Method and device for directly analyzing full-time-domain short-circuit current of network construction type power electronic conversion equipment

Abstract

The invention relates to the field of power system protection and control, in particular to a full-time-domain short-circuit current direct analysis method and device for network construction type power electronic conversion equipment, and the method comprises the steps: calculating a virtual short-circuit fault parameter of a grid-connected point of the network construction type power electronic conversion equipment, and building a fault power grid dimension reduction equivalent model; calculating port voltage amplitudes and power angles of the network construction type power electronic conversion equipment in a subtransient stage, a transient stage and a steady-state stage under a power grid fault; establishing external characteristic equivalent models of a subtransient stage, a transient stage and a steady-state stage of the network construction type power electronic conversion equipment under a power grid fault; and calculating the short-circuit current in the sub-transient stage, the transient stage and the steady-state stage of the network construction type power electronic conversion equipment. The method does not depend on actual fault parameters, and online calculation of subtransient, transient and steady-state short-circuit currents of the network construction type power electronic conversion equipment at any fault position and fault transition resistance is achieved.

Description

Technical Field

[0001] The present invention relates to the field of power system protection and control, and in particular to a method and device for directly analyzing full-time-domain short-circuit current of grid-type power electronic conversion equipment. Background Art

[0002] With the widespread adoption of power electronics at the source, grid, and load levels, new power systems are becoming highly electronic. To ensure that power electronic converters operate within a safe stress range, their control during grid faults exhibits multi-scale cascading and sequential switching. Traditional fault analysis methods, based on the linear superposition principle and focusing on synchronous motors, struggle to accurately analyze the response characteristics of power electronic converters during grid faults, challenging the effectiveness of the grid's "three lines of defense."

[0003] Domestic and international scholars have conducted extensive research on the modeling of grid-connected power electronic converters. Currently, relatively detailed fault response models for both single-unit and cluster-level grid-connected power electronic converters have been established. However, the control structures of grid-connected and grid-connected power electronic converters are distinct, making their fault response models incompatible. Because the grid's frequency and voltage immunity decreases with the decreasing proportion of synchronous motors, virtual synchronous machine-controlled power electronic converters, which provide inertia and damping for the grid, have attracted research attention. Existing modeling of grid-connected power electronic converters is primarily focused on scenarios such as power flow calculations or small-signal stability analysis, and research on fault response models for grid-connected power electronic converters is still in its infancy. Some researchers model grid-connected power electronic converters under grid faults as equivalent to a voltage source series reactance model, but ignore the controller's response process. Based on the differences in control response speeds of the current inner loop, reactive power-voltage outer loop, and active power-phase outer loop, some researchers have developed a second-order equivalent model for grid-connected power electronic converters under grid faults and a transient model for grid-connected power electronic converters that accounts for voltage dynamics. However, the existing technology ignores the sudden change of the complex impedance of the faulty grid caused by the three-phase short-circuit fault, and it is difficult to characterize the coupling of active and reactive power, port voltage amplitude and phase in the modeling of grid-type power electronic conversion equipment under the influence of the complex impedance of the faulty grid, which affects the accuracy of the fault response model.

[0004] In power grid planning and relay protection configuration, the short-circuit current level of grid-type power electronic conversion equipment is usually calculated offline based on the fault response model and the fault grid model. Using node voltage as an intermediate variable, technicians jointly establish the node voltage matrix of the fault grid and the fault response model of the grid-type power electronic conversion equipment modeling, and propose a full-grid quasi-Newton iterative calculation method and a regional iterative method for short-circuit current, respectively. To avoid non-convergence of the iteration of the high-order node voltage matrix for the modeling of grid-type power electronic conversion equipment, some technicians reduce the order of the detailed fault grid to the form of a voltage source in series with the reactance. Based on this, some technicians take into account the balanced current and fault current limiting control strategy during asymmetric short circuits, and propose analytical methods for short-circuit current modeling of grid-type power electronic conversion equipment under symmetrical faults and asymmetric faults, respectively. The above studies all assume that the parameters such as the potential amplitude and reactance of the fault grid are known. However, online calculation of short-circuit current is often required during real-time operation of power grids. However, due to the limitations of fault detection and communication delays, the technical route of sending actual fault parameters to grid-type power electronic conversion equipment for modeling and then analyzing the short-circuit current is difficult to meet the online calculation requirements of short-circuit current level monitoring and dynamic setting of protection devices.

[0005] In summary, how to identify the fault grid parameters by relying solely on the electrical quantities at the ports of the grid-type power electronic conversion equipment, quantify the coupling of the complex power and voltage amplitude of the grid-type power electronic conversion equipment under the influence of the complex impedance of the fault grid, establish an equivalent model of the external characteristics of the grid-type power electronic conversion equipment, and realize the online calculation of the short-circuit current of the grid-type power electronic conversion equipment without relying on the actual fault parameters has become an urgent problem that technicians in this field need to solve. Summary of the Invention

[0006] In order to achieve online calculation of short-circuit current of grid-type power electronic conversion equipment without relying on actual fault parameters, the present invention proposes a direct analysis method for the full-time domain short-circuit current of grid-type power electronic conversion equipment. The rectifier of the grid-type power electronic conversion equipment adopts constant DC voltage control, and the inverter adopts virtual synchronous machine control. The inverter controlled by the virtual synchronous machine includes an active power-phase outer loop controller, a reactive power-voltage outer loop controller, and an AC current limit controller. The full-time domain short-circuit current refers to the fault response process of the reference synchronous motor. According to the time scale of the response of the grid-type power electronic conversion equipment controller, the short-circuit current of the grid-type power electronic conversion equipment is divided into a sub-transient stage, a transient stage, and a steady-state stage. The short-circuit current analysis is achieved by using the electrical quantities of the port of the grid-type power electronic conversion equipment, which specifically includes the following steps:

[0007] S101: monitoring the grid connection point voltage of the grid-connected power electronic conversion equipment, and determining that a grid fault has occurred when the grid connection point voltage drops outside the normal operating range;

[0008] S102: collecting voltage amplitude, voltage phase, active power and reactive power at the port of grid-forming power electronic conversion equipment at the moment of grid fault;

[0009] S103: Calculate the parameters of a virtual short-circuit fault occurring at the grid-connected point of the grid-connected power electronic conversion equipment, and establish a dimensionality reduction equivalent model of the faulty power grid;

[0010] S104: Calculate the port voltage amplitude and power angle of the grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage under the power grid fault;

[0011] S105: Establish an equivalent model of the external characteristics of grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage under power grid fault;

[0012] S106: Calculate the short-circuit current of the grid-type power electronic conversion equipment in the sub-transient, transient and steady-state stages.

[0013] Existing technologies ignore the sudden change in the complex impedance of the faulty grid caused by three-phase short-circuit faults, making it difficult to characterize the coupling of active and reactive power, port voltage amplitude, and phase of grid-type power electronic conversion equipment under the influence of the faulty grid complex impedance, thus affecting the accuracy of the external characteristic equivalent model. Furthermore, existing technologies assume that fault parameters such as the voltage drop amplitude at the grid connection point are known, and online short-circuit current calculations are often required during real-time grid operation. However, due to fault detection and communication delays, the technical approach of sending actual fault parameters to the grid-type power electronic conversion equipment and then analyzing the short-circuit current is unable to meet the online calculation requirements for short-circuit current level monitoring and dynamic setting of protection devices. Compared with the existing technology, the present invention combines the faulty grid dimensionality reduction equivalent model and the grid-type power electronic conversion equipment external characteristic equivalent model to directly calculate the full-time domain short-circuit current of the grid-type power electronic conversion equipment. In other words, the present invention can achieve online calculation of subtransient, transient, and steady-state short-circuit currents of the grid-type power electronic conversion equipment under any fault location and fault transition resistance without relying on actual fault parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to make the purpose, technical solutions and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0015] Figure 1 This is a flow chart of a method for direct analysis of full-time domain short-circuit current in grid-type power electronic conversion equipment according to an embodiment of the present invention;

[0016] Figure 2 Schematic diagram of a full-time domain short-circuit current direct analysis device for grid-type power electronic conversion equipment according to an embodiment of the present invention.

[0017] Figure 3 This is a structural diagram of a grid-type power electronic conversion device under a power grid fault according to an embodiment of the present invention;

[0018] Figure 4 These are effect diagrams under the embodiments of the present invention, wherein Figure (a) is a relationship diagram between time and short-circuit current of grid-type power electronic conversion equipment, Figure (b) is a relationship diagram between time and port voltage of grid-type power electronic conversion equipment, Figure (c) is a relationship diagram between time and phase of grid-type power electronic conversion equipment, Figure (d) is a relationship diagram between time and active power of grid-type power electronic conversion equipment, and Figure (e) is a relationship diagram between time and reactive power of grid-type power electronic conversion equipment. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] The present invention proposes a direct analysis method for the full-time domain short-circuit current of a grid-type power electronic conversion equipment. The rectifier of the grid-type power electronic conversion equipment adopts constant DC voltage control, and the inverter adopts virtual synchronous machine control. The inverter controlled by the virtual synchronous machine includes an active power-phase outer loop controller, a reactive power-voltage outer loop controller and an AC current limit controller. The full-time domain short-circuit current refers to the fault response process of the reference synchronous motor. According to the time scale of the response of the controller of the grid-type power electronic conversion equipment, the short-circuit current of the grid-type power electronic conversion equipment is divided into a sub-transient stage, a transient stage and a steady-state stage. The electrical quantities of the port of the grid-type power electronic conversion equipment are used to realize the short-circuit current analysis, such as Figure 1 , specifically including the following steps:

[0021] S101: monitoring the grid connection point voltage of the grid-connected power electronic conversion equipment, and determining that a grid fault has occurred when the grid connection point voltage drops outside the normal operating range;

[0022] S102: collecting voltage amplitude, voltage phase, active power and reactive power at the port of grid-forming power electronic conversion equipment at the moment of grid fault;

[0023] S103: Calculate the parameters of a virtual short-circuit fault occurring at the grid-connected point of the grid-connected power electronic conversion equipment, and establish a dimensionality reduction equivalent model of the faulty power grid;

[0024] S104: Calculate the port voltage amplitude and power angle of the grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage under the power grid fault;

[0025] S105: Establish an equivalent model of the external characteristics of grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage under power grid fault;

[0026] S106: Calculate the short-circuit current of the grid-type power electronic conversion equipment in the sub-transient, transient and steady-state stages.

[0027] Figure 1 Flowchart of the method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to an embodiment of the present invention. Figure 1 As shown, the method includes the following steps:

[0028] In step S101 of the embodiment of the present invention, a voltage threshold can be set in the protection and control system of the grid-type power electronic equipment. When the grid connection point voltage exceeds or falls below the set value, an alarm signal is issued to start the disclosed invention. The voltage threshold here can be a preset voltage threshold, which can be set to 0.9pu. That is, when the grid connection point voltage of the grid-type power electronic equipment drops below 0.9pu, it can be determined that a three-phase short circuit fault has occurred in the power grid, and the full-time domain short-circuit current direct analysis of the grid-type power electronic conversion equipment is started.

[0029] In step S102 of the embodiment of the present invention, a synchronized phasor measurement unit is installed at the outlet of the grid-type power electronic conversion equipment, which can measure the port voltage amplitude and phase, active power and reactive power in real time with high precision.

[0030] In step S103 of the embodiment of the present invention, the virtual short-circuit fault parameters include the virtual short-circuit fault transition resistance and reactance, which are determined as follows:

[0031] S1031-A: Based on the instantaneous voltage and phase of the grid-forming power electronic conversion equipment, the reactive power of the grid-forming power electronic conversion equipment, the equivalent potential and reactance of the grid during normal operation, and the equivalent reactance of the connecting transformer, the first parameter of the virtual short-circuit fault is calculated and expressed as:

[0032]

[0033] Among them, α is the first parameter of virtual short circuit fault; U GFC.f The port voltage of the grid-type power electronic conversion equipment at the moment of grid failure; Q GFC.f For the instantaneous construction of grid-type power electronic conversion equipment reactive power for power grid failure; X T is the equivalent reactance of the grid when connected to the transformer; X G.N E is the equivalent reactance of the power grid during normal operation; G.N is the equivalent potential of the power grid during normal operation; θ GFC.f The voltage phase of the port of grid-type power electronic conversion equipment is constructed at the moment of grid fault.

[0034] S1031-B: Based on the instantaneous voltage and phase of the grid-forming power electronic conversion equipment port, the active power of the grid-forming power electronic conversion equipment, the equivalent potential and reactance of the grid during normal operation, and the equivalent reactance of the connecting transformer, the second parameter of the virtual short-circuit fault is calculated and expressed as:

[0035] β=P GFC.f (X T +X G.N )-E G.N U GFC.f sinθ GFC.f

[0036] Among them, β is the second parameter of virtual short circuit fault; P GFC.f It is a grid-type power electronic conversion device that can convert active power to meet the instantaneous power grid failure.

[0037] S1031-C: Based on the instantaneous voltage at the port of the grid-forming power electronic conversion equipment, the active and reactive power of the grid-forming power electronic conversion equipment, the equivalent reactance of the grid during normal operation, the equivalent reactance of the connecting transformer, and the first and second parameters of the virtual short-circuit fault, the virtual short-circuit fault transition resistance and reactance are calculated, including:

[0038]

[0039] Among them, R V.f is the virtual short-circuit fault transition resistance; X V.f It is the transition reactance of virtual short circuit fault.

[0040] In step S103 of the embodiment of the present invention, the fault power grid dimensionality reduction equivalent model is composed of a constant voltage source, a series reactance, and a parallel virtual short-circuit fault transition impedance. The constant voltage source and the series reactance are the equivalent potential and equivalent reactance of the power grid during normal operation, respectively. The equivalent potential of the power grid during normal operation is equal to the rated voltage. The equivalent reactance of the power grid during normal operation is determined by the following method:

[0041] S1032-A: Based on the active and reactive power of the grid-forming power electronic conversion equipment during normal operation, the port voltage of the grid-forming power electronic conversion equipment during normal operation, and the equivalent potential of the grid during normal operation, the first parameter of the equivalent reactance of the grid during normal operation is calculated and expressed as:

[0042]

[0043] S1032-B: Based on the active and reactive power of the grid-forming power electronic conversion equipment during normal operation and the port voltage of the grid-forming power electronic conversion equipment during normal operation, the second parameter of the equivalent reactance of the grid during normal operation is calculated and expressed as:

[0044]

[0045] S1032-C: The equivalent reactance of the grid during normal operation is calculated by subtracting the equivalent reactance of the connected transformer from the sum of the first and second parameters of the grid equivalent reactance during normal operation, that is:

[0046]

[0047] Among them, P GFC.N It is the active power of the grid-type power electronic conversion equipment during normal operation; Q GFC.N It is the reactive power of the grid-type power electronic conversion equipment during normal operation; U GFC.N It is the port voltage of grid-type power electronic conversion equipment during normal operation.

[0048] In the present invention, the port voltage and power angle of a grid-type power electronic conversion device under a power grid fault can be obtained based on a synchronized phasor measurement unit. In step S104 of an embodiment of the present invention, a method for confirming the port voltage and power angle of a grid-type power electronic conversion device during a sub-transient phase under a power grid fault is proposed, wherein obtaining the power angle and port voltage of the grid-type power electronic conversion device during a sub-transient phase under a power grid fault includes:

[0049] S1041-A: Based on the active power of the grid-type power electronic conversion equipment during normal operation, the equivalent reactance of the grid during normal operation, and the equivalent reactance of the connecting transformer, the first parameter of the power angle in the sub-transient phase, namely P GFC.N (X G.N +X T ).

[0050] S1041-B: Based on the port voltage of the grid-type power electronic conversion equipment and the equivalent potential of the grid during normal operation, the second parameter of the power angle in the sub-transient phase, namely U GFC.N E G.N .

[0051] S1041-C: The power angle of the grid-connected power electronic conversion equipment in the subtransient phase under a power grid fault is calculated by dividing the first parameter of the power angle in the subtransient phase by the arc sine of the second parameter, and is expressed as:

[0052]

[0053] in, The power angle of the grid-type power electronic conversion equipment in the sub-transient stage under power grid fault is constructed.

[0054] The acquisition of the port voltage of the grid-type power electronic conversion equipment in the sub-transient stage under a power grid fault includes:

[0055] S1042-A: Calculate the first parameter of the fault grid equivalent resistance based on the product of the virtual short-circuit fault transition resistance and the equivalent reactance of the grid during normal operation. Calculate the second parameter of the fault grid equivalent resistance based on the sum of the square of the virtual short-circuit fault transition reactance and the equivalent reactance of the grid during normal operation and the virtual short-circuit fault transition resistance. Calculate the fault grid equivalent resistance by dividing the first parameter of the fault grid equivalent resistance by the second parameter, that is:

[0056]

[0057] S1042-B: Calculate the first parameter of the fault grid equivalent reactance based on the virtual short-circuit fault transition resistance and reactance and the equivalent reactance of the grid during normal operation; calculate the second parameter of the fault grid equivalent reactance based on the square of the virtual short-circuit fault transition resistance, the square of the sum of the virtual short-circuit fault transition reactance and the equivalent reactance of the grid during normal operation; calculate the equivalent reactance of the fault grid by dividing the first parameter of the fault grid equivalent reactance by the second parameter, that is:

[0058]

[0059] S1042-C: The first parameter of the equivalent potential of the fault grid is obtained by taking the square root of the sum of the squares of the equivalent resistance and the equivalent reactance of the fault grid. The equivalent potential of the fault grid is calculated by dividing the first parameter of the equivalent potential of the fault grid by the equivalent reactance of the normal operation grid and then multiplying it by the equivalent potential of the normal operation grid, that is:

[0060]

[0061] The vector form of the equivalent potential of the fault power grid is expressed as:

[0062]

[0063] Among them, e G.N is the equivalent potential vector of the power grid during normal operation; e G.f is the equivalent potential vector of the fault power grid; R G.f is the resistance component of the fault grid equivalent impedance; X G.f is the reactance component of the equivalent impedance of the fault grid; j represents an imaginary unit.

[0064] S1042-D: Based on the reactive power-voltage droop coefficient of the grid-type power electronic conversion equipment, the equivalent reactance of the fault grid, and the equivalent reactance of the connecting transformer, the first voltage parameter of the subtransient stage is calculated, namely:

[0065] A=K GFC (X G.f +X T ).

[0066] S1042-E: Based on the equivalent resistance and reactance of the fault grid, the equivalent reactance of the connecting transformer, the equivalent potential of the fault grid, the reactive power-voltage droop coefficient, and the power angle of the grid-type power electronic conversion equipment in the subtransient phase under the grid fault, the second voltage parameter in the subtransient phase is calculated, namely:

[0067]

[0068] Among them, the parameter Z f and ε Z is the intermediate parameter.

[0069] S1042-F: Based on the reactive power-voltage droop coefficient of the grid-type power electronic conversion equipment, the reactive power reference value of the grid-type power electronic conversion equipment, the rated voltage, the equivalent resistance and reactance of the fault grid, and the equivalent reactance of the connecting transformer, the third voltage parameter in the subtransient phase is calculated, namely:

[0070]

[0071] S1042-G: Based on the first, second, and third voltage parameters of the sub-transient phase, calculate the port voltage of the grid-type power electronic conversion equipment during the sub-transient phase under the power grid fault, that is:

[0072]

[0073] in, It is the port voltage of the grid-type power electronic conversion equipment in the sub-transient stage under power grid fault.

[0074] In step S104 of the embodiment of the present invention, the port voltage and power angle of the grid-type power electronic conversion equipment in the transient phase under the power grid fault are determined as follows:

[0075] S1043-A: Based on the reactive power-voltage droop coefficient of the grid-type power electronic conversion equipment, the equivalent potential of the fault grid, the equivalent resistance and reactance of the fault grid, and the equivalent reactance of the connecting transformer, a sub-function of the power angle in the transient phase is constructed. Based on the sub-function of the power angle in the transient phase and the first and third voltage parameters in the sub-transient phase, a function of the port voltage of the grid-type power electronic conversion equipment in the transient phase under the grid fault with respect to the power angle is constructed. This function is expressed as:

[0076]

[0077]

[0078] in, It is the function of the port voltage of the grid-type power electronic conversion equipment in the transient stage with respect to the power angle under the power grid fault; is the sub-function of the power angle in the transient stage; It is the power angle of the grid-type power electronic conversion equipment in the transient stage under power grid fault.

[0079] S1043-B: Based on the virtual inertia coefficient and damping coefficient of the grid-type power electronic conversion equipment, the equivalent potential of the fault grid, the equivalent resistance and reactance of the fault grid, the equivalent reactance of the connecting transformer, and the function of the port voltage of the grid-type power electronic conversion equipment in the transient phase under the grid fault with respect to the power angle, a differential equation for the transient power angle of the grid-type power electronic conversion equipment under the grid fault is constructed, which is expressed as:

[0080]

[0081] Among them, J GFC The virtual inertia coefficient of the grid-type power electronic conversion equipment; D GFC Provide virtual damping coefficient for grid-type power electronic conversion equipment; It is the first-order derivative of the power angle of the grid-type power electronic conversion equipment in the transient stage under the power grid fault; The second-order derivative of the power angle of the grid-type power electronic conversion equipment in the transient phase under power grid fault; It is the active power reference value of grid-type power electronic conversion equipment.

[0082] S1043-C: Use the Runge-Kutta algorithm to solve the differential equation of the power angle of the grid-type power electronic conversion equipment in the transient phase under the power grid fault, and obtain the time domain analytical expression of the power angle of the grid-type power electronic conversion equipment in the transient phase under the power grid fault; substitute the time domain analytical expression of the power angle of the grid-type power electronic conversion equipment in the transient phase under the power grid fault into the function of the port voltage with respect to the power angle, and obtain the time domain analytical expression of the port voltage in the transient phase under the power grid fault.

[0083] In step S104 of the embodiment of the present invention, the port voltage and power angle of the grid-type power electronic conversion equipment in the steady-state phase under a grid fault are determined as follows:

[0084] S1044-A1: If the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current, the grid-type power electronic conversion equipment maintains the voltage source characteristics in the steady-state phase under a grid fault. The voltage source characteristic parameters are calculated based on the equivalent potential of the fault grid, the equivalent resistance and reactance of the fault grid, the equivalent reactance of the interconnecting transformer, and the active and reactive power control reference values ​​of the grid-type power electronic conversion equipment. The port voltage of the grid-type power electronic conversion equipment in the steady-state phase under a grid fault is calculated based on the voltage source characteristic parameters, the equivalent resistance and reactance of the fault grid, the equivalent reactance of the interconnecting transformer, and the active and reactive power control reference values ​​of the grid-type power electronic conversion equipment, and is expressed as:

[0085]

[0086] in, is the port voltage of the grid-type power electronic conversion equipment in the steady state under grid fault; D is an intermediate parameter, and its expression is

[0087] S1044-A2: Based on the equivalent resistance and reactance of the faulty grid, the equivalent potential of the faulty grid, the equivalent reactance of the connecting transformer, the reactive power control reference value of the grid-type power electronic conversion equipment, and the port voltage of the grid-type power electronic conversion equipment in the steady-state stage under the grid fault, the power angle of the grid-type power electronic conversion equipment in the steady-state stage under the grid fault is calculated and expressed as:

[0088]

[0089] in, The power angle of the grid-type power electronic conversion equipment in the steady state stage is constructed under power grid fault.

[0090] S1044-B1: If the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is greater than the maximum allowable AC current, the grid-type power electronic conversion equipment switches to a current source characteristic in the steady-state phase under a grid fault. The first parameter of the current source characteristic is calculated based on the maximum allowable AC current of the grid-type power electronic conversion equipment, the AC current phase when the AC current limiting control of the grid-type power electronic conversion equipment is activated, the equivalent resistance and reactance of the fault grid, and the equivalent reactance of the connecting transformer. The port voltage of the grid-type power electronic conversion equipment in the steady-state phase under the grid fault is calculated based on the first parameter of the current source characteristic, the maximum allowable AC current of the grid-type power electronic conversion equipment, the equivalent resistance and reactance of the fault grid, and the equivalent potential of the fault grid, and is expressed as:

[0091]

[0092] Among them, μ is an intermediate parameter, expressed as The maximum allowable AC current for grid-type power electronic conversion equipment.

[0093] S1044-B2: Based on the port voltage of the grid-type power electronic conversion equipment in the steady-state phase under a grid fault, the maximum allowable AC current of the grid-type power electronic conversion equipment, the AC current phase when the AC current limit control of the grid-type power electronic conversion equipment is activated, the equivalent resistance and reactance of the fault grid, and the equivalent reactance of the connecting transformer, the power angle of the grid-type power electronic conversion equipment in the steady-state phase under a grid fault is calculated and expressed as:

[0094]

[0095] in, AC current phase when AC current limit control is activated for grid-type power electronic conversion equipment.

[0096] In step S105 of the embodiment of the present invention, the equivalent model of the external characteristics of the grid-type power electronic conversion equipment in the sub-transient, transient and steady-state stages under the power grid fault is determined as follows:

[0097] The port voltage and power angle of the grid-type power electronic conversion equipment in the sub-transient phase under power grid faults constitute the external characteristic equivalent model of the sub-transient phase, which can be equivalent to a constant voltage source with constant amplitude and phase;

[0098] The port voltage and power angle of the grid-type power electronic conversion equipment in the transient phase under power grid fault constitute the external characteristic equivalent model of the transient phase, which can be equivalent to a controlled voltage source with time-varying amplitude and phase.

[0099] If the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current, the port voltage and power angle of the grid-type power electronic conversion equipment in the steady-state stage under a grid fault constitute an external characteristic equivalent model of the steady-state stage, which can be equivalent to a constant voltage source with constant amplitude and phase; otherwise, the AC current amplitude and phase of the grid-type power electronic conversion equipment in the steady-state stage under a grid fault constitute an external characteristic equivalent model of the steady-state stage, which is equivalent to a constant current source with constant amplitude and phase.

[0100] In step S106 of the embodiment of the present invention, the short-circuit current of the grid-type power electronic conversion equipment in the sub-transient stage under the power grid fault is determined according to the following method:

[0101] S1061-A: Based on the port voltage and power angle of the grid-type power electronic conversion equipment in the subtransient phase under the power grid fault, and the equivalent potential of the fault grid, the first parameter of the short-circuit current in the subtransient phase is calculated; based on the equivalent potential of the fault grid, the first parameter of the short-circuit current in the subtransient phase, the power angle of the grid-type power electronic conversion equipment in the subtransient phase under the power grid fault, the equivalent resistance and reactance of the fault grid, and the equivalent reactance of the connecting transformer, the short-circuit current amplitude of the grid-type power electronic conversion equipment in the subtransient phase under the power grid fault is calculated, namely:

[0102]

[0103] in, is the short-circuit current amplitude of the grid-connected power electronic conversion equipment in the subtransient stage under power grid fault; M is an intermediate parameter, expressed as:

[0104] S1061-B: The second and third parameters of the subtransient short-circuit current are calculated based on the equivalent potential of the fault grid, the first parameter of the subtransient short-circuit current, the power angle of the grid-type power electronic conversion equipment during the subtransient phase under the grid fault, the equivalent resistance and reactance of the fault grid, and the equivalent reactance of the connecting transformer. The phase of the short-circuit current of the subtransient short-circuit current of the grid-type power electronic conversion equipment during the subtransient phase under the grid fault is obtained by dividing the second parameter of the subtransient short-circuit current by the inverse tangent of the third parameter, that is:

[0105]

[0106] in, It represents the short-circuit current phase of the grid-connected power electronic conversion equipment in the sub-transient stage under a power grid fault.

[0107] In step S106 of the embodiment of the present invention, the short-circuit current of the grid-type power electronic conversion equipment in the transient phase under the power grid fault is determined as follows:

[0108] S1062-A: The first parameter of the short-circuit current in the transient phase is obtained based on the equivalent resistance and reactance of the fault grid, the equivalent potential of the fault grid, the port voltage amplitude and the power angle time-domain analytical expression of the grid-type power electronic conversion equipment in the transient phase under the grid fault; the second parameter of the short-circuit current in the transient phase is obtained based on the first parameter of the short-circuit current in the transient phase, the first and third voltage parameters in the subtransient phase, the power angle time-domain analytical expression of the grid-type power electronic conversion equipment in the transient phase under the grid fault, and the equivalent potential of the fault grid; the third parameter of the short-circuit current in the transient phase is calculated based on the first voltage parameter in the subtransient phase, the equivalent resistance and reactance of the fault grid, and the equivalent reactance of the connecting transformer; the amplitude of the short-circuit current in the transient phase of the grid-type power electronic conversion equipment in the transient phase under the grid fault is calculated by dividing the second parameter of the transient short-circuit current by the third parameter of the short-circuit current and taking the root, that is:

[0109]

[0110] in, It is the short-circuit current amplitude of the grid-type power electronic conversion equipment in the transient stage under the power grid fault; is a function of the power angle of the grid-type power electronic conversion equipment in the transient phase, which can be expressed as:

[0111] S1062-B: Based on the first parameter of the short-circuit current in the transient phase, the equivalent resistance and reactance of the fault grid, the equivalent potential of the fault grid, the equivalent reactance of the connecting transformer, the first and third parameters of the voltage in the subtransient phase, and the time-domain analytical expression of the power angle of the grid-type power electronic conversion equipment in the transient phase under the grid fault, the fourth and fifth parameters of the short-circuit current in the transient phase are calculated; by dividing the fourth parameter of the short-circuit current in the transient phase by the fifth parameter and then taking the arcsine, the short-circuit current phase of the grid-type power electronic conversion equipment in the transient phase under the grid fault is calculated, that is:

[0112]

[0113] in, It is the instantaneous power angle of the grid-type power electronic conversion equipment in the transient stage under power grid fault.

[0114] In step S106 of the embodiment of the present invention, the short-circuit current of the grid-type power electronic conversion equipment in the steady-state phase under the power grid fault is determined as follows:

[0115] S1063-A: If the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current, a first parameter of the short-circuit current in the steady-state phase is obtained based on the equivalent resistance and reactance of the fault grid, the equivalent potential of the fault grid, and the port voltage and power angle of the grid-type power electronic conversion equipment in the steady-state phase under the grid fault. A second parameter of the short-circuit current in the steady-state phase is calculated based on the first parameter of the short-circuit current in the steady-state phase, the equivalent potential of the fault grid, and the power angle of the grid-type power electronic conversion equipment in the steady-state phase under the grid fault. A third parameter of the short-circuit current in the steady-state phase is calculated based on the equivalent resistance and reactance of the fault grid and the equivalent reactance of the connecting transformer. The amplitude of the short-circuit current in the steady-state phase of the grid-type power electronic conversion equipment under the grid fault is calculated by dividing the second parameter of the steady-state short-circuit current by the third parameter and taking the root, namely:

[0116]

[0117] in, It represents the short-circuit current amplitude of the grid-type power electronic conversion equipment in the steady state under the power grid fault; N is an intermediate parameter, which is expressed as

[0118] S1063-B: The fourth and fifth parameters of the short-circuit current in the steady-state phase are calculated based on the first parameter of the short-circuit current in the steady-state phase, the equivalent resistance and reactance of the fault grid, the equivalent potential of the fault grid, the equivalent reactance of the connecting transformer, and the power angle of the grid-type power electronic conversion equipment in the steady-state phase under the grid fault. The phase of the short-circuit current in the steady-state phase of the grid-type power electronic conversion equipment in the steady-state phase under the grid fault is calculated by dividing the fourth parameter of the short-circuit current in the steady-state phase by the fifth parameter and then calculating the arc sine, that is:

[0119]

[0120] in, It is the short-circuit current phase of the grid-type power electronic conversion equipment in the steady-state stage under power grid fault.

[0121] S1063-C: If the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is greater than or equal to the maximum allowable AC current, the short-circuit current of the grid-type power electronic conversion equipment in the steady-state phase under a grid fault is determined as follows:

[0122]

[0123] in, The maximum permissible AC current for grid-type power electronic conversion equipment; The current phase of the grid-forming power electronic conversion equipment in the steady state under a grid fault when the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-forming power electronic conversion equipment is greater than or equal to the maximum allowable AC current; Indicates the reactive current reference value of grid-type power electronic conversion equipment; It represents the active current reference value of grid-type power electronic conversion equipment.

[0124] The embodiment of the present invention establishes an equivalent model of the external characteristics of the grid-type power electronic conversion equipment through steps S101-S106, relying solely on port electrical quantities, and describes the variation patterns of the port voltage amplitude and phase of the grid-type power electronic conversion equipment in the subtransient, transient, and steady-state stages. It also proposes a direct analysis principle for the short-circuit current of the grid-type power electronic conversion equipment that does not rely on actual fault parameters, and realizes the online calculation of the short-circuit current of the grid-type power electronic conversion equipment under any fault location and fault transition resistance.

[0125] The embodiment of the present invention also provides a full-time domain short-circuit current direct analysis device for grid-type power electronic conversion equipment, such as Figure 2 As shown. It includes: a synchronized phasor measurement unit and a direct analysis unit; wherein the direct analysis unit includes:

[0126] A virtual short-circuit fault parameter calculation module is used to calculate the virtual short-circuit fault transition resistance and reactance;

[0127] Fault power grid dimension reduction equivalent modeling module, used to establish an equivalent network consisting of a constant voltage source, series reactance and parallel virtual short-circuit fault transition impedance;

[0128] External characteristic equivalent modeling module, used to calculate the port voltage amplitude and power angle of grid-type power electronic conversion equipment in the sub-transient, transient and steady-state stages under power grid faults;

[0129] The short-circuit current direct analysis module calculates the short-circuit current of grid-type power electronic conversion equipment in the sub-transient, transient and steady-state stages.

[0130] In order to verify the effectiveness of the present invention, Figure 3 The structural diagram of the grid-type power electronic conversion equipment under the power grid fault shown in the figure is used as an example for analysis. In this embodiment, the grid-type power electronic conversion equipment is connected to the 2-zone 4-machine network through a step-up transformer. The rated capacity of the grid-type power electronic conversion equipment is 100MW, and the virtual inertia and damping coefficient are 0.3kg×m 2 and 1000, the reactive power-AC voltage droop coefficient of the grid-type power electronic conversion equipment is 0.002, and the maximum allowable AC current is 1.1pu; the rated voltage of the grid is 220kV, and the unit reactance of the transmission line is 0.94×10 -3 H / km; a three-phase short-circuit fault occurs in the grid at 0.3s, and the fault is cleared after 200ms. During the grid fault, the active and reactive power reference values ​​of the grid-connected power electronic conversion equipment are determined in accordance with the "T / CES243-2023 Technical Specifications for Grid Connection of Grid-Connected Energy Storage Systems" to avoid the grid-connected power electronic conversion equipment from being locked due to transient synchronous instability and AC current exceeding the limit.

[0131] To validate the disclosed method for direct analysis of short-circuit currents in the full time domain of grid-connected power electronic converters, the comparison group included numerical simulation results of a detailed model of the grid-connected power electronic converter under grid fault conditions. The short-circuit current, port voltage amplitude and phase, and active and reactive power of the grid-connected power electronic converter were recorded and analyzed.

[0132] According to the aforementioned step S101, the proposed method starts after detecting that the grid-type power electronic conversion equipment drops below 0.9 pu;

[0133] According to the aforementioned step S102, electrical quantities at the ports of the grid-forming power electronic conversion equipment at the moment of the grid fault are collected;

[0134] According to the aforementioned step S103, the phase of the complex impedance of the faulty grid is 72.3°, indicating that the resistance component in the equivalent impedance of the faulty grid cannot be ignored;

[0135] According to the aforementioned step S104, the voltage amplitude and phase of the port of the grid-forming power electronic conversion equipment during the grid fault are calculated;

[0136] According to the aforementioned step S105 , the short-circuit current of the grid-connected power electronic conversion equipment during the grid fault is calculated.

[0137] Figure 4(a) through (e) are waveforms of the short-circuit current, port voltage amplitude and phase, and active and reactive power of a grid-connected power electronic conversion device. The horizontal axis represents time, while the vertical axis represents the short-circuit current, port voltage amplitude and phase, and active and reactive power of the grid-connected power electronic conversion device. The solid line represents the comparison curve, while the dashed line represents the curve obtained using the method disclosed in this invention for direct analysis of the full-time-domain short-circuit current of a grid-connected power electronic conversion device.

[0138] according to Figure 4 As can be seen from (a) to (e), there is a certain amplitude and phase deviation between the analytical waveform and the simulated waveform in the first few milliseconds after the fault occurs, but the analytical waveform soon coincides with the simulated waveform. The maximum error of the external characteristics appears at the initial moment of the sub-transient stage, and its value is about 5.4%; the maximum error of the three-phase short-circuit current in the transient and steady-state stages is about 2.1%. Since the current deviation caused by the non-ideal response of the filter resistance and the current inner loop controller is very small, the calculation error will remain within a small range under different fault conditions. Therefore, the direct analysis method for the full-time domain short-circuit current of the grid-type power electronic conversion equipment disclosed in the present invention can accurately capture the fault external characteristics of the direct analysis method for the full-time domain short-circuit current of the grid-type power electronic conversion equipment under different fault locations, transition resistances and control parameters.

[0139] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A direct analytical method for the full-time domain short-circuit current of a grid-type power electronic conversion equipment, wherein the rectifier of the grid-type power electronic conversion equipment adopts constant DC voltage control, and the inverter adopts virtual synchronous machine control. The inverter controlled by the virtual synchronous machine includes an active power-phase outer loop controller, a reactive power-voltage outer loop controller, and an AC current limit controller; the full-time domain short-circuit current refers to the fault response process of a reference synchronous motor, and according to the time scale of the response of the controller of the grid-type power electronic conversion equipment, the short-circuit current of the grid-type power electronic conversion equipment is divided into a sub-transient stage, a transient stage, and a steady-state stage; the characteristics are: Using the electrical quantities at the ports of the grid-type power electronic conversion equipment, direct analysis of the short-circuit current is achieved, which specifically includes the following steps: S101: monitoring the grid connection point voltage of the grid-connected power electronic conversion equipment, and determining that a grid fault has occurred when the grid connection point voltage drops outside the normal operating range; S102: collecting voltage amplitude, voltage phase, active power and reactive power at the port of grid-forming power electronic conversion equipment at the moment of grid fault; S103: Calculate the parameters of a virtual short-circuit fault occurring at the grid-connected point of the grid-connected power electronic conversion equipment, and establish a dimensionality reduction equivalent model of the faulty power grid; S104: Calculate the port voltage amplitude and power angle of the grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage under the power grid fault; S105: Establish an equivalent model of the external characteristics of grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage under power grid fault; S106: Calculate the short-circuit current of the grid-type power electronic conversion equipment in the sub-transient, transient and steady-state stages.

2. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 1 is characterized in that: The calculation process of virtual short-circuit fault parameters includes: β=P GFC.f (X T +X G.N )-E G.N U GFC.f sinth GFC.f Among them, R V.f is the transition resistance of the virtual short-circuit fault; β is the second parameter of the virtual short-circuit fault; U GFC.f The port voltage of the grid-type power electronic conversion equipment at the moment of power grid failure; X G.N is the equivalent reactance of the power grid during normal operation; α is the first parameter of the virtual short-circuit fault; P GFC.f Active power of grid-connected power electronic conversion equipment at the moment of grid failure; Q GFC.f For the instantaneous construction of grid-type power electronic conversion equipment reactive power for power grid failure; X T is the equivalent reactance of the connected transformer; X V.f E is the virtual short-circuit fault transition reactance; G.N is the equivalent potential of the power grid during normal operation; θ GFC.f The voltage phase of the port of grid-type power electronic conversion equipment is constructed at the moment of grid fault.

3. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 1 is characterized in that: The dimensionality reduction equivalent model of the fault power grid is an equivalent network composed of a constant voltage source, a series reactance and a parallel virtual short-circuit fault transition impedance. The constant voltage source and the series reactance are the equivalent potential and equivalent reactance of the power grid during normal operation, respectively. During normal operation, the equivalent potential of the power grid is equal to the rated voltage.

4. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 2 or 3, characterized in that: The acquisition of equivalent reactance of the power grid during normal operation includes: Among them, X G.N U is the equivalent reactance of the power grid during normal operation; GFC.N P is the port voltage of the grid-type power electronic conversion equipment during normal operation; GFC.N It is the active power of the grid-type power electronic conversion equipment during normal operation; Q GFC.N The reactive power of the grid-type power electronic conversion equipment during normal operation; E G.N is the equivalent potential of the power grid during normal operation; X T is the equivalent reactance of the connected transformer.

5. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 1, characterized in that: The process of constructing the equivalent model of the external characteristics of grid-connected power electronic conversion equipment in the sub-transient stage, transient stage, and steady-state stage under power grid faults includes: The port voltage and power angle of the grid-type power electronic conversion equipment in the sub-transient phase under power grid faults constitute the external characteristic equivalent model of the sub-transient phase, which is equivalent to a constant voltage source with constant amplitude and phase. The port voltage and power angle of the grid-type power electronic conversion equipment in the transient phase under power grid faults constitute the external characteristic equivalent model of the transient phase, which is equivalent to a controlled voltage source with time-varying amplitude and phase. If the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current, the port voltage and power angle of the grid-type power electronic conversion equipment in the steady-state stage under a grid fault constitute an external characteristic equivalent model of the steady-state stage, which is equivalent to a constant voltage source with constant amplitude and phase; otherwise, the AC current amplitude and phase of the grid-type power electronic conversion equipment in the steady-state stage under a grid fault constitute an external characteristic equivalent model of the steady-state stage, which is equivalent to a constant current source with constant amplitude and phase.

6. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 1 or 5, characterized in that: The short-circuit current amplitude and current phase of the grid-connected power electronic conversion equipment in the sub-transient stage under power grid fault are: in, is the short-circuit current amplitude of the grid-connected power electronic conversion equipment in the sub-transient stage under power grid fault; M is an intermediate parameter; E G.f is the equivalent potential of the fault power grid; is the power angle of the grid-type power electronic conversion equipment in the sub-transient stage under power grid fault; R G.f is the resistance component of the fault grid equivalent impedance; X G.f is the reactance component of the fault grid equivalent impedance; X T is the equivalent reactance of the connected transformer; To construct the short-circuit phase of the sub-transient stage of the grid-type power electronic conversion equipment under power grid fault; It is the port voltage amplitude of the grid-type power electronic conversion equipment in the sub-transient stage under power grid fault.

7. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 1 or 5, characterized in that: The short-circuit current amplitude and current phase of the grid-connected power electronic conversion equipment in the transient stage under power grid fault are: in, It is the short-circuit current amplitude of the grid-type power electronic conversion equipment in the transient stage under the power grid fault; is the function of the power angle of the grid-type power electronic conversion equipment in the transient stage; E G.f is the equivalent potential of the fault power grid; is the instantaneous power angle of the grid-type power electronic conversion equipment during the transient phase under power grid fault; R G.f is the resistance component of the fault grid equivalent impedance; X G.f is the reactance component of the fault grid equivalent impedance; X T is the equivalent reactance of the connected transformer; K GFC Reactive power-voltage droop coefficient for grid-type power electronic conversion equipment; Z f , ε Z is the intermediate parameter; A is the first voltage parameter in the sub-transient stage; C is the third voltage parameter in the sub-transient stage; It is the reactive power reference value of the grid-connected power electronic conversion equipment during the power grid fault period; U0 is the rated voltage; It is the short-circuit phase of the transient stage of the grid-type power electronic conversion equipment under the power grid fault.

8. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 1 or 5, characterized in that: When the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current, the short-circuit current amplitude and current phase of the grid-type power electronic conversion equipment in the steady-state stage under a grid fault are: in, The short-circuit current amplitude when the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current; N is the intermediate parameter; E G.f is the equivalent potential of the fault power grid; When the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current, the power angle of the grid-type power electronic conversion equipment; R G.f is the resistance component of the fault grid equivalent impedance; X G.f is the reactance component of the fault grid equivalent impedance; X T is the equivalent reactance of the connected transformer; The short-circuit current phase when the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current; It is the voltage amplitude at the port of the grid-type power electronic conversion equipment when the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is less than the maximum allowable AC current.

9. The method for direct analysis of full-time domain short-circuit current of grid-type power electronic conversion equipment according to claim 1 or 5, characterized in that: When the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-forming power electronic conversion equipment is greater than or equal to the maximum allowable AC current, the short-circuit current amplitude and current phase of the grid-forming power electronic conversion equipment in the steady-state stage under a grid fault are: in, The short-circuit current amplitude when the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-type power electronic conversion equipment is greater than the maximum allowable AC current, The maximum allowable AC current of grid-type power electronic conversion equipment; The current phase of the grid-forming power electronic conversion equipment in the steady state under a grid fault when the modulus of the active and reactive current reference values ​​output by the voltage inner loop of the grid-forming power electronic conversion equipment is greater than or equal to the maximum allowable AC current; Indicates the reactive current reference value of grid-type power electronic conversion equipment; It represents the active current reference value of grid-type power electronic conversion equipment.

10. A full-time domain short-circuit current direct analysis device for grid-type power electronic conversion equipment, characterized in that: The method for directly analyzing the full-time domain short-circuit current of the grid-type power electronic conversion equipment according to claim 1 comprises a synchronized phasor measurement unit and a direct analysis unit, wherein the direct analysis unit comprises: A virtual short-circuit fault parameter calculation module is used to calculate the virtual short-circuit fault transition resistance and reactance; Fault power grid dimension reduction equivalent modeling module, used to establish an equivalent network consisting of a constant voltage source, series reactance and parallel virtual short-circuit fault transition impedance; External characteristic equivalent modeling module, used to calculate the port voltage amplitude and power angle of grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage under power grid fault; The short-circuit current calculation module calculates the short-circuit current of the grid-type power electronic conversion equipment in the sub-transient stage, transient stage and steady-state stage.

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