Ship power management method and device based on power grid forming shaft generator and ship

Abstract

Disclosed are a ship power management method and apparatus for stably connecting an axle generator to a ship power system and stably inputting power thereof, and a ship using the same. The ship power management method includes: connecting an axle generator to a ship power system; a generator-side converter controlling a power converter connected to the axle generator with a zero power reference; charging a DC link capacitor of the power converter; the shaft generator is excited by using the current of the DC link capacitor so as to realize self power generation; a grid-side converter controlling the power converter with a zero power reference; controlling the generator-side converter to charge the DC link capacitor with the power of the axle generator; and performing secondary voltage control in the power converter such that the axle generator operates as a distributed generator of the marine power system.

Description

Technical Field

[0001] This invention relates to a shipboard microgrid management technology based on a grid-forming shaft generator, and more specifically, to a ship power management method and apparatus for stably inputting power from a grid-forming shaft generator into a shipboard microgrid and stably connecting the shaft generator to the shipboard microgrid, as well as a ship using the method and apparatus. Background Technology

[0002] To reduce carbon emissions from ships, the demand for alternative energy sources for ship propulsion and electricity generation is increasing. Alternative energy sources such as batteries, fuel cells, and solar power are gaining attention, and shaft generators, which mount generators on the propeller shafts of conventional power plants, have recently been adopted as an alternative energy source in many ships.

[0003] The ship's electrical management system is configured to control the operation of multiple synchronous generators and power converters for shaft-driven generators connected to the ship's propeller shaft (see...). Figure 1 For decades, control systems for shipboard microgrids have been standardized based on synchronous generators, and due to industry characteristics, rather than altering the structure of proven overall control systems, it is preferable that power converters for alternative energy sources mimic traditional synchronous generators. Therefore, power converters for alternative energy sources should simulate the characteristics of traditional synchronous generator control methods, namely voltage droop and frequency droop characteristics.

[0004] On the other hand, in most alternative energy power converters, impedance in the circuit causes voltage drop due to the grid-forming voltage control loop of the power converter and the circuit impedance caused by the isolation transformer applied to the output to block common-mode noise. However, it is impossible to simulate the same voltage droop characteristics as synchronous generators based on load current, and currently, there is no secondary voltage controller in marine power control systems capable of compensating for this problem.

[0005] Therefore, when alternative energy sources such as grid-forming shaft generators are used in shipboard microgrids, problems arise such as reactive power feed-in during parallel operation and voltage drop during stand-alone operation, thus requiring a suitable solution to address these issues. Summary of the Invention

[0006] [Technical Issues] This invention is proposed to meet the requirements of related technologies and aims to provide a shipboard power management method and device, wherein virtual impedance is applied to the voltage control of a power converter connected to a grid-forming shaft generator to allow the power converter to have sufficient inertia to disturbances and the power generated by the shaft generator can be effectively supplied to the shipboard microgrid.

[0007] The present invention also aims to provide a ship power management method and apparatus that can effectively compensate for voltage drops in the shaft generator system of the power converter of the shaft generator connected to the ship's microgrid using a novel self-secondary voltage control algorithm.

[0008] The present invention also aims to provide a ship power management method and apparatus that, even in a ship power management system where a separate secondary voltage controller is not available, can perform self-secondary voltage control using a power converter connected to the shaft-driven generator, depending on whether the shaft-driven generator is operating in parallel or independently.

[0009] The present invention also aims to provide a ship using the above-described ship power management method or ship power management equipment.

[0010] [Technical Solution] According to one aspect of the present invention for solving the above-mentioned technical problems, a ship power management device based on a grid-forming shaft generator—the device being a ship power management device for a shipboard microgrid based on a grid-forming shaft generator—comprising: at least one command, including a sequence of grid inputs to the shaft generator; and a processor connected to a memory configured to store the at least one command and execute the at least one command. The processor, through the at least one command, executes: electrically connecting the shaft generator to the shipboard microgrid; controlling a generator-side converter connected to a power converter of the shaft generator based on zero-power reference control; charging a DC link capacitor of the power converter; exciting the shaft generator using the current from the DC link capacitor; causing the shaft generator to perform self-generation; controlling the grid-side converter of the power converter based on zero-power reference control; controlling the generator-side converter of the power converter to charge the DC link capacitor with power from the shaft generator; and performing self-secondary voltage control via the power converter, causing the shaft generator to operate as a distributed generator of the shipboard microgrid.

[0011] According to another aspect of the present invention for solving the above-mentioned technical problems, a ship power management method based on a grid-forming shaft generator includes: electrically connecting the shaft generator to a shipboard microgrid; a generator-side converter connected to a power converter of the shaft generator based on zero-power reference control; charging a DC link capacitor of the power converter; energizing the shaft generator using the current of the DC link capacitor; enabling the shaft generator to perform self-generation; controlling the grid-side converter of the power converter based on zero-power reference control; controlling the generator-side converter of the power converter to charge the DC link capacitor with the power of the shaft generator; and performing self-secondary voltage control by the power converter, so that the shaft generator operates as a distributed generator of the shipboard microgrid.

[0012] Charging the DC link capacitor of a power converter connected to a shaft-driven generator can include controlling the grid-side converter to charge the DC link capacitor to at least a portion of its rated voltage. The charged DC voltage can be maintained through control of the power converter.

[0013] The ship power management method (hereinafter also referred to as the "method") may further include controlling the grid-side converter in grid-feed mode before energizing the shaft-driven generator.

[0014] The method may further include: when the DC link capacitor is charged to the rated voltage or preset voltage by the power of the shaft-driven generator, switching the grid-side converter from grid feeding mode to grid forming mode.

[0015] Performing secondary voltage control may include: performing voltage control of the grid-side converter based on a control droop coefficient determined or selected based on preset or real-time acquired measurements.

[0016] Performing self-secondary voltage control may further include: subtracting each of the feedback output voltage reference and the preset fixed virtual impedance from the output voltage reference, and transmitting the result of the subtraction to the voltage controller.

[0017] Virtual impedance can be obtained by adding virtual inductance and virtual resistance.

[0018] The method may further include performing at least one of torque control and flux control on the shaft-driven generator to maintain the voltage of the DC link capacitor.

[0019] The method may further include performing at least one of torque control and flux control on the shaft-driven generator to connect the power converter to the common coupling point of the shipboard microgrid.

[0020] The method may further include: adaptively estimating the stator resistance of the shaft-driven generator using a semi-positive definite Lyapunov function defined to include the stator resistance error used for torque control or flux control of the shaft-driven generator.

[0021] This estimate can further include: when solving the equation using the derivative of a semi-definite Lyapunov function, using a low-pass filter to perform integral control to achieve fast convergence of the equation solution.

[0022] According to another aspect of the present invention for solving the above-mentioned technical problems, a ship using a ship power management method based on a grid-forming shaft generator power management system includes: a ship power management device, including a memory configured to store at least one command for implementing a grid input sequence of the shaft generator, and a processor connected to the memory and configured to execute the at least one command; and a hull on which the ship power management device is mounted. Here, the processor, through at least one command, executes: electrically connecting the shaft generator to an onboard microgrid; a generator-side converter connected to a power converter of the shaft generator based on zero-power reference control; charging a DC link capacitor of the power converter; exciting the shaft generator using the current of the DC link capacitor; causing the shaft generator to perform self-generation; controlling the grid-side converter of the power converter based on zero-power reference control; controlling the generator-side converter of the power converter to charge the DC link capacitor with power from the shaft generator; and performing self-secondary voltage control through the power converter, causing the shaft generator to operate as a distributed generator of the onboard microgrid.

[0023] When charging the DC link capacitor of the power converter connected to the shaft-driven generator, the processor can control the grid-side converter to charge the DC link capacitor to at least a portion of its rated voltage, and maintain the charged DC link voltage through the control of the power converter.

[0024] In ships, before energizing the shaft-driven generator, the processor can further execute control of the grid-side converter in grid-fed mode.

[0025] In a ship, when the DC link capacitor is charged to its rated voltage or preset voltage by the power of the shaft-driven generator, the processor can further execute the switch of the grid-side converter from grid-feed mode to grid-forming mode.

[0026] In ships, when performing secondary voltage control, the processor can determine or select a control droop coefficient based on preset or real-time acquired measurement values ​​to perform voltage control of the grid-side converter.

[0027] In a ship, when performing secondary voltage control, the processor can further subtract each of the feedback output voltage reference and the preset fixed virtual impedance from the output voltage reference, and transmit the result to the voltage controller.

[0028] In a ship, the processor can further perform at least one of torque control and flux control on the shaft-driven generator to maintain the voltage of the DC link capacitor.

[0029] In a ship, the processor can further perform adaptive estimation of the stator resistance of the shaft-driven generator using a semi-positive definite Lyapunov function defined to include the stator resistance error used for torque control or flux control of the shaft-driven generator.

[0030] According to another aspect of the present invention for solving the above-mentioned technical problems, a ship including a hull equipped with ship power management equipment can be provided.

[0031] [Beneficial Effects] According to the present invention, an efficient grid connection method for a grid-forming shaft generator applied to a ship can be provided, as well as a self-secondary voltage control method for improving the power quality of a shipboard microgrid. In particular, a grid-forming control mode based on virtual impedance can be provided to ensure the stability of the power converter connected to the shaft generator when switching between grid feed control mode and grid forming control mode, thereby efficiently supplying power from the shaft generator based on a squirrel-cage induction device to the grid.

[0032] Furthermore, according to the present invention, when simulating the voltage droop characteristics and / or frequency droop characteristics of a synchronous generator in a shaft-driven generator, the power converter performs self-secondary voltage control according to each preset voltage standard for parallel operation and independent operation to compensate for voltage drops occurring in grid-forming power converters and connection devices such as isolation transformers, thereby enabling the shaft-driven generator to effectively perform grid-forming operation in a shipboard microgrid. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a shipboard microgrid that can be applied to a ship power management method based on a grid-forming shaft generator according to an embodiment of the present invention.

[0034] Figure 2 It is used to describe what can be done. Figure 1 A graph showing the voltage droop characteristics of the ship power management system used in the shipboard microgrid.

[0035] Figure 3 It is used to describe what can be done. Figure 1 A graph showing the frequency droop characteristics of the ship power management system used in the shipboard microgrid.

[0036] Figure 4 It is possible Figure 1 A schematic block diagram of the shipboard power management equipment used in the shipboard microgrid.

[0037] Figure 5 It is used to describe what can be done. Figure 4 A block diagram illustrating the control process of a squirrel-cage induction generator used in ship electrical management equipment.

[0038] Figure 6 It can be made by Figure 5 The flowchart shows the control phase of the squirrel-cage induction generator (SCIG) performed by the ship's electrical management equipment.

[0039] Figure 7 It is used to describe Figure 6 A block diagram of the first operating mode (stage I) in the SCIG control phase.

[0040] Figure 8 It is used to describe Figure 6 A block diagram of the second operating mode (stage II) in the SCIG control phase.

[0041] Figure 9 It is used to describe Figure 6 A block diagram of the third operating mode (stage III) in the SCIG control phase.

[0042] Figure 10 It is used to describe what can be applied to Figure 6 A block diagram of the adaptive flux control process in the SCIG control phase.

[0043] Figure 11 It is used to describe what can be done. Figure 4 A block diagram of the voltage control process based on virtual impedance for a grid-forming power converter used in ship power management equipment.

[0044] Figure 12 This is an exemplary diagram illustrating a self-secondary voltage control structure that can be used in a shipboard microgrid management method according to another embodiment of the present invention.

[0045] Figures 13a to 13c This is a graph showing the root locus of a stability verification model for a shipborne microgrid management method according to this embodiment, with specific parameter modifications.

[0046] Figure 14 This is a diagram illustrating the simulation control configuration that can be used in the shipborne microgrid management method of this embodiment.

[0047] Figure 15a and Figure 15b It shows the basis Figure 14 The simulation control configuration is shown in the graphs of active and reactive power simulation results during the control mode switching between grid feeding and grid formation.

[0048] Figure 16a and Figure 16bThis is a graph showing the simulation results of active and reactive power during the control mode switching between grid feeding and grid formation when the shipboard microgrid management method of this embodiment is applied to an actual ship.

[0049] Figure 17a and Figure 17b This is a graph showing the power factor, active power, and reactive power during parallel operation of the grid-forming power converter and synchronous generator before and after the application of secondary voltage control in the shipboard microgrid management method of this embodiment.

[0050] Figure 18a and Figure 18b This is a graph showing the reference voltage and output voltage curves before and after the application of secondary voltage control in the shipborne microgrid management method of this embodiment, when the grid-forming power converter and the synchronous generator are operating in parallel.

[0051] Figure 19a and Figure 19b This is a graph showing the power factor, active power, and reactive power during independent operation of the grid-forming power converter in the shipborne microgrid management method of this embodiment.

[0052] Figure 20a and Figure 20b This is a graph showing the reference voltage and output voltage during independent operation of the grid-forming power converter in the shipborne microgrid management method of this embodiment. Detailed Implementation

[0053] This invention can be modified in various forms, and specific embodiments thereof will be described and illustrated in the accompanying drawings. However, it should be understood that this is not intended to limit the disclosure to the specific embodiments, but rather that the invention includes all variations, equivalents, and alternatives encompassed within the spirit and scope of this disclosure.

[0054] The terms "first," "second," etc., may be used simply to describe various constituent elements, but these constituent elements are not limited by these terms. The terms are used only to distinguish one constituent element from others. For example, without departing from the scope of this disclosure, a first constituent element may be referred to as a second constituent element, and similarly, a second constituent element may be referred to as a first constituent element. The term "and / or" includes a combination of multiple related listed items or any one of multiple related listed items.

[0055] In embodiments of this application, "at least one of A and B" can refer to "at least one of A or B" or "at least one of one or more combinations of A and B". Additionally, in embodiments of this application, "one or more of A and B" can refer to "one or more of A or B" or "one or more of one or more combinations of A and B".

[0056] When it is said that a component is "connected" or "linked" to another component, it should be understood that the component can be directly connected or linked to the other component, but other components may exist in between. On the other hand, when it is said that a component is "directly connected" or "directly linked" to another component, it should be understood that no other component exists in between.

[0057] The terminology used herein is for describing particular embodiments only and is not intended to limit this disclosure. Expressions used in the singular include plural expressions unless the context clearly distinguishes them. In this application, the words “comprising” or “having” are used to specifically describe the presence of features, numbers, processes, operations, constituent elements, components, or combinations thereof, and it should be understood that the presence or other possibilities of one or more other features or numbers, processes, operations, constituent elements, components, or combinations thereof are not excluded in advance.

[0058] Unless otherwise defined, all terms used herein, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will be further understood that terms such as those defined in common dictionaries shall be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and shall not be interpreted as having an idealized or overly formal meaning unless explicitly defined herein.

[0059] In the following description, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, the same reference numerals are used for the same components in the drawings to facilitate overall understanding, and repeated descriptions of the same components will be omitted.

[0060] Figure 1 This is a schematic diagram of a shipboard microgrid that can be applied to a power management method for a shipboard microgrid including a grid-forming shaft generator according to an embodiment of the present invention (hereinafter referred to as the "shipboard power management method").

[0061] Reference Figure 1 The shipboard microgrid installed on the vessel 1000 may include synchronous generators 100, 110 and 120, switchboard 130, shaft-driven generator (SG) 150, power converter 200, isolation transformer 230 and circuit breaker 250.

[0062] For maintenance purposes, synchronous generators 100, 110, and 120 can be products of the same manufacturer. All three synchronous generators 100, 110, and 120 can be used simultaneously as distributed power sources, or only one or two of them can be used as distributed power sources.

[0063] Furthermore, synchronous generators 100, 110, and 120 constitute the main power generation units in the shipboard microgrid. Despite their different sizes, synchronous generators 100, 110, and 120 can be supplied by the same manufacturer and can use the same governor and automatic voltage regulator (AVR). Therefore, reactive power distribution among the synchronous generators can be adequately achieved through primary voltage control performed by the AVR. Secondary frequency control (SFC) is typically applied in the governor frequency control because even identical engines may have different combustion characteristics. The frequency and voltage droop curves for all synchronous generators in the shipboard microgrid can be designed with droops of 3% and 2.5%, respectively.

[0064] The switchboard 130 may include circuit breakers, each of which is connected to one of the synchronous generators. These circuit breakers may be referred to as the first circuit breaker, the second circuit breaker, and the third circuit breaker.

[0065] SG 150 can be mounted on the propeller shaft connecting the propeller 140 and the main engine 160 of the vessel, and can convert the kinetic energy of the main engine 160 transmitted through the propeller shaft into electrical energy. SG 150 may include an induction generator, and the induction generator may include a squirrel-cage induction generator (SCIG). In the following description, SG 150 may also be referred to as SCIG 150.

[0066] Power converter 200 can be positioned between SG 150 and isolation transformer 230, and can be implemented as a back-to-back converter. This back-to-back converter may include: a generator-side converter, including SG 150; a grid-side converter, including the point of common coupling (PCC) of the shipboard microgrid; and a DC link capacitor connected between the generator-side converter and the grid-side converter. The generator-side converter and the grid-side converter can be configured to share the DC link voltage of the DC link capacitor. The PCC may refer to a common bus of the shipboard power generation resource that supplies power to internal and external loads connected to the distributed shipboard microgrid.

[0067] Furthermore, unlike wind or solar control such as maximum power point tracking, the grid-side converter of a back-to-back converter controls the power flow. Accordingly, the generator-side converter can be configured to maintain the DC link voltage of the DC link capacitor at a desired level by controlling the torque of the SCIG 150, and the grid-side converter can be configured to generate electricity as one of a group of generating units including independent distributed generators or synchronous generators.

[0068] The isolation transformer 230 is used to physically isolate the branch grid, including the SG 150 and the power converter 200, which serve as alternative energy sources in the shipboard microgrid, from the main grid of the shipboard microgrid.

[0069] Circuit breaker 250 is used to selectively connect or disconnect the branch system, including SG 150, power converter 200, and isolation transformer 230, from the main grid of the shipboard microgrid. Circuit breaker 250 can be mounted on the switchboard 130 along with other circuit breakers. In this case, circuit breaker 250 can be referred to as the fourth circuit breaker.

[0070] The aforementioned shipboard microgrid can be managed by the shipboard power management system (SPMS) 300. The SPMS 300 can control the power of synchronous generators 100, 110 and 120, SG 150, and power converter 200.

[0071] Additionally, when the SG 150 needs to be operated, the SPMS 300 can implement the generator-side converter of the power converter 200 as an active front-end converter, enabling the external reactive power to be fed to the excitation of the SG 150.

[0072] In addition, the SMPS 300 can be configured to apply a grid input control sequence that allows the power generated by the SG 150 to be efficiently supplied to the shipboard microgrid.

[0073] In addition, in order to stabilize the grid-forming distributed generation of SG 150, considering the ratio of the combined impedance X to the resistance R of the shipboard microgrid (combined X / R ratio), SMPS 300 can be configured to apply a preset fixed virtual impedance (abbreviated as "VImp") to the voltage control circuit of SMPS 300.

[0074] Additionally, the SPMS 300 can be configured to enable the grid-side converter of the power converter 200 to perform SFC. Furthermore, the SPMS 300 can be configured to enable the power converter 200 itself to perform secondary voltage control in a shipboard microgrid where a secondary voltage controller is not present.

[0075] Secondary voltage control can be configured to control voltage based on different target values ​​depending on parallel and stand-alone operation. For example, during parallel operation of SG 150 with at least one synchronous generator 100, SMPS 300 can perform voltage control based on a target power factor. During stand-alone operation of SG 150, SMPS 300 can perform voltage control of SG 150, power converter 200, or marine microgrid by setting the secondary voltage of isolation transformer 230 to a target voltage (e.g., 1 pu).

[0076] For reference, since most ships use AC power grids, this alternative energy source should be connected to the ship's power grid via a power converter. The power converter should essentially operate in parallel with the existing shipboard synchronous generator to supply power to the ship's loads, and should also have the capability to independently supply power to the ship's loads based on the ship's operating conditions. Therefore, the ship's alternative energy-based power converter should implement grid-forming control and can also perform grid feed control based on the characteristics of the alternative energy source.

[0077] For example, grid feed control is necessary for purposes such as reference power point tracking (PQ control) for maximum power point tracking of photovoltaic power generation and power feed limitation during the initial excitation phase of SCIG. Furthermore, since the shipboard microgrid is an independent, islanded grid and should always be able to supply power to the shipboard loads, even when the power converter is performing grid feed control, the converter should be able to instantaneously switch its control mode to grid-forming control mode at any time to enable independent operation of the alternative energy source.

[0078] In grid-fed mode, active and reactive power control is performed synchronously with the grid via a phase-locked loop (PLL). In grid-forming mode, however, the output voltage amplitude and frequency target values ​​are determined by a set droop (load distribution). Therefore, when switching from grid-fed mode to grid-forming mode, the output voltage of the power converter connected to the alternative energy source changes instantaneously, and in this case, the power converter's output voltage has a different phase, amplitude, and frequency than the grid voltage. This creates a disturbance to the power converter's grid control, and because the low inertia of typical power converters cannot withstand this disturbance, the alternative energy source may fail to switch to grid-forming mode and may disconnect from the grid due to frequency and voltage divergence.

[0079] Therefore, in this embodiment, virtual impedance is applied to the voltage control of the power converter connected to the grid-forming SG, thereby providing a vessel in which the power converter can have sufficient inertia to disturbances, and the power generated by the SG can be effectively supplied to the shipboard microgrid. Additionally, according to this embodiment, a vessel can be provided in which, by using a self-secondary voltage control algorithm, voltage drops within the shaft-driven generator system can be effectively compensated by the power converter connected to the SG in the shipboard microgrid, and even in an SMPS without a secondary voltage controller, self-secondary voltage control can be performed by using the power converter connected to the SG, depending on whether the SG operates in parallel or independently.

[0080] Figure 2 It is used to describe what can be done. Figure 1 A graph showing the voltage droop characteristics of SMPS used in a shipboard microgrid. Figure 3 It is used to describe what can be done. Figure 1 The curve shows the frequency droop characteristics of the SMPS used in the shipborne microgrid.

[0081] like Figure 2 As shown, due to maintenance considerations, three or four products from the same manufacturer are installed as synchronous generators. Therefore, the voltage droop characteristics of each synchronous generator caused by the AVR may be very similar between the synchronous generators, and thus can be fixed without applying individual secondary voltage control (SVC). AVRs can be supplied integrated with synchronous generators.

[0082] On the other hand, such as Figure 3 As shown, even synchronous generators of the same type may have different combustion characteristics. Therefore, the frequency droop characteristics among multiple synchronous generators used in a ship's onboard microgrid can be adjusted using SFC (Synchronous Frequency Control).

[0083] Furthermore, in a distributed shipboard microgrid that includes a synchronous generator and alternative energy sources, particularly a SG connected to the ship's propeller shaft, it is necessary to implement at least one of SVC and SFC so that the power of the SG can be effectively supplied to the PCC of the shipboard microgrid in a grid-forming operation mode, i.e., the SG can operate in coordination with the synchronous generator.

[0084] Therefore, the ship power management equipment of this embodiment can be configured to enable the shaft-driven generator system, including the SG and power converter, to operate as a plug-and-play distributed power source that replicates the operation of a synchronous generator.

[0085] Specifically, while the SG is typically operated as an independent distributed generator during normal ship operations, limitations exist due to factors such as reduced residual power in the engine's propulsion system and the dependence of shaft generator power on shaft speed. To ensure the safe and efficient operation of the SG, the ship's electrical management equipment can be configured to monitor these limitations and implement measures such as load reduction or activation of the synchronous generator under specific circumstances. These measures may include addressing situations such as SG overload caused by high power loads in the ship's microgrid, mechanical load fluctuations in the propulsion engine due to severe sea conditions, and engine deceleration.

[0086] In this way, the ship power management device of this embodiment can be configured to apply the fast grid input sequence of the SG in a distributed shipboard microgrid including the SG. Additionally, the ship power management device can be configured to apply a control algorithm based on fixed virtual impedance to stably switch the operating mode from grid feeding to grid formation. Furthermore, the ship power management device can be configured to apply power from the SVC via the SG in grid formation operating mode.

[0087] Figure 4 It is possible Figure 1 A schematic block diagram of the ship's power management equipment used in the SMPS of the ship's microgrid.

[0088] Reference Figure 4 Ship power management equipment 400 can correspond to management Figure 1 The shipboard microgrid SPMS 300. The shipboard power management device 400 may include at least one processor 410 and a memory 420. Additionally, the shipboard power management device 400 may further include a transceiver 430, which is connected to a user's or manager's terminal or communication device of the ship's network, an external dedicated power distribution network, or a commercial power distribution network to perform communication. Furthermore, the shipboard power management device 400 may further include an input interface device 440, an output interface device 450, a storage device 460, etc. The various components included in the shipboard power management device 400 can be connected to each other via a bus 470 for communication.

[0089] More specifically, processor 410 can execute software modules or program commands stored in at least one of memory 420 and storage device 460. As an example, processor 410 may include a virtual impedance control unit 412, a shaft-driven generator grid input unit 414, a secondary voltage controller 416, and a mode switching unit 418. These components may be installed on processor 410 as software modules or program commands, and their configuration and / or function will be described in detail below. Processor 410 may be implemented as a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor that executes methods according to embodiments of the present invention.

[0090] Each of the memory 420 and the storage device 460 may include at least one of volatile storage media and non-volatile storage media. For example, the memory 420 may include at least one of read-only memory (ROM) and random access memory (RAM).

[0091] Transceiver 430 may include a communication interface or sub-communication system for communication inside or outside the ship or between the inside and outside of the ship, such as a short-range wireless network, cable connection, satellite communication or wireless communication with a general base station.

[0092] The input interface device 440 may include at least one selected from an input unit and an input signal processing unit, wherein the input unit is such as a keyboard, microphone, touchpad and touch screen, and the input signal processing unit maps or processes signals input through at least one input unit according to pre-stored commands.

[0093] The output interface device 450 may include: an output signal processing unit, under the control of the processor 410, to process or output signals in the form of pre-stored signals or through level mapping; and at least one output unit, based on the signal from the output signal processing unit, to output a corresponding signal or information contained in the signal in at least one of vibration, light, and sound at a predetermined level. The at least one output unit may include at least one of output units selected from devices such as speakers, display devices, printers, optical output devices, and vibration output devices.

[0094] Figure 5 It is used to describe what can be done. Figure 4 A block diagram of the SCIG control process used in ship electrical management equipment.

[0095] First, the control environment of the SCIG 150 will be described below. Direct Torque Control (DTC) can be used to control the SCIG 150. Unlike flux vector control, which relies on rotor angular position for closed-loop control, the DTC method does not require a position encoder to provide feedback on rotor shaft speed or position. The DTC method is model-based and therefore relies on accurate model parameters to achieve optimal control performance. Therefore, the stator flux vector and the torque generated by that vector can be estimated based on the SCIG 150 motor model.

[0096] In this way, the estimation of stator flux linkage is crucial in the SCIG control process of this embodiment. Since the estimation of stator flux linkage depends on the accuracy of the stator resistance measured in the SCIG 150, accurate monitoring of the stator resistance in real time is necessary for accurate estimation of the stator flux linkage. That is, a power outage may occur on board when torque control fails due to uncertainties in the SCIG model parameters, and an imbalance arises between power supply and power demand.

[0097] On the other hand, the SCIG 150 is not designed to perform self-excitation, therefore excitation requires external reactive power. Accordingly, the power converter connected to the ship's power management equipment in this embodiment can be configured to use an active front-end converter instead of a passive converter.

[0098] like Figure 5 As shown, the ship's power management device in this embodiment can be configured to input the motor voltage and current, DC voltage, and switching commands of the SCIG 150 to the motor model, and receive torque and flux linkage values ​​or signals from the motor model. The DC voltage can be the voltage between the DC link capacitor terminals connected to the generator-side converter of the SCIG 150, and can correspond to the DC link voltage.

[0099] Additionally, the ship's electrical management equipment can be configured to generate a torque reference based on a DC voltage reference and a DC voltage reference, and compare the torque with the torque reference using a torque comparator to calculate the torque error (Δtorque, ΔT). Furthermore, the ship's electrical management equipment can be configured to compare the flux linkage with a flux linkage reference using a flux linkage comparator to calculate the flux error (Δflux, ΔF). The ship's electrical management equipment can be configured to input the torque error and flux error to a hysteresis pulse selector (HPS), and generate a switching command based on the torque error and flux error using the HPS. This switching command can be used to control the generator-side converter connected to the SCIG 150.

[0100] The aforementioned ship power management equipment can perform the SCIG control phase, which will be described below, to allow the SCIG 150 to be used as a distributed generator.

[0101] In the description of this embodiment, the term "reference" may refer to an electronic device that ideally generates a constant or fixed corresponding physical quantity unaffected by load, power fluctuations, temperature changes, and time, or it may refer to a reference physical quantity generated by the electronic device. For example, a voltage reference may refer to an electronic device that ideally generates a constant or fixed voltage unaffected by the surrounding environment or conditions, or the voltage generated by the electronic device. The generated voltage may correspond to a reference voltage.

[0102] Figure 6 It can be made by Figure 5 A flowchart of the SCIG control phase performed by the ship's electrical management equipment. Figure 7 It is used to describe Figure 6 A block diagram of the first operating mode (stage I) in the SCIG control phase. Figure 8 It is used to describe Figure 6 A block diagram of the second operating mode (stage II) in the SCIG control phase. Figure 9 It is used to describe Figure 6 A block diagram of the third operating mode (stage III) in the SCIG control phase.

[0103] Reference Figure 6 The ship's power management equipment can execute three control phases or first to third operating modes as a grid input sequence for a grid-forming SCIG. Specifically, the ship's power management method executed by the ship's power management equipment can include: operation S610, connecting the SG to the grid as at least part of the ship's microgrid, and using the grid-side current charged in the DC link capacitor to excite the shaft generator; operation S630, performing power control on the grid-side converter with a zero-power reference to generate self-generation before the shaft generator feeds power to the grid, causing the generator-side converter to charge the DC link capacitor; and operation S650, executing a self-SVC for distributed generation of the SG, causing the SG to operate as a distributed generator of the ship's microgrid.

[0104] To describe each operation in more detail, such as Figure 7 As shown, in the first control phase (Phase I), the grid-side converter 220, under the control of the ship's power management equipment, receives power P from the ship's microgrid connected to at least one synchronous generator 100 to charge the DC link capacitor 215. The grid-side converter 220 can perform power control to charge the DC link capacitor 215 to 90% of its rated DC voltage and maintain the charged DC voltage.

[0105] Additionally, in the first control phase, the generator-side converter 210 can excite the rotor of the SCIG using the DC link voltage of the DC link capacitor 215. Excitation can be a process of generating a magnetic field by allowing current to flow in the coils of the SG according to a predetermined voltage Vs of the generator-side converter 210, and can be referred to as the ability to generate magnetomotive force, i.e., magnetic flux or magnetic current, in the coils. In the first control phase, since the SG has not yet started generating electricity, the generator torque can be controlled to zero.

[0106] The second control phase (Phase II) is the operation that allows the SG to start self-generating electricity and checks whether the SG is generating electricity normally. For example... Figure 8 As shown, in the second control phase, the grid-side converter 220 can be controlled in grid-feed mode to prevent power from being supplied to the generator from the grid that is receiving power from at least one synchronous generator 100. In this case, the power reference value of the grid-side converter 220 is zero. That is, the grid-side converter 220 can be power controlled using a zero power reference.

[0107] Additionally, in the second control phase, the generator-side converter 210 can be controlled to begin self-generating electricity and charge the DC link capacitor 215 to its rated voltage. For this purpose, the ship's power management equipment can control the torque of the SG. When self-generating electricity is performed normally, and the electrical energy of the SG charges the DC link capacitor 215 from its DC link voltage to its rated voltage, the ship's power management equipment can switch the control mode of the shaft-driven generator system to the third control phase.

[0108] In the third control phase (Phase III), such as Figure 9 As shown, the grid-side converter 220 can be switched to grid-forming mode, allowing the SCIG-based SG to perform the same role as the synchronous generator 100 of the shipboard microgrid. In this case, to ensure sufficient inertia for the grid-side converter 220 in the virtual impedance-based grid-forming mode, the ship's power management equipment can perform voltage control (with droop voltage control) on the voltage control circuit of the grid-side converter 220 based on a control droop coefficient determined or selected based on preset or real-time acquired measurements. Therefore, the grid-side converter 220 can switch from grid-feed mode to grid-forming mode stably and quickly, i.e., instantaneously. The ship's power management equipment can keep the circuit breaker 250 in the open state until the mode switching of the grid-side converter 220 is performed.

[0109] Additionally, in the third control phase, the generator-side converter 210 can operate as a grid-forming power converter to supply power to the shipboard microgrid according to its PCC, ensuring proper connection to the shipboard microgrid, and / or maintaining the voltage of the DC link capacitor 215. That is, the ship's power management equipment can control at least one of the SG and the generator-side converter 210 to perform at least one of torque control and flux control on the SG.

[0110] Based on the first to third control stages of this embodiment described above, unnecessary circuit breaker operations and synchronization processes can be omitted, thereby achieving the advantage of fast and efficient system operation.

[0111] Figure 10 It is used to describe what can be applied to Figure 6 A block diagram of the adaptive flux control process in the SCIG control phase.

[0112] Reference Figure 10 An adaptive flux observer (referred to as "adaptive observer") that can be provided in ship electrical management equipment can be based on the stator voltage vector V of SG. s The rotor speed ω of the SCIG obtained from the engine governor r and the estimated resistance obtained from the stator resistance adaptive scheme processor Generate the estimated stator current vector î s And it can be obtained from the stator current i from the SCIG s Subtract the estimated stator current vector from the middle s The operation generates the observer's state estimation error vector ε. i The state estimation error vector can be input to the stator resistance adaptive scheme processor through a low-pass filter (LPF), and the estimated stator current vector from the adaptive flux observer can be input to the LPF.

[0113] In this way, in this embodiment, assuming that the ship's electrical management equipment can obtain the rotor speed measured by the engine governor, it can be understood that the accurate determinant resistance of the SCIG can be estimated through the DTC of the SCIG. In fact, since the rotor speed is measured by the engine governor, this assumption can be applied to distributed applications.

[0114] For example, a state-space model of SCIG can be set up on the rotor reference dq axis. In this case, the state observer uses the estimated state matrix as a positive semi-definite matrix and can be used to resolve the uncertain stator resistance in the state matrix A. By using such a state observer, the state estimation error of SG can be calculated, and an error vector with stator current error can be defined. By defining a quadratic function including the error vector and a positive semi-definite Lyapunov function with positive gain for the stator resistance error, the state observer can adaptively estimate the stator resistance.

[0115] A positive semi-definite Lyapunov function is one method for determining stability without solving for the state matrix, where all components of the estimated state matrix can be real numbers, and a correction matrix with a predetermined symmetric magnitude can be defined to satisfy specific inequalities for all vectors. Since such a positive semi-definite Lyapunov function is convex downwards in a three-dimensional graph, it converges to a minimum when its derivative is zero.

[0116] Based on the derivative of the positive semi-definite Lyapunov function, and considering that the error vector inherently depends on the estimated resistance, the minimum point of the Lyapunov function can be obtained by minimizing the sum of the sums. Therefore, the stator resistance can be estimated by solving the equation using the derivative of the positive semi-definite Lyapunov function. In this case, integral control using the LPF can be applied to achieve fast convergence of the equation solution.

[0117] Figure 11 It is used to describe what can be done. Figure 4 A block diagram of the voltage control process based on virtual impedance for a grid-forming power converter used in ship power management equipment.

[0118] like Figure 11 As shown, the ship's power management equipment can perform voltage control of the power converter connected to the SG based on virtual impedance. When the power converter operates in grid-forming mode, in addition to the feedback control circuit structure using a voltage controller, current controller, pulse width modulation (PWM) controller, inductor filter (L filter), and capacitor filter (C filter), the power converter can also have an output current i of the inductor filter. l The current feedback circuit structure reflected in the input of the current controller, and the structure in which the virtual impedance 411 is applied to the input of the voltage controller.

[0119] In this way, the control loop of the grid-side converter can be divided into an outer loop and an inner loop. The outer loop can be referred to as the outer control loop, and the inner loop can be referred to as the inner control loop. The outer control loop can be configured to adjust the reference voltage based on the measured power and droop function. The inner control loop can be configured to use two controllers, namely a voltage controller and a current controller, to control the output voltage according to the reference of the outer control loop.

[0120] Specifically, when the ship's power management equipment inputs a phase angle reference with the output voltage of the grid-side converter to the voltage controller... Output voltage reference At this time, the ship's power management equipment can control the voltage control operation of the grid-side converter to reflect and feedback the output voltage reference. The error, and simultaneously reflects the corresponding grid-side converter output current i o The predetermined virtual impedance is 411.

[0121] As described above, the ship's power management equipment can perform voltage control on the grid-side converter based on virtual impedance 411 to ensure system stability during power converter mode switching. Virtual impedance 411 can include a predetermined or fixed virtual impedance. Virtual impedance 411 can have a virtual inductance L... v and virtual resistance R v The form obtained by addition. When performing a Laplace transform on the virtual impedance 411, the virtual impedance 411 can be expressed as " Virtual inductance can also be called virtual inductance component, and virtual resistance can also be called virtual resistance component.

[0122] According to the voltage control based on virtual impedance in this embodiment, the grid-side converter operates as a voltage source, and the output voltage can be effectively controlled according to a predefined droop function similar to that of a synchronous generator. Furthermore, by employing a predetermined virtual impedance to change the output impedance of the grid-side converter, the closed-loop transfer function of the inner control loop can be adjusted. The impact of the virtual impedance on system dynamics can be analyzed by tracking eigenvalues.

[0123] Figure 12 This is an exemplary diagram illustrating a self-SVC structure that can be used in a shipboard microgrid operation method according to another embodiment of the present invention.

[0124] Reference Figure 12 The self-secondary voltage controller 416, which may be included in the ship's electrical controller, may include a power factor calculator, an adder / subtractor, a hysteresis comparator, and a transfer switch for switching to independent operation, and may be configured to provide a power to the grid-forming power converter by means of an offset voltage V offsetApply to the nominal output voltage V nom The obtained controlled nominal output voltage. For example... Figure 11 As shown, grid-forming power converters can have impedance due to current feedback circuits.

[0125] In this embodiment, the problem to be solved is that when an isolation transformer is installed at the output of the shaft-driven generator system to reduce common-mode noise, a voltage drop occurs depending on the output current. Therefore, it is difficult to control the same voltage droop characteristics as the AVR of a synchronous generator. To address issues such as reactive power sharing with the synchronous generator and voltage drop during independent operation, a self-SVC is applied.

[0126] Based on the self-secondary voltage controller structure described above, the voltage value of the voltage droop curve can be adjusted according to the control value based on hysteresis. During parallel operation with a synchronous generator, SVC can be performed based on a target power factor value, i.e., the power factor value of a typical marine load, such as 0.8. During stand-alone operation, SVC can be performed to maintain the voltage on the secondary side of the isolation transformer at the rated voltage. To prevent the self-SVC from interfering with the damping function of the virtual impedance, the bandwidth of the self-secondary voltage controller 416 can be selected to be approximately 1 / 20 of the bandwidth of the grid-forming power converter.

[0127] In the following sections, to verify virtual impedance control, shaft generator grid connection sequence, and self-SVC, stability assessments using root locus will be described, along with simulation and experimental results.

[0128] First, in order to model the grid-forming power converter and perform stability assessment based on root locus, an equation model of the grid-forming power converter was generated, and the stability of the system was assessed based on whether virtual impedance was applied and whether combined components were used.

[0129] The detailed definitions of the symbols used in the equations of the equation model described below are shown in Table 1.

[0130] Table 1

[0131] First, the active and reactive power generated by SG can be expressed as shown in Equation 1.

[0132] Equation 1 In Equation 1, and .

[0133] Based on the frequency and amplitude of the drooping voltage reflecting the secondary frequency control performed by the ship's electrical controller, it can be defined as shown in Equation 2. The ship's electrical controller can be included in the ship's electrical management equipment.

[0134] Equation 2 on the other hand, Figure 11 The voltage control equation model of the grid-forming power converter used can be expressed as shown in Equation 3 below.

[0135] Equation 3 In equation 3, .

[0136] According to Equation 3, it can be seen that the output voltage of the grid-forming power converter is obtained by subtracting the impedance from the transfer function G(s) based on the voltage target value and the voltage output value. It is determined by multiplying the output current. Figure 11 In this context, the output voltage model of a power converter excluding virtual impedance can be expressed as shown in Equation 4.

[0137] Equation 4 Since only impedance is involved in equations 3 and 4 and Unlike other systems, the performance of virtual impedance can be evaluated simply by changing the impedance value after the system model is generated.

[0138] By substituting the voltage amplitude defined in Equation 2 into Equation 4, the following voltage amplitude equation 5 can be generated.

[0139] Equation 5 By applying LPF to Equation 1 above and substituting the result into Equation 5, we can obtain Equation 6 below.

[0140] Equation 6 By integrating the frequency equation of Equation 2 above, applying the LPF to the active power value applied to Equation 1, and substituting it into Equation 4, we can obtain the following Equation 7.

[0141] Equation 7 Here, δ0 represents the load angle of the power converter and is defined by a trigonometric function as shown in Equation 8 below.

[0142] Equation 8 In Equation 8, it is assumed that the value of δ0 is relatively very small and Then equation 8 can be simplified as shown in equation 9 below.

[0143] Equation 9 On the other hand, Equation 1, which applies LPF, can be expressed in a linearized form as shown in Equation 10 below.

[0144] Equation 10 In equation 10, .

[0145] also, By substituting Equation 10 into Equation 6, a linear model of the voltage amplitude of the grid-forming power converter can be obtained. The linear model of the voltage amplitude of the grid-forming power converter can be expressed as shown in Equation 11.

[0146] Equation 11 In equation 11, .

[0147] By substituting equations 9 and 10 into equation 7, a linear model of the voltage phase of the grid-forming power converter can be obtained. The linear model of the voltage phase of the grid-forming power converter can be expressed as shown in equation 12.

[0148] Equation 12 In equation 12, .

[0149] Next, by combining equations 11 and 12, the state-space model of the grid-forming power converter can be obtained. The state-space model of the grid-forming power converter can be expressed as shown in equation 13.

[0150] Equation 13 In equation 13, D n It represents the nth-order differential.

[0151] The parameters used in Equation 13 above can be obtained as follows. First, G(s) used in Equation 11 can be rearranged into Equation 15.

[0152] Equation 14 In Equation 14 and .

[0153] Next, by substituting equation 14 into equation 11, we can obtain... The differential equation is shown in Equation 15.

[0154] Equation 15 The detailed definitions of the parameters in Equation 15 are as follows.

[0155] In a similar manner to the above, by substituting equation 14 into equation 12, we can obtain... The differential equation is shown in Equation 16.

[0156] Equation 16 By using the constants defined above, A is defined in Equation 13. gf The matrix can be expressed as shown in Equation 17 below.

[0157] Equation 17 The detailed definitions of the parameters in Equation 17 are as follows.

[0158] Here, a 11 and a 21 Represents the coefficient.

[0159] Figures 13a to 13c This is a graph showing the root locus of a stability verification model for a shipborne microgrid operation method according to this embodiment, with specific parameter modifications.

[0160] Figure 13a The root locus of the initial value of the phase difference between the grid forming controller and the grid is shown. According to... Figure 13a It can be confirmed that as the initial phase difference with the shipboard microgrid increases, the specific root has a positive real number, thus the system becomes unstable.

[0161] Figure 13bThe green root locus is shown, obtained by changing the virtual impedance value when the system is unstable due to the initial phase difference. Figure 13b As shown, it can be confirmed that when the virtual inductance component of the virtual impedance is increased, the roots with positive values ​​become negative, and thus the system becomes stable.

[0162] On the other hand, such as Figure 13c As shown, it can be confirmed that when only the virtual resistance component of the virtual impedance is increased, the system stabilization effect is not significant, and the negative real root shifts from the origin, thereby achieving the effect of reducing the damping characteristics of the system.

[0163] Figure 14 This is a diagram illustrating the simulation control configuration that can be used in the shipborne microgrid operation method of this embodiment.

[0164] Figure 14 This corresponds to at least a portion of the structure of the ship's power controller used for simulation when the SCIG's power converter switches the control mode from grid feeding to grid forming. The ship's power controller may include a grid feeding control unit 417 and a grid forming control unit 418.

[0165] The power grid feed control unit 417 may include: converting the three-phase (abc) voltage V along the dq axis. abc To output the q-axis output voltage V oq and d-axis output voltage v od The grid forming control unit 418 may include a power equation processing unit, a droop function processing unit, a voltage controller, a current controller, two DQ conversion units, and a DQ inverse conversion unit.

[0166] The first converter voltage command u generated by the power grid feed control unit 417 abc,feed and the second converter voltage command u generated by the power grid forming control unit 418 abc,form Based on the switching operation of the circuit breaker on the distribution board at the first moment (t=T1), the PWM control module of the ship's power controller can be selectively applied to switch the operating mode of the power converter connected to the SG in the ship's microgrid.

[0167] That is, when the power converter of SG switches the control mode, the ship's power controller can perform control to make the reference power value become zero in the grid-fed state before the first time T1, and then immediately switch the control mode to the grid formation mode after the first time T1.

[0168] Figure 15a and Figure 15b It shows the basis Figure 14The simulation control configuration is shown in the graphs of active and reactive power simulation results during the control mode switching between grid feeding and grid formation.

[0169] Figure 15a and Figure 15b The simulation results for active and reactive power during control mode switching are shown, depending on whether virtual impedance is applied and whether components are combined. The simulation results are presented numerically in Table 2.

[0170] Table 2 from Figure 15a and Figure 15b The results for group A show that, without virtual impedance, it can be confirmed that active power, reactive power, voltage, and frequency all experienced severe fluctuations during the control mode switching, leading to disconnection from the grid.

[0171] The results for group B, which only has a virtual resistance component, also showed no significant difference from those for group A, leading to disconnection from the power grid.

[0172] On the other hand, in groups C and D with virtual inductance components, it can be seen that all indicators show no significant fluctuations, indicating successful connection to the grid and allowing grid formation control to be initiated. Since grid formation control is executed normally, power can be supplied to the loads of the shipboard microgrid independently, even when the synchronous generator operation is stopped.

[0173] In this way, simulation can confirm that switching to grid forming control mode requires a virtual inductor, and as referenced Figure 5 The efficient operation sequence for SCIG described is possible. Furthermore, it can be confirmed that the simulation results are consistent with the above references. Figures 13a to 13c The described root locus results are similar.

[0174] Figure 16a and Figure 16b This is a diagram illustrating the simulation results of active and reactive power during the control mode switching between grid feeding and grid formation when the shipboard microgrid operation method of this embodiment is applied to an actual ship.

[0175] like Figure 16a and Figure 16b As shown, in order to verify the ship power controller of this embodiment on an actual ship, in conjunction with the above reference... Figure 15a and Figure 15b Under the same simulation conditions, an experiment on the effect of virtual impedance was performed when the control mode was switched to grid formation mode. The experimental results obtained for the four sets of virtual impedances are shown in Table 3.

[0176] Table 3 When there is no virtual impedance as in group A, it can be confirmed that active power, reactive power, voltage and frequency all experienced severe fluctuations during control mode switching, which caused the shaft generator system to disconnect from the shipboard microgrid.

[0177] In addition, it can be seen that in group B, which only has virtual resistance components, the shaft-driven generator system is also disconnected from the shipboard microgrid due to control instability.

[0178] Similar to the simulation results, in groups C and D with virtual inductance components, it can be confirmed that all indicators do not fluctuate significantly, and the shaft-driven generator system is connected to the shipboard microgrid to initiate grid formation control.

[0179] As can be seen, these experimental results are similar to the root locus results and simulation results of the above embodiments.

[0180] Figure 17a and Figure 17b This is a graph showing the power factor, active power, and reactive power during parallel operation of the grid-forming power converter and synchronous generator before and after the application of the SVC in the shipborne microgrid operation method of this embodiment. Figure 18a and Figure 18b This is a graph showing the reference voltage and output voltage curves before and after the application of the SVC, when the grid-forming power converter and the synchronous generator are operating in parallel.

[0181] Figure 17a , Figure 17b , Figure 18a and Figure 18b The experimental verification results from the SVC are shown. Specifically, the waveforms of active power, reactive power, power factor, and output voltage during parallel operation of the synchronous generator and the grid-forming power converter are displayed by different grayscale levels.

[0182] When no SVC is applied, as the load increases due to the impedance of the power converter and the voltage drop on the isolation transformer side, the final voltage amplitude output voltage droop characteristic curve (load-voltage) becomes lower than the synchronous generator's droop curve (load-voltage), resulting in... Figure 17a and Figure 18b The phenomenon shown is that reactive power cannot be stably supplied to the shipboard microgrid.

[0183] As shown in these figures, with the ship's load power factor at 0.8, the power factor of the power converter increases to 0.9, causing the power factor of other synchronous generators to drop to 0.7, resulting in an imbalance in reactive power distribution. Since a reactive power imbalance exceeding 10% is unacceptable according to classification society standards defining ship safety standards, this operating condition does not meet safety standards.

[0184] As mentioned above Figure 12 The experimental results obtained by applying the self-SVC structure of this embodiment are as follows: Figure 17b and Figure 18b As shown in the figures, it can be confirmed that, with the power factor of the ship's load fixed at 0.8, reactive power is smoothly fed at a power factor of 0.8, similar to other synchronous generators.

[0185] Figure 19a and Figure 19b This is a diagram illustrating the power factor, active power, and reactive power during independent operation of the grid-forming power converter in the shipborne microgrid operation method of this embodiment. Figure 20a and Figure 20b This is a diagram showing the reference voltage and output voltage during independent operation of the grid-forming power converter in the shipborne microgrid operation method of this embodiment.

[0186] Figure 19a , Figure 19b , Figure 20a and Figure 20b The experimental verification results of the grid-forming power converter during independent operation are shown, and the waveforms of active power, reactive power, power factor and output voltage are displayed by different gray levels depending on whether they are applied from SVC.

[0187] When no SVC is applied during the independent operation of the grid-forming power converter in a shipboard microgrid, due to the impedance of the power converter and the voltage drop on the isolation transformer side, the final voltage amplitude, in addition to the output voltage droop, is also accompanied by a voltage drop due to the output current. Therefore, it can be confirmed that, Figure 19a and Figure 20a As shown, depending on the load size, the voltage drop can be as high as 4% of the rated voltage.

[0188] On the other hand, Figure 19b and Figure 20b The experimental waveforms obtained during independent operation of the power converter with SVC can be confirmed. When SVC is executed to maintain the voltage on the secondary side of the isolation transformer at 1 pu based on the rated voltage, the impedance of the power converter control closed loop and the voltage drop of the isolation transformer can be compensated, thus confirming that the voltage on the secondary side of the isolation transformer is maintained at 1 pu.

[0189] As described in the above embodiments, the present invention provides an efficient grid connection control method for a grid-forming SG applied to a ship, and a self-SVC method for improving the power quality of the shipboard power grid. Furthermore, when simulating the droop characteristics of a synchronous generator, self-SVC can be performed to compensate for voltage drops occurring in the grid-forming power converter and connection devices such as isolation transformers. In this case, self-SVC can be applied based on voltage references for both parallel and independent operations. Additionally, to ensure the stability of the power converter during control mode switching between grid feeding and grid forming, a grid-forming control mode based on virtual impedance can be applied, and an efficient grid input sequence for a squirrel-cage induction-based SG using this mode can be provided. The effectiveness of the present invention has been verified by evaluating stability using root locus-based equation models, performing MATLAB / SIMULINK simulations, and conducting verification experiments on ships with actual SGs.

[0190] The method described above according to the present invention can be implemented by program instructions that can be executed by various computers and recorded in a computer-readable medium. The computer-readable medium may include data files, data structures, etc., alone or in combination with the program instructions. The program instructions recorded in the computer-readable medium may be specifically designed and configured for the present invention, or may be known and available to those skilled in the art of computer software.

[0191] Examples of computer-readable media include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, etc. Examples of program instructions include machine code generated by a compiler, and high-level code that can be executed by a computer using an interpreter, etc. The aforementioned hardware devices can be provided to operate as one or more software modules to perform the operations of the present invention, and vice versa.

[0192] Although the invention has been described with reference to embodiments, those skilled in the art will understand that various changes and modifications may be made without departing from the spirit and scope of this disclosure as defined by the appended claims.

Claims

1. A method for ship power management, comprising: Connect the shaft-driven generator electrically to the shipboard microgrid; A generator-side converter connected to the power converter of the shaft-driven generator based on zero-power reference control; Charge the DC link capacitor of the power converter; The current of the DC link capacitor is used to excite the shaft-driven generator; The shaft-driven generator is made to perform self-generation; The grid-side converter of the power converter is based on zero-power reference control; The generator-side converter controls the power converter to charge the DC link capacitor with the power from the shaft-driven generator; as well as The power converter performs self-secondary voltage control, enabling the shaft-driven generator to operate as a distributed generator in the shipboard microgrid.

2. The ship power management method according to claim 1, wherein, Charging the DC link capacitor of the power converter connected to the shaft-driven generator includes: controlling the grid-side converter to charge the DC link capacitor to at least a portion of its rated voltage, and maintaining the charged DC voltage through the control of the power converter.

3. The ship power management method according to claim 1, further comprising: Before energizing the shaft-driven generator, the grid-side converter is controlled in grid-feed mode.

4. The ship power management method according to claim 3, further comprising: When the DC link capacitor is charged to the rated voltage or preset voltage using the power from the shaft-driven generator, the grid-side converter is switched from the grid feeding mode to the grid forming mode.

5. The ship power management method according to claim 4, wherein, Performing the self-secondary voltage control includes: determining or selecting a control droop coefficient based on preset or real-time acquired measurement values, and performing voltage control of the grid-side converter.

6. The ship power management method according to claim 5, wherein, The execution of secondary voltage control further includes: subtracting each of the feedback output voltage reference and the preset fixed virtual impedance from the output voltage reference, and transmitting the result of the subtraction to the voltage controller.

7. The ship power management method according to claim 5, further comprising: At least one of torque control and flux control is performed on the shaft-driven generator to maintain the voltage of the DC link capacitor.

8. The ship power management method according to claim 5, further comprising: At least one of torque control and flux control is performed on the shaft-driven generator to connect the power converter to the common coupling point of the shipboard microgrid.

9. The ship power management method according to claim 8, further comprising: The stator resistance of the shaft-driven generator is adaptively estimated using a semi-positive definite Lyapunov function that includes the stator resistance error used for torque control or flux control of the shaft-driven generator.

10. The ship power management method according to claim 9, wherein, The estimation further includes: when solving the equation using the derivative of the semi-definite Lyapunov function, using a low-pass filter to perform integral control to achieve fast convergence of the equation solution.

11. A shipboard power management device for a shipboard microgrid based on a grid-forming shaft-driven generator, the shipboard power management device comprising: At least one command, including a sequence of grid connection for the shaft-driven generator; as well as A processor, connected to a memory storing the at least one command, executes the at least one command. The processor executes, via the at least one command: Connect the shaft-driven generator electrically to the shipboard microgrid; A generator-side converter connected to the power converter of the shaft-driven generator based on zero-power reference control; Charge the DC link capacitor of the power converter; The current of the DC link capacitor is used to excite the shaft-driven generator; The shaft-driven generator is made to perform self-generation; The grid-side converter of the power converter is based on zero-power reference control; The generator-side converter controls the power converter to charge the DC link capacitor with power from the shaft-driven generator; and The power converter performs self-secondary voltage control, enabling the shaft-driven generator to operate as a distributed generator in the shipboard microgrid.

12. The ship power management equipment according to claim 11, wherein, When charging the DC link capacitor of the power converter connected to the shaft generator, the processor controls the grid-side converter to charge the DC link capacitor to at least a portion of its rated voltage, and maintains the charged DC link voltage under the control of the power converter.

13. The ship power management equipment according to claim 11, wherein, The processor further performs the following: controlling the grid-side converter in grid-feed mode before energizing the shaft-driven generator.

14. The ship power management equipment according to claim 13, wherein, The processor further executes the following: when the DC link capacitor is charged to the rated voltage or preset voltage using the power from the shaft generator, the grid-side converter is switched from the grid feeding mode to the grid forming mode.

15. The ship power management equipment according to claim 14, wherein, When performing the self-secondary voltage control, the processor determines or selects a control droop coefficient based on preset or real-time acquired measurement values ​​to perform voltage control of the grid-side converter.

16. The ship power management equipment according to claim 15, wherein, When performing the self-secondary voltage control, the processor further performs the following: subtracting each of the feedback output voltage reference and the preset fixed virtual impedance from the output voltage reference, and transmitting the result of the subtraction to the voltage controller.

17. The ship power management equipment according to claim 15, wherein, The processor further performs at least one of torque control and flux control on the shaft-driven generator to maintain the voltage of the DC link capacitor.

18. The ship power management equipment according to claim 15, wherein, The processor further performs the following: adaptively estimating the stator resistance of the shaft-driven generator using a semi-positive definite Lyapunov function defined to include the stator resistance error used for torque control or flux control of the shaft-driven generator.

19. A vessel, comprising a hull, the hull being equipped with a vessel electrical management device according to any one of claims 11 to 18.

20. A vessel using the vessel power management method according to any one of claims 1 to 10.

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