Modular multilevel converter and power system using the same

Abstract

The invention relates to a modular multilevel converter and a power system using the same. The modular multilevel converter may include a first converter unit having a branch according to a preset phase, the branch having an upper arm and a lower arm, and each of the upper arm and the lower arm having a plurality of series-connected sub-modules, a first converter to convert DC power input to the input terminal into AC power having a phase, and to output the AC power through the first output terminal; the second converter unit converts the DC power input to the input terminal into AC power having a lower voltage level than the AC power output from the first converter, and outputs the AC power through the second output terminal.

Description

Technical Field

[0001] The embodiments disclosed in this specification relate to modular multilevel converters and power systems using such converters. Background Art

[0002] Generally, a modular multilevel converter (MMC) achieves high-voltage output through cascaded connections between multiple converter valve sub-module units. The modular multilevel converter does not need to be directly cascaded with switching elements and has low requirements for the triggering consistency of components. In addition, the modular multilevel converter has excellent scalability, low switching frequency, low operating losses, and high-quality output voltage waveforms.

[0003] Therefore, there has emerged a need to use modular multilevel converters in the power systems of ships. Summary of the Invention

[0004] Technical Problem

[0005] The embodiments disclosed in this specification provide a power system using a modular multilevel converter.

[0006] The embodiments disclosed in this specification provide a power system for reducing the cost of operating large electric propulsion ships.

[0007] The embodiments disclosed in this specification provide a power system that is easy to interoperate with multiple energy sources when operating large electric propulsion ships.

[0008] The embodiments disclosed in this specification provide a power system for effectively utilizing the limited space on a ship.

[0009] The technical problems to be solved by the present disclosure are not limited to the above problems, and those skilled in the art to which the present disclosure pertains will clearly understand any other technical problems not mentioned herein through the following description.

[0010] Technical Solution

[0011] According to the embodiments disclosed in this specification, the modular multilevel converter may include: a first converter device having a leg according to a preset phase, the leg having an upper arm and a lower arm, and each of the upper arm and the lower arm including a plurality of sub-modules connected in series to convert the direct current (DC) power input to the input terminal into alternating current (AC) power having a phase and output the AC power through a first output terminal; and a second converter device that converts the DC power input to the input terminal into AC power having a voltage level lower than the voltage level of the AC power output from the first converter device and outputs the AC power through a second output terminal.

[0012] In an embodiment, the second converter device may include at least one of a first low-voltage converter device or a second low-voltage converter device, where the first low-voltage converter device is composed of a plurality of additional sub-modules connected in series with the upper arm of a branch of the first converter device in a full-bridge manner, the plurality of adjacent additional sub-modules are connected in parallel with each other, and the plurality of additional sub-modules convert the DC power of the input terminal into AC power with a voltage level lower than the voltage level of the AC power output from the first converter device; the second low-voltage converter device is composed of a plurality of additional sub-modules connected in series with the lower arm of a branch of the first converter device in a full-bridge manner, the plurality of adjacent additional sub-modules are connected in parallel with each other, and the plurality of additional sub-modules convert the DC power of the input terminal into AC power with a voltage level lower than the voltage level of the AC power output from the first converter device.

[0013] In an embodiment, the modular multilevel converter may further include a controller for controlling the power conversion of the first low-voltage converter device and the second low-voltage converter device.

[0014] In an embodiment, the first converter device may be a bidirectional converter that, when AC power is input to the first output terminal, converts the AC power input to the first output terminal into a preset DC power and outputs the preset DC power to the input terminal.

[0015] In an embodiment, the first converter device and the second converter device may convert the DC power of the input terminal into three-phase AC power with different voltage levels and output the three-phase AC power.

[0016] According to the embodiments disclosed in this specification, the power system may include: a first modular multilevel converter having a plurality of output terminals; a propulsion motor that receives AC power from a first output terminal among the plurality of output terminals, a low-voltage alternating current (LVAC) distribution device that receives AC power from a second output terminal among the plurality of output terminals, and a medium-voltage direct current (MVDC) distribution device that supplies DC power to the first modular multilevel converter.

[0017] In an embodiment, the voltage level of the AC power output through the second output terminal may be lower than the voltage level of the AC power output through the first output terminal.

[0018] In an embodiment, the DC power supplied to the first modular multilevel converter by the MVDC distribution device may be directly or indirectly generated by at least one of an energy storage system, a fuel cell system, or a generator.

[0019] In an embodiment, the power system may further include a second modular multilevel converter, which is electrically connected to the generator and the MVDC power distribution device, and the second modular multilevel converter includes at least one output terminal.

[0020] In an embodiment, the second modular multilevel converter may have a third output terminal for outputting DC power to the MVDC power distribution device, and a fourth output terminal for outputting AC power to the service load power distribution device.

[0021] In an embodiment, the second modular multilevel converter may have a fifth output terminal for outputting DC power to the MVDC power distribution device, and a sixth output terminal for outputting DC power to the service load power distribution device.

[0022] In an embodiment, the voltage level of the DC power output through the sixth output terminal can be lower than the voltage level of the DC power output through the fifth output terminal.

[0023] In an embodiment, the second output terminal and the LVAC power distribution device can be electrically connected through an isolation transformer.

[0024] In an embodiment, the isolation transformer can be one of a double-winding transformer and a three-winding transformer.

[0025] In an embodiment, the power system may further include a bus tie connected to the MVDC power distribution device and exchanging DC power with another power system.

[0026] Advantageous Effects

[0027] The embodiments disclosed in this specification can provide a power system using a modular multilevel converter.

[0028] The embodiments disclosed in this specification can provide a power system for reducing the cost of operating a large electric propulsion ship.

[0029] The embodiments disclosed in this specification can provide a power system that is easy to interoperate with multiple energy sources when operating a large electric propulsion ship.

[0030] The embodiments disclosed in this specification can provide a power system for effectively utilizing the limited space on board a ship.

[0031] In addition, various effects that can be directly or indirectly understood through the present disclosure can be provided. Brief Description of the Drawings

[0032] Figure 1 is a schematic diagram schematically illustrating a modular multilevel converter according to an embodiment disclosed in this specification.

[0033] Figure 2It is a schematic circuit diagram of a sub-module of a modular multilevel converter according to an embodiment disclosed in this specification.

[0034] Figure 3 It is a schematic diagram schematically illustrating a modular multilevel converter according to an embodiment disclosed in this specification.

[0035] Figures 4a to 4c It is a schematic diagram of a modular multilevel converter and a power system using the converter according to an embodiment disclosed in this specification.

[0036] Figures 5a to 5b It is a schematic diagram of a power system in which a modular multilevel converter with a single output terminal according to an embodiment disclosed in this specification is placed between an MVDC power distribution device and a propulsion motor.

[0037] Figures 6a to 6c It is a schematic diagram of a power system in which a modular multilevel converter according to an embodiment disclosed in this specification is additionally placed between an MVDC power distribution device and a generator.

[0038] Figure 7a and Figure 7b It is a schematic diagram of a power system in which a modular multilevel converter with multiple output terminals according to an embodiment disclosed in this specification is placed between an MVDC power distribution device and a propulsion motor.

[0039] Figures 8a to 8c It is a schematic diagram of a power system in which a modular multilevel converter according to an embodiment disclosed in this specification is additionally placed between an MVDC power distribution device and a generator.

[0040] Figure 9a and Figure 9b It is a schematic diagram of a power system in which a modular multilevel converter with multiple output terminals according to an embodiment disclosed in this specification is placed between an MVDC power distribution device and a propulsion motor.

[0041] Figures 10a to 10c It is a schematic diagram of a power system in which a modular multilevel converter according to an embodiment disclosed in this specification is additionally placed between an MVDC power distribution device and a generator.

[0042] Figures 11a to 11e It is a schematic diagram of a power system in which a modular multilevel converter according to an embodiment disclosed in this specification is placed between an MVAC power distribution device and a propulsion motor.

[0043] Figure 12It is a schematic diagram showing a modular multilevel converter and a rectifier according to an embodiment disclosed in this specification.

[0044] Figures 13a to 13c It is a schematic diagram of a power system in which a modular multilevel converter according to an embodiment disclosed in this specification is placed between an MVDC power distribution device and a generator.

[0045] Figures 14a to 14j It is a schematic diagram of a power system in which a modular multilevel converter according to an embodiment disclosed in this specification is additionally placed between an MVDC power distribution device and a propulsion motor.

[0046] Figures 15a to 15d It schematically shows a power system according to an embodiment disclosed in this specification, in which the power grids of essential loads and service loads are separated from each other.

[0047] Regarding the description of the drawings, the same or similar components may be labeled with the same or similar reference numerals. Detailed Description of the Embodiment

[0048] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the drawings. When adding reference numerals to the components in each drawing, it should be noted that although the same components appear in another drawing, they include the same reference numerals. When describing the embodiments disclosed in this specification, the detailed description of known functions or configurations may be omitted when it may unnecessarily make the subject matter of the present disclosure difficult to understand.

[0049] When describing the elements of the exemplary embodiments of the present disclosure, terms such as first, second, A, B, (a), (b), etc. may be used herein. These terms are only used to distinguish one element from another element, but do not limit the corresponding element without considering the nature, order, and priority of the corresponding element. In addition, unless otherwise defined, all terms (including technical and scientific terms) used in the present disclosure should be interpreted in accordance with the common practice in the field to which the present disclosure belongs. It should be understood that the terms used in the present disclosure should be interpreted to include meanings consistent with their meanings in the text of the present disclosure and the related fields, and should not be interpreted as idealized or overly formal meanings unless explicitly defined in this specification.

[0050] Hereinafter, the embodiments disclosed in this specification will be described in detail with reference to the drawings.

[0051] Figure 1 It is a schematic diagram showing a modular multilevel converter having a single output terminal.

[0052] Reference Figure 1, A modular multilevel converter with a single output terminal may include a plurality of submodule (SM) units (CELL), and may drive a load (such as a propulsion motor, etc.) by converting input DC power (e.g., medium-voltage direct current (MVDC)) into AC power with a phase (e.g., low-voltage alternating current (LVAC)) and outputting the AC power through a single output terminal.

[0053] Figure 2 is a schematic circuit diagram of a submodule of a modular multilevel converter.

[0054] Reference Figure 2 , the submodule (SM) can be implemented in a half-wave bridge or full-wave bridge manner, and can also be implemented in other circuits. The submodule (SM) can perform switching operations under the control of a controller.

[0055] For reference, Figure 2 the submodule shown can be equipped in Figure 1 a modular multilevel converter with a single output terminal, but is not limited thereto, and can also be equipped in a modular multilevel converter with multiple output terminals that will be referenced subsequently Figure 3 , Figure 4a and Figure 4b described.

[0056] Figure 3 is a schematic diagram showing a modular multilevel converter (100) with multiple output terminals according to an embodiment disclosed in the present specification. That is, it can be understood that Figure 1 the modular multilevel converter shown has a single output terminal, but Figure 3 the modular multilevel converter shown has multiple output terminals.

[0057] Reference Figure 3 , the modular multilevel converter (100) may include a first converter device (110) and a second converter device (121, 122).

[0058] For example, the first converter device (110) can convert the DC power input to the input terminal into AC power with a phase, and can output the AC power to the output terminal. For example, the first converter device (110) may have a plurality of branches according to a preset phase. In this case, each of the plurality of branches may have an upper arm and a lower arm, and each of the upper arm and the lower arm may include a plurality of submodules (SM). Hereinafter, this will be described in more detail in the description of Figure 4a .

[0059] For reference, in Figure 3 , for convenience, an example in which a motor is used as a load is shown, but the type of load that receives power from the modular multilevel converter is not limited to a motor. Other types of loads other than the motor can receive power from the modular multilevel converter.

[0060] Meanwhile, separated from the AC power of each branch from the first converter device (110), the second converter devices (121 and 122) can convert the DC power input to the input terminals into power (AC power or DC power) whose voltage level is lower than the voltage level of the AC power output from the first converter device (110).

[0061] For example, the second converter device may include at least one of a first low-voltage converter device (121) and a second low-voltage converter device (122). For reference, for better understanding, Figure 3 both the first low-voltage converter device (121) and the second low-voltage converter device (122) are shown, but this does not exclude the fact that the second converter device is only located at one of the upper end or the lower end of the first converter device (110). In other words, the first low-voltage converter device (121) may be only located at the upper end of the first converter device (110), or the second low-voltage converter device (122) may be only located at the lower end of the first converter device (110).

[0062] For example, the first low-voltage converter device (121) can convert the DC power from the input terminals into power whose voltage level is lower than the voltage level of the AC power output from the first converter device (110), and can output power with that voltage level.

[0063] For example, the second low-voltage converter device (122) can convert the DC power from the input terminals into AC power whose voltage level is lower than the voltage level of the AC power output from the first converter device (110), and can output AC power with that voltage level.

[0064] That is to say, the modular multilevel converter (100) according to the embodiments disclosed in this specification may have multiple output terminals (the first output terminal corresponding to the first converter device and the second output terminal corresponding to the second converter device), so as to provide low-voltage power and medium-voltage power simultaneously.

[0065] For reference, depending on the structure of the second converter device, the type of power output from the output terminals of the second converter device (i.e., the auxiliary output terminals) can be different. Among them, the modular multilevel converter with auxiliary output terminals that output AC power will be described later with reference to Figure 4a for details.

[0066] Figure 4a It is a schematic diagram showing a modular multilevel converter (100) with multiple output terminals according to an embodiment disclosed in this specification.

[0067] Reference Figure 4a , the modular multilevel converter (100) may include a first converter device (110) and a second converter device (120). In this case, the modular multilevel converter (100) may further include a controller (130).

[0068] For example, the first converter device (110) may have branches (L1, L2, L3) according to a preset phase. The branches (L1, L2, L3) may respectively have upper arms (UA1, UA2, UA3) and lower arms (LA1, LA2, LA3). The upper arms (UA1, UA2, UA3) and the lower arms (LA1, LA2, LA3) may each have a plurality of sub-modules (SM) connected in series to convert the input DC power into AC power with a phase.

[0069] For example, the DC power input to the first converter device (110) may be medium-voltage DC power (MVDC). The first converter device (110) may convert the DC power into AC power to drive a load. In this case, the converted AC power may be three-phase AC power.

[0070] As a reference, in Figure 4a , for convenience, an example of a motor as a load is shown, but the type of load receiving power from the modular multilevel converter is not limited to a motor. Other types of loads other than a motor may receive power from the modular multilevel converter.

[0071] In this case, the first to third branches (L1, L2, L3) may respectively have upper arms (UA1, UA2, UA3) and lower arms (LA1, LA2, LA3). The upper arms (UA1, UA2, UA3) and the lower arms (LA1, LA2, LA3) respectively included in the first to third branches (L1, L2, L3) may have "N" sub-modules (SM) connected in series (where "N" is a natural number). The voltage of the upper arm or the lower arm of one branch may be the voltage (Vmvdc) of the medium-voltage DC power (MVDC) input to the input terminal. The voltage between the upper and lower ends of the ground (gnd) and the DC power terminal may be shown as 0.5Vmvdc.

[0072] For example, the first converter device (110) may convert the DC power input to the input terminal into AC power with a phase and output the AC power to the output terminal.

[0073] As a reference, referring to Figure 2The sub-modules are described, so redundant descriptions will be omitted.

[0074] Meanwhile, separated from the AC power of each branch (L1, L2, L3) of the first converter device (110), the second converter device (120) can convert the DC power input to the input terminal into AC power with a voltage level lower than the voltage level of the AC power output from the first converter device (110).

[0075] For example, the second converter device (120) may include a first low-voltage converter device (121) and a second low-voltage converter device (122).

[0076] For example, the first low-voltage converter device (121) can be implemented using a plurality of additional sub-modules configured in a full-bridge configuration. Each additional sub-module can be connected in series with each of the upper arms (UA1, UA2, UA3) corresponding to the branches (L1, L2, L3) of the first converter device (110) respectively. In addition, each additional sub-module connected in series with the upper arms (UA1, UA2, UA3) can be connected in parallel with each other. In this case, the first low-voltage converter device (121) can convert the DC power from the input terminal into AC power with a voltage level lower than the voltage level of the AC power output from the first converter device (110), and can output the AC power with that voltage level.

[0077] For example, the second low-voltage converter device (121) can be implemented using a plurality of additional sub-modules configured in a full-bridge configuration. Each additional sub-module can be connected in series with each of the lower arms (L1, L2, L3) corresponding to the branches (L1, L2, L3) of the first converter device (110) respectively. In addition, each additional sub-module connected in series with the lower arms (L1, L2, L3) can be connected in parallel with each other. The second low-voltage converter device (121) can convert the DC power from the input terminal into AC power with a voltage level lower than the voltage level of the AC power output from the first converter device (110), and can output the AC power with that voltage level.

[0078] Therefore, the modular multilevel converter (100) according to the embodiments disclosed in this specification can provide low-voltage AC power and medium-voltage AC power simultaneously. In other words, the modular multilevel converter (100) according to the embodiments disclosed in this specification can have a plurality of output terminals (a first output terminal and a second output terminal).

[0079] The modular multilevel converter (100) according to the embodiments disclosed in this specification may further include a controller (130). The controller (130) can control the power conversion operations of the first converter device (110) and the second converter device (120).

[0080] For example, the controller (130) may control the switching operations of the first low-voltage converter device (121) and the second low-voltage converter device (122) of the second converter device (120). Each switching circuit of the first low-voltage converter device (121) and the second low-voltage converter device (122) may, under the control of the controller (130), convert the power of the corresponding upper arm or the corresponding lower arm into AC power with a voltage level lower than the voltage level of the AC power of the first converter device (110) by performing a switching operation, and output the converted AC power.

[0081] In this case, the controller (130) may be composed of at least one processing unit and a memory. For example, the processing unit may include a central processing unit (CPU), a graphics processing unit (GPU), a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc., and may have multiple cores. The memory may be a volatile memory (such as a random access memory (RAM), etc.), a non-volatile memory (such as a read-only memory (ROM), a flash memory, etc.) or a combination thereof.

[0082] Figure 4b is a schematic diagram of a modular multilevel converter according to another embodiment disclosed in this specification.

[0083] Reference Figure 4b , a modular multilevel converter (200) according to another embodiment disclosed in this specification may include a first converter device (210), a second converter device (220), and a controller (230).

[0084] For example, Figure 4b the first converter device (210) shown may have the same configuration as Figure 4a the first converter device (110) shown. For example, the first converter device (210) may be a bidirectional converter. In the case where the first converter device (210) is a bidirectional converter, when medium-voltage AC power from a generator is input to the Figure 4a output terminal in Figure 4a , the first converter device (210) may output medium-voltage DC power to the

[0085] input terminal in Figure 4a . The low-voltage DC power may refer to DC power less than 1500V. The medium-voltage DC power may refer to DC power greater than 1500V and less than 100kV. Figure 4bThe modular multilevel converter (200) therein can receive input AC power, can output DC power through a first output terminal (the position corresponding to the input terminal in 4a), and can output AC power through a second output terminal (the position corresponding to Figure 4a the second output terminal in

[0086] The configuration and operation of each of the first converter device (210), the second converter device (220), and the controller (230) are the same as those in the description of Figure 4a , so the description of the configuration and operation is omitted.

[0087] Figure 4c is a schematic diagram of a power system using a modular multilevel converter with multiple output terminals according to an embodiment disclosed in the present specification.

[0088] For example, a power system using a modular multilevel converter with multiple output terminals according to an embodiment disclosed in the present specification can provide low-voltage AC power corresponding to a low-voltage load that requires low-voltage AC power through an auxiliary output terminal without a conventional transformer, as Figure 4c shown.

[0089] In this way, low-voltage AC power can be provided to the low-voltage load without installing an additional transformer, thereby reducing costs and reducing the weight and volume of the equipment.

[0090] Figure 5a and Figure 5b are schematic diagrams of a power system using a modular multilevel converter (MMC) according to an embodiment disclosed in the present specification.

[0091] As a reference, like the modular multilevel converter shown in Figure 1 , the modular multilevel converter (10) shown in Figures 5a to 5b can be a modular multilevel converter with a single output terminal.

[0092] As a reference, as shown in Figure 5a and Figure 5b , the modular multilevel converter 10 with a single output terminal can be used between a medium-voltage DC (MVDC) distribution device (20) and a propulsion motor (30), while a conventional inverter / converter or modular multilevel converter can be used between the MVDC distribution device (20) and other devices (for example, generators, large motors, etc.).

[0093] Refer to Figure 5a and 5b, A power system using a modular multilevel converter (10) with a single output terminal according to an embodiment disclosed in this specification may include an MVDC distribution device (20), a modular multilevel converter (10), and a propulsion (Prop.) motor (30). In this case, the modular multilevel converter (10) may be placed between the MVDC distribution device (20) and the propulsion motor (30).

[0094] When a general converter is used instead of the modular multilevel converter (10) between the MVDC distribution device (20) and the propulsion motor (30), the capacity of the power that the converter needs to handle becomes too large, and high-specification components are required to handle the capacity of the power, which inevitably leads to problems in terms of parts supply and cost.

[0095] On the other hand, the modular multilevel converter includes a plurality of sub-modules. Therefore, even when the modular multilevel converter is connected to a large-capacity power (distribution device), the capacity that each sub-module needs to handle will be reduced.

[0096] Therefore, components with general specifications can be used by using a modular multilevel converter in a large power propulsion ship with a propulsion motor that requires a large capacity of power, thereby ensuring competitiveness in terms of parts supply and price.

[0097] In addition, since the modular multilevel converter can be used by flexibly adding or removing sub-modules according to the situation, the modular multilevel converter has an advantage in terms of scalability.

[0098] In addition, by applying the MVDC distribution device to a large power propulsion ship, it is easier to interoperate with other energy sources (power supplies), and the robustness of the system can be improved.

[0099] Meanwhile, as Figure 5a and Figure 5b shown, when the modular multilevel converter (10) located between the MVDC distribution device (20) and the propulsion motor (30) has a single output terminal, an additional inverter may be required to supply power to a service load or a corresponding LVAC distribution device (LVAC).

[0100] For example, as Figure 5a shown, power can be transmitted from the MVDC distribution device (20) to the LVAC distribution device (LVAC) through a DC / AC power conversion device (40).

[0101] Another example is that, as Figure 5bAs shown, power can first be transmitted from the MVDC power distribution device (20) to the LVDC power distribution device (LVDC) through the DC / DC power conversion device (40), and second, power can be transmitted from the LVDC power distribution device (LVDC) to the LVAC power distribution device (LVAC) through the DC / AC power conversion device.

[0102] In addition, a power supply can be additionally included. For example, as Figure 5a and Figure 5b shown, at least a part of an energy storage system (ESS), a fuel cell system (SOFC), a diesel generator (DG), and a shaft generator can be additionally included.

[0103] For example, the capacity of a large motor (e.g., several hundred kilowatts to several megawatts) may be smaller than the capacity of a propulsion motor (e.g., 10 megawatts or more). In this case, the large motor can be connected differently according to the line type. When the large motor is connected to the MVDC, the step of increasing the voltage when the voltage transfers from Aft to Fwd can be omitted. Therefore, considering that the size of a large-capacity medium-voltage motor is smaller than that of a large-capacity low-voltage motor, a medium-voltage motor can be used, thereby reducing the size of the motor.

[0104] For example, a power conversion device can be used to transfer the power provided by the power supply to the MVDC power distribution device (20). In this case, as Figure 5a and Figure 5b shown, a general inverter or converter can be used as the power conversion device, but it is not limited thereto. A modular multilevel converter with a single output terminal or multiple output terminals can be used.

[0105] Figures 6a to 6c An embodiment is shown in which a modular multilevel converter (50) with a single output terminal or multiple output terminals is additionally placed between the MVDC power distribution device (20) and the generator (DG) (60). In the power system, as Figure 5a and Figure 5b depicted, a modular multilevel converter (10) with a single output terminal is placed between the MVDC power distribution device (20) and the propulsion motor (30).

[0106] As a reference, as Figures 6a to 6c shown, a modular multilevel converter (10) with a single output terminal can be used between the MVDC power distribution device (20) and the propulsion motor (30), while a general inverter / converter or a modular multilevel converter can be used between the MVDC power distribution device (20) and other devices (e.g., an energy storage system, a large motor, etc.) except the generator (60).

[0107] First, referring toFigure 6a , it can be seen that a modular multilevel converter (50) having a single output terminal is additionally placed between the MVDC power distribution device (20) and the generator (60). As described above, the modular multilevel converter includes a plurality of sub-modules. Therefore, even when the modular multilevel converter is connected to a large-capacity power source (generator), the capacity that each sub-module needs to handle is reduced.

[0108] In addition, referring to Figure 6b , it can be seen that a modular multilevel converter (50) having a plurality of output terminals is additionally placed between the MVDC power distribution device (20) and the generator (60). In this case, it can be seen that the main output terminal (medium-voltage DC power output terminal) of the modular multilevel converter (50) having a plurality of output terminals transmits power to the MVDC power distribution device (20), while the auxiliary output terminal (low-voltage AC power output terminal) transmits power to the service load (LVAC). For example, Figure 6b The modular multilevel converter (50) having a plurality of output terminals shown can be the same / similar in structure and operation to the Figure 4b modular multilevel converter (200) shown.

[0109] In this case, to prevent accidents, the modular multilevel converter (50) having a plurality of output terminals and the service load (LVAC) can be electrically connected through an isolation transformer. In this case, the isolation transformer can be a two-winding transformer or a three-winding transformer. For reference, two two-winding transformers may be required, or one three-winding transformer may be required.

[0110] In addition, referring to Figure 6c , it can be seen that a modular multilevel converter (50) having a plurality of output terminals is additionally placed between the MVDC power distribution device (20) and the generator (60). In this case, it can be seen that the main output terminal (medium-voltage DC power output terminal) of the modular multilevel converter (50) having a plurality of output terminals transmits power to the MVDC power distribution device (20), while the auxiliary output terminal (low-voltage DC power output terminal) transmits power to the service load (LVDC).

[0111] In addition, the power system according to the embodiments disclosed in this specification may additionally include a bus tie for exchanging power with another power system.

[0112] For example, the bus tie can be located between the first power system and the second power system, and the bus tie can include a bus tie breaker for controlling the connection and disconnection between the first power system and the second power system. In this case, the bus tie breaker can be as Figure 5aThe solid state circuit breaker (SSCB) shown, but not limited to this, can also be a mechanical circuit breaker.

[0113] For reference, in the description given below, those skilled in the art will easily understand the same description as the above reference Figures 1 to 6c given description, so these descriptions will be omitted.

[0114] Figure 7a and Figure 7b is a schematic diagram of a power system using a modular multilevel converter (10) with multiple output terminals according to an embodiment disclosed in this specification. In this case, similar to Figure 4a the modular multilevel converter (100) shown, Figures 7a to 7b the modular multilevel converter shown can be a modular multilevel converter with multiple output terminals. In addition, the first output terminal among the multiple output terminals can output medium voltage AC power for driving the propulsion motor (30), and its second output terminal can output low voltage AC power.

[0115] For reference, as shown in Figure 7a and Figure 7b shown, the modular multilevel converter (10) with multiple output terminals can be used between the MVDC distribution device (20) and the propulsion motor (30), while a general inverter / converter or modular multilevel converter can be used between the MVDC distribution device (20) and other devices (such as energy storage systems, large motors, etc.).

[0116] Referring to Figure 7a and Figure 7b , the power system using the modular multilevel converter (10) with multiple output terminals can include an MVDC distribution device (20), an LVAC distribution device (LVAC) (70), a modular multilevel converter (10), and a propulsion (Prop.) motor (30). In this case, the modular multilevel converter (10) can be placed between the MVDC distribution device (20) and the propulsion motor (30).

[0117] Different from the power system using a modular multilevel converter with a single output terminal as shown in Figure 5a and Figure 5b shown, the modular multilevel converter (10) of the power system as shown in Figure 7a and Figure 7b shown has multiple output terminals, so there is no need for an additional separate inverter to supply power to the service load or its corresponding LVAC distribution device (70). Accordingly, the power system can be implemented smaller and simpler, thereby reducing the number of required components, improving productivity, and being easy to manage and maintain.

[0118] For example, at least a part of an energy storage system (ESS), a fuel cell system (SOFC), a diesel generator (DG), and a shaft generator can be used as a power source for supplying power to an MVDC power distribution device (20).

[0119] For example, an energy storage system (ESS) and a fuel cell system (SOFC) can directly generate DC power to supply power to an MVDC power distribution device (20). That is, a separate AC / DC conversion process may not be required.

[0120] Another example is that a diesel generator (DG) and a shaft generator can indirectly generate DC power for supplying an MVDC power distribution device (20). That is, a separate process may be required to convert the AC power generated by the diesel generator (DG) and the shaft generator into DC power.

[0121] In addition, to prevent accidents, a modular multilevel converter (10) having multiple output terminals and a service load (70) can be electrically connected through an isolation transformer. In this case, the isolation transformer can be a two-winding transformer or a three-winding transformer.

[0122] Figures 8a to 8c An embodiment is shown in which a modular multilevel converter (50) having a single output terminal or multiple output terminals is additionally placed between an MVDC power distribution device (20) and a generator (60) in a power system, in which Figure 7a and Figure 7b a modular multilevel converter (10) having multiple output terminals is placed between an MVDC power distribution device (20) and a propulsion motor (30).

[0123] As a reference, as Figures 8a to 8c shown, a modular multilevel converter (10) having multiple output terminals can be used between an MVDC power distribution device (20) and a propulsion motor (30), while a general inverter / converter or a modular multilevel converter can be used between an MVDC power distribution device (20) and other devices (such as an energy storage system, a large motor, etc.) other than a generator.

[0124] First, referring to Figure 8a , it can be seen that a modular multilevel converter (50) having a single output terminal is additionally placed between an MVDC power distribution device (20) and a generator (60). As described above, the modular multilevel converter (50) includes a plurality of sub-modules. Therefore, even when the modular multilevel converter (50) is connected to a large-capacity power source (generator), the capacity that each sub-module needs to handle is reduced.

[0125] In addition, referring to Figure 8b, it can be seen that a modular multilevel converter (50) with multiple output terminals is additionally placed between the MVDC power distribution device (20) and the generator (60). In this case, it can be seen that the main output terminal (medium-voltage DC power output terminal) of the modular multilevel converter (50) with multiple output terminals transmits power to the MVDC power distribution device (20), while the auxiliary output terminal (low-voltage AC power output terminal) transmits power to the service load (LVAC). For example, Figure 8b the modular multilevel converter (50) with multiple output terminals shown placed between the MVDC power distribution device (20) and the generator (60) may have the same / similar structure as Figure 4b the following.

[0126] In this case, to prevent accidents, the modular multilevel converter (50) with multiple output terminals and the service load (LVAC) may be electrically connected through an isolation transformer. In this case, the isolation transformer may be a two-winding transformer or a three-winding transformer.

[0127] Furthermore, referring to Figure 8c , it can be seen that a modular multilevel converter (50) with multiple output terminals is additionally placed between the MVDC power distribution device (20) and the generator (60). In this case, it can be seen that the main output terminal (medium-voltage DC power output terminal) of the modular multilevel converter (50) with multiple output terminals transmits power to the MVDC power distribution device (20), while the auxiliary output terminal (low-voltage DC power output terminal) transmits power to the service load (LVDC). For example, power can first be transmitted from the modular multilevel converter (50) with multiple output terminals located between the MVDC power distribution device (20) and the generator (60) to the LVDC, and then can be transmitted from the LVDC to the LVAC through a DC / AC power conversion device.

[0128] Figure 9a and Figure 9b are schematic diagrams of a power system using a modular multilevel converter (10) with multiple output terminals according to the embodiments disclosed in this specification.

[0129] For reference, as shown in the above Figure 7a and Figure 7b , the modular multilevel converter with multiple output terminals may output medium-voltage AC power for driving the propulsion motor (30) through the first output terminal and may output low-voltage AC power LVAC through the second output terminal. On the other hand, as Figures 9a to 9bThe modular multilevel converter (10) with multiple output terminals as shown can output medium-voltage AC power for driving a propulsion motor (30) through a first output terminal, and can output low-voltage DC power (LVDC) through a second output terminal. Therefore, since the LVDC can be supplied to in-vehicle loads (such as LED lights) without adding a separate power conversion device, the power system can be made smaller and simpler, thus reducing the number of required components, improving productivity, and being easy to manage and maintain. The low-voltage AC power can refer to AC power less than 1000V, and the medium-voltage AC power can refer to AC power greater than 1000V and less than 35kV.

[0130] For reference, the modular multilevel converter (10) with multiple output terminals can be used between an MVDC power distribution device (20) and a propulsion motor (30), as Figure 9a and Figure 9b shown, while a general inverter / converter or modular multilevel converter can be used between the MVDC power distribution device (20) and other devices (such as an energy storage system, a large motor, etc.).

[0131] Reference Figure 9a and Figure 9b , a power system using the modular multilevel converter (10) with multiple output terminals can include an MVDC power distribution device (20), an LVDC power distribution device (LVAC) (80), a modular multilevel converter (10), and a propulsion (Prop.) motor (30). In this case, the modular multilevel converter (10) can be placed between the MVDC power distribution device (20) and the propulsion motor (30).

[0132] Similar to the power systems as Figure 7a and Figure 7b shown, the modular multilevel converter (10) of the power system as Figure 9a and Figure 9b shown has multiple output terminals, so no additional separate inverter / converter is required to supply power to the service load or the corresponding LVDC power distribution device (80).

[0133] For example, at least a part of an energy storage system (ESS), a fuel cell system (SOFC), a diesel generator (DG), and a shaft generator can be used as a power source for supplying power to the MVDC power distribution device (20).

[0134] For example, the energy storage system (ESS) and the fuel cell system (SOFC) can directly generate DC power to supply power to the MVDC power distribution device (20). That is, a separate AC / DC conversion process may not be required.

[0135] Another example is that a diesel generator (DG) and a shaft generator can indirectly generate DC power to supply power to the MVDC power distribution device (20). That is, a separate process may be required to convert the AC power generated by the diesel generator (DG) and the shaft generator into DC power.

[0136] Figures 10a to 10c An embodiment is shown in which a modular multilevel converter (50) having a single output terminal or multiple output terminals is additionally placed between the MVDC power distribution device (20) and the diesel generator (DG) in a power system, in which, as Figure 9a and Figure 9b described, a modular multilevel converter (10) having multiple output terminals is placed between the MVDC power distribution device (20) and the propulsion motor (30).

[0137] For reference, a modular multilevel converter (10) having multiple output terminals can be used between the MVDC power distribution device (20) and the propulsion motor (30) as Figures 10a to 10c shown, while a general inverter / converter or modular multilevel converter can be used between the MVDC power distribution device (20) and other devices other than the generator (e.g., an energy storage system, a large motor, etc.).

[0138] First, referring to Figure 10a , it can be seen that a modular multilevel converter (50) having a single output terminal is additionally placed between the MVDC power distribution device (20) and the generator. As described above, the modular multilevel converter (50) includes a plurality of sub-modules. Therefore, even when the modular multilevel converter (50) is connected to a high-capacity power source (generator), the capacity that each sub-module needs to handle is reduced.

[0139] In addition, referring to Figure 10b , it can be seen that a modular multilevel converter (50) having multiple output terminals is additionally placed between the MVDC power distribution device (20) and the generator (60). In this case, it can be seen that the main output terminal (medium-voltage DC power output terminal) of the modular multilevel converter (50) having multiple output terminals transmits power to the MVDC power distribution device (20), while the auxiliary output terminal (low-voltage AC power output terminal) transmits power to the service load (LVAC). For example, Figure 10b shown, the modular multilevel converter (50) having multiple output terminals located between the MVDC power distribution device (20) and the generator may have the same / similar structure as Figure 4b .

[0140] In this case, to prevent accidents, a modular multilevel converter (50) having multiple output terminals and a service load (LVAC) can be electrically connected via an isolation transformer. In this case, the isolation transformer can be a two-winding transformer or a three-winding transformer.

[0141] In addition, referring to Figure 10c , it can be seen that a modular multilevel converter (50) having multiple output terminals is additionally placed between the MVDC power distribution device (20) and the generator. In this case, it can be seen that the main output terminals (medium-voltage DC power output terminals) of the modular multilevel converter (50) having multiple output terminals transmit power to the MVDC power distribution device (20), while the auxiliary output terminals (low-voltage DC power output terminals) transmit power to the service load (LVDC). For example, power can first be transmitted from the modular multilevel converter (50) having multiple output terminals placed between the MVDC power distribution device (20) and the generator to the LVDC, and secondly, power can be transmitted from the LVDC to the LVAC through a DC / AC power converter device.

[0142] Figure 11a is a schematic diagram of a power system including a modular multilevel converter having a single output terminal and a medium-voltage alternating current (MVAC) power distribution device (90) according to an embodiment disclosed in this specification.

[0143] For reference, as described in reference Figure 1 , since the modular multilevel converter (10) having a single output terminal as shown in Figure 11a receives medium-voltage DC power MVDC as input and outputs medium-voltage AC power for driving a load (e.g., a propulsion motor (30)), when the power system includes an MVAC power distribution device (90) instead of an MVDC power distribution device, after a rectifier (10_1) is additionally placed at the front end of the modular multilevel converter (10) having a single output terminal, the rectifier (10_1) can convert AC power into DC power and transmit the DC power to the modular multilevel converter.

[0144] For reference, the rectifier (10_1) and the modular multilevel converter (10) having a single output terminal can be used between the MVAC power distribution device (90) and the propulsion motor (30) as shown in Figure 11a . On the other hand, a general inverter / converter or a modular multilevel converter can be used between the MVAC power distribution device (90) and other devices (e.g., an energy storage system (ESS), a fuel cell system (SOFC), a large motor, etc.).

[0145] Figure 11b and Figure 11cSchematic diagram of a power system including a modular multilevel converter (10) having a plurality of output terminals and a medium voltage alternating current (MVAC) power distribution device (90) according to an embodiment disclosed in the present specification.

[0146] For reference, Figure 11b and Figure 11c The power system shown is generally similar to the Figure 11a power system shown, except that Figure 11b and Figure 11c the power system shown includes a modular multilevel converter having a plurality of output terminals instead of a modular multilevel converter having a single output terminal. In other words, due to the additional inclusion of auxiliary output terminals for outputting low voltage AC power, low voltage AC power corresponding to low voltage loads requiring low voltage AC power can be supplied without the Figure 11a power conversion device of the power system shown.

[0147] For reference, a rectifier (10_1) and a modular multilevel converter (10) having a plurality of output terminals can be used between an MVAC power distribution device (90) and a propulsion motor (30) as shown in Figure 11b and Figure 11c On the other hand, a general inverter / converter or modular multilevel converter can be used between an MVAC power distribution device (90) and other devices (e.g., an energy storage system, a large motor, etc.).

[0148] As Figure 11a the above description given, Figure 11b and Figure 11c in the power system shown, the modular multilevel converter (10) having a plurality of output terminals receives medium voltage DC power MVDC as input and outputs medium voltage AC power for driving a propulsion motor (30). Therefore, when the power system includes an MVAC power distribution device (90), a rectifier (10_1) can be additionally placed at the front end of the modular multilevel converter (10) having a plurality of output terminals.

[0149] In this case, to prevent accidents, the modular multilevel converter (10) having a plurality of output terminals and the service load (70) can be electrically connected through an isolation transformer. In this case, the isolation transformer can be a two-winding transformer or a three-winding transformer.

[0150] Figure 11d and Figure 11e Schematic diagrams of a power system including a modular multilevel converter (10) having a plurality of output terminals and an MVAC power distribution device according to an embodiment disclosed in the present specification.

[0151] For reference, Figure 11d andFigure 11e The power system shown is generally similar to Figure 11a the power system shown, but differs in that Figure 11d and Figure 11e the power system shown includes a modular multilevel converter having a plurality of output terminals instead of a modular multilevel converter having a single output terminal. In other words, due to the additional inclusion of auxiliary output terminals for outputting low-voltage DC power, low-voltage AC power corresponding to a low-voltage load requiring low-voltage DC power can be supplied without Figure 11a the power converter device (91) of the power system shown. In addition, Figure 11d and Figure 11e the power system shown is generally similar to Figure 11b and Figure 11c the power system shown, except that the auxiliary output terminals output DC power instead of AC power.

[0152] For reference, the rectifier (10_1) and the modular multilevel converter (10) having a plurality of output terminals can be used between the MVAC distribution device (90) and the propulsion motor (30) as shown in Figure 11d and Figure 11e On the other hand, a general inverter / converter or modular multilevel converter can be used between the MVAC distribution device (90) and other devices (e.g., energy storage system, large motor, etc.).

[0153] As Figure 11a described above, Figure 11d and Figure 11e in the power system shown, the modular multilevel converter (10) having a plurality of output terminals receives medium-voltage DC power MVDC as input and outputs medium-voltage AC power for driving the propulsion motor (30). Therefore, when the power system includes the MVAC distribution device (90), the rectifier (10_1) can be additionally placed at the front end of the modular multilevel converter (10) having a plurality of output terminals.

[0154] In addition, as shown in Figure 11d , the low-voltage DC power can be transmitted to the LVDC distribution device. However, as shown in Figure 11e , the power can first be transmitted to the LVDC distribution device, and secondly, the power can be transmitted from the LVDC distribution device to the LVAC distribution device through an inverter.

[0155] Meanwhile, Figures 11a to 11e the rectifier (10_1) shown can have the same / similar structure as the modular multilevel converter having a single output terminal, which will be described with reference to Figure 12 .

[0156] Figure 12It is a schematic diagram showing a modular multilevel converter (10) and a rectifier arranged at its front end.

[0157] Referring to Figure 12 , it can be seen that the rectifier (10_1) has the same / similar structure as the modular multilevel converter with a single output terminal described in Figure 1 . In other words, it can be seen that the rectifier receives medium-voltage AC power from the MVAC distribution device through the input terminal, converts the medium-voltage AC power to medium-voltage DC power MVDC, and outputs the medium-voltage DC power MVDC, and the modular multilevel converter (10) receives the medium-voltage DC power MVDC from the rectifier (10_1) through the input terminal, converts the medium-voltage DC power MVDC to AC power, and outputs the AC power to the load (such as a motor).

[0158] As a reference, for convenience, Figure 12 an example of using a propulsion motor as the load is shown, but the load of the power system according to the embodiments disclosed in this specification is not limited to the propulsion motor.

[0159] In addition, Figure 12 the modular multilevel converter shown can be a modular multilevel converter with a single output terminal as shown in Figure 11a , but is not limited thereto, and can be a modular multilevel converter with multiple output terminals as shown in Figure 11b and Figure 11c .

[0160] Figures 13a to 13c It is a schematic diagram of a power system, where the modular multilevel converter (50) according to the embodiments disclosed in this specification is located between the MVDC distribution device (20) and the generator (60).

[0161] For example, referring to Figure 13a , the power system may include an MVDC distribution device (20), a modular multilevel converter (50) with a single output terminal, and a generator (60). In this case, the modular multilevel converter (50) with a single output terminal can be placed between the MVDC distribution device (20) and the generator (60).

[0162] Another example is that, referring to Figure 13b and Figure 13c , the power system may include an MVDC distribution device (20), a modular multilevel converter (50) with multiple output terminals, and a generator (60). In this case, the modular multilevel converter (50) with multiple output terminals can be placed between the MVDC distribution device (20) and the generator (60).

[0163] Compared with using asFigure 13a is different from the power system of the modular multilevel converter having a single output terminal as shown in Figure 13b and 13c the modular multilevel converter (50) of the power system shown in has multiple output terminals, so there is no need for an additional separate inverter to supply power to the service load. In this case, the limited space on the ship can be effectively utilized and the maintenance becomes simple.

[0164] For reference, Figure 13b the modular multilevel converter (50) located between the MVDC distribution device (20) and the generator (60) in receives AC power from the generator (60), outputs DC power to the MVDC distribution device (70), and outputs low-voltage AC power LVAC to the LVAC distribution device (70) to supply AC power to the service load. On the other hand, Figure 13c the modular multilevel converter (50) located between the MVDC distribution device (20) and the generator (60) in receives AC power from the generator (60) to output DC power to the MVDC distribution device (20), and outputs low-voltage DC power LVDC to the LVDC distribution device (80) to supply AC power to the service load.

[0165] Conventional circuit breakers for MVDC distribution devices are expensive; conventional circuit breakers are large in size; and there are few commercial products for conventional circuit breakers. However, as shown in Figures 13a to 13c when the modular multilevel converter (50) is placed between the MVDC distribution device (20) and the generator (60), a power system without a circuit breaker can be achieved, thus overcoming the above problems.

[0166] Figures 14a to 14j shows an embodiment in which a modular multilevel converter (10) having a single output terminal or multiple output terminals is additionally placed between the MVDC distribution device (20) and the propulsion motor (30) in the power system, in the power system, as shown in Figure 13a and Figure 13c the modular multilevel converter (50) depicted is placed between the MVDC distribution device (20) and the generator (60).

[0167] First, referring to Figure 14a it can be seen that in the power system, a modular multilevel converter (10) having a single output terminal is additionally placed between the MVDC distribution device (20) and the propulsion motor (30), in which power system a modular multilevel converter (50) having a single output terminal is placed between the MVDC distribution device (20) and the generator (60).

[0168] In addition, referring to Figure 14b, it can be seen that in the power system, a modular multilevel converter (10) with multiple output terminals is additionally placed between the MVDC distribution device (20) and the propulsion motor (30). In this power system, a modular multilevel converter (50) with a single output terminal is placed between the MVDC distribution device (20) and the generator (60). For reference, Figure 14b illustrates (but is not limited to) a modular multilevel converter (10) with multiple output terminals that transmits low-voltage DC power to the LVDC distribution device (80) through an auxiliary output terminal (e.g., the second output terminal). For example, the modular multilevel converter (10) with multiple output terminals can also transmit low-voltage AC power to the LVAC distribution device through an auxiliary output terminal (e.g., the second output terminal).

[0169] In addition, referring to Figures 14c to 14e , it can be seen that in the power system, a modular multilevel converter (10) with a single output terminal or multiple output terminals is additionally placed between the MVDC distribution device (20) and the propulsion motor (30). In this power system, a modular multilevel converter (50) with multiple output terminals is placed between the MVDC distribution device (20) and the generator (60).

[0170] For reference, in Figure 14c it can be seen that a modular multilevel converter (10) with a single output terminal is additionally placed between the MVDC distribution device (20) and the propulsion motor (30), so an additional separate power conversion device 40 is required to supply power to the service load.

[0171] On the other hand, it can be seen that as shown in Figure 14d and Figure 14e , the modular multilevel converter (10) additionally placed between the MVDC distribution device (20) and the propulsion motor (30) has multiple output terminals, so no additional separate power converter device is required to supply power to the service load.

[0172] For reference, Figure 14d illustrates that a modular multilevel converter (10) with multiple output terminals transmits low-voltage AC power to the LVAC distribution device (70) through an auxiliary output terminal (e.g., the second output terminal). On the other hand, Figure 14e illustrates that a modular multilevel converter (10) with multiple output terminals transmits low-voltage DC power to the LVDC distribution device (80) through an auxiliary output terminal (e.g., the second output terminal).

[0173] In addition, referring to Figures 14f to 14j, it can be seen that in the power system, a modular multilevel converter (10) having a single output terminal or multiple output terminals is additionally placed between the MVDC distribution device (20) and the propulsion motor (30), and in this power system, a modular multilevel converter (50) having multiple output terminals is placed between the MVDC distribution device (20) and the generator (60).

[0174] As a reference, it can be seen that in Figures 14c to 14e the power system shown, the modular multilevel converter (50) having multiple output terminals placed between the MVDC distribution device (20) and the generator (60) receives medium-voltage AC power from the generator and outputs medium-voltage DC power and low-voltage AC power. On the other hand, it can be seen that in Figures 14f to 14j the power system shown, the modular multilevel converter (50) having multiple output terminals placed between the MVDC distribution device (20) and the generator (60) receives medium-voltage AC power from the generator (60) and outputs medium-voltage DC power and low-voltage DC power.

[0175] First, referring to Figures 14f to 14g , it can be seen that in the power system, a modular multilevel converter (10) having multiple output terminals is additionally placed between the MVDC distribution device (20) and the propulsion motor (30), and in this power system, a modular multilevel converter (50) having multiple output terminals is placed between the MVDC distribution device (20) and the generator (60). As a reference, Figure 14f shows that such an additionally placed modular multilevel converter (10) transmits low-voltage AC power to the LVAC distribution device (70) through an auxiliary output terminal (e.g., the second output terminal). On the other hand, Figure 14g shows that such an additionally placed modular multilevel converter (10) transmits low-voltage DC power to the LVDC distribution device (80) through an auxiliary output terminal (e.g., the second output terminal).

[0176] In addition, Figure 14h the power system shown is the same as Figure 14f the power system shown in that the power from the modular multilevel converter (50) located between the MVDC distribution device (20) and the generator (60) is converted and transmitted from this modular multilevel converter (50) to the LVDC distribution device (80). However, Figure 14h the power system shown is different from Figure 14f the power system shown in that in Figure 14h the power system shown, power is additionally transmitted from the LVDC distribution device (80) to the LVAC distribution device (70) through a separate inverter. In addition, Figure 14f the power system shown is the same asFigure 14h The difference in the power system shown is that, Figure 14f in the power system shown, a modular multilevel converter (10) having a plurality of output terminals is additionally placed between the MVDC distribution device (20) and the propulsion motor (30). However, Figure 14h in the power system shown, a modular multilevel converter (10) having a single output terminal is additionally placed between the MVDC distribution device (20) and the propulsion motor (30).

[0177] In addition, Figure 14i the power system shown is the same as Figure 14f the power system shown in that the power from the modular multilevel converter (50) located between the MVDC distribution device (20) and the generator (60) is converted and transmitted from the modular multilevel converter (50) to the LVDC distribution device (80). However, Figure 14i the power system shown is different from Figure 14f the power system shown in that, Figure 14i in the power system shown, the power is additionally transmitted from the LVDC distribution device (80) to the LVAC distribution device (70) through a separate inverter.

[0178] In addition, Figure 14j the power system shown is different from Figure 14i the power system shown in that, Figure 14j in the power system shown, the power is additionally transmitted from the LVDC distribution device through a separate inverter (80) to the LVAC distribution device (70).

[0179] In addition, the propulsion motor (30) requires a large amount of power. In this case, according to the embodiments disclosed in this specification, when the modular multilevel converter (10) is additionally placed between the MVDC distribution device (20) and the propulsion motor (30), the propulsion motor (30) can be stably powered.

[0180] Meanwhile, Figures 15a to 15d a power system according to the embodiments disclosed in this specification is schematically shown, in which the grids of the essential loads and the service loads are separated from each other.

[0181] For reference, essential loads refer to the loads necessary for operating the ship, while service loads refer to the loads that can vary according to circumstances. Essential loads can be continuously powered, while service loads can be variably powered.

[0182] Conventionally, essential loads and service loads are included in the same grid, so it is difficult to control service loads.

[0183] On the other hand, as shown in FIGS. 15Aa toFigure 15d As shown, when the power grid (1600) for essential loads and the power grid (1700) for service loads are separated from each other, the service loads can be easily controlled, thereby effectively managing power.

[0184] First, referring to Figure 15a and Figure 15b it can be seen that the first power grid (1600) corresponding to essential loads and the second power grid (1700) corresponding to service loads are electrically isolated from each other.

[0185] In this case, the first power grid (1600) may include an MVDC distribution device (1620), a propulsion motor (1630), and a modular multilevel converter (1610). In addition, a power supply source for supplying power may be additionally included in the first power grid (1600). For example, at least a part of an energy storage system (ESS), a fuel cell system (SOFC), a diesel generator (DG), and a shaft generator (large motor) may be additionally included. In this case, power conversion equipment may be used to transfer the power supplied from the power source to the MVDC distribution device (1620). In this case, a general inverter, a general converter, etc. may be used as the power conversion equipment, but it is not limited thereto. A modular multilevel converter having a single output terminal or multiple output terminals may be used. In addition, the modular multilevel converter (1610) of the first power grid (1600) may be a modular multilevel converter having a single output terminal as shown in Figure 15b but is not limited thereto, and may be a modular multilevel converter having multiple output terminals as shown in Figure 15a When the modular multilevel converter (1610) has multiple output terminals as shown in Figure 15a power can be transferred to the propulsion motor (30) and the lower load (1670) simultaneously.

[0186] In addition, the second power grid (1700) may include an LVAC distribution device (1710), service loads (1720), and a variable speed generator (1730).

[0187] Meanwhile, when the variable speed generator (1730) included in the second power grid (1700) fails, power may not be supplied to the service loads (1720). Therefore, the first power grid and the second power grid may be electrically isolated as shown in Figure 15a and Figure 15b In some cases, power from the first power grid (1600) may be assisted in being transferred to the second power grid (1700) through switch operations as shown in Figure 15c and Figure 15d shown.

[0188] For example, as shown in Figure 15cAs shown, the switch (1640) is placed between the auxiliary output terminal (second output terminal) of the modular multilevel converter (1610) having multiple output terminals of the second power grid (1700) and the first power grid (1600), so as to share the power of the first power grid (1600) with the second power grid (1700) in an emergency. Compared with Figure 15a the power system of Figure 15c it can be seen that the switch (1640) is added to one side of the auxiliary output terminal of the modular multilevel converter (1610) of the first power grid (1600) having multiple output terminals. As a reference, in Figure 15c the modular multilevel converter (1610) of the first power grid (1600) is shown to transmit low-voltage AC power to the second power grid (1700), but it is not limited thereto. For example, the modular multilevel converter (1610) of the first power grid may transmit low-voltage DC power to the second power grid.

[0189] Another example is that, as Figure 15d shown, the switch (1640) is placed between the modular multilevel converter (1650) having a single output terminal and the MVDC distribution device (1620), so as to share the power of the first power grid (1600) with the second power grid (1700) in an emergency. Compared with Figure 15b the power system of Figure 15d it can be seen that the switch (1640) is additionally connected to the MVDC distribution device (1620) of the first power grid (1600) of

[0190] and the modular multilevel converter (1650) having a single output terminal is additionally placed between the corresponding switch (1640) and the second power grid (1700).

[0191] Therefore, the embodiments of the present disclosure are intended to explain rather than limit the technical idea of the present disclosure, and the scope and concept of the present disclosure are not limited to the above embodiments. The protection scope of the present disclosure should be interpreted by the appended claims, and all its equivalents should be interpreted as being included within the scope of the present disclosure.

Claims

1. A modular multilevel converter, comprising: A first converter device having branches according to a preset phase, wherein each of the branches has an upper arm and a lower arm, and each of the upper arm and the lower arm includes a plurality of sub-modules connected in series to convert the DC power input to the input terminal into AC power having a phase and output the AC power through a first output terminal; and A second converter device configured to convert the DC power input to the input terminal into AC power having a voltage level lower than the voltage level of the AC power output from the first converter device and output the AC power through a second output terminal.

2. The modular multilevel converter according to claim 1, wherein, The second converter device includes at least one of the following: A first low-voltage converter device composed of a plurality of additional sub-modules connected in series with the upper arm of the branch of the first converter device in a full-bridge manner, wherein a plurality of adjacent additional sub-modules are connected in parallel with each other, and the plurality of additional sub-modules convert the DC power of the input terminal into AC power having a voltage level lower than the voltage level of the AC power output from the first converter device; or A second low-voltage converter device composed of a plurality of additional sub-modules connected in series with the lower arm of the branch of the first converter device in a full-bridge manner, wherein a plurality of adjacent additional sub-modules are connected in parallel with each other, and the plurality of additional sub-modules convert the DC power of the input terminal into AC power having a voltage level lower than the voltage level of the AC power output from the first converter device.

3. The modular multilevel converter according to claim 2, further comprising: A controller configured to control the power conversion of the first low-voltage converter device and the second low-voltage converter device.

4. The modular multilevel converter according to claim 1, wherein, The first converter device is a bidirectional converter configured to convert the AC power input to the first output terminal into a preset DC power and output the preset DC power to the input terminal when the AC power is input to the first output terminal.

5. The modular multilevel converter according to claim 1, wherein, The first converter device and the second converter device convert the DC power of the input terminal into three-phase AC power having different voltage levels and output the three-phase AC power.

6. A power system, comprising: A first modular multilevel converter having a plurality of output terminals; A propulsion motor configured to receive AC power from a first output terminal among the plurality of output terminals; A low-voltage alternating current (LVAC) distribution device configured to receive AC power from a second output terminal among the plurality of output terminals; A medium-voltage direct current (MVDC) distribution device configured to supply DC power to the first modular multilevel converter.

7. The power system according to claim 6, wherein, The voltage level of the AC power output through the second output terminal is lower than the voltage level of the AC power output through the first output terminal.

8. The power system according to claim 6, wherein, the DC power supplied to the first modular multilevel converter by the MVDC power distribution device is directly or indirectly generated by at least one of an energy storage system, a fuel cell system, or a generator.

9. The power system according to claim 8, further comprising: a second modular multilevel converter configured to electrically connect the generator and the MVDC power distribution device, wherein the second modular multilevel converter has at least one output terminal.

10. The power system according to claim 9, wherein, the second modular multilevel converter has a third output terminal for outputting DC power to the MVDC power distribution device and a fourth output terminal for outputting AC power to the service load power distribution device.

11. The power system according to claim 9, wherein, the second modular multilevel converter has a fifth output terminal for outputting DC power to the MVDC power distribution device and a sixth output terminal for outputting DC power to the service load power distribution device.

12. The power system according to claim 11, wherein, the voltage level of the DC power output through the sixth output terminal is lower than the voltage level of the DC power output through the fifth output terminal.

13. The power system according to claim 6, wherein, the second output terminal and the LVAC power distribution device are electrically connected through an isolation transformer.

14. The power system according to claim 13, wherein, the isolation transformer is one of a two-winding transformer and a three-winding transformer.

15. The power system according to claim 6, further comprising: a bus tie connected to the MVDC power distribution device and configured to exchange DC power with another power system.

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