KR102460405B1 - Fuel sypply system - Google Patents

Abstract

The present invention compresses the boil-off gas generated in the cargo tank in multiple stages so as to match the pressure value of the boil-off gas required by the engine to control the opening amount of the valve installed in the circulation line connecting the input end and the output end of the multi-stage compression unit. It relates to a supply system and a method for controlling boil-off gas pressure thereof.
In the fuel supply system for supplying boil-off gas (BOG) generated in a cargo tank according to an embodiment of the present invention to an engine, the fuel supply system comprising: a compressor receiving and compressing boil-off gas generated in the cargo tank; valves installed in a recirculation line connecting an input end and an output end of the multi-stage compression unit in the compressor; and controllers for controlling an opening amount of the valves to match the pressure value of the boil-off gas required by the engine.

Description

Fuel supply system {FUEL SYPPLY SYSTEM}

The present invention relates to a fuel supply system and a method for controlling the BOG pressure thereof, and more particularly, the input and output terminals of the multi-stage compression unit to match the BOG pressure value required by the engine by compressing BOG generated in a cargo tank in multiple stages. To a fuel supply system capable of controlling the opening degree of a valve installed in a circulation line connecting

In recent years, the consumption of liquefied gas such as LNG (Liquefied Natural Gas) or LPG (Liquefied Petroleum Gas) is rapidly increasing worldwide. The liquefied gas is transported in a gaseous state through a gas pipeline on land or at sea, or stored in a liquefied gas carrier in a liquefied state and transported to a remote consumer. Liquefied gas such as LNG or LPG is obtained by cooling natural gas or petroleum gas to cryogenic temperatures (approximately -163℃ in the case of LNG). .

Liquefied gas carriers, such as LNG carriers, are for loading and unloading liquefied gas to destinations on land by navigating the sea with liquefied gas. called) is included.

Since the liquefaction temperature of natural gas is a cryogenic temperature of about -163°C at normal pressure, LNG is evaporated even if its temperature is slightly higher than -163°C at normal pressure. Taking the case of a conventional LNG carrier as an example, although the LNG storage tank of the LNG carrier is insulated, external heat is continuously transferred to the LNG. Boil-off gas (BOG) is generated in the LNG storage tank as it is continuously vaporized in the LNG storage tank.

The generated BOG is compressed through a high-pressure compressor system and supplied as fuel for the catfish engine.

The conventional fuel supply system for supplying BOG to the engine is the BOG pressure value at the input stage, the BOG pressure value at the output stage for each multi-stage compression unit in the high-pressure compressor system, the current value of the installed motor for each compression unit, the valve seat limit value, and the feedforward. Configure individual controllers for values.

However, in the conventional fuel supply system, it is necessary to apply a control method suitable for the multi-stage compression unit for each individual controller in order to supply a stable pressure of boil-off gas to the catfish engine.

Therefore, there is a need for an improved fuel supply system capable of supplying a stable BOG pressure in a catfish engine by controlling the multi-stage compression unit in a standardized control method, rather than in a different control method for each individual controller.

Republic of Korea Patent Publication No. 2014-0052814 (2014.05.07) "A fuel supply system and method for a marine engine"

It is an object of the present invention to control the amount of opening of a valve installed in a circulation line connecting the input and output terminals of the multi-stage compression unit to match the pressure value of the boil-off gas required by the engine by compressing the boil-off gas generated in the cargo tank in multiple stages. An object of the present invention is to provide a fuel supply system and a method for controlling the boil-off gas pressure thereof.

In the fuel supply system for supplying boil-off gas (BOG) generated in the cargo tank according to an embodiment of the present invention for achieving the above object to the engine, the compressor receiving the boil-off gas generated in the cargo tank and compressing it; valves installed in a recirculation line connecting an input end and an output end of the multi-stage compression unit in the compressor; and controllers for controlling an opening amount of the valves to match the pressure value of the boil-off gas required by the engine.

The controllers include a first main controller for controlling the pressure of the boil-off gas compressed by the first compression unit receiving the boil-off gas generated from the cargo tank, and the boil-off gas supplied and compressed by the first main controller. A second main controller for controlling the pressure of the boil-off gas compressed by the second compression unit, and a final pressure of the boil-off gas compressed by the third compression unit receiving and compressing the boil-off gas controlled by the second main controller A third main controller for controlling may be included.

The first main controller compares the final pressure value of the boil-off gas measured through a fourth pressure sensor installed in a supply line for supplying the boil-off gas compressed by the third compression unit to the engine and a preset final reference pressure value. The first sub-controller that determines the final BOG control value through the difference, the difference between the input end BOG pressure value measured through the first pressure sensor installed at the input end of the first compression unit and the preset input terminal reference pressure value A second sub-controller that determines the input BOG control value, and the output BOG control through the difference between the output BOG pressure value measured from the second pressure sensor installed at the output end of the first compression unit and the preset output BOG control value It may be connected to a third sub-controller that determines a value.

The first main controller is configured to include a final stage control value received from the first sub-controller, an input stage BOG control value received from the second sub-controller, an output stage BOG control value received from the third sub-controller, and in the compressor. The first final valve opening degree calculated using the current control value determined through the difference between the motor current value and the reference current value, the preset valve limit value, and the feedforward value, between the input terminal and the output terminal of the first compression unit It is possible to control the first valve installed in the.

The first final valve opening degree is a preset maximum subtotal value obtained by multiplying the final stage control value, the input stage BOG control value, the output stage BOG control value, and the current control value and the valve limit value. It may be a value obtained by adding the feedforward value after subtracting it from the measurement.

The second main controller is a fourth sub-controller configured to determine an input BOG control value based on a difference between the input terminal BOG pressure value of the second compression unit measured from the second pressure sensor and a preset input terminal reference pressure value; It may be connected to a fifth sub-controller that determines the output BOG control value through a difference between the output terminal BOG pressure value measured by the third pressure sensor installed at the output terminal of the second compression unit and a preset output terminal reference pressure value.

The second main controller uses the difference between the input BOG control value received from the fourth sub-controller, the output BOG control value received from the fifth sub-controller, and the current value of the motor in the compressor and the reference current value. The second valve installed between the input end and the output end of the second compression unit may be controlled by the second final valve opening degree calculated using the determined current control value, the preset valve limit value, and the feedforward value.

The third main controller is a fifth sub-controller configured to determine an input BOG control value based on a difference between the input terminal BOG pressure value of the third compression unit measured by the third pressure sensor and a preset input terminal reference pressure value; It may be connected to a seventh sub-controller that determines an output BOG control value through a difference between the output BOG pressure value measured from the fourth pressure sensor and a preset output terminal reference pressure value.

The third main controller is configured to use the input terminal BOG control value received from the sixth sub-controller, the output BOG control value received from the seventh sub-controller, and the difference between the current value of the motor in the compressor and the reference current value. The third valve installed between the input terminal and the output terminal of the third compression unit may be controlled by the third final valve opening degree calculated using the determined current control value, the preset valve limit value, and the feedforward value.

The sub-controllers connected to the first to third main controllers have a gain value set for each preset current section, determine a section to which the measured motor current value for each of the first to third compression units belongs, and enter the determined section. PID control can be performed with the set gain value.

In addition, according to another embodiment of the present invention, as a method of controlling the BOG pressure of a fuel supply system for supplying the pressure of BOG generated in the cargo tank to the engine, multi-stage compression in the compressor that receives BOG generated in the cargo tank and compresses it. Each of the controllers controlling the valves installed between the input terminal and the output terminal of the negative input terminal BOG pressure value and the output terminal BOG pressure value received from the input terminal and the output terminal of the multi-stage compression unit, respectively, the preset input terminal reference pressure value and the output terminal reference pressure value Each of the valves receives an input and output BOG control value corresponding to the difference by comparing with each other, and reflects the received input and output BOG control values to match the BOG pressure value required by the engine. There is provided a boil-off gas pressure control method of a fuel supply system, characterized in that controlling the dose.

Each of the controllers determines a section to which the current value of the motor measured for each multi-stage compression unit belongs by using a storage unit that stores a gain value set for each preset current section, and through the gain value set in the determined section PID control can be performed.

According to an embodiment of the present invention, the amount of opening of the valve installed in the circulation line connecting the input end and the output end of the multi-stage compression unit can be controlled to match the pressure value of the boil-off gas required by the engine by compressing the boil-off gas generated in the cargo tank in multiple stages. can have an effect.

1 is a view for explaining a fuel supply system according to an embodiment of the present invention;
Figure 2 is a view for explaining the first main controller shown in Figure 1;
3 is a view for explaining the second main controller shown in FIG. 1, and
FIG. 4 is a view for explaining a third main controller shown in FIG. 1;

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a fuel supply system according to an embodiment of the present invention, FIG. 2 is a diagram illustrating the first main controller illustrated in FIG. 1, and FIG. 3 is FIG. FIG. 4 is a diagram illustrating the third main controller illustrated in FIG. 1 , and FIG. 4 is a diagram illustrating the third main controller illustrated in FIG. 1 .

Referring to FIG. 1 , a fuel supply system according to an embodiment of the present invention includes a compressor 100 for compressing boil-off gas generated in a cargo tank 50 in multiple stages, and a multistage compression unit 110 , 120 , 130 in the compressor 100 . ) of the valves (B1, B2, B3) installed in the recirculation line (L1) connecting the input and output terminals of the It is configured to include controllers for controlling the measurement.

The cargo tank 50 stores the liquefied natural gas, and when the liquefied natural gas is vaporized by heat transferred from the outside and the boil-off gas generated is higher than a certain pressure, it is discharged to the outside.

The controllers include a first main controller 111 that controls the pressure of the boil-off gas compressed by the first compression unit 110 receiving the boil-off gas generated from the cargo tank 50, and the first main controller 111. A second main controller 121 that controls the pressure of the boil-off gas compressed by the second compression unit 120 that receives the controlled boil-off gas and compresses it, and supplies the boil-off gas controlled by the second main controller 121 and a third main controller 131 for controlling the final pressure of the boil-off gas compressed by the third compression unit 130 that receives and compresses. BOG having a final pressure controlled by the third main controller 131 is supplied as fuel to the catfish engine.

The first to third main controllers (111, 121, 131) are first to third valves ( The pressure of BOG compressed by the first to third compression units 110, 120, 130 can be controlled by calculating the opening degrees of B1, B2, and B3 and controlling the corresponding valves with the calculated opening degrees of the valves. have.

The first main controller 111 includes the input stage BOG control value, the output stage BOG control value, the final BOG control value, the current control value of the motor, the valve opening limit value and the operation of the catfish engine of the first compression unit 110 . Receives the feedforward value predicted according to the amount, received input BOG control value (A), output BOG control value (B), final BOG control value (C), and motor current control value (D) And by substituting the valve opening limit value (E) in Equation 1 below to calculate the subtotal value (Cal-A), and calculate the subtotal value (Cal-A) and the feedforward value (F) by the following equation The first valve B1 is controlled by the opening degree Cal-B of the first valve B1 calculated by applying Equation 2 to the calculation. At this time, the first main controller 111 receives the position of the first valve B1 and performs valve control to match the calculated opening amount.

The first main controller 111 is the final pressure of the boil-off gas measured through the fourth pressure sensor PT04 installed in the supply line L2 for supplying the boil-off gas compressed by the third compression unit 130 to the catfish engine. Through the first sub-controller 111a that determines the final boil-off gas control value through the difference between the value and the preset final reference pressure value, the first pressure sensor PT01 installed at the input terminal of the first compression unit 110 A second sub-controller 111b that determines an input-end control value based on a difference between the measured input terminal BOG pressure value and a preset input terminal reference pressure value, and a second pressure sensor installed at the output terminal of the first compression unit 111 ( It is connected to the third sub-controller 111c that determines the output BOG control value through the difference between the output BOG pressure value measured from PT02) and the preset output terminal reference pressure value.

Referring to FIG. 2 , the first main controller 111 is a current controller ( 100a), a valve limit controller 100b that controls not to exceed a preset valve limit value, and a feedforward controller 100c that predicts a feedforward value based on the operation amount of the catfish engine. .

The first main controller 111 controls the input stage BOG received from the first to third sub-controllers 111a, 111b, 111c, the current controller 111d, the valve limit controller 111e and the feedforward controller 111f. By receiving the value (A), the output stage BOG control value (B), the final stage BOG control value (C), the motor current control value (D), the valve opening limit value (E), and the feed forward value (F) An opening amount for controlling the first valve B1 may be calculated through Equations 1 and 2 described above.

Accordingly, it is possible to control the boil-off gas pressure of the first compression unit 110 that receives and compresses the boil-off gas generated from the cargo tank 50 . The first compression unit 110 has two compression units connected in parallel.

Hereinafter, the second and third main controllers 121 and 131 will be described.

Referring to FIG. 3 , the second main controller 121 evaporates the input terminal through a difference between the input terminal BOG pressure value of the second compression unit 120 measured from the second pressure sensor PT02 and a preset input terminal reference pressure value. The difference between the output terminal BOG pressure value measured from the fourth controller 121a that determines the gas control value, and the third pressure sensor PT03 installed at the output terminal of the second compression unit 120 and the preset output terminal reference pressure value It is connected to the fifth sub-controller 121b, the current controller 100a, the valve limit controller 100b, and the feedforward controller 100c described above for determining the output stage BOG control value through .

The second main controller 121 includes the input terminal BOG control value A of the second compression unit 120 received from the fourth and fifth controllers 121a and 121b, and the output terminal evaporation of the second compression unit 120 . the gas control value B, the current control value D, the valve limit value E, and A subtotal value (Cal-A) is calculated using the feedforward value (F) and Equation (3).

In addition, the second main controller 121 applies the calculated sub-total value and the feed-forward value F to Equation 2 described above to calculate the second final valve opening degree Cal-B, and the calculated second final valve The opening amount controls the second valve B2 installed between the input end and the output end of the second compression unit 120 .

Accordingly, the BOG pressure of the second compression unit 120 that receives and compresses the BOG compressed through the first compression unit 110 may be controlled. The second compression unit 120 may include a two-stage compression unit and a three-stage compression unit, in which the two compression units are connected in series.

Referring to FIG. 4 , the third main controller 131 is configured through the difference between the input terminal BOG pressure value of the third compression unit 130 measured from the above-described third pressure sensor PT03 and the preset input terminal reference pressure value. The sixth sub-controller 131a that determines the input terminal BOG control value, the output terminal BOG control value through the difference between the output terminal BOG pressure value measured from the above-described fourth pressure sensor PT04 and a preset output terminal reference pressure value It is connected to the seventh sub-controller 131b, the above-described current controller 100a, the above-described valve limit controller 100b, and the above-mentioned feedforward controller 100c, which determines

The third main controller 131 includes the input terminal BOG control value of the third compression unit 130 received from the sixth and seventh controllers 131a and 131b, the output terminal BOG control value of the third compression unit 130 and , the current control value, the valve limit value and the feedforward value received from the above-mentioned current controller 100a, the above-mentioned valve limit controller 100b and the above-mentioned feedforward controller 100c, and the above-mentioned Equation 3 The third final valve opening degree (Cal-B) calculated by calculating the total value (Cal-A) and substituting the calculated subtotal value (Cal-A) and the feed forward value (F) into Equation 2 above to control the third valve B3 installed between the input end and the output end of the third compression unit 130 .

Accordingly, the BOG pressure of the third compression unit 130 that receives and compresses the BOG compressed through the second compression unit 120 may be controlled to supply the controlled BOG pressure to the catfish engine. The third compression unit 130 may include a 4-stage compression unit and a 5-stage compression unit in which two compression units are connected in series.

As such, the first main controller 111 calculates the BOG control value of the input and output terminals of the first compression unit 110, the final BOG control value, the current control value, the valve limit value, and the feedforward value. The first final valve opening degree controls the pressure of the boil-off gas compressed by the first compression unit 110 , and the second and third main controllers 121 and 131 include the second and third compression units 121 and 131 . ) in the second and third compression units 121 and 131 with the second and third final valve opening degrees calculated in consideration of the BOG control value, current control value, valve limit value, and feedforward value of the input and output terminals. It is possible to control the pressure of the boil-off gas compressed by the

Meanwhile, in the sub-controllers connected to the first to third main controllers 111, 121, and 131 described above, gain values for each preset current section may be set as shown in Table 1 below, and the first to third compression units ( A section to which the current value of the motor received from the current controller 100a belongs is determined for each 110, 120, and 130, and PID control can be performed with a gain value set in the determined section. A preset gain value for each current section may be stored in a storage unit (not shown) provided in the sub-controllers.

Motor current value P Gain I Gain 0-50 X1 Y1 51-75 X2 Y2 76 to 100 X3 Y3

A method of controlling the BOG pressure of the fuel supply system having such a configuration will be described as follows.

Each of the controllers for controlling the valves installed between the input end and the output end of the multi-stage compression unit in the compressor for receiving and compressing boil-off gas generated from the cargo tank are input terminals respectively received from the input terminals and the output terminals of the multi-stage compression units 110 , 120 , 130 . By comparing the BOG pressure value and the output BOG pressure value with the preset input terminal reference pressure value and the output terminal reference pressure value, respectively, the input terminal and output terminal BOG control values corresponding to the difference are received, respectively, and the received input terminal and output terminal BOG control By reflecting the value, the opening degree of the valves can be controlled to match the BOG pressure required by the engine, particularly the catfish engine, which is a propulsion engine.

More specifically, among the controllers, the first main controller 111 receives the final BOG control value from the first sub-controller 111a, and the second and third sub-controllers 111b and 111c described above. Receives the input terminal BOG control value and the output terminal BOG control value of the first compression unit 110 from, and the current control value from the above-described current controller 100a, valve limit controller 100b and feedforward controller 100c, Receive valve limit values and feedforward values. In this case, the order in which the first main controller 111 receives the final BOG control value, the input BOG control value, the output BOG control value, the current control value, the valve limit value, and the feedforward value does not limit the present invention. .

The first main controller 111 converts the received final BOG control value, the input BOG control value of the first compression unit 110, the output BOG control value, the current control value, and the valve limit value to Equation 1 described above. Subtotal value is calculated by substituting it, and the calculated subtotal value and feedforward value are substituted in Equation 2 to calculate the opening degree of the first valve B1.

The first main controller 111 controls the position of the corresponding valve according to the calculated opening degree of the first valve B1. In this case, the first main controller 111 may precisely control the degree of opening with the amount of the opening of the first valve B1 calculated by sensing the position of the corresponding valve.

The second main controller 121 receives the BOG control value of the input terminal of the second compression unit 120 and the BOG control value of the output terminal of the second compression unit 120 from the fourth and fifth sub-controllers 121a and 121b. and receives the current control value, the valve limit value and the feedforward value from the current controller 100a, the valve limit controller 100b and the feedforward controller 100c described above.

Thereafter, the second main controller 121 substitutes the received input terminal BOG control value, the output terminal BOG control value, the current control value, and the valve limit value of the second compression unit 120 into the above-described Equation 3 to obtain a subtotal The value is calculated, and the opening degree of the second valve B2 is calculated by substituting the calculated subtotal value and the feedforward value into Equation (2). The pressure of the boil-off gas compressed by the second compression unit 120 may be controlled by controlling the position of the corresponding valve according to the calculated amount of opening of the second valve B2 .

Finally, the third main controller 131 controls the input BOG control value of the third compression unit 130 and the output BOG control value of the third compression unit 130 from the sixth and seventh sub-controllers 131a and 131b. Receive values and receive current control values, valve limit values and feedforward values from current controller 100a, valve limit controller 100b and feedforward controller 100c described above.

Thereafter, the third main controller 131 substitutes the received input terminal BOG control value, the output terminal BOG control value, the current control value, and the valve limit value of the third compression unit 130 into Equation 3 above to obtain a subtotal value. , and substituting the calculated subtotal value and the feedforward value into Equation 2 to calculate the opening degree of the third valve B3. The pressure of the boil-off gas compressed by the third compression unit 130 may be controlled by controlling the position of the corresponding valve according to the calculated opening amount of the third valve B3 .

In addition, each of the sub-controllers connected to the first to third main controllers 111 , 121 , and 131 has a gain value set for each preset current section, and is measured for each of the first to third compression units 110 , 120 , 130 . It is possible to determine a section to which the current value of the determined motor belongs, and perform PID control with a gain value set in the determined section. The stability of the fuel supply system may be maintained by varying the PID gain value for each section as described above.

By doing this, Equations 1 and 2 or Equations 2 and 3 formalized by the first to third main controllers 111, 121, 131 to match the pressure value of boil-off gas required by the catfish engine It is possible to control the valve by calculating the final valve opening degree.

The present invention is not limited by the above-described embodiments, and various modifications and changes can be made by those skilled in the art, which are included in the spirit and scope of the present invention as defined in the appended claims.

100: compressor 100a: current controller
100b: valve limit controller 100c: feedforward controller
110, 120, 130n: first to third compression units
111, 121, 131: first to third main controllers
111a, 111b, 111c: first to third sub-controllers
121a, 121b: fourth and fifth sub-controllers
131a, 131b: sixth and seventh sub-controllers

Claims (12)

In the fuel supply system for supplying boil-off gas (BOG) generated in the cargo tank to the engine,
a compressor for receiving and compressing the boil-off gas generated from the cargo tank;
valves installed in a recirculation line connecting an input end and an output end of each of the multi-stage compression units constituting the compressor; and
And controllers for controlling the opening degree of the valves to match the pressure value of the boil-off gas required by the engine,
The controllers are
a first main controller for controlling an opening degree of a first valve installed on a first recirculation line connecting an input end and an output end of a first compression unit receiving the boil-off gas generated from the cargo tank;
a second main controller for controlling an opening degree of a second valve installed on a second recirculation line connecting an input end and an output end of a second compression unit that receives and compresses boil-off gas from the first compression unit; and
and a third main controller for controlling an opening degree of a third valve installed on a first recirculation line connecting an input end and an output end of a third compression unit for receiving and compressing boil-off gas from the second compression unit,
The first main controller,
Final stage evaporation through the difference between the final pressure value of the boil-off gas measured through the fourth pressure sensor installed in the supply line for supplying the boil-off gas compressed by the third compression unit to the engine and the preset final reference pressure value a first sub-controller for determining a gas control value;
a second sub-controller configured to determine an input BOG control value based on a difference between an input terminal BOG pressure value measured by a first pressure sensor installed at the input terminal of the first compression unit and a preset input terminal reference pressure value; and
characterized in that it is connected to a third sub-controller that determines an output BOG control value through a difference between an output terminal BOG pressure value measured by a second pressure sensor installed at the output terminal of the first compression unit and a preset output terminal reference pressure value fuel supply system. delete delete The method according to claim 1,
The first main controller is configured to include a final stage control value received from the first sub-controller, an input stage BOG control value received from the second sub-controller, an output stage BOG control value received from the third sub-controller, and in the compressor. Controlling the first valve with the first final valve opening degree calculated using the current control value determined through the difference between the motor current value and the reference current value, preset valve limit values, and feedforward values fuel supply system. 5. The method according to claim 4,
The first final valve opening degree is a preset maximum subtotal value obtained by multiplying the final stage control value, the input stage BOG control value, the output stage BOG control value, and the current control value and the valve limit value. A fuel supply system, characterized in that it is a value obtained by adding the feedforward value after subtracting it from the metric. The method according to claim 1,
The second main controller,
a fourth sub-controller configured to determine an input BOG control value based on a difference between the input terminal BOG pressure value of the second compression unit measured from the second pressure sensor and a preset input terminal reference pressure value; and
and a fifth sub-controller that determines an output BOG control value through a difference between an output BOG pressure value measured by a third pressure sensor installed at the output end of the second compression unit and a preset output reference pressure value. fuel supply system. 7. The method of claim 6,
The second main controller uses the difference between the input BOG control value received from the fourth sub-controller, the output BOG control value received from the fifth sub-controller, and the current value of the motor in the compressor and the reference current value. The fuel supply system according to claim 1, wherein the second valve is controlled by the second final valve opening degree calculated using the determined current control value, the preset valve limit value, and the feedforward value. The method according to claim 1,
The third main controller,
a sixth sub-controller configured to determine an input BOG control value based on a difference between the input terminal BOG pressure value of the third compression unit measured by the third pressure sensor and a preset input terminal reference pressure value; and
The fuel supply system, characterized in that it is connected to a seventh sub-controller that determines the output stage BOG control value through a difference between the output stage BOG pressure value measured by the fourth pressure sensor and a preset output stage reference pressure value. 9. The method of claim 8,
The third main controller is configured to use the input terminal BOG control value received from the sixth sub-controller, the output BOG control value received from the seventh sub-controller, and the difference between the current value of the motor in the compressor and the reference current value. The fuel supply system, characterized in that the third valve is controlled by the third final valve opening degree calculated using the determined current control value, the preset valve limit value, and the feedforward value. 9. The method according to any one of claims 1, 6 and 8,
The sub-controllers connected to any one of the first to third main controllers have a gain value set for each preset current section, and determine a section to which the measured current value of the motor for each of the first to third compression units belongs, A fuel supply system, characterized in that the PID control is performed with a gain value set in the determined section. delete delete

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