Method and apparatus for ship power management based on grid-forming shaft generator, and ship using same

Abstract

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

Description

Method and device for managing power of a ship based on a grid-forming shaft generator and a ship using the same

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

[0002] To reduce the carbon footprint of ships, demand is growing for ship propulsion and power generation utilizing alternative energy sources. Batteries, fuel cells, and solar power are gaining attention as alternative energy sources. Shaft generators, which install a generator on the propeller shaft of a conventional power unit, are also being adopted by many ships as an alternative energy source.

[0003] A ship power management system (SPMS) controls the operation of multiple synchronous generators and a power converter connected to the shaft generator on the ship's propeller shaft (see Figure 1). The control system for ship power systems has been standardized for decades based on synchronous generators. Given the industry's specifics, it's preferable for power converters for alternative energy sources to mimic existing synchronous generators, rather than restructuring the entire proven control system. Therefore, power converters for alternative energy sources must mimic the control behavior of existing synchronous generators, i.e., the voltage droop and frequency droop characteristics.

[0004] Meanwhile, most power converters for alternative energy sources suffer from voltage drop due to impedance within the circuit due to grid-forming voltage control loops and the use of isolation transformers at the output stage to block common-mode noise. However, it is impossible to replicate the voltage droop characteristics of a synchronous generator depending on the load current, and currently, no secondary voltage controller exists in ship 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 of reactive power supply during parallel operation and voltage drop during single operation occur, and appropriate measures are required to resolve these problems.

[0006] The present invention has been derived to meet the needs of the prior art, and the purpose of the present invention is to provide a ship power management method and device that can apply virtual impedance to the voltage control of a power converter connected to a grid-forming shaft generator so that the power converter can have sufficient inertia against external disturbances and effectively input the power generated by the shaft generator into the ship power system.

[0007] Another object of the present invention is to provide a ship power management method and device capable of effectively compensating for voltage drop in a shaft generator system in a power converter connected to a shaft generator of a ship power system by using a novel self-secondary voltage control algorithm.

[0008] Another object of the present invention is to provide a ship power management method and device capable of performing self-secondary voltage control using a power converter connected to a shaft generator according to the parallel operation or single operation mode of the shaft generator even in a ship power management system in which a separate secondary voltage controller does not exist.

[0009] Another object of the present invention is to provide a ship using the ship power management method or ship power management device described above.

[0010] According to an aspect of the present invention for solving the above technical problem, a grid-forming shaft generator-based ship power management device is a ship power management device for a grid-forming shaft generator-based ship power system, comprising: at least one command having a shaft generator system input sequence; and a processor connected to a memory storing the at least one command and executing the at least one command. The processor is configured to perform the following steps: electrically connecting the shaft generator to the ship power system by the at least one command; controlling a generator-side converter of a power converter connected to the shaft generator to a zero power reference; charging a DC link capacitor of the power converter; magnetizing the shaft generator using a current of the DC link capacitor; generating self-power from the shaft generator; controlling a grid-side converter of the power converter to a zero power reference; controlling a generator-side converter of the power converter to charge the DC link capacitor with power from the shaft generator; And a step of performing self-secondary voltage control through the power converter so that the shaft generator operates as a distributed generator of the ship power system is performed.

[0011] According to another aspect of the present invention for solving the above technical problem, a grid-forming shaft generator-based ship power management method comprises the steps of: electrically connecting a shaft generator to a ship power system; controlling a generator-side converter of a power converter connected to the shaft generator with a zero power reference; charging a DC link capacitor of the power converter; magnetizing the shaft generator using a current of the DC link capacitor; generating self-power from the shaft generator; controlling a grid-side converter of the power converter with a zero power reference; controlling a 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 so that the shaft generator operates as a distributed generator of a ship power system.

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

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

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

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

[0016] The step of performing the above-described self-secondary voltage control may further include 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 the voltage controller.

[0017] The above virtual impedance can be composed by adding a virtual inductance and a virtual resistance.

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

[0019] The method may further include a step of connecting the power converter to a common coupling point of the ship power system by performing at least one of torque control and flux control for the shaft generator.

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

[0021] The above estimating step may further include performing integration control using a low-pass filter to quickly converge the solution to the equation when solving the equation using the derivative of the semi-definite Lyapunov function.

[0022] According to another aspect of the present invention for solving the above technical problem, a ship using a ship power management method for a grid-forming shaft generator-based ship power system comprises: a ship power management device having a memory storing at least one command for implementing a shaft generator system input sequence and a processor connected to the memory for executing the at least one command; and a hull on which the ship power management device is mounted. Here, the processor is configured to perform the steps of: electrically connecting the shaft generator to the ship power system by the at least one command; controlling a generator-side converter of a power converter connected to the shaft generator to a zero power reference; charging a DC link capacitor of the power converter; magnetizing the shaft generator using a current of the DC link capacitor; generating self-power from the shaft generator; controlling a grid-side converter of the power converter to a zero power reference; controlling a generator-side converter of the power converter to charge the DC link capacitor with power from the shaft generator; And a step of performing self-secondary voltage control through the power converter so that the shaft generator operates as a distributed generator of the ship power system is performed.

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

[0024] In the above vessel, the processor may further perform a step of controlling the grid-side converter to a grid-feeding mode before performing the step of magnetizing the shaft generator.

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

[0026] In the above vessel, the processor can perform voltage control of the grid-side converter according to a control droop coefficient determined or selected based on measurement values ​​that are preset or collected in real time, in the step of performing the self-secondary voltage control.

[0027] In the above ship, the processor may further perform a step of performing the self-secondary voltage control, in which the fed-back output voltage reference and the preset fixed virtual impedance are each subtracted from the output voltage reference and transmitted to the voltage controller.

[0028] In the above vessel, the processor may further perform a step of maintaining the voltage of the DC link capacitor by performing at least one of torque control and flux control for the shaft generator.

[0029] In the above vessel, the processor may further perform a step of adaptively estimating the stator resistance for the shaft generator using a quasi-determined Lyapunov function defined to include a stator resistance error for torque control or flux control for the shaft generator.

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

[0031] According to the present invention, an efficient grid-connection method for a grid-forming shaft generator applied to a ship and a self-secondary voltage control method for improving the power quality of a ship's power system can be provided. In particular, a virtual impedance-based grid-forming control mode can be provided to ensure stability when switching between grid-feeding and grid-forming control modes of a power converter connected to a shaft generator, thereby enabling efficient power grid input of a squirrel-cage induction machine-based shaft generator.

[0032] In addition, 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 resolve the voltage drop occurring in a grid-forming power converter and associated equipment (such as an isolation transformer), the power converter performs its own secondary voltage control in accordance with a preset voltage standard for each of parallel operation and single operation, thereby enabling the shaft generator to effectively perform grid-forming operation in a ship power system.

[0033] FIG. 1 is a schematic diagram of a ship power system to which a grid-forming shaft generator-based ship power management method according to one embodiment of the present invention can be applied.

[0034] FIG. 2 is a graph for explaining the voltage droop characteristics of a ship power management system that can be employed in the ship power system of FIG. 1.

[0035] Fig. 3 is a graph for explaining the frequency droop characteristics of a ship power management system that can be employed in the ship power system of Fig. 1.

[0036] Figure 4 is a schematic block diagram of a ship power management device that can be employed in the ship power system of Figure 1.

[0037] Fig. 5 is a block diagram for explaining a control process of a squirrel-cage induction generator that can be employed in the ship power management device of Fig. 4.

[0038] FIG. 6 is a flowchart of SCIG control steps that can be performed by the ship power management device of FIG. 5.

[0039] Figure 7 is a block diagram for explaining the first operation mode (Phase Ⅰ) among the SCIG control steps of Figure 6.

[0040] Figure 8 is a block diagram for explaining the second operation mode (Phase Ⅱ) among the SCIG control steps of Figure 6.

[0041] Figure 9 is a block diagram for explaining the third operating mode (Phase Ⅲ) among the SCIG control steps of Figure 6.

[0042] FIG. 10 is a block diagram illustrating an adaptive flux control process that can be applied to the SCIG control steps of FIG. 6.

[0043] Fig. 11 is a block diagram for explaining a virtual impedance-based voltage control process of a grid-forming power converter that can be employed in the ship power management device of Fig. 4.

[0044] FIG. 12 is an exemplary diagram illustrating a self-secondary voltage control structure that can be employed in a ship power management method according to another embodiment of the present invention.

[0045] Figures 13a to 13c are diagrams showing root trajectories according to specific factor modifications to the stability verification model of the ship power management method of the present embodiment.

[0046] Figure 14 is a simulation control configuration diagram that can be employed in the ship power management method of the present embodiment.

[0047] Figures 15a and 15b are graphs showing simulation results for active power and reactive power between control mode switching of grid feeding and grid forming according to the simulation control configuration of Figure 14.

[0048] Figures 16a and 16b are graphs showing simulation results for active power and reactive power between control mode switching of grid feeding and grid forming by applying the ship power management method of the present embodiment to an actual ship.

[0049] Figures 17a and 17b are graphs showing the power factor, active power, and reactive power when the grid-forming power converter is operated in parallel with a synchronous generator before and after applying its own secondary voltage control in the ship power management method of the present embodiment.

[0050] Figures 18a and 18b are graphs showing the reference voltage and output voltage when the grid-forming power converter operates in parallel with the synchronous generator before and after applying its own secondary voltage control in the ship power management method of the present embodiment.

[0051] Figures 19a and 19b are graphs showing the power factor, active power, and reactive power when the grid-forming power converter is operated alone in the ship power management method of the present embodiment.

[0052] Figures 20a and 20b are graphs showing the reference voltage and output voltage when the grid-forming power converter is operated alone in the ship power management method of the present embodiment.

[0053] The present invention is susceptible to various modifications and embodiments. Specific embodiments are illustrated and described in detail in the drawings. However, this is not intended to limit the present invention to specific embodiments, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0054] While terms such as "first" and "second" may be used to describe various components, these components should not be limited by these terms. These terms are used solely to distinguish one component from another. For example, without departing from the scope of the present invention, a first component could be referred to as a "second component," and similarly, a second component could also be referred to as a "first component." The term "and / or" includes any combination of multiple related items described herein or any one of multiple related items described herein.

[0055] In the embodiments of the present application, 'at least one of A and B' may mean 'at least one of A or B' or 'at least one of combinations of one or more of A and B'. Furthermore, in the embodiments of the present application, 'at least one of A and B' may mean 'at least one of A or B' or 'at least one of combinations of one or more of A and B'.

[0056] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. Conversely, when a component is referred to as being "directly connected" or "connected" to another component, it should be understood that there are no other components in between.

[0057] The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprises" or "has" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

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

[0059] Hereinafter, with reference to the attached drawings, preferred embodiments of the present invention will be described in more detail. In order to facilitate an overall understanding in describing the present invention, identical reference numerals will be used for identical components in the drawings, and redundant descriptions of identical components will be omitted.

[0060] FIG. 1 is a schematic diagram of a ship power system to which a power management method for a ship power system having a grid-forming shaft generator according to one embodiment of the present invention (hereinafter simply referred to as the “ship power management method”) can be applied.

[0061] Referring to FIG. 1, a ship power system mounted on a ship (1000) may include synchronous generators (100, 110, 120), a switchboard (130), a shaft generator (SG, 150), a power converter (200), an insulating transformer (230), and a circuit breaker (250).

[0062] Synchronous generators (100, 110, 120) may be installed from the same manufacturer for ease of maintenance. All three synchronous generators (100, 110, 120) may be used simultaneously as distributed power sources, or only one or two of them may be used as a distributed power source.

[0063] In addition, synchronous generators (100, 110, 120) constitute the main power generation devices in the shipboard power system, and 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, primary voltage control by the AVR is sufficient for reactive power sharing among the synchronous generators. Secondary frequency control (SFC) is generally applied for the governor's frequency control because the combustion characteristics of engines can differ even for the same engine. The frequency and voltage droop curves of all synchronous generators in the shipboard microgrid can be designed with a droop of 3% and 2.5%, respectively.

[0064] The switchboard (130) may be equipped with circuit breakers connected to each of the synchronous generators. The circuit breakers may be referred to as first, second, and third circuit breakers.

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

[0066] The power converter (200) may be arranged 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 be composed of a generator-side converter having the shaft generator (150), a grid-side converter having a point of common coupling (PCC) of the ship's power system, and a DC-link capacitor connected therebetween, 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 PCC may refer to a common bus of power generation resources on board the ship that supplies power to loads inside and outside the ship connected to the distributed ship power system.

[0067] Additionally, the grid-side converter of the back-to-back converter controls power flow differently from wind power control or solar power control, such as maximum power point tracking. 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 power as one of the power generation units, including independent distributed generators or synchronous generators.

[0068] The isolation transformer (230) functions to physically separate a branch system including a shaft generator (150) and a power converter (200), which are alternative energy resources in the ship power system, from the main system of the ship power system.

[0069] A circuit breaker (250) functions to selectively connect or disconnect a branch system including a shaft generator (150), a power converter (200), and an isolation transformer (230) from the main system of the ship's power system. The circuit breaker (250) may be installed together with other circuit breakers on a switchboard (130). In that case, the circuit breaker (250) may be referred to as a fourth circuit breaker.

[0070] 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).

[0071] In addition, the SPMS (300) can implement the generator-side converter of the power converter (200) as an active front-end converter so that external reactive power can be supplied for magnetization of the shaft generator (150) when the shaft generator (150) is to be started.

[0072] In addition, the SMPS (300) can be configured to apply a system input control sequence that can efficiently input power generated from the shaft generator (150) into the ship power system.

[0073] In addition, the SMPS (300) may be configured to apply a preset fixed virtual impedance ('VImp' for short) to the voltage control circuit of the SMPS (300) in consideration of the limited impedance (X) and resistance (R) ratio (bounded X / R ratio) of the ship power system in order to stabilize the grid-forming distributed power generation of the shaft generator (150).

[0074] Additionally, the SPMS (300) may be configured to perform secondary frequency control (SFC) by the grid-side converter of the power converter (200). Furthermore, the SMPS (300) may be configured to perform secondary voltage control in the power converter (200) itself in a ship power system where a secondary voltage controller does not exist.

[0075] The self-secondary voltage control can be configured to control the voltage based on different target values ​​depending on parallel operation and single operation. For example, the SMPS (300) can perform voltage control based on the target power factor value when the shaft generator (150) and at least one synchronous generator (100) are operated in parallel, and when the shaft generator (150) is operated alone, the secondary voltage of the insulation transformer (230) can be set as the target voltage (e.g., 1 [pu]) to perform voltage control of the shaft generator (150), power converter (200), or ship power system.

[0076] For reference, since most ships use AC power grids, these alternative energy sources must be connected to the ship's power grid via power converters. Power converters must operate in parallel with existing onboard synchronous generators to supply power to onboard loads. They must also be capable of independently supplying power to onboard loads depending on the ship's operating conditions. Therefore, power converters on ships based on alternative energy sources must perform grid-forming control, and depending on the characteristics of the alternative energy source, they may also perform grid-feeding control.

[0077] For example, grid-feeding control is necessary for purposes such as target power value tracking control (P, Q control) for maximum power point estimation control of solar power generation and power supply limitation during the initial magnetization stage of a squirrel-cage induction generator. In addition, since the power system of a ship is an independent standalone system, power must always be supplied to the onboard load. Therefore, even when the power converter performs grid-feeding control, it must be possible to instantaneously switch to grid-forming control mode at any time, thereby enabling independent operation of alternative energy sources.

[0078] While grid-feeding mode synchronizes with the grid through a phase-locked loop to control active and reactive power, grid-forming mode determines the target output voltage and frequency 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 of the grid voltage. This acts as a kind of disturbance to the power converter control system, and the low inertia of a typical power converter cannot withstand this disturbance, so the alternative energy resource cannot switch to grid-forming mode and is dropped from the grid due to frequency and voltage divergence.

[0079] Accordingly, in this embodiment, a ship can be provided in which a virtual impedance is applied to the voltage control of a power converter connected to a grid-forming shaft generator, so that the power converter can have sufficient inertia against disturbances and the power generated by the shaft generator can be effectively input into the ship's power system. In addition, according to this embodiment, a ship can be provided in which a voltage drop in a shaft generator system can be effectively compensated for in a power converter connected to the shaft generator of a ship's power system by using its own secondary voltage control algorithm, and in which a ship power management system in which a secondary voltage controller does not exist can perform its own secondary voltage control by using a power converter connected to the shaft generator according to the parallel operation or single operation mode of the shaft generator.

[0080] Fig. 2 is a graph for explaining the voltage droop characteristics of a ship power management system that can be employed in the ship power system of Fig. 1. And Fig. 3 is a graph for explaining the frequency droop characteristics of a ship power management system that can be employed in the ship power system of Fig. 1.

[0081] As illustrated in Fig. 2, since synchronous generators in a ship power system are typically installed in groups of three or four from the same manufacturer for maintenance reasons, the voltage droop characteristics of each synchronous generator, as determined by an automatic voltage regulator (AVR), are very similar among the synchronous generators, and can be fixed without applying a separate secondary voltage control (SVC). The AVR can be provided as an integral part of the synchronous generator.

[0082] Meanwhile, as illustrated in Fig. 3, even synchronous generators of the same type may have different combustion characteristics of their generator engines. Therefore, the frequency droop characteristics among multiple synchronous generators used in a single vessel's marine power system can be adjusted by secondary frequency control (SFC).

[0083] Moreover, in a distributed ship power system including an alternative energy source, particularly a shaft generator coupled to a ship's propeller shaft, together with synchronous generators, it is necessary to perform at least one of secondary voltage control and secondary frequency control so that the power of the shaft generator can be effectively connected to the point of common coupling (PCC) of the ship's power system in the grid-forming operation mode of the shaft generator, i.e. so that the shaft generator can operate like a synchronous generator.

[0084] Therefore, the ship power management device of the present embodiment can be configured so that the shaft generator system including the shaft generator and the power converter operates as a plug-and-play distributed power source that replicates the operation of the synchronous generator.

[0085] In particular, shaft generators typically operate as stand-alone distributed generators during normal ship operations. However, they face limitations due to the reduced surplus power of propulsion systems such as engines and the dependence of shaft generator power on shaft speed. To ensure safe and efficient operation of shaft generators, ship power management systems can be configured to monitor the aforementioned limitations and implement actions such as load shedding or synchronous generator operation in specific situations. These actions can also include measures to address situations such as shaft generator overload due to high-power loads on the ship's power system, mechanical load fluctuations on the propulsion engines due to rough seas, and propulsion engine deceleration.

[0086] As such, the ship power management device of the present embodiment can be configured to apply a rapid grid-initiating sequence of a shaft generator in a distributed ship power system including a shaft generator. Furthermore, the ship power management device can be configured to apply a fixed virtual impedance-based control algorithm to stably switch the operating mode from grid-feeding to grid-forming. Furthermore, the ship power management device can be configured to apply its own secondary voltage control by the power converter of the shaft generator in the grid-forming operating mode.

[0087] Fig. 4 is a schematic block diagram of a ship power management device that can be employed in the ship power management system of the ship power system of Fig. 1.

[0088] Referring to FIG. 4, a ship power management device (400) may correspond to a ship power management system (SPMS, 300) that manages a ship power system of FIG. 1. The ship power management device (400) may include at least one processor (410) and a memory (420). In addition, the ship power management device (400) may further include a transmission / reception device (430) that is connected to a terminal or communication device of a ship network, an external dedicated power distribution network, a manager, a user, etc., and performs communication. In addition, the ship power management device (400) may further include an input interface device (440), an output interface device (450), a storage device (460), etc. Each component included in the ship power management device (400) may be connected by a bus (bus, 470) and communicate with each other.

[0089] More specifically, the processor (410) can execute a software module or program command stored in at least one of the memory (420) and the storage device (460). For example, the processor (410) may include a virtual impedance control unit (412), a shaft generator system input unit (414), an own secondary voltage control unit (416), and a mode switching unit (418). These components may be mounted on the processor (410) in the form of software modules or program commands, and their configurations and / or functions will be described in detail below. The processor (410) described above may be implemented as a central processing unit (CPU), a graphics processing unit (GPU), or a dedicated processor in which methods according to embodiments of the present invention are performed.

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

[0091] The transceiver (430) may include a communication interface or sub-communication system for communication within, outside, or between the inside and outside of the ship, for example, a short-range wireless network, cable connection, satellite communication, or wireless communication with a universal base station.

[0092] The input interface device (440) may include at least one input means selected from input means such as a keyboard, microphone, touchpad, and touch screen, and an input signal processing unit that maps or processes a signal input through at least one input means to a pre-stored command.

[0093] The output interface device (450) may include an output signal processing unit that maps or processes a signal output under the control of the processor (410) into a pre-stored signal form or level, and at least one output means that outputs the signal or information included in the signal in at least one form selected from vibration, light, sound, etc. of a predetermined level according to a 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, a display device, a printer, an optical output device, and a vibration output device.

[0094] Fig. 5 is a block diagram for explaining a control process of a squirrel-cage induction generator that can be employed in the ship power management device of Fig. 4.

[0095] First, the control environment for the squirrel cage induction generator (SCIG, 150) is described as follows. The SCIG (150) can be controlled using the direct torque control (DTC) method. Unlike the flux vector control that relies on the rotor angular position for closed-loop control, the DTC method does not require a position encoder to provide feedback on the rotor shaft speed or position. Since the DTC method is model-based, it relies on accurate 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 SCIG (150).

[0096] As such, estimation of stator flux linkage is crucial in the SCIG control process of this embodiment. Furthermore, since estimation of stator flux linkage depends on the accuracy of the stator resistance measured by the SCIG (150), real-time monitoring of accurate stator resistance is necessary for accurate estimation of stator flux linkage. In other words, uncertainty in the SCIG model parameters can lead to torque control failure and an imbalance in power supply and demand, which can result in a power outage on the ship.

[0097] Meanwhile, since the SCIG (150) is not designed to perform self-excitation, external reactive power is required for magnetization. Therefore, the power converter connected to the ship power management device of the present embodiment may be configured to use an active front-end converter instead of a passive converter.

[0098] The ship power management device of the present embodiment can be configured to input the motor voltage and current, direct current (DC) voltage, and switching command of the SCIG (150) into the motor model as shown in Fig. 5, and to receive values ​​or signals for torque and flux linkage from the motor model. The DC voltage can correspond to the DC link voltage as the voltage between the DC link capacitor terminals of the generator-side converter connected to the SCIG (150).

[0099] In addition, the ship power management device may be configured to generate a torque reference based on a DC voltage reference and a DC voltage, and to compare the torque and the torque reference through a torque comparator to calculate a torque error (ΔTorque, ΔT). In addition, the ship power management device may be configured to compare the flux linkage and the flux linkage reference through a flux linkage comparator to calculate a flux error (ΔFlux, ΔF). In addition, the ship power management device may be configured to input the torque error and the flux error to a hysteresis pulse selector (HPS), and to generate switch commands based on the torque error and the flux error through the HPS. The switch commands may be used to control a generator-side converter connected to the SCIG (150).

[0100] The aforementioned ship power management device can perform the SCIG control steps described below to enable the SCIG (150) to function as a distributed generator.

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

[0102] Fig. 6 is a flowchart of the SCIG control steps that can be performed by the ship power management device of Fig. 5. Fig. 7 is a block diagram for explaining the first operation mode (Phase I) of the SCIG control steps of Fig. 6. Fig. 8 is a block diagram for explaining the second operation mode (Phase II) of the SCIG control steps of Fig. 6. And, Fig. 9 is a block diagram for explaining the third operation mode (Phase III) of the SCIG control steps of Fig. 6.

[0103] Referring to FIG. 6, the ship power management device can perform three control steps or first to third operation modes as a grid input sequence of the grid-forming SCIG. That is, the ship power management method performed by the ship power management device can include a step (S610) of connecting a shaft generator to a grid, which is at least a part of a ship power system, and magnetizing the shaft generator using a grid-side current charged in a DC link capacitor, a step (S630) of performing power control on a grid-side converter with a zero power reference before the shaft generator supplies power to the grid so that the generator-side converter generates its own power so as to charge the DC link capacitor, and a step (S650) of performing self-secondary voltage control for distributed power generation of the shaft generator so that the shaft generator operates as a distributed generator of the ship power system.

[0104] To explain each step in more detail, as shown in Fig. 7, in the first control phase (phase Ⅰ), the grid-side converter (220) can charge the DC link capacitor (215) by receiving power (P) from the ship power system to which at least one synchronous generator (100) is connected under the control of the ship power management device. The grid-side converter (220) can perform power control so as to charge the DC link capacitor (215) up to 90% of the rated DC voltage and maintain the charged DC voltage.

[0105] In addition, in the first control stage, the generator-side converter (210) can magnetize the rotor of the squirrel cage induction generator (SCIG) by utilizing the DC-link voltage of the DC-link capacitor (215). The magnetization is performed by applying a predetermined voltage (V) of the generator-side converter (210). S ) to create a magnetic field by flowing a current through the coil of the shaft generator, which can refer to the creation of a magnetomotive force, i.e., the ability to generate magnetic flux or magnetic flow, in the coil. In the first control stage, since the shaft generator has not started generating power, the torque of the generator can be controlled to 0.

[0106] The second control phase (phase Ⅱ) is a phase in which the shaft generator starts self-generation and checks whether the shaft generator is generating normally. As shown in Fig. 8, in the second control phase, the grid-side converter (220) can be controlled in grid-feeding mode to block the supply of power from the grid side, which is receiving power from at least one synchronous generator (100), to the generator side. At this time, the power reference value of the grid-side converter (220) is 0. In other words, the grid-side converter (220) can be controlled for power with a zero power reference.

[0107] In addition, in the second control stage, the generator-side converter (210) can be controlled to start self-generation and charge the DC link capacitor (215) to the rated voltage. To this end, the ship power management device can control the torque of the shaft generator. When self-generation is performed normally and the electric energy of the shaft generator charges the DC link voltage of the DC link capacitor (215) to the rated voltage, the ship power management device can switch the control mode of the shaft generator system to the third control stage.

[0108] In the third control phase (phase Ⅲ), as shown in FIG. 9, the grid-side converter (220) can be switched to grid-forming mode so that the shaft generator based on the squirrel cage induction generator can perform the same role as the synchronous generator (100) of the ship power system. At this time, the ship power management device can perform voltage control (voltage control with droop) according to a control droop coefficient that is preset for the voltage control circuit of the grid-side converter (220) or determined or selected based on measured values ​​collected in real time so that the grid-side converter (220) has sufficient inertia for the grid-forming mode based on virtual impedance. As a result, the grid-side converter (220) can stably and quickly switch from grid-feeding mode to grid-forming mode, i.e., switch instantaneously. The ship power management device can keep the circuit breaker (250) open until just before performing the mode switch of the grid-side converter (220).

[0109] In addition, in the third control step, the generator-side converter (210) may operate as a grid-forming power converter to supply power to the ship power system in accordance with the common coupling point (PCC) of the ship power system so as to be properly connected with the ship power system, and / or to maintain the voltage of the DC link capacitor (215). That is, the ship power management device may 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 for the shaft generator.

[0110] According to the first to third control steps of the above-described embodiment, unnecessary circuit breaker operation and synchronization process can be omitted, so that the advantage of rapid and efficient system operation can be obtained.

[0111] FIG. 10 is a block diagram illustrating an adaptive flux control process that can be applied to the SCIG control steps of FIG. 6.

[0112] Referring to Fig. 10, an adaptive flux observer (abbreviated as 'adaptive observer') that can be equipped in a ship power management device is configured to measure the stator voltage vector of the shaft generator ( ), the rotor speed of the SCIG obtained from the engine governor ( ), and the estimated resistance obtained from the stator resistance adaptive scheme processor. ) based on the estimated stator current vector, ) and generate the stator current ( obtained from SCIG). ) is used to subtract the estimated stator current vector from the observer's state estimation error vector (state estimation error vector, ) can be generated. The state estimation error vector can be input to the stator resistance adaptive mode processor through a low-pass filter (LPF), and the estimated stator current vector from the adaptive flux observer can be input.

[0113] Thus, in this embodiment, it is assumed that the ship power management device can obtain the rotor speed measured by the engine governor, and it can be seen that the direct torque control (DTC) of the SCIG can accurately estimate the stator resistance. In fact, this assumption can be applied to distributed applications, as the rotor speed is measured by the engine governor.

[0114] For example, the state space model of SCIG can be set up on the rotor reference dq-axis. In this case, a state observer using an estimated state matrix, which is a semi-positive definite matrix, can be used to resolve the uncertain stator resistance in the state matrix (A). Using this state observer, the state estimation error of the shaft generator can be calculated, and an error vector with the stator current error can be defined. In addition, a semi-positive definite Lyapunov function including the quadratic function of the error vector and the stator resistance error with positive gain can be defined so that the state observer can adaptively estimate the stator resistance.

[0115] The semi-definite Lyapunov function is one of the methods for determining stability without finding a solution. It can be defined such that all elements of the estimated state matrix are real numbers, and a correction matrix of a given symmetric size satisfies certain inequalities for all vectors. Since this semi-definite Lyapunov function is convex downward on a three-dimensional graph, it can converge to a minimum when its derivative equals zero.

[0116] According to the derivative of the semi-definite Lyapunov function, the minimum of the Lyapunov function can be obtained by minimizing the sum of sums, considering that the error vector essentially depends on the estimated resistance. Therefore, the stator resistance can be estimated by solving an equation that utilizes the derivative of the semi-definite Lyapunov function. In this case, integration control using a low-pass filter (LPF) can be applied to quickly converge the equation solution.

[0117] Fig. 11 is a block diagram for explaining a virtual impedance-based voltage control process of a grid-forming power converter that can be employed in the ship power management device of Fig. 4.

[0118] As illustrated in Fig. 11, the ship power management device can perform voltage control of a power converter connected to a shaft generator based on virtual impedance. When the power converter operates in grid-forming mode, in addition to a feedback control circuit structure using a voltage controller, a current controller, a pulse width modulation controller (PWM controller), an inductor filter (L filter), and a capacitor filter (C filter), an output current (i) of the inductor filter l ) can be configured to have a structure that applies virtual impedance (411) to the input of the voltage controller while having a current feedback circuit structure that reflects the current to the input of the current controller.

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

[0120] In particular, the ship power management device references the phase angle of the output voltage of the grid-side converter ( ) with output voltage reference ( ) is input to the voltage controller, the fed-back output voltage reference ( ) while simultaneously reflecting the error with the grid-side converter's output current (i o) can control the voltage control operation of the grid-side converter to reflect a predetermined virtual impedance (411).

[0121] As described above, the ship power management device can perform voltage control based on virtual impedance (411) for the grid-side converter to ensure system stability during mode switching of the power converter. The virtual impedance (411) can include a fixed virtual impedance that is predetermined or fixed. The virtual impedance (411) can be a virtual inductance (L v ) and virtual resistance (R v ) can have a form that adds to it. If this virtual impedance (411) is Laplace transformed, " " can be expressed as follows. The virtual inductance can also be referred to as a virtual inductance component, and the virtual resistance can also be referred to as a virtual resistance component.

[0122] 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 a synchronous generator. Furthermore, by adopting a predetermined virtual impedance and changing the output impedance of the grid-side converter, the closed-loop transfer function of the internal control loop can be adjusted. The impact of the virtual impedance on system dynamics can be analyzed by tracking its eigenvalues.

[0123] FIG. 12 is an exemplary diagram for explaining a self-secondary voltage control structure that can be employed in a ship power system operation method according to another embodiment of the present invention.

[0124] Referring to Fig. 12, a self-secondary voltage controller (416) that can be included in a ship power controller is provided with a power factor calculation, an accumulator, hysteresis comparators, a transfer switch for switching at standalone operation, and a nominal output voltage (V nom ) to the offset voltage (V offset ) can be configured to provide a controlled nominal output voltage obtained by adding a current feedback circuit to the grid-forming power converter. The grid-forming power converter may include impedance due to the current feedback circuit as shown in FIG. 11.

[0125] In this embodiment, the problem to be solved is that when an isolation transformer is installed at the output terminal of a shaft generator system to reduce common mode noise, a voltage drop occurs depending on the output current. Therefore, it is difficult to control the voltage droop characteristics identical to those of an automatic voltage regulator of a synchronous generator. Therefore, to solve the problem of reactive power sharing with the synchronous generator and the voltage drop problem during single-phase operation, a self-secondary voltage control is applied.

[0126] According to the aforementioned self-secondary voltage controller structure, the voltage value of the voltage droop curve can be adjusted to a hysteresis-based control value. When operating in parallel with a synchronous generator, the secondary voltage control can be performed at a target power factor value, that is, a power factor value of a general ship power load, for example, 0.8, and when operating alone, the secondary voltage control can be performed so as to maintain the voltage of the secondary side of the isolation transformer at the rated voltage. In addition, to prevent the self-secondary voltage control from interfering with the braking role of the virtual impedance, the bandwidth of the self-secondary voltage controller (416) can be selected to be 1 / 20 of the bandwidth of the grid-forming power converter.

[0127] Below, we describe the stability evaluation, simulation, and experimental results utilizing root locus to verify virtual impedance control, shaft generator system linkage sequence, and self-secondary voltage control.

[0128] First, for grid-forming power converter modeling and root-locus-based stability evaluation, a mathematical model of the grid-forming power converter was created and the stability of the system was evaluated according to whether virtual impedance was applied and whether component combinations were used.

[0129] The detailed definitions of symbols used in the mathematical formulas of the formula model described below are as shown in Table 1 below.

[0130]

[0131] First, the active power and reactive power of the power generated from the shaft generator can be expressed as in mathematical equation 1.

[0132]

[0133] In mathematical equation 1, And, am.

[0134] The frequency and magnitude of the voltage according to the droop, which reflects the secondary frequency control by the ship power controller, can be defined as in mathematical expression 2. The ship power controller can be included in the ship power management device.

[0135]

[0136] Meanwhile, the voltage control formula model of the grid-forming power converter used in Fig. 11 can be expressed as in mathematical formula 3 below.

[0137]

[0138] In mathematical expression 3, am.

[0139] According to mathematical expression 3, the output voltage of the grid-forming power converter is the impedance subtracted by the transfer function G(s) and the output current according to the voltage target value and the voltage output value. It can be seen that it is composed of . In Fig. 11, the model of the power converter output voltage, excluding the virtual impedance, can be expressed as in mathematical expression 4.

[0140]

[0141] Comparing Equations 3 and 4, the impedance and Because they are different, the performance of the virtual impedance can be evaluated by changing only the impedance values ​​after creating the system model.

[0142] By substituting the voltage magnitude defined in Equation 2 into Equation 4, Equation 5 for the following voltage magnitude can be generated.

[0143]

[0144] By applying a low-pass filter to the above mathematical equation 1 and substituting it into mathematical equation 5, we can obtain the mathematical equation 6 below.

[0145]

[0146] By integrating the frequency formula of the above mathematical formula 2, applying a low-pass filter to the effective power value applied to mathematical formula 1, and then substituting mathematical formula 4, the following mathematical formula 7 can be obtained.

[0147]

[0148] Here, δ0 is the load angle of the power converter, and is defined by trigonometric functions as in mathematical equation 8 below.

[0149]

[0150] In mathematical expression 8, the value of δ0 is relatively very small. Assuming this, mathematical expression 8 can be simply expressed as mathematical expression 9 below.

[0151]

[0152] Meanwhile, mathematical expression 1 with a low-pass filter applied can be expressed in a linearized form as in mathematical expression 10 below.

[0153]

[0154] In mathematical expression 10 am.

[0155] and am.

[0156] By substituting Equation 10 into Equation 6, the voltage magnitude linear model of the grid-forming power converter can be obtained. The voltage magnitude linear model of the grid-forming power converter can be expressed as Equation 11.

[0157]

[0158] In mathematical expression 11 am.

[0159] By substituting Equations 9 and 10 above into Equation 7, the voltage phase linear model of the grid-forming power converter can be obtained. The voltage phase linear model of the grid-forming power converter can be expressed as Equation 12.

[0160]

[0161] In equation 12 am.

[0162] 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 Equation 13.

[0163]

[0164] In equation 13 It is. D n represents the nth order differentiation.

[0165] The factors used in the above mathematical expression 13 can be obtained as follows. First, G(s) used in mathematical expression 11 can be organized as in mathematical expression 15.

[0166]

[0167] In mathematical expression 14, and am.

[0168] Next, if we substitute equation 14 into equation 11, A differential equation for can be created as in Equation 15.

[0169]

[0170] The detailed definition of the factors in mathematical expression 15 is as follows.

[0171]

[0172] If we substitute Equation 14 into Equation 12 in a similar manner as above, The differential equation for can be created as in Equation 16.

[0173]

[0174] A defined in mathematical expression 13 using the constants defined above gf The matrix can be expressed as the following mathematical expression (17).

[0175]

[0176] The detailed definitions of the factors used in mathematical expression 17 are as follows.

[0177]

[0178] Here, a11 and a21 represent coefficients.

[0179] Figures 13a to 13c are diagrams showing root loci according to specific factor modifications to the stability verification model of the ship power system operation method of the present embodiment.

[0180] Figure 13a shows the root locus for the initial phase difference between the grid-forming controller and the system. As shown in Figure 13a, as the initial phase difference with the ship's power system increases, certain roots become positive real numbers, leading to system instability.

[0181] Figure 13b is a green root locus diagram showing the virtual impedance value changing while the system is unstable due to the initial phase difference. As shown in Figure 13b, when the virtual inductance component of the virtual impedance is increased, the positive root shifts to a negative value, confirming that the system becomes stable.

[0182] Meanwhile, as shown in Fig. 13c, when only the virtual resistance component of the virtual impedance is increased, the system stabilization effect is not large, and it can be confirmed that there is an effect of worsening the system braking characteristics by moving the negative real root away from the center point.

[0183] Figure 14 is a simulation control configuration diagram that can be adopted in the ship power system operation method of this embodiment.

[0184] Fig. 14 may correspond to at least a portion of the structure of a ship power controller for simulation when a power converter of a squirrel cage induction generator switches its control mode from grid feeding to grid forming. The ship power controller may include a grid feeding control unit (417) and a grid forming control unit (418).

[0185] The grid feeding control unit (417) converts the three-phase (abc) voltage (vabc) along the dq-axis to the q-axis output voltage (v oq ) and d-axis output voltage (v od) may be provided with a DQ converter that outputs a phase locked loop (PLL), a current controller, and a DQ inverse converter. The grid podding control unit (418) may be provided with a power equation processing unit, a droop function processing unit, a voltage controller, a current controller, two DQ converters, and a DQ inverse converter.

[0186] The first converter voltage command (uabc,feed) generated from the grid feeding control unit (417) and the second converter voltage command (uabc,form) generated from the grid forming control unit (418) can be selectively applied to the PWM control module of the ship power controller according to the switched operation of the circuit breaker of the switchboard at the first time (t=T1) to switch the operation mode of the power converter connected to the shaft generator in the ship power system.

[0187] That is, the ship power controller can control the reference power value to be 0 in the grid feeding state before the first time (T1) when the power converter of the shaft generator switches the control mode, and then immediately switch the control mode to the grid forming mode after the first time (T1).

[0188] Figures 15a and 15b are graphs showing simulation results for active power and reactive power between control mode switching of grid feeding and grid forming according to the simulation control configuration of Figure 14.

[0189] Figures 15a and 15b show simulation results of the active and reactive power between control mode transitions, depending on the application of virtual impedance and the component combination. The numerical results of the simulation are presented in Table 2.

[0190]

[0191] As can be seen from the results of Set A in FIGS. 15a and 15b, when there is no virtual impedance, it can be confirmed that when the control mode is switched, the active power, reactive power, voltage, and frequency all experience severe fluctuations and are dropped from the system.

[0192] And the results of Set B, which only has virtual resistance components, also show results that are not significantly different from Set A, and it can be confirmed that it is eliminated from the system.

[0193] Meanwhile, for Sets C and D, which have virtual inductance components, grid-connection is observed without significant fluctuations in all indicators, and grid-forming control begins. Since grid-forming control is performed normally, even if the synchronous generator is stopped, power can be supplied to the ship's power system load independently.

[0194] In this way, it can be confirmed through simulation that a virtual inductance is required for switching to grid-forming control mode, and that an efficient squirrel cage induction generator operating sequence as described in Fig. 5 is possible. In addition, it can be confirmed that the root locus results and simulation results described above are similar with reference to Figs. 13a to 13c.

[0195] Figures 16a and 16b are graphs showing simulation results for active power and reactive power between control mode switching between grid feeding and grid forming by applying the ship power system operation method of this embodiment to an actual ship.

[0196] As shown in Figs. 16a and 16b, verification of the ship power controller of the present embodiment on an actual ship involved conducting experiments on the effect of virtual impedance when switching the control mode to grid-forming mode under the same conditions as the simulation described above with reference to Figs. 15a and 15b. The experimental results obtained for four sets of virtual impedances are shown in Table 3.

[0197]

[0198] In cases where there is no virtual impedance, such as Set A, it can be seen that the shaft generator system is removed from the ship power system due to severe fluctuations in active power, reactive power, voltage, and frequency when the control mode is switched.

[0199] Additionally, it can be seen that Set B, which has only virtual resistance components, is also removed from the ship power system due to control instability.

[0200] In the case of Set C and Set D, which have virtual inductance components identical to the simulation results, it can be confirmed that the shaft generator system started grid forming control by being linked to the ship power system without significant changes in all indicators.

[0201] It can be seen that these experimental results are similar to the root locus results and simulation results of the above-described examples.

[0202] 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 its own secondary voltage control in the ship power system operation method of the present embodiment. And 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 its own secondary voltage control in the ship power system operation method of the present embodiment.

[0203] Figures 17a, 17b, 18a, and 18b show the experimental verification results for self-secondary voltage control. That is, the waveforms for 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 the difference in gray color intensity.

[0204] If the self-secondary voltage control is not applied, the droop characteristic curve (load-voltage) of the final voltage magnitude output voltage becomes lower than the synchronous generator droop curve (load-voltage) as the load increases due to the impedance of the power converter and the voltage drop on the isolation transformer side, resulting in a phenomenon in which reactive power cannot be smoothly supplied to the ship's power system, as shown in Figs. 17a and 18a.

[0205] As the power factor of the power converter increased to 0.9 from a power factor of 0.8 for the ship's load, the power factor of the other synchronous generators decreased to 0.7, resulting in an imbalance in the reactive power distribution, as shown in these drawings. Because the classification society's safety standards for ships do not allow for an imbalance of more than 10% of reactive power, this is an operating condition that does not meet safety standards.

[0206] The experimental results obtained by applying the self-secondary voltage control structure of this embodiment, as illustrated in Fig. 12 above, are as shown in Figs. 17b and 18b. According to these drawings, it can be confirmed that, while the power factor of the ship load is fixed at 0.8, reactive power is smoothly supplied at a power factor of 0.8, similar to other synchronous generators.

[0207] Figures 19a and 19b are graphs showing the power factor, active power, and reactive power when the grid-forming power converter is operated alone in the ship power system operation method of the present embodiment. Figures 20a and 20b are graphs showing the reference voltage and output voltage when the grid-forming power converter is operated alone in the ship power system operation method of the present embodiment.

[0208] Figures 19a, 19b, 20a and 20b are experimental verification results for a grid-forming power converter in standalone operation, showing waveforms for active power, reactive power, power factor and output voltage according to whether or not self-secondary voltage control is applied, distinguished by differences in the intensity of gray color.

[0209] When the secondary voltage control is not applied during the independent operation of the shaft generator system in the ship power system, the final voltage size is accompanied by a voltage drop due to the output current in addition to the droop of the output voltage due to the impedance of the power converter and the voltage drop on the isolation transformer side, and it can be confirmed that the voltage drop occurs up to 4% of the rated voltage depending on the load size, as shown in Figs. 19a and 20a.

[0210] Meanwhile, the waveforms of the standalone operation experiment results of a power converter with its own secondary voltage control applied can be confirmed in Figs. 19b and 20b. The secondary voltage control is performed to maintain the voltage of the secondary side of the isolation transformer at 1pu based on the rated voltage, thereby compensating for the impedance of the power converter control closed loop and the voltage drop of the isolation transformer. Therefore, it can be confirmed that the secondary side voltage of the isolation transformer is maintained at 1pu.

[0211] As described above, the present invention can provide an efficient grid-connected control method for a grid-forming shaft generator applied to a ship and a self-secondary voltage control method for improving the power quality of the ship's power grid. Furthermore, when simulating the droop characteristics of a synchronous generator, self-secondary voltage control can be performed to address voltage drops occurring in a grid-forming power converter and associated equipment (such as an isolation transformer). At this time, the control can be applied according to the voltage standards of parallel operation and single operation, respectively. Furthermore, a virtual impedance-based grid-forming control mode can be applied to ensure stability when switching between grid-feeding and grid-forming control modes of the power converter, and an efficient grid-feeding sequence for a squirrel-cage induction machine-based shaft generator utilizing this can be provided. In addition, the stability was evaluated using a root-locus diagram using a mathematical model, and the effectiveness of the present invention was verified through MATLAB / SIMULINK simulations and demonstration experiments on a ship with an actual shaft generator applied.

[0212] The methods according to the present embodiment described above may be implemented in the form of program commands that can be executed by various computer means and recorded on a computer-readable medium. The computer-readable medium may include program commands, data files, data structures, etc., either singly or in combination. The program commands recorded on the computer-readable medium may be those specifically designed and configured for the present invention, or may be known and usable by those skilled in the art of computer software.

[0213] 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 language codes generated by a compiler, but also high-level language codes that can be executed by a computer using an interpreter, etc. The hardware devices described above may be configured to operate with at least one software module to perform the operations of the present invention, and vice versa.

[0214] Although the present invention has been described with reference to the above embodiments, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below.

Claims

1. Step of electrically connecting the shaft generator to the ship power system; A step of controlling the generator-side converter of the power converter connected to the above-mentioned shaft generator to zero power reference; A step of charging a DC link capacitor of the above power converter; A step of magnetizing the shaft generator using the current of the DC link capacitor; A step for generating self-power using the above-mentioned shaft generator; A step of controlling the grid-side converter of the above power converter to zero power reference; A step of controlling the generator-side converter of the power converter to charge the DC link capacitor with the power of the shaft generator; and A step of performing self-secondary voltage control through the power converter so that the above-mentioned shaft generator operates as a distributed generator of the ship's power system; A method for managing ship power, comprising:

2. In claim 1, A method for managing power in a ship, wherein the step of charging the DC link capacitor of the power converter connected to the above-mentioned shaft generator includes controlling the grid-side converter to charge at least a portion of the rated voltage of the DC link capacitor, and the charged DC voltage is maintained by controlling the power converter.

3. In claim 1, A method for managing power in a ship, further comprising a step of controlling the grid-side converter to a grid-feeding mode before the step of magnetizing the shaft generator.

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

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

6. In claim 5, A ship power management method, wherein the step of performing the above-described self-secondary voltage control further includes the 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 the voltage controller.

7. In claim 5, A method for managing power in a ship, further comprising the step of maintaining the voltage of the DC link capacitor by performing at least one of torque control and flux control for the above-described shaft generator.

8. In claim 5, A method for managing power in a ship, further comprising the step of connecting the power converter to a common coupling point of the ship power system by performing at least one of torque control and flux control for the shaft generator.

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

10. In claim 9, A ship power management method, wherein the above estimating step further includes performing integral control using a low-pass filter for rapid convergence of the solution to the equation when solving the equation using the derivative of the semi-definite Lyapunov function.

11. As a ship power management device for a ship power system based on grid-forming shaft generator, At least one command having a shaft generator system initiation sequence; and A processor connected to a memory storing at least one command and executing the at least one command; Including, The above processor, by at least one instruction, Step of electrically connecting the shaft generator to the ship's power system; A step of controlling the generator-side converter of the power converter connected to the above-mentioned shaft generator to zero power reference; A step of charging a DC link capacitor of the above power converter; A step of magnetizing the shaft generator using the current of the DC link capacitor; A step for generating self-power using the above-mentioned shaft generator; A step of controlling the grid-side converter of the above power converter to zero power reference; A step of controlling the generator-side converter of the power converter to charge the DC link capacitor with the power of the shaft generator; and A step of performing self-secondary voltage control through the power converter so that the above-mentioned shaft generator operates as a distributed generator of the ship's power system; A ship power management device that performs the function.

12. In claim 11, A ship power management device, wherein the processor controls the grid-side converter to charge at least a portion of the rated voltage of the DC link capacitor in the step of charging the DC link capacitor of the power converter connected to the shaft generator, and maintains the charged DC link voltage through control of the power converter.

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

14. In claim 13, A ship power management device, 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 link capacitor is charged to the rated voltage or the preset voltage by the power of the shaft generator.

15. In claim 14, A ship power management device, wherein the processor, in the step of performing the self-secondary voltage control, performs voltage control of the grid-side converter according to a control droop coefficient determined or selected based on measurement values ​​that are preset or collected in real time.

16. In claim 15, A ship power management device, wherein the processor further performs, in the step of performing the self-secondary voltage control, the 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 the voltage controller.

17. In claim 15, A ship power management device, wherein the processor further performs a step of maintaining the voltage of the DC link capacitor by performing at least one of torque control and flux control for the shaft generator.

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

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

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

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