Power system based on variable frequency driving and floating liquefied natural gas production, storage and unloading device

Abstract

The utility model provides a power system based on variable frequency driving and a floating liquefied natural gas production, storage and unloading device, the power system comprises a power device and a variable frequency driver, the power device at least comprises a plurality of induction motors and power equipment, the induction motors are used for electrically driving the power equipment, and the variable frequency driver is used for electrically driving the power equipment. The power equipment comprises at least one of a water injection pump and gas compression equipment; the variable frequency driver is electrically connected with the input end of at least one induction motor, the variable frequency driver is used for driving the power device in a variable frequency mode, the variable frequency driver at least comprises a plurality of variable frequency units, and one variable frequency unit comprises an active front-end rectifier and a passive front-end rectifier. The performance of the power system can be improved.

Description

Technical Field

[0001] The present application relates to the field of power systems, and in particular to a power system based on variable frequency drive and a floating liquefied natural gas production, storage and unloading device. Background Art

[0002] Floating Production Storage and Offloading (FPSO) is usually equipped with a power generation system consisting of gas turbine generators and diesel generators to ensure stable power supply during its production and storage. However, in traditional power system design, motors are mostly started directly online and cannot be operated at variable speeds, resulting in problems such as low motor power factor and poor performance.

[0003] Therefore, there is an urgent need for a power system to solve the problem of low power system performance. Utility Model Content

[0004] The main purpose of the present application is to provide a power system based on variable frequency drive and a floating liquefied natural gas production, storage and unloading device to solve the problem of low performance of the power system in the prior art.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, there is provided an electric power system based on variable frequency drive, comprising: an electric power device, comprising at least a plurality of induction motors and electric power equipment, wherein the induction motors are used to electrically drive the electric power equipment, and the electric power equipment comprises at least one of a water injection pump and a gas compression equipment; a variable frequency drive, electrically connected to the input end of at least one of the induction motors, wherein the variable frequency drive is used to variable frequency drive the electric power device, wherein the variable frequency drive comprises at least a plurality of frequency conversion units, and one of the frequency conversion units comprises an active front-end rectifier and a passive front-end rectifier.

[0006] Optionally, the active front-end rectifier includes a first H-bridge, a second H-bridge and a first capacitor, the first end of the first H-bridge, the first end of the second H-bridge and the first end of the first capacitor are electrically connected, the second end of the first H-bridge, the second end of the second H-bridge and the second end of the first capacitor are electrically connected, the first H-bridge includes a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor and a sixth transistor, the first end of the first transistor, the first end of the second transistor and the first end of the third transistor are electrically connected and are the first end of the first H-bridge, the second end of the first transistor is electrically connected to the first end of the fourth transistor, the second end of the second transistor is electrically connected to the first end of the fifth transistor The first end of the first transistor is electrically connected to the first end of the sixth transistor, the second end of the fourth transistor, the fifth transistor and the second end of the sixth transistor are electrically connected and form the second end of the first H-bridge, the second H-bridge includes a seventh transistor, an eighth transistor, a ninth transistor and a tenth transistor, the first end of the seventh transistor is electrically connected to the first end of the eighth transistor and forms the first end of the second H-bridge, the second end of the seventh transistor is electrically connected to the first end of the ninth transistor, the second end of the eighth transistor is electrically connected to the first end of the tenth transistor, the second end of the ninth transistor is electrically connected to the second end of the tenth transistor and forms the second end of the second H-bridge.

[0007] Optionally, the first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, the sixth transistor, the seventh transistor, the eighth transistor, the ninth transistor and the tenth transistor are insulated gate bipolar transistors, and the first capacitor is a DC link capacitor.

[0008] Optionally, the passive front-end rectifier includes a rectifier bridge, a second capacitor and a third H-bridge, the first end of the rectifier bridge, the first end of the second capacitor and the first end of the third H-bridge are electrically connected, the second end of the rectifier bridge, the second end of the second capacitor and the second end of the third H-bridge are electrically connected, the rectifier bridge includes a first diode, a second diode, a third diode, a fourth diode, a fifth diode and a sixth diode, the first end of the first diode, the first end of the second diode and the first end of the third diode are electrically connected and are the first end of the rectifier bridge, the second end of the first diode is electrically connected to the first end of the fourth diode, and the second end of the second diode is electrically connected to the first end of the fifth diode , the second end of the third diode is electrically connected to the first end of the sixth diode, the second ends of the fourth diode, the fifth diode and the sixth diode are electrically connected and form the second end of the rectifier bridge, the third H-bridge includes an eleventh transistor, a twelfth transistor, a thirteenth transistor and a fourteenth transistor, the first end of the eleventh transistor is electrically connected to the first end of the twelfth transistor and forms the first end of the third H-bridge, the second end of the eleventh transistor is electrically connected to the first end of the thirteenth transistor, the second end of the twelfth transistor is electrically connected to the first end of the fourteenth transistor, the second end of the thirteenth transistor is electrically connected to the second end of the fourteenth transistor and forms the second end of the third H-bridge.

[0009] Optionally, the eleventh transistor, the twelfth transistor, the thirteenth transistor and the fourteenth transistor are insulated gate bipolar transistors, and the second capacitor is a DC link capacitor.

[0010] Optionally, the frequency conversion driver further includes: an isolation transformer electrically connected to the first ends of the plurality of frequency conversion units, the isolation transformer being used to convert three-phase alternating current into an input voltage of the frequency conversion unit.

[0011] Optionally, the electric power device also includes: a first generator set, including a plurality of first generators, input ends of the plurality of first generators are electrically connected to the first bus, and a portion of the induction motors are electrically connected to the first bus; a second generator set, including a plurality of second generators, input ends of the plurality of second generators are electrically connected to the second bus, and another portion of the induction motors are electrically connected to the second bus; a feeder, a first end of the feeder is electrically connected to the first bus, and a second end of the feeder is electrically connected to the second bus.

[0012] Optionally, the power device further includes: a first constant power load, wherein an input end of the first constant power load is electrically connected to the first bus.

[0013] Optionally, the power device also includes: a step-down transformer, a first end of the step-down transformer is electrically connected to the first bus or the second bus; and a second constant power load, a first end of the second constant power load is electrically connected to the second end of the step-down transformer.

[0014] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a floating liquefied natural gas production storage and unloading device is provided, comprising any one of the power systems based on variable frequency drive.

[0015] By applying the technical solution of the present application, a power system based on variable frequency drive is provided, including a power device and a variable frequency drive, the power device at least includes a plurality of induction motors and power equipment, the induction motor is used to electrically drive the power equipment, and the power equipment includes at least one of a water injection pump and a gas compression device; the variable frequency drive is electrically connected to the input end of at least one induction motor, the variable frequency drive is used to variable frequency drive the power device, the variable frequency drive at least includes a plurality of frequency conversion units, and one frequency conversion unit includes an active front-end rectifier and a passive front-end rectifier. By introducing a variable frequency drive into the power system, especially by combining a passive front-end and an active front-end rectifier, the motor of the power system can be soft-started, the short-circuit current can be reduced, a stronger voltage sag resistance and energy-saving operation can be provided, and the reactive power exchange with the power grid can be effectively controlled, thereby improving the power factor, reducing the system load, improving the power quality and overall performance of the power system, and solving the problem of low performance of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0017] Figure 1 A schematic structural diagram of a power system based on variable frequency drive according to an embodiment of the present application is shown;

[0018] Figure 2 A schematic structural diagram of an active front-end rectifier according to an embodiment of the present application is shown;

[0019] Figure 3 A schematic structural diagram of a passive front-end rectifier according to an embodiment of the present application is shown;

[0020] Figure 4 A schematic structural diagram of another power system based on variable frequency drive according to an embodiment of the present application is shown;

[0021] Figure 5 A schematic structural diagram of an electric power device according to an embodiment of the present application is shown.

[0022] The above drawings include the following reference numerals:

[0023] 100, power device; 101, induction motor; 102, power equipment; 103, first generator set; 104, second generator set; 105, first bus; 106, second bus; 107, feeder; 108, first constant power load; 109, step-down transformer; 110, second constant power load; 200, variable frequency drive; 201, frequency conversion unit; 202, active front-end rectifier; 203, passive front-end rectifier; 204, first H-bridge; 205, second H-bridge; 206, first capacitor; 207, first transistor; 208, second transistor; 209, third transistor; 210, a fourth transistor; 211, a fifth transistor; 212, a sixth transistor; 213, a seventh transistor; 214, an eighth transistor; 215, a ninth transistor; 216, a tenth transistor; 217, a rectifier bridge; 218, a second capacitor; 219, a third H-bridge; 220, a first diode; 221, a second diode; 222, a third diode; 223, a fourth diode; 224, a fifth diode; 225, a sixth diode; 226, an eleventh transistor; 227, a twelfth transistor; 228, a thirteenth transistor; 229, a fourteenth transistor; 230, an isolation transformer. DETAILED DESCRIPTION

[0024] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0025] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0026] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be intermediate elements. Moreover, in the specification and claims, when an element is described as being "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element through a third element.

[0027] As introduced in the background technology, the performance of the existing power system is not high. In order to solve the above technical problems, this application proposes a power system based on variable frequency drive and a floating liquefied natural gas production, storage and unloading device.

[0028] Figure 1 is a schematic diagram of the structure of a power system based on variable frequency drive according to an embodiment of the present application. Figure 1 As shown, the power system based on variable frequency drive includes:

[0029] The electric device 100 comprises at least a plurality of induction motors 101 and electric equipment 102, wherein the induction motors 101 are used to electrically drive the electric equipment 102, and the electric equipment 102 comprises at least one of a water injection pump and a gas compression device;

[0030] Specifically, the above-mentioned power device can be applied to the fields of industrial production, transportation, communication and information technology, new energy industry, aerospace, etc. The main function of the induction motor is to convert electrical energy into mechanical energy for driving various equipment and machinery. It operates through the induction principle and rotating magnetic field. It is usually used in various equipment and machinery in industrial production, such as fans, pumps, compressors, conveyor belts, etc. The induction motor has the advantages of high efficiency, reliability, and low cost.

[0031] The variable frequency drive 200 is electrically connected to the input end of at least one of the induction motors 101. The variable frequency drive 200 is used to variable frequency drive the power device 100. The variable frequency drive 200 includes at least a plurality of frequency conversion units 201. One of the frequency conversion units 201 includes an active front-end rectifier 202 and a passive front-end rectifier 203.

[0032] Specifically, the variable frequency drive is a power electronic device that adjusts the speed and torque of an AC motor, and achieves continuous adjustment of the motor's operating speed by changing the frequency and voltage of the motor's power supply. The passive front-end rectifier is the rectifier part of the inverter, which only contains uncontrolled devices and cannot actively control the input current; while the active front-end rectifier contains controllable switching devices, which can achieve control of the input current and reactive power.

[0033] In the above embodiment, a power system based on variable frequency drive is provided, including a power device and a variable frequency drive, the power device at least includes a plurality of induction motors and power equipment, the induction motor is used to electrically drive the power equipment, and the power equipment includes at least one of a water injection pump and a gas compression device; the variable frequency drive is electrically connected to the input end of at least one induction motor, the variable frequency drive is used to variable frequency drive the power device, the variable frequency drive at least includes a plurality of frequency conversion units, and one frequency conversion unit includes an active front-end rectifier and a passive front-end rectifier. By introducing a variable frequency drive into the power system, especially by combining a passive front-end and an active front-end rectifier, the motor of the power system can be soft-started, the short-circuit current can be reduced, a stronger voltage drop resistance and energy-saving operation can be provided, and the reactive power exchange with the power grid can be effectively controlled, thereby improving the power factor, reducing the system load, improving the power quality and overall performance of the power system, and solving the problem of low performance of the power system.

[0034] In one embodiment, Figure 2As shown, the active front end rectifier includes a first H-bridge 204, a second H-bridge 205 and a first capacitor 206, the first end of the first H-bridge 204, the first end of the second H-bridge 205 and the first end of the first capacitor 206 are electrically connected, the second end of the first H-bridge 204, the second end of the second H-bridge 205 and the second end of the first capacitor 206 are electrically connected, the first H-bridge 204 includes a first transistor 207, a second transistor 208, a third transistor 209, a fourth transistor 210, a fifth transistor 211 and a sixth transistor 212, the first end of the first transistor 207, the first end of the second transistor 208 and the first end of the third transistor 209 are electrically connected and are the first end of the first H-bridge 204, the second end of the first transistor 207 is electrically connected to the first end of the fourth transistor 210, the second end of the second transistor 208 is electrically connected to the fifth transistor 211 1, the second end of the third transistor 209 is electrically connected to the first end of the sixth transistor 212, the second ends of the fourth transistor 210, the fifth transistor 211 and the sixth transistor 212 are electrically connected and form the second end of the first H-bridge 204, the second H-bridge 205 includes a seventh transistor 213, an eighth transistor 214, a ninth transistor 215 and a tenth transistor 216, the first end of the seventh transistor 213 is electrically connected to the first end of the eighth transistor 214 and forms the first end of the second H-bridge 205, the second end of the seventh transistor 213 is electrically connected to the first end of the ninth transistor 215, the second end of the eighth transistor 214 is electrically connected to the first end of the tenth transistor 216, the second end of the ninth transistor 215 is electrically connected to the second end of the tenth transistor 216 and forms the second end of the second H-bridge 205. This structure can further quickly realize the control of input current and reactive power.

[0035] Specifically, the first H-bridge is used to convert AC power into DC power; the first capacitor is used to smooth the output DC voltage and reduce the ripple voltage; the second H-bridge is used to adjust the stability of the output voltage. In addition, the active front-end rectifier also includes an input filter circuit and an output capacitor. The input filter circuit is used to remove high-frequency noise and interference in the input AC signal to make the input current more stable; the output capacitor is used to store electrical energy and provide a stable output voltage. The entire structure can achieve the functions of effective rectification of the input AC power and stable output of DC power through the combination of the above parts.

[0036] In another embodiment, the first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, the sixth transistor, the seventh transistor, the eighth transistor, the ninth transistor and the tenth transistor are insulated gate bipolar transistors, and the first capacitor is a DC link capacitor. This structure can further simplify the internal structure of the active front end rectifier.

[0037] Specifically, since the active front-end rectifier includes a controllable switching device such as an insulated gate bipolar transistor (IGBT), the input current and reactive power can be further quickly controlled.

[0038] In another embodiment, Figure 3 As shown, the passive front-end rectifier includes a rectifier bridge 217, a second capacitor 218 and a third H-bridge 219, the first end of the rectifier bridge 217, the first end of the second capacitor 218 and the first end of the third H-bridge 219 are electrically connected, the second end of the rectifier bridge 217, the second end of the second capacitor 218 and the second end of the third H-bridge 219 are electrically connected, the rectifier bridge 217 includes a first diode 220, a second diode 221, a third diode 222, a fourth diode 223, a fifth diode 224 and a sixth diode 225, the first end of the first diode 220, the first end of the second diode 221 and the first end of the third diode 222 are electrically connected and are the first end of the rectifier bridge 217, the second end of the first diode 220 is electrically connected to the first end of the fourth diode 223, the second end of the second diode 221 is electrically connected to the first end of the fifth diode 224 The third diode 222 is electrically connected to the first end of the sixth diode 225, the second end of the fourth diode 223, the fifth diode 224 and the second end of the sixth diode 225 are electrically connected and form the second end of the rectifier bridge 217, the third H-bridge 219 includes an eleventh transistor 226, a twelfth transistor 227, a thirteenth transistor 228 and a fourteenth transistor 229, the first end of the eleventh transistor 226 is electrically connected to the first end of the twelfth transistor 227 and forms the first end of the third H-bridge 219, the second end of the eleventh transistor 226 is electrically connected to the first end of the thirteenth transistor 228, the second end of the twelfth transistor 227 is electrically connected to the first end of the fourteenth transistor 229, the second end of the thirteenth transistor 228 is electrically connected to the second end of the fourteenth transistor 229 and forms the second end of the third H-bridge 219. This structure can further quickly realize the rectification function.

[0039] Specifically, a passive front-end rectifier is a rectifier that does not require an external power source. Its working principle is to use the conduction and cutoff of a diode to achieve a rectification function. It converts the input AC signal into a DC signal through the conduction and cutoff of a diode. The above-mentioned rectifier bridge plays a role of rectification, converting the input AC signal into a unidirectional current, and the second capacitor is used to smooth the output DC signal to ensure voltage stability.

[0040] In order to further simplify the internal structure of the passive front-end rectifier, the eleventh transistor, the twelfth transistor, the thirteenth transistor and the fourteenth transistor are insulated gate bipolar transistors, and the second capacitor is a DC link capacitor.

[0041] Specifically, DC link capacitors can store charge and energy in DC circuits, as well as provide voltage stability and filtering functions. It can help smooth DC voltage fluctuations, reduce noise and interference in the circuit, and also provide short-term power support.

[0042] In a specific embodiment, Figure 4 As shown, the frequency conversion driver further includes: an isolation transformer 230 electrically connected to the first ends of the plurality of frequency conversion units 201, and the isolation transformer 230 is used to convert the three-phase alternating current into the input voltage of the frequency conversion unit 201. This structure can further protect the frequency conversion unit.

[0043] Specifically, the main function of the above isolation transformer is to isolate the input and output circuits to prevent electrical interference and conduction between the circuits, so as to adapt to the needs of different electrical equipment and systems. In addition, the isolation transformer can also provide additional safety protection to prevent current overload and voltage fluctuations from damaging electrical equipment.

[0044] like Figure 5 As shown, the power device further includes: a first generator set 103, including a plurality of first generators, the input ends of the plurality of first generators are electrically connected to the first bus 105, and a part of the induction motors are electrically connected to the first bus 105; a second generator set 104, including a plurality of second generators, the input ends of the plurality of second generators are electrically connected to the second bus 106, and another part of the induction motors are electrically connected to the second bus 106; a feeder 107, a first end of the feeder 107 is electrically connected to the first bus 105, and a second end of the feeder 107 is electrically connected to the second bus 106. This circuit can further realize rapid power supply of the power system.

[0045] Specifically, the feeder is used to transmit electric energy from a power plant or substation to a user, and can also transmit electric energy from one place to another. In addition, the feeder can also be used to connect and distribute power grids to ensure a stable supply of electric energy.

[0046] In another specific embodiment, the power system is a power system of an FPSO, the first busbar is a busbar located on the deck, and the second busbar is a busbar located on the hull. The first generator is a gas generator, and the second generator may be a diesel generator.

[0047] The power device further includes: a first constant power load 108, the input end of which is electrically connected to the first bus 105. The circuit can further improve the power factor of the power system, making the system run more efficiently.

[0048] Specifically, the constant power load can simulate the actual load, provide a stable power load when testing power supplies and other electronic devices, and maintain a constant power factor, so that the power system can perform stable performance tests under different load conditions. At the same time, the constant power load can also provide accurate current and voltage waveforms to ensure that the device under test can work properly under various load conditions.

[0049] In another specific embodiment, the power device further includes: a step-down transformer 109, a first end of which is electrically connected to the first bus 105 or the second bus 106; and a second constant power load 110, a first end of which is electrically connected to the second end of the step-down transformer 109. This structure can further ensure stable power supply and effective energy utilization.

[0050] Specifically, the step-down transformer can reduce the voltage to an appropriate level, and the second constant power load can keep the power of the load constant to ensure stable voltage and power load in the power system.

[0051] An embodiment of the present application also provides a floating liquefied natural gas production storage and unloading device, comprising any one of the above-mentioned variable frequency drive-based power systems.

[0052] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0053] The power system based on variable frequency drive of the present application includes a power device and a variable frequency drive. The power device includes at least a plurality of induction motors and power equipment. The induction motor is used to electrically drive the power equipment. The power equipment includes at least one of a water injection pump and a gas compression device. The variable frequency drive is electrically connected to the input end of at least one induction motor. The variable frequency drive is used to variable frequency drive the power device. The variable frequency drive includes at least a plurality of variable frequency units. One variable frequency unit includes an active front-end rectifier and a passive front-end rectifier. By introducing a variable frequency drive into the power system, especially by combining a passive front-end and an active front-end rectifier, it is possible to achieve soft starting of the motor of the power system, reduce short-circuit current, provide stronger voltage sag resistance and energy-saving operation, and effectively control reactive power exchange with the power grid, thereby improving the power factor, reducing the system load, improving the power quality and overall performance of the power system, and solving the problem of low performance of the power system.

[0054] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A power system based on variable frequency drive, characterized in that: include: An electric device, comprising at least a plurality of induction motors and electric equipment, wherein the induction motors are used to electrically drive the electric equipment, and the electric equipment comprises at least one of a water injection pump and a gas compression device; A variable frequency drive is electrically connected to the input end of at least one of the induction motors, and is used to drive the power device in a variable frequency manner. The variable frequency drive includes at least a plurality of frequency conversion units, and one of the frequency conversion units includes an active front-end rectifier and a passive front-end rectifier.

2. The power system based on variable frequency drive according to claim 1, characterized in that: The active front end rectifier includes a first H-bridge, a second H-bridge and a first capacitor, wherein the first end of the first H-bridge, the first end of the second H-bridge and the first end of the first capacitor are electrically connected, and the second end of the first H-bridge, the second end of the second H-bridge and the second end of the first capacitor are electrically connected, and the first H-bridge includes a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor and a sixth transistor, wherein the first end of the first transistor, the first end of the second transistor and the first end of the third transistor are electrically connected and form the first end of the first H-bridge, the second end of the first transistor is electrically connected to the first end of the fourth transistor, and the second end of the second transistor is electrically connected to the first end of the fifth transistor. The second end of the third transistor is electrically connected to the first end of the sixth transistor, the second ends of the fourth transistor, the fifth transistor and the sixth transistor are electrically connected and form the second end of the first H-bridge, the second H-bridge includes a seventh transistor, an eighth transistor, a ninth transistor and a tenth transistor, the first end of the seventh transistor is electrically connected to the first end of the eighth transistor and forms the first end of the second H-bridge, the second end of the seventh transistor is electrically connected to the first end of the ninth transistor, the second end of the eighth transistor is electrically connected to the first end of the tenth transistor, the second end of the ninth transistor is electrically connected to the second end of the tenth transistor and forms the second end of the second H-bridge.

3. The power system based on variable frequency drive according to claim 2, characterized in that: The first transistor, the second transistor, the third transistor, the fourth transistor, the fifth transistor, the sixth transistor, the seventh transistor, the eighth transistor, the ninth transistor and the tenth transistor are insulated gate bipolar transistors, and the first capacitor is a DC link capacitor.

4. The power system based on variable frequency drive according to claim 1, characterized in that: The passive front-end rectifier includes a rectifier bridge, a second capacitor and a third H-bridge, the first end of the rectifier bridge, the first end of the second capacitor and the first end of the third H-bridge are electrically connected, the second end of the rectifier bridge, the second end of the second capacitor and the second end of the third H-bridge are electrically connected, the rectifier bridge includes a first diode, a second diode, a third diode, a fourth diode, a fifth diode and a sixth diode, the first end of the first diode, the first end of the second diode and the first end of the third diode are electrically connected and form the first end of the rectifier bridge, the second end of the first diode is electrically connected to the first end of the fourth diode, the second end of the second diode is electrically connected to the first end of the fifth diode, and the The second end of the third diode is electrically connected to the first end of the sixth diode, the second ends of the fourth diode, the fifth diode and the sixth diode are electrically connected and form the second end of the rectifier bridge, the third H-bridge includes an eleventh transistor, a twelfth transistor, a thirteenth transistor and a fourteenth transistor, the first end of the eleventh transistor is electrically connected to the first end of the twelfth transistor and forms the first end of the third H-bridge, the second end of the eleventh transistor is electrically connected to the first end of the thirteenth transistor, the second end of the twelfth transistor is electrically connected to the first end of the fourteenth transistor, the second end of the thirteenth transistor is electrically connected to the second end of the fourteenth transistor and forms the second end of the third H-bridge.

5. The power system based on variable frequency drive according to claim 4, characterized in that: The eleventh transistor, the twelfth transistor, the thirteenth transistor, and the fourteenth transistor are insulated gate bipolar transistors, and the second capacitor is a DC link capacitor.

6. The power system based on variable frequency drive according to claim 1, characterized in that: The variable frequency drive further comprises: An isolation transformer is electrically connected to the first ends of the plurality of frequency conversion units, and the isolation transformer is used to convert three-phase alternating current into an input voltage of the frequency conversion unit.

7. The power system based on variable frequency drive according to claim 1, characterized in that: The electric device further comprises: A first generator set includes a plurality of first generators, input ends of the plurality of first generators are electrically connected to a first bus, and a portion of the induction motors are electrically connected to the first bus; A second generator set includes a plurality of second generators, wherein input ends of the plurality of second generators are electrically connected to a second bus, and another part of the induction motors are electrically connected to the second bus; A feeder, wherein a first end of the feeder is electrically connected to the first busbar, and a second end of the feeder is electrically connected to the second busbar.

8. The power system based on variable frequency drive according to claim 7, characterized in that: The electric device further comprises: A first constant power load, wherein an input end of the first constant power load is electrically connected to the first bus.

9. The power system based on variable frequency drive according to claim 7, characterized in that: The electric device further comprises: a step-down transformer, wherein a first end of the step-down transformer is electrically connected to the first busbar or the second busbar; A second constant power load, wherein a first end of the second constant power load is electrically connected to a second end of the step-down transformer.

10. A floating liquefied natural gas production, storage and unloading device, characterized in that: A power system based on variable frequency drive comprising any one of claims 1 to 9.

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