A method and system for calculating SLCC commutation overlap angle considering SVF bearing capacity

Abstract

The present invention discloses a method and system for calculating the SLCC commutation overlap angle taking into account the SVF carrying capacity. The method includes establishing an SLCC equivalent commutation circuit based on the coupling effect between the SVF output current and voltage and the LCC at the common connection point; analyzing the SLCC equivalent commutation circuit using Kirchhoff's law to determine the relationship between the SLCC commutation current, the SVF equivalent output voltage, and the SVF equivalent output current; combining the electrical characteristics of the SLCC during the commutation process to obtain the relationship between the SLCC commutation current change rate and various SLCC electrical quantities; obtaining the SLCC DC current based on the change in the SVF equivalent output voltage during the SVF carrying capacity, and obtaining the initial commutation overlap angle; and adjusting the initial commutation overlap angle to obtain the final commutation overlap angle. The present invention performs well in DC current fitting and commutation overlap angle calculation, and can be used for quantitative analysis and carrying capacity assessment of SLCC.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage direct current (HVDC) transmission, and in particular to a method and system for calculating a SLCC commutation overlap angle taking into account SVF carrying capacity. Background Art

[0002] SLCC (Self-adaption Statcom and Line commutation Converter) DC transmission technology is a new attempt to combine the characteristics of LCC (Line commutation Converter) and VSC (Voltage Source Converter) technologies. It uses a parallel structure of LCC and valve-side direct-mounted SVF (Static Var & Filter) to form an SLCC with the characteristics of both current source and voltage source converters. It has the advantages of low weak system overvoltage, good system networking performance, low probability of commutation failure, low risk of equipment failure, high economy and environmental friendliness. It can effectively support the overall optimization of converter stations in DC projects for future large-scale renewable energy integration and is of great significance to improving the reliability of converter station equipment and the operation level and quality of UHVDC projects.

[0003] However, existing research has focused solely on optimizing SLCC performance through the lens of control strategies. The established SLCC mathematical model still relies on numerical analysis, where the receiving-end voltage source and the SVF are equated into a single voltage source and then substituted into the LCC commutation process. Due to the lack of understanding of the influence of the SVF output current on the commutation process, the expression for the commutation overlap angle in the SLCC mathematical model differs significantly from the actual commutation overlap angle. This makes it impossible to further optimize the control and protection strategies and evaluate the SVF load capacity of the SLCC from a fundamental perspective. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for calculating the SLCC commutation overlap angle taking into account the SVF carrying capacity, taking into account the influence of SVF equivalent output voltage fluctuations in the SVF carrying capacity, improving the calculation accuracy of the commutation overlap angle, and can be used for quantitative analysis and carrying capacity evaluation of SLCC.

[0005] The present invention adopts the following technical solution: a method for calculating the SLCC commutation overlap angle considering the SVF bearing capacity, comprising the following steps:

[0006] S1. Based on the coupling effect between the SVF output current and voltage and the LCC at the common connection point, an SLCC equivalent commutation circuit is established.

[0007] S2. Analyze the SLCC equivalent commutation circuit using Kirchhoff's law to obtain the corresponding KCL (Kirchhoff's Current Law) equation and determine the relationship between the SLCC commutation current, SVF equivalent output voltage, and SVF equivalent output current.

[0008] S3. Based on the relationship between the SLCC commutation current, SVF equivalent output voltage, and SVF equivalent output current, combined with the electrical characteristics of the SLCC during the commutation process, the relationship between the SLCC commutation current change rate and various SLCC electrical quantities is obtained. Based on the change in the SVF equivalent output voltage in the SVF carrying capacity, the SLCC DC current is obtained, and the initial commutation overlap angle is obtained.

[0009] S4. Adjust the initial commutation overlap angle to obtain a final commutation overlap angle.

[0010] Furthermore, in step S1, the SVF is equivalent to a voltage source and substituted into the commutation process of the LCC to obtain an SLCC equivalent commutation circuit.

[0011] The SLCC equivalent commutation circuit includes the A-phase thyristor , B-phase thyristor , C-phase thyristor , SVF equivalent output A phase voltage source , SVF equivalent output B phase voltage source , SVF equivalent output C phase voltage source , equivalent DC current source , SVF valve side A phase equivalent inductance , SVF valve side B phase equivalent inductance , SVF valve side C phase equivalent inductance , the sum of the A-phase line inductance on the receiving side and the transformer leakage inductance , the sum of the B-phase line inductance on the receiving side and the transformer leakage inductance , the sum of the C-phase line inductance on the receiving side and the transformer leakage inductance , receiving end A phase voltage source , receiving end B phase voltage source , receiving end C phase voltage source .

[0012] Equivalent DC current source The positive pole of the C-phase thyristor is connected cathode, equivalent DC current source The negative poles of the A-phase thyristors are connected Anode, B-phase thyristor Anode of C-phase thyristor The anodes are connected to the sum of the C-phase line inductance on the receiving side and the transformer leakage inductance. One end of the SVF valve side C phase equivalent inductance One end of the A-phase thyristor The cathode of the receiving terminal is connected to the sum of the A-phase line inductance and the transformer leakage inductance. One end of the SVF valve side A phase equivalent inductance One end of the B-phase thyristor The cathode of the receiving terminal is connected to the sum of the B-phase line inductance and the transformer leakage inductance. One end of the SVF valve side B phase equivalent inductance The sum of the A-phase line inductance and the transformer leakage inductance on the receiving side The other end is connected to the receiving end A phase voltage source The positive pole, the sum of the B-phase line inductance on the receiving side and the transformer leakage inductance The other end is connected to the receiving end B phase voltage source The positive pole, the sum of the C-phase line inductance on the receiving side and the transformer leakage inductance The other end is connected to the receiving end C phase voltage source The positive pole of the receiving end is the A phase voltage source The negative pole and the receiving end B phase voltage source The negative pole and the receiving end C phase voltage source The negative poles are connected to the neutral point O, and the equivalent inductance of phase A on the SVF valve side The other end is connected to the SVF equivalent output A phase voltage source The positive pole, SVF valve side B phase equivalent inductance The other end is connected to the SVF equivalent output B phase voltage source The positive pole, SVF valve side C phase equivalent inductance The other end is connected to the SVF equivalent output C phase voltage source The positive pole of SVF is equivalent to outputting the A-phase voltage source. The negative pole of SVF is equivalent to the output of B-phase voltage source The negative pole of SVF is equivalent to outputting the C-phase voltage source The negative poles are connected to the neutral point .

[0013] Furthermore, in step S2, based on the SVF equivalent voltage source electromotive force, reactance voltage drop, and receiving end phase voltage in the SLCC equivalent commutation circuit, the KCL equations of the LCC phase A branch and the SVF phase A branch and the KCL equations of the LCC phase B branch and the SVF phase B branch are obtained, and the relationship between the SLCC commutation current, the SVF equivalent output voltage, and the SVF equivalent output current is obtained. The specific expression is:

[0014] (1);

[0015] (2);

[0016] in, It represents the current flowing through the A-phase thyristor in the SLCC equivalent commutation circuit. It represents the current flowing through the B-phase thyristor in the SLCC equivalent commutation circuit. Indicates the SVF equivalent A-phase output voltage, Indicates the SVF equivalent output A phase current, Indicates the system time, Indicates the receiving end A phase voltage, Indicates the SVF equivalent B-phase output voltage, Indicates the SVF equivalent output B phase current, Indicates the receiving end B phase voltage.

[0017] Furthermore, in step S3, obtaining the initial commutation overlap angle includes the following:

[0018] According to the KCL equation obtained in step S2, the change rate of the commutation current of phase A and phase B of the SLCC is obtained. The specific expression is:

[0019] (3);

[0020] (4).

[0021] Based on the AC voltage and current waveforms during the SLCC commutation process and Kirchhoff's law, the potentials of the points where the A-phase and B-phase branches of the SVF are connected to the LCC are equal during the commutation process. The specific expression is:

[0022] (5);

[0023] Based on the three-phase symmetry of SLCC, let , , 、 Both represent intermediate variables.

[0024] The difference between the SLCC phase A commutation current change rate and the phase B commutation current change rate is calculated. According to formula (5), the relationship between the SLCC commutation current change rate and the electrical quantity in the SLCC equivalent commutation circuit is obtained. The specific expression is:

[0025] (6).

[0026] According to the AC voltage and current waveforms during the SLCC commutation process, the SLCC DC current is obtained by integrating the difference between the SLCC A phase commutation current change rate and the B phase commutation current change rate. The relationship with the SLCC commutation overlap angle is expressed as follows:

[0027] (7);

[0028] in, represents the trigger angle, Indicates the initial commutation overlap angle.

[0029] Based on the change of SVF equivalent output voltage in SVF carrying capacity, the SVF equivalent A-phase output voltage is obtained. The specific expression is:

[0030] (8);

[0031] in, Indicates the phase voltage amplitude of the SVF equivalent output voltage, Indicates the initial phase of the SVF equivalent output voltage, Indicates the angular frequency of the SVF equivalent output voltage.

[0032] Combining formulas (6), (7) and (8), the expression of SLCC DC current is obtained, which is:

[0033] (9);

[0034] in, represents the SLCC angular frequency, Indicates the receiving end voltage amplitude.

[0035] The expression of the initial commutation overlap angle is:

[0036] (10);

[0037] Among them, A and B are parameters, specifically:

[0038] .

[0039] Furthermore, in step S4, the SLCC DC current is simplified using the Taylor first-order approximation method, and the specific expression is:

[0040] (11).

[0041] in, It represents the final commutation overlap angle obtained by Taylor's first-order approximation method.

[0042] By taking the inverse sine function on both sides of formula (11), we can get , the specific expression is:

[0043] (12).

[0044] Furthermore, in step S4, the SLCC DC current is simplified using the sum-difference-product formula simplification method to obtain the simplified SLCC DC current, which is specifically expressed as:

[0045] (13).

[0046] in, It represents the final commutation overlap angle obtained by simplifying the sum-difference-product formula.

[0047] Based on the characteristics of the commutation overlap angle, set , the simplified SLCC DC current is further simplified, and the specific expression is:

[0048] (14).

[0049] Obtained Expressed as:

[0050] (15).

[0051] Further, in step S4, a Correlation coefficient , and the iterative coefficient method is used to simplify the SLCC DC current. The specific expression is:

[0052] (16).

[0053] in, Represents the final commutation overlap angle obtained using the iterative coefficient method.

[0054] Obtained Expressed as:

[0055] (17).

[0056] Furthermore, the present invention also proposes a system for calculating the SLCC commutation overlap angle taking into account the SVF bearing capacity, including:

[0057] The circuit construction module is used to establish an SLCC equivalent commutation circuit based on the coupling effect between the SVF output current and voltage and the LCC at the common connection point.

[0058] The KCL equation acquisition module is used to analyze the SLCC equivalent commutation circuit using Kirchhoff's law, obtain the corresponding KCL equation, and determine the relationship between the SLCC commutation current, SVF equivalent output voltage, and SVF equivalent output current.

[0059] The commutation overlap angle acquisition module is used to obtain the relationship between the SLCC commutation current change rate and various SLCC electrical quantities based on the relationship between the SLCC commutation current, SVF equivalent output voltage and SVF equivalent output current, combined with the electrical characteristics of the SLCC during the commutation process. Based on the change in the SVF equivalent output voltage within the SVF carrying capacity, the SLCC DC current and the initial commutation overlap angle are obtained; the initial commutation overlap angle is adjusted to obtain the final commutation overlap angle.

[0060] Furthermore, the present invention also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the computer program, the steps of the SLCC commutation overlap angle calculation method considering the SVF bearing capacity are implemented.

[0061] Furthermore, the present invention also proposes a computer-readable storage medium, which stores a computer program. When the computer program is run by a processor, it executes the SLCC commutation overlap angle calculation method considering the SVF carrying capacity.

[0062] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0063] 1. The present invention establishes an SLCC equivalent commutation circuit, analyzes the commutation circuit through Kirchhoff's law, and derives a DC current expression and a commutation overlap angle formula that considers the influence of SVF output voltage. This takes into account the influence of SVF equivalent output voltage fluctuations on SVF carrying capacity and improves the calculation accuracy of the commutation overlap angle.

[0064] 2. The present invention performs three simplifications on the commutation overlap angle formula, effectively reducing the deviation from the actual value. It performs well in DC current fitting and commutation overlap angle calculation, and can be used for quantitative analysis and load-bearing capacity evaluation of SLCC. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is an overall implementation flow chart of the present invention.

[0066] Figure 2 This is the SLCC equivalent commutation circuit diagram of the present invention.

[0067] Figure 3 This is a three-dimensional relationship diagram between the final commutation overlap angle and various electrical quantities of the SLCC obtained by the present invention using the Taylor first-order approximation method.

[0068] Figure 4 This is a three-dimensional relationship diagram between the final commutation overlap angle and various electrical quantities of the SLCC obtained by the present invention using the simplified sum-difference-product formula method.

[0069] Figure 5 It is a three-dimensional relationship diagram between the final commutation overlap angle and various electrical quantities of the SLCC obtained by the iterative coefficient method of the present invention.

[0070] Figure 6 This is a diagram of the SVF control module built in an embodiment of the present invention.

[0071] Figure 7 3 is a result diagram of the actual value of the commutation overlap angle in an embodiment of the present invention. DETAILED DESCRIPTION

[0072] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0073] To achieve the above objectives, the present invention proposes a method for calculating the SLCC commutation overlap angle considering the SVF bearing capacity, such as Figure 1 The specific steps are as follows:

[0074] S1. Based on the coupling effect between the SVF output current and voltage and the LCC at the common connection point, an SLCC equivalent commutation circuit is established. Specifically:

[0075] Substituting the SVF into a voltage source and into the commutation process of the LCC, the SLCC equivalent commutation circuit is obtained.

[0076] like Figure 2 As shown, the SLCC equivalent commutation circuit includes the A-phase thyristor , B-phase thyristor , C-phase thyristor , SVF equivalent output A phase voltage source , SVF equivalent output B phase voltage source , SVF equivalent output C phase voltage source , equivalent DC current source , SVF valve side A phase equivalent inductance , SVF valve side B phase equivalent inductance , SVF valve side C phase equivalent inductance , the sum of the A-phase line inductance on the receiving side and the transformer leakage inductance , the sum of the B-phase line inductance on the receiving side and the transformer leakage inductance , the sum of the C-phase line inductance on the receiving side and the transformer leakage inductance , receiving end A phase voltage source , receiving end B phase voltage source , receiving end C phase voltage source .

[0077] Equivalent DC current source The positive pole of the C-phase thyristor is connected cathode, equivalent DC current source The negative poles of the A-phase thyristors are connected Anode, B-phase thyristor Anode of C-phase thyristor The anodes are connected to the sum of the C-phase line inductance on the receiving side and the transformer leakage inductance. One end of the SVF valve side C phase equivalent inductance One end of the A-phase thyristor The cathode of the receiving terminal is connected to the sum of the A-phase line inductance and the transformer leakage inductance. One end of the SVF valve side A phase equivalent inductance One end of the B-phase thyristor The cathode of the receiving terminal is connected to the sum of the B-phase line inductance and the transformer leakage inductance. One end of the SVF valve side B phase equivalent inductance The sum of the A-phase line inductance and the transformer leakage inductance on the receiving side The other end is connected to the receiving end A phase voltage source The positive pole, the sum of the B-phase line inductance on the receiving side and the transformer leakage inductance The other end is connected to the receiving end B phase voltage source The positive pole, the sum of the C-phase line inductance on the receiving side and the transformer leakage inductance The other end is connected to the receiving end C phase voltage source The positive pole of the receiving end is the A phase voltage source The negative pole and the receiving end B phase voltage source The negative pole and the receiving end C phase voltage source The negative poles are connected to the neutral point O, and the equivalent inductance of phase A on the SVF valve side The other end is connected to the SVF equivalent output A phase voltage source The positive pole, SVF valve side B phase equivalent inductance The other end is connected to the SVF equivalent output B phase voltage source The positive pole, SVF valve side C phase equivalent inductance The other end is connected to the SVF equivalent output C phase voltage source The positive pole of SVF is equivalent to outputting the A-phase voltage source. The negative pole of SVF is equivalent to the output of B-phase voltage source The negative pole of SVF is equivalent to outputting the C-phase voltage source The negative poles are connected to the neutral point .

[0078] S2. Analyze the SLCC equivalent commutation circuit using Kirchhoff's law to obtain the corresponding KCL (Kirchhoff's Current Law) equation and determine the relationship between the SLCC commutation current, SVF equivalent output voltage, and SVF equivalent output current. Specifically:

[0079] Based on the SVF equivalent voltage source electromotive force, reactance voltage drop, and receiving-end phase voltage in the SLCC equivalent commutation circuit, the KCL equations of the LCC phase A branch and the SVF phase A branch, and the KCL equations of the LCC phase B branch and the SVF phase B branch are obtained. The relationship between the SLCC commutation current, the SVF equivalent output voltage, and the SVF equivalent output current is obtained. The specific expressions are:

[0080] (18);

[0081] (19);

[0082] in, It represents the current flowing through the A-phase thyristor in the SLCC equivalent commutation circuit. It represents the current flowing through the B-phase thyristor in the SLCC equivalent commutation circuit. Indicates the SVF equivalent A-phase output voltage, Indicates the SVF equivalent output A phase current, Indicates the system time, Indicates the receiving end A phase voltage, Indicates the SVF equivalent B-phase output voltage, Indicates the SVF equivalent output B phase current, Indicates the receiving end B phase voltage.

[0083] S3. Based on the relationship between the SLCC commutation current, SVF equivalent output voltage, and SVF equivalent output current, combined with the electrical characteristics of the SLCC during the commutation process, the relationship between the SLCC commutation current change rate and the various electrical quantities of the SLCC is obtained. Based on the change in the SVF equivalent output voltage in the SVF carrying capacity, the SLCC DC current is obtained, and the initial commutation overlap angle is obtained. Specifically:

[0084] According to the KCL equation obtained in step S2, the change rate of the commutation current of phase A and phase B of the SLCC is obtained. The specific expression is:

[0085] (20);

[0086] (twenty one).

[0087] Based on the AC voltage and current waveforms during the SLCC commutation process and Kirchhoff's law, the potentials of the points where the A-phase and B-phase branches of the SVF are connected to the LCC are equal during the commutation process. The specific expression is:

[0088] (twenty two);

[0089] in, Indicates the voltage at the common connection point where SVF and LCC are connected.

[0090] Since the SLCC is designed with three-phase symmetry in mind, , , 、 Both represent intermediate variables.

[0091] The difference between the SLCC phase A commutation current change rate and the phase B commutation current change rate is calculated. According to formula (22), the relationship between the SLCC commutation current change rate and the electrical quantity in the SLCC equivalent commutation circuit is obtained. The specific expression is:

[0092] (twenty three).

[0093] According to the AC voltage and current waveforms during the SLCC commutation process, the SLCC DC current is obtained by integrating the difference between the SLCC A phase commutation current change rate and the B phase commutation current change rate. The relationship with the SLCC commutation overlap angle is expressed as follows:

[0094] (twenty four);

[0095] in, represents the trigger angle, Indicates the initial commutation overlap angle.

[0096] In actual engineering, the SVF carrying capacity is reflected in the fact that the capacitor voltage of its submodule should be less than the set value. If the capacitor voltage of the SVF submodule is within the normal range, the SVF equivalent output voltage is normal; if the capacitor voltage of the SVF submodule is greater than its set value, the SVF will be locked and the SVF equivalent output voltage will be 0.

[0097] Based on the change of SVF equivalent output voltage in SVF carrying capacity, the SVF equivalent A-phase output voltage is obtained. The specific expression is:

[0098] (25);

[0099] in, Indicates the phase voltage amplitude of the SVF equivalent output voltage, Indicates the initial phase of the SVF equivalent output voltage, Indicates the angular frequency of the SVF equivalent output voltage.

[0100] Combining formulas (23), (24) and (25), the expression of the SLCC DC current is obtained, which is:

[0101] (26);

[0102] in, Indicates the SLCC angular frequency, generally , Indicates the receiving end voltage amplitude.

[0103] The expression of the initial commutation overlap angle is:

[0104] (27);

[0105] Among them, A and B are parameters, specifically:

[0106] .

[0107] S4. Considering that the required commutation overlap angle expression is a quartic equation and the calculation is complex, three methods are used to adjust the initial commutation overlap angle to obtain the final commutation overlap angle. The three methods include Taylor's first-order approximation method, the sum-difference-product formula simplification method, and the iterative coefficient method. Specifically:

[0108] (1) Taylor’s first-order approximation method is used to simplify the SLCC DC current. The specific expression is:

[0109] (28).

[0110] in, It represents the final commutation overlap angle obtained by Taylor's first-order approximation method.

[0111] By taking the inverse sine function on both sides of formula (28), we can obtain , the specific expression is:

[0112] (29).

[0113] Where, and 、 Proportional, Inversely proportional. Figure 3 As shown, the final commutation overlap angle obtained using Taylor's first-order approximation method is plotted. Three-dimensional relationship diagram between various electrical quantities of SLCC. Figure 3 (a) is The three-dimensional relationship diagram of the SVF equivalent output phase voltage amplitude and the SVF equivalent output phase voltage initial phase can be seen from the figure. As the SVF equivalent output phase voltage initial phase changes from arrive When the change decreases, Because in the event of an abnormal fall, the SVF output can be increased To prevent the commutation overlap angle from increasing. Figure 3 (b) is The three-dimensional relationship diagram of the receiving end voltage amplitude and the SVF equivalent output phase voltage amplitude can be seen from the figure It is inversely proportional to the SVF equivalent output phase voltage amplitude and the receiving end voltage amplitude. When the SVF reactive output changes, the output voltage phase When changes occur, the commutation overlap angle can be increased to prevent commutation failure in the LCC. Figure 3 (c) is The three-dimensional relationship diagram of the SVF equivalent output phase voltage amplitude and SLCC DC current shows that and SLCC DC current Proportional, when Because when the fault rises, it is necessary to adjust SVF to increase the output voltage To reduce the commutation overlap angle, and when When it decreases, the reactive output of SVF can be reduced accordingly. and its phase Can be lowered.

[0114] (2) The SLCC DC current is simplified by using the sum-difference-product formula simplification method to obtain the simplified SLCC DC current. The specific expression is:

[0115] (30).

[0116] in, It represents the final commutation overlap angle obtained by simplifying the sum-difference-product formula.

[0117] Considering the small value of the commutation overlap angle, Close to 0, It can be approximately equal to 1, so the simplified SLCC DC current is further simplified, and the specific expression is:

[0118] (31).

[0119] Obtained for:

[0120] (32).

[0121] like Figure 4 As shown, the final commutation overlap angle obtained by simplifying the sum-difference-product formula is plotted. Three-dimensional relationship diagram between various electrical quantities of SLCC. Figure 4 (a) is The three-dimensional relationship diagram of the SVF equivalent output phase voltage amplitude and the SVF equivalent output phase voltage initial phase, As the SVF equivalent output phase voltage initial phase changes from arrive Change and decrease. Figure 4 (b) is The three-dimensional relationship diagram of the SVF equivalent output phase voltage amplitude and the receiving end voltage amplitude, It is inversely proportional to the SVF equivalent output phase voltage amplitude and the receiving end voltage amplitude. Figure 4 (c) is The three-dimensional relationship diagram of the SVF equivalent output phase voltage amplitude and SLCC DC current, Proportional to the SLCC DC current.

[0122] contrast Figure 3 and Figure 4 , The values ​​​​are to be compared under different working conditions Larger, it can better fit the SLCC commutation overlap angle.

[0123] (3) Taking into account It is just close to 1 and cannot be directly equal to 1, so a final commutation overlap angle is set to be obtained by simplifying the sum-difference-product formula. Correlation coefficient , and the iterative coefficient method is used to simplify the SLCC DC current. The specific expression is:

[0124] (33).

[0125] in, Represents the final commutation overlap angle obtained using the iterative coefficient method.

[0126] Obtained Expressed as:

[0127] (34).

[0128] like Figure 5 As shown, the final commutation overlap angle obtained by the iterative coefficient method is plotted. Three-dimensional relationship diagram between various electrical quantities of SLCC. Figure 5 (a) is The three-dimensional relationship diagram of the initial phase of the SVF equivalent output phase voltage and the amplitude of the SVF equivalent output phase voltage is shown in the figure. As the SVF equivalent output phase voltage initial phase changes from arrive Change and decrease. Figure 5 (b) is The three-dimensional relationship diagram of the SVF equivalent output phase voltage amplitude and the receiving end voltage amplitude is shown in the figure. It is inversely proportional to the SVF equivalent output phase voltage amplitude and the receiving end voltage amplitude. Figure 5 (c) is The three-dimensional relationship diagram of the SVF equivalent output phase voltage amplitude and SLCC DC current is shown in the figure. Proportional to the SLCC DC current, Figure 4 and Figure 5 It can be seen that compared to Bigger, more precise.

[0129] Example:

[0130] The actual operating data of SLCC under the operating conditions of 1.0 pu and 0.8 pu are obtained, as shown in Table 1.

[0131] Table 1 SLCC actual operation data

[0132]

[0133] Based on the data in Table 1, 、 、 and overlaps with the actual value of the SLCC commutation angle Compared with DC current, the comparison results are shown in Table 2 and Table 3.

[0134] Table 2 Data and errors under 1.0 pu operating conditions

[0135]

[0136] Table 3 Data and errors under 0.8 pu operating conditions

[0137]

[0138] According to the results in Table 2 and Table 3, under these two working conditions, the DC current values ​​obtained after the analysis of the SLCC commutation process established based on the coupling of SVF and LCC are 0.75% and 3.2% respectively, and the initial commutation overlap angle is derived. In both working conditions, it is even less than 0.1%, which is almost consistent with the actual simulation value. The above results show that the SLCC commutation process established based on the coupling of SVF and LCC can better fit the actual SLCC commutation process. There is a big difference between the actual value and The difference from the actual commutation overlap angle is greatly reduced. The difference from the actual commutation overlap angle is further reduced, indicating that the method proposed in the present invention can be used for further quantitative analysis and load-bearing capacity evaluation of SLCC.

[0139] like Figure 6 As shown in the figure, the SVF control module in the SLCC circuit simulation platform built using PLESM is demonstrated. The simulation platform is used to analyze the SLCC commutation waveform and obtain the SLCC electrical quantity data under different working conditions.

[0140] like Figure 7 As shown in the figure, the red line, blue line and green line respectively represent the waveforms of the AC phase A, phase B and phase C voltages on the SLCC inverter side during the commutation process. Figure 7 The marked part is the commutation time from phase A to phase B. Converting the commutation time into an angle gives the actual commutation angle from phase A to phase B. The actual commutation angle in the figure is 0.16838s.

[0141] The initial commutation overlap angle calculation formula obtained by Maple software is:

[0142] .

[0143] The initial commutation overlap angle is 0.16842. It can be seen that the difference between the initial commutation overlap angle value and the actual SLCC commutation overlap angle is very small, verifying the correctness of the formula.

[0144] The embodiment of the present invention also proposes an SLCC commutation overlap angle calculation system that takes into account the SVF carrying capacity, including a circuit construction module, a KCL equation acquisition module, a commutation overlap angle acquisition module, and a computer program that can be run on a processor. It should be noted that each module in the above system corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method. For technical details not fully described in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0145] An embodiment of the present invention further provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable by the processor. It should be noted that when the processor executes the computer program, it corresponds to the specific steps of the method provided in the embodiment of the present invention and has the corresponding functional modules and beneficial effects of the method. For technical details not fully described in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0146] The present invention also provides a computer-readable storage medium storing a computer program. It should be noted that when executed by a processor, the computer program corresponds to the specific steps of the method provided in the present invention and has the corresponding functional modules and beneficial effects. For technical details not fully described in this embodiment, please refer to the method provided in the present invention.

[0147] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for calculating the SLCC commutation overlap angle considering the SVF bearing capacity, characterized in that: include: S1. Based on the coupling effect between the SVF output current and voltage and the LCC at the common connection point, an SLCC equivalent commutation circuit is established. S2. Analyze the SLCC equivalent commutation circuit using Kirchhoff's law to obtain the KCL equation, and determine the relationship between the SLCC commutation current, the SVF equivalent output voltage, and the SVF equivalent output current; specifically: Based on the SVF equivalent voltage source electromotive force, reactance voltage drop, and receiving-end phase voltage in the SLCC equivalent commutation circuit, the KCL equations of the LCC phase A branch and the SVF phase A branch, and the KCL equations of the LCC phase B branch and the SVF phase B branch are obtained. The relationship between the SLCC commutation current, the SVF equivalent output voltage, and the SVF equivalent output current is obtained. The specific expressions are: Among them, i 1a Indicates the current flowing through the A-phase thyristor in the SLCC equivalent commutation circuit, i1 b represents the current flowing through the B-phase thyristor in the SLCC equivalent commutation circuit, u2a represents the SVF equivalent A-phase output voltage, i2a represents the SVF equivalent output A-phase current, t represents the system time, usa represents the receiving-end A-phase voltage, u2b represents the SVF equivalent B-phase output voltage, i2b represents the SVF equivalent output B-phase current, usb represents the receiving-end B-phase voltage, La represents the SVF valve-side A-phase equivalent inductance, Lsa represents the sum of the receiving-end A-phase line inductance and the transformer leakage inductance, Lb represents the SVF valve-side B-phase equivalent inductance, and Lsb represents the sum of the receiving-end B-phase line inductance and the transformer leakage inductance; S3. Based on the relationship between the SLCC commutation current, the SVF equivalent output voltage, and the SVF equivalent output current, and in combination with the electrical characteristics of the SLCC during the commutation process, the relationship between the SLCC commutation current change rate and the various SLCC electrical quantities is obtained. Based on the change in the SVF equivalent output voltage in the SVF carrying capacity, the SLCC DC current is obtained, and the initial commutation overlap angle is obtained; specifically: According to the KCL equation obtained in step S2, the commutation current change rate of phase A and phase B of the SLCC is obtained; Based on the three-phase symmetry of SLCC, let Lsa = Ls b =Lsc=Ls,L a =L b =L c =L, where L sc It represents the sum of the C-phase line inductance on the receiving side and the transformer leakage inductance, Lc represents the C-phase equivalent inductance on the SVF valve side, and L s , L both represent intermediate variables; According to the AC voltage and current waveforms during the SLCC commutation process, the SLCC DC current Id is obtained by integrating the difference between the SLCC A phase commutation current change rate and the B phase commutation current change rate. c The relationship with the SLCC commutation overlap angle is expressed as follows: Where α represents the trigger angle, μ represents the initial commutation overlap angle; Based on the SVF equivalent output voltage change in the SVF carrying capacity and the SVF equivalent A-phase output voltage, the SLCC DC current is obtained. The specific expression is: Where ω0 represents the SLCC angular frequency, U s Indicates the receiving end voltage amplitude, U indicates the phase voltage amplitude of the SVF equivalent output voltage, Indicates the initial phase of the SVF equivalent output voltage; The expression of the initial commutation overlap angle is: Among them, A and B are parameters, specifically: S4. Adjust the initial commutation overlap angle to obtain a final commutation overlap angle.

2. The SLCC commutation overlap angle calculation method considering SVF bearing capacity according to claim 1 is characterized in that: In step S1, the SVF is equivalent to a voltage source and substituted into the commutation process of the LCC to obtain the SLCC equivalent commutation circuit; The SLCC equivalent commutation circuit includes A-phase thyristor V4, B-phase thyristor V6, C-phase thyristor V5, SVF equivalent output A-phase voltage source ua, SVF equivalent output B-phase voltage source u b , SVF equivalent output C-phase voltage source uc, equivalent DC current source i dc , SVF valve side A phase equivalent inductance L a , SVF valve side B phase equivalent inductance Lb, SVF valve side C phase equivalent inductance L c , the sum of the A-phase line inductance and the transformer leakage inductance on the receiving side Lsa, the sum of the B-phase line inductance and the transformer leakage inductance on the receiving side Ls b , the sum of the C-phase line inductance and the transformer leakage inductance on the receiving side Lsc, the A-phase voltage source u3a on the receiving side, the B-phase voltage source u3b on the receiving side, and the C-phase voltage source u3c on the receiving side; Equivalent DC current source i dc The positive electrode is connected to the cathode of the C-phase thyristor V5, and the equivalent DC current source i dc The negative poles are connected to the anodes of the A-phase thyristor V4 and the B-phase thyristor V6, and the anodes of the C-phase thyristor V5 are connected to one end of the sum of the C-phase line inductance and the transformer leakage inductance Lsc on the receiving side and the C-phase equivalent inductance L on the SVF valve side. c The cathode of the A-phase thyristor V4 is connected to one end of the sum of the A-phase line inductance and the transformer leakage inductance Lsa on the receiving side, and the equivalent inductance L of the A-phase on the SVF valve side. a The cathode of the B-phase thyristor V6 is connected to the sum of the B-phase line inductance and the transformer leakage inductance Ls on the receiving side. b One end of the SVF valve side B phase equivalent inductance Lb, the other end of the receiving side A phase line inductance and the transformer leakage inductance Lsa is connected to the positive electrode of the receiving end A phase voltage source u3a, the receiving side B phase line inductance and the transformer leakage inductance Ls b The other end of the receiving end is connected to the positive electrode of the B-phase voltage source u3b, the other end of the sum of the C-phase line inductance and the transformer leakage inductance Lsc on the receiving end is connected to the positive electrode of the C-phase voltage source u3c on the receiving end, the negative electrode of the A-phase voltage source u3a on the receiving end, the negative electrode of the B-phase voltage source u3b on the receiving end, and the negative electrode of the C-phase voltage source u3c on the receiving end are all connected to the neutral point O, and the equivalent inductance L of the A-phase on the SVF valve side is L. a The other end of the SVF valve side B phase equivalent inductor Lb is connected to the positive electrode of the SVF equivalent output B phase voltage source ub, and the other end of the SVF valve side C phase equivalent inductor L is connected to the positive electrode of the SVF equivalent output B phase voltage source ub. c The other end is connected to the positive pole of the SVF equivalent output C-phase voltage source uc, and the negative pole of the SVF equivalent output A-phase voltage source ua, the negative pole of the SVF equivalent output B-phase voltage source ub, and the negative pole of the SVF equivalent output C-phase voltage source uc are all connected to the neutral point O′.

3. The SLCC commutation overlap angle calculation method considering SVF bearing capacity according to claim 1 is characterized in that: In step S4, the SLCC DC current is simplified using the Taylor first-order approximation method to obtain the simplified SLCC DC current, which is specifically expressed as: Wherein, μ1 represents the final commutation overlap angle obtained by Taylor's first-order approximation method; By taking the arc sine function of the simplified SLCC DC current, μ1 is obtained. The specific expression is:

4. The SLCC commutation overlap angle calculation method considering SVF bearing capacity according to claim 1 is characterized in that: In step S4, the SLCC DC current is simplified by using the sum-difference-product formula simplification method to obtain the simplified SLCC DC current, which is specifically expressed as follows: Wherein, μ2 represents the final commutation overlap angle obtained by simplifying the sum-difference-product formula; set up The simplified SLCC DC current is further simplified to the following expression: The obtained μ2 is expressed as:

5. The SLCC commutation overlap angle calculation method considering SVF bearing capacity according to claim 4 is characterized in that: In step S4, a coefficient ξ is set that is related to the final commutation overlap angle obtained by simplifying the sum-difference-product formula, and the SLCC DC current is simplified by the iterative coefficient method. The specific expression is: Wherein, μ3 represents the final commutation overlap angle obtained by the iterative coefficient method; The obtained μ3 is expressed as:

6. A system for calculating the SLCC commutation overlap angle considering SVF bearing capacity as claimed in claim 1, characterized in that: include: A circuit construction module for establishing an SLCC equivalent commutation circuit based on the coupling effect between the SVF output current and voltage and the LCC at the common connection point; The KCL equation acquisition module is used to analyze the SLCC equivalent commutation circuit using Kirchhoff's law, obtain the corresponding KCL equation, and determine the relationship between the SLCC commutation current, SVF equivalent output voltage, and SVF equivalent output current; The commutation overlap angle acquisition module is used to obtain the relationship between the SLCC commutation current change rate and various SLCC electrical quantities based on the relationship between the SLCC commutation current, SVF equivalent output voltage and SVF equivalent output current, combined with the electrical characteristics of the SLCC during the commutation process. Based on the change in the SVF equivalent output voltage within the SVF carrying capacity, the SLCC DC current and the initial commutation overlap angle are obtained; the initial commutation overlap angle is adjusted to obtain the final commutation overlap angle.

7. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the method for calculating the SLCC commutation overlap angle considering the SVF bearing capacity as described in any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for calculating the SLCC commutation overlap angle considering the SVF bearing capacity according to any one of claims 1 to 5 is executed.

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