Multi-motor series type free piston linear power generation system and control method

Abstract

The application discloses a kind of multi-motor series free piston linear power generation system and control method, belong to power generation system technical field, comprising: linear motor and two free piston engines respectively arranged in the two sides of linear motor;Engine cylinder cylinder is provided with lubricating oil oil sprayer;Piston assembly is slidably arranged in the cylinder of engine cylinder, and lubricating oil oil sprayer is used to spray lubricating oil to the friction contact of piston ring and engine cylinder;Linear motor includes first linear motor, second linear motor and third linear motor;First linear motor, second linear motor and third linear motor share same linear motor mover;Linear motor mover is provided with magnetic scale displacement sensor;Wherein, in the process of system operation, second linear motor as main motor, always in generator operating mode, first linear motor and third linear motor as auxiliary motor, for the cold start of system and piston displacement trajectory control.

Description

Technical Field

[0001] This invention belongs to the field of power generation system technology, specifically relating to a multi-motor series-connected free piston linear power generation system and its control method. Background Technology

[0002] Internal combustion engines are used in all aspects of society and are a typical energy conversion device. However, with the increasing demand for electrification and intelligentization in transportation, the traditional internal combustion engine, which mainly outputs mechanical energy, urgently needs to be transformed. Researchers are actively exploring new energy conversion devices, and the free-piston linear generator is one such new energy conversion device developed in this context.

[0003] A free-piston linear generator is a combination of a free-piston engine and a linear motor. The engine piston and the motor rotor reciprocate in linear motion, converting chemical energy into electrical energy. Compared to traditional engines, free-piston linear generators feature a compact power structure, a short energy transfer chain, and a flexible, variable system compression ratio. They are adaptable to multiple fuels and combustion models, and the system can be modularly arranged to achieve distributed drive, demonstrating broad application prospects.

[0004] Current research on the configuration of free-piston linear generators mainly focuses on piston configurations, such as double-piston and single-piston types. The linear motors connected to the pistons are mostly single-motor configurations. Free-piston linear motors, however, do not have the crankshaft and connecting rod constraints of traditional internal combustion engines, allowing for flexible and adjustable piston trajectories.

[0005] However, in a free piston linear motor, near the dead center of the piston trajectory, the piston is subjected to the pressure of the compressed gas and the expansion of the combustion gas, causing the piston speed to switch rapidly in the opposite direction. The residence time is short, resulting in incomplete combustion, insufficient energy release, and low power generation efficiency. Summary of the Invention

[0006] To address the technical problem of incomplete combustion, insufficient energy release, and low power generation efficiency caused by the piston rapidly reversing its speed near the dead center of the piston trajectory in current free piston linear motors due to the pressure of compressed and combustion gases, resulting in a short dwell time, this invention provides a multi-motor series-connected free piston linear power generation system and control method.

[0007] First aspect

[0008] This invention provides a multi-motor series-connected free piston linear power generation system, comprising: a linear motor and two free piston engines respectively disposed on both sides of the linear motor;

[0009] The free piston engine includes a piston assembly and an engine cylinder;

[0010] The engine cylinder includes a cylinder block and a cylinder head;

[0011] The engine cylinder block is provided with an air inlet and an exhaust outlet, and an intake valve is provided on the air inlet.

[0012] The engine cylinder block is equipped with a lubricating oil injector.

[0013] The cylinder head of the engine cylinder is equipped with spark plugs, fuel injectors and cylinder pressure sensors.

[0014] The piston assembly includes a piston, a piston pin, piston rings, and an oil ring;

[0015] The piston assembly is slidably disposed in the cylinder block of the engine cylinder, and the lubricating oil injector is used to spray lubricating oil onto the friction contact points of the piston ring and the engine cylinder.

[0016] The linear motor includes a first linear motor, a second linear motor, and a third linear motor;

[0017] The first linear motor, the second linear motor, and the third linear motor share the same linear motor actuator;

[0018] A magnetic grating displacement sensor is installed on the linear motor mover. The magnetic grating displacement sensor is used to detect the position of the linear motor mover, thereby determining the fuel injection position of the fuel injector and the ignition position of the spark plug.

[0019] The linear motor actuator is equipped with a permanent magnet;

[0020] The piston assemblies of the two free piston engines on both sides are connected by the linear motor actuator;

[0021] During system operation, the second linear motor serves as the main motor and is always in generator mode, while the first and third linear motors serve as auxiliary motors for system cold start and piston displacement trajectory control.

[0022] Second aspect

[0023] This invention provides a control method applied to the multi-motor series-connected free piston linear power generation system described in the first aspect, comprising:

[0024] S1: During the cold start phase, the second linear motor is controlled to operate in generator mode, and the first linear motor and the third linear motor operate in electric motor mode, thereby starting the system through the first linear motor and the third linear motor;

[0025] S2: During the stable operation phase, the second linear motor is controlled to operate in generator mode, and the first linear motor and the third linear motor are alternately controlled to operate in electric motor mode to adjust the piston force at different strokes.

[0026] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0027] (1) In this invention, when the piston moves to near the dead center, a linear motor can be used to apply resistance in the opposite direction to the piston, thereby extending the piston's dwell time at the dead center, increasing the isochoric combustion time, fully burning the fuel, fully releasing energy, and improving power generation efficiency.

[0028] (2) In this invention, the power generation system is controlled by a series connection of multiple motors. The excellent control characteristics of the motor can be used to flexibly control the piston trajectory to improve the power output of the engine. The functions of the generator and the motor are decoupled to improve the power generation efficiency of the system.

[0029] (3) In this invention, a magnetic scale displacement sensor is set on the linear motor mover, and the method of integrating the displacement sensor with the motor mover improves the compactness of the system. Attached Figure Description

[0030] The preferred embodiments will now be described in a clear and easy-to-understand manner, in conjunction with the accompanying drawings, to further explain the above-mentioned characteristics, technical features, advantages, and implementation methods of the present invention.

[0031] Figure 1 This is a schematic diagram of a multi-motor series-connected free piston linear power generation system provided by the present invention.

[0032] Figure 2 This is a schematic diagram of the system operation when the piston assembly reaches the right dead center, as provided by the present invention.

[0033] Figure 3 This is a schematic diagram of the system operation when the piston assembly reaches the left dead center, as provided by the present invention.

[0034] Figure 4 This is a flowchart illustrating a control method provided by the present invention. Detailed Implementation

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0036] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0037] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0038] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections. They can refer to mechanical connections or electrical connections. They can refer to direct connections or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0039] Furthermore, in the description of this invention, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0040] Example 1

[0041] In one embodiment, refer to the appendix to the specification. Figure 1 This diagram illustrates the structure of a multi-motor series-connected free piston linear power generation system provided by the present invention. (See attached specification.) Figure 2 This diagram illustrates the operation of a piston assembly as it reaches right dead center, as provided by the present invention. (See attached specification.) Figure 3 The diagram shows a schematic of the system operation when a piston assembly, provided by the present invention, reaches the left dead center.

[0042] The present invention provides a multi-motor series-connected free piston linear power generation system, comprising: a linear motor and two free piston engines respectively disposed on both sides of the linear motor.

[0043] A free-piston engine consists of a piston assembly and an engine cylinder.

[0044] The engine cylinder includes the cylinder block 12 and the cylinder head 4.

[0045] The cylinder block 12 of the engine cylinder has an air inlet 13 and an exhaust port 6, and an intake valve is provided on the air inlet 13.

[0046] A lubricating oil injector 14 is installed on the cylinder block 12 of the engine cylinder.

[0047] Among them, the lubricating oil injector 14 is used to spray lubricating oil.

[0048] Optionally, a heat sink 5 can also be installed on the cylinder block 12 of the engine cylinder to dissipate heat from the power generation system, which helps to maintain the system temperature within a suitable range and improve the system's reliability and lifespan.

[0049] The cylinder head 4 of the engine cylinder is equipped with a spark plug 2, a fuel injector 3 and a cylinder pressure sensor 1.

[0050] Spark plug 2 is used to ignite the fuel.

[0051] Among them, fuel injector 3 is used to inject fuel.

[0052] Among them, cylinder pressure sensor 1 is used to measure the gas pressure inside the cylinder.

[0053] The piston assembly includes piston 9, piston pin 8, piston ring 7, and oil ring.

[0054] Piston 9 is used for sealing and transmitting gas force.

[0055] Among them, the piston pin 8 is used to connect the piston 9 and the connecting rod, so that the piston 9 can swing freely under the guidance of the connecting rod, and convert the up and down movement of the piston 9 into the rotational movement of the connecting rod.

[0056] Among them, piston ring 7 is used to prevent air leakage.

[0057] The oil ring is installed at the tail of the piston 9, which can improve the piston 9's ability to store lubricating oil and distribute oil to the cylinder wall during high-speed movement.

[0058] The piston assembly is slidably disposed in the cylinder block 12 of the engine cylinder, and the lubricating oil injector 14 is used to spray lubricating oil onto the friction contact points between the piston ring 7 and the engine cylinder.

[0059] The linear motors include a first linear motor 22, a second linear motor 20, and a third linear motor 18.

[0060] The first linear motor 22, the second linear motor 20, and the third linear motor 18 share the same linear motor actuator 15.

[0061] In this invention, a multi-motor series connection is used to control the power generation system, which can fully utilize the excellent control characteristics of the motors, flexibly control the piston trajectory, and improve the engine's power output. This helps to improve the overall efficiency and performance of the system.

[0062] A magnetic scale 24 displacement sensor is installed on the linear motor mover 15. The magnetic scale 24 displacement sensor is used to detect the position of the linear motor mover 15, thereby determining the fuel injection position of the fuel injector 3 and the ignition position of the spark plug 2.

[0063] In this invention, a magnetic scale 24 displacement sensor is installed on the linear motor mover 15 to detect the position of the linear motor mover 15, thereby determining the fuel injection position of the fuel injector 3 and the ignition position of the spark plug 2. This integrated sensor design improves the system's compactness and helps optimize the motion control of the piston 9.

[0064] A permanent magnet 11 is provided on the linear motor mover 15.

[0065] The piston assemblies of the two free piston engines on both sides are connected by a linear motor mover 15.

[0066] During system operation, the second linear motor 20 serves as the main motor and is always in generator mode, while the first linear motor 22 and the third linear motor 18 serve as auxiliary motors for system cold start and piston 9 displacement trajectory control.

[0067] In this invention, the system integrates a linear motor and a free-piston engine, achieving more efficient energy conversion through the combination of electric motor power and an internal combustion engine. This integrated design helps improve the system's energy efficiency and performance.

[0068] In one possible implementation, the first linear motor 22 includes a first stator winding 21, the second linear motor 20 includes a second stator winding, and the third linear motor 18 includes a third linear winding 17. The first stator winding 21, the second stator winding, and the third stator winding are all mounted on the linear motor rotor 15.

[0069] In this invention, by mounting the stator windings on the same linear motor mover 15, a shared motor structure can be achieved. This helps simplify system design and manufacturing, reduces the number and redundancy of parts, and improves the overall compactness of the system. Simultaneously, sharing the same linear motor mover 15 structure can reduce the system size. This is crucial for space-constrained applications or systems requiring compact design, as it can improve system integration.

[0070] In one possible implementation, the multi-motor series-connected free piston linear power generation system further includes: a first sealed bearing 10 and a second sealed bearing 10.

[0071] The first sealed bearing 10 is located on the outside of the first linear motor 22.

[0072] The second sealed bearing 10 is located on the outside of the third linear motor 18.

[0073] In this invention, the sealed bearing 10 effectively prevents external dust, impurities, and moisture from entering the motor. This is crucial for protecting the moving parts, bearings, and other critical components inside the motor, contributing to improved system reliability and lifespan.

[0074] In one possible implementation, the multi-motor series-connected free piston linear power generation system further includes: a displacement sensor reading head 23.

[0075] The displacement sensor reading head 23 is used in conjunction with the magnetic scale 24 displacement sensor installed on the linear motor mover 15 to detect the position of the linear motor mover 15.

[0076] In this invention, through the coordinated operation of the displacement sensor reading head 23 and the magnetic scale 24, the system can acquire the position information of the linear motor mover 15 in real time. This real-time position feedback is crucial for the precise control and adjustment of the system's motion. Furthermore, by monitoring the position of the linear motor mover 15 in real time, the system can perform more precise control of the motor. This helps ensure that the movement trajectory, speed, and dwell position of the piston 9 are within a predetermined range, improving the system's stability and control performance.

[0077] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0078] (1) In this invention, when the piston 9 moves to near the dead point, a linear motor can be used to apply resistance in the opposite direction to the piston 9, thereby extending the dwell time of the piston 9 at the dead point, increasing the isochoric combustion time, fully burning the fuel, fully releasing energy, and improving the power generation efficiency.

[0079] (2) In this invention, the power generation system is controlled by a series connection of multiple motors. The excellent control characteristics of the motor can be used to flexibly control the trajectory of the piston 9 to improve the power output of the engine. The functions of the generator and the motor are decoupled to improve the power generation efficiency of the system.

[0080] (3) In this invention, a magnetic scale 24 displacement sensor is provided on the linear motor mover 15. The integration of the displacement sensor with the motor mover 15 improves the compactness of the system.

[0081] Example 2

[0082] In one embodiment, refer to the appendix to the specification. Figure 4 The diagram shows a flowchart of a control method provided by the present invention.

[0083] The present invention provides a control method applied to the multi-motor series-connected free piston linear power generation system of Embodiment 2, comprising:

[0084] S1: During the cold start phase, the second linear motor is controlled to operate in generator mode, and the first and third linear motors operate in electric motor mode, thereby starting the system through the first and third linear motors.

[0085] A cold start typically refers to the process of restarting a system or device after it has not been running or has been stopped for a period of time, and bringing it back to a normal working state.

[0086] In this invention, setting the second linear motor to generator mode and setting the first and third linear motors to electric motor mode to start the system helps to achieve stable and efficient operation of the system during the cold start phase.

[0087] In one possible implementation, S1 specifically includes sub-steps S101 to S105:

[0088] S101: In the initial state, the piston assembly of the two free piston engines is located in the middle position of the free piston engine, and the two free piston engines are the first free piston engine and the second free piston engine.

[0089] S102: Control the first linear motor and the third linear motor to work in electric motor mode, and the second linear motor to work in generator mode. Drive the piston to move to the first side through the first linear motor and the third linear motor. When the piston speed is zero, the first linear motor and the third linear motor switch the driving direction and drive the piston to move to the second side to compress the gas in the engine cylinder.

[0090] It should be noted that by setting the first and third linear motors to electric motor mode and the second linear motor to generator mode, the system can obtain sufficient power during cold starts. This coordinated operation provides enough starting force to initiate piston movement. By controlling the linear motors to drive the piston to one side, and switching the drive direction when the piston speed reaches zero, the piston is pushed to the other side, thereby compressing the gas in the engine cylinder. This helps to increase the pressure of the piston within the engine cylinder, providing more sufficient conditions for subsequent ignition.

[0091] S103: When the piston displacement reaches the preset fuel injector injection position of the first free piston engine, the fuel injector injects fuel into the cylinder block.

[0092] It should be noted that when the piston displacement reaches the preset fuel injector injection position of the first free piston engine, fuel is injected into the cylinder block through the fuel injector. This helps to form a combustible mixture, creating conditions for subsequent ignition.

[0093] S104: The piston continues to move to the second side, increasing the pressure of the combustible mixture formed by the mixing of oil mist and gas in the cylinder.

[0094] S105: When the piston displacement reaches the preset ignition position of the first free piston engine, the spark plug ignites the combustible mixture, generating expansion work and pushing the piston to the first side.

[0095] It should be noted that when the piston reaches the preset ignition position of the first free piston engine, the combustible mixture is ignited by the spark plug, generating expansion and work. This step pushes the piston to one side, completing the cold start process.

[0096] This invention fully utilizes the synergistic effect of the electric motor and engine to ensure the compression and combustion process of gas within the cylinder, thereby achieving efficient cold starts. This offers advantages in improving efficiency and performance for applications such as free-piston linear generator systems that require coordinated operation under different working modes.

[0097] S2: During the stable operation phase, the second linear motor is controlled to operate in generator mode, and the first and third linear motors are alternately controlled to operate in electric motor mode to adjust the piston force at different strokes.

[0098] In this invention, when the piston moves to near the dead center, a first linear motor or a third linear motor can be used to apply resistance in the opposite direction to the piston, thereby extending the piston's dwell time at the dead center, increasing the isochoric combustion time, fully burning the fuel, fully releasing energy, and improving power generation efficiency.

[0099] In one possible implementation, S2 specifically includes sub-steps S201 and S202:

[0100] S201: In the first stroke, the first free piston engine expands and the second free piston engine compresses, and the piston moves from the left dead center to the right dead center.

[0101] In one possible implementation, S201 specifically includes:

[0102] S2011: Ignite the combustible mixture in the cylinder of the first free piston engine, which pushes the piston of the first free piston engine from the left dead center to the right dead center.

[0103] S2012: Control the first linear motor to work in motor mode, apply resistance in the opposite direction to the piston, prolong the piston's dwell time at the dead center, and increase the isochoric combustion time.

[0104] In this invention, controlling the first linear motor to operate in motor mode applies resistance in the opposite direction to the piston, which helps to prolong the piston's residence time at dead center and increase the isochoric combustion time. In this way, the combustion process can be made more complete, improving fuel utilization and thus enhancing system efficiency.

[0105] S2013: During the motion of the linear motor mover, the magnetic lines of force cut the second stator winding of the second linear motor, generating an induced electromotive force in the second stator winding and outputting electrical work to the outside.

[0106] In this invention, the magnetic lines of force of the linear motor mover cutting the second stator winding of the second linear motor during its motion generate an induced electromotive force, which outputs electrical work. This provides additional electrical energy output, helping to maintain the system's power balance and improve overall efficiency.

[0107] S2014: When the piston displacement reaches the preset fuel injector injection position of the second free piston engine, the fuel injector injects fuel into the cylinder block.

[0108] S2015: When the piston displacement reaches the preset ignition position of the second free piston engine, the spark plug ignites the combustible mixture, generating expansion work and pushing the piston to the second side to enter the second stroke.

[0109] In this invention, the efficiency and performance of the entire system are improved by controlling the expansion and compression of the piston, combined with steps such as the reverse resistance of the electric motor, electrical power output, and fuel injection ignition.

[0110] S202: In the second stroke, the first free piston engine compresses, the second free piston engine expands, and the piston moves from right dead center to left dead center.

[0111] In one possible implementation, S202 specifically includes:

[0112] S2021: The combustible mixture in the cylinder of the second free piston engine is ignited, which pushes the piston of the second free piston engine from the right dead center to the left dead center.

[0113] S2022: Control the third linear motor to work in motor mode, apply resistance in the opposite direction to the piston, prolong the piston's dwell time at the dead center, and increase the isochoric combustion time.

[0114] S2023: During the motion of the linear motor mover, the magnetic lines of force cut the second stator winding of the second linear motor, generating an induced electromotive force in the second stator winding and outputting electrical work to the outside.

[0115] S2024: When the piston displacement reaches the preset fuel injector injection position of the first free piston engine, the fuel injector injects fuel into the cylinder block.

[0116] S2025: When the piston displacement reaches the preset ignition position of the first free piston engine, the spark plug ignites the combustible mixture, generating expansion work and pushing the piston to the first side to enter the first stroke.

[0117] The specific details of the second stroke can be found in the content of the first stroke. To avoid repetition, the present invention will not repeat them.

[0118] In one possible implementation, the control method further includes spraying lubricating oil onto the friction contact points between the piston rings and the engine cylinder at fixed time intervals via a lubricating oil injector.

[0119] In this invention, the spraying of lubricating oil can effectively reduce friction between the piston rings and the cylinder wall, thereby reducing frictional losses. This is crucial for the piston's movement within the cylinder, as reduced friction improves system efficiency and minimizes energy loss during energy conversion.

[0120] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0121] (1) In this invention, when the piston moves to near the dead center, a linear motor can be used to apply resistance in the opposite direction to the piston, thereby extending the piston's dwell time at the dead center, increasing the isochoric combustion time, fully burning the fuel, fully releasing energy, and improving power generation efficiency.

[0122] (2) In this invention, the power generation system is controlled by a series connection of multiple motors. The excellent control characteristics of the motor can be used to flexibly control the piston trajectory to improve the power output of the engine. The functions of the generator and the motor are decoupled to improve the power generation efficiency of the system.

[0123] (3) In this invention, a magnetic scale displacement sensor is set on the linear motor mover, and the method of integrating the displacement sensor with the motor mover improves the compactness of the system.

[0124] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0125] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A control method applied to a multi-motor series-connected free piston linear power generation system, characterized in that, The multi-motor series-connected free piston linear power generation system includes: a linear motor and a first free piston engine and a second free piston engine respectively disposed on both sides of the linear motor; The free piston engine includes a piston assembly and an engine cylinder; The engine cylinder includes a cylinder block and a cylinder head; The engine cylinder block is provided with an air inlet and an exhaust outlet, and an intake valve is provided on the air inlet. The engine cylinder block is equipped with a lubricating oil injector. The cylinder head of the engine cylinder is equipped with spark plugs, fuel injectors and cylinder pressure sensors. The piston assembly includes a piston, a piston pin, piston rings, and an oil ring; The piston assembly is slidably disposed in the cylinder block of the engine cylinder, and the lubricating oil injector is used to spray lubricating oil onto the friction contact points of the piston ring and the engine cylinder. The linear motor includes a first linear motor, a second linear motor, and a third linear motor; The first linear motor, the second linear motor, and the third linear motor share the same linear motor actuator; A magnetic grating displacement sensor is installed on the linear motor mover. The magnetic grating displacement sensor is used to detect the position of the linear motor mover, thereby determining the fuel injection position of the fuel injector and the ignition position of the spark plug. The linear motor actuator is equipped with a permanent magnet; The piston assemblies of the two free piston engines on both sides are connected by the linear motor actuator; During system operation, the second linear motor acts as the main motor, always operating in generator mode. The first and third linear motors act as auxiliary motors, used for cold starts and piston displacement trajectory control. The control method includes: S1: During the cold start phase, the second linear motor is controlled to operate in generator mode, and the first linear motor and the third linear motor operate in motor mode, thereby starting the system through the first linear motor and the third linear motor; S2: During the stable operation phase, control the second linear motor to work in generator mode, and alternately control the first linear motor and the third linear motor to work in motor mode to adjust the piston force at different strokes. Specifically, S2 includes: S2011: Ignite the combustible mixture in the cylinder of the first free piston engine, which pushes the piston of the first free piston engine from the left dead center to the right dead center; S2012: Control the first linear motor to work in motor mode, apply resistance in the opposite direction to the piston, prolong the piston's dwell time at the dead center, and increase the isochoric combustion time; S2013: During the motion of the linear motor mover, the magnetic lines of force cut the second stator winding of the second linear motor, generating an induced electromotive force in the second stator winding and outputting electrical work to the outside. S2014: When the piston displacement reaches the preset fuel injector injection position of the second free piston engine, the fuel injector injects fuel into the cylinder block. S2015: When the piston displacement reaches the preset ignition position of the second free piston engine, the spark plug ignites the combustible mixture, generating expansion work and pushing the piston to the second side to enter the second stroke; S2021: Ignite the combustible mixture in the cylinder of the second free piston engine, which pushes the piston of the second free piston engine from the right dead center to the left dead center; S2022: Control the third linear motor to work in motor mode, apply resistance in the opposite direction to the piston, prolong the piston's dwell time at the dead center, and increase the isochoric combustion time; S2023: During the motion of the linear motor mover, the magnetic lines of force cut the second stator winding of the second linear motor, generating an induced electromotive force in the second stator winding and outputting electrical work to the outside. S2024: When the piston displacement reaches the preset fuel injector injection position of the first free piston engine, the fuel injector injects fuel into the cylinder block. S2025: When the piston displacement reaches the preset ignition position of the first free piston engine, the spark plug ignites the combustible mixture, generating expansion work and pushing the piston to the first side to enter the first stroke.

2. The control method according to claim 1, characterized in that, S1 specifically includes: S101: In the initial state, the piston assembly of the two free piston engines is located in the middle position of the free piston engines, and the two free piston engines are the first free piston engine and the second free piston engine, respectively. S102: Control the first linear motor and the third linear motor to work in motor mode, and the second linear motor to work in generator mode. Drive the piston to move to the first side through the first linear motor and the third linear motor. When the piston speed is zero, the first linear motor and the third linear motor switch the driving direction and drive the piston to move to the second side to compress the gas in the engine cylinder. S103: When the piston displacement reaches the preset fuel injector injection position of the first free piston engine, the fuel injector injects fuel into the cylinder block. S104: The piston continues to move to the second side, increasing the pressure of the combustible mixture formed by the mixing of oil mist and gas in the cylinder; S105: When the piston displacement reaches the preset ignition position of the first free piston engine, the spark plug ignites the combustible mixture, generating expansion work and pushing the piston to the first side.

3. The control method according to claim 1, characterized in that, Also includes: Lubricating oil is sprayed onto the friction contact points between the piston rings and the engine cylinders through a lubricating oil injector at fixed time intervals.

4. The control method according to claim 1, characterized in that, The first linear motor includes a first stator winding, the second linear motor includes a second stator winding, and the third linear motor includes a third stator winding. The first stator winding, the second stator winding, and the third stator winding are all sleeved on the moving part of the linear motor.

5. The control method according to claim 1, characterized in that, The multi-motor series-connected free piston linear power generation system also includes: a first sealed bearing and a second sealed bearing; The first sealed bearing is located on the outside of the first linear motor; The second sealed bearing is located on the outside of the third linear motor.

6. The control method according to claim 1, characterized in that, The multi-motor series-connected free piston linear power generation system also includes: a displacement sensor reading head; The displacement sensor reading head is used in conjunction with the magnetic grating displacement sensor installed on the linear motor mover to detect the position of the linear motor mover.

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