A ship power management method and apparatus based on a grid-forming shaft generator, and a ship using the same.

Abstract

A ship power management method, apparatus, and ship using the same are disclosed for stably connecting a shaft generator to a ship's power system and stably supplying its power. The ship power management method involves connecting a shaft generator to a ship's power system, controlling the generator-side converter of a power converter connected to the shaft generator with a zero-power reference, charging the DC-end capacitor of the power converter, using the current from the DC-end capacitor to magnetize the shaft generator and cause it to generate its own power, controlling the grid-side converter of the power converter with a zero-power reference, controlling the generator-side converter to charge the DC-end capacitor with the power from the shaft generator, and performing secondary voltage control in the power converter so that the shaft generator operates as a distributed generator in the ship's power system.

Description

[Technical Field]

[0001] The present invention relates to ship power system management technology based on grid-forming shaft generators, and more particularly to a ship power management method and apparatus for stably supplying power from a grid-forming shaft generator to a ship power system and stably connecting the shaft generator to the ship power system, and to a ship using the same. [Background technology]

[0002] To reduce carbon emissions from ships, there is a growing demand for ship propulsion and power production using alternative energy resources. Batteries, fuel cells, and solar thermal power are among the alternative energy resources that are attracting attention, and shaft generators, which install generators on the propeller shafts of existing power systems, have also been applied to many ships in recent years as part of the alternative energy source.

[0003] A ship power management system is configured to control the operation of power converters connected to multiple synchronous generators and shaft generators on the ship's propeller shafts (see Figure 1). The control systems for ship power systems have been standardized over decades based on synchronous generators, and due to industrial characteristics, it is preferred that power converters for alternative energy resources mimic existing synchronous generators rather than modifying the structure of the validated overall control system. Therefore, power converters for alternative energy sources must mimic the control methods of existing synchronous generators, namely the voltage droop and frequency droop characteristics.

[0004] On the other hand, in most power converters for alternative energy resources, voltage drops occur due to circuit impedance, specifically the impedance caused by the grid-forming voltage control loop of the power converter and the use of isolation transformers in the output stage to block common-mode noise. However, it is impossible to simulate the same voltage droop characteristics as a synchronous generator depending on the load current, and currently, there are no secondary voltage controllers in marine power control systems that can compensate for this.

[0005] Therefore, when using alternative energy resources such as grid-forming shaft generators in ship power systems, problems arise with reactive power supply during parallel operation and voltage drop during island operation, and appropriate measures are needed to solve these problems. [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention was derived to meet the requirements of the prior art, and its objective is to provide a ship power management method and apparatus that applies virtual impedance to the voltage control of a power converter connected to a grid-forming shaft generator, thereby enabling the power converter to have sufficient inertia against disturbances and effectively supplying the power generated by the shaft generator to the ship's power system.

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

[0008] Another object of the present invention is to provide a ship power management method and apparatus that can perform self-secondary voltage control using a power converter connected to the shaft generator, depending on the parallel operation or single operation mode of the shaft generator, even in a ship power management system where a separate secondary voltage controller is not present.

[0009] Another object of the present invention is to provide a ship that uses the aforementioned ship power management method or ship power management device. [Means for solving the problem]

[0010] A ship power management device based on a grid-forming shaft generator according to one aspect of the present invention for solving the above technical problems is a ship power management device for a ship power system based on a grid-forming shaft generator, comprising: at least one instruction comprising a shaft generator system connection sequence; and a processor connected to a memory storing the at least one instruction and executing the at least one instruction. The processor performs the steps of: electrically connecting the shaft generator to the ship power system by the at least one instruction; controlling the generator-side converter of a power converter connected to the shaft generator with a zero power reference; charging the DC-end capacitor of the power converter; magnetizing the shaft generator using the current of the DC-end capacitor; causing the shaft generator to generate its own power; controlling the grid-side converter of the power converter with a zero power reference; controlling the generator-side converter of the power converter to charge the DC-end capacitor with the power of the shaft generator; and performing self-secondary voltage control via the power converter so that the shaft generator operates as a distributed generator in the ship power system.

[0011] A ship power management method based on a grid-forming shaft generator according to another aspect of the present invention for solving the above technical problems includes the steps of: electrically connecting the shaft generator to a ship power system; controlling the generator-side converter of a power converter connected to the shaft generator with a zero power reference; charging the DC-end capacitor of the power converter; magnetizing the shaft generator using the current of the DC-end capacitor; causing the shaft generator to generate its own power; controlling the grid-side converter of the power converter with a zero power reference; controlling the generator-side converter of the power converter to charge the DC-end capacitor with the power of the shaft generator; and performing self-secondary voltage control via the power converter so that the shaft generator operates as a distributed generator in the ship power system.

[0012] The step of charging the DC-end capacitor of a power converter connected to the shaft generator may include controlling the grid-side converter to charge at least a portion of the rated voltage of the DC-end capacitor. The charged DC voltage may be maintained by controlling the power converter.

[0013] The aforementioned ship power management method (hereinafter also simply referred to as "the method") may further include the step of controlling the grid-side converter in grid-feeding mode before the step of magnetizing the shaft generator.

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

[0015] The step of performing the self-secondary voltage control may include controlling the voltage of the grid-side converter according to a control droop coefficient determined or selected based on a preset or real-time acquired measurement value.

[0016] The step of performing the self-secondary voltage control may further include the step of subtracting the feedbacked output voltage reference and the preset fixed virtual impedance from the output voltage reference and transmitting the result to the voltage controller.

[0017] The aforementioned virtual impedance can be constructed by adding a virtual inductance and a virtual resistance.

[0018] The method may further include the step of maintaining the voltage of the DC end capacitor by performing at least one of the torque control and magnetic flux control of the shaft generator.

[0019] The method may further include the step of performing at least one of torque control and magnetic flux control on the shaft generator to connect the power converter to the common coupling point of the ship's power system.

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

[0021] The estimation step may further include performing integral control using a low-pass filter to ensure rapid convergence of the solution to the equation when solving the equation using the derivative of the quasi-positive definite Lyapunov function.

[0022] A ship using a ship power management method according to another aspect of the present invention for solving the above technical problems is a ship using a ship power management method for a ship power system based on a grid-forming shaft generator, and includes a memory storing at least one instruction for implementing a shaft generator system startup sequence, and a processor connected to the memory for executing the at least one instruction, and a hull on which the ship power management device is mounted. Here, the processor, by the at least one instruction, electrically connects a shaft generator to a ship power system, controls a generator-side converter of a power converter connected to the shaft generator with a zero power reference, charges a DC-side capacitor of the power converter, magnetizes the shaft generator using the current of the DC-side capacitor, self-generates the shaft generator, controls a grid-side converter of the power converter with a zero power reference, controls the generator-side converter of the power converter to charge the DC-side capacitor with the power of the shaft generator, and performs self-secondary voltage control via the power converter so that the shaft generator operates as a distributed generator of a ship power supply system.

[0023] In the ship, when charging the DC-side capacitor of the power converter connected to the shaft generator, the processor can control the grid-side converter to charge at least a part of the rated voltage of the DC-side capacitor and maintain the DC-side voltage charged by the control of the power converter.

[0024] In the ship, before executing the step of magnetizing the shaft generator, the processor can further execute the step of controlling the grid-side converter in a grid feeding mode.

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

[0026] In the ship, in the step of performing the self-secondary voltage control, the processor can perform voltage control of the grid-side converter according to a control loop coefficient determined or selected based on a measurement value preset or collected in real time.

[0027] In the ship, in the step of performing the self-secondary voltage control, the processor can further execute a step of subtracting each of the fed-back output voltage reference and the preset fixed virtual impedance from the output voltage reference and transmitting the result to a voltage controller.

[0028] In the ship, the processor can further execute a step of maintaining the voltage of the DC-link capacitor by performing at least one of torque control and flux control of the shaft generator.

[0029] In the ship, the processor can further execute a step of adaptively estimating the stator resistance of the shaft generator by using a positive definite Lyapunov function defined to include the stator resistance error for torque control or flux control of the shaft generator.

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

Advantages of the Invention

[0031] According to the present invention, it is possible to provide an efficient grid connection method for grid-forming shaft generators applied to ships, and a self-secondary voltage control method for improving the power quality of ship power systems. In particular, in order to ensure stability when switching between the grid-feeding control mode and the grid-forming control mode of a power converter connected to a shaft generator, a grid-forming control mode based on virtual impedance can be provided, thereby enabling efficient power grid connection of shaft generators based on cage-type induction equipment.

[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 generator, in order to solve the voltage drop that occurs in the grid forming power converter and interconnection equipment (isolation transformer, etc.), the power converter performs self-secondary voltage control according to a preset voltage reference for both parallel operation and island operation, respectively, thereby enabling the shaft generator to effectively perform grid forming operation in the ship's power system. [Brief explanation of the drawing]

[0033] [Figure 1] This is a schematic diagram of a ship's power system to which a ship's power management method based on a grid-forming shaft generator according to one embodiment of the present invention can be applied. [Figure 2] Figure 1 is a graph illustrating the voltage droop characteristics of a ship power management system that can be used in a ship's power grid. [Figure 3] Figure 1 is a graph illustrating the frequency droop characteristics of a ship power management system that can be used in a ship's power grid. [Figure 4] Figure 1 is a schematic block diagram of a ship power management device that can be used in the ship's power system. [Figure 5] This is a block diagram illustrating the control process of a cage-type induction generator that can be used in the ship's power management system shown in Figure 4. [Figure 6]Figure 5 is a flowchart of the SCIG control steps that can be performed by the ship's power management system. [Figure 7] This is a block diagram illustrating the first operating mode (Phase I) of the SCIG control steps shown in Figure 6. [Figure 8] This is a block diagram illustrating the second operating mode (Phase II) of the SCIG control steps shown in Figure 6. [Figure 9] This is a block diagram illustrating the third operating mode (Phase III) of the SCIG control steps shown in Figure 6. [Figure 10] This is a block diagram illustrating the adaptive flux control process applicable to the SCIG control step in Figure 6. [Figure 11] Figure 4 is a block diagram illustrating the virtual impedance-based voltage control process of a grid-forming power converter applicable to the ship's power management system. [Figure 12] This is an illustrative diagram illustrating a self-secondary voltage control structure that can be used in a ship power management method according to another embodiment of the present invention. [Figures 13a-13c] This figure shows the root locus of the stability verification model for the ship power management method of this embodiment, obtained by correcting specific factors. [Figure 14] This is a simulation control configuration diagram that can be used in the ship power management method of this embodiment. [Figures 15a-15b] Figure 14 is a graph showing the simulation results for active power and reactive power during switching between grid feeding control mode and grid forming control mode using the simulation control configuration. [Figures 16a-16b] This graph shows the simulation results for active and reactive power during switching between grid feeding control mode and grid forming control mode when the ship power management method of this embodiment is applied to an actual ship. [Figures 17a-17b]This graph shows the power factor, active power, and reactive power when the grid-forming power converter operates in parallel with the synchronous generator before and after applying self-secondary voltage control in the ship power management method of this embodiment. [Figures 18a-18b] This graph shows the reference voltage and output voltage when the grid-forming power converter operates in parallel with the synchronous generator before and after applying self-secondary voltage control in the ship power management method of this embodiment. [Figures 19a-19b] This graph shows the power factor, active power, and reactive power when the grid forming power converter is operating independently in the ship power management method of this embodiment. [Figures 20a-20b] This graph shows the reference voltage and output voltage when the grid forming power converter is operated independently in the ship power management method of this embodiment. [Modes for carrying out the invention]

[0034] The present invention can be modified in various ways and may have various embodiments; therefore, specific embodiments are shown in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, but should be understood to include all modifications, equivalents, or substitutions that fall within the scope of the idea and art of the present invention.

[0035] Terms such as "first," "second," etc., may be used to describe a variety of components, but such components should not be limited by these terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the invention, the first component may be referred to as the second component, and similarly, the second component may be referred to as the first component. The term "and / or" includes a combination of multiple items described in relation or any of multiple items described in relation.

[0036] In the embodiments of this application, "at least one of A and B" can mean "at least one of A or B" or "at least one of one or more combinations of A and B." Furthermore, in the embodiments of this application, "one or more of A and B" can mean "one or more of A or B" or "one or more combinations of one or more of A and B."

[0037] When one component is referred to as being "linked" or "connected" to another component, it should be understood that it is either directly linked to the other component, or may be connected to it, but other components may be involved in between. On the other hand, when one component is referred to as being "directly linked" or "directly connected" to another component, it should be understood that no other components are involved in between.

[0038] The terminology used in this application is used solely to describe specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates a different meaning. In this application, terms such as “includes” or “having” are intended to specify the presence of features, figures, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features or figures, steps, actions, components, parts, or combinations thereof.

[0039] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as they are generally understood by a person of ordinary skill in the art to which this invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an ideal or overly formal sense unless explicitly defined herein.

[0040] Preferred embodiments of the present invention will be described in more detail below with reference to the attached drawings. To facilitate overall understanding in this description of the present invention, the same reference numerals are used for identical components in the drawings, and redundant descriptions of identical components are omitted.

[0041] Figure 1 is a schematic diagram of a ship's power system to which a power management method for a ship's power system having a grid-forming shaft generator according to one embodiment of the present invention (hereinafter simply referred to as the "ship's power management method") can be applied.

[0042] Referring to Figure 1, the ship's power system installed on the ship 1000 may include synchronous generators 100, 110, 120, a switchboard 130, a shaft generator 150 (SG), a power converter 200, an isolation transformer 230, and a circuit breaker 250.

[0043] Synchronous generators 100, 110, and 120 may be installed from the same manufacturer for maintenance purposes. All three synchronous generators 100, 110, and 120 may be used simultaneously as distributed power sources, or only one or two of them may be used as distributed power sources.

[0044] Furthermore, synchronous generators 100, 110, and 120 constitute the main power generation equipment in the shipboard microgrid. Although they may differ in size, they are supplied by the same manufacturer and can use the same governor and automatic voltage regulator (AVR). Therefore, sharing of reactive power between synchronous generators is sufficient with primary voltage control by the AVR alone. Secondary frequency control (SFC) is generally applied to governor frequency control because even with the same engine, the combustion characteristics of the engines can differ. The droop curves for frequency and voltage of all synchronous generators in the shipboard microgrid can be designed with 3% and 2.5% droop, respectively.

[0045] The switchboard 130 may be equipped with circuit breakers connected to the synchronous generators. The circuit breakers may be referred to as the first, second, and third circuit breakers.

[0046] The shaft generator 150 is mounted on the propeller shaft connecting the ship's propeller 140 and the main engine 160, and can convert the kinetic energy of the main engine 160 transmitted via the propeller shaft into electrical energy. The shaft generator 150 may include an induction generator, which may include a squirrel-cage induction generator (SCIG). In the following description, the shaft generator 150 may also be referred to as SCIG 150.

[0047] The power converter 200 may be positioned between the shaft generator 150 and the isolation transformer 230 and may be implemented as a back-to-back converter. The back-to-back converter may consist of a generator-side converter where the shaft generator 150 is located, a grid-side converter where the point of common coupling (PCC) of the ship's power system is located, and a DC-link capacitor connected between them, and the generator-side converter and the grid-side converter may be configured to share the DC-link voltage of the DC-link capacitor. The point of common coupling (PCC) may refer to a common busbar of onboard power resources that supplies power to onboard and offboard loads connected to a distributed ship's power system.

[0048] Furthermore, unlike wind power control or solar power control such as maximum power point tracking, the grid-side converter in a back-to-back converter controls the flow of power. Therefore, the generator-side converter may be configured to maintain the DC-end voltage of the DC-end capacitor at a desired level by controlling the torque of the SCIG150, and the grid-side converter may be configured to generate power as one of a power generation unit including independent distributed generators or synchronous generators.

[0049] The isolation transformer 230 functions to physically separate the branch system, which includes the shaft generator 150 and power converter 200, which are alternative energy resources, from the main system of the ship's power grid.

[0050] Circuit breaker 250 functions to selectively connect or disconnect a branch system, including the shaft generator 150, power converter 200, and isolation transformer 230, from the main system of the ship's power system. Circuit breaker 250 may be installed on the switchboard 130 together with other circuit breakers. In that case, circuit breaker 250 may be referred to as the fourth circuit breaker.

[0051] The aforementioned ship power system can be managed by a ship power management system (SPMS) 300. The SPMS 300 can control the power of the synchronous generators 100, 110, 120, the shaft generator 150, and the power converter 200.

[0052] Furthermore, the SPMS300 can implement the generator-side converter of the power converter 200 as an active front-end converter so that it can supply external reactive power for magnetization of the shaft generator 150 when starting the shaft generator 150.

[0053] Furthermore, the SMPS300 may be configured to apply a grid-connection control sequence that can efficiently supply the power generated by the shaft generator 150 to the ship's power grid.

[0054] Furthermore, the SMPS300 may be configured to apply a pre-set fixed virtual impedance (VImp for short) to the voltage control circuit of the SMPS300, taking into account the limited impedance (X) to resistance (R) ratio (bonded X / R ratio) of the ship's power system, in order to stabilize the gridforming distributed power generation of the shaft generator 150.

[0055] Furthermore, the SPMS300 may be configured to perform secondary frequency control (SFC) using the grid-side converter of the power converter 200. In addition, the SMPS300 may be configured so that the power converter 200 itself performs secondary voltage control in a ship's power system where a secondary voltage controller is not present.

[0056] Self-secondary voltage control can be configured to control the voltage based on different target values ​​depending on whether the system is operating in parallel or isolated. For example, the SMPS300 can perform voltage control based on a target power factor value when the shaft generator 150 is operating in parallel with at least one synchronous generator 100, and can perform voltage control of the shaft generator 150, the power converter 200, or the ship's power system when the shaft generator 150 is operating in isolated mode, using the secondary voltage of the isolation transformer 230 as the target voltage (e.g., 1 [pu]).

[0057] For reference, since most ships utilize AC power grids, such alternative energy resources must be connected to the ship's power grid via power converters. Power converters must essentially operate in parallel with existing onboard synchronous generators to supply power to the ship's loads, and must also have the capability to supply power to the ship's loads independently depending on the ship's operating conditions. Therefore, power converters based on alternative energy sources on ships must necessarily perform grid-forming control, and may also perform grid-feeding control depending on the characteristics of the alternative energy source.

[0058] For example, grid feeding control is necessary for purposes such as target power value tracking control (P, Q control) for estimating the maximum power point of solar power generation, and power supply limitation during the initial magnetization step of cage-type induction generators. Furthermore, since a ship's power system is an independent, standalone system, it must be possible to continuously supply power to the onboard load. Therefore, even when a power converter is performing grid feeding control, it must always be possible to instantly switch to grid forming control mode, and independent operation of alternative energy sources must be possible.

[0059] In grid feeding mode, active and reactive power are controlled in synchronization with the grid via a phase-fixed loop, whereas in grid forming mode, the target values ​​for output voltage magnitude and frequency are determined by the set droop (load sharing). Therefore, when switching from grid feeding mode to grid forming mode, the output voltage of the power converter connected to the alternative energy resource changes instantaneously, and at this time, the output voltage of the power converter inherently contains differences in phase, magnitude, and frequency from the grid voltage. This acts as a kind of disturbance in the power converter's control system, and the low inertia of typical power converters cannot withstand this disturbance, so the alternative energy resource cannot switch to grid forming mode and drops out of the grid due to frequency and voltage divergence.

[0060] As a result, in this embodiment, by applying a virtual impedance to the voltage control of the power converter connected to the grid-forming shaft generator, the power converter can have sufficient inertia against disturbances, and a ship can be provided that can effectively supply the power generated by the shaft generator to the ship's power system. Furthermore, according to this embodiment, by using a self-secondary voltage control algorithm, the voltage drop within the shaft generator system can be effectively compensated by the power converter connected to the shaft generator of the ship's power system, and even in a ship's power management system that does not have a secondary voltage controller, a ship can be provided that can perform self-secondary voltage control using the power converter connected to the shaft generator according to the parallel operation or single operation mode of the shaft generator.

[0061] Figure 2 is a graph illustrating the voltage droop characteristics of the ship power management system that can be used in the ship power system shown in Figure 1. And Figure 3 is a graph illustrating the frequency droop characteristics of the ship power management system that can be used in the ship power system shown in Figure 1.

[0062] As shown in Figure 2, in a ship's power system, three or four synchronous generators from the same manufacturer are installed for maintenance purposes. Therefore, the voltage droop characteristics of each synchronous generator controlled by the automatic voltage regulator are very similar among the generators and can be fixed without applying separate secondary voltage control (SVC). The automatic voltage regulator may be supplied integrated with the synchronous generator.

[0063] On the other hand, as illustrated in Figure 3, even synchronous generators of the same type can have different combustion characteristics. Therefore, the frequency droop characteristics between multiple synchronous generators used in the power system of a single vessel can be adjusted by secondary frequency control (SFC).

[0064] Furthermore, in distributed ship power systems that include alternative energy resources along with synchronous generators, particularly shaft generators coupled to the propeller shafts of ships, it is necessary to perform at least one of secondary voltage control and secondary frequency control in the grid-forming operating mode of the shaft generator so that the power of the shaft generator can be effectively connected to the point of common coupling (PCC) of the ship power system, that is, so that the shaft generator can operate in the same way as a synchronous generator.

[0065] Therefore, the ship power management system of this embodiment may be configured so that the shaft generator system, including the shaft generator and power converter, operates as a plug-and-play distributed power source that replicates the operation of a synchronous generator.

[0066] In particular, shaft generators are typically operated as independent distributed generators during normal ship operation, but they have limitations due to the reduction of surplus power from propulsion systems such as engines and the shaft speed dependence of shaft generator power. To ensure the safe and efficient operation of shaft generators, ship power management systems may be configured to monitor the aforementioned limitations and implement measures such as load shedding or starting synchronous generators under specific circumstances. Such measures may also include measures to address situations such as shaft generator overload due to high-power loads in the ship's power system, mechanical load fluctuations of propulsion engines due to rough seas, and propulsion engine deceleration.

[0067] Thus, the ship power management system of this embodiment can be configured to apply a rapid grid-on sequence for shaft generators in a distributed ship power system including shaft generators. Furthermore, the ship power management system can be configured to apply a control algorithm based on a fixed virtual impedance to stably switch between grid-feeding and grid-forming operating modes. Additionally, the ship power management system can be configured to apply self-secondary voltage control by the power converter of the shaft generator in grid-forming operating mode.

[0068] Figure 4 is a schematic block diagram of a ship power management device that can be used in the ship power management system of the ship power system shown in Figure 1.

[0069] Referring to Figure 4, the ship power management device 400 may correspond to the ship power management system 300 (SPMS) that manages the ship's power system shown in Figure 1. The ship power management device 400 may include at least one processor 410 and memory 420. The ship power management device 400 may further include a transceiver 430 that connects to and communicates with terminals and communication devices of administrators, users, etc., of the ship network or external dedicated or commercial power distribution network. The ship power management device 400 may further include an input interface device 440, an output interface device 450, a storage device 460, and so on. Each component included in the ship power management device 400 can communicate with each other by being connected by a bus 470.

[0070] More specifically, the processor 410 can execute software modules or program commands stored in at least one of the memory 420 and the storage device 460. As an example, the processor 410 may include a virtual impedance control unit 412, a shaft generator system switching unit 414, a self-secondary voltage control unit 416, and a mode switching unit 418, and such components may be mounted on the processor 410 in the form of software modules or program commands, the configuration and / or functions thereof will be described in detail below. The aforementioned processor 410 may be embodied in a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor on which the method according to the embodiment of the present invention is performed.

[0071] Each of the memory 420 and the storage device 460 may consist of at least one of a volatile storage medium and a non-volatile storage medium. For example, the memory 420 may consist of at least one of a read-only memory (ROM) and a random access memory (RAM).

[0072] The transceiver 430 may include a communication interface or sub-communication system for communication inside, outside, or between inside and outside a ship, such as short-range wireless networks, cable connections, satellite communications, or wireless communication with general-purpose base stations.

[0073] The input interface device 440 may include at least one input means selected from a keyboard, microphone, touchpad, touchscreen, etc., and an input signal processing unit that maps or processes signals input via at least one input means to pre-stored commands.

[0074] The output interface device 450 may include an output signal processing unit that maps or processes a signal output according to the control of the processor 410 to a pre-stored signal form or level, and at least one output means that outputs the signal or information contained in the signal in at least one form selected from a predetermined level of vibration, light, sound, etc., according to the signal of the output signal processing unit. The at least one output means may include at least one selected from output means such as a speaker, display device, printer, optical output device, and vibration output device.

[0075] Figure 5 is a block diagram illustrating the control process of a cage-type induction generator that can be used in the ship's power management system shown in Figure 4.

[0076] First, the environment for controlling the SCIG-type induction generator 150 is described as follows. The SCIG150 can be controlled using direct torque control (DTC). Unlike flux vector control, which depends on the 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. Because the DTC method is model-based, it relies on precise model parameters for optimal control performance. Therefore, the stator flux linkage vector and the torque generated by this vector can be estimated based on the motor model of the SCIG150.

[0077] Thus, estimating the stator flux linkage is crucial in the SCIG control process of this embodiment. Furthermore, since the estimation of the stator flux linkage depends on the accuracy of the stator resistance measured by SCIG150, it is necessary to monitor the accurate stator resistance in real time in order to accurately estimate the stator flux linkage. In other words, if torque control fails due to uncertainty in the SCIG model parameters, and an imbalance occurs between power supply and demand, a power outage may occur on the ship.

[0078] On the other hand, since the SCIG150 is not designed to self-excitation, it requires external reactive power for magnetization. Therefore, the power converter connected to the ship's power management device in this embodiment may be configured to use an active front-end converter instead of a passive converter.

[0079] As shown in Figure 5, the ship's power management device of this embodiment may be configured to receive motor voltage and current, DC voltage, and switching commands from the SCIG150 as input to the motor model, and to receive values ​​or signals related to torque and flux linkage from the motor model. The DC voltage may correspond to the DC end voltage as the voltage between the DC end capacitor terminals of the generator-side converter connected to the SCIG150.

[0080] Furthermore, the ship's power management system may be configured to generate a torque reference based on a DC voltage reference and DC voltage, and to calculate the torque error (ΔTorque, ΔT) by comparing the torque with the torque reference via a torque comparator. The ship's power management system may also be configured to calculate the flux error (ΔFlux, ΔF) by comparing the flux linkage with a flux linkage reference using a flux linkage comparator. Finally, the ship's power management system may be configured to input the torque error and flux error to a hysteresis pulse selector (HPS), and to generate switch commands based on the torque error and flux error via the HPS. These switch commands may be used to control the generator-side converter connected to the SCIG150.

[0081] The aforementioned ship power management device can perform the SCIG control steps described later in order to enable the SCIG150 to function as a distributed generator.

[0082] In this description of the embodiment, the term "reference" may refer to an electronic device that ideally generates a physical quantity at a constant or fixed rate, regardless of load, power supply fluctuations, temperature changes, and time, or to a reference physical quantity generated by such an electronic device. For example, a voltage reference may refer to an electronic device that ideally generates a constant or fixed voltage, regardless of the surrounding environment or conditions, or to a voltage generated by such an electronic device. The generated voltage may correspond to a reference voltage.

[0083] Figure 6 is a flowchart of the SCIG control steps that can be performed by the ship power management device shown in Figure 5. Figure 7 is a block diagram illustrating the first operating mode (Phase I) of the SCIG control steps in Figure 6. Figure 8 is a block diagram illustrating the second operating mode (Phase II) of the SCIG control steps in Figure 6. And Figure 9 is a block diagram illustrating the third operating mode (Phase III) of the SCIG control steps in Figure 6.

[0084] Referring to Figure 6, the ship's power management device can perform three control steps or first to third operating modes as the grid-forming SCIG grid-on-grid sequence. Specifically, the ship's power management method performed by the ship's power management device may include the steps of: connecting a shaft generator to a grid, which is at least part of the ship's power system, and magnetizing the shaft generator using the grid-side current charged in the DC-end capacitor (S610); power controlling the grid-side converter with a zero-power reference before the shaft generator feeds power to the grid, thereby generating self-power so that the generator-side converter charges the DC-end capacitor (S630); and controlling the self-secondary voltage for distributed power generation of the shaft generator so that the shaft generator operates as a distributed generator in the ship's power system (S650).

[0085] To explain each step in more detail, as shown in Figure 7, in the first control step (phase I), the grid-side converter 220 can charge the DC end capacitor 215 by receiving power P from the ship's power system, to which at least one synchronous generator 100 is connected, under the control of the ship's power management device. The grid-side converter 220 can charge the DC end capacitor 215 to 90% of its rated DC voltage and perform power control to maintain the charged DC voltage.

[0086] Furthermore, in the first control step, the generator-side converter 210 can magnetize the rotor of the cage-type induction generator SCIG by utilizing the DC-link voltage of the DC-end capacitor 215. Magnetization refers to the operation of the generator-side converter 210 with a predetermined voltage V S This can be described as generating a magnetomotive force, i.e., magnetic flux or magnetic flow, in the windings of a shaft generator by passing a corresponding current through them to form a magnetic field. In the first control step, since the shaft generator did not start generating power, the torque of the generator can be controlled to zero.

[0087] The second control step (phase II) is to enable the shaft generator to start generating power on its own and to confirm that the shaft generator is generating power normally. As shown in Figure 8, in the second control step, the grid-side converter 220 may be controlled in grid-feed mode to cut off the supply of power from the grid side to the generator side, which is powered by at least one synchronous generator 100. In this case, the power reference value of the grid-side converter 220 is 0. That is, the grid-side converter 220 may be power-controlled with a zero power reference.

[0088] Furthermore, in the second control step, the generator-side converter 210 may be controlled to start self-generation and charge the DC-end capacitor 215 to its rated voltage. For this purpose, the ship's power management system can control the torque of the shaft generator. Once self-generation is performed successfully and the electrical energy of the shaft generator charges the DC-end voltage of the DC-end capacitor 215 to its rated voltage, the ship's power management system can switch the control mode of the shaft generator system to the third control step.

[0089] In the third control step (Phase III), as shown in Figure 9, the grid-side converter 220 can be switched to grid-forming mode so that the shaft generator based on the cage-type induction generator can perform the same role as the synchronous generator 100 of the ship's power system. At this time, the ship's power management system can perform voltage control with droop on the voltage control circuit of the grid-side converter 220 according to a control droop coefficient determined or selected based on a preset or real-time collected measurement value, so that the grid-side converter 220 has sufficient inertia to the grid-forming mode based on the virtual impedance. This allows the grid-side converter 220 to switch from grid-feeding mode to grid-forming mode stably and quickly, i.e., instantaneously. The ship's power management system can keep the circuit breaker 250 open until immediately before performing the mode switching of the grid-side converter 220.

[0090] Furthermore, in the third control step, the generator-side converter 210 can operate as a grid-forming power converter to supply power to the ship's power system in a manner that conforms to the common coupling point (PCC) of the ship's power system, thereby enabling proper connection with the ship's power system, and / or to maintain the voltage of the DC end capacitor 215. In other words, the ship's power management system can control at least one of the shaft generator and the generator-side converter 210 to perform at least one of torque control and flux control on the shaft generator.

[0091] According to the first to third control steps of this embodiment described above, unnecessary circuit breaker operation and synchronization processes can be omitted, thus offering the advantage of rapid and efficient system operation.

[0092] Figure 10 is a block diagram illustrating the adaptive flux control process applicable to the SCIG control step in Figure 6.

[0093] Referring to Figure 10, an adaptive flux observer (abbreviated as "adaptive observer") that may be installed in a ship's power management system measures the stator voltage vector of the shaft generator. TIFF2026529167000002.tif97), the rotor speed of the SCIG obtained from the engine governor, TIFF2026529167000003.tif77), and estimated resistance obtained from the stator resistance adaptive scheme processor, Estimated stator current vector based on TIFF2026529167000004.tif1514 Generate TIFF2026529167000005.tif1411) and obtain the stator current from SCIG ( The observer's state estimation error vector is obtained by subtracting the estimated stator current vector from TIFF2026529167000006.tif95. It is possible to generate TIFF2026529167000007.tif95). The stator resistance adaptive processing unit receives a state estimation error vector via a low-pass filter (LPF), and an estimated stator current vector from an adaptive flux observer.

[0094] Thus, in this embodiment, assuming that the ship's power management system can obtain the rotor speed measured by the engine governor, it can be seen that the SCIG's direct torque control (DTC) can accurately estimate the stator resistance. In fact, such an assumption can be applied to distributed applications because the rotor speed is measured by the engine governor.

[0095] For example, the state-space model of SCIG can be set up with a rotor reference dq-axis. In this case, a state observer can be used that uses an estimated state matrix, which is a semi-positive definite matrix, to resolve the uncertain stator resistance in the state matrix (A). Using such a state observer, the state estimation error of the axis generator can be calculated and an error vector with the stator current error can be defined. Then, a semi-positive definite Lyapunov function can be defined that includes a quadratic function of the error vector and a stator resistance error with positive gain, so that the state observer can adaptively estimate the stator resistance.

[0096] The quasi-positive definite Lyapunov function is a method for determining stability without directly finding the solution. It can be defined such that all components of the estimated state matrix are real and a positive definite matrix of a given symmetric size satisfies a specific inequality for all vectors. Such a quasi-positive definite Lyapunov function is convex downwards in its three-dimensional graph and can converge to its minimum value when its derivative is equal to zero.

[0097] According to the derivative of the quasi-positive definite Lyapunov function, the minimum point of the Lyapunov function can be obtained by minimizing the sum of the error vectors, taking into account that the error vectors essentially depend on the estimated resistance. Therefore, the stator resistance can be estimated by solving the equation using the derivative of the quasi-positive definite Lyapunov function. In this case, integral control using an LPF may be applied to ensure fast convergence of the equation solution.

[0098] Figure 11 is a block diagram illustrating the virtual impedance-based voltage control process of a grid-forming power converter applicable to the ship power management system shown in Figure 4.

[0099] As shown in Figure 11, the ship's power management system can control the voltage of a power converter connected to a shaft generator based on virtual impedance. The power converter may be configured to have a feedback control circuit structure using a voltage controller, current controller, pulse width modulation controller, inductor filter (L filter), and capacitor filter (C filter) when operating in grid forming mode, as well as a current feedback circuit configuration that reflects the output current (i1) of the inductor filter to the input of the current controller, and a structure that applies a virtual impedance 411 to the input of the voltage controller.

[0100] Thus, the control loop of a grid-side converter can be configured as an external loop and an internal loop. The external loop may be called the external control loop, and the internal loop may be called the internal control loop. The external control loop may be configured to adjust the reference voltage based on the measured power and droop function. The internal control loop may then be configured to control the output voltage to conform to the reference of the external control loop using two controllers, namely a voltage controller and a current controller.

[0101] In particular, the ship's power management system uses a phase angle reference for the output voltage of the grid-side converter. Output voltage reference (TIFF2026529167000008.tif65) When inputting TIFF2026529167000009.tif1017) to the voltage controller, the feedback output voltage reference ( The voltage control operation of the grid-side converter can be controlled to reflect the error with TIFF2026529167000010.tif917) while simultaneously reflecting a predetermined virtual converter 411 corresponding to the output current (io) of the grid-side converter.

[0102] As mentioned above, the ship's power management system can perform voltage control based on a virtual impedance 411 for the grid-side converter to ensure system stability during power converter mode switching. The virtual impedance 411 can include a fixed virtual impedance that is predetermined or fixed. The virtual impedance 411 is a virtual inductance (L v ) and virtual resistance (R v It can take the form of adding ). When such a virtual impedance 411 is Laplace transformed, It can be expressed as "TIFF2026529167000011.tif919". Virtual inductance can also be called the virtual inductance component, and virtual resistance can also be called the virtual resistance component.

[0103] According to the virtual impedance-based voltage control of this embodiment, the grid-side converter operates as a voltage source and can effectively control the output voltage according to a predefined droop function similar to that of a synchronous generator. Furthermore, by changing the output impedance of the grid-side converter using a predetermined virtual impedance, the closed-loop transmission function of the internal control loop can be adjusted. The effect of the virtual impedance on system dynamics can be analyzed by tracking eigenvalues.

[0104] Figure 12 is an illustrative diagram illustrating a self-secondary voltage control structure applicable to a method of operating a ship's power system according to another embodiment of the present invention.

[0105] Referring to Figure 12, the self-secondary voltage controller 416, which may be included in the ship's power controller, is equipped with a power factor calculator, an adder / subtractor, a hysteresis comparator, and a changeover switch for switching to standalone operation, and has a nominal output voltage (V nom ) with offset voltage (V offset The gridforming power converter may be configured to provide a controlled nominal output voltage obtained by adding ( ). The gridforming power converter can contain impedance through a current feedback circuit, as shown in Figure 11.

[0106] In this embodiment, the problem to be solved is that when an isolation transformer for common-mode noise reduction is installed in the output stage of a shaft generator system, a voltage drop occurs depending on the output current. Therefore, it becomes difficult to control the voltage droop characteristics in the same way as the automatic voltage regulator of a synchronous generator, and self-secondary voltage control is applied to solve the problems of reactive power sharing with the synchronous generator and the voltage drop during island operation.

[0107] According to the self-secondary voltage controller structure described above, the voltage level of the voltage droop curve can be adjusted by a control value based on hysteresis. When operating in parallel with a synchronous generator, the secondary voltage control is performed at a target power factor value, i.e., the power factor value of a typical ship power load, for example, 0.8. When operating alone, the secondary voltage control can be performed to maintain the secondary voltage of the isolation transformer at the rated voltage. Furthermore, to ensure that the self-secondary voltage control does not interfere with the role of damping the virtual impedance, the bandwidth of the self-secondary voltage controller 416 can be set to 1 / 20th of the bandwidth of the grid-forming power converter.

[0108] Below, we describe the stability evaluation using root locus, simulations, and experimental results for verifying virtual impedance control, shaft generator grid connection sequences, and self-secondary voltage control.

[0109] First, to model the grid-forming power converter and evaluate its stability based on root locus, a mathematical model of the grid-forming power converter was constructed, and the system stability was evaluated depending on whether or not virtual impedance was applied and the combination of its components.

[0110] The detailed definitions of the symbols used in the mathematical models described below are shown in Table 1.

[0111] [Table 1]

[0112] First, the active power and reactive power of the electricity generated by the shaft generator can be expressed as shown in Equation 1.

[0113] [Formula 1] TIFF2026529167000013.tif21169 In equation 1, The filename is TIFF2026529167000014.tif1773. TIFF2026529167000015.tif1891 exists. The frequency and magnitude of the voltage due to the droop, which reflects secondary frequency control by the ship's power controller, can be defined as shown in Equation 2. The ship's power control device may be included in the ship's power management system.

[0114] [Formula 2] TIFF2026529167000016.tif24129 On the other hand, the voltage control mathematical model of the grid-forming power converter used in Figure 11 can be expressed as shown in Equation 3 below.

[0115] [Formula 3] TIFF2026529167000017.tif37142 In equation 3, TIFF2026529167000018.tif12133 exists. According to Equation 3, the output voltage of a grid-forming power converter is the impedance subtracted by the transfer function G(s) and output current, which depend on the voltage target value and the voltage output value. It can be seen that it consists of TIFF2026529167000019.tif1829. Excluding the virtual impedance in Figure 11, the model of the power converter output voltage can be expressed as shown in Equation 4.

[0116] [Equation 4] TIFF2026529167000020.tif29149 Comparing equations 3 and 4, impedance TIFF2026529167000021.tif1829 and Since only TIFF2026529167000022.tif1528 is different, after creating the system model, you can evaluate the performance of the virtual impedance by changing only the impedance value. Substituting the voltage magnitude defined in Equation 2 into Equation 4, we can generate Equation 5 for the voltage magnitude as follows.

[0117] [Formula 5] TIFF2026529167000023.tif19117 Applying a low-pass filter to equation 1 above and substituting it into equation 5 yields the following equation 6.

[0118] [Formula 6] TIFF2026529167000024.tif41156 By integrating the frequency equation in Equation 2 above, applying a low-pass filter to the active power value applied to Equation 1, and then substituting it into Equation 4, we can obtain the following Equation 7.

[0119] [Equation 7] TIFF2026529167000025.tif24148 Here, δ0 is the load angle of the power converter and is defined by trigonometric functions as shown in equation 8 below.

[0120] [Equation 8] TIFF2026529167000026.tif33144 In equation 8, the δ0 value is relatively very small. Assuming the filename is TIFF2026529167000027.tif1644, equation 8 can be simplified as shown in equation 9 below.

[0121] [Formula 9] TIFF2026529167000028.tif23130 On the other hand, Equation 1, with a low-pass filter applied, can be expressed in a linearized form as shown in Equation 10 below. [Formula 10] TIFF2026529167000029.tif18136 In equation 10, The filename is TIFF2026529167000030.tif2077. and, The filename is TIFF2026529167000031.tif18133. Substituting equation 10 into equation 6, we can obtain a linear model of the voltage magnitude of the grid-forming power converter. The linear model of the voltage magnitude of the grid-forming power converter can be expressed as shown in equation 11.

[0122] [Equation 11] TIFF2026529167000032.tif18141 In equation 11, The filename is TIFF2026529167000033.tif18137. Substituting equations 9 and 10 above into equation 7, we can obtain a voltage-phase linear model of the grid-forming power converter. The voltage-phase linear model of the grid-forming power converter can be expressed as shown in equation 12.

[0123] [Formula 12] TIFF2026529167000034.tif18150 In equation 12, The filename is TIFF2026529167000035.tif17138. Next, by combining equations 11 and 12, we can obtain the state-space model of the grid-forming power converter. The state-space model of the grid-forming power converter can be expressed as shown in equation 13.

[0124] [Formula 13] TIFF2026529167000036.tif23155 In equation 13, The filename is TIFF2026529167000037.tif10157. n This represents the nth derivative. The factors used in equation 13 above can be determined as follows. First, G(s) used in equation 11 can be rearranged as shown in equation 15.

[0125] [Formula 14] TIFF2026529167000038.tif18128 In equation 14, TIFF2026529167000039.tif15146TIFF2026529167000040.tif14127TIFF2026529167000041.tif16163TIFF2026529167000042.tif11141TIFF2026529167000043.tif1684TIFF2026529167000044.tif16163 and The filename is TIFF2026529167000045.tif16122. Next, substituting equation 14 into equation 11, The differential equation for TIFF2026529167000046.tif1324 can be constructed as shown in equation 15.

[0126] [Formula 15] TIFF2026529167000047.tif20134 The detailed definition of the factors in equation 15 is as follows: TIFF2026529167000048.tif68150 Substituting equation 14 into equation 12 using the same method as above, The differential equation for TIFF2026529167000049.tif1422 can be constructed as shown in equation 16.

[0127] [Formula 16] TIFF2026529167000050.tif31145 Using the constants defined above, A defined in equation 13 gf A matrix can be represented as shown in equation 17 below.

[0128] [Formula 17] TIFF2026529167000051.tif46143 The detailed definitions of the factors used in equation 17 are as follows: TIFF2026529167000052.tif105130 Here, a11 and a21 represent coefficients. Figures 13a to 13c show the root locus obtained by modifying specific factors for the stability verification model of the ship power system operation method of this embodiment. Figure 13a shows the root locus for the initial phase difference between the grid forming controller and the power grid. Figure 13a shows that as the initial phase difference with the ship's power grid increases, certain roots will have positive real numbers, and the system will become unstable.

[0129] FIG. 13b is a root locus diagram drawn while changing the virtual impedance value with the system in an unstable state due to the initial phase difference. When increasing the virtual inductance component of the virtual impedance as shown in FIG. 13(b), the roots with positive numbers move to have negative numbers, so it can be confirmed that the system is stabilized. On the other hand, when only increasing the virtual resistance component of the virtual impedance as shown in FIG. 13c, the stabilizing effect of the system is not large, and the real part with a negative number is moved away from the center point, so it can be confirmed that there is an effect of deteriorating the system braking characteristics.

[0130] FIG. 14 is a simulation control configuration diagram applicable to the ship power system operation method of the present embodiment.

[0131] FIG. 14 can correspond to at least a part of the structure of a ship power controller for simulation when the power converter of the cage induction generator switches the control mode from grid feeding control to grid forming. The ship power control device can include a grid feeding control unit 417 and a grid forming control unit 418.

[0132] The grid feeding control unit 417 can include a DQ conversion unit that outputs the q-axis output voltage (v[[ID=ID=15]] oq ) and the d-axis output voltage (v od ) obtained by converting the three-phase (abc) voltage (vabc) according to the dq-axis, a phase-locked loop (PLL), a current controller, and a DQ inverse conversion unit. The grid forming control unit 418 can include a power balance processing unit, a droop function processing unit, a voltage controller, a current controller, two DQ conversion units, and a DQ inverse conversion unit.

[0133] The first converter voltage command (uabc,feed) generated by the grid feeding control unit 417 and the second converter voltage command (uabc,form) generated by the grid forming control unit 418 are selectively applied to the PWM control module of the ship's power controller in response to the switching operation of the circuit breaker on the switchboard in the first time (t=T1), and can function to switch the operating mode of the power converter connected to the shaft generator of the ship's power system.

[0134] In other words, the ship's power controller can control the power converter of the power storage generator so that the reference power value becomes 0 in the grid feeding state before the first time (T1), and immediately switch the control mode to grid forming mode after the first time (T1).

[0135] Figures 15a and 15b are graphs showing the simulation results for active and reactive power during the switching between control modes between grid feeding and grid forming, based on the simulation control configuration in Figure 14. Figures 15a and 15b show the simulation results for active and reactive power during control mode switching, depending on the application of virtual impedance and the combination of its components. The numerical simulation results are shown in Table 2.

[0136] [Table 2]

[0137] As can be seen from the results for Set A in Figures 15a and 15b, in the absence of virtual impedance, it can be confirmed that active power, reactive power, voltage, and frequency all fluctuate significantly during control mode switching, causing the system to drop out of the grid.

[0138] Furthermore, the results for Set B, which contains only a virtual resistance component, show no significant difference from those of Set A, confirming that it should be eliminated from the lineage.

[0139] On the other hand, in the case of Set C and Set D, which have virtual inductance components, it can be confirmed that grid connection and grid forming control can be initiated without significant fluctuations in all indicators. To ensure that grid forming control is performed correctly, power can be supplied to the ship's power grid loads independently even if the synchronous generator is stopped.

[0140] Thus, through simulation, we can confirm that a virtual inductance is necessary to switch to grid forming control mode, and that an efficient operation sequence for a cage-type induction generator, as explained in Figure 5, is possible. Furthermore, referring to Figures 13a to 13c, we can confirm that the results of the root locus diagram and the simulation results are similar.

[0141] Figures 16a and 16b are graphs showing the simulation results for active and reactive power during the switching between grid feeding and grid forming control modes, when the ship power system operation method of this embodiment is applied to an actual ship.

[0142] As shown in Figures 16a and 16b, the actual onboard verification of the ship power controller of this embodiment was conducted by experimenting with the effect of virtual impedance when switching the control mode to grid forming mode under the same conditions as the simulation described above, referring to Figures 15a and 15b. The experimental results obtained for four virtual impedance sets are shown in Table 3.

[0143] [Table 3]

[0144] In the case of Set A, where there is no virtual impedance, it can be confirmed that during control mode switching, the active power, reactive power, voltage, and frequency all fluctuate significantly, causing the shaft generator system to disconnect from the ship's power grid.

[0145] Furthermore, it can be confirmed that Set B, which has only a virtual resistance component, also disconnects from the ship's power system due to control instability.

[0146] Similar to the simulation results, in the case of Set C and Set D, which have virtual inductance components, it can be confirmed that the shaft generator system was connected to the ship's power grid without significant fluctuations in all indicators, and that the shaft generator system initiated grid forming control.

[0147] These experimental results are similar to the root locus diagram results and simulation results of the embodiment described above.

[0148] Figures 17a and 17b are graphs showing the power factor, active power, and reactive power when the grid-forming power converter operates in parallel with a synchronous generator before and after applying self-secondary voltage control in the ship power system operation method of this embodiment. Figures 18a and 18b are graphs showing the reference voltage and output voltage when the grid-forming power converter operates in parallel with a synchronous generator before and after applying self-secondary voltage control in the ship power system operation method of this embodiment.

[0149] Figures 17a, 17b, 18a, and 18b show the experimental verification results for self-secondary voltage control. Specifically, the waveforms related to active power, reactive power, power factor, and output voltage when a synchronous generator and a grid-forming power converter are operated in parallel are shown, distinguished by differences in the shade of gray.

[0150] If self-secondary voltage control is not applied, the impedance of the power converter and the voltage drop on the isolation transformer side cause the droop characteristic curve (load-voltage) of the output voltage with the magnitude of the final voltage to become lower than the droop curve (load-voltage) of the synchronous generator as the load increases, resulting in a phenomenon where reactive power cannot be smoothly supplied to the ship's power system, as shown in Figures 17a and 18A.

[0151] As shown in these diagrams, when the power factor of the ship's load was 0.8, the power factor of the power converter rose to 0.9, causing the power factor of other synchronous generators to drop to the 0.7 level, resulting in an imbalance in the distribution of reactive power. According to the classification society standards (line) that define the safety standards for ships, an imbalance of more than 10% in reactive power is not permitted, so the operating conditions do not conform to the safety standards.

[0152] As shown in Figure 12 above, the results of experiments applying the self-secondary voltage control structure of this embodiment are shown in Figures 17b and 18b. According to these figures, it can be confirmed that, with the power factor of the ship's load fixed at 0.8, reactive power was smoothly supplied at a power factor of 0.8, similar to other synchronous generators.

[0153] Figures 19a and 19b are graphs showing the power factor, active power, and reactive power when the grid forming power converter is operating independently in the ship power system operation method of this embodiment. Figures 20a and 20b are graphs showing the reference voltage and output voltage when the grid forming power converter is operating independently in the ship power system operation method of this embodiment.

[0154] Figures 19a, 19b, 20a, and 20b show the experimental verification results when the grid forming power converter is operated independently. The waveforms for active power, reactive power, power factor, and output voltage, depending on whether or not self-secondary voltage control is applied, are distinguished by differences in gray density.

[0155] When a shaft generator system in a ship's power grid is operated independently without self-secondary voltage control, the magnitude of the final voltage is affected not only by the output voltage droop but also by the voltage drop due to the output current, due to the impedance of the power converter and the voltage drop on the isolation transformer side. As can be seen in Figures 19a and 20a, the voltage drop can reach up to 4% of the rated voltage depending on the load.

[0156] On the other hand, the waveforms of the standalone operation experiment results of the power converter with self-secondary voltage control applied can be seen in Figures 19b and 20b. Secondary voltage control was performed so that the voltage on the secondary side of the isolation transformer was maintained at 1 pu relative to the rated voltage, and it can be confirmed that the voltage on the secondary side of the isolation transformer was maintained at 1 pu to compensate for the closed-loop impedance of the power converter control and the voltage drop of the isolation transformer.

[0157] Similar to the embodiments described above, the present invention can provide an efficient grid connection control method for grid-forming shaft generators applied to ships and a self-secondary voltage control method for improving the power quality of the ship's power system. Furthermore, when simulating the droop characteristics of a synchronous generator, self-secondary voltage control can be performed to resolve the voltage drop that occurs in grid-forming power converters and connection equipment (such as isolation transformers). This can be applied according to the respective voltage references for parallel operation and islanding operation. In addition, a grid-forming control mode based on virtual impedance can be applied to ensure stability when switching between grid feeding and grid-forming control modes of the power converter, and an efficient grid connection sequence for shaft generators based on cage-type induction equipment can be provided utilizing this. The stability was evaluated using a root locus diagram through a mathematical model, and the effects of the present invention were verified through MATLAB® / SIMULINK® simulations and demonstration experiments on ships to which actual shaft generators were applied.

[0158] The method according to the embodiment described above can be embodied in the form of program instructions executable through various computer means and can be recorded on a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, etc., individually or in combination. The program instructions recorded on the computer-readable medium may be specifically designed and configured for the present invention, or they may be publicly known and usable by those skilled in the art of computer software.

[0159] Examples of computer-readable media include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The aforementioned hardware devices may be configured to operate as at least one software module to perform the operations of the present invention, and vice versa.

[0160] As described above with reference to embodiments, those skilled in the art will understand that the present invention can be modified and altered in various ways without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. The steps include electrically connecting a shaft generator to the ship's power system, The steps include controlling the generator-side converter of the power converter connected to the shaft generator with a zero power reference, The steps include charging the DC terminal capacitor of the power converter, The steps include: magnetizing the shaft generator using the current from the DC terminal capacitor; The steps include: making the shaft generator generate its own power, The steps include controlling the grid-side converter of the power converter with a zero-power reference, The steps include controlling the generator-side converter of the power converter to charge the DC end capacitor with the power of the shaft generator, The steps include: performing self-secondary voltage control via the power converter so that the shaft generator operates as a distributed generator in the ship's power system; A method for managing ship power, including a method for managing ship power.

2. The ship power management method according to claim 1, wherein the step of charging the DC end capacitor of a power converter connected to the shaft generator includes controlling the grid-side converter to charge at least a portion of the rated voltage of the DC end capacitor, and the charged DC voltage is maintained by control of the power converter.

3. The ship power management method according to claim 1, further comprising the step of controlling the grid-side converter in grid-feeding mode before the step of magnetizing the shaft generator.

4. The ship power management method according to claim 3, further comprising the step of switching the grid-side converter from the grid feeding mode to the grid forming mode when the DC end capacitor is charged to the rated voltage or a pre-constant voltage by the power of the shaft generator.

5. The ship power management method according to claim 4, wherein the step of performing the self-secondary voltage control includes performing voltage control of the grid-side converter according to a control droop coefficient determined or selected based on a preset or real-time collected measurement value.

6. The ship power management method according to claim 5, wherein the step of performing the self-secondary voltage control further includes the step of subtracting the feedbacked output voltage reference and the preset fixed virtual impedance from the output voltage reference and transmitting the result to the voltage controller.

7. The ship power management method according to claim 5, further comprising the step of maintaining the voltage of the DC end capacitor by performing at least one of torque control and magnetic flux control of the shaft generator.

8. The ship power management method according to claim 5, further comprising the step of performing at least one of torque control and magnetic flux control on the shaft generator to connect the power converter to the common connection point of the ship's power system.

9. The ship power management method according to claim 8, further comprising the step of adaptively estimating the stator resistance of the shaft generator using a quasi-positive definite Lyapunov function defined to include a stator resistance error for torque control or magnetic flux control of the shaft generator.

10. The ship power management method according to claim 9, wherein the estimation step further includes performing integral control using a low-pass filter to rapidly converge the solution to the equation when solving the equation using the derivative of the quasi-positive definite Lyapunov function.

11. A ship power management device for a ship power system based on a grid-forming shaft generator, At least one instruction comprising a shaft generator system activation sequence, A processor connected to a memory that stores the at least one instruction and executes the at least one instruction, Includes, The processor, by the at least one instruction, The steps include electrically connecting a shaft generator to the ship's power system, The steps include controlling the generator-side converter of the power converter connected to the shaft generator with a zero power reference, The steps include charging the DC terminal capacitor of the power converter, The steps include: magnetizing the shaft generator using the current from the DC terminal capacitor; The steps include: making the shaft generator generate its own power, The steps include controlling the grid-side converter of the power converter with a zero-power reference, The steps include controlling the generator-side converter of the power converter to charge the DC end capacitor with the power of the shaft generator, The steps include: performing self-secondary voltage control via the power converter so that the shaft generator operates as a distributed generator in the ship's power system; A ship's power management system that performs this function.

12. The ship power management device according to claim 11, wherein the processor, in the step of charging the DC end capacitor of a power converter connected to the shaft generator, controls the grid-side converter to charge at least a portion of the rated voltage of the DC end capacitor and maintains the charged DC end voltage by controlling the power converter.

13. The ship power management device according to claim 11, wherein the processor further performs the step of controlling the grid-side converter in grid-feeding mode before performing the step of magnetizing the shaft generator.

14. The ship power management device according to claim 13, wherein the processor further performs the step of switching the grid-side converter from the grid feeding mode to the grid forming mode when the DC end capacitor is charged to a rated voltage or a preset voltage by the power of the shaft generator.

15. The ship power management device according to claim 14, wherein the processor, in the step of performing the self-secondary voltage control, controls the voltage of the grid-side converter according to a control droop coefficient determined or selected based on a preset or real-time collected measurement value.

16. The ship power management device according to claim 15, wherein the processor further performs the step of subtracting the feedbacked output voltage reference and the preset fixed virtual impedance from the output voltage reference and transmitting the result to the voltage controller in the step of performing the self-secondary voltage control.

17. The ship power management device according to claim 15, wherein the processor further performs the step of maintaining the voltage of the DC end capacitor by performing at least one of the torque control and magnetic flux control of the shaft generator.

18. The ship power management device according to claim 15, wherein the processor further performs the step of adaptively estimating the stator resistance of the shaft generator using a quasi-positive definite Lyapunov function defined to include a stator resistance error for torque control or magnetic flux control of the shaft generator.

19. A vessel including a hull equipped with a ship power management device according to any one of claims 11 to 18.

20. A ship using the ship power management method described in any one of claims 1 to 10.

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