50% of the rated load, while triggering the corresponding fault handling action to maintain stable operation at low load. The third step is the severe fault protection. When a severe fault such as power grid failure, unit surge, excessive vibration, generator short circuit, or severe steam water carryover is detected, emergency protection is triggered within 200ms: the regulating valve is fully closed to cut off the steam intake, the generator output contactor is disconnected to isolate the power grid, the power grid failure fault is synchronously closed to consume excess electrical energy by closing the energy consumption braking unit switch, and the steam water carryover fault is synchronously fully opened by opening all drain valves.

[0015] On the other hand, a four-quadrant variable frequency differential voltage power generation control method adapted to steelmaking steam is characterized by the following specific steps: S1. Real-time steam parameter acquisition: Through the flow meter, pressure sensor, temperature sensor, and speed sensor of the parameter monitoring module, the steam pressure, temperature, steam flow rate, and real-time speed of the turbine inlet and outlet are collected in real time, and all data are synchronously transmitted to the control system. S2. Steam passage pretreatment control: The control system controls the steam-water separator to complete the separation of steam condensate according to the collected steam parameters, and discharges the condensate from the pipeline through the steam trap. At the same time, the control system adjusts the opening and change rate of the unit's regulating valve according to the steam flow and pressure fluctuation amplitude to ensure the stability of the dryness and parameters of the steam entering the turbine. S3, Variable speed adaptive power generation control: The control system calculates the steam pressure difference based on real-time steam parameters, calculates the turbine target speed based on preset variable operating condition logic, and adjusts the generator torque current through the four-quadrant frequency conversion grid-connected module using vector control algorithm, so that the actual speed of the unit accurately follows the target speed, and the turbine operates at the optimal aerodynamic operating point under any operating condition, driving the coaxial generator to output the corresponding AC power. S4. Flexible grid connection and adaptive power adjustment: The rectifier of the four-quadrant frequency conversion grid connection module rectifies the frequency conversion AC power output by the generator into stable DC power, realizing the decoupling of the generator speed and the grid frequency. The inverter tracks the phase, frequency and amplitude of the grid voltage through the phase-locked loop, and inverts the DC power into power frequency AC power synchronized with the grid. After filtering, it is sent to the plant grid through the grid connection cabinet. At the same time, the control system dynamically adjusts the inverter output power according to the available steam energy. S5. Full-condition auxiliary and safety protection control: The control system completes full-condition drainage, lubricating oil cooling and shaft seal system adaptive control through the auxiliary system module. At the same time, it monitors the system operating status in real time and triggers corresponding grade protection actions according to the fault level to ensure the safe and stable operation of the unit throughout the entire process.

[0016] Compared with existing technologies, this four-quadrant variable frequency differential pressure power generation system and control method adapted to steelmaking steam has the following advantages: I. By introducing a four-quadrant frequency converter and variable speed adaptive control technology, this system enables the turbine to dynamically adjust its speed according to the actual pressure difference of the steelmaking steam. Specifically, the system's built-in turbine variable speed target value adaptive calculation unit accurately calculates the optimal target speed of the turbine based on parameters such as the real-time pressure difference, mass flow rate, and downstream pipeline pressure of the steam. The four-quadrant frequency converter adjusts the torque current of the generator in real time, ensuring that the turbine always operates at the optimal aerodynamic operating point. This technological innovation completely solves the stall and surge problems that traditional constant-speed units are prone to when steam parameters fluctuate, and significantly improves the system's adaptability to changing operating conditions.

[0017] II. This system uses a four-quadrant frequency converter as the core grid-connected equipment. Through its unique back-to-back dual PWM converter structure, it achieves decoupled control of generator speed and grid frequency. During grid connection, the inverter on the grid side tracks the phase and frequency of the grid voltage in real time through a phase-locked loop and gradually adjusts the output voltage to ensure complete synchronization with the grid without voltage difference. This ensures a smooth and shock-free grid connection process. In addition, this technology eliminates the dependence on complex synchronization devices, simplifies the operation process, reduces the technical requirements for operators, and truly realizes one-button start / stop and unattended operation.

[0018] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 A flowchart illustrating the overall architecture and collaborative process of a four-quadrant variable frequency differential pressure power generation system adapted to steelmaking steam. Figure 2 A flowchart of a four-quadrant variable frequency graded synchronous flexible grid-connected control system adapted to steelmaking steam; Figure 3 This is a flowchart of a four-quadrant variable frequency differential voltage power generation control method adapted to steelmaking steam. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0022] Example I. Project Overview and Design Requirements This embodiment is applied to the steelmaking plant area of a large domestic integrated iron and steel enterprise. The steam source is the vaporization cooling system supporting 4 350t converters, and 12 150m³ steam accumulators are supported at the back end to buffer the steam parameter fluctuations caused by the intermittent production of the converters. The rated operating condition parameters of the system design are: the rated inlet pressure of steam is 2.5MPa, the rated pressure difference is 1.5MPa, the rated steam flow rate is 23t / h, the set pressure of the downstream steam pipe network is 1.0MPa, the steam medium is saturated steam, and the corresponding saturated temperature range is 217~243°C. The plant power grid is a 10kV / 50Hz industrial frequency AC power grid, and the rated power generation of the system design is 670kW.

[0023] II. System Hardware Configuration The four-quadrant variable-frequency differential pressure power generation system adapted to steelmaking steam adopted in this embodiment is completely configured with a main steam passage module, a rotating power generation module, a four-quadrant variable-frequency grid-connected module, a parameter monitoring module, an auxiliary system module and a supporting control system. The specific configuration of each module is as follows: Main steam passage module: The steam inlet pipeline and isolation valve group, high-efficiency cyclone steam-water separator, high-precision pneumatic regulating valve of the unit, centripetal radial flow turbine expander, steam outlet pipeline and isolation valve group are configured in sequence. At the same time, a pre-treatment linkage control unit electrically connected to the steam-water separator, the unit regulating valve and the parameter monitoring module is configured; Rotating power generation module: It adopts an integrated rigid coaxial direct connection structure of a turbine expander and a high-speed permanent magnet synchronous generator, without a reduction gearbox design. The rated speed of the turbine is 23000r / min, and the minimum anti-surge speed is 6900r / min. A full-condition vibration suppression control unit is supported; Four-quadrant variable-frequency grid-connected module: It adopts a four-quadrant frequency converter with a back-to-back dual PWM converter structure, and is configured with a generator output contactor, a rectifier, a DC bus, an inverter, an LCL filter unit, and a 380V grid-connected cabinet in sequence. An energy consumption braking unit and an energy consumption resistor are connected in parallel to the DC bus. The output end of the frequency converter is connected to the 10kV power grid of the plant through a 380V / 10kV step-up transformer. A hierarchical synchronous flexible grid-connected control unit is built in the module; Parameter monitoring module: A vortex flowmeter, an inlet pressure sensor, an inlet temperature sensor, an intermediate pressure sensor, an intermediate temperature sensor, an outlet pressure sensor, and an outlet temperature sensor are installed in sequence in the main steam passage. A magnetoelectric speed sensor is supported in the rotating power generation module. All sensors are electrically connected to the control system. A real-time correction calculation unit for the dryness of steelmaking saturated steam is built in the module; Auxiliary system module: A steam pipeline steam trap, a turbine body steam trap, a lubricating oil cooler, and a shaft seal cooler are configured. A full-condition steam trap and shaft seal adaptive linkage control unit is built in the module; Control system: It adopts a PLC redundant control system, with built-in turbine variable speed target value adaptive calculation unit, negative power standby mode fully automatic switching control unit, and full-condition graded fault protection linkage control unit, which can realize bidirectional data communication and linkage control with the plant's DCS system.

[0024] III. Detailed Implementation Steps The first step is system startup preparation and cold-state warm-up control. After completing static checks and safety interlock tests on all system equipment, confirming that the cooling water passages of the auxiliary system modules (oil cooler, shaft seal cooler) are normal, the lubricating oil system operating parameters meet standards, and all isolation valve groups are in normal condition, the cold-state warm-up process is initiated. The control system collects real-time steam inlet temperature and pressure data through the parameter monitoring module, and accurately calculates the steam dryness using the built-in steelmaking saturated steam dryness real-time correction calculation unit. The core correction formula is: ,in The corrected real-time dryness of the steam; The theoretical dryness fraction of saturated steam is obtained by interpolation from the steam thermodynamic property table based on the inlet pressure P1 and temperature T1. Adjust weights to account for traffic fluctuations; This is the absolute value of the difference between the current time and the average steam flow rate of the previous 10 seconds; Adjust the weights for warm-up time; This is the difference between the warm-up time and the standard warm-up time. Adjust the weights for hydrophobic states; To determine the steam trap state coefficient, the pre-treatment linkage control unit and the full-condition steam trap and shaft seal adaptive linkage control unit are activated simultaneously. This controls the steam-water separator drain valve to be fully open and the unit regulating valve to be fully closed. At the same time, all pipeline steam traps and turbine steam traps are fully opened, and the shaft seal cooler cooling water regulating valve is fully open. Sealing steam is introduced into the shaft seal system to maintain a slightly positive pressure state. The pipelines and equipment are continuously warmed up and drained until the steam dryness stabilizes above 98%, the inlet steam temperature exceeds the corresponding saturation temperature by 5°C, and the temperature difference between the upper and lower cylinders of the turbine cylinder is ≤30°C. The warm-up process is then completed, and the opening of the pipeline steam traps is gradually reduced to maintain continuous drainage.

[0025] The second step involves unit start-up and tiered synchronous flexible grid connection control. After warm-up, the control system, through the pre-processing linkage control unit, controls the unit's regulating valve to open a preheating micro-opening, allowing steam to enter the turbine expander and drive the rotor to start. The speed sensor collects the unit's speed data in real time and feeds it back to the control system. When the generator speed reaches 30% of the rated speed, the tiered synchronous flexible grid connection control unit of the four-quadrant inverter grid connection module is activated. First, it collects grid voltage, frequency, and phase data through the grid connection cabinet voltage transformer to complete the benchmark calibration. At the same time, it pre-charges the inverter output filter unit to eliminate the initial harmonic impact of grid connection. Then, it starts the rectifier and maintains the DC bus voltage stability. When the inverter starts in no-load mode, the control unit tracks the grid phase and frequency in real time through a phase-locked loop, correcting the phase deviation every 20ms. When the phase deviation is ≤0.5°, the frequency deviation is ≤0.05Hz, and the voltage amplitude deviation is ≤1%, the synchronization state is maintained for 30 seconds. After the synchronization state is stable, the control unit first closes the grid-side isolating switch, and then gradually adjusts the inverter output power to make the grid-connected current rise smoothly, controlling the closing inrush current to be ≤5% of the rated current, thus completing the impact-free flexible grid connection. After the grid connection is completed, the inverter output power is gradually increased to the optimal power generation power under the current operating conditions according to the changes in steam parameters.

[0026] The third step is adaptive control during normal variable operating conditions. After the unit is connected to the grid and enters the normal operating phase, the parameter monitoring module collects real-time operating data on steam inlet and outlet pressure, temperature, steam flow, and real-time unit speed, and transmits this data synchronously to the control system. The control system, through its built-in turbine variable speed target value adaptive calculation unit, calculates the real-time target turbine speed in conjunction with the real-time collected steam parameters. The core adaptive calculation formula is as follows: ,in The real-time target speed of the turbine; This refers to the rated speed of the turbine. This refers to the real-time differential pressure of the steam. The unit is designed with a rated differential pressure. This refers to the real-time mass flow rate of steam. Design the rated steam flow rate for the unit; Real-time steam outlet pressure; Set pressure for the downstream pipeline network; This is the pressure difference weighting coefficient. For traffic weighting coefficients, To correct the back pressure weighting coefficient, a vector control algorithm is used through a four-quadrant frequency converter grid-connected module to adjust the generator torque and current, ensuring that the actual unit speed accurately follows the target speed. This allows the turbine to operate at its optimal aerodynamic operating point under any conditions, driving the coaxial generator to output corresponding AC power. During operation, the pre-processing linkage control unit collects steam flow data in real time. If a flow fluctuation exceeds 20% within 10 seconds, it triggers secondary condensation of the steam-water separator and limits the rate of change of the unit's regulating valve opening to prevent sudden changes in turbine intake parameters. The full-condition vibration suppression control unit collects speed and bearing housing vibration data in real time, ensuring that the unit's radial runout deviation is ≤0.02mm and the end face runout is ≤0.02mm through an integrated rigid coupling. Dynamic deviation ≤0.01mm eliminates additional vibration caused by coaxiality deviation. At the same time, a stable dynamic pressure oil film is formed across the entire speed range through the tilting pad sliding bearing. When the bearing temperature exceeds 65℃, the cooling water regulating valve of the oil cooler is triggered to open wider to enhance cooling. When the vibration value exceeds 2.8mm / s, the generator torque is finely adjusted through the four-quadrant frequency converter module to suppress vibration. At the same time, the opening of the regulating valve is finely adjusted to keep the turbine away from the surge boundary range. The full-condition condensate drain and shaft seal adaptive linkage control unit closes the turbine body condensate drain valve and adjusts the condensate drain cycle of the pipeline condensate drain to a short-term condensate drain every 10 minutes according to the steam parameters. At the same time, the cooling water volume is adjusted according to the shaft seal exhaust temperature to control the exhaust temperature within the range of 40~60℃.

[0027] The fourth step is the switching and recovery control of the low-load negative power standby mode. During normal operation, the control system collects steam flow data in real time through the fully automatic switching control unit for negative power standby mode. When the converter enters the smelting interval, if the steam flow is detected to be lower than the minimum power generation flow threshold for 30 consecutive seconds and the inlet pressure difference is lower than 30% of the rated pressure difference, the standby prediction is triggered, and a warning signal is sent to the plant's DCS system to open the high and low pressure steam bypasses in advance. Subsequently, the control unit gradually closes the unit's regulating valve to reduce the intake air flow, while controlling the frequency converter module to gradually reduce the power generation to 0, and then switches to reverse electric mode to draw power from the grid to drive the unit to maintain the minimum anti-surge speed. The switching process is completed within 60 seconds. During the standby stable operation phase, the control unit monitors the steam parameters in real time, maintains the minimum anti-surge speed of the unit, continuously monitors the condensate status, and controls the power drawn from the grid to within 10% of the rated power. When the converter smelting is completed and the steam parameters are restored, if the steam flow rate is detected to be higher than the minimum power generation threshold for 10 consecutive seconds and the inlet pressure difference is restored to more than 30% of the rated pressure difference, the control unit gradually opens the regulating valve, simultaneously reduces the reverse electric power, and automatically switches back to the power generation mode when the turbine output torque exceeds the electric torque. The power increase is completed within 8 seconds, and the normal power generation operation is restored.

[0028] Step 5: Full-condition graded fault protection linkage control. Throughout the entire operating cycle of the unit, the control system monitors the system's operating status in real time through a multi-condition graded fault protection linkage control unit, classifying faults into warning level, general fault level, and severe fault level for graded protection. When warning faults such as low steam dryness, slightly excessive bearing temperature, small fluctuations in grid voltage, and vibration values ​​approaching the threshold are detected, a warning signal is sent to the plant's DCS system, and corresponding component fine-tuning control is triggered to eliminate potential faults without reducing the load. When general faults such as sudden changes in steam parameters exceeding the adjustment range, excessive grid harmonics, and continuous rise in bearing temperature are detected, the regulating valve is gradually closed to reduce the unit load to 50% of the rated load, and corresponding fault handling actions are triggered to maintain stable operation at low load. When severe faults such as grid power outage, unit surge, severely excessive vibration values, generator short circuit, and severe steam water carryover are detected, an emergency protection action is triggered within 200ms, fully closing the regulating valve to cut off the steam intake, disconnecting the generator output contactor to isolate the grid, and simultaneously closing the energy consumption braking unit switch to consume excess electrical energy in the grid power outage fault, and simultaneously fully opening all drain valves in the steam water carryover fault to ensure the safety of the unit equipment.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam, characterized in that, The system includes the following components: The main steam passage module includes, in sequence, a steam inlet pipeline and isolation valve group, a steam-water separator, a unit regulating valve, a turbine expander, and a steam outlet pipeline and isolation valve group, which are used to transport and process steelmaking saturated steam and provide energy carriers for the system. The rotary power generation module includes a coaxially connected turbine expander and a high-speed permanent magnet synchronous generator. The output shaft of the turbine expander is rigidly connected to the rotor shaft of the high-speed permanent magnet synchronous generator. It has no reduction gearbox structure and is used to convert the thermal energy of steam into mechanical energy, and then into variable frequency and variable voltage alternating current. The four-quadrant frequency converter grid-connected module includes a generator output contactor, rectifier, DC bus, inverter, filter unit, and grid-connected cabinet connected in sequence. The DC bus is connected in parallel with an energy-saving braking unit. The rectifier and inverter are back-to-back dual PWM converter structures to achieve four-quadrant operation. The input terminal of the four-quadrant frequency converter grid-connected module is electrically connected to the output terminal of the high-speed permanent magnet synchronous generator, and the output terminal is electrically connected to the power grid of the plant area. It is used to convert the frequency-converted AC power output by the generator into power frequency AC power with the same frequency and phase as the power grid, so as to achieve impact-free flexible grid connection. At the same time, it can realize reverse power supply from the grid side to the generator side to drive the generator to run as a motor. The parameter monitoring module includes a flow meter, an inlet pressure sensor, an inlet temperature sensor, an intermediate pressure sensor, an intermediate temperature sensor, an outlet pressure sensor, and an outlet temperature sensor installed in the main steam passage, as well as a speed sensor installed in the rotating power generation module. All sensors are electrically connected to the control system to collect system operating parameters in real time and transmit them to the control system. The auxiliary system modules include steam pipeline steam traps, turbine steam traps, oil coolers, and shaft seal coolers, which are used to ensure the safe and stable operation of the system.

2. The four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The main steam passage module is also equipped with a pre-treatment linkage control unit electrically connected to the steam-water separator, unit regulating valve, and parameter monitoring module. Its control steps are as follows: First, during the start-up and warm-up phase, the control unit receives data from the inlet temperature and pressure sensors to determine the steam dryness. When the dryness is below 95%, it controls the steam-water separator drain valve to be fully open and the unit regulating valve to be fully closed until the dryness stabilizes above 98% before opening the regulating valve for preheating with a slight opening. Second, during the normal variable operating condition phase, the control unit collects steam flow data in real time. When it detects a flow fluctuation exceeding 20% ​​within 10 seconds, it triggers the secondary drainage of the steam-water separator and simultaneously limits the rate of change of the unit regulating valve opening. Third, during the shutdown or standby phase, the control unit first fully closes the unit regulating valve and then closes the steam-water separator drain valve after a 30-second delay to ensure that residual condensate in the pipeline is completely discharged.

3. The four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The parameter monitoring module has a built-in real-time correction calculation unit for the dryness of steelmaking saturated steam, and its core correction formula is: ,in The corrected real-time dryness of the steam; The theoretical dryness fraction of saturated steam is obtained by interpolation from the steam thermodynamic property table based on the inlet pressure P1 and temperature T1. Adjust weights to account for traffic fluctuations; This is the absolute value of the difference between the current time and the average steam flow rate of the previous 10 seconds; Adjust the weights for warm-up time; This is the difference between the warm-up time and the standard warm-up time. Adjust the weights for hydrophobic states; This is the state coefficient of the steam trap.

4. A four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The rotary power generation module's turbine expander and high-speed permanent magnet synchronous generator adopt an integrated rigid coaxial direct connection structure, equipped with a full-condition vibration suppression control unit. Its structure and control steps are as follows: First, the turbine output shaft and generator rotor shaft are connected by an integrally forged rigid coupling. The coupling has a centering calibration reference surface and is calibrated using a dual dial indicator method, with radial runout ≤0.02mm and end face runout ≤0.01mm, eliminating additional vibration caused by coaxiality deviation. Second, both the turbine and generator are supported by tilting pad sliding bearings. The bearing lubrication oil circuit has independent throttling orifices, forming a stable dynamic pressure oil film across the entire speed range. The bearing is equipped with a temperature sensor; when the bearing temperature exceeds 65℃, it triggers the cooling water regulating valve of the oil cooler to open wider, enhancing cooling. Third, the vibration suppression control unit collects speed and bearing housing vibration data in real time. When the detected vibration value exceeds 2.8mm / s, it uses a four-quadrant frequency converter module to fine-tune the generator torque to suppress vibration, while simultaneously fine-tuning the regulating valve opening to keep the turbine away from the surge boundary range.

5. A four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The control system incorporates an adaptive calculation unit for the turbine's variable speed target value, and its core adaptive calculation formula is as follows: ,in The real-time target speed of the turbine; This refers to the rated speed of the turbine. This refers to the real-time differential pressure of the steam. The unit is designed with a rated differential pressure. This refers to the real-time mass flow rate of steam. Design the rated steam flow rate for the unit; Real-time steam outlet pressure; Set pressure for the downstream pipeline network; This is the pressure difference weighting coefficient. For traffic weighting coefficients, The weighting coefficient is used to correct the back pressure.

6. A four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The four-quadrant frequency converter grid-connected module has a built-in hierarchical synchronous flexible grid-connected control unit. Its control steps are as follows: First step, pre-synchronization preparation stage. Before the unit starts up, the control unit collects grid voltage, frequency and phase data through the grid-connected cabinet voltage transformer to complete the benchmark calibration. At the same time, it pre-charges the inverter output filter unit to eliminate the initial harmonic impact of grid connection. The second step is the no-load synchronization stage. When the generator speed increases to 30% of the rated speed, the rectifier starts and maintains the DC bus voltage stability. The inverter starts the no-load mode. The control unit tracks the grid phase and frequency through the phase-locked loop and corrects the phase deviation every 20ms. When the phase deviation is ≤0.5°, the frequency deviation is ≤0.05Hz, and the voltage amplitude deviation is ≤1%, the synchronization state is maintained for 30 seconds. The third step, the grid connection and closing stage, involves the control unit first closing the grid-side isolating switch, and then gradually adjusting the inverter output power to make the grid connection current rise smoothly, with the closing inrush current ≤ 5% of the rated current. The fourth step is the power regulation stage after grid connection. The control unit gradually increases the inverter output power to the optimal power generation power under the current operating conditions based on changes in steam parameters.

7. A four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The auxiliary system module has a built-in all-condition drainage and shaft seal adaptive linkage control unit, which is electrically connected to the steam pipeline drain valve, turbine drain valve, shaft seal cooler, and parameter monitoring module. Its control steps are as follows: First, during the cold start warm-up stage, the control unit controls all pipeline drain valves and turbine drain valves to be fully open, and the shaft seal cooler cooling water regulating valve to be fully open. The shaft seal system is kept under slight positive pressure by sealing steam. When the inlet steam temperature exceeds the saturation temperature by 5°C and the temperature difference between the upper and lower cylinders of the turbine block is ≤30°C, the opening of the pipeline drain valves is gradually reduced to maintain continuous drainage. Second, during the rated load operation stage, the control unit closes the turbine body drain valve and adjusts the drainage cycle of the pipeline drain valve to a short-term drainage every 10 minutes according to the steam parameters. At the same time, the cooling water volume is adjusted according to the shaft seal exhaust temperature to control the exhaust temperature at 40~60°C. Third, during the low load or standby stage, the control unit reopens the turbine body drain valve, keeps the pipeline drain valves fully open, and increases the cooling water volume of the shaft seal cooler.

8. A four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The control system has a built-in fully automatic switching control unit for negative power standby mode. Its control steps are as follows: First, in the standby mode trigger judgment stage, the control unit collects steam flow data in real time. When it detects that the flow rate is continuously lower than the minimum power generation flow threshold for 30 seconds and the inlet pressure difference is lower than 30% of the rated pressure difference, it triggers standby prediction, sends a warning signal to the plant's DCS system, and preemptively opens the high and low pressure steam bypasses. Second, in the power generation to standby switching stage, the control unit gradually closes the unit's regulating valve to reduce the intake air flow, while simultaneously controlling the frequency converter module to gradually reduce the power generation to 0, and then switches to reverse electric mode to draw power from the grid. The electric drive unit maintains the minimum anti-surge speed, and the switching process is completed within 60 seconds. In the third step, during the standby stable operation phase, the control unit monitors the steam parameters in real time, maintains the minimum anti-surge speed of the unit, continuously monitors the condensate status, and controls the power drawn from the grid to within 10% of the rated power. In the fourth step, during the standby power generation switching phase, when the steam flow rate is detected to be higher than the minimum power generation threshold for 10 consecutive seconds and the inlet pressure difference recovers to more than 30% of the rated pressure difference, the control unit gradually opens the regulating valve, simultaneously reduces the reverse electric power, and automatically switches back to the power generation mode when the turbine output torque exceeds the electric torque, completing the power increase within 8 seconds.

9. A four-quadrant variable frequency differential voltage power generation system adapted to steelmaking steam according to claim 1, characterized in that, The control system incorporates a full-condition graded fault protection linkage control unit, classifying faults into warning level, general fault level, and severe fault level for graded protection. The control steps are as follows: First, warning level fault protection: When warning faults such as low steam dryness, slightly excessive bearing temperature, small fluctuations in grid voltage, or vibration values ​​approaching the threshold are detected, a warning signal is sent to the plant's DCS system, simultaneously triggering fine-tuning control of corresponding components to eliminate potential fault hazards without reducing load; Second, general fault level protection: When sudden changes in steam parameters exceeding the adjustment range, excessive grid harmonics, or bearing... In the event of a general fault such as a sustained increase in temperature, the regulating valve is gradually closed to reduce the unit load to 50% of the rated load, while triggering the corresponding fault handling action to maintain stable operation at low load. The third step is the severe fault protection. When a severe fault such as a power grid outage, unit surge, excessive vibration, generator short circuit, or severe steam water carryover is detected, emergency protection is triggered within 200ms: the regulating valve is fully closed to cut off the steam intake, the generator output contactor is disconnected to isolate the power grid, the energy consumption braking unit switch is closed simultaneously to consume excess electrical energy in the power grid outage fault, and all steam traps are fully opened simultaneously in the steam water carryover fault.

10. A four-quadrant variable frequency differential pressure power generation control method adapted to steelmaking steam, applicable to the four-quadrant variable frequency differential pressure power generation system adapted to steelmaking steam as described in any one of claims 1-9, characterized in that, The specific steps of this method are as follows: S1. Real-time steam parameter acquisition: Through the flow meter, pressure sensor, temperature sensor, and speed sensor of the parameter monitoring module, the steam pressure, temperature, steam flow rate, and real-time speed of the turbine inlet and outlet are collected in real time, and all data are synchronously transmitted to the control system. S2. Steam passage pretreatment control: The control system controls the steam-water separator to complete the separation of steam condensate according to the collected steam parameters, and discharges the condensate from the pipeline through the steam trap. At the same time, the control system adjusts the opening and change rate of the unit's regulating valve according to the steam flow and pressure fluctuation amplitude to ensure the stability of the dryness and parameters of the steam entering the turbine. S3, Variable speed adaptive power generation control: The control system calculates the steam pressure difference based on real-time steam parameters, calculates the turbine target speed based on preset variable operating condition logic, and adjusts the generator torque current through the four-quadrant frequency conversion grid-connected module using vector control algorithm, so that the actual speed of the unit accurately follows the target speed, and the turbine operates at the optimal aerodynamic operating point under any operating condition, driving the coaxial generator to output the corresponding AC power. S4. Flexible grid connection and adaptive power adjustment: The rectifier of the four-quadrant frequency conversion grid connection module rectifies the frequency conversion AC power output by the generator into stable DC power, realizing the decoupling of the generator speed and the grid frequency. The inverter tracks the phase, frequency and amplitude of the grid voltage through the phase-locked loop, and inverts the DC power into power frequency AC power synchronized with the grid. After filtering, it is sent to the plant grid through the grid connection cabinet. At the same time, the control system dynamically adjusts the inverter output power according to the available steam energy. S5. Full-condition auxiliary and safety protection control: The control system completes full-condition drainage, lubricating oil cooling and shaft seal system adaptive control through the auxiliary system module. At the same time, it monitors the system operating status in real time and triggers corresponding grade protection actions according to the fault level to ensure the safe and stable operation of the unit throughout the entire process.

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