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KR-102963599-B1 - Grid impedance estimation system and method

KR102963599B1KR 102963599 B1KR102963599 B1KR 102963599B1KR-102963599-B1

Abstract

A system impedance estimation system and method are provided. A system impedance estimation system according to an embodiment of the present invention comprises: a basic calculation data acquisition unit that injects a perturbation signal and measures voltage and current to acquire basic calculation data; a hypothetical system impedance derivation unit that performs a preset calculation using the basic calculation data to derive a hypothetical system impedance; and a final impedance estimation unit that corrects the signal from the calculation result to estimate the system impedance in the low-frequency band and estimates the final impedance using a mathematical estimation technique.

Inventors

  • 박정욱
  • 윤지현

Assignees

  • 연세대학교 산학협력단

Dates

Publication Date
20260511
Application Date
20240711

Claims (15)

  1. A basic operation data acquisition unit that injects a perturbation signal and measures voltage and current to acquire basic operation data; A household system impedance derivation unit that derives a household system impedance by performing a preset operation using the above basic operation data; and A final impedance estimation unit that estimates the system impedance in the low-frequency band by correcting the signal from the calculation result of the above-mentioned system impedance derivation unit, and estimates the final impedance using a mathematical estimation technique; The above-mentioned household system impedance derivation unit is, A system impedance estimation system that performs the above-preset operation on the above-preset system impedance assumed as in Equation 2 below using the above-preset basic operation data. Equation 2 (Here, the above Z grid is the above-mentioned household system impedance)
  2. In Article 1, The above basic operation data acquisition unit is, The above perturbation signal is a maximum length binary sequence (MLBS) signal, and a perturbation signal injection module that injects the MLBS signal by repeating it P times, which is a preset number; and A system impedance estimation system comprising: a basic calculation data measurement module for measuring the above voltage and current.
  3. In Paragraph 2, A system impedance estimation system in which the above MLBS signal is repeated with a period N, and the period N is expressed by the following Equation 1 using n, which is the number of shift registers. Equation 1
  4. In Paragraph 2, The above perturbation signal is injected into a PFC converter, which is one of the components constituting an electric vehicle charger (On-Board Charger, OBC) connected to the grid voltage during electric vehicle charging, in a grid impedance estimation system.
  5. In Paragraph 4, A grid impedance estimation system in which the above voltage and current are an input voltage v in , which is a voltage measured from a PFC converter, which is one of the components constituting an electric vehicle charger (On-Board Charger, OBC) connected to the grid voltage during electric vehicle charging, and an input current i in , which is a current input to the PFC.
  6. delete
  7. In Article 1, A system impedance estimation system in which the operation set above is the Discrete Fourier Transform (DFT).
  8. In Article 7, A grid impedance estimation system that derives the assumed grid impedance by removing the grid voltage V in (jω grid ) to remove noise information in Equation 2 above.
  9. In Article 1, The above final impedance estimation unit is, A system impedance estimation system that estimates a prior impedance, which is an impedance including the above-mentioned household system impedance and the impedance of an EMI filter, which is one of the components constituting an electric vehicle charger (On-Board Charger, OBC) connected to the system voltage during electric vehicle charging.
  10. In Article 9, For the Bode plot of the above final impedance, gain A system impedance estimation system in which the frequency f z1 corresponding to the first zero is expressed by Equation 3 below using the low-frequency band equivalent resistive component R eq and the low-frequency band equivalent inductance component L LF . Equation 3
  11. In Article 10, The above final impedance estimation unit is, A system impedance estimation system that estimates the final impedance using the R grid and L grid derived using Equation 3 above.
  12. In Paragraph 11, A system impedance estimation system in which the R grid is expressed by the following Equation 4 using the above Equation 3. Equation 4
  13. In Paragraph 12, The above gain A system impedance estimation system in which f z1 , the minimum value among frequencies having a value greater than a preset dB, is expressed by the following Equation 5. Equation 5
  14. In Paragraph 13, A system impedance estimation system in which the L grid is expressed by the following Equation 6 using the above Equations 3 and 5. Equation 6
  15. A basic operation data acquisition step of injecting a perturbation signal using a basic operation data acquisition unit and acquiring basic operation data by measuring voltage and current; A household system impedance derivation step in which a household system impedance derivation unit performs a preset operation using the above basic operation data to derive the household system impedance; and A final impedance estimation step comprising: estimating the system impedance in the low-frequency band by correcting the signal from the calculation result of the assumed system impedance derivation unit through the final impedance estimation unit, and estimating the final impedance using a mathematical estimation technique; The above-mentioned household system impedance derivation unit is, A method for estimating system impedance, which performs the above-preset operation on the above-preset system impedance assumed as in Equation 2 below using the above-previous basic operation data. Equation 2 (Here, the above Z grid is the above-mentioned household system impedance)

Description

Grid impedance estimation system and method The present invention relates to a system and method for estimating grid impedance, and in particular, to a system and method for estimating grid impedance capable of estimating grid impedance during the operation of an electric vehicle on-board charger (OBC). Electric vehicles experience charging in various environments. During actual charging of electric vehicles, grid impedance exists, and stability issues may arise depending on the grid impedance conditions. Since evaluating system stability by considering the grid conditions at the time of charging is very complex, an impedance-based method is generally used to evaluate stability after equating the system to source output impedance (Z S ) and load input impedance (Z L ). Conventional impedance-based stability evaluation methods are designed to evaluate the entire system as stable when the input power sources VS and ZL are stable and the ratio of the two impedances in a preset stability equation satisfies the Nyquist stability criterion. When designing an OBC for an electric vehicle, the system is designed to be stable, so it must be possible to estimate the unknown system impedance to evaluate the stability of the OBC. Most existing grid-connected power electronic systems consist of three-phase inverter-based systems. Accordingly, grid impedance estimation techniques have also been devised based on three-phase inverters. Conventionally, when estimating grid impedance to evaluate the stability of a grid-connected three-phase inverter, a method of injecting a perturbation signal into a DQ-converted control command signal or a PQ control method was adopted. However, most OBCs are single-phase, making it difficult to use the DQ conversion control method applied in a three-phase rotating coordinate system, and there is a problem in that it is difficult to apply existing methods because the input voltage and current are in phase with the PFC converter at the input stage, so no reactive power is generated. FIG. 1 is a block diagram of a system impedance estimation system according to an embodiment of the present invention. Figure 2 is the basic operation data acquisition unit of Figure 1. FIG. 3 is a flowchart of a system impedance estimation method according to an embodiment of the present invention. Figure 4 is a flowchart of step S11 of Figure 3. FIG. 5 is a figure showing the state in which an electric vehicle charger (OBC) is connected to the grid voltage according to one embodiment of the present invention. FIG. 6 is an example of a block diagram showing a system and method specifically connected according to one embodiment of the present invention. Figure 7 is an example graph of the Bode plot of the final impedance in the present invention. Figure 8 is a figure showing the results of a simulation performed to compare the performance of the present invention. Hereinafter, some embodiments of the present disclosure will be described in detail with reference to the exemplary drawings. In assigning reference numerals to the components of each drawing, the same components may have the same reference numeral as much as possible, even if they are shown in different drawings. Furthermore, in describing the embodiments, if it is determined that a detailed description of related known components or functions may obscure the essence of the technical concept, such detailed description may be omitted. Where terms such as "comprising," "having," or "consisting of" are used in this specification, other parts may be added unless "only" is used. Where a component is expressed in the singular, it may include a plural unless otherwise specified. Additionally, terms such as first, second, A, B, (a), (b), etc., may be used to describe the components of the present disclosure. These terms are used merely to distinguish the components from other components, and the nature, order, sequence, or number of the components are not limited by such terms. In describing the positional relationship of components, where it is stated that two or more components are "connected," "combined," or "joined," it should be understood that while the two or more components may be directly "connected," "combined," or "joined," they may also be "connected," "combined," or "joined" with other components "intervened." Here, the other components may be included in one or more of the two or more components that are "connected," "combined," or "joined" with one another. In describing the temporal flow relationship regarding components, methods of operation, or methods of production, for example, when the temporal or sequential relationship is described using "after," "following," "next," or "before," it may include cases where the relationship is not continuous unless "immediately" or "directly" is used. Meanwhile, where numerical values or corresponding information regarding a component (e.g., levels, etc.) are mentioned, even without separate explicit notat