Closed hydraulic cylinder lifting compensation system for ocean drilling rig and control method for implementation mechanism of closed hydraulic cylinder lifting compensation system

Abstract

The invention discloses a closed hydraulic cylinder lifting compensation system for an ocean drilling rig, which comprises a drilling rig derrick, a lifting hydraulic cylinder is arranged on the drilling rig derrick, a lifting pulley block is arranged at the driving end of the lifting hydraulic cylinder, and a lifting hook is wound on the lifting pulley block; the drilling machine derrick is further provided with a compensation energy accumulator, a nitrogen cylinder set, a main hydraulic station and an energy storage power distribution unit. The invention further discloses a control method for the implementation mechanism of the closed hydraulic cylinder lifting compensation system for the ocean drilling rig. The hydraulic cylinder lifting system solves the problem of valve control heating of an existing hydraulic cylinder lifting system, the problem that equipment complexity is increased by an additional drill column compensation device and the problem of lowering potential energy recycling.

Description

Technical Field

[0001] The invention belongs to the technical field of marine drilling equipment, and in particular relates to a closed hydraulic cylinder lifting compensation system for a marine drilling rig, and also relates to a control method for the implementation mechanism of the closed hydraulic cylinder lifting compensation system for a marine drilling rig. Background Art

[0002] For offshore oil and gas drilling and ocean scientific research operations of offshore floating drilling vessels, the offshore drilling rig is the key equipment that determines its drilling capacity, operating efficiency, and safety performance. The drilling rig lifting system (referred to as the lifting system) is the core component of the offshore drilling rig. The performance of the system directly determines the energy efficiency of the entire offshore drilling operation. Generally, the main functions of the lifting system are: lifting and lowering the drill rod to ensure normal drilling operations, lifting and lowering the watertight pipe to ensure the establishment of a complete riser channel, and lowering and recovering underwater equipment to ensure the safety of drilling and mining. The lifting system is divided into two types according to the drive type: winch and hydraulic cylinder. Among them, the winch type drilling lifting system (referred to as the winch lifting system) is mainly composed of an electric drive (hydraulic drive) drilling winch, wire rope, derrick crane pulley block, traveling block hook, etc.; the hydraulic cylinder type drilling lifting system (referred to as the hydraulic cylinder lifting system) is mainly composed of a hydraulic cylinder, wire rope, guide pulley block, traveling block hook, etc. The winch lifting system has the characteristics of mature technology, relatively low procurement cost, excellent reliability and speed regulation characteristics, and is still used by most marine floating drilling vessels today. The hydraulic cylinder lifting system is a technology that has gradually developed and matured in the past 20 years. Compared with the winch lifting system, it has obvious advantages in overall system weight, center of gravity control and deck space occupation, and is increasingly used in new deepwater and ultra-deepwater drilling platforms (drilling ships).

[0003] The cylinder lifting system usually adopts an open hydraulic system to drive and control the cylinder. The speed control of the cylinder is achieved by adjusting the throttling element in the oil circuit, which will cause the throttling element to generate a lot of heat when the cylinder lifts and lowers the load. Especially in the special working conditions where a large number of risers and drill pipes need to be lowered during drilling operations, the open hydraulic system should reserve more sufficient heat dissipation capacity. At the same time, the reliability of the throttling element will gradually decrease with the long-term heating of the element, increasing the subsequent use and maintenance costs.

[0004] The current mainstream hydraulic cylinder lifting system often achieves the drill string compensation function of drilling by adding a drill string compensation device to the lifting wire rope path. Since the top of the lifting cylinder is a guide pulley group, the installation of the crown type drill string compensation device requires the support of a huge crown frame and is therefore rarely used. The traveling type and dead rope end drill string compensation devices are more commonly used, but the additional compensation device increases the overall height of the derrick to a certain extent. At the same time, its mechanical, hydraulic and electrical interfaces also increase the complexity of the derrick structure and bring new problems such as pipeline layout, electrical control and increased center of gravity of the derrick.

[0005] During the drilling process, the lifting system has operating conditions of heavy load and low speed lowering and light load and fast lifting. The heavy load lowering mainly occurs when lowering the watertight pipe and the drill string. A large amount of gravitational potential energy will be generated during the lowering process. If the gravity potential energy is converted into electrical energy and directly fed back to the ship's AC power grid, a large amount of secondary harmonics will be generated, which will cause certain interference to the entire ship's AC power grid. In severe cases, it will affect the normal operation of the ship at sea. Under normal circumstances, the gravity potential energy of the load lowering is dissipated through friction, braking resistance, hydraulic throttling and other forms of heat generation, and the lowering potential energy cannot be recovered and reused, which is not conducive to energy conservation and emission reduction of the entire marine drilling ship.

[0006] As marine oil and gas exploration and development and ocean scientific research operations gradually shift from shallow waters to deep seas, the requirements for the overall center of gravity of the drilling package of floating drilling vessels required for exploration and development, occupied deck area, operating efficiency, use and maintenance costs, energy conservation and emission reduction are also increasing year by year. In order to meet the current and future requirements, it is particularly urgent to design and develop a new type of marine drilling rig hydraulic cylinder lifting system and propose innovative implementation mechanisms and control methods. Summary of the invention

[0007] The first object of the present invention is to provide a closed hydraulic cylinder lifting compensation system for an offshore drilling rig, which solves the problems of valve control heating in the existing hydraulic cylinder lifting system, the problem of additional drill string compensation devices increasing the complexity of the equipment, and the problem of recycling and reusing the lowering potential energy.

[0008] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a closed hydraulic cylinder lifting compensation system for an offshore drilling rig, comprising a drilling rig derrick, a lifting hydraulic cylinder is arranged on the drilling rig derrick, a lifting pulley block is arranged at the driving end of the lifting hydraulic cylinder, and a lifting hook is installed around the lifting pulley block; a compensation accumulator, a nitrogen bottle group, a main hydraulic station, and an energy storage distribution unit are also arranged on the drilling rig derrick.

[0009] As a preferred technical solution of the present invention, the main hydraulic station adopts multiple closed pump groups in parallel to supply oil.

[0010] The second object of the present invention is to provide a control method for the mechanism of a closed hydraulic cylinder lifting compensation system for an offshore drilling rig, so as to solve the problems of valve control heating of the existing hydraulic cylinder lifting system, the problem of increased equipment complexity due to additional drill string compensation devices, and the problem of recovery and reuse of the lowered potential energy.

[0011] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a control method for realizing the mechanism of a closed hydraulic cylinder lifting compensation system for an offshore drilling rig, comprising:

[0012] S1, used to realize the drill string compensation function, specifically:

[0013] The lifting cylinder 2 is switched through the oil circuit of the cylinder valve group 14, and is changed from a double-acting cylinder to a plunger cylinder. The compensating accumulator 8 is divided into a lower passive accumulator and an upper constant-speed cylinder. The lower passive accumulator is a piston accumulator, whose liquid end is connected to the lifting cylinder 2, and whose gas end is connected to the nitrogen bottle group 9. The plunger-type lifting cylinder 2, the compensating accumulator 8 and the nitrogen bottle group 9 together form a "liquid-gas spring", which has the ability of passive drill string compensation;

[0014] When it is necessary to improve the compensation accuracy, the upper constant velocity cylinder of the compensation accumulator 8 will be switched from the follow-up state to the working state. The switching function is realized by the accumulator valve group 15. When the constant velocity cylinder is opened, the oil circuit switching valve 12.1 inside the main hydraulic station 12 is controlled to switch the oil supply circuit of the closed pump group to the A2 and B2 circuits. By controlling the displacement of the closed pump, the A2 and B2 circuits directly drive the upper constant velocity cylinder of the compensation accumulator 8. The piston rod of the constant velocity cylinder is directly connected to the piston of the lower passive accumulator. Under the action of the bottom hole drilling pressure control method, the control system drives the lower and upper constant velocity cylinders to extend and retract and drives the lifting cylinder to overcome the inertia and friction during passive drill string compensation, actively improve the compensation accuracy of drill string compensation, and realize the active and passive combined compensation function.

[0015] As a preferred technical solution of the present invention, it includes:

[0016] S2, used to realize normal and boosted lifting and lowering, and automatic drilling, specifically:

[0017] When lifting and lowering the load normally, the lifting cylinder 2 is a double-acting cylinder, and when lifting and lowering the load by boosting, the lifting cylinder 2 is a plunger cylinder. The oil circuit switching of the cylinder valve group 14 can realize the switching of the working mode of the lifting cylinder 2. When the oil supply capacity of the main hydraulic station 12 remains unchanged, the maximum lifting capacity of the lifting system in the boosting mode will be reduced, and the maximum lifting speed will be greatly improved. With the introduction of the boosting mode, the lifting system will greatly improve its operating efficiency under light load while ensuring the lifting capacity of heavy loads. The automatic drilling function should be used in conjunction with the active and passive combined drill string compensation function, and in conjunction with the multi-objective control method of lowering speed and bottom hole drilling pressure, the opening of the proportional relief valve in the oil circuit switching valve group 12.1 and the stroke of the compensation accumulator 8 are controlled at the same time, so that the drilling speed of the lifting system is accurately controlled and the bottom hole drilling pressure is kept constant.

[0018] As a preferred technical solution of the present invention, it includes:

[0019] S3, used to achieve energy recovery and reuse, specifically:

[0020] The power supply and distribution unit 13 integrates an AC / DC rectifier, a DC / AC inverter, and a bidirectional DC-DC converter, and uses a plurality of supercapacitor cells to form a supercapacitor group as a module for rapid energy storage and release. The control system, in conjunction with the motor speed control and the charge and discharge control method, can convert the gravitational potential energy of the load when it is lowered into electrical energy. During the secondary lifting, the electrical energy stored in the lowered load can also be reused, thereby improving the energy utilization efficiency.

[0021] As a preferred technical solution of the present invention, it includes:

[0022] S4, a method for realizing load speed control under normal and boost conditions, specifically:

[0023] A dual closed-loop control strategy is adopted, with a closed pump swash plate controlling the inner loop and a load speed controlling the outer loop. The outer loop is responsible for finding the difference between the actual load speed and the set speed. After PID calculation, the target angle value of the closed pump swash plate is obtained and the difference is found from the actual angle value of the swash plate. After PID calculation, the closed pump swash plate is driven to control the proportional valve to adjust the output flow of the closed pump, thereby realizing closed-loop control of the load movement speed.

[0024] As a preferred technical solution of the present invention, in S1: the bottom hole drilling pressure control method under the active and passive combined drill string compensation working condition adopts a double closed-loop control strategy of a closed pump swash plate controlling an inner loop and a constant velocity cylinder speed controlling an outer loop; the control system collects the ship heave signal and the lifting cylinder 2 position signal and obtains the target speed of the constant velocity cylinder through calculation, the outer loop is responsible for subtracting the actual speed and the target speed of the constant velocity cylinder, and after PID calculation, the target angle value of the closed pump swash plate is obtained and the difference is obtained from the actual angle value of the swash plate, and after PID calculation, the closed pump swash plate is driven to control the proportional valve to adjust the output flow of the closed pump to realize closed-loop control of the constant velocity cylinder speed, the constant velocity cylinder drives the compensation accumulator 8 piston, and drives the lifting cylinder to fine-tune the passive compensation movement to realize the active and passive combined compensation function.

[0025] As a preferred technical solution of the present invention, in S2: a multi-objective control method for lowering speed and bottom hole drilling pressure under automatic drilling conditions, based on a bottom hole drilling pressure control method, is nested with a load lowering speed closed-loop control circuit based on a proportional relief valve. The lowering speed control circuit and the bottom hole drilling pressure control circuit exchange data through an integral signal of the drilling speed, thereby ensuring the drilling effect while maintaining the bottom hole drilling pressure within a set range while the lowering speed is accurately controlled.

[0026] As a preferred technical solution of the present invention, in S3: a motor speed control and charge and discharge control method under the condition of potential energy recovery and reuse, the constant motor speed is a prerequisite for the realization of this condition, the inverter and the variable frequency motor will keep the motor speed constant under the action of the speed PID controller and the closed-loop control method; the power conditions of the inverter and the supercapacitor are detected in real time, and the energy of the DC busbar and the supercapacitor group can be quickly exchanged under the control of the charge and discharge power PI controller and the bidirectional DC / DC converter; a load speed control method is used to realize the lifting and lowering of the load under normal and boost conditions. When the load is lowered, the closed pump drive motor acts as a generator to convert the gravitational potential energy into electrical energy, and stores it in the supercapacitor through the DC busbar. When the load rises, the electrical energy in the supercapacitor flows to the DC busbar and is supplied to the closed pump drive motor, thereby realizing the recovery and reuse of the potential energy released.

[0027] The beneficial effects of the present invention are as follows: the closed hydraulic cylinder lifting compensation system for an offshore drilling rig of the present invention adopts an innovative hydraulic system design and control method development, meets all the use conditions of the floating drilling ship drilling rig hydraulic cylinder lifting system, has a drill string compensation function, and has certain technical advantages in energy saving and emission reduction, including the following aspects: (1) The system generates little heat. A closed hydraulic system is used as the main power source for driving the lifting cylinder, and the throttling control is changed to pump control. The speed closed-loop control of the cylinder is achieved by adjusting the pressure of the lifting circuit, and the load is driven to achieve the lifting and lowering functions. The hydraulic circuit does not have throttling elements, the system heat generation will be greatly reduced, the corresponding equipment heat dissipation investment will also be reduced, and the life attenuation of the hydraulic components caused by temperature rise will be effectively extended. (2) Integrated drill string compensation function. A set of compensation accumulators and gas cylinder groups are designed, which can realize the pure passive and active and passive combined drill string compensation functions in conjunction with the lifting cylinder, and do not occupy the space in the derrick, and the system integration is further improved. (3) The energy saving effect is significant. By using closed pump groups, variable frequency motors, bidirectional DC-DC converters, supercapacitor groups and other electrical components in conjunction with control strategies, the potential energy released during heavy loads can be effectively recovered and reused, effectively reducing the overall energy consumption of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of the closed hydraulic cylinder lifting compensation system for an offshore drilling rig of the present invention;

[0029] Figure 2 It is a schematic diagram of the principle of the closed hydraulic cylinder lifting compensation system for an offshore drilling rig of the present invention;

[0030] Figure 3 This is the realization mechanism of the present invention for lifting and lowering loads under normal working conditions;

[0031] Figure 4 This is the realization mechanism of the present invention for lifting and lowering the load under supercharging conditions;

[0032] Figure 5 The present invention is a load speed control method under normal and boost conditions;

[0033] Figure 6 This is the implementation mechanism of the present invention under the drill string compensation working condition;

[0034] Figure 7 The present invention is a method for controlling bottom hole drilling pressure under active and passive combined compensation working conditions;

[0035] Figure 8 This is the implementation mechanism of the present invention under the automatic drilling condition;

[0036] Fig. 9 The present invention is a multi-objective control method for drilling speed and bottom drilling pressure under automatic drilling conditions

[0037] Fig.10 It is the realization mechanism of the present invention under the condition of energy recovery and reuse;

[0038] Fig.11 The present invention is a method for controlling the motor speed under energy recovery and reuse conditions;

[0039] Fig.12 The present invention is a charge and discharge control method under energy recovery and reuse conditions;

[0040] In the figure, 1. drilling rig mast, 2. lifting cylinder, 3. lifting pulley block, 4. lifting wire rope, 5. lifting hook, 6. guide rail, 7. top drive, 8. compensation accumulator, 9. nitrogen bottle group, 10. gas control skid, 11. high-pressure gas source, 12. main hydraulic station, 12.1 oil circuit switching valve, 13. energy storage distribution unit, 14. cylinder valve group, 15. accumulator valve group. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with the accompanying drawings, tables and specific embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] The present invention is further described below by way of examples, but is not limited to the following embodiments.

[0043] Example 1

[0044] See attached Figure 1 The invention discloses a closed hydraulic cylinder lifting compensation system for an offshore drilling rig. The drilling rig derrick 1 formed by splicing steel structures is installed on the drilling platform of an offshore drilling vessel. The drilling rig derrick 1 is a non-load-bearing structure. The derrick does not bear the lifting load and only serves as a support for the lifting hydraulic cylinder 2 and a guide for the lifting pulley block 3. An odd number of lifting hydraulic cylinders 2 ( Figure 1There are three lifting cylinders in the derrick 1, and the number of corresponding cylinders can be increased or decreased according to the load capacity) connected to the lifting pulley block 3. One end of the lifting wire rope 4 is connected to the dead rope end of the drilling floor, and the other end bypasses the lifting pulley block 3 and is connected to the lifting hook 5. The lifting hook 5 is connected to the top drive 7 through a mechanical structure. A guide rail 6 is designed on the inner side of the derrick 1, and the guide pulley of the lifting pulley block 3 limits it from sliding up and down inside the guide rail 6. The extension and retraction of the lifting cylinder 2 will push the lifting pulley block 3 to move up and down, and the lifting wire rope 4 transmits the thrust to drive the top drive 7 and the load to move up and down, realizing the lifting and lowering function of the load. In order to realize all functions of the closed hydraulic cylinder lifting compensation system, the system also includes a series of key auxiliary equipment, including: the main hydraulic station 12 that provides power source for the system, the compensation accumulator 8 that realizes the drill string compensation function, the nitrogen bottle group 9 used to increase the accumulator volume, the gas control skid 10 that realizes the drill string compensation pressure regulation function, and the high-pressure gas source 11 that provides gas source for the gas circuit system, and the energy storage distribution unit 13 that provides power distribution and potential energy recovery and reuse for the system. Among them, the compensation accumulator 8, nitrogen bottle group 9, and gas control skid 10 should be installed close to the lifting cylinder to reduce pipeline losses during the drill string compensation process and improve the compensation effect. Figure 1 As shown, it is installed on the drilling platform. The high-pressure gas source 11, the main hydraulic station 12, and the energy storage distribution unit 13 involve the issues of corrosion and explosion-proof. In order to reduce costs, they are designed to be installed in a safe area in the cabin.

[0045] Reference Figure 2 The schematic diagram of the closed hydraulic cylinder lifting compensation system shown in the figure shows that the main hydraulic station 12 adopts multiple closed pump groups in parallel to supply oil. The six main motors M1, M2 to M6 shown in the figure drive 12 closed pumps. At the same time, oil replenishment circuits are designed on the A and B outlet oil lines of the closed pumps. The oil replenishment flow of the oil replenishment circuit is consistent with the oil supply flow of the closed pump group. The oil replenishment oil route is composed of two oil replenishment motors M7 and M8 driving 12 open oil replenishment pumps with the same displacement as the closed pump. The oil replenishment pressure is set to 1.2MPa. Adequate oil replenishment flow can ensure that the closed pump group does not experience air suction.

[0046] Reference Figure 2, an oil circuit switching valve 12.1 is designed at the oil circuit outlet of each closed pump, and is integrated with the main hydraulic station 12. Four sets of cartridge valves are designed for each closed pump inside the oil circuit switching valve 12.1. The 12 closed pumps correspond to 48 sets of oil circuit switching cartridge valves. Through the control of the cartridge valves, the main hydraulic station 12 can achieve seamless switching of the oil supply for the A1 (B1) and A2 (B2) oil circuits. At the same time, the redundancy of the system is increased, and the failure of a single closed pump will not cause the entire system to be unusable. There is also a C oil circuit in the oil circuit switching valve 12.1, which is connected to the proportional relief valve and is used for the lowering control of the lifting system when the drill is automatically fed. The A1 (B1) oil circuit is the oil circuit for the lifting cylinder 2, and the A2 (B2) oil circuit is the oil circuit for the compensation accumulator 8. A1, A2 and B2 oil circuits are high-pressure oil circuits, and B1 oil circuit is a low-pressure oil circuit. The maximum pressures during operation are limited by the 34.1MPa and 1.5MPa overflow valves integrated in the oil circuit switching valve 12.1, respectively.

[0047] A cylinder valve group 14 is designed near the installation position of the lifting cylinder 2. Since a hydraulically controlled one-way valve is integrated at the bottom of the plug cavity of the lifting cylinder 2, a hydraulically controlled pilot oil circuit is integrated inside the cylinder valve group 14, which can realize the opening and closing control of the hydraulically controlled one-way valve at the outlet of the cylinder plug cavity. At the same time, 5 cartridge valves are designed on the cylinder control oil circuit in the cylinder valve group 12. Through the operation of the valves, three main functions can be realized: opening and closing the oil supply circuit of the designated cylinder, controlling the connection between the cylinder plug cavity and the rod cavity, and connecting the automatic drilling oil circuit. The number of lifting cylinders 2 working at the same time can be adjusted according to the lifting load. The unused lifting cylinders 2 will be in a completely retracted closed state. The lifting system of the present invention has three lifting cylinders. In order to maintain load balance, according to the number of lifting cylinders 2 working at the same time, it has three operation modes: mode 1 (1#, 2#, 3# cylinders work at the same time); mode 2 (1#, 3# cylinders work at the same time); mode 3 (2# cylinder works alone). It can be seen that, when the oil supply capacity of the main hydraulic station 12 is constant, the lifting system corresponding to mode 1 has the strongest load capacity, and the lifting system corresponding to mode 3 has the fastest operating speed.

[0048] An accumulator valve group 15 is designed near the installation position of the compensation accumulator 8. Since the compensation accumulator 8 is composed of a lower passive accumulator and an upper constant velocity cylinder, the piston of the passive accumulator can be driven by the upper constant velocity cylinder through the piston rod. The accumulator valve group 15 includes two two-position two-way cartridge valves and two two-position four-way cartridge valves to form a constant velocity cylinder control circuit, which is used to control the constant velocity cylinder to follow and open / close the active compensation function. The accumulator valve group 15 also includes two 10-inch FSVs (fast cut-off valves) at the liquid end outlet of the passive accumulator. The valve group can sense the flow through the main valve. When the flow exceeds the set value, the fluid channel is automatically cut off under the action of hydraulic pressure to achieve safety protection against drill pipe fracture conditions during drill pipe compensation. The liquid end of the lower passive accumulator of the compensation accumulator 8 is connected to the lifting cylinder 2, and the working medium of the gas end is nitrogen. After the gas circuit passes through the gas control skid 10, it is connected to the nitrogen cylinder group 9. The nitrogen cylinder group 9 is divided into two types: a working cylinder group and a spare cylinder group. The working cylinder group is directly connected to the gas end of the lower passive accumulator of the compensation accumulator 8, which can greatly increase the volume of the passive accumulator. The spare cylinder group is pre-filled with high-pressure nitrogen, which can realize the rapid replenishment of the working cylinder group. The gas control skid 10 is also designed with a pressure reducing valve and a vent valve to achieve precise regulation of the internal pressure of the working cylinder group. At the same time, the gas control skid 10 is also designed with a shut-off valve on the main gas line to control the on and off of the main gas line, thereby realizing the remote opening and closing of the drill string compensation gas line.

[0049] The main hydraulic station 12 uses 6 variable frequency main motors, and the energy storage distribution unit 13 contains a high-power AC / DC rectifier module, which is responsible for rectifying the three-phase AC power of the ship's AC power grid into DC power and uploading it to the DC busbar. The DC busbar is connected in parallel with 6 main motor inverter modules, which can realize constant power control of the main pump motor and constant speed control during motor energy recovery, and convert the recovered electric energy to the DC busbar. The DC busbar is connected in parallel with a bidirectional DC-DC converter, which is a conversion unit for energy recovery and reuse. The bidirectional DC-DC converter is connected to the supercapacitor group. By controlling the bidirectional DC-DC converter, the DC busbar-supercapacitor group electric energy exchange can be realized. When the load is lowered, the gravity potential energy is converted into hydraulic energy by the hydraulic cylinder, and the hydraulic energy is converted into electrical energy through the pump group and the variable frequency motor. After the electrical energy is inverted, the DC bus voltage increases. Under the action of the bidirectional DC-DC converter, the DC bus charges the supercapacitor, and the electrical energy is stored. When the lifting system needs to lift the load, the DC bus voltage drops, and the bidirectional DC-DC converter controls the supercapacitor to release electrical energy to the DC bus, so that the DC bus voltage is maintained within a certain range. This realizes the recovery and reuse of the lowered potential energy.

[0050] Example 2

[0051] A control method of the present invention based on the realization mechanism of the closed hydraulic cylinder lifting compensation system for an offshore drilling rig according to claim 2 comprises:

[0052] S2, used to realize normal and boosted lifting and lowering, and automatic drilling, specifically:

[0053] When lifting and lowering the load normally, the lifting cylinder 2 is a double-acting cylinder, and when lifting and lowering the load by boosting, the lifting cylinder 2 is a plunger cylinder. The oil circuit switching of the cylinder valve group 14 can realize the switching of the working mode of the lifting cylinder 2. When the oil supply capacity of the main hydraulic station 12 remains unchanged, the maximum lifting capacity of the lifting system in the boosting mode will be reduced, and the maximum lifting speed will be greatly improved. With the introduction of the boosting mode, the lifting system will greatly improve its operating efficiency under light load while ensuring the lifting capacity of heavy loads. The automatic drilling function should be used in conjunction with the active and passive combined drill string compensation function, and in conjunction with the multi-objective control method of lowering speed and bottom hole drilling pressure, the opening of the proportional relief valve in the oil circuit switching valve group 12.1 and the stroke of the compensation accumulator 8 are controlled at the same time, so that the drilling speed of the lifting system is accurately controlled and the bottom hole drilling pressure is kept constant.

[0054] The realization mechanism of the closed hydraulic cylinder lifting compensation system proposed in the present invention under four working conditions is based on the attached Figure 2 See the attached hydraulic principle diagram. Figure 3 The lifting compensation system shown in the figure shows the mechanism for lifting and lowering the load under normal working conditions. In the figure, multiple lifting cylinders are replaced by a single cylinder, 6 closed pump groups are replaced by a belt M1, and the supplementary oil pump group is replaced by M7. When lifting the load under normal working conditions, A1 is the high-pressure oil circuit, B1 is the low-pressure oil circuit, and the swash plate angle of the closed pump is adjusted to control the flow of hydraulic oil flowing into the plug cavity of the lifting cylinder 2 through the A1 oil circuit, so as to extend the cylinder and drive the load to lift. Due to the area difference between the plug cavity and the rod cavity of the cylinder, the oil discharged from the rod cavity when the lifting cylinder 2 rises is not enough to meet the oil supply demand of the plug cavity. The supplementary oil pump group M7 will replenish the required hydraulic oil for the B1 oil circuit. At the same time, the excess hydraulic oil flows back to the oil tank through the overflow valve on the side of the supplementary oil pump group. When lowering the load under normal working conditions, adjust the slant plate angle of the closed pump to control the flow of hydraulic oil flowing out of the plug chamber of the lifting cylinder 2 through the A1 oil circuit. The cylinder will retract and drive the load to descend. After passing through the closed pump, the hydraulic oil flows into the B1 oil circuit. Due to the difference in cylinder area, when the cylinder descends, the oil flow discharged from the plug chamber will be much greater than the flow supplied to the rod chamber. The excess oil flows back to the tank through the overflow valve on the B1 circuit.

[0055] By controlling the plug valve inside the cylinder valve group 14, the plug cavity and rod cavity of the lifting cylinder 2 can be connected, and the lifting cylinder 2 is changed from a double-acting cylinder to a plunger cylinder. The cylinder action area will be changed from the plug cavity to the cross-sectional area of ​​the piston rod. Therefore, under the same oil supply capacity, the lifting load of the lifting system will be reduced, and the operating speed of the lifting system will be greatly improved. This mode is also called the boost mode. The operating mechanism of lifting and lowering loads in the boost mode is shown in the attached Figure 4 As shown, the biggest difference between the boost mode and the normal mode is the oil supply circuit of the hydraulic cylinder. In the boost mode, the plug chamber and the rod chamber of the hydraulic cylinder are connected. When lifting the load, the closed pump group supplies oil to the plug chamber and the rod chamber at the same time through the A1 oil circuit. Since there is no oil return from the rod chamber, the oil replenishment pump group will provide all the required hydraulic oil for the closed pump group. When lowering the load, the oil inside the hydraulic cylinder returns to the closed pump group through the A1 oil circuit, adjusts the displacement of the closed pump group, and then controls the pressure of the A1 oil circuit to achieve load speed control. The hydraulic oil discharged by the closed pump group flows back to the oil tank through the overflow valve on the B1 oil circuit side. The introduction of the boost mode can enable the lifting system to achieve faster operating speed under light load. Combined with the constant power control of the closed pump group and the adjustment of the number of lifting cylinders 2 working at the same time, it can achieve faster light load movement speed than the traditional hydraulic lifting system.

[0056] Attached Figure 7 This is the implementation mechanism of the present invention under the condition of automatic drill delivery. Automatic drill delivery is an important function that saves the labor intensity of drilling operators. For the lifting system that separately designs and controls the drill string compensation device and the lifting mechanism, it is only necessary to control the load lowering speed to be stable and start the active compensation of the drill string compensation device to achieve relative constancy of the bottom hole drilling pressure and the drill delivery speed. However, the present invention integrates the drill string compensation device and the lifting mechanism, and its implementation mechanism and control difficulty of automatic drill delivery will be greatly improved. Figure 7 It can be seen that the automatic drilling condition of the present invention should be put into use after the active and passive combined compensation is turned on. As the bottom hole drilling pressure remains constant, the plug-in valve inside the cylinder valve group 14 is used to open the C oil circuit, control the electric proportional overflow valve inside the oil circuit switching valve 12.1, and adjust the pressure inside the lifting cylinder 2. The oil inside the cylinder-accumulator slowly flows back to the oil tank under the control of the overflow valve. At the same time, under the control of active compensation, the piston of the compensation accumulator 8 fluctuates up and down at a constant position to ensure that the thrust of the lifting cylinder does not change with the retraction of the cylinder. The movement of the top drive of the lifting system during the automatic drilling process will be a synthetic movement of the ship's heave movement and the automatic drilling movement.

[0057] In order to ensure that the bottom hole drilling pressure and the drilling speed remain constant during the automatic drilling process of the present invention, a multi-objective control method for the lowering speed and the bottom hole drilling pressure is proposed. Fig. 9As shown in the figure, the control method is divided into two parts: drilling speed control and bottom hole drilling pressure control. The bottom hole drilling pressure control has been described in detail in the control method under the active and passive combined compensation working condition in the previous article, and will not be repeated here. The drilling speed control is that the control system receives the drilling speed signal from the operator, and sends it to the drilling speed PI controller after subtracting it from the real-time lowering speed signal. After the controller calculates, the opening adjustment signal of the proportional relief valve is obtained. The change in the opening will cause the pressure of the lifting cylinder-accumulator oil circuit to change, and cause the corresponding oil to overflow and reduce, and the retraction speed of the lifting cylinder will be controlled. The drill speed control loop and the bottom hole drilling pressure control loop are nested with each other through fine-tuning of the drilling pressure signal. By integrating the drill signal, the accumulated distance of the drill string lowered over time is obtained, and then the drilling pressure adjustment signal is subtracted to obtain the drilling pressure adjustment signal accumulated over time. The active compensation drilling pressure signal is adjusted to make the piston position of the compensation accumulator 8 fluctuate around a constant middle position during the drill feeding process. The bottom hole drilling pressure during drill feeding will be the same as after the active compensation function is turned on, and will be in a constant state for a long time.

[0058] Example 3

[0059] A control method for realizing a mechanism of a closed hydraulic cylinder lifting compensation system for an offshore drilling rig according to the present invention is characterized in that it comprises:

[0060] S4, a method for realizing load speed control under normal and boost conditions, specifically:

[0061] A dual closed-loop control strategy is adopted, with the closed pump swash plate controlling the inner loop and the load speed controlling the outer loop. The outer loop is responsible for calculating the difference between the actual load speed and the set speed. After PID calculation, the target angle value of the closed pump swash plate is calculated and the difference is calculated from the actual angle value of the swash plate. After PID calculation, the closed pump swash plate is driven to control the proportional valve to adjust the output flow of the closed pump, thus realizing closed-loop control of the load movement speed.

[0062] Reference Figure 5The load speed control method under normal and boost conditions shown in the figure adopts a double closed-loop control idea with the swash plate control of the closed pump as the inner loop and the speed control of the load as the outer loop. The control system collects the load speed control signal from the operator, and after subtracting the actual speed value of the load and calculating it through the load speed PID controller, outputs a closed pump swash plate target swing angle signal. The swash plate target swing angle is then subtracted from the actual swash plate swing angle to obtain the angle difference and bring it into the closed pump swash plate swing angle PID controller. After the controller calculates, a proportional valve current signal for swash plate swing angle control is obtained, and the proportional valve is driven to achieve the change of the swash plate swing angle of the closed pump. The direction and size of the closed pump output flow are effectively controlled, which is reflected in the lifting circuit, that is, the pressure of the circuit changes, and the lifting cylinder 2 extends and retracts with the change of the lifting circuit pressure. At the same time, the position sensor installed on the lifting cylinder 2 detects the cylinder stroke, and the actual speed of the cylinder is obtained through the control system. After multiplying it by the rope coefficient K, the actual speed of the load is obtained. After the actual speed of the load is brought into the closed-loop control system, the speed of the load can be accurately controlled.

[0063] Example 4

[0064] A control method of the present invention based on the realization mechanism of the closed hydraulic cylinder lifting compensation system for an offshore drilling rig according to claim 2 comprises:

[0065] S1, used to realize the drill string compensation function, specifically:

[0066] The lifting cylinder 2 is switched through the oil circuit of the cylinder valve group 14, and is changed from a double-acting cylinder to a plunger cylinder. The compensating accumulator 8 is divided into a lower passive accumulator and an upper constant-speed cylinder. The lower passive accumulator is a piston accumulator, whose liquid end is connected to the lifting cylinder 2, and whose gas end is connected to the nitrogen bottle group 9. The plunger-type lifting cylinder 2, the compensating accumulator 8 and the nitrogen bottle group 9 together form a "liquid-gas spring", which has the ability of passive drill string compensation;

[0067] When it is necessary to improve the compensation accuracy, the upper constant velocity cylinder of the compensation accumulator 8 will be switched from the follow-up state to the working state. The switching function is realized by the accumulator valve group 15. When the constant velocity cylinder is opened, the oil circuit switching valve 12.1 inside the main hydraulic station 12 is controlled to switch the oil supply circuit of the closed pump group to the A2 and B2 circuits. By controlling the displacement of the closed pump, the A2 and B2 circuits directly drive the upper constant velocity cylinder of the compensation accumulator 8. The piston rod of the constant velocity cylinder is directly connected to the piston of the lower passive accumulator. Under the action of the bottom hole drilling pressure control method, the control system drives the lower and upper constant velocity cylinders to extend and retract and drives the lifting cylinder to overcome the inertia and friction during passive drill string compensation, actively improve the compensation accuracy of drill string compensation, and realize the active and passive combined compensation function.

[0068] Reference Figure 6, the implementation mechanism of the lifting compensation system proposed in the present invention under the drill string compensation working condition. The drill string compensation working condition is divided into two working modes: passive compensation and active and passive combined compensation. Passive compensation is suitable for drilling operations in shallow water and good sea conditions, and active and passive combined compensation is suitable for drilling operations and underwater installation operations in deep water and bad sea conditions. Under the drill string compensation working condition, the lifting cylinder 2 will continue to be in the plunger cylinder mode under the control of the cylinder valve group 14. During passive compensation, the lifting cylinder 2, the compensating accumulator 8, and the nitrogen bottle group 9 form a "liquid-gas spring". The lifting system provides a certain lifting force for the top of the drill string. This lifting force is not enough to overcome the entire weight of the drill string. The remaining weight of the drill string will act on the bottom of the well as the drilling pressure. As the ship rises and falls, the lifting cylinder extends and retracts under the drive of the inertial force of the drill string. The oil will flow freely between the lifting cylinder 2 and the compensating accumulator 8, and at the same time compress and expand the high-pressure nitrogen at the gas end of the compensating accumulator 8. Since the nitrogen bottle group 9 greatly increases the volume of the gas, the pressure of the system will fluctuate within a small range, and the corresponding lifting force acting on the top of the drill string will also be in a nearly constant state, and the drilling pressure at the bottom of the well will be effectively controlled. During passive compensation, the two working chambers of the constant velocity cylinder on the upper part of the compensating accumulator 8 remain connected, and the constant velocity cylinder will be in a follow-up state to avoid affecting the passive compensation. Active and passive combined compensation is a function of active control enabled on the basis of passive compensation. After the active compensation is turned on, the upper constant velocity cylinder of the compensation accumulator 8 is converted from a follow-up state to a working state, and its two working chambers will be connected to the main hydraulic station 12 through the A2 and B2 oil circuits. The stroke of the constant velocity cylinder is directly controlled by 6 closed pump groups to achieve active adjustment of the lower piston position of the compensation accumulator 8, and drive the lifting cylinder 2 to fine-tune the stroke, thereby overcoming the inertia and mechanical friction during the compensation movement. The fluctuation of the lifting force of the lifting system on the top of the drill string will be improved, and the fluctuation of the drilling pressure at the bottom of the well will also be improved, and the compensation accuracy will be improved.

[0069] Since passive compensation is a follow-up process, there is no complex control algorithm. The present invention only describes the bottom hole drilling control method under the active and passive combined compensation working condition. Figure 7As shown, the drilling pressure control method is also composed of a double closed loop of the swash plate control inner loop of the closed pump and the speed control outer loop of the constant speed cylinder. After the control system collects the heave motion position signal of the ship, it calculates the difference with the real-time position signal of the lifting cylinder 2, and then multiplies it by the rope coefficient K1 to obtain the relative displacement signal of the load. The operator provides the control system with a reference signal of the bottom hole drilling pressure. The target displacement difference is obtained by subtracting the drilling pressure adjustment signal from the relative displacement signal of the load. The speed difference is obtained by differentiation. K2 is the ratio of the liquid end effective area of ​​the lifting cylinder 2 and the compensation accumulator 8. The speed difference is multiplied by K2 to obtain the target speed of the constant velocity cylinder. The speed difference is obtained by subtracting the speed difference from the real-time speed of the constant velocity cylinder. After calculation by the constant velocity cylinder speed PID controller, a swash plate swing angle signal of a closed pump is obtained. Consistent with the lifting and lowering working conditions, the swash plate swing angle control loop will drive the closed pump swash plate to a preset position. The closed pump group actively controls the stroke of the constant velocity cylinder to change. The constant velocity cylinder will drive the lower piston position of the compensation accumulator 8 to change, and then drive the stroke of the lifting cylinder to be fine-tuned, thereby achieving the reduction of the bottom hole drilling pressure fluctuation during drill string compensation.

[0070] Example 5

[0071] A control method for realizing a mechanism of a closed hydraulic cylinder lifting compensation system for an offshore drilling rig of the present invention comprises:

[0072] S3, used to achieve energy recovery and reuse, specifically:

[0073] The power supply and distribution unit 13 integrates an AC / DC rectifier, a DC / AC inverter, and a bidirectional DC-DC converter, and uses a plurality of supercapacitor cells to form a supercapacitor group as a module for rapid energy storage and release. The control system, in conjunction with the motor speed control and the charge and discharge control method, can convert the gravitational potential energy of the load when it is lowered into electrical energy. During the secondary lifting, the electrical energy stored in the lowered load can also be reused, thereby improving the energy utilization efficiency.

[0074] Reference Fig.10This is the realization mechanism of the energy recovery and reuse working condition described in the present invention. When the lifting system is lowering the drill string or the water-proof pipe string, there is huge gravitational potential energy. The recovery and reuse of the lowering potential energy will greatly improve the energy-saving characteristics of the drilling package. Taking the normal mode as an example, as the lifting load decreases, the lifting cylinder 2 gradually shrinks, and the fluid flows back to the oil tank through the plug cavity of the lifting cylinder 2 through the closed pump. The closed pump maintains a constant speed driven by the variable frequency motor. By adjusting the displacement of the closed pump, the load lowering speed is controlled. During the lowering process, the gravitational potential energy is converted into hydraulic energy. Under the push of the hydraulic cylinder, the oil will drive the closed pump to overspeed. The variable frequency motor connected to the closed pump will also be in an overspeed state driven by the reverse torque of the closed pump. According to the inherent characteristics of the motor, the motor will be in a power generation state. The control system relies on the motor speed closed-loop control method to control the inverter to make the motor generate reverse torque to prevent the closed pump from overspeeding, and the motor speed is maintained constant. The three-phase electric energy generated by the motor will be transmitted to the DC busbar through the AC / DC inverter, and the voltage on the DC busbar will increase accordingly. A bidirectional DC-DC converter is installed on the DC busbar. Under the control of the charge and discharge control strategy, the electric energy will be stored in the supercapacitor group through the DC busbar. The selection of supercapacitors as the storage medium for the potential energy is based on the characteristics of supercapacitors such as fast charging and discharging speed, long service life, safety and environmental protection. The supercapacitor group absorbs the electric energy generated by the DC busbar due to the load release, and has a short-term energy storage capacity. When the lifting system lifts the load for the second time, the motor will consume electric energy as the prime mover. At this time, the DC busbar voltage will become low. Under the control of the charge and discharge control strategy, the bidirectional DC-DC converter will guide the supercapacitor to release the stored electric energy to realize the reuse of the potential energy released.

[0075] The realization of the energy recovery and reuse working condition described in the present invention is based on the motor speed control method and the charge and discharge control method. Fig.11 and attached Fig.12As shown, since the motor speed is kept constant, the speed control of lowering and lifting the load should be consistent with the load speed control method under normal and boost conditions. For the motor speed control method, the control system will give a reference speed of the motor (such as 1480RPM), and after taking the difference from the actual speed of the motor, it will be brought into the speed PID controller. After calculation, the torque of the motor is obtained, and then after taking the difference from the reference torque of the motor, it will be brought into the inverter torque vector controller. The inverter torque vector controller simultaneously collects the motor speed, three-phase winding current and DC bus voltage, and controls the DC / AC inverter after comprehensive calculation to keep the speed of the variable frequency motor constant. The variable frequency motor will be in two working modes according to the load: motor mode and generator mode. When lifting the load, the motor is in motor mode, and when energy is recovered, the motor will be in generator mode. For the charge and discharge control method, the control system detects the power flowing into the inverter from the DC bus, and subtracts it from the input power of the supercapacitor, and brings it into the charge and discharge power PI controller. After calculation, the target voltage value of the supercapacitor is obtained, and the target voltage value is subtracted from the actual voltage value and brought into the supercapacitor voltage controller. The charge and discharge operation of the supercapacitor is realized by controlling the bidirectional DC / DC converter. The voltage on the DC bus will be maintained within a specific range, and the charge and discharge operation can be automatically performed according to the operation status of the lifting system, ensuring energy recovery when the load is lowered and automatic energy release when it is lifted again.

Claims

1. A closed cylinder lifting compensation system for offshore drilling rigs, characterized in that: The invention comprises a drilling rig derrick (1), wherein a lifting hydraulic cylinder (2) is arranged on the drilling rig derrick (1), a lifting pulley block (3) is arranged at the driving end of the lifting hydraulic cylinder (2), and a lifting hook (5) is wound around the lifting pulley block (3); the drilling rig derrick (1) is also provided with a compensation accumulator (8), a nitrogen bottle group (9), a main hydraulic station (12), and an energy storage distribution unit (13).

2. The closed cylinder lifting compensation system for offshore drilling rigs according to claim 1 is characterized in that: The main hydraulic station adopts multiple closed pump groups connected in parallel to supply oil.

3. A control method based on the realization mechanism of the closed hydraulic cylinder lifting compensation system for offshore drilling rigs as claimed in claim 2, characterized in that: include: S1, used to realize the drill string compensation function, specifically: The lifting cylinder (2) is switched through the oil circuit of the cylinder valve group (14) from a double-acting cylinder to a plunger cylinder. The compensating accumulator (8) is divided into a lower passive accumulator and an upper constant velocity cylinder. The lower passive accumulator is a piston accumulator, whose liquid end is connected to the lifting cylinder (2) and whose gas end is connected to the nitrogen bottle group (9). The plunger-type lifting cylinder (2), the compensating accumulator (8) and the nitrogen bottle group (9) together form a "liquid-gas spring" to enable it to have the ability of passive drill string compensation. When the compensation accuracy needs to be improved, the upper constant velocity cylinder of the compensation accumulator (8) will be switched from the follow-up state to the working state. The switching function is realized by the accumulator valve group (15). When the constant velocity cylinder is opened, the oil circuit switching valve (12.1) inside the main hydraulic station (12) is controlled to switch the oil supply circuit of the closed pump group to the A2 and B2 circuits. By controlling the displacement of the closed pump, the A2 and B2 circuits directly drive the upper constant velocity cylinder of the compensation accumulator (8). The piston rod of the constant velocity cylinder is directly connected to the piston of the lower passive accumulator. Under the action of the bottom hole drilling pressure control method, the control system drives the upper and lower constant velocity cylinders to extend and retract and drives the lifting cylinder to overcome the inertia and friction during passive drill string compensation, actively improve the compensation accuracy of the drill string compensation, and realize the active and passive combined compensation function.

4. The control method for realizing the mechanism of the closed hydraulic cylinder lifting compensation system for offshore drilling rigs according to claim 3 is characterized in that: include: S2, used to realize normal and boosted lifting and lowering, and automatic drilling, specifically: When lifting and lowering the load normally, the lifting cylinder (2) is a double-acting cylinder. When lifting and lowering the load in boosted mode, the lifting cylinder (2) is a plunger cylinder. By switching the oil circuit of the cylinder valve group (14), the switching of the working mode of the lifting cylinder (2) can be realized. When the oil supply capacity of the main hydraulic station (12) remains unchanged, the maximum load lifting capacity of the lifting system in the boosted mode will be reduced, and the maximum lifting speed will be greatly improved. With the introduction of the boosted mode, the lifting system will greatly improve its operating efficiency under light load while ensuring the lifting capacity of heavy load. The automatic drilling function should be used in conjunction with the active and passive combined drill string compensation function, and in conjunction with the multi-objective control method of lowering speed and bottom hole drilling pressure, the opening of the proportional relief valve in the oil circuit switching valve group (12.1) and the stroke of the compensation accumulator (8) are controlled at the same time, so that the drilling speed of the lifting system is accurately controlled and the bottom hole drilling pressure is kept constant.

5. The control method for realizing the mechanism of the closed hydraulic cylinder lifting compensation system for offshore drilling rigs according to claim 4 is characterized in that: include: S3, used to achieve energy recovery and reuse, specifically: The power supply and distribution unit (13) integrates an AC / DC rectifier, a DC / AC inverter, and a bidirectional DC-DC converter, and uses a plurality of supercapacitor monomers to form a supercapacitor group as a module for rapid energy storage and release. The control system cooperates with the motor speed control and the charge and discharge control method to convert the gravitational potential energy of the load when it is lowered into electrical energy. During the secondary lifting, the electrical energy stored in the lowered load can be reused, thereby improving the energy utilization efficiency.

6. The control method for realizing the mechanism of the closed hydraulic cylinder lifting compensation system for offshore drilling rigs according to claim 5 is characterized in that: include: S4, a method for realizing load speed control under normal and boost conditions, specifically: A dual closed-loop control strategy is adopted, with a closed pump swash plate controlling the inner loop and a load speed controlling the outer loop. The outer loop is responsible for finding the difference between the actual load speed and the set speed. After PID calculation, the target angle value of the closed pump swash plate is obtained and the difference is found from the actual angle value of the swash plate. After PID calculation, the closed pump swash plate is driven to control the proportional valve to adjust the output flow of the closed pump, thereby realizing closed-loop control of the load movement speed.

7. The control method for realizing the mechanism of the closed hydraulic cylinder lifting compensation system for offshore drilling rigs according to claim 6 is characterized in that: In S1: the bottom hole drilling pressure control method under the active and passive combined drill string compensation working condition adopts a double closed-loop control strategy of a closed pump swash plate controlling an inner loop and a constant velocity cylinder speed controlling an outer loop; the control system collects the ship heave signal and the lifting cylinder (2) position signal and obtains the target speed of the constant velocity cylinder through calculation; the outer loop is responsible for calculating the difference between the actual speed and the target speed of the constant velocity cylinder, and the target angle value of the closed pump swash plate is calculated after PID calculation, and the difference between the actual angle value of the swash plate is calculated, and the closed pump swash plate is driven after PID calculation to control the proportional valve, adjust the output flow of the closed pump, and realize the closed-loop control of the constant velocity cylinder speed, the constant velocity cylinder drives the compensation accumulator (8) piston, and drives the lifting cylinder to fine-tune the passive compensation movement, so as to realize the active and passive combined compensation function.

8. The control method for realizing the mechanism of the closed hydraulic cylinder lifting compensation system for offshore drilling rigs according to claim 7 is characterized in that: In S2: a multi-objective control method for lowering speed and bottom hole drilling pressure under automatic drilling conditions is based on a bottom hole drilling pressure control method, and a load lowering speed closed-loop control loop based on a proportional relief valve is nested. The lowering speed control loop and the bottom hole drilling pressure control loop exchange data through the integral signal of the drilling speed, thereby ensuring that the lowering speed is accurately controlled while the bottom hole drilling pressure is maintained within the set range of drilling effect.

9. The control method for realizing the mechanism of the closed hydraulic cylinder lifting compensation system for offshore drilling rigs according to claim 8 is characterized in that: In S3: motor speed control and charge-discharge control method under the condition of potential energy recovery and reuse. Constant motor speed is the prerequisite for the realization of this condition. Under the action of the speed PID controller and the closed-loop control method, the speed of the inverter and the variable frequency motor will remain constant; the power conditions of the inverter and the supercapacitor are detected in real time. Under the control of the charge-discharge power PI controller and the bidirectional DC / DC converter, the energy of the DC busbar and the supercapacitor group can be quickly exchanged; the load speed control method under normal and boost conditions is used to lift and lower the load. When lowering the load, the closed pump drive motor acts as a generator to convert the gravitational potential energy into electrical energy, and stores it in the supercapacitor through the DC busbar. When the load rises, the electrical energy in the supercapacitor flows to the DC busbar and is supplied to the closed pump drive motor, thereby realizing the recovery and reuse of the potential energy released.

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