Method and apparatus for compensating harmonic components

Abstract

The present disclosure relates to a method and apparatus for compensating harmonics. A method for compensating harmonics according to one aspect may include: a step of extracting a harmonic voltage component applied to a grid from voltage data sampled by a voltage sensor; a step of modeling a harmonic current component flowing into the grid based on the harmonic voltage component; a step of calculating a compensation voltage to be output by a power converter connected to the grid to compensate for the modeled harmonic current component; and a step of controlling the grid-side output voltage of the power converter based on the calculated compensation voltage.

Description

Technology Field

[0001] The present disclosure relates to a method and apparatus for compensating harmonics. Background Technology

[0002] Generally, power systems contain numerous nonlinear loads, and harmonic currents generated from these loads can flow into the power grid, causing problems such as voltage distortion, equipment malfunction, and power quality degradation. These issues can be further exacerbated in microgrid power systems, such as marine power systems.

[0003] Methods utilizing passive or active filters to compensate for or attenuate harmonics have been studied. However, since passive filters have fixed filtering characteristics for specific harmonic orders, their application is limited in environments with permissible frequency fluctuations, such as marine power systems. Furthermore, voltage drop caused by the impedance of the filter itself can impair system performance. Additionally, active filters require additional power converters and current and voltage sensors to implement, which may present limitations in that installation costs and space requirements increase.

[0004] The aforementioned background technology is technical information that the inventor possessed for the derivation of the present invention or acquired during the process of deriving the present invention, and it cannot be considered as prior art disclosed to the general public prior to the filing of the present invention. The problem to be solved

[0005] The technical problem that the present invention aims to solve is to provide a method and apparatus for compensating harmonics. Additionally, it aims to provide a computer-readable recording medium that records a program for executing the method on a computer. The technical problems to be solved are not limited to those described above, and other technical problems may exist. means of solving the problem

[0006] As a technical means for achieving the aforementioned technical problem, the first aspect of the present disclosure may provide a method for compensating harmonics, comprising: a step of extracting a harmonic voltage component applied to a grid from voltage data sampled by a voltage sensor; a step of modeling a harmonic current component flowing into the grid based on the harmonic voltage component; a step of calculating a compensation voltage to be output by a power converter connected to the grid to compensate for the modeled harmonic current component; and a step of controlling the grid-side output voltage of the power converter based on the calculated compensation voltage.

[0007] A second aspect of the present disclosure may provide a computer-readable recording medium that records a program for executing a method according to a first aspect on a computer.

[0008] A third aspect of the present disclosure comprises: a memory storing at least one program; and at least one processor executing said at least one program, wherein the at least one processor extracts a harmonic voltage component applied to a grid from voltage data sampled by a voltage sensor, models a harmonic current component flowing into the grid based on said harmonic voltage component, and calculates a compensation voltage to be output by a power converter connected to the grid to compensate for said modeled harmonic current component.

[0009] A harmonic compensation device can be provided that controls the grid-side output voltage of the power converter based on the above-calculated compensation voltage.

[0010] In addition, other methods for implementing the present invention, other systems, and computer-readable recording media storing a computer program for executing said methods may be further provided.

[0011] Other aspects, features, and advantages other than those described above will become clear from the following drawings, claims, and detailed description of the invention. Effects of the invention

[0012] According to the means for solving the problem of the present disclosure described above, by modeling the current flowing into the system based on voltage data sampled by a voltage sensor, harmonics can be compensated without having a separate current sensor.

[0013] According to the means for solving the problem of the present disclosure described above, harmonics can be compensated without providing additional components by controlling a power converter already provided in the system to perform power conversion for a device in the power system and compensating for harmonics.

[0014] According to the means for solving the problem of the present disclosure described above, the control logic of a power converter can be simplified by performing a coordinate transformation between a reference coordinate system in which harmonic current components are expressed and a synchronous coordinate system.

[0015] The effects of the embodiments of the present disclosure are not limited to the effects mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in this specification. Brief explanation of the drawing

[0016] FIG. 1 is a conceptual diagram for explaining a power system according to one embodiment. FIG. 2 is a conceptual diagram for explaining a power system according to one embodiment. FIG. 3 is a flowchart of a harmonic compensation method according to one embodiment. FIG. 4 is a conceptual diagram illustrating a method for modeling current flowing into a grid based on voltage sampling data according to one embodiment. FIG. 5 is a block diagram illustrating a method for modeling harmonic current components based on voltage sampling data according to one embodiment. FIG. 6 is a block diagram illustrating a method for calculating a compensation voltage based on harmonic current components according to one embodiment. FIG. 7 is a block diagram illustrating a harmonic compensation device according to one embodiment. Specific details for implementing the invention

[0017] The advantages and features of the present disclosure and the methods for achieving them will become clear by referring to the embodiments described in detail together with the accompanying drawings. However, the present disclosure is not limited to the embodiments presented below, but can be implemented in various different forms and should be understood to include all modifications, equivalents, and substitutions that fall within the spirit and scope of the present disclosure. The embodiments presented below are provided to make the present disclosure complete and to fully inform those skilled in the art of the scope of the invention. In describing the present disclosure, detailed descriptions of related prior art are omitted where it is determined that such detailed descriptions may obscure the essence of the present invention.

[0018] The terms used herein are used merely to describe specific embodiments and are not intended to limit the disclosure. Unless otherwise defined, all terms used herein have the same meaning as generally understood by those skilled in the art to which this disclosure pertains.

[0019] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. Furthermore, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0020] Additionally, terms including ordinal numbers, such as "first" or "second" as used herein, may be used to describe various components, but the components should not be limited by the terms. The terms are used solely for the purpose of distinguishing one component from another.

[0021] Phrases such as "in one embodiment," "according to one embodiment," "related to one embodiment," or "according to an implementation of one embodiment" in this specification do not necessarily refer to the same embodiment. Furthermore, throughout this specification, "examples" are arbitrary distinctions to facilitate the description of the present disclosure, and each embodiment does not need to be mutually exclusive. For example, configurations mentioned for the description of one embodiment may be applied and / or implemented in other embodiments, and may be modified and applied and / or implemented to the extent that they do not depart from the scope of the present disclosure.

[0022] Some embodiments of the present disclosure may be represented by functional block configurations and various processing steps. Some or all of these functional blocks may be implemented by various numbers of hardware and / or software configurations that perform specific functions. For example, the functional blocks of the present disclosure may be implemented by one or more microprocessors or by circuit configurations for a specific function.

[0023] Additionally, for example, the functional blocks of the present disclosure may be implemented in various programming or scripting languages. The functional blocks may be implemented as algorithms executed on one or more processors. Furthermore, the present disclosure may employ prior art for electronic configuration, signal processing, and / or data processing, etc. Terms such as "mechanism," "element," "means," and "configuration" may be used broadly and are not limited to mechanical and physical configurations. Additionally, terms such as "-part," "-module," etc. refer to a unit that processes at least one function or operation, which may be implemented in hardware or software, or as a combination of hardware and software.

[0024] Furthermore, the connecting lines or connecting members between the components depicted in the drawings are merely illustrative of functional connections and / or physical or circuit connections. In the actual device, connections between components may be represented by various alternative or added functional connections, physical connections, or circuit connections.

[0025] In addition, some components in the drawings may be depicted with their size or proportions slightly exaggerated. Also, components depicted in one drawing may not be depicted in another drawing.

[0026] The present disclosure will be described in detail below with reference to the attached drawings.

[0027] FIG. 1 is a conceptual diagram for explaining a power system according to one embodiment.

[0028] In the present disclosure, the power system (1) may be a power system (1) equipped in a ship.

[0029] Referring to FIG. 1, the power system (1) may include a controller (100), a power converter (110), a device (120), a non-linear load (130), and a grid (140).

[0030] In the present disclosure, the controller (100) can control and manage various operations performed in the power system (1). That is, the controller (100) can control and manage the operations of the power converter (110), the device (120), and / or the grid (140) so that the power system (1) can be operated stably.

[0031] The controller (100) may include a processor. The controller (100) can control various operations performed in the power system (1) by generating and transmitting control signals. For example, the controller (100) can control the power conversion operation of the power converter (110) by generating control signals.

[0032] A power converter (110) can be understood as a device that converts and transports power between a device (120) and a grid (140). For example, the power converter (110) may include a power conversion device, such as a converter (including an inverter), that converts the voltage, current, and / or frequency of the input power and outputs it.

[0033] In one embodiment, the power converter (110) may include a plurality of power conversion blocks (Power Electronic Building Blocks, PEBBs). For example, the power converter (110) may include a grid-side power conversion block (111) and a machine-side power conversion block (112), as shown in FIG. 1. Here, a machine refers to a device that generates or consumes power and may include a generator (e.g., a shaft generator) or a load (e.g., a motor), as described below.

[0034] In one embodiment, the grid-side power conversion block (111) may include a switching element (transistor) and a gate driving unit (GDU), and the gate driving unit can convert the output voltage applied to the grid-side output terminal by controlling the switching of the switching element based on a control signal transmitted from the controller (100).

[0035] Likewise, the device-side power conversion block (112) may include a switching element (transistor) and a gate driving unit, and may convert the output voltage applied to the device-side output terminal based on a control signal transmitted from the controller (100).

[0036] In one embodiment, the power converter (110) can perform bidirectional power conversion between the device (120) and the grid (140). To this end, the grid-side power conversion block (111) and the device-side power conversion block (112) can each be implemented as an Active Front End (AFE) topology.

[0037] In the present disclosure, the device (120) may be understood as any device that produces power or any device that consumes power. For example, the device (120) may include a generator such as a diesel generator. In this case, power output from the device (120) may be supplied to the grid (140). As another example, the device (120) may be a load such as a motor that is substantially the same as a generator but has opposite directionality. In this case, power output from the grid (140) may be supplied to the device (120). As yet another example, the device (120) may be a device capable of both producing and consuming power, such as a shaft generator. In this case, depending on the operating conditions of the shaft generator system, power output from the device (120) may be supplied to the grid (140) (e.g., PTO operation), or power output from the grid (140) may be supplied to the device (120) (e.g., PTI operation).

[0038] In the present disclosure, a nonlinear load (130) may mean a load that generates harmonic current by consuming a current that is not proportional to the applied voltage. For example, the load (130) may be a load including a diode rectifier.

[0039] In the present disclosure, the system (140) may be understood as a power system and may be a system that serves as a central hub for operating and maintaining the ship. The system (140) may support the safety and efficient operation of the ship, such as by supplying power to various devices requiring power, including the propulsion system which is a major device of the ship, and by enabling the main functions of the ship to operate in the event of a power outage or emergency.

[0040] In addition, in addition to the components shown in FIG. 1, the power system (1) may further include any components necessary for power transmission within the ship.

[0041] Meanwhile, harmonic currents generated by a non-linear load (130) may flow into the system (140), and in this case, problems such as shortened lifespan of power equipment and communication failure may occur, such as distortion of the voltage waveform or heat generation due to increased system impedance. That is, harmonic currents can degrade the power quality of the system (1) and interfere with the normal operation of the components included in the system (1).

[0042] Referring to FIG. 1, the system (1) may include a current sensor (141) and a system voltage sensor (142) that sample the system current. The controller (100) may control the power converter (110) based on current data and voltage data sampled by the current sensor (141) and the voltage sensor (142) to compensate for harmonics generated by the nonlinear load (130).

[0043] Specifically, in one embodiment, the controller (100) can receive current and voltage sampling data from the current sensor (141) and the voltage sensor (142), respectively. The controller (100) can obtain phase and frequency information from the received voltage sampling data and, based thereon, extract current harmonic components from the current sampling data. Subsequently, the controller (100) can compensate for harmonics by controlling the power converter (110) so that a compensation voltage for canceling out the harmonic components of the current is output from the power converter (110).

[0044] Meanwhile, according to the above-described embodiment, since the system (1) must include both a current sensor and a voltage sensor for harmonic compensation, there may be a problem in that the design of the system becomes complex and the hardware construction cost increases. To solve this problem, in one embodiment, a system that compensates for harmonics by modeling the harmonic current component flowing into the grid (140) using voltage data sampled from the voltage sensor may be provided. Specific details regarding this will be explained in more detail with reference to FIG. 2.

[0045] FIG. 2 is a conceptual diagram for explaining a power system according to another embodiment of the present disclosure.

[0046] In the present disclosure, the power system (2) may be a power system (2) equipped in a ship.

[0047] Referring to FIG. 2, the power system (2) may include a controller (200), a power converter (210), a device (220), a nonlinear load (230), and a grid (240). The controller (200), power converter (210), device (220), nonlinear load (230), and grid (240) of the power system (2) may correspond to the controller (100), power converter (110), device (120), nonlinear load (130), and grid (140) of the power system (1) described above with reference to FIG. 1. Accordingly, redundant descriptions of each component constituting the power system (2) will be omitted.

[0048] Referring to FIG. 2, the power system (2) may be a system that does not have a separate current sensor for sampling the current flowing into the grid. In this case, the controller (200) can compensate for harmonics even in a power system (2) that does not have a current sensor for sampling the grid current by modeling the grid current using the grid voltage sampled by the voltage sensor (241).

[0049] Specifically, in one embodiment, the controller (200) can extract a harmonic voltage component applied to the grid from voltage data sampled by the voltage sensor (241) and model a harmonic current component flowing into the grid based on the extracted harmonic voltage component. Subsequently, the controller (200) can calculate a compensation voltage required to compensate for the modeled harmonic current component and control the grid-side output voltage of the power converter (210) based on the calculated compensation voltage.

[0050] Meanwhile, FIG. 2 illustrates a case where the voltage sensor (241) and the power converter (210) are separate components, but the present disclosure is not limited thereto. For example, power converters often have a voltage sensor built in, and in such cases, even if a voltage sensor for sampling the voltage applied to the grid is not provided separately from the power converter, the controller (200) can perform the aforementioned operation using the voltage sensor built into the power converter.

[0051] That is, in one embodiment, the voltage sensor (241) may be a voltage sensor included in at least one of the grid-side power conversion block (211) or the device-side power conversion block (212) of the power converter (210). In this case, the voltage sensor (241) embedded in the power converter (210) may sample the voltage of the grid-side output terminal of the power converter (210), and the sampled voltage of the grid-side output terminal may be the same as the voltage applied to the grid (240). According to this embodiment, separate voltage sensor placement and wiring are not required, so the design of the power system is simplified, and installation and maintenance costs can also be reduced.

[0052] Hereinafter, with reference to FIGS. 3 to 6, a harmonic compensation method according to various embodiments of the present disclosure will be described.

[0053] FIG. 3 is a flowchart of a harmonic compensation method according to one embodiment.

[0054] The method described below with reference to FIG. 3 can be performed by the harmonic compensation device (700) of FIG. 7, and specifically by the processor (710) included in the harmonic compensation device (700).

[0055] Referring to FIG. 3, in step 310, the processor can extract harmonic voltage components applied to the grid from voltage data sampled by the voltage sensor.

[0056] In one embodiment, the processor can extract harmonic voltage components applied to the grid from voltage data using a band-pass filter (BPF). Here, the band-pass filter may refer to a filter that passes only components of a specific frequency band from an input voltage signal and removes components outside that band. In one embodiment, the band-pass filter may be implemented as a digital filter that can be computed on a digital signal processor (DSP), but is not limited thereto.

[0057] Meanwhile, among the odd-order harmonic components generated by nonlinear loads, there is a need to intensively compensate for harmonic components that have an adverse effect on the system, excluding harmonics of the third order (such as 5th, 7th, 11th, and 13th order harmonics). In particular, since harmonic components have the characteristic that their magnitude increases as their order decreases, there is a need to prioritize the compensation of 5th and 7th order harmonic components, which have the greatest impact on system stability.

[0058] In one embodiment, the processor may use a band-pass filter (BPF) to extract a first harmonic voltage component and a second harmonic voltage component applied to the grid from voltage data. Here, the first harmonic voltage component and the second harmonic voltage component may be a 7th harmonic voltage component and a 5th harmonic voltage component, respectively. Alternatively, the first harmonic voltage component and the second harmonic voltage component may be an 11th harmonic voltage component and a 13th harmonic voltage component, respectively. More specific details regarding this will be described later in FIG. 5.

[0059] In step 320, the processor can model the harmonic current components flowing into the grid based on the harmonic voltage components.

[0060] In one embodiment, the processor can determine a transfer function based on the relationship between the grid current and the grid voltage. The processor can also model the current flowing into the grid based on the transfer function and voltage data. Here, the transfer function may refer to a function representing the relationship between the grid voltage, which is an input value, and the grid current, which is an output value. In one embodiment, the transfer function may be defined in the complex frequency domain and may include the form of an approximation function of a low-pass filter. More specific details regarding this will be described later in FIG. 4.

[0061] Meanwhile, when the first harmonic voltage component and the second harmonic voltage component applied to the system are extracted as described above in step 310, the processor can model a harmonic current component in which the first harmonic current component and the second harmonic current component are summed based on the first harmonic voltage component and the second harmonic voltage component. More specific details regarding this will be described later in FIG. 5.

[0062] In step 330, the processor can calculate a compensation voltage to be output from a power converter connected to the grid to compensate for the modeled harmonic current component.

[0063] Meanwhile, in one embodiment, voltage data sampled by a voltage sensor may be voltage data sampled in a reference coordinate system, and harmonic current components modeled based thereon may also be harmonic current components expressed in a reference coordinate system. Here, the reference coordinate system refers to a coordinate system in which voltage data sampled by a voltage sensor is expressed, and may include, for example, a three-phase ABC coordinate system.

[0064] In this case, since the harmonic current component expressed in the reference coordinate system is an AC signal that oscillates continuously over time, if control logic to compensate for the harmonic current component is implemented in the reference coordinate system, dynamic control is required, which makes the control logic complex and increases the amount of computation, potentially reducing processing efficiency in a digital control environment.

[0065] In one embodiment, the aforementioned control logic can be simplified by converting the harmonic current component value in the reference coordinate system into the harmonic current component value in the rotating synchronous coordinate system. Here, the synchronous coordinate system is a two-dimensional coordinate system that represents three-phase voltage / current components on two orthogonal axes and can rotate at a constant angular velocity corresponding to the frequency of the voltage / current. For example, the rotating synchronous coordinate system may be a DQ coordinate system that rotates at an integer multiple speed (e.g., 360Hz) of the fundamental frequency (e.g., 60Hz), but is not limited thereto.

[0066] Meanwhile, in a rotating synchronous coordinate system, a harmonic current component of a specific order having a frequency corresponding to the rotational speed of the coordinate system may appear as a static component (i.e., a DC component) whose value does not change over time. This may be because a component having the same frequency as the reference angular velocity of the rotating coordinate system is observed to be relatively stationary in the coordinate system. For example, if the synchronous coordinate system rotates in the forward direction at a speed six times the fundamental frequency (e.g., 360 Hz), the 7th harmonic current component may appear as a stationary DC component.

[0067] In this way, the processor can calculate a compensation voltage to compensate for the harmonic current component based on simpler control logic (e.g., PI control) by performing a coordinate system transformation of the harmonic current component.

[0068] In one embodiment, the processor can convert the harmonic current component value in the reference coordinate system into the harmonic current component value in the synchronous coordinate system that rotates at a predetermined multiple of the fundamental frequency. In this case, the converted harmonic current component value (the harmonic current component value in the rotating synchronous coordinate system) may include a direct current component that does not change over time and an alternating current component whose value changes over time.

[0069] The processor can extract the DC component value of the converted harmonic current component value. At this time, the processor can extract the DC component of the converted harmonic current component value using a low-pass filter (LPF). Here, the low-pass filter may refer to a filter that passes only low-frequency components below the cutoff frequency from the input voltage signal and removes high-frequency components above the cutoff frequency. In one embodiment, the band-pass filter may be implemented as a digital filter that can be computed on a digital signal processor, but is not limited thereto.

[0070] Furthermore, the processor can calculate a compensation voltage to control the extracted DC component value to zero. Specifically, the processor can set the extracted DC component value as an error and calculate the compensation voltage based on feedback control logic to reduce the error. For example, the processor can calculate the compensation voltage based on PI control logic that calculates the compensation voltage by considering the proportional and integral components of the error, but is not limited thereto.

[0071] At this time, the compensation voltage can be calculated as a value in a rotating synchronous coordinate system. In this case, in one embodiment, the processor may further perform the operation of converting the compensation voltage value in the synchronous coordinate system into a compensation voltage value in the reference coordinate system. For example, the compensation voltage calculated in the rotating synchronous coordinate system can be converted into the respective voltage values ​​of the three phases (a, b, and c phases), which are the compensation voltage values ​​in the reference coordinate system.

[0072] Meanwhile, as described above in step 320, the processor can model a harmonic current component in which the first harmonic current component and the second harmonic current component are summed, based on the first harmonic voltage component and the second harmonic voltage component.

[0073] In this case, in one embodiment, the processor can convert the summed harmonic current component value in the reference coordinate system into a first current component value in a synchronous coordinate system that rotates forward by a predetermined multiple of the fundamental frequency, and extract a first DC component value from the first current component value. At the same time, the processor can convert the summed harmonic current component value in the reference coordinate system into a second current component value in a synchronous coordinate system that rotates backward by a predetermined multiple of the fundamental frequency, and extract a second DC component value of the second current component value. Here, the first current component value and the second current component value each refer to the value that the summed harmonic current component value in the reference coordinate system has in a synchronous coordinate system that rotates forward by a predetermined multiple of the fundamental frequency and the value that it has in a synchronous coordinate system that rotates backward by a predetermined multiple of the fundamental frequency. Additionally, the first DC component value and the second DC component value each refer to the DC component value included in the first current component value and the DC component value included in the second current component value.

[0074] Subsequently, the processor can calculate a first compensation voltage value for controlling the first DC component value, which is the DC component value of the first harmonic current component value, to zero, and a second compensation voltage value for controlling the second DC component value, which is the DC component value of the second harmonic current component value, to zero.

[0075] Subsequently, the processor can calculate the final compensation voltage by converting the first compensation voltage value and the second compensation voltage value into values ​​in the abc coordinate system, respectively, and then summing the two compensation voltage values. More specific details regarding this will be described later in FIG. 6.

[0076] Meanwhile, due to the processor's internal computation time, control loop delays, and PWM signal generation, there may be a time difference between the time when the processor calculates the compensation voltage and the time when the grid-side output voltage is actually applied through the power converter. Accordingly, the phase of the compensation voltage calculated at the current time (target phase) and the phase of the output voltage at the current time actually applied to the grid based on that compensation voltage (actual phase) may differ from each other.

[0077] To solve these problems, in one embodiment, the processor can predict a phase error at the time of calculating the compensation voltage and correct the phase of the compensation voltage by an amount corresponding to the phase error.

[0078] In one embodiment, the processor may correct the aforementioned phase error based on the expected time until the compensation voltage is actually applied to the grid, based on the sampling period of the voltage sensor and / or the system control period, etc. As a specific example, the processor may correct the phase of the compensation voltage by a predetermined period (e.g., 1.5 sampling periods) based on the sampling period of the voltage sensor, but is not limited thereto. In this case, the predetermined period may vary depending on specific design specifications of the system (e.g., computational delay within the controller, PWM modulation method, computational structure and processing priority of the DSP, etc.) and may be a value set based on empirical / statistical analysis.

[0079] In step 340, the processor can control the grid-side output voltage of the power converter based on the calculated compensation voltage.

[0080] In one embodiment, the processor can calculate a reference voltage by summing the current grid-side output voltage of the power converter and the compensation voltage value calculated according to step 330. Subsequently, the processor can control the power converter so that the grid-side output voltage of the power converter becomes the reference voltage.

[0081] Here, the reference voltage refers to the final target voltage that must be output to the grid side by the power converter, the compensation voltage refers to the voltage for compensating for harmonic current components flowing into the grid, and the current grid-side output voltage may refer to the voltage required for the operation of the system (e.g., generator operation).

[0082] In other words, the processor can calculate a final reference voltage that enables normal operation while compensating for harmonics by summing the output voltage (basic voltage) according to the system operation purpose and the compensation voltage for harmonic elimination.

[0083] Here, the compensation voltage may be a value calculated in a rotating synchronous coordinate system as described above and converted into a reference coordinate system (e.g., ABC coordinate system), and the processor can control the grid-side output voltage by performing switching control (transistor) of the power converter based on the reference voltage value in the reference coordinate system.

[0084] FIG. 4 is a conceptual diagram illustrating a method for modeling current flowing into a grid based on voltage sampling data according to one embodiment.

[0085] With reference to FIG. 4, the operation described below can be performed by the harmonic compensation device (700) of FIG. 7, and specifically by the processor (710) included in the harmonic compensation device (700).

[0086] The device (410) and system (420) illustrated in FIG. 4 may correspond to the device (120) and system (140) described above with reference to FIG. 1 or the device (220) and system (240) described above with reference to FIG. 2, respectively.

[0087] In one embodiment, the processor can model the current flowing into the system (420) based on voltage sampling data of the system (420) obtained using a voltage sensor.

[0088] The relationship between the grid current and the grid voltage in the time domain can be expressed as shown in Equation 1 below. In Equation 1, i(t) represents the grid current at time t, v(t) represents the grid voltage at time t, and L represents the equivalent inductance of the device (410). Here, a person skilled in the art will easily understand that L may include the equivalent inductance component existing between the device (410) and the grid (420).

[0089]

[0090] Meanwhile, since voltage sampling data has discrete values, when modeling the grid current based on Equation 1, problems such as offset accumulation, calculation instability, and noise amplification may occur as integral operations are performed repeatedly. To solve this, in one embodiment, the processor can model the grid current based on a transfer function that defines the relationship between the input voltage and the output current defined in the complex frequency domain.

[0091] The relationship between the system current and the system voltage in the complex frequency domain can be expressed as shown in Equation 2 below. In Equation 2, I(s) is the system (420) current in the complex frequency domain, V(s) is the system voltage in the complex frequency domain, and w c represents the pre-set cutoff frequency, and L in Equation 2 is the same as L in Equation 1.

[0092]

[0093] In one embodiment, the relationship between the grid current and grid voltage in the complex frequency domain represents an ideal integrator. It can be configured with a transfer function based on [this]. However, in actual systems, an ideal integrator has the problem that, as mentioned above, the output may diverge or become unstable as the DC offset or low-frequency noise components included in the input accumulate infinitely over time. Accordingly, in one embodiment, as shown in Equation 2, the form of an approximate function of a low-pass filter It can be composed of a transfer function based on

[0094] In one embodiment, the processor is a transfer function representing the relationship between the input voltage and the output current expressed in Equation 2. Based on this, the system current can be modeled from voltage data. Here, the transfer function is a function that expresses the input / output characteristics of a continuous-time system in the form of a rational function in the complex frequency domain (s-domain). If the processor is configured as a digital signal processor (DSP), the processor can perform current modeling through digital approximation techniques (e.g., digital filter structures), such as the z-transform of the transfer function.

[0095] Meanwhile, the transfer function may be appropriately modified according to specific system design specifications, such as reactance, filter cutoff frequency, and controller response speed. A person skilled in the art will be able to appropriately change the transfer function according to the implementation environment in which the present invention is implemented by inferring from the aforementioned embodiments.

[0096] FIG. 5 is a block diagram illustrating a method for modeling harmonic current components based on voltage sampling data according to one embodiment.

[0097] The method described with reference to FIG. 5 may correspond to steps 310 and 320 of FIG. 3. Additionally, the method described below with reference to FIG. 5 may be performed by the harmonic compensation device (700) of FIG. 7, and specifically by the processor (710) included in the harmonic compensation device (700).

[0098] Referring to FIG. 5, in one embodiment, a processor can acquire voltage data (510) sampled by a voltage sensor. Subsequently, the processor can extract the first harmonic voltage component (521) and the second harmonic voltage component (522) by using a band-pass filter that passes the first harmonic voltage component (521) having a frequency band corresponding to the first harmonic component and the second harmonic voltage component (522) having a frequency band corresponding to the second harmonic component among the input voltage data (510).

[0099] Subsequently, the processor can model a harmonic current component (530) based on the first harmonic voltage component (521) and the second harmonic voltage component (522). Here, the modeled harmonic current component (530) may be a harmonic current component obtained by summing the first harmonic current component and the second harmonic current component.

[0100] And, the processor can model the harmonic current component (530) based on a transfer function representing the relationship between the input value, the grid voltage, and the output value, the grid current, as described above with reference to FIG. 4.

[0101] Meanwhile, referring to FIG. 5, the aforementioned first and second harmonics may refer to the 7th and 5th harmonics, respectively. This may be because, as previously mentioned, harmonic components have the characteristic of increasing in magnitude as their order decreases, and thus there is a need to prioritize compensation for the 5th and 7th harmonic components, which have the greatest impact on system stability. However, a person skilled in the art will easily understand that the aforementioned details, referring to FIG. 5, can be inferred even when the first and second harmonics are the 11th and 13th harmonics, respectively.

[0102] FIG. 6 is a block diagram illustrating a method for calculating a compensation voltage based on harmonic current components according to one embodiment.

[0103] The method described with reference to FIG. 6 may correspond to step 330 of FIG. 3. Additionally, the method described below with reference to FIG. 5 may be performed by the harmonic compensation device (700) of FIG. 7, and specifically by the processor (710) included in the harmonic compensation device (700).

[0104] In one embodiment, the processor can extract the first harmonic current component and the second harmonic current component from the harmonic current component (610) which is the sum of the first harmonic current component and the second harmonic current component, by performing coordinate transformation operations and filtering operations, etc., which will be described later. Then, the processor can calculate a first compensation voltage for compensating the extracted first harmonic current component and a second compensation voltage for compensating the extracted second harmonic current component, respectively, and calculate a final compensation voltage (650) by summing them in the ABC coordinate system.

[0105] Specifically, referring to FIG. 6, in one embodiment, the processor may perform a coordinate system transformation for the harmonic current component (610). In one embodiment, the harmonic current component (610) may be the harmonic current component (530) described above with reference to FIG. 5. In this case, the harmonic current component (610) may include a current component modeled based on a first harmonic voltage component and a current component modeled based on a second harmonic voltage component.

[0106] In one embodiment, the harmonic current component (610) may be a current component expressed in a three-phase ABC coordinate system. The processor may convert the value of the harmonic current component (610) in the three-phase ABC coordinate system into a value of a first current component (621) expressed in a DQ coordinate system that rotates in the forward direction by a predetermined multiple of the fundamental frequency. Here, the first current component (621) is a term for referring to the harmonic current component (610) expressed in the DQ coordinate system that rotates in the forward direction by a predetermined multiple of the fundamental frequency.

[0107] At this time, the first current component (621) may include a first DC component (631) value, which is a current component value that does not change over time, and a first AC component value, which is a current component value that changes over time. This may be because, as described above, in a DQ coordinate system that rotates at a predetermined multiple of the fundamental frequency, a harmonic current component of a specific order corresponding to a predetermined multiple of the fundamental frequency appears as a fixed value, while a harmonic current component of the remaining order appears as a continuously fluctuating value.

[0108] For example, in a DQ coordinate system that rotates in the forward direction by a multiple of 6 times the fundamental frequency, the current component value of the 7th harmonic appears as a fixed value that does not change over time, while the current component values ​​of other harmonics appear as fluctuating values ​​that change over time.

[0109] The processor can extract the first DC component (631) by using a low-pass filter that passes only the first DC component (631) having a frequency band corresponding to the first harmonic component among the input first current components (621). In this case, the extracted first DC component (631) may correspond to the first harmonic current component.

[0110] The processor can calculate a first compensation voltage (641) for controlling the first DC component (631) to zero on a DQ coordinate system that rotates in the forward direction by a predetermined multiple of the fundamental frequency. For example, the processor can calculate the first compensation voltage (641) for controlling the first DC component (631) to zero using a PI control technique.

[0111] Likewise, in one embodiment, the processor can convert the value of the harmonic current component (610) in the three-phase ABC coordinate system into a value of the second current component (622) expressed in the DQ coordinate system, which is reverse-rotated by a predetermined multiple of the fundamental frequency. Here, the second current component (622) is a term for the harmonic current component (610) expressed in the DQ coordinate system, which is reverse-rotated by a predetermined multiple of the fundamental frequency.

[0112] At this time, the second current component (622) may include a second DC component (632) value, which is a current component value that does not change over time, and a second AC component value, which is a current component value that changes over time.

[0113] The processor can extract the second DC component (632) by using a low-pass filter that passes only the second DC component (632) having a frequency band corresponding to the second harmonic component among the input second current components (622). In this case, the extracted second DC component (632) may correspond to the first harmonic current component.

[0114] The processor can calculate a second compensation voltage (642) for controlling the second DC component (632) to zero on a DQ coordinate system that rotates in reverse at a predetermined multiple of the fundamental frequency.

[0115] Meanwhile, in one embodiment, the processor can perform the calculation process of the first compensation voltage (641) and the calculation process of the second compensation voltage (642) described above in parallel (simultaneously).

[0116] Afterwards, the processor can convert the first compensation voltage (641) and the second compensation voltage (642) into values ​​in the three-phase ABC coordinate system, respectively, and calculate the final compensation voltage (650) by summing them.

[0117] For convenience of explanation, the above-described operation will be explained assuming that the first harmonic and the second harmonic are the 7th and 5th harmonics, respectively. However, a person skilled in the art will easily understand that the following contents can be inferred even if the first harmonic and the second harmonic are the 13th and 11th harmonics, respectively.

[0118] In one embodiment, the harmonic current component (610) may include a fifth harmonic current component and a seventh harmonic current component.

[0119] The processor can convert the harmonic current component (610) into a first current component (621) represented in a DQ coordinate system that rotates at a multiple of 6 times the fundamental frequency (e.g., 300 Hz). Subsequently, the processor can extract a first DC component (631) from the first current component (621) using a low-pass filter, wherein the extracted first DC component (631) may correspond to a 7th harmonic current component. Subsequently, the processor can calculate a first compensation voltage (641) to control the extracted first DC component (631) to zero.

[0120] At the same time, the processor can convert the harmonic current component (610) into a second current component (622) represented in a DQ coordinate system that rotates at a multiple of 6 times (300 Hz) of the fundamental frequency. Subsequently, the processor can extract a second DC component (632) from the second current component (622) using a low-pass filter, and the extracted second DC component (632) can correspond to a fifth harmonic current component. Subsequently, the processor can calculate a second compensation voltage (642) to control the extracted second DC component (632) to zero.

[0121] The processor can convert the values ​​of the first compensation voltage (641) and the second compensation voltage (642) into voltage values ​​in the ABC coordinate system, and calculate the final compensation voltage (650) by summing the two compensation voltage values.

[0122] FIG. 7 is a block diagram illustrating a harmonic compensation device according to one embodiment.

[0123] A harmonic compensation device according to various embodiments of the present disclosure may be the controller (100) of FIG. 1 or the controller (200) of FIG. 2, and a method of compensating for harmonics according to various embodiments may be understood to be performed by the controller (100) or the controller (200). Alternatively, a harmonic compensation device according to various embodiments of the present disclosure may be included in the controller (100) or the controller (200) or may be a part of the controller (100) or the controller (200).

[0124] Referring to FIG. 7, the harmonic compensation device (700) may include a processor (710) and a memory (720). Only the components related to the embodiment are shown in the harmonic compensation device (700) of FIG. 7. Therefore, a person skilled in the art will understand that other general-purpose components may be included in addition to the components shown in FIG. 7.

[0125] The memory (720) is hardware that stores various data processed within the harmonic compensation device (700) and can store a program for processing and controlling the processor (710).

[0126] The memory (720) may include RAM (random access memory), such as DRAM (dynamic random access memory) and SRAM (static random access memory), ROM (read-only memory), EEPROM (electrically erasable programmable read-only memory), CD-ROM, Blu-ray or other optical disc storage, HDD (hard disk drive), SSD (solid state drive), or flash memory.

[0127] The processor (710) controls the overall operation of the harmonic compensation device (700). For example, the processor (710) can control the input unit (not shown), display (not shown), communication unit (not shown), memory (720), etc., by executing programs stored in memory (720). The processor (710) can control the operation of the harmonic compensation device (700) by executing programs stored in memory (720).

[0128] The processor (710) can control at least some of the operations of the harmonic compensation device (700) described above in FIGS. 1 to 6. For example, the processor (710) can control at least some of the operations of extracting a harmonic voltage component applied to the grid from voltage data sampled by a voltage sensor, modeling a harmonic current component flowing into the grid based on the harmonic voltage component, calculating a compensation voltage to be output by a power converter connected to the grid to compensate for the modeled harmonic current component, and controlling the grid-side output voltage of the power converter based on the calculated compensation voltage. Meanwhile, a specific example of the operation of the processor (710) is the same as described above with reference to FIGS. 1 to 6. Therefore, a specific description of the operation of the processor (710) is omitted below.

[0129] The processor (710) may be implemented using at least one of ASICs (application specific integrated circuits), DSPs (digital signal processors), DSPDs (digital signal processing devices), PLDs (programmable logic devices), FPGAs (field programmable gate arrays), controllers, microcontrollers, microprocessors, and other electrical units for performing functions.

[0130] In one embodiment, the harmonic compensation device (700) may be a mobile electronic device. For example, the harmonic compensation device (700) may be implemented as a smartphone, tablet PC, PC, smart TV, PDA (personal digital assistant), laptop, media player, navigation, a device equipped with a camera, and other mobile electronic devices. Additionally, the harmonic compensation device (700) may be implemented as a wearable device such as a watch, glasses, a hair band, and a ring equipped with communication functions and data processing functions.

[0131] In another embodiment, the harmonic compensation device (700) may be an electronic device embedded within the vessel. For example, the harmonic compensation device (700) may be an electronic device inserted into the vessel through tuning after the production process. In this case, the location of the harmonic compensation device (700) and the aforementioned vessel may be the same.

[0132] In another embodiment, the harmonic compensation device (700) may be a server located outside the vessel. The server may be implemented as a computer device or a plurality of computer devices that communicate through a network to provide commands, code, files, content, services, etc.

[0133] In another embodiment, the process performed in the harmonic compensation device (700) may be performed by at least some of a mobile electronic device, an electronic device embedded within the vessel, and a server located outside the vessel.

[0134] An embodiment according to the present invention may be implemented in the form of a computer program that can be executed through various components on a computer, and such a computer program may be recorded on a computer-readable medium. In this case, the medium may include a magnetic medium such as a hard disk, a floppy disk, and a magnetic tape, an optical recording medium such as a CD-ROM and a DVD, a magneto-optical medium such as a floptical disk, and a hardware device specifically configured to store and execute program instructions, such as a ROM, RAM, or flash memory.

[0135] Meanwhile, the above-mentioned computer program may be one specifically designed and configured for the present invention, or one known and available to those skilled in the art of computer software. Examples of computer programs may include machine code, such as that generated by a compiler, as well as high-level language code that can be executed by a computer using an interpreter, etc.

[0136] According to one embodiment, the method according to various embodiments of the present disclosure may be provided by being included in a computer program product. The computer program product may be traded between a seller and a buyer as a product. The computer program product may be distributed in the form of a device-readable storage medium (e.g., compact disc read-only memory (CD-ROM)), or distributed online (e.g., download or upload) through an application store (e.g., Play Store™) or directly between two user devices. In the case of online distribution, at least a portion of the computer program product may be temporarily stored or temporarily created in a device-readable storage medium, such as the memory of a manufacturer's server, an application store's server, or a relay server.

[0137] Unless explicitly stated or contrary to the order of the steps constituting the method according to the present invention, said steps may be performed in a suitable order. The present invention is not necessarily limited by the order in which said steps are described. The use of all examples or exemplary terms in the present invention is merely for the purpose of describing the present invention in detail, and the scope of the present invention is not limited by said examples or exemplary terms unless limited by the claims. Furthermore, those skilled in the art will understand that various modifications, combinations, and changes may be made according to design conditions and factors within the scope of the claims or equivalents to which they are added.

[0138] Accordingly, the scope of the present invention should not be limited to the embodiments described above, and all scopes equivalent to or equivalently modified from the claims set forth below, as well as the claims set forth below, shall be considered to fall within the scope of the concept of the present invention.

Claims

Claim 1 A method for compensating harmonics comprises: a step of extracting a harmonic voltage component applied to a grid from voltage data sampled by a voltage sensor; a step of modeling a harmonic current component flowing into the grid based on the harmonic voltage component; a step of calculating a compensation voltage to be output by a power converter connected to the grid to compensate for the modeled harmonic current component; and a step of controlling the grid-side output voltage of the power converter based on the calculated compensation voltage; wherein the step of modeling comprises a step of modeling the harmonic current component corresponding to the harmonic voltage component using a transfer function representing the relationship between the grid voltage and the grid current. Claim 2 The method according to claim 1, wherein the extraction step comprises the step of extracting a first harmonic voltage component and a second harmonic voltage component applied to the system from the voltage data using a band pass filter (BPF). Claim 3 delete Claim 4 In claim 2, the modeling step comprises the step of modeling a harmonic current component obtained by summing a first harmonic current component and a second harmonic current component based on the first harmonic voltage component and the second harmonic voltage component. Claim 5 The method of claim 1, wherein the calculating step comprises: a step of converting the harmonic current component value in a reference coordinate system into the harmonic current component value in a synchronous coordinate system (synchronous frame) that rotates at a predetermined multiple of the fundamental frequency; a step of extracting the direct current (DC) component value of the converted harmonic current component value; and a step of calculating a compensation voltage to control the extracted DC component value to zero. Claim 6 In claim 5, the step of extracting the DC component comprises the step of extracting the DC component using a low-pass filter (LPF). Claim 7 In claim 4, the calculating step comprises: a step of converting the summed harmonic current component value in the reference coordinate system into a first current component value in the synchronous coordinate system rotating in the forward direction by a predetermined multiple of the fundamental frequency to extract a first DC component value of the first current component value; a step of converting the summed harmonic current component value in the reference coordinate system into a second current component value in the synchronous coordinate system rotating in the reverse direction by the predetermined multiple of the fundamental frequency to extract a second DC component value of the second current component value; and a step of calculating a first compensation voltage value for controlling the first DC component value, which is the DC component value of the first harmonic current component value, to zero, and a second compensation voltage value for controlling the second DC component value, which is the DC component value of the second harmonic current component value, to zero. Claim 8 A method according to claim 5, wherein the compensation voltage is calculated in the synchronous coordinate system, and the calculating step further comprises the step of converting the compensation voltage value in the synchronous coordinate system into a compensation voltage value in the reference coordinate system. Claim 9 A method according to claim 1, wherein the calculating step comprises a step of correcting a phase error of the compensation voltage caused by a time difference between the time of calculating the compensation voltage and the time of applying the compensation voltage to the system. Claim 10 In claim 9, the correction step comprises the step of correcting the phase of the compensation voltage by a predetermined period based on the sampling period of the voltage sensor; a method. Claim 11 A method according to claim 1, wherein the controlling step comprises: a step of calculating a reference voltage by summing the current grid-side output voltage of the power converter and the calculated compensation voltage value; and a step of controlling the grid-side output voltage of the power converter to the reference voltage. Claim 12 A method according to claim 1, wherein the power converter is a power converter having one end connected to a shaft generator and the other end connected to the grid to perform bidirectional power conversion between the shaft generator and the grid. Claim 13 A computer-readable recording medium storing a program for executing the method of claim 1 on a computer. Claim 14 A device for compensating harmonics comprises: a memory in which at least one program is stored; and at least one processor for executing said at least one program, wherein the at least one processor extracts a harmonic voltage component applied to a grid from voltage data sampled by a voltage sensor, models a harmonic current component flowing into the grid based on said harmonic voltage component, calculates a compensation voltage to be output by a power converter connected to the grid to compensate for said modeled harmonic current component, and controls the grid-side output voltage of said power converter based on said calculated compensation voltage, wherein the at least one processor models said harmonic current component corresponding to said harmonic voltage component using a transfer function representing the relationship between the grid voltage and the grid current.

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