Converter station modeling method and device suitable for initial transient period of fault

Abstract

The application discloses a converter station modeling method and device suitable for a fault initial transient period. The method calculates a first equivalent inductance and a first equivalent resistance of a converter transformer in a converter station model according to a leakage reactance unit value of the converter transformer, a high-voltage side rated voltage of the converter transformer, a rated capacity of the converter transformer and a copper loss unit value of the converter transformer; calculates a first inductance and a first capacitance of a filter in the converter station model according to the high-voltage side rated voltage of the converter transformer, a low-voltage side rated voltage of the converter transformer, an actual inductance of the filter in the converter station and an actual capacitance of the filter in the converter station; and constructs an equivalent circuit of the converter station according to the first equivalent inductance, the first equivalent resistance, the first inductance and the first capacitance to obtain the converter station model. The application can simplify the construction of the converter station model and reduce the complexity of model construction.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid, and particularly relates to a converter station modeling method and device suitable for a fault initial transient period. BACKGROUND

[0002] The power source in the new power system is transitioning from the traditional synchronous generator to the inverter type power electronic equipment, and as the proportion of new energy power generation is getting higher and higher, the structure, parameters and characteristics of the power grid have also changed significantly, which brings great challenges to fault analysis and relay protection. The power electronic type power equipment acts as a power source after a fault, which is characterized by being controlled, time-varying and nonlinear, and its fault transient process is very different from the traditional power system with synchronous generators as the main body, thereby causing the conventional relay protection device to possibly malfunction. As of now, there have been many cases of new energy power generation system and AC-DC hybrid system protection malfunction in the power grid, which brings great challenges to the safe operation of the power grid, and ensuring the safe operation of the low-inertia new power system has become a major and urgent national demand.

[0003] In a low-inertia system with a large number of power electronic equipment access, studying the modeling method of the converter station is a prerequisite for clarifying the fault mechanism of the system and accurately conducting fault analysis, which is of great value to ensuring the safe and reliable operation of the low-inertia new power system and quickly and accurately removing faults, thereby shortening the power outage time.

[0004] The converter station is the hub of the low-inertia new power system, and the current modeling method for the converter station in the initial transient period of a fault still uses a detailed model for simulation calculation, which is too complex and cannot be well applied to the low-inertia system scenario with a large number of power electronic equipment access. SUMMARY

[0005] The embodiment of the present application provides a converter station modeling method and device suitable for a fault initial transient period, which can simplify the modeling of the converter station in the initial transient period of a fault.

[0006] The embodiment of the present application provides a converter station modeling method suitable for a fault initial transient period, comprising: calculating a first equivalent inductance of a converter transformer in a converter station model according to a leakage reactance per unit of the converter transformer winding, a high-voltage side rated voltage of the converter transformer and a rated capacity of the converter transformer;

[0007] calculating a first equivalent resistance of the converter transformer in the converter station model according to the leakage reactance per unit of the converter transformer winding, the high-voltage side rated voltage of the converter transformer and a copper loss per unit of the converter transformer;

[0008] calculating a first inductance of a filter in the converter station model according to the high-voltage side rated voltage of the converter transformer, a low-voltage side rated voltage of the converter transformer and an actual inductance of the filter in the converter station;

[0009] Calculate the first capacitance of the filter in the converter station model based on the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station;

[0010] An equivalent circuit of the converter station is constructed according to the first equivalent inductor, the first equivalent resistor, the first inductor, and the first capacitor to obtain a converter station model.

[0011] Furthermore, the calculation of the first equivalent inductance of the converter transformer in the converter station model according to the per-unit value of the converter transformer winding leakage reactance, the rated voltage of the high-voltage side of the converter transformer, and the rated capacity of the converter transformer includes:

[0012] The first equivalent inductance is calculated using the following formula:

[0013] Among them, L" s is the first equal value inductor; X” pu is the per-unit leakage reactance of the converter transformer winding; U NH is the rated voltage of the high-voltage side of the converter transformer; f is the power frequency, S N is the rated capacity of the converter transformer.

[0014] Furthermore, the first equivalent resistance of the converter transformer in the converter station model is calculated according to the per-unit value of the converter transformer winding leakage reactance, the rated voltage of the high-voltage side of the converter transformer, and the per-unit value of the copper loss of the converter transformer, including:

[0015] Calculate the first equal value resistor according to the following formula:

[0016] Among them, R s is the first equal value resistor; R pu is the per-unit value of the converter transformer copper loss.

[0017] Furthermore, the calculating of the first inductance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual inductance of the filter in the converter station includes:

[0018] The first inductance is calculated using the following formula:

[0019] Among them, L' s is the first inductor; U NL is the rated voltage of the low-voltage side of the converter transformer; L is the actual inductance of the filter in the converter station.

[0020] Furthermore, the calculating of the first capacitance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station includes:

[0021] The first capacitance is calculated using the following formula:

[0022] Among them, C s is the first capacitor; C is the actual capacitance of the filter in the converter station.

[0023] Based on the above method embodiment, the present invention provides a corresponding device embodiment;

[0024] An embodiment of the present invention provides a converter station modeling device suitable for the initial transient period of a fault, comprising: a first equivalent inductance determination module, a first equivalent resistance determination module, a first inductance determination module, a first capacitance determination module, and a simplified model construction module;

[0025] The first equivalent inductance determination module is configured to calculate the first equivalent inductance of the converter transformer in the converter station model according to the per-unit value of the leakage reactance of the converter transformer winding, the rated voltage of the high-voltage side of the converter transformer, and the rated capacity of the converter transformer;

[0026] A first equivalent resistance determination module is configured to calculate a first equivalent resistance of the converter transformer in the converter station model according to a per-unit value of the leakage reactance of the converter transformer winding, a per-unit value of the rated voltage on the high-voltage side of the converter transformer, and a per-unit value of the copper loss of the converter transformer;

[0027] a first inductance determination module, configured to calculate a first inductance of the filter in the converter station model according to the rated voltage on the high-voltage side of the converter transformer, the rated voltage on the low-voltage side of the converter transformer, and the actual inductance of the filter in the converter station;

[0028] A first capacitance determination module is configured to calculate a first capacitance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station;

[0029] The simplified model construction module is used to construct an equivalent circuit of the converter station according to the first equivalent inductor, the first equivalent resistor, the first inductor and the first capacitor to obtain a converter station model.

[0030] Furthermore, the first equivalent inductance determination module calculates the first equivalent inductance using the following formula:

[0031] Among them, L" s is the first equal value inductor; X” pu is the per-unit leakage reactance of the converter transformer winding; U NH is the rated voltage of the high-voltage side of the converter transformer; f is the power frequency, S N is the rated capacity of the converter transformer.

[0032] Furthermore, the first equivalent resistance determination module calculates the first equivalent resistance according to the following formula:

[0033] Among them, R s is the first equal value resistor; R pu is the per-unit value of the converter transformer copper loss.

[0034] Furthermore, the first inductance determination module calculates the first inductance using the following formula:

[0035] Among them, L' s is the first inductor; U NL is the rated voltage of the low-voltage side of the converter transformer; L is the actual inductance of the filter in the converter station.

[0036] Furthermore, the first capacitance determination module calculates the first capacitance using the following formula:

[0037] Among them, C s is the first capacitor; C is the actual capacitance of the filter in the converter station.

[0038] The following beneficial effects are achieved by implementing the present invention:

[0039] An embodiment of the present invention provides a converter station modeling method and device suitable for the initial instant of a fault. During the initial instant of a fault, the converter station has not yet responded to the disturbance. This stage is short and is a wave process stage. The signal energy is concentrated in the high frequency band. This type of high-frequency signal is blocked outside the filter circuit and cannot reach the converter. Therefore, it is only necessary to consider the response of the converter station filter circuit and the converter transformer to the high-frequency signal transmitted from the outside. For this reason, the response characteristics of the converter station to the first traveling wave of the initial instant of a fault can be equivalent to the series connection of the equivalent impedance of the converter transformer and the AC LC filter, thereby constructing a converter station model. To this end, the present invention calculates the first equivalent inductance and first equivalent resistance of the converter transformer in the converter station model based on the per-unit value of the converter transformer winding leakage reactance, the rated voltage on the high-voltage side of the converter transformer, the rated capacity of the converter transformer, and the per-unit value of the converter transformer copper loss. The present invention also calculates the first inductance and first capacitance of the filter in the converter station model based on the rated voltage on the high-voltage side of the converter transformer, the rated voltage on the low-voltage side of the converter transformer, the actual inductance of the filter in the converter station, and the actual capacitance of the filter in the converter station. Finally, an equivalent circuit of the converter station is constructed based on the first equivalent inductance, first equivalent resistance, first inductance, and first capacitance to obtain the converter station model. Compared with the prior art, this method only needs to consider the response of the converter transformer and filter in the converter station to external high-frequency signals, greatly simplifying the converter station model construction process, reducing the amount of computation required, and ensuring balanced accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The figure is a flow chart of a converter station modeling method applicable to the initial transient period of a fault, provided by one embodiment of the present invention.

[0041] Figure 2 This is a schematic diagram of the structure of a typical solar photovoltaic grid-connected system.

[0042] Figure 3 Schematic diagram of the equivalent model of the converter station in the photovoltaic grid-connected system during the initial fault period.

[0043] Figure 4 This is a schematic diagram of the equivalent circuit of the converter station in the photovoltaic grid-connected system during the initial fault period.

[0044] Figure 5 This is a schematic diagram of the Peterson equivalent circuit of a single-mode fault component when a fault occurs in an AC line.

[0045] Figure 6 Figure 3 is a diagram showing the relative error between the single-mode fault component voltage at the grid connection point based on traveling wave theory and the simulation results.

[0046] Figure 7 This is a schematic structural diagram of a converter station modeling device suitable for the initial transient period of a fault, provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0047] 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. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0048] like Figure 1 As shown, an embodiment of the present invention provides a converter station modeling method applicable to the initial transient period of a fault, comprising:

[0049] Step S101: Calculate the first equivalent inductance of the converter transformer in the converter station model according to the per-unit value of the converter transformer winding leakage reactance, the rated voltage of the high-voltage side of the converter transformer, and the rated capacity of the converter transformer.

[0050] Step S102: Calculate the first equivalent resistance of the converter transformer in the converter station model according to the per-unit value of the converter transformer winding leakage reactance, the rated voltage of the high-voltage side of the converter transformer, and the per-unit value of the copper loss of the converter transformer.

[0051] Step S103: Calculate the first inductance of the filter in the converter station model according to the rated voltage on the high-voltage side of the converter transformer, the rated voltage on the low-voltage side of the converter transformer, and the actual inductance of the filter in the converter station.

[0052] Step S104: Calculate the first capacitance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station.

[0053] Step S105: constructing an equivalent circuit of the converter station according to the first equivalent inductor, the first equivalent resistor, the first inductor, and the first capacitor to obtain a converter station model.

[0054] Regarding step S101, in a preferred embodiment, the first equivalent inductance of the converter transformer in the converter station model is calculated according to the per-unit value of the converter transformer winding leakage reactance, the rated voltage of the high-voltage side of the converter transformer, and the rated capacity of the converter transformer, including:

[0055] The first equivalent inductance is calculated using the following formula:

[0056] Among them, L" s is the first equal value inductor; X” pu is the per-unit leakage reactance of the converter transformer winding; U NH is the rated voltage of the high-voltage side of the converter transformer; f is the power frequency, S N is the rated capacity of the converter transformer.

[0057] Regarding step S102, in a preferred embodiment, calculating the first equivalent resistance of the converter transformer in the converter station model according to the per-unit value of the converter transformer winding leakage reactance, the rated voltage of the high-voltage side of the converter transformer, and the per-unit value of the converter transformer copper loss includes:

[0058] Calculate the first equal value resistor according to the following formula:

[0059] Among them, R s is the first equal value resistor; R pu is the per-unit value of the converter transformer copper loss.

[0060] Regarding step S103, in a preferred embodiment, calculating the first inductance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual inductance of the filter in the converter station includes:

[0061] The first inductance is calculated using the following formula:

[0062] Among them, L' s is the first inductor; U NL is the rated voltage of the low-voltage side of the converter transformer; L is the actual inductance of the filter in the converter station.

[0063] Regarding step S104, in a preferred embodiment, calculating the first capacitance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station includes:

[0064] The first capacitance is calculated using the following formula:

[0065] Among them, C s is the first capacitor; C is the actual capacitance of the filter in the converter station.

[0066] For step S105, specifically, after calculating the first equivalent inductance, the first equivalent resistance, the first inductance and the first capacitance, an equivalent circuit of the converter transformer and the filter connected in series is constructed, and the constructed equivalent circuit is used as the converter station model to complete the construction of the converter station model.

[0067] In order to better illustrate the technical solution disclosed in the present invention, the technical solution disclosed in the present invention is further described below.

[0068] like Figure 2 As shown, Figure 2 This is a typical solar photovoltaic grid-connected system, which includes solar photovoltaic power supply, DC-DC boost converter, two-level VSC grid-connected inverter, filter and converter transformer and other main equipment. During the initial fault period, the converter station only needs to consider the response of the converter station filter circuit and converter transformer to the high-frequency signal transmitted from the outside, so the converter station can be equivalent to Figure 3 At this time, the first equivalent inductance, the first equivalent resistance, the first inductance and the first capacitance are calculated according to the above steps S101-S104, and then the first equivalent inductance and the first capacitance are constructed. Figure 4 The equivalent circuit shown is the final converter station model. Figure 4 Ls is the sum of the first equal-value inductance and the first inductance.

[0069] Furthermore, the converter station model is obtained by using step S105. In order to eliminate the coupling between the lines, the corresponding Karenbauer phase model transformation decoupling transformation is:

[0070]

[0071] Among them, F a 、F b 、F c is a three-phase voltage, where F0, F1, and F2 are the voltage 0, 1, and 2 mode components respectively.

[0072] like Figure 5 As shown, Figure 5This is the Peterson equivalent circuit of the first-mode fault component when an AC line fault occurs. Focus on the fault component network under the first mode, Δu f1 It represents the amplitude of the traveling wave of the fault component voltage at the fault point. According to Peterson's law, the power supply potential in the equivalent circuit is equal to twice the incident wave of the fault component voltage. c1 Indicates the first-mode impedance of the line, C s1 , L s1 and R s1 Represents the first-mode parameters of the filter and converter transformer.

[0073] In the equivalent circuit, the fault component voltage traveling wave propagates from the fault point to the photovoltaic grid-connected point, encounters the photovoltaic grid-connected system boundary at this point, and is then reflected. Therefore, the single-mode fault component voltage at the PCC point is the superposition of the incident wave and the reflected wave at the PCC point, which can be expressed as:

[0074]

[0075] Where Z s1 The equivalent impedance of the converter station boundary elements is:

[0076]

[0077] Δu f1 Represents the amplitude of the voltage traveling wave of the first-mode fault component:

[0078]

[0079] Where U a (0 - ), U b (0 - ), U c (0 - ) represent the voltage amplitude of each phase before the fault, Z c1 , Z c2 , Z c0 Respectively represent the first mode, second mode and zero mode wave impedance of the line, R f represents the transition resistance, f (AG) , f (AB) , f (ABG) , f (ABC) They represent single-phase grounding, two-phase short circuit, two-phase grounding short circuit and three-phase short circuit faults respectively.

[0080] Based on this, the single-mode fault component voltage at the PCC point when a fault occurs is:

[0081]

[0082] Furthermore, through the inverse Laplace transform, the time domain expression of the single-mode fault component voltage at the PCC point when the fault occurs is obtained:

[0083]

[0084] Among them, α and β represent the attenuation coefficients:

[0085]

[0086] At the initial moment of the fault, the first traveling wave of the single-mode fault component voltage at the grid connection point can be interpreted as the initial traveling wave at the fault point superimposed with two attenuation exponents.

[0087] The time domain expression of the single-mode fault component voltage at the PCC point when the fault occurs is compared with the simulation results.

[0088] In a specific example, the relative error between the voltage of a fault component of a module and the relative error of the simulation result is shown as follows: Figure 6 The results show that the converter station model constructed by the present invention is effective in the initial transient stage of the fault.

[0089] Based on the above method embodiment, the present invention provides a corresponding device embodiment;

[0090] like Figure 7 As shown, an embodiment of the present invention provides a converter station modeling device suitable for the initial transient period of a fault, comprising: a first equivalent inductance determination module, a first equivalent resistance determination module, a first inductance determination module, a first capacitance determination module, and a simplified model construction module;

[0091] The first equivalent inductance determination module is configured to calculate the first equivalent inductance of the converter transformer in the converter station model according to the per-unit value of the leakage reactance of the converter transformer winding, the rated voltage of the high-voltage side of the converter transformer, and the rated capacity of the converter transformer;

[0092] A first equivalent resistance determination module is configured to calculate a first equivalent resistance of the converter transformer in the converter station model according to a per-unit value of the leakage reactance of the converter transformer winding, a per-unit value of the rated voltage on the high-voltage side of the converter transformer, and a per-unit value of the copper loss of the converter transformer;

[0093] a first inductance determination module, configured to calculate a first inductance of the filter in the converter station model according to the rated voltage on the high-voltage side of the converter transformer, the rated voltage on the low-voltage side of the converter transformer, and the actual inductance of the filter in the converter station;

[0094] A first capacitance determination module is configured to calculate a first capacitance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station;

[0095] The simplified model construction module is used to construct an equivalent circuit of the converter station according to the first equivalent inductor, the first equivalent resistor, the first inductor and the first capacitor to obtain a converter station model.

[0096] In a preferred embodiment, the first equivalent inductance determination module calculates the first equivalent inductance by the following formula: Among them, L" s is the first equal value inductor; X” pu is the per-unit leakage reactance of the converter transformer winding; U NH is the rated voltage of the high-voltage side of the converter transformer; f is the power frequency, S N is the rated capacity of the converter transformer.

[0097] In a preferred embodiment, the first equivalent resistance determination module calculates the first equivalent resistance according to the following formula: Among them, R s is the first equal value resistor; R pu is the per-unit value of the converter transformer copper loss.

[0098] In a preferred embodiment, the first inductance determination module calculates the first inductance by the following formula: Among them, L' s is the first inductor; U NL is the rated voltage of the low-voltage side of the converter transformer; L is the actual inductance of the filter in the converter station.

[0099] In a preferred embodiment, the first capacitance determination module calculates the first capacitance using the following formula: Among them, C s is the first capacitor; C is the actual capacitance of the filter in the converter station.

[0100] It should be noted that the device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed across multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment. In addition, in the drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art can understand and implement the present invention without inventive effort.

[0101] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0102] The above is the preferred embodiment of the present application, it should be pointed out that, for those skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements are also considered to be within the scope of the present application.

Claims

1. A converter station modeling method suitable for the initial fault period, characterized in that: include: Calculate the first equivalent inductance of the converter transformer in the converter station model based on the per-unit value of the converter transformer winding leakage reactance, the rated voltage on the high-voltage side of the converter transformer, and the rated capacity of the converter transformer; Calculate the first equivalent resistance of the converter transformer in the converter station model based on the rated voltage of the high-voltage side of the converter transformer and the per-unit value of the copper loss of the converter transformer; Calculate the first inductance of the filter in the converter station model based on the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual inductance of the filter in the converter station; Calculate the first capacitance of the filter in the converter station model based on the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station; constructing an equivalent circuit of the converter station according to the first equivalent inductor, the first equivalent resistor, the first inductor, and the first capacitor to obtain a converter station model; The first equal-value inductance is calculated using the following formula: ; in, is the first equal value inductance; is the per-unit leakage reactance of the converter transformer winding; U NH is the rated voltage of the high-voltage side of the converter transformer; f is the power frequency, S N is the rated capacity of the converter transformer; The first equal value resistor is calculated according to the following formula: ; in, is the first equal value resistor; R pu is the per-unit value of the converter transformer copper loss; The first inductance is calculated by the following formula: ; in, is the first inductor; U NL is the rated voltage of the low-voltage side of the converter transformer; is the actual inductance of the filter in the converter station; The first capacitance is calculated by the following formula: ; in, is the first capacitor; is the actual capacitance of the filter in the converter station.

2. A converter station modeling device suitable for the initial fault period, characterized in that: include: a first equivalent inductance determination module, a first equivalent resistance determination module, a first inductance determination module, a first capacitance determination module, and a simplified model construction module; The first equivalent inductance determination module is configured to calculate the first equivalent inductance of the converter transformer in the converter station model according to the per-unit value of the leakage reactance of the converter transformer winding, the rated voltage of the high-voltage side of the converter transformer, and the rated capacity of the converter transformer; A first equivalent resistance determination module is configured to calculate a first equivalent resistance of the converter transformer in the converter station model according to the rated voltage of the high-voltage side of the converter transformer and the per-unit value of the copper loss of the converter transformer; a first inductance determination module, configured to calculate a first inductance of the filter in the converter station model according to the rated voltage on the high-voltage side of the converter transformer, the rated voltage on the low-voltage side of the converter transformer, and the actual inductance of the filter in the converter station; A first capacitance determination module is configured to calculate a first capacitance of the filter in the converter station model according to the rated voltage of the high-voltage side of the converter transformer, the rated voltage of the low-voltage side of the converter transformer, and the actual capacitance of the filter in the converter station; a simplified model construction module, configured to construct an equivalent circuit of the converter station according to the first equivalent inductor, the first equivalent resistor, the first inductor, and the first capacitor, to obtain a converter station model; The first equal-value inductance is calculated using the following formula: ; in, is the first equal value inductance; is the per-unit leakage reactance of the converter transformer winding; U NH is the rated voltage of the high-voltage side of the converter transformer; f is the power frequency, S N is the rated capacity of the converter transformer; The first equal value resistor is calculated according to the following formula: ; in, is the first equal value resistor; R pu is the per-unit value of the converter transformer copper loss; The first inductance is calculated by the following formula: ; in, is the first inductor; U NL is the rated voltage of the low-voltage side of the converter transformer; is the actual inductance of the filter in the converter station; The first capacitance is calculated by the following formula: ; in, is the first capacitor; is the actual capacitance of the filter in the converter station.

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