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CN-121688950-B - Photovoltaic inverter harmonic suppression system and method

CN121688950BCN 121688950 BCN121688950 BCN 121688950BCN-121688950-B

Abstract

The invention provides a photovoltaic inverter harmonic suppression system and a method, which are used for acquiring a target current error in a current period, repeatedly controlling a branch circuit to generate branch circuit period delay of the current period according to the target current error and a corresponding gain coefficient and the branch circuit period delay of a previous period, summarizing the branch circuit period delay of the current period into a current period total delay, and inputting the current period total delay into a PI controller so as to enable the current period total delay to generate a target voltage instruction. The tracking capability of the PI controller to the fundamental wave current is reserved, the current inner loop design of a general inverter is not affected, and the inhibiting effect on periodic harmonic waves is enhanced through the repeated controller. Meanwhile, by optimizing the design of the repetitive controller, the repetitive controller becomes a composite repetitive controller comprising at least two repetitive control branches, the effective bandwidth of the repetitive controller is widened, and the repetitive controller can adapt to the fluctuation of the power grid frequency, so that the excellent grid-connected current harmonic suppression performance is maintained in a wider frequency variation range.

Inventors

  • WANG SILIANG

Assignees

  • 成都森未科技有限公司

Dates

Publication Date
20260512
Application Date
20260211

Claims (8)

  1. 1. The photovoltaic inverter harmonic suppression system is characterized by comprising a first operation unit, a composite repetitive controller and a PI controller, wherein the composite repetitive controller comprises at least two repetitive control branches and a second operation unit; the first operation unit is used for obtaining a target current error of the current period, wherein the target current error is a d-phase current error or a q-phase current error of the inverter; the repeated control branch is used for generating the branch period delay of the current period according to the target current error, the corresponding gain coefficient and the branch period delay of the previous period; the second operation unit is used for summarizing the branch period delay of each repeated control branch in the current period into the total delay of the current period; the PI controller is used for generating a target voltage instruction according to the total delay of the current period, wherein when the target current error is a d-phase current error, the target voltage instruction is a d-phase voltage instruction, and when the target current error is a q-phase current error, the target voltage instruction is a q-phase voltage instruction; The gain coefficient corresponding to each repetitive control branch is matched with the design frequency and the grid stabilizing frequency corresponding to the repetitive control branch; The calculation formula of the gain coefficient corresponding to the repetitive control branch is as follows: Wherein, the Indicating the gain factor corresponding to the ith repetitive control arm, Representing the triangular membership degree corresponding to the ith repeated control branch, Representing the membership degree of the triangle corresponding to the j-th repeated control branch, Indicating the grid stability frequency, The design frequency corresponding to the ith repeated control branch is represented, N is the total number of the repeated control branches in the composite repeated controller, and i is more than or equal to 1 and less than or equal to N.
  2. 2. The photovoltaic inverter harmonic suppression system of claim 1, wherein the repetitive control branch comprises a gain unit, a third arithmetic unit, and a filtering unit; the gain unit is used for multiplying the target current error by a corresponding gain coefficient and providing the product to the third operation unit; The filtering unit is used for processing the branch period delay of the previous period by utilizing a filtering function and providing the obtained delay error for the third operation unit; and the third operation unit is used for adding the obtained product and the delay error to obtain the branch cycle delay of the current cycle.
  3. 3. The photovoltaic inverter harmonic suppression system of claim 1, further comprising a comb filter; The comb filter is used for processing the total delay of the current period output by the second operation unit and transmitting a comb filtering result to the PI controller; and the PI controller is used for generating a target voltage instruction according to the comb filtering result.
  4. 4. The photovoltaic inverter harmonic suppression system of claim 3 wherein the comb filter is represented as: Wherein, the Representing the comb filtering result corresponding to the comb filter, Indicating the total delay of the current period.
  5. 5. The photovoltaic inverter harmonic suppression system of claim 1, wherein the grid stabilization frequency acquisition process comprises the photovoltaic inverter extracting the frequency of the grid positive sequence voltage through a phase-locked loop and appropriately filtering to obtain the grid stabilization frequency.
  6. 6. The photovoltaic inverter harmonic suppression system of claim 1, D-phase current error = d-phase current reference value of inverter-d-phase current actual value of inverter; q-phase current error = q-phase current reference value of inverter-q-phase current actual value of inverter.
  7. 7. A method of harmonic suppression of a photovoltaic inverter, applied to the photovoltaic inverter harmonic suppression system of any of claims 1-6, the method comprising: obtaining a target current error of a current period, wherein the target current error is a d-phase current error or a q-phase current error of an inverter; Inputting the target current error into each repetitive control branch in a composite repetitive controller, and generating the branch period delay of the current period by combining the corresponding gain coefficient and the branch period delay of the previous period; summarizing the branch period delay of each repeated control branch in the current period into the total delay of the current period; inputting the total delay of the current period into a PI controller so as to enable the PI controller to generate a target voltage instruction; Wherein the target voltage command is a d-phase voltage command when the target current error is a d-phase current error, and is a q-phase voltage command when the target current error is a q-phase current error.
  8. 8. The method of harmonic rejection of a photovoltaic inverter of claim 7, wherein after summing the leg periods delays of each repetitive control leg at the current period to a current period total delay, the method further comprises: Processing the total delay of the current period by using a comb filter, and transmitting a comb filtering result to the PI controller; and the PI controller generates a target voltage instruction according to the comb filtering result.

Description

Photovoltaic inverter harmonic suppression system and method Technical Field The invention relates to the field of photovoltaics, in particular to a harmonic suppression system and method for a photovoltaic inverter. Background Photovoltaic installed capacity has grown rapidly over the world for many years and photovoltaic power plants are converting from supplemental energy sources to dominant energy sources. This means that its effect on the grid is not insignificant anymore, but rather of importance. The photovoltaic inverter is a key interface for connecting the photovoltaic array with a power grid, and the performance of the photovoltaic inverter directly determines the quality of electric energy and the stability of a system. The conventional control strategy, such as Proportional-Integral (PI) control, has good capability of adjusting the direct current signal under the synchronous rotation coordinate system, but has limited capability of restraining periodic alternating current harmonics, especially when the frequency fluctuates, the restraining effect is reduced. The grid standard has strict limits on the total harmonic distortion rate and the content of each subharmonic of the grid-connected current. Unqualified electric energy quality can cause the problems of overheating of a transformer and a circuit, misoperation of relay protection, damage of precision equipment and the like. Disclosure of Invention The present invention is directed to a photovoltaic inverter harmonic suppression system and method to improve the above-mentioned problems. In order to achieve the above object, the technical scheme adopted by the embodiment of the invention is as follows: in a first aspect, an embodiment of the present invention provides a photovoltaic inverter harmonic suppression system, where the photovoltaic inverter harmonic suppression system includes a first operation unit, a composite repetitive controller, and a PI controller, where the composite repetitive controller includes at least two repetitive control branches and a second operation unit; the first operation unit is used for obtaining a target current error of the current period, wherein the target current error is a d-phase current error or a q-phase current error of the inverter; the repeated control branch is used for generating the branch period delay of the current period according to the target current error, the corresponding gain coefficient and the branch period delay of the previous period; the second operation unit is used for summarizing the branch period delay of each repeated control branch in the current period into the total delay of the current period; The PI controller is used for generating a target voltage instruction according to the total delay of the current period, wherein the target voltage instruction is a d-phase voltage instruction when the target current error is a d-phase current error, and the target voltage instruction is a q-phase voltage instruction when the target current error is a q-phase current error. In a second aspect, an embodiment of the present invention provides a method for suppressing a harmonic of a photovoltaic inverter, which is applied to the above-mentioned harmonic suppression system of a photovoltaic inverter, where the method includes: obtaining a target current error of a current period, wherein the target current error is a d-phase current error or a q-phase current error of an inverter; Inputting the target current error into each repetitive control branch in a composite repetitive controller, and generating the branch period delay of the current period by combining the corresponding gain coefficient and the branch period delay of the previous period; summarizing the branch period delay of each repeated control branch in the current period into the total delay of the current period; inputting the total delay of the current period into a PI controller so as to enable the PI controller to generate a target voltage instruction; Wherein the target voltage command is a d-phase voltage command when the target current error is a d-phase current error, and is a q-phase voltage command when the target current error is a q-phase current error. Compared with the prior art, the photovoltaic inverter harmonic suppression system and method provided by the embodiment of the invention acquire a target current error of a current period, wherein the target current error is a d-phase current error or a q-phase current error of an inverter, the target current error is input into each repetitive control branch in a composite repetitive controller, the repetitive control branches are combined with corresponding gain coefficients and the branch period delays of the previous period to generate the branch period delays of the current period, the branch period delays of each repetitive control branch in the current period are summarized to be the total delay of the current period, and the total delay of the current