DC feed-in short-circuit ratio calculation method and system considering AC load influence

Abstract

The invention discloses a direct current feed-in short circuit ratio calculation method considering the alternating current load influence, and discloses a system and a medium with the direct current feed-in short circuit ratio calculation method considering the alternating current load influence, and the direct current feed-in short circuit ratio calculation method considering the alternating current load influence proposes a pi-type equivalent system considering the alternating current load influence. A Thevenin circuit in classical DC short-circuit ratio calculation is replaced, the problem of classical Thevenin equivalence abnormity evaluation is improved, and a DC load retention short-circuit ratio (LPSCR) and matched index calculation method is provided based on a pi-type equivalence system.

Description

Technical Field

[0001] The present invention relates to the technical field of high - voltage direct - current (HVDC) power transmission, and particularly to a method and system for calculating the short - circuit ratio of DC feeding considering the influence of AC load. Background Art

[0002] High - voltage direct - current (HVDC) power transmission systems are widely used in long - distance and large - capacity power transmission. Some HVDC projects can already provide active power up to 11 GW. Evaluating whether the AC system has sufficient strength to accommodate large - capacity HVDC is an important issue, and a large number of studies have been carried out in related fields. These studies have proposed indicators and tools such as voltage stability index (VSI), maximum power curve (MPC), control sensitivity index (CSI), etc. Among them, the short - circuit ratio (SCR) is one of the most commonly used. Its physical meaning is clear and the definition is intuitive.

[0003] When describing the strength of a power system with HVDC feeding, the classical SCR is defined as the ratio of the AC short - circuit capacity (SCC) to the DC power. The larger the short - circuit ratio, the stronger the system. For example, when SCR > 3, the system is considered a strong system. The critical short - circuit ratio (CSCR) is the short - circuit ratio when the system is at the unstable boundary, which is usually considered to be around 2. In addition, some other SCR indicators have also been defined to describe the system from multiple aspects. For example, the effective short - circuit ratio (ESCR) additionally considers the influence of shunt capacitors and filters, the operating short - circuit ratio (OSCR) considers the changes in the AC system configuration and DC power, and the Q - ESCR considers the reactive power consumption of the converter. All the above indicators are described in IEEE standard 1204 - 1997 and are all based on the classical SCR definition.

[0004] The intuitiveness and simplicity of the classical indicators based on SCR largely depend on the Thevenin equivalent circuit, which provides an intuitive connection between the converter and the AC network. Even for complex meshed AC networks, they can be simplified to a two - bus Thevenin equivalent circuit for research.

[0005] In practice, it is found that the Thevenin equivalent circuit adopted by the classical indicators is not applicable to many newly built HVDC projects, especially for large - capacity (about 8000 MW) extra - high - voltage DC power transmission projects based on line - commutated converters (LCCs). In order to more effectively absorb HVDC power, many HVDCs are directly fed into load centers. The interaction between the HVDC power transmission system and the load is becoming more and more important in stability analysis. Unfortunately, the Thevenin circuit is difficult to capture these interactions because the Thevenin equivalent circuit does not explicitly include the AC load. Therefore, the classical indicators based on SCR may provide inaccurate evaluation results. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. For this purpose, the present invention proposes a method for calculating the DC feed-in short-circuit ratio considering the influence of AC load, which can propose a π-type equivalent system considering the influence of AC load to replace the Thevenin circuit in the classical DC short-circuit ratio calculation, and improve the abnormal evaluation problem of the classical Thevenin equivalent; and based on the proposed π-type equivalent system, a calculation method for the DC load retention short-circuit ratio (LPSCR) and supporting indicators is proposed.

[0007] The present invention also proposes a system having the above-mentioned method for calculating the DC feed-in short-circuit ratio considering the influence of AC load.

[0008] The method for calculating the DC feed-in short-circuit ratio considering the influence of AC load according to the embodiment of the first aspect of the present invention is characterized by including the following steps:

[0009] Equivalent the power system with DC feed-in to an equivalent AC network including AC load;

[0010] Convert the equivalent AC network into a π-type equivalent circuit, and the π-type equivalent circuit includes three equivalent impedances, which are obtained by star-delta transformation of the AC load and the AC system impedance respectively;

[0011] Based on the π-type equivalent circuit, calculate the DC load retention short-circuit ratio LPSCR, and its expression is:

[0012]

[0013] where E is the equivalent power supply amplitude, Z eq is the total equivalent impedance of the system, P dc is the active power injected by DC, P LDeq is the active power consumed by the equivalent load.

[0014] The method for calculating the DC feed-in short-circuit ratio considering the influence of AC load according to the embodiment of the present invention has at least the following beneficial effects: In this application, the AC system is equivalent to a π-type equivalent system considering the influence of AC load through the HVDC feed-in AC system, so as to replace the classical Thevenin equivalent system used in the classical short-circuit ratio calculation, improve the abnormal evaluation problem of the classical Thevenin equivalent, and based on the π-type equivalent system, a calculation method for the DC load retention short-circuit ratio (LPSCR) and supporting indicators is proposed.

[0015] According to some embodiments of the present invention, the step of calculating the DC load retention short-circuit ratio LPSCR based on the π-type equivalent circuit further includes: calculating the complex form of the DC load retention short-circuit ratio LPSCR C , and its expression is:

[0016]

[0017] Among them, SCC C ∠θ C is the short-circuit capacity in complex form, S˙ dc and S˙ LDeq are the complex power of DC injection and the complex power of equivalent load respectively.

[0018] According to some embodiments of the present invention, in the step of converting the equivalent AC network into a π-type equivalent circuit, the π-type equivalent circuit includes three equivalent impedances, and the equivalent impedances of the π-type equivalent circuit in the step of obtaining them by star-delta transformation from the AC load and the AC system impedance are calculated by the following formula:

[0019]

[0020] Among them, Z1 and Z2 are the equivalent impedances of the original system, and Z LD is the load impedance of the original system.

[0021] According to some embodiments of the present invention, the method further includes the step of determining the system stability boundary based on the LPSCR and LPSCR C through the following formula:

[0022]

[0023] Among them, S eq 、P eq 、Q eq are the equivalent total complex power, equivalent active power and equivalent reactive power respectively, and SCC P and SCC Q are the short-circuit capacity components based on the equivalent resistance and reactance of the system.

[0024] According to some embodiments of the present invention, the method of equivalent to an equivalent AC network including an AC load in the step of equivalent the power system with DC feed-in to an equivalent AC network includes the REI equivalent, WARD equivalent or the method of identifying Thevenin parameters based on measurements.

[0025] According to the DC feed-in short-circuit ratio calculation system considering the influence of AC load in the second aspect embodiment of the present invention, it is characterized by including:

[0026] The first conversion module is used to equivalent the power system with DC feed-in to an equivalent AC network including an AC load;

[0027] The second conversion module is used to convert the equivalent AC network into a π-type equivalent circuit, and the π-type equivalent circuit includes three equivalent impedances, which are obtained by star-delta transformation from the AC load and the AC system impedance respectively;

[0028] A calculation module, configured to calculate a direct-current load retention short-circuit ratio LPSCR based on the π-type equivalent circuit, and the expression thereof is as follows:

[0029]

[0030] wherein, E is the equivalent power supply amplitude, Z eq is the total equivalent impedance of the system, P dc is the active power injected by direct current, P LDeq is the active power consumed by the equivalent load.

[0031] According to some embodiments of the present invention, the calculation module includes:

[0032] Calculating the direct-current load retention short-circuit ratio LPSCR in complex form C , and the expression thereof is as follows:

[0033]

[0034] wherein, SCC C ∠θ C is the short-circuit capacity in complex form, S˙ dc and S˙ LDeq are the complex power injected by direct current and the complex power of the equivalent load respectively.

[0035] According to some embodiments of the present invention, in the second conversion module, the equivalent impedance of the π-type equivalent circuit is calculated by the following formula:

[0036]

[0037] wherein, Z1 and Z2 are the equivalent impedances of the original system, and Z LD is the load impedance of the original system.

[0038] According to some embodiments of the present invention, the system further includes:

[0039] A stability boundary solving module, capable of determining the system stability boundary based on the LPSCR and LPSCR C , through the following formula:

[0040]

[0041] wherein, S eq , P eq , Q eq are the equivalent total complex power, equivalent active power and equivalent reactive power respectively, SCC P and SCC Q are the short-circuit capacity components based on the equivalent resistance and reactance of the system.

[0042] A computer-readable storage medium according to an embodiment of the third aspect of the present invention stores computer-executable instructions for executing the above-described method for calculating the DC injection short-circuit ratio considering the influence of AC loads.

[0043] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention.

[0044] Figure illustration

[0045] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of the embodiments in conjunction with the accompanying drawings, where:

[0046] Figure 1 Schematic diagram of the Thevenin equivalent circuit adopted by the classical SCR; this circuit uses an ideal voltage source E th ∠0° (Thevenin equivalent power source) connected to the coupling point (PCC) of the DC converter accessing the AC power grid through an impedance Z th ∠θ th (Thevenin equivalent impedance), and when a short circuit occurs at the PCC point, the corresponding short-circuit capacity is calculated as the numerator of the classical SCR. In the figure, Z f represents the equivalent fault impedance of the equivalent circuit when a fault occurs. V PCC represents the AC system voltage at the coupling point, and P d represents the active power of the DC injection into the AC power grid.

[0047] Figure 2 Schematic diagram of the equivalent circuit of the system with equivalent loads for DC injection into a large power grid; this circuit uses an ideal voltage source E∠0° (Thevenin equivalent power source) connected to the bus where the equivalent load Z LD ∠θ LD is located through an equivalent impedance Z1∠θ1. The equivalent load is connected to the coupling point (PCC) of the DC converter accessing the AC power grid through another equivalent impedance Z2∠θ2. Z f represents the equivalent fault impedance of the equivalent circuit when a fault occurs, and is used to calculate the short-circuit capacity at this point by accessing the PCC point. V PCC represents the AC system voltage at the coupling point, and P d represents the active power of the DC injection into the AC power grid.

[0048] Figure 3 For Figure 2 the equivalent process schematic diagram of the system shown being equivalent to the Thevenin equivalent current adopted by the classical SCR; in the appendix Figure 2 the bus where the load is located is eliminated, and part of the load is equivalent to the Thevenin equivalent power source E th ∠0° in Another part of the load is equivalent to the Thevenin equivalent impedance Z th ∠θ th in Z LD ∠θ LD ;

[0049] Figure 4 is a schematic diagram of the steps of the DC feed-in short-circuit ratio calculation method considering the influence of AC load provided by an embodiment of the present invention;

[0050] Figure 5 is Figure 4 a schematic diagram of the equivalent process of the Π-type equivalent circuit in the DC feed-in short-circuit ratio calculation method considering the influence of AC load shown in the figure; Attached Figure 2 the bus where the load is located is eliminated, and a part of the load is equivalent to three equivalent impedances Z LDs ∠θ LDs , Z LNeq ∠θ LNeq , Z LDeq ∠θ LDeq . The first equivalent impedance Z LDs ∠θ LDs is incorporated into the bus where the equivalent power supply E∠0° is located, and the second equivalent impedance 2Z LNeq ∠θ LNeq is connected in series between the equivalent impedances Z1∠θ1 and Z2∠θ2, and the third equivalent impedance is incorporated into the bus where the PCC point is located. U t represents the voltage amplitude at the PCC point;

[0051] Figure 6 is a system diagram for simulation testing provided by an embodiment of the present invention;

[0052] Figure 7 is a schematic diagram of the time-domain simulation curve of system load shedding provided by an embodiment of the present invention;

[0053] Figure 8 is the index provided by an embodiment of the present invention a schematic diagram of the change during the load shedding process;

[0054] Figure 9 is a comparison diagram of the system operation boundary when P eq = 0 provided by an embodiment of the present invention;

[0055] Figure 10 is a comparison diagram of the system operation boundary when P eq = -1.0 provided by an embodiment of the present invention;

[0056] Figure 11 is a structural block diagram of the DC feed-in short-circuit ratio calculation system considering the influence of AC load provided by an embodiment of the present invention. Detailed implementation manners

[0057] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0058] In the description of the present invention, it should be understood that for the orientation description, such as the orientation or positional relationship indicated by up, down, front, back, left, right, etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0059] In the description of the present invention, the meaning of several is one or more, the meaning of multiple is more than two, and understandings such as greater than, less than, exceeding, etc. do not include the present number, and understandings such as above, below, within, etc. include the present number. If there is a description of first and second, it is only for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0060] In the description of the present invention, unless otherwise clearly defined, words such as setting, installing, connecting, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the present invention in combination with the specific content of the technical solution.

[0061] Figure 1 For calculating the classical short-circuit ratio, the Thevenin equivalent current diagram adopted. Any complex power system network with DC feeding for which the short-circuit ratio to be calculated can be equivalent to Figure 2 the equivalent AC network form shown, which includes an AC equivalent load and DC feeding for which the short-circuit ratio is to be calculated, by using system equivalent methods (such as REI equivalent, WARD equivalent, measurement-based Thevenin parameter identification methods, etc.). The system equivalent method used in the above process belongs to the prior art, and its principle will not be elaborated in detail here.

[0062] In view of the phenomenon that the Thevenin equivalent circuit adopted for classical indicators is not applicable to many newly built HVDC projects, especially for large-capacity (about 8000 MW) ultra-high voltage DC transmission projects based on line-commutated converters (LCC). The present invention provides a method for calculating the short-circuit ratio of DC feeding considering the influence of AC loads. Specifically as follows:

[0063] Embodiment 1

[0064] 1. Calculate the classical short-circuit ratio (Short Current Ratio, SCR).

[0065] Figure 1 The Thevenin equivalent circuit representing an AC power system, based on the Thevenin equivalent circuit, the classical short-circuit ratio calculation method is shown in Equation (1).

[0066]

[0067] Where P d is the active power sent out by the DC system, and SCC represents the short-circuit flux of the AC system, and the calculation method is shown in Equation (2).

[0068]

[0069] Where, E th represents the amplitude of the Thevenin equivalent electromotive force, and Z th represents the amplitude of the Thevenin equivalent impedance.

[0070] When calculating Figure 2 the classical SCR index of the system, it is necessary to simplify the AC system into Figure 1 a Thevenin equivalent circuit as shown, and then repeat the previous steps for calculation to obtain the SCR.

[0071] From Figure 2 the calculation method of the Thevenin equivalent impedance is:

[0072] Z th ∠θ th = Z2∠θ2 + (Z1∠θ1) || (Z LD ∠θ LD )(3)

[0073] The calculation method of the Thevenin equivalent source is:

[0074]

[0075] In the formula, (Z1∠θ1) || (Z LD ∠θ LD ) represents the total impedance of two parallel impedances. Finally, calculate the classical short-circuit ratio index of the simple system according to Equation (1) and Equation (2). The above conversion process can be described as Figure 2 , and the load is equivalently incorporated into the power supply and impedance of the Thevenin equivalent. Figure 3

[0076] Second, calculate the DC-injected short-circuit ratio with the π-type equivalent circuit calculation method for calculating LPSCR and related indexes such as LPSCR. As Figure 4 shown, it includes:

[0077] Step S100: Equivalent the power system with DC injection into an equivalent AC network including AC loads.

[0078] ​An electrical power system with a fed-in direct current is equivalent to an electrical power system as shown in Figure 2 The equivalent methods include, but are not limited to: REI equivalence, WARD equivalence, measurement-based Thevenin parameter identification, multiple star-delta transformations, etc.

[0079] Step S200: Convert the equivalent AC network into a π-type equivalent circuit, which includes three equivalent impedances obtained by star-delta transformation of the AC load and the AC system impedance respectively.

[0080] Figure 5 Illustrates the conversion process from the system in Figure 2 to the π-type equivalent circuit. This process is no longer processed like the traditional Thevenin equivalent circuit, but through star-delta transformation, three additional impedances are introduced and equivalent into the form of a π-type equivalent circuit.

[0081] In Figure 5 , three additional impedances are introduced and calculated through equations (5)-(7).

[0082]

[0083] Figure 5 The physical meaning of the π-type equivalent circuit in Figure 1 is to divide the AC load into two parts. One part is powered by the AC power supply, and the other part is powered by the high-voltage direct current transmission. In contrast, Figure 5 the physical meaning of the classical Thevenin circuit is to convert the load into an equivalent source, and there is no longer a load in the equivalent circuit. Since the π-type equivalent circuit retains the load, the proposed circuit is called a load-holding π-type equivalent circuit, that is,

[0084] Step S300: Calculate the DC load retention short-circuit ratio LPSCR based on the π-type equivalent circuit.

[0085] The calculation formula is defined as:

[0086]

[0087] where P dc is the active power provided by the DC in Figure 5 , P LDeq is the active power consumed by the load Z LDeq ∠θ LDeq , Z eq represents the equivalent impedance of the system, and the calculation method is:

[0088]

[0089] Z eq ∠θ eq= Z1∠θ1 + Z2∠θ2 + Z LNeq ∠θ LNeq (11)

[0090] Wherein, represents the square of the system voltage amplitude at the access point of the equivalent AC load. characterizes taking the real part of a complex number; Z1∠θ1, Z2∠θ2, Z LNeq ∠θ LNeq etc. are Figure 5 the equivalent impedance obtained from the system equivalent in , and E is the amplitude of the equivalent electromotive force obtained from the system equivalent.

[0091] Furthermore, the method further includes:

[0092] Step S400, based on the LPSCR and LPSCR C , determine the system stability boundary.

[0093] The expression characterizing the system stability boundary is:

[0094]

[0095] Wherein:

[0096]

[0097] R eq = Z eq cosθ eq (18)

[0098] X eq = Z eq sinθ eq (19)

[0099]

[0100] After calculating the indexes through formulas (15), (16), (17), (20), and (21), substitute them into formula (14) to verify whether the calculated system is in a stable operating state.

[0101] If formula (22) is satisfied, it indicates that the system is in an unstable state, otherwise it indicates that the system is in a stable state. Thus, it can be seen that expression (14) is the system operating stability boundary constructed by the proposed indexes.

[0102] Embodiment 2:

[0103] Taking the IEEE-39 system as an example to characterize the inventive effect of the proposed calculation system and verify that the invented content is more practical than the classical calculation system.

[0104] The system is as Figure 6As shown. After the system configures the corresponding parameters, it performs load shedding three times continuously. The process of load shedding is as shown in the content of Appendix 1:

[0105] Appendix 1 Load Shedding Process

[0106]

[0107] Appendix 2 Calculation Results of Classical SCR and the Proposed Indexes

[0108]

[0109] The system response is as Figure 7 (a)-(c) shown.

[0110] From the perspective of AC voltage, the first two load sheds seem to improve the strength of the system, but the system suddenly collapses after the third load shed. If we further observe the details of the system response, it can be found that, in fact, during each of the three load shedding processes, each transient response makes the system become more and more unstable, indicating that the system becomes weaker as the load shedding progresses.

[0111] The classical SCR and the proposed "LPSCR", "LPSCR C " in this patent are respectively used to evaluate the strength of the system. Appendix 2 lists the calculated index values.

[0112] According to the classical SCR, the SCR value increases with load shedding, indicating that the system becomes stronger through load shedding. This corresponds to the increase in AC voltage. On the contrary, the values of "LPSCR", "LPSCR C " decrease as the load shedding progresses, indicating that the system is becoming weaker, corresponding to severe transient responses and the ultimate collapse of the system. Obviously, the above calculation results show that the classical index may give conclusions completely contrary to the actual state of the system, while the proposed index can accurately give the state of the system strength.

[0113] The above phenomenon can be well explained by the complex exponential "LPSCRC∠φ C ", whose value is shown in the complex plane of Figure 8 Load shedding rotates LPSCRC∠φ C from quadrant I to quadrant III and reduces the magnitude of the exponent. The reduction in magnitude reflects the reduction in system strength. The rotation of the phase angle reflects the direction of the power flow, indicating that the AC voltage increases. When t = 0s to 0.5s, the power flow is from the equivalent power source to the PCC, indicating that the active power consumed by the AC load is more than the active power provided by the HVDC.

[0114] As the receiving end, the PCC is at a low voltage. When t = 1.5s - 2.5s, LPSCRC∠φ CLocated in Quadrant III, i.e., the power flow is from the PCC to the AC power source. The PCC becomes the power sending end, which explains the reason for the high voltage in the AC system during the time-domain simulation.

[0115] However, sending does not necessarily mean stability. From the magnitude of LPSCRC∠φ C it can be seen that the system is weakened due to load shedding, eventually leading to voltage collapse.

[0116] Embodiment III

[0117] Illustrate the accuracy and applicability of the system stability boundary expression (14) through simulation.

[0118] To verify the correctness of the boundary, a power system as shown in Figure 2 is built in the Power System Analysis Software Package (PSASP) environment, and the critical operating points are obtained through numerical simulation. All the critical operating points obtained from the simulation calculations are marked with cross symbols in Figure 9 and Figure 10 The dotted line in the figure is the boundary given by the classical SCR index, and the other solid lines are the calculated boundaries depicted by the proposed formula (14). Obviously, the boundaries are fitted quite well. Boundary point simulation process: Calculate the power flow by using the specified equivalent active power and equivalent reactive power and calculate with an equivalent impedance step of 1Ω. Once the power flow does not converge to a certain equivalent impedance, the equivalent active and reactive powers used in the previous step are marked as the critical points.

[0119] Figure 9 Shows the situation where the HVDC active power is locally consumed. In particular, the solid line with Qeq = 0.1 gives the boundary when the inverter reactive power consumption compensates for most of the reactive power. In this case, the classical SCR is less than 1.0 (see the line graph in the lower left corner), but the system can still operate stably, and this curve is already outside the boundary described by the classical SCR. Obviously, compared with the boundary index based on LPSCR, the classical SCR index performs better. Similarly, this phenomenon also appears in Figure 10

[0120] An embodiment of another aspect of the present invention provides a DC feeding short-circuit ratio calculation system considering the influence of AC loads, as shown in Figure 11 The system 110 includes:

[0121] A first conversion module 1101 for equivalent the power system with DC feeding into an equivalent AC network including AC loads;

[0122] ​The second conversion module 1102 is used to convert the equivalent AC network into a π-type equivalent circuit. The π-type equivalent circuit includes three equivalent impedances, which are obtained by the star-delta transformation of the AC load and the AC system impedance respectively;

[0123] The calculation module 1103 is used to calculate the direct current load retention short circuit ratio LPSCR based on the π-type equivalent circuit. Its expression is:

[0124]

[0125] where E is the equivalent power supply amplitude, Z eq is the total equivalent impedance of the system, P dc is the active power injected by the direct current, P LDeq is the active power consumed by the equivalent load.

[0126] The calculation module 1103 further includes:

[0127] The stability boundary solving module can determine the system stability boundary based on the LPSCR and LPSCR C through the following formula:

[0128]

[0129] where S eq , P eq , Q eq are the equivalent total complex power, equivalent active power and equivalent reactive power respectively, SCC P and SCC Q are the short circuit capacity components based on the equivalent resistance and reactance of the system.

[0130] The calculation module 1103 further includes:

[0131] Calculate the complex form of the direct current load retention short circuit ratio LPSCR C , and its expression is:

[0132]

[0133] where SCC C ∠θ C is the complex form of the short circuit capacity, S˙ dc and S˙ LDeq are the complex power injected by the direct current and the complex power of the equivalent load respectively.

[0134] The equivalent impedance of the π-type equivalent circuit is calculated by the following formula:

[0135]

[0136] where Z1 and Z2 are the equivalent impedances of the original system, ZLD is the load impedance of the original system.

[0137] An embodiment of another aspect of the present invention provides a computer-readable storage medium storing computer-executable instructions for executing the above-mentioned Figure 4 DC feed-in short-circuit ratio calculation method considering the influence of AC load as shown.

[0138] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0139] Those of ordinary skill in the art can understand that all or some of the steps and systems disclosed above can be implemented as software, firmware, hardware, and their appropriate combinations. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit. Such software can be distributed on a computer-readable medium, which can include a computer storage medium (or non-transitory medium) and a communication medium (or transitory medium). As is well known to those of ordinary skill in the art, the term computer storage medium includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory, or other memory technologies, CD-ROM, digital versatile disk (DVD), or other optical disk storage, magnetic cassette, tape, magnetic disk storage, or other magnetic storage devices, or any other medium that can be used to store the desired information and can be accessed by a computer. In addition, as is well known to those of ordinary skill in the art, a communication medium typically includes computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and can include any information delivery medium.

[0140] The above is a specific description of the preferred embodiments of the present application, but the present application is not limited to the above embodiments. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present application, and these equivalent deformations or substitutions are all included in the scope defined by the claims of the present application.

Claims

1. A calculation method for the short-circuit ratio of DC feed-in considering the influence of AC load, characterized in that, Including the following steps: Equivalent a power system with DC feed-in into an equivalent AC network containing AC loads; Convert the equivalent AC network into a π-type equivalent circuit, and the π-type equivalent circuit includes three equivalent impedances, which are obtained by star-delta transformation of the AC loads and the AC system impedance respectively; Based on the π-type equivalent circuit, calculate the DC load retention short-circuit ratio LPSCR, and its expression is: Among them, E is the equivalent power supply amplitude, and Z eq is the total equivalent impedance of the system, and P dc is the active power injected by DC, { LDeq is the active power consumed by the equivalent load.

2. The method according to claim 1, characterized in that, Based on the π - type equivalent circuit, the step of calculating the direct - current load retention short - circuit ratio LPSCR further includes: calculating the direct - current load retention short - circuit ratio LPSCR in complex form C , and its expression is: Among them, SCC C ∠θ C is the short-circuit capacity in complex form, and are the complex power of DC injection and the complex power of equivalent load respectively.

3. The method according to claim 1, characterized in that In the step of converting the equivalent AC network into a π-type equivalent circuit, where the π-type equivalent circuit includes three equivalent impedances obtained by star-delta transformation of the AC loads and the AC system impedance respectively, the equivalent impedance of the π-type equivalent circuit is calculated by the following formula: Among them, Z1 and Z2 are the equivalent impedances of the original system, and Z LD is the load impedance of the original system.

4. The method according to claim 1, wherein The method further includes the step of: based on the LPSCR and LPSCR C , determining the system stability boundary through the following formula: Among them, S eq , P eq , Q eq are the equivalent total complex power, equivalent active power, and equivalent reactive power respectively, and SCC P and SCC Q are the short-circuit capacity components based on the equivalent resistance and reactance of the system.

5. The method according to any one of claims 1-4, characterized in that In the step of equivalent the power system with DC feed-in into an equivalent AC network containing AC loads, the method of equivalent to the equivalent AC network includes REI equivalent, WARD equivalent or the method of identifying Thevenin parameters based on measurements.

6. A DC feeding short-circuit ratio calculation system considering the influence of AC loads, characterized in that, Including: A first conversion module for equivalent a power system with DC feed-in into an equivalent AC network containing AC loads; A second conversion module for converting the equivalent AC network into a π-type equivalent circuit, and the π-type equivalent circuit includes three equivalent impedances, which are obtained by star-delta transformation of the AC loads and the AC system impedance respectively; A calculation module for calculating the DC load retention short-circuit ratio LPSCR based on the π-type equivalent circuit, and its expression is: Among them, E is the equivalent power supply amplitude, and Z eq is the total equivalent impedance of the system, and P dc is the active power injected by DC, and P LDeq is the active power consumed by the equivalent load.

7. The system according to claim 6, wherein The calculation module includes: Calculate the DC load in complex form and retain the short-circuit ratio LPSCR C , and its expression is: Among them, SCC C ∠θ C is the short-circuit capacity in complex form, and are the complex power of DC injection and the complex power of equivalent load respectively.

8. The system according to claim 6, characterized in that, In the second conversion module, the equivalent impedance of the π-type equivalent circuit is calculated by the following formula: Among them, Z1 and Z2 are the equivalent impedances of the original system, and Z LD is the load impedance of the original system.

9. The system according to claim 6, wherein The system further includes: A stable boundary solving module, capable of determining the system stable boundary based on the LPSCR and LPSCR C , through the following formula: Among them, S eq , P eq , Q eq are the equivalent total complex power, equivalent active power, and equivalent reactive power respectively, and SCC P and SCC Q are the short-circuit capacity components based on the equivalent resistance and reactance of the system.

10. A computer-readable storage medium, characterized in that, A computer program is stored, and when the program is executed by a processor, it realizes the steps of the method according to any one of claims 1-5.

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