Power supply system high-voltage side negative sequence current detection method for corner joint SVG (Static Var Generator)

Abstract

The invention relates to a power supply system high-voltage side negative sequence current detection method for an angle joint SVG, and the method comprises the steps: collecting a high-voltage bus HV voltage signal PTH and a current signal CTH, and collecting a network side bus MV voltage signal PTM; the synchronous angle of the grid-side fundamental positive sequence voltage is locked and is used as a reference signal for SVG detection and control; the high-voltage side power grid current amplitude and phase shift angle conversion is used for converting the detected high-voltage side current negative sequence component into an SVG angle; and calculating a negative sequence current instruction signal, wherein the instruction signal is the closed-loop control target value of the current in the SVG angle. The method has the advantages that a negative-sequence current instruction can be quickly and accurately obtained, control is carried out by directly taking the current in the SVG angle as feedback, closed-loop control is more visual, and the response speed is higher; a load negative-sequence current instruction is directly superposed with a fundamental wave reactive current instruction and a harmonic current instruction to generate a total control instruction, so that comprehensive control of electric energy quality is realized; the negative sequence current detection method is especially suitable for a power supply system with a complex structure.

Description

Technical Field

[0001] The invention relates to the field of flexible alternating current transmission, and in particular to a method for detecting negative sequence current on a high-voltage side of a power supply system for a delta-connected SVG. Background Art

[0002] With the development of industry, the proportion of reactive power loads, harmonic sources, and unbalanced loads in the power system has increased year by year, and the power quality problem has become particularly prominent; in the user-side power supply system, the power quality assessment point is usually set on the high-voltage side of the power supply system, especially for some large power load users, the assessment point is generally on the 110kV and 220kV sides. Usually, passive compensation equipment can be used to treat power factor problems on-site, but for systems with complex structures, diverse and dispersed load types, centralized compensation with the power quality on the high-voltage side of the power supply system as the control target is more advantageous.

[0003] At present, power electronics technology is developing rapidly. H-bridge power unit modules composed of fully controlled devices (IGBT, IGCT, etc.) have been applied on a large scale. The chain-type delta-connected SVG with H-bridge cascade structure can be independently controlled in phases, and has technical advantages such as fast response speed and easy implementation of complex control algorithms. It is an ideal device for unbalanced load management.

[0004] However, due to problems such as insulation technology and withstand voltage of fully controlled devices, chain-type delta-connected SVGs are mainly hung directly on medium-voltage or low-voltage busbars for power quality management. If the negative sequence current on the high-voltage side is directly used as the control target, a negative sequence current detection method on the high-voltage side of the power supply system suitable for delta-connected SVG control is required. Summary of the invention

[0005] The purpose of the present invention is to provide a method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG, which can quickly and accurately extract the negative sequence current component on the high-voltage side of the power supply system suitable for the delta-connected SVG, and effectively solve the problem of compensating unbalanced current on the high-voltage side of the power supply system;

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG, comprising a main transformer T N Connect the corner to SVG, and change the main part to T N The input end is connected to the high voltage bus HV, the main transformer T N The output end of is connected to the grid-side busbar MV, and the grid-side busbar MV is connected to the delta connection SVG, and the method includes:

[0008] S1, collect high voltage bus HV voltage signal PT H , current signal CT H, collect the grid-side bus MV voltage signal PT M ;

[0009] S2, grid-side fundamental positive-sequence voltage synchronous angle locking, serving as a reference signal for SVG detection and control;

[0010] S3, high-voltage side grid current amplitude and phase shift angle transformation, used to convert the detected high-voltage side current negative sequence component into the SVG angle;

[0011] S4. Calculation of negative sequence current command signal, which is the closed-loop control target value of the current in the SVG angle.

[0012] In S1, the voltage signal on the high-voltage side of the power supply system is the high-voltage bus HV voltage signal PT H The current signal on the high-voltage side of the power supply system is the total incoming current signal CT on the high-voltage side or multiple main transformers T N High voltage side current signal CT N The sum of .

[0013] In S2, the grid-side fundamental positive sequence voltage synchronization angle is locked, including the use of soft phase locking, that is, taking the grid-side voltage q-axis component as zero as the control target, and performing closed-loop control to achieve synchronization angle locking; or using a hardware analog circuit to capture the zero-crossing point of the A-phase voltage, which is the locked synchronization moment, as follows:

[0014] The grid voltage is collected by the PT of the medium and low voltage bus MV (LV), and the phase-locked loop PLL obtains the grid voltage fundamental positive sequence synchronization angle θ, which is a radian rotating at an angular frequency ω (ω=2πf, f represents the power frequency).

[0015] In S3, the current amplitude and phase shift angle of the high-voltage side grid are transformed as follows:

[0016] Collect high voltage bus HV voltage PT H Signal, based on θ, synchronously perform Park positive sequence dq transformation on the three-phase voltage and perform mean filtering to obtain the positive sequence dq axis component U of the high-voltage side grid voltage d_top and U q_top , let Φ be the phase difference between the synchronization angle θ and the synchronization angle of the high-voltage side voltage, let the transformation ratio of the main transformer connected to the SVG be A, and consider that the internal synchronization angle of the SVG angle leads the external synchronization angle by π / 6, calculate the sine and cosine amplitudes and the phase shift angle coefficients AcosФ and AsinФ.

[0017] In step S4, the negative sequence current command signal is calculated, including

[0018] 1) Extraction of negative sequence component of current in the corner of the corner-connected SVG

[0019] The Hall sensor installed in the SVG corner collects the current signal in the SVG corner. Because the SVG current feedback uses the current in the SVG corner, and the current amplitudes in the corner and outside the corner differ times, so the feedback current needs to be multiplied by the coefficient Based on θ+π / 6, Park negative sequence dq transformation is performed and mean filtering is performed to obtain the negative sequence dq axis component I of the SVG angle current. ndsvg and I nqsvg ;

[0020] 2) Extraction of negative sequence current component on the grid side

[0021] The HV current CT signal on the high-voltage side is collected, and the negative-sequence Park transform is performed based on θ+π / 6 and the mean filter is performed to obtain the negative-sequence dq axis component, which is converted into the negative-sequence dq component I of the SVG angle current according to the amplitude and phase shift angle. ndtop and I nqtop ;

[0022] 3) Calculate the difference between the grid-side negative sequence current dq component and the SVG negative sequence current dq component to obtain the load current negative sequence dq component, and make further adjustments, that is, invert the angle of the synchronization angle to generate a new load current negative sequence dq component I' ndload , I' nqload ;

[0023] 4) The dq-axis component of the load current obtained by 1)-3) is then inverted to obtain the negative sequence current instruction I of the delta-connected SVG. ndref and I nqref , the command signal finally detected is a DC quantity.

[0024] SVG is a medium and low voltage power equipment. The power units between phases are cascaded and connected in a triangle. The number of power units is ≧1.

[0025] There is no need to consider the connection group of the main transformer to which the SVG is connected, and the phase shift angle information is obtained by calculating the sine and cosine amplitudes and the phase shift angle coefficient.

[0026] The current in the SVG corner is detected by the Hall current sensor installed inside the SVG.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. Accurate compensation can be achieved without considering the connection group, impedance ratio and other transformer nameplate parameters of the on-site main transformer;

[0029] 2. This detection method can quickly and accurately obtain the negative sequence current command, which can be directly controlled by using the current in the SVG angle as feedback, making the closed-loop control more intuitive and more responsive;

[0030] 3. The load negative sequence current command obtained by the present invention can be directly superimposed with the fundamental reactive current command and the harmonic current command to generate a total control command, thereby realizing comprehensive control of power quality;

[0031] 4. The negative sequence current detection method mentioned in the present invention is particularly suitable for power supply systems with complex structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Negative sequence current detection flow chart of the high voltage side of the power supply system;

[0033] Figure 2 This is a schematic diagram of signal sampling in a typical power supply system of a power plant;

[0034] Figure 3 This is the topological structure diagram of the chain-type angle-connected SVG power unit valve group; DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0036] See Figure 1-3 A method for detecting negative sequence current on the high voltage side of a power supply system for a delta-connected SVG, comprising a main transformer T N Connect the corner to SVG, and change the main part to T N The input end is connected to the high voltage bus HV, the main transformer T N The output end is connected to the grid-side busbar MV, and the grid-side busbar MV is connected to the delta-connected SVG; the delta-connected SVG power unit valve group adopts a cascade structure, the number of power units is ≧1, and the cascade power unit is a triangle connection, and the method includes:

[0037] S1, the voltage signal on the high-voltage side of the power supply system is the high-voltage bus HV voltage signal PT H The current signal on the high-voltage side of the power supply system is the total incoming current signal CT on the high-voltage side or multiple main transformers T N High voltage side current signal CT N The sum of .

[0038] S2. The grid-side fundamental positive sequence voltage synchronous angle is locked, including the use of soft phase locking, that is, taking the grid-side voltage q-axis component as zero as the control target, and performing closed-loop control to achieve synchronous angle locking; hardware analog circuits can also be used to capture the zero-crossing point of the A-phase voltage, and the zero-crossing point is the locked synchronization moment, as follows:

[0039] The grid-side voltage u is collected through the PT of the medium and low voltage bus MV (LV) a 、u b 、u cThe phase-locked loop PLL can obtain the grid-side voltage fundamental positive sequence synchronization angle θ, which is the radian rotated by the angular frequency ω (ω=2πf, f represents the power frequency).

[0040] S3, the phase shift angle of the high-voltage side grid current is changed, as follows:

[0041] Collect high voltage bus HV voltage PT H The signal is u a_top 、u b_top 、u c_top , taking θ as the reference, the three-phase voltage is synchronously transformed into a Park positive sequence dq and mean filtered to obtain the positive sequence dq axis component U of the high-voltage side grid voltage d_top and U q_top , where Φ is the phase difference between the synchronization angle θ and the synchronization angle of the high-voltage side voltage; assuming that the transformation ratio of the main transformer connected to the SVG is A, and considering that the internal synchronization angle of the SVG angle leads the external synchronization angle by π / 6, the sine and cosine amplitudes and the phase shift angle coefficients AcosФ and AsinФ are calculated as follows:

[0042] AcosΦ=(0.866*U dtop -0.5*U qtop ) / U mag ①

[0043] AsinФ=(0.866*U qtop +0.5*U dtop ) / U mag ②

[0044] In formulas ① and ②, U d_top Indicates the positive sequence d-axis component of the high-voltage side voltage, U qtop It represents the positive sequence q-axis component of the high-voltage side voltage, U mag Indicates the voltage amplitude on the high voltage side.

[0045] S4, negative sequence current command signal calculation, including:

[0046] 1) Extraction of negative sequence component of current in the corner of the corner-connected SVG

[0047] The Hall sensor installed in the SVG corner collects the current signal i in the SVG corner svgab 、i svgbc 、i svgca , because the SVG current feedback uses the SVG inner corner current, and the inner corner current and the outer corner current amplitude difference times, so the feedback current needs to be multiplied by the coefficient Based on θ+π / 6, Park negative sequence dq transformation is performed and mean filtering is performed to obtain the negative sequence dq axis component I of the SVG angle current. ndsvg and I nqsvg ;

[0048] 2) Extraction of negative sequence current component on the grid side

[0049] Collect the HV current CT signal i on the high voltage side a_top 、i b_top 、i c_top , using θ+π / 6 as the reference, perform negative sequence Park transform and mean filter to obtain the negative sequence dq axis component I ndo and I nqo , according to the amplitude and phase shift angle, it is converted into the negative sequence dq component I of the SVG angle current ndtop and I nqtop , calculated as follows:

[0050] I ndtop =I ndo *AcosФ+I nqo *AsinФ③

[0051] I nqtop =I nqo *AcosФ-I ndo *AsinФ④;

[0052] 3) The negative sequence dq component of the load current is obtained by the difference between the negative sequence component of the grid current and the negative sequence component of the current in the SVG angle. In order to take into account the control of the fundamental reactive power, further adjustment is made, that is, the angle of the synchronization angle is inverted to generate a new negative sequence component of the load current I' ndload , I' nqload , calculated as follows;

[0053] I' ndload =I ndtop -I ndsvg ⑤

[0054] I' nqload =-(I nqtop -I nqsvg )⑥;

[0055] 4) The dq-axis component of the load current finally obtained in the above steps is then numerically inverted to obtain the negative sequence current instruction I of the delta-connected SVG. ndref and I nqref , the command signal finally detected is a DC quantity, which can achieve zero-difference regulation;

[0056] The Park positive sequence dq conversion formula described in S3 and S4 is as follows, which is applicable to voltage and current conversion; where θ is the synchronization angle, a, b, c are input quantities, d, q are output quantities, and the synchronization angle can be reversed during negative sequence dq conversion. The formula is as follows:

[0057]

[0058] The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[0059] [Example 1]

[0060] The grid-side voltage u is collected through the PT of the medium and low voltage bus MV (LV) a 、u b 、u c (like Figure 1 , 2 ), the grid-side voltage fundamental positive sequence synchronization angle θ can be obtained by the phase-locked loop PLL. The synchronization angle is the radian rotating at the angular frequency ω (ω=2πf, f represents the power frequency).

[0061] Collect high voltage bus HV voltage PT H Signal u a_top 、u b_top 、u c_top (like Figure 1 , 2 ), taking θ as the reference, the three-phase voltage is synchronously transformed into a Park positive sequence dq and mean filtered to obtain the positive sequence dq axis component U of the high-voltage side grid voltage d_top and U q_top , where Φ is the phase difference between the synchronization angle θ and the synchronization angle of the high-voltage side voltage; assuming that the transformation ratio of the main transformer connected to the SVG is A, and considering that the internal synchronization angle of the SVG angle leads the external synchronization angle by π / 6, the sine and cosine amplitudes and the phase shift angle coefficients AcosФ and AsinФ are calculated as follows:

[0062] AcosΦ=(0.866*U dtop -0.5*U qtop ) / U mag ①

[0063] AsinФ=(0.866*U qtop +0.5*U dtop ) / U mag ②

[0064] In formulas ① and ②, U d_top Indicates the positive sequence d-axis component of the high-voltage side voltage, U qtop It represents the positive sequence q-axis component of the high-voltage side voltage, U mag Indicates the voltage amplitude on the high voltage side.

[0065] The Hall sensor installed in the SVG corner collects the current signal i in the SVG corner svgab 、i svgbc 、i svgca (like Figure 1 ,3 ), because the SVG current feedback uses the SVG inner corner current, and the inner corner current and the outer corner current amplitude are different times, so the feedback current needs to be multiplied by the coefficient Based on θ+π / 6, Park negative sequence dq transformation is performed and mean filtering is performed to obtain the negative sequence dq axis component I of the SVG angle current. ndsvg and I nqsvg .

[0066] Collect the HV current CT signal i on the high voltage side a_top 、i b_top 、i c_top (like Figure 1 , 2 ), Park negative sequence dq transformation is performed based on θ+π / 6 and mean filtering is performed to obtain the negative sequence dq axis component I of the high voltage side current ndo and I nqo , according to the amplitude and phase shift angle, it is converted into the negative sequence dq component I of the SVG angle current ndtop and I nqtop , calculated as follows:

[0067] I ndtop =I ndo *AcosФ+I nqo *AsinФ ③

[0068] I nqtop =I nqo *AcosФ-I ndo *AsinФ ④

[0069] Negative sequence dq component of load current I ndload and I nqload The calculation is as follows:

[0070] I ndload =I ndtop -I ndsvg ⑤

[0071] I nqload =I nqtop -I nqsvg ⑥

[0072] In order to take into account the control of fundamental reactive power, the negative sequence dq component of the load current is further adjusted, that is, the angle of the synchronization angle is inverted to generate a new negative sequence dq component of the load current, which is calculated as follows:

[0073] I' ndload =I ndload ⑦

[0074] I' nqload =-I nqload ⑧

[0075] The dq-axis component of the load current finally obtained by the above steps is then numerically inverted to obtain the negative sequence current command I of the delta-connected SVG. ndref and I nqref The command signal finally detected is a DC quantity, which can achieve zero-difference regulation.

[0076] The present invention can realize accurate compensation without considering the connection group, impedance ratio and other transformer nameplate parameters of the on-site main transformer; the detection method can quickly and accurately obtain the negative-sequence current instruction, which can be directly controlled by using the current in the SVG angle as feedback, and the closed-loop control is more intuitive and has a faster response speed; the load negative-sequence current instruction obtained by the present invention can be directly superimposed with the fundamental reactive current instruction and the harmonic current instruction to generate a total control instruction, thereby realizing comprehensive control of the power quality; the negative-sequence current detection method mentioned in the present invention is particularly suitable for power supply systems with complex structures.

Claims

1. A method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG, comprising a main transformer T N Connect the corner to SVG, and change the main part to T N The input end is connected to the high voltage bus HV, the main transformer T N The output end is connected to the grid-side busbar MV, and the grid-side busbar MV is connected to the delta connection SVG, characterized in that: The method includes: S1, collect high voltage bus HV voltage signal PT H , current signal CT H , collect the grid-side bus MV voltage signal PT M ; S2, grid-side fundamental positive-sequence voltage synchronous angle locking, serving as a reference signal for SVG detection and control; S3, high-voltage side grid current amplitude and phase shift angle transformation, used to convert the detected high-voltage side current negative sequence component into the SVG angle; S4. Calculation of negative sequence current command signal, which is the closed-loop control target value of the current in the SVG angle.

2. The method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG according to claim 1, characterized in that: In S1, the voltage signal on the high-voltage side of the power supply system is the high-voltage bus HV voltage signal PT H The current signal on the high-voltage side of the power supply system is the total incoming current signal CT on the high-voltage side or multiple main transformers T N High voltage side current signal CT N The sum of .

3. The method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG according to claim 1, characterized in that: In S2, the grid-side fundamental positive sequence voltage synchronization angle locking includes adopting a soft phase locking method, that is, taking the grid-side voltage q-axis component as zero as the control target, and performing closed-loop control to achieve synchronization angle locking; or adopting a hardware analog circuit to capture the zero-crossing point of the A-phase voltage, and the zero-crossing point is the locked synchronization moment, and the content is as follows: The grid voltage is collected by the PT of the medium and low voltage bus MV (LV), and the phase-locked loop PLL obtains the grid voltage fundamental positive sequence synchronization angle θ, which is a radian rotating at an angular frequency ω (ω=2πf, f represents the power frequency).

4. The method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG according to claim 1, characterized in that: In S3, the current amplitude and phase shift angle of the high-voltage side grid are transformed as follows: Collect high voltage bus HV voltage PT H Signal, based on θ, synchronously perform Park positive sequence dq transformation on the three-phase voltage and perform mean filtering to obtain the positive sequence dq axis component U of the high-voltage side grid voltage d_top and U q_top , let Φ be the phase difference between the synchronization angle θ and the synchronization angle of the high-voltage side voltage, let the transformation ratio of the main transformer connected to the SVG be A, and consider that the internal synchronization angle of the SVG angle leads the external synchronization angle by π / 6, calculate the sine and cosine amplitudes and the phase shift angle coefficients AcosФ and AsinФ.

5. The method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG according to claim 1, characterized in that: In step S4, the negative sequence current command signal calculation includes: 1) Extraction of negative sequence component of current in the corner of the corner-connected SVG The Hall sensor installed in the SVG corner collects the current signal in the SVG corner. Because the SVG current feedback uses the current in the SVG corner, and the current amplitudes in the corner and outside the corner differ times, so the feedback current needs to be multiplied by the coefficient Based on θ+π / 6, Park negative sequence dq transformation is performed and mean filtering is performed to obtain the negative sequence dq axis component I of the SVG angle current. ndsvg and I nqsvg ; 2) Extraction of negative sequence current component on the grid side The HV current CT signal on the high-voltage side is collected, and the negative-sequence Park transform is performed based on θ+π / 6 and the mean filter is performed to obtain the negative-sequence dq axis component, which is converted into the negative-sequence dq component I of the SVG angle current according to the amplitude and phase shift angle. ndtop and I nqtop ; 3) Calculate the difference between the grid-side negative sequence current dq component and the SVG negative sequence current dq component to obtain the load current negative sequence dq component, and make further adjustments, that is, invert the angle of the synchronization angle to generate a new load current negative sequence dq component I' ndload , I' nqload ; 4) The dq-axis component of the load current obtained by 1)-3) is then inverted to obtain the negative sequence current instruction I of the delta-connected SVG. ndref and I nqref , the command signal finally detected is a DC quantity.

6. The method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG according to claim 1, characterized in that: SVG is a medium and low voltage power equipment. The power units between phases are cascaded and connected in a triangle. The number of power units is ≧1.

7. The method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG according to claim 4, characterized in that: There is no need to consider the connection group of the main transformer to which the SVG is connected, and the phase shift angle information is obtained by calculating the sine and cosine amplitudes and the phase shift angle coefficient.

8. The method for detecting negative sequence current on the high-voltage side of a power supply system for a delta-connected SVG according to claim 5, characterized in that: The SVG corner current is detected by a Hall current sensor installed inside the SVG.

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