Conservative virtual synchronous generator impedance setting method and device and medium

Abstract

The invention discloses a conservative virtual synchronous generator impedance setting method and device and a medium, and the method comprises the steps: obtaining a first voltage reference value and a second voltage reference value through building an open-loop voltage control model; when the current flowing through the grid-forming converter is smaller than the current limiting amplitude, the voltage of the grid-forming converter is adjusted to be a first voltage reference value, and otherwise, the voltage is adjusted to be a second voltage reference value; and the resistance and inductance of the virtual impedance are controlled in a conservative feasible region. According to the conservative virtual synchronous generator impedance setting method and device and the medium provided by the invention, the voltage is correspondingly adjusted according to the numerical value of the current flowing through the grid-forming converter, and the converter can be ensured to stably operate under various power grid conditions by limiting the parameter of the virtual impedance to change within the preset range; the problem that it is difficult to conduct current limiting on a network-forming type current converter in a simple and convenient virtual impedance setting mode so as to improve the overall performance of the current converter can be solved.

Description

Technical Field

[0001] The invention relates to the field of electric power technology, and in particular to a conservative virtual synchronous generator impedance setting method, device and medium. Background Art

[0002] The massive access to new energy sources has led to a continuous increase in the proportion of power electronic converter-type power sources; at the same time, grid-type converters are more popular than grid-type converters because they can spontaneously provide inertia or frequency support when the power system needs it. However, the grid-type converter has limited current tolerance and requires additional current limiting measures to ensure the safe operation of the converter. Among the traditional current limiting measures, the virtual impedance method and the saturation current method are the two main methods for current limiting grid-type converters, which respectively achieve current limiting protection for grid-type converters by simulating impedance elements and utilizing the saturation characteristics of the elements to ensure their safe operation.

[0003] However, the traditional virtual impedance control mode is relatively complex, and its adjusted virtual impedance can easily cause the converter fault current to be over-restricted under shallow faults, thereby affecting the power delivery of the converter under faults, causing it to fail to meet the low voltage ride-through requirements. Summary of the invention

[0004] The present invention provides a conservative virtual synchronous generator impedance setting method, device and medium to solve the problem that it is difficult to limit the current of a grid-type converter by a simple virtual impedance setting method to improve the overall performance of the converter.

[0005] Obtaining control data of a grid-type converter;

[0006] According to the control data, a first voltage reference value is obtained by establishing an open-loop voltage control model;

[0007] Based on the open-loop voltage control model, a second voltage reference value is established by adding resistance and inductance of a virtual impedance;

[0008] When a fault occurs and causes the current flowing through the grid-type converter to be less than the current limit, the voltage of the grid-type converter is adjusted to the first voltage reference value; otherwise, the voltage is adjusted to the second voltage reference value;

[0009] Controlling the resistance and inductance of the virtual impedance within a conservative feasible domain; wherein the conservative feasible domain is based on the feasible domain of the virtual impedance resistance and the virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops;

[0010] Among them, the feasible domain of the virtual impedance resistor and the virtual impedance inductor is:

[0011]

[0012] Among them, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

[0013] The present invention can obtain a first voltage reference value by establishing an open-loop voltage control model. The first voltage reference value mainly reflects the influence of the internal parameters of the converter on the voltage reference value. Therefore, when it is detected that the current flowing through the grid-type converter is less than the current limit, it means that the system may be experiencing a certain fault or abnormal situation, but has not yet reached a serious overload state; at this time, by quickly adjusting the voltage to the first voltage reference value, it can be ensured that the fluctuation of the output voltage is within an acceptable range. By adding the resistance and inductance of the virtual impedance, the second voltage reference value more comprehensively considers the influence of the resistance and inductance of the entire system on the voltage reference value, which can better adapt to the characteristics of the power grid and reduce the mismatch and conflict with the power grid; therefore, when it is detected that the current flowing through the grid-type converter is greater than or equal to the current limit, it means that the system may be experiencing a certain fault or abnormal situation and has reached a serious overload state, so it is necessary to consider the influence of the entire system on the converter voltage control. At this time, by quickly adjusting the voltage to the second voltage reference value, customized control of the converter voltage output can be achieved, improving the overall performance and efficiency of the system. In addition, the setting of the conservative feasible region is based on the extreme case of grid-side voltage drop. By limiting the resistance and inductance of the virtual impedance within this range, it can ensure that the converter can maintain stable output voltage and current when the grid voltage fluctuates or fails, thereby avoiding system instability or collapse.

[0014] Compared with the prior art, the present invention adjusts the voltage of the mesh converter according to the value of the current flowing through the mesh converter. This flexible and simple fault response mechanism ensures the stability and reliability of the system under different working conditions. By limiting the change of the parameters of the virtual impedance within a preset range, it can ensure that the converter can operate stably under various power grid conditions and achieve effective current limiting. Therefore, it can solve the problem of difficulty in current limiting the mesh converter through a simple virtual impedance setting method to improve the overall performance of the converter.

[0015] As a preferred solution, according to the control data, an open-loop voltage control model is established to obtain a first voltage reference value, specifically:

[0016] In the grid-type converter, based on the control data, a system model is established by equating the right circuit of the common coupling point to an equivalent circuit consisting of an infinite voltage source and a series reactance; wherein the system model represents the difference between the output voltage of the grid-type converter and the voltage at the common coupling point;

[0017] Based on the system model, the open-loop voltage control model is established by controlling the voltage of the common coupling point to be parallel to the d-axis, and the first voltage reference value is obtained according to the open-loop voltage control model.

[0018] This preferred solution can greatly reduce the complexity of the system model by simplifying the complex power system network into an equivalent voltage source and series reactance. This simplification not only reduces the amount of calculation, but also improves the understandability and controllability of the system. In the control of the grid-type converter, by setting the voltage control target to be parallel to the d-axis, that is, the direct axis component in the synchronous rotating coordinate system, the stability of the common coupling point voltage can be more effectively maintained.

[0019] As a preferred solution, the conservative feasible region is based on the feasible region of virtual impedance resistance and virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops, specifically:

[0020] When the grid-side voltage drops, establishing a voltage equation at the common coupling point;

[0021] In combination with the second voltage reference value and the voltage equation, a current equation is established by replacing the voltage and current in the second voltage reference value with the voltage and current when the fault occurs;

[0022] By limiting the current in the current equation to not exceed a preset maximum threshold, a feasible domain of the virtual impedance resistor and the virtual impedance inductor that can meet the current limiting condition is established;

[0023] Based on the feasible domains of the virtual impedance resistor and the virtual impedance inductor, the conservative feasible domain is established according to the voltage of the common coupling point when the grid-side voltage drops.

[0024] In this preferred solution, when the voltage on the grid side drops, by establishing voltage equations and current equations, the grid fault can be evaluated and responded to in real time. By substituting the voltage and current at the time of the fault into the current equation, and combining the condition that the current is limited to not exceed the preset maximum threshold, the feasible range of virtual impedance resistance and inductance values ​​that meet the current limiting conditions can be accurately calculated. In addition, the establishment of the conservative feasible domain not only takes into account the current limiting conditions, but also combines the voltage conditions of the common coupling point when the grid side voltage drops. This comprehensive consideration helps to optimize the operating efficiency and performance of the system while ensuring the safe and stable operation of the system.

[0025] As a preferred solution, based on the feasible domain of the virtual impedance resistor and the virtual impedance inductor, the conservative feasible domain is established according to the voltage of the common coupling point when the grid side voltage drops, specifically:

[0026] When the grid-side voltage drops, a first voltage limiting equation is established by controlling the voltage of the common coupling point to be not higher than the voltage modulus of the common coupling point in a steady state;

[0027] The first voltage limiting equation is calculated by defining the voltage of the common coupling point on the d-axis when the grid-side voltage drops as the negative value of the voltage modulus to obtain a second voltage limiting equation;

[0028] The conservative feasible region is established according to the feasible region of the virtual impedance resistor and the virtual impedance inductor, and the second voltage limiting equation.

[0029] This preferred solution can ensure that the fluctuation of the converter output voltage is limited to a controllable range when the grid-side voltage drops by controlling the voltage at the common coupling point to be no higher than its voltage modulus in the steady state, thereby enhancing the voltage stability.

[0030] As a preferred solution, the conservative feasible region is established according to the feasible region of the virtual impedance resistor and the virtual impedance inductor, and the second voltage limiting equation, specifically:

[0031] The maximum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the second voltage limiting equation is defined as the minimum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the feasible domain of the virtual impedance resistor and the virtual impedance inductor, to obtain an initial conservative feasible domain;

[0032] The frequency in the initial conservative feasible region is replaced by the minimum frequency of the grid-type converter to obtain the conservative feasible region.

[0033] This preferred solution defines the maximum value of the parameters of the second voltage limiting equation as the minimum boundary of the parameters in the feasible domain of the virtual impedance resistor and the virtual impedance inductor, which can ensure that the voltage and current of the system are still limited to a safe range under extreme conditions such as voltage drops, which helps to ensure the safe and stable operation of the system. In addition, by combining the relationship between the virtual impedance resistor and the virtual impedance inductor with the voltage limiting equation, an initial conservative feasible domain that satisfies both voltage limitation and current control can be obtained. By replacing the frequency in the initial conservative feasible domain with the minimum frequency of the converter, it can be ensured that the converter can still operate stably at the lowest frequency, which helps to optimize the performance of the converter and reduce the impact of frequency fluctuations on system stability.

[0034] As a preferred solution, the conservative feasible region is specifically:

[0035]

[0036] Among them, R v is the virtual impedance resistor, L v is the virtual impedance inductor, ω min is the minimum frequency of the grid-type converter, U p is the voltage modulus, I max is the preset maximum current threshold.

[0037] The present invention also provides a conservative virtual synchronous generator impedance setting device, comprising a data module, a model module, a parameter module, an adjustment module and a control module;

[0038] Wherein, the data module is used to obtain control data of the grid-type converter;

[0039] The model module is used to obtain a first voltage reference value by establishing an open-loop voltage control model according to the control data;

[0040] The parameter module is used to establish a second voltage reference value by adding resistance and inductance of a virtual impedance based on the open-loop voltage control model;

[0041] The adjustment module is used to adjust the voltage of the meshed converter to the first voltage reference value when a fault occurs and causes the current flowing through the meshed converter to be less than the current limit, otherwise, adjust the voltage to the second voltage reference value;

[0042] The control module is used to control the resistance and inductance of the virtual impedance within a conservative feasible domain; wherein the conservative feasible domain is based on the feasible domain of the virtual impedance resistance and the virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops;

[0043] Among them, the feasible domain of the virtual impedance resistor and the virtual impedance inductor is:

[0044]

[0045] Among them, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

[0046] As a preferred solution, the model module includes a model unit and a numerical unit;

[0047] The model unit is used to establish a system model in the grid-type converter based on the control data by equating the right circuit of the common coupling point to an equivalent circuit consisting of an infinite voltage source and a series reactance; wherein the system model represents the difference between the output voltage of the grid-type converter and the voltage at the common coupling point;

[0048] The numerical unit is used to establish the open-loop voltage control model based on the system model by controlling the voltage of the common coupling point to be parallel to the d-axis, and obtain the first voltage reference value according to the open-loop voltage control model.

[0049] As a preferred solution, the control module includes a voltage unit, a current unit, a construction unit and a threshold unit;

[0050] Wherein, the voltage unit is used to establish a voltage equation at the common coupling point when the grid-side voltage drops;

[0051] The current unit is used to combine the second voltage reference value and the voltage equation to establish a current equation by replacing the voltage and current in the second voltage reference value with the voltage and current when a fault occurs;

[0052] The construction unit is used to establish a feasible domain of the virtual impedance resistor and the virtual impedance inductor that can meet the current limiting condition by limiting the current in the current equation to not exceed a preset maximum threshold;

[0053] The threshold unit is used to establish the conservative feasible region based on the feasible region of the virtual impedance resistor and the virtual impedance inductor and according to the voltage of the common coupling point when the grid side voltage drops.

[0054] As a preferred solution, the threshold unit includes a voltage subunit, a limit subunit and a threshold subunit;

[0055] The voltage subunit is used to establish a first voltage limiting equation by controlling the voltage of the common coupling point to be not higher than the voltage modulus of the common coupling point in a steady state when the grid side voltage drops;

[0056] The limiting subunit is used to calculate the first voltage limiting equation by defining the voltage of the common coupling point on the d-axis when the grid-side voltage drops as the negative value of the voltage modulus to obtain a second voltage limiting equation;

[0057] The threshold subunit is used to establish the conservative feasible domain according to the feasible domain of the virtual impedance resistor and the virtual impedance inductor, and the second voltage limit equation.

[0058] As a preferred solution, the threshold subunit is specifically:

[0059] The maximum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the second voltage limiting equation is defined as the minimum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the feasible domain of the virtual impedance resistor and the virtual impedance inductor, to obtain an initial conservative feasible domain;

[0060] The frequency in the initial conservative feasible region is replaced by the minimum frequency of the grid-type converter to obtain the conservative feasible region.

[0061] As a preferred solution, the conservative feasible region is specifically:

[0062]

[0063] Among them, R v is the virtual impedance resistor, L v is the virtual impedance inductor, ω min is the minimum frequency of the grid-type converter, U p is the voltage modulus, I max is the preset maximum current threshold.

[0064] The present application also provides a storage medium, on which a computer program is stored. The computer program is called and executed by a computer to implement the conservative virtual synchronous generator impedance setting method as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a flowchart of a conservative virtual synchronous generator impedance setting method provided in an embodiment of the present application;

[0066] Figure 2 It is a topological schematic diagram and a control block diagram of a test system provided in an embodiment of the present application;

[0067] Figure 3 is a current and voltage waveform diagram of the test system provided by the embodiment of the present application under fault;

[0068] Figure 4 It is a structural schematic diagram of a conservative virtual synchronous generator impedance setting device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0069] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0070] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "several" means two or more.

[0071] A conservative virtual synchronous generator impedance setting method provided in an embodiment of the present application is mainly used in control situations where a simplified virtual impedance method is required, and a suitable virtual impedance setting scheme is provided to improve the overall performance of the converter.

[0072] Embodiment 1:

[0073] See also Figure 1 The embodiment of the present application provides a conservative virtual synchronous generator impedance setting method, including S1 to S5, and the specific implementation steps are as follows:

[0074] S1. Obtain control data of the grid-connected converter.

[0075] Step S1 of the embodiment of the present application is specifically as follows:

[0076] The control data of a VSC is obtained; wherein the VSC is connected to an infinite bus system via a transmission line, and the VSC adopts a virtual synchronous control strategy.

[0077] S2. Obtaining a first voltage reference value by establishing an open-loop voltage control model according to the control data.

[0078] Step S2 of the embodiment of the present application is specifically as follows:

[0079] In the grid-type converter, based on the control data, when the parallel capacitor at the point of common coupling (PCC) is less than the preset value, the parallel capacitor C is ignored by using the Thevenin theorem to equate the right circuit of the common coupling point to an equivalent circuit consisting of an infinite voltage source and a series reactance. fThe influence of isotropic converter is considered, and a system model is established; wherein the system model represents the difference between the output voltage of the grid-type converter and the voltage at the common coupling point;

[0080] Based on the system model, an open-loop voltage control model (a virtual synchronous generator open-loop voltage control model) is established by controlling the voltage of the common coupling point to be parallel to the d-axis, and a first voltage reference value is obtained according to the open-loop voltage control model, and the first voltage reference value is defined as a steady-state control strategy;

[0081] Among them, the equation for the grid-type converter connected to the infinite bus system via a transmission line can be written as follows:

[0082]

[0083] Expanding the above formula, we can get the system model, that is, the circuit equation:

[0084]

[0085] The voltage at the control common coupling point is parallel to the d-axis and can be expressed as:

[0086]

[0087] The open-loop voltage control model is:

[0088]

[0089] Among them, R c and L c is the resistance and inductance of the phase reactor, U p is the voltage modulus of the common coupling point in steady state, and are the voltage reference values ​​of the grid-type converter on the d-axis and q-axis respectively, and are the voltage reference values ​​of the common coupling point on the d-axis and q-axis respectively, and are the current reference values ​​of the grid-type converter on the d-axis and q-axis respectively, and are voltage reference values ​​of the first voltage reference value on the d-axis and on the q-axis respectively, j is an imaginary unit, and ω is an angular frequency.

[0090] This embodiment S2 can greatly reduce the complexity of the system model by simplifying the complex power system network into an equivalent voltage source and series reactance. This simplification not only reduces the amount of calculation, but also improves the understandability and controllability of the system. In the control of the grid-type converter, by setting the voltage control target to be parallel to the d-axis, that is, the direct axis component in the synchronous rotating coordinate system, the stability of the common coupling point voltage can be more effectively maintained;

[0091] Moreover, the steady-state control strategy can control the voltage at the common coupling point without introducing a voltage outer loop; at the same time, the control strategy does not need to control the voltage u on the grid side. s and angular frequency ω s The measurement is carried out regardless of the strength of the receiving power grid.

[0092] S3. Based on the open-loop voltage control model, a second voltage reference value is established by adding resistance and inductance of the virtual impedance.

[0093] Step S3 of the embodiment of the present application is specifically as follows:

[0094] Based on the open-loop voltage control model, a second voltage reference value is established by adding the resistance and inductance of the virtual impedance, and the second voltage reference value is defined as a virtual impedance control strategy;

[0095] The second voltage reference value is:

[0096]

[0097] Among them, R c and L c is the resistance and inductance of the phase reactor, U p is the voltage modulus of the common coupling point in steady state, and are the current reference values ​​of the grid-type converter on the d-axis and q-axis respectively, and are the voltage reference values ​​of the second voltage reference value on the d-axis and the q-axis respectively, ω is the angular frequency, R ν and L ν are the resistance and inductance of the virtual impedance respectively.

[0098] S4. When a fault occurs and causes the current flowing through the grid-type converter to be less than the current limit, the voltage of the grid-type converter is adjusted to a first voltage reference value; otherwise, the voltage is adjusted to a second voltage reference value.

[0099] Step S4 of the embodiment of the present application is specifically as follows:

[0100] According to the current i flowing through the grid-type converter when a fault occurs, c With the preset current limit I cmaxEstablish an algebraic variable criterion and a state variable criterion respectively for the relationship between them;

[0101] Based on the algebraic variable criterion and the state variable criterion, when a fault occurs and the absolute value of the current flowing through the network-forming converter is less than the current limit, that is, when |i c |<I cmax At this time, or when -arccos(d) < θ c < arccos(d), adjust the voltage of the network-forming converter to the first voltage reference value, so that the network-forming converter still operates under the steady-state control strategy of the first voltage reference value;

[0102] Based on the algebraic variable criterion and the state variable criterion, when a fault occurs and the absolute value of the current flowing through the network-forming converter is greater than or equal to the current limit, that is, when |i c |≥I cmax At this time, or when "θ c ≤ -arccos(d) or θ c (d)", adjust the voltage of the network-forming converter to the second voltage reference value, so that the network-forming converter operates under the virtual impedance control strategy of the second voltage reference value;

[0103] Among them, the algebraic variable criterion is:

[0104]

[0105] The state variable criterion is:

[0106]

[0107] θ c =arccos(d)

[0108] Among them, U p is the voltage magnitude of the point of common coupling at steady state, U s is the magnitude of the grid-side voltage, I cmax is the maximum value of the current flowing through the network-forming converter, θ c is the power factor angle of the network-forming converter, d is the cosine value of the power factor, R l and L l are the resistance and inductance of the transmission line respectively, j is the imaginary unit, ω is the angular frequency, and i c is the current flowing through the network-forming converter.

[0109] In this embodiment S4, when a fault occurs, by means of voltage switching, the magnitude of the current flowing through the network-forming converter can be controlled, thereby limiting the overcurrent caused by the grid-side voltage u s drop.

[0110] S5. Control the resistance and inductance of the virtual impedance within the conservative feasible domain; wherein the conservative feasible domain is based on the feasible domain of the virtual impedance resistance and the virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops;

[0111] Among them, the feasible domain of virtual impedance resistance and virtual impedance inductance is:

[0112]

[0113] Among them, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

[0114] Step S5 of the embodiment of the present application includes S5.1 to S5.2; specifically, it is:

[0115] S5.1, on the grid side voltage u s When the voltage drops, the voltage at the common coupling point becomes u pf , thereby establishing the voltage equation (circuit equation) at the common coupling point;

[0116] The open-loop control speed of the converter is very fast, so it can be considered Combining the second voltage reference value and the voltage equation, the voltage u at the time of the fault is calculated by cf and current i cf Substitute u in the second voltage reference value c and i c , establish the transition voltage equation;

[0117] Solve the transition voltage equation to obtain the current equation;

[0118] By limiting the current in the current equation to not exceed the preset maximum threshold I max , establish the feasible domain of virtual impedance resistance and virtual impedance inductance that can meet the current limiting conditions;

[0119] The voltage equation is:

[0120]

[0121] The transition voltage equation is:

[0122]

[0123] The current equation is:

[0124]

[0125] The control current does not exceed the preset maximum threshold, which can be expressed as:

[0126]

[0127] The feasible domain of virtual impedance resistance and virtual impedance inductance is:

[0128]

[0129] Among them, R c and L c is the resistance and inductance of the phase reactor, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltages of the grid-type converter on the d-axis and q-axis during the drop, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, and is the grid side voltage u s The current of the grid-type converter on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

[0130] In this embodiment S5.1, when the grid voltage drops, the grid fault can be evaluated and responded to in real time by establishing the voltage equation and the current equation. By substituting the voltage and current at the time of the fault into the current equation, and combining the condition that the current is limited to not exceed the preset maximum threshold, the feasible range of virtual impedance resistance and inductance values ​​that meet the current limiting condition can be accurately calculated.

[0131] S5.2, based on the feasible domain of virtual impedance resistance and virtual impedance inductance, record the ellipse This formula represents the virtual impedance resistance R in the parameter space ν and virtual impedance inductor L ν The constraint is an ellipse;

[0132] remember Then the feasible domain of virtual impedance resistance and virtual impedance inductance shows that R ν and L ν The feasible region is about R ν and L νThe area outside the ellipse Γ;

[0133] In order to obtain a conservative feasible region that satisfies the current limiting condition, it is necessary to The value of is estimated.

[0134] When the grid voltage drops, the voltage at the common coupling point is controlled not to be higher than the voltage modulus U at the common coupling point in steady state. p , establish the first voltage limiting equation;

[0135] Performing equivalent processing on the first voltage limiting equation to obtain an equivalent voltage limiting equation;

[0136] The first voltage limiting equation also implies that To estimate The maximum value of the voltage at the common coupling point on the d-axis when the grid voltage drops is defined as the voltage modulus U p The negative value of the voltage limiting equation is calculated to obtain the second voltage limiting equation;

[0137] Combining the feasible domain of virtual impedance resistance and virtual impedance inductance, and the second voltage limiting equation, the initial conservative feasible domain is obtained by defining the maximum value of the comprehensive calculation result of the virtual impedance resistance and virtual impedance inductance in the second voltage limiting equation as the minimum value of the comprehensive calculation result of the virtual impedance resistance and virtual impedance inductance in the feasible domain of virtual impedance resistance and virtual impedance inductance;

[0138] Considering the frequency limiting of the converter, the frequency ω in the initial conservative feasible region is replaced by the minimum frequency ω of the grid-type converter. min , and obtain the conservative feasible region;

[0139] Control the resistance and inductance of the virtual impedance to be within the conservative feasible region;

[0140] Among them, the first voltage limiting equation is:

[0141]

[0142] The equivalent voltage limit equation is:

[0143]

[0144] The second voltage limiting equation is:

[0145]

[0146] The initial conservative feasible region is:

[0147]

[0148] The inverter frequency limit is:

[0149] ω min ≤∑≤∑ max

[0150] The conservative feasible region is:

[0151]

[0152] Among them, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltages of the common coupling point on the d-axis and q-axis respectively during the drop, ω is the angular frequency;

[0153] R ν is the virtual impedance resistor, L ν is the virtual impedance inductor, ω min is the minimum frequency of the grid-type converter, ω max is the maximum frequency of the grid-type converter, I max is the preset maximum current threshold.

[0154] In this embodiment S5.2, by controlling the voltage of the common coupling point not to be higher than its voltage modulus in the steady state, it can ensure that when the grid-side voltage drops, the fluctuation of the converter output voltage is limited to a controllable range, thereby enhancing the voltage stability;

[0155] Moreover, by defining the maximum value of the parameter of the second voltage limiting equation as the minimum boundary of the parameter in the feasible domain of the virtual impedance resistor and the virtual impedance inductor, it can be ensured that under extreme conditions such as voltage drop, the voltage and current of the system are still limited to a safe range, which helps to ensure the safe and stable operation of the system. Moreover, by combining the relationship between the virtual impedance resistor and the virtual impedance inductor with the voltage limiting equation, an initial conservative feasible domain that satisfies both voltage limitation and current control can be obtained. By replacing the frequency in the initial conservative feasible domain with the minimum frequency of the converter, it can be ensured that the converter can still operate stably at the lowest frequency, which helps to optimize the performance of the converter and reduce the impact of frequency fluctuations on system stability.

[0156] For Example S5, it is difficult to obtain a unified virtual impedance by traditional methods so that the current can be limited within a safe range under any external interference. This Example S5 gives a minimum unified virtual setting scheme to ensure that the current does not exceed the limit through theoretical derivation. Under the premise of the virtual impedance control strategy, parameter control based on the conservative feasible domain can be used to ensure that the converter current and frequency do not exceed the limit during the fault process.

[0157] Please refer to Table 1, which is a table of test system parameters provided in an embodiment of the present application, indicating system parameters used to verify a conservative virtual synchronous generator impedance setting method.

[0158] Table 1 Test system parameters

[0159]

[0160] To apply the embodiments of this application, please refer to Figure 2 , Figure 2 It is a topological schematic diagram and a control block diagram of a test system provided in an embodiment of the present application, representing a main circuit diagram and a control block diagram of a meshed converter connected to an infinite AC bus through a transmission line.

[0161] See also Figure 3 , Figure 3 This is the current and voltage waveform diagram of the test system under fault conditions provided by the embodiment of the present application, which shows the voltage and current waveform diagram when the voltage drops by 50%. At 5 seconds, the grid voltage drops to 0.5pu, and the fault is cleared after 50ms. The voltage and current waveforms before and after the fault are as follows: Figure 3 As shown, it can be seen that the fault current does not exceed 1.4 pu during the voltage drop. Therefore, by adopting the virtual impedance control strategy proposed in this embodiment, the current of the inverter can be limited after a fault occurs.

[0162] Overall, the embodiments of the present application have the following beneficial effects:

[0163] The present invention can obtain a first voltage reference value by establishing an open-loop voltage control model. The first voltage reference value mainly reflects the influence of the internal parameters of the converter on the voltage reference value. Therefore, when it is detected that the current flowing through the grid-type converter is less than the current limit, it means that the system may be experiencing a certain fault or abnormal situation, but has not yet reached a serious overload state; at this time, by quickly adjusting the voltage to the first voltage reference value, it can be ensured that the fluctuation of the output voltage is within an acceptable range. By adding the resistance and inductance of the virtual impedance, the second voltage reference value more comprehensively considers the influence of the resistance and inductance of the entire system on the voltage reference value, which can better adapt to the characteristics of the power grid and reduce the mismatch and conflict with the power grid; therefore, when it is detected that the current flowing through the grid-type converter is greater than or equal to the current limit, it means that the system may be experiencing a certain fault or abnormal situation and has reached a serious overload state, so it is necessary to consider the influence of the entire system on the converter voltage control. At this time, by quickly adjusting the voltage to the second voltage reference value, customized control of the converter voltage output can be achieved, improving the overall performance and efficiency of the system. In addition, the setting of the conservative feasible region is based on the extreme case of grid-side voltage drop. By limiting the resistance and inductance of the virtual impedance within this range, it can ensure that the converter can still maintain a stable output voltage and current when the grid voltage fluctuates or fails, thereby avoiding system instability or collapse.

[0164] Therefore, the embodiment of the present application first establishes an open-loop voltage control model of a virtual synchronous generator, and then proposes a virtual impedance control strategy based on the proposed open-loop voltage control model. Finally, a conservative virtual impedance setting scheme is proposed. This scheme adjusts the virtual impedance required to limit the converter current under the most serious fault, thereby ensuring that the converter fault current does not exceed the limit under any fault type, which is beneficial to improving the safe and stable operation capability of the converter.

[0165] Embodiment 2:

[0166] See also Figure 4 , an embodiment of the present application provides a conservative virtual synchronous generator impedance setting device, including a data module 10, a model module 20, a parameter module 30, an adjustment module 40 and a control module 50;

[0167] Wherein, the data module 10 is used to obtain control data of the grid-type converter;

[0168] The model module 20 is used to obtain a first voltage reference value by establishing an open-loop voltage control model according to the control data;

[0169] The parameter module 30 is used to establish a second voltage reference value by adding the resistance and inductance of the virtual impedance based on the open-loop voltage control model;

[0170] The adjustment module 40 is used to adjust the voltage of the grid-type converter to the first voltage reference value when a fault occurs and causes the current flowing through the grid-type converter to be less than the current limit, otherwise, adjust the voltage to the second voltage reference value;

[0171] The control module 50 is used to control the resistance and inductance of the virtual impedance within a conservative feasible domain; wherein the conservative feasible domain is based on the feasible domain of the virtual impedance resistance and the virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops;

[0172] Among them, the feasible domain of the virtual impedance resistor and the virtual impedance inductor is:

[0173]

[0174] Among them, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

[0175] In one embodiment, the data module 10 is specifically:

[0176] The control data of a VSC is obtained; wherein the VSC is connected to an infinite bus system via a transmission line, and the VSC adopts a virtual synchronous control strategy.

[0177] In one embodiment, the model module 20 includes a model unit and a value unit;

[0178] The model unit is used to, in the grid-type converter, based on the control data, when the parallel capacitor at the point of common coupling (PCC) is less than a preset value, by using the Thevenin theorem to equate the right circuit of the common coupling point to an equivalent circuit consisting of an infinite voltage source and a series reactance, thereby ignoring the parallel capacitor C f The influence of isotropic converter is considered, and a system model is established; wherein the system model represents the difference between the output voltage of the grid-type converter and the voltage at the common coupling point;

[0179] A numerical unit is used to establish an open-loop voltage control model (a virtual synchronous generator open-loop voltage control model) based on a system model by controlling the voltage of the common coupling point to be parallel to the d-axis, obtain a first voltage reference value according to the open-loop voltage control model, and define the first voltage reference value as a steady-state control strategy;

[0180] Among them, the equation for the grid-type converter connected to the infinite bus system via a transmission line can be written as follows:

[0181]

[0182] Expanding the above formula, we can get the system model, that is, the circuit equation:

[0183]

[0184] The voltage at the control common coupling point is parallel to the d-axis and can be expressed as:

[0185]

[0186] The open-loop voltage control model is:

[0187]

[0188] Among them, R c and L c is the resistance and inductance of the phase reactor, U p is the voltage modulus of the common coupling point in steady state, and are the voltage reference values ​​of the grid-type converter on the d-axis and q-axis respectively, and are the voltage reference values ​​of the common coupling point on the d-axis and q-axis respectively, and are the current reference values ​​of the grid-type converter on the d-axis and q-axis respectively, and are voltage reference values ​​of the first voltage reference value on the d-axis and on the q-axis respectively, j is an imaginary unit, and ω is an angular frequency.

[0189] The model module 20 of this embodiment can greatly reduce the complexity of the system model by simplifying the complex power system network into an equivalent voltage source and series reactance. This simplification not only reduces the amount of calculation, but also improves the understandability and controllability of the system. In the control of the grid-type converter, by setting the voltage control target to be parallel to the d-axis, that is, the direct axis component in the synchronous rotating coordinate system, the stability of the common coupling point voltage can be more effectively maintained;

[0190] Moreover, the steady-state control strategy can control the voltage at the point of common coupling without introducing an outer voltage loop; meanwhile, this control strategy does not require the measurement of the voltage u s and the angular frequency ω s and is independent of the strength of the receiving-end power grid.

[0191] In one embodiment, the parameter module 30 is specifically:

[0192] Based on the open-loop voltage control model, by adding the resistance and inductance of the virtual impedance, a second voltage reference value is established, and the second voltage reference value is defined as the virtual impedance control strategy;

[0193] Among them, the second voltage reference value is:

[0194]

[0195] Among them, R c and L c are the resistance and inductance of the phase reactor, U p is the voltage magnitude at the point of common coupling in the steady state, and are the current reference values of the network-forming converter on the d-axis and on the q-axis respectively, and are the voltage reference values of the second voltage reference value on the d-axis and on the q-axis respectively, ω is the angular frequency, R ν and L ν are the resistance and inductance of the virtual impedance respectively.

[0196] In one embodiment, the adjustment module 40 is specifically:

[0197] According to the relationship between the current i c flowing through the network-forming converter when a fault occurs and the preset current limit I cmax , an algebraic variable criterion and a state variable criterion are established respectively;

[0198] Based on the algebraic variable criterion and the state variable criterion, when a fault causes the absolute value of the current flowing through the network-forming converter to be less than the current limit, that is, when |i c |<I cmax or -arccos(d)<θ c <arccos(d), the voltage of the network-forming converter is adjusted to the first voltage reference value, so that the network-forming converter still operates under the steady-state control strategy of the first voltage reference value;

[0199] Based on the algebraic variable criterion and the state variable criterion, when a fault causes the absolute value of the current flowing through the network-forming converter to be greater than or equal to the current limit, that is, when |i c |≥Icmax When, or "θ c ≤-arccos(d) or θ c (d)”, adjusting the voltage of the grid-type converter to a second voltage reference value, so that the grid-type converter operates under a virtual impedance control strategy of the second voltage reference value;

[0200] Among them, the algebraic variable criterion is:

[0201]

[0202] The state variable criterion is:

[0203]

[0204] θ c =arccos(d)

[0205] Among them, U p is the voltage modulus of the common coupling point in steady state, U s is the voltage amplitude on the grid side, I cmax is the maximum current flowing through the grid-type converter, θ c is the power factor angle of the grid-type converter, d is the cosine value of the power factor, R l and L l are the resistance and inductance of the transmission line, j is the imaginary unit, ω is the angular frequency, i c is the current flowing through the grid-type converter.

[0206] In the present embodiment, the adjustment module 40 can control the current flowing through the grid-type converter by means of voltage switching when a fault occurs, thereby limiting the current caused by the grid-side voltage u s Overcurrent caused by falling.

[0207] In one embodiment, the control module 50 includes a voltage unit, a current unit, a construction unit, a voltage sub-unit, a limiting sub-unit and a threshold sub-unit; specifically:

[0208] Voltage unit, used for grid-side voltage u s When the voltage drops, the voltage at the common coupling point becomes u pf , thereby establishing the voltage equation (circuit equation) at the common coupling point;

[0209] The current unit is used for the open-loop control of the converter at a very fast speed. Combining the second voltage reference value and the voltage equation, the voltage u at the time of the fault is calculated by cf and current i cf Substitute u in the second voltage reference value c and i c, establish the transition voltage equation;

[0210] The current unit is also used to solve the transition voltage equation to obtain the current equation;

[0211] A building block is used to limit the current in the current equation to not exceed a preset maximum threshold value I max , establish the feasible domain of virtual impedance resistance and virtual impedance inductance that can meet the current limiting conditions;

[0212] The voltage equation is:

[0213]

[0214] The transition voltage equation is:

[0215]

[0216] The current equation is:

[0217]

[0218] The control current does not exceed the preset maximum threshold, which can be expressed as:

[0219]

[0220] The feasible domain of virtual impedance resistance and virtual impedance inductance is:

[0221]

[0222] Among them, R c and L c is the resistance and inductance of the phase reactor, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltages of the grid-type converter on the d-axis and q-axis during the drop, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, and is the grid side voltage u s The current of the grid-type converter on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

[0223] In the voltage unit, current unit and construction unit of this embodiment, when the voltage on the grid side drops, by establishing the voltage equation and the current equation, the grid fault can be evaluated and responded to in real time. By substituting the voltage and current at the time of the fault into the current equation, and combining the condition that the current is limited to not exceed the preset maximum threshold, the feasible range of virtual impedance resistance and inductance values ​​that meet the current limiting condition can be accurately calculated.

[0224] Voltage subunit, used for feasible domain based on virtual impedance resistance and virtual impedance inductance, record ellipse This formula represents the virtual impedance resistance R in the parameter space ν and virtual impedance inductor L ν The constraint is an ellipse;

[0225] Voltage subunit, also used to record Then the feasible domain of virtual impedance resistance and virtual impedance inductance shows that R ν and L ν The feasible region is about R ν and L ν The area outside the ellipse Γ;

[0226] The voltage subunit is also used to obtain a conservative feasible region that satisfies the current limiting condition. The value of is estimated.

[0227] The voltage subunit is also used to control the voltage of the common coupling point not to be higher than the voltage modulus U of the common coupling point in steady state when the voltage on the grid side drops. p , establish the first voltage limiting equation;

[0228] The voltage subunit is further used to perform equivalent processing on the first voltage limiting equation to obtain an equivalent voltage limiting equation;

[0229] The limiting subunit, used in the first voltage limiting equation, also implies To estimate The maximum value of the voltage modulus U is defined by defining the voltage of the common coupling point on the d-axis when the grid voltage drops as the voltage modulus U p The negative value of the voltage limiting equation is calculated to obtain the second voltage limiting equation;

[0230] A threshold subunit is used to combine the feasible domain of virtual impedance resistor and virtual impedance inductor and the second voltage limiting equation, and obtain an initial conservative feasible domain by defining the maximum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the second voltage limiting equation as the minimum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the feasible domain of the virtual impedance resistor and the virtual impedance inductor;

[0231] Considering the frequency limiting of the converter, the frequency ω in the initial conservative feasible region is replaced by the minimum frequency ω of the grid-type converter. min , and obtain the conservative feasible region;

[0232] Control the resistance and inductance of the virtual impedance to be within the conservative feasible region;

[0233] Among them, the first voltage limiting equation is:

[0234]

[0235] The equivalent voltage limit equation is:

[0236]

[0237] The second voltage limiting equation is:

[0238]

[0239] The initial conservative feasible region is:

[0240]

[0241] The inverter frequency limit is:

[0242] ω min ≤ω≤ω max

[0243] The conservative feasible region is:

[0244]

[0245] Among them, U p is the voltage amplitude at the common coupling point, and is the voltage u on the grid side s The voltages at the common coupling point on the d-axis and q-axis respectively during the drop, ω is the angular frequency;

[0246] R ν is the virtual impedance resistor, L ν is the virtual impedance inductor, ω min is the minimum frequency of the grid-type converter, ω max is the maximum frequency of the grid-type converter, U p is the voltage modulus, I max is the preset maximum current threshold.

[0247] The voltage subunit, the limiting subunit and the threshold subunit of this embodiment can ensure that the fluctuation of the converter output voltage is limited within a controllable range when the grid side voltage drops by controlling the voltage of the common coupling point not to be higher than its voltage modulus in the steady state, thereby enhancing the voltage stability.

[0248] Moreover, by defining the maximum value of the parameter of the second voltage limiting equation as the minimum boundary of the parameter in the feasible domain of the virtual impedance resistor and the virtual impedance inductor, it can be ensured that under extreme conditions such as voltage drop, the voltage and current of the system are still limited to a safe range, which helps to ensure the safe and stable operation of the system. Moreover, by combining the relationship between the virtual impedance resistor and the virtual impedance inductor with the voltage limiting equation, an initial conservative feasible domain that satisfies both voltage limitation and current control can be obtained. By replacing the frequency in the initial conservative feasible domain with the minimum frequency of the converter, it can be ensured that the converter can still operate stably at the lowest frequency, which helps to optimize the performance of the converter and reduce the impact of frequency fluctuations on system stability.

[0249] For the control module 50 of the embodiment, it is difficult to obtain a unified virtual impedance by traditional methods so as to ensure that the current is limited within a safe range under any external interference. The control module 50 of this embodiment gives a minimum unified virtual setting scheme to ensure that the current does not exceed the limit through theoretical derivation. Under the premise of the virtual impedance control strategy, the parameter control based on the conservative feasible domain can achieve the goal of ensuring that the converter current and frequency do not exceed the limit during the fault process.

[0250] Please refer to Table 1, which is a table of test system parameters provided in an embodiment of the present application, indicating system parameters used to verify a conservative virtual synchronous generator impedance setting device.

[0251] Table 1 Test system parameters

[0252]

[0253]

[0254] To apply the embodiments of this application, please refer to Figure 2 , Figure 2 It is a topological schematic diagram and a control block diagram of a test system provided in an embodiment of the present application, representing a main circuit diagram and a control block diagram of a meshed converter connected to an infinite AC bus through a transmission line.

[0255] See also Figure 3 , Figure 3 This is the current and voltage waveform diagram of the test system under fault conditions provided by the embodiment of the present application, which shows the voltage and current waveform diagram when the voltage drops by 50%. At 5 seconds, the grid voltage drops to 0.5pu, and the fault is cleared after 50ms. The voltage and current waveforms before and after the fault are as follows: Figure 3 As shown, it can be seen that the fault current does not exceed 1.4 pu during the voltage drop. Therefore, by adopting the virtual impedance control strategy proposed in this embodiment, the current of the inverter can be limited after a fault occurs.

[0256] Overall, the embodiments of the present application have the following beneficial effects:

[0257] The present invention can obtain a first voltage reference value by establishing an open-loop voltage control model. The first voltage reference value mainly reflects the influence of the internal parameters of the converter on the voltage reference value. Therefore, when it is detected that the current flowing through the grid-type converter is less than the current limit, it means that the system may be experiencing a certain fault or abnormal situation, but has not yet reached a serious overload state; at this time, by quickly adjusting the voltage to the first voltage reference value, it can be ensured that the fluctuation of the output voltage is within an acceptable range. By adding the resistance and inductance of the virtual impedance, the second voltage reference value more comprehensively considers the influence of the resistance and inductance of the entire system on the voltage reference value, which can better adapt to the characteristics of the power grid and reduce the mismatch and conflict with the power grid; therefore, when it is detected that the current flowing through the grid-type converter is greater than or equal to the current limit, it means that the system may be experiencing a certain fault or abnormal situation and has reached a serious overload state, so it is necessary to consider the influence of the entire system on the converter voltage control. At this time, by quickly adjusting the voltage to the second voltage reference value, customized control of the converter voltage output can be achieved, improving the overall performance and efficiency of the system. In addition, the setting of the conservative feasible region is based on the extreme case of grid-side voltage drop. By limiting the resistance and inductance of the virtual impedance within this range, it can ensure that the converter can still maintain a stable output voltage and current when the grid voltage fluctuates or fails, thereby avoiding system instability or collapse.

[0258] Therefore, the embodiment of the present application first establishes an open-loop voltage control model of a virtual synchronous generator, and then proposes a virtual impedance control strategy based on the proposed open-loop voltage control model. Finally, a conservative virtual impedance setting scheme is proposed, which can adjust the virtual impedance required to limit the converter current under the most serious fault in a simple way, thereby ensuring that the converter fault current does not exceed the limit under any fault type, which is beneficial to improving the safe and stable operation capability of the converter.

[0259] Embodiment three:

[0260] An embodiment of the present application provides a computer-readable storage medium, wherein the computer-readable storage medium includes a stored computer program, wherein when the computer program is executed, the device where the computer-readable storage medium is located is controlled to execute the conservative virtual synchronous generator impedance setting method;

[0261] Wherein, the conservative virtual synchronous generator impedance setting method, if implemented in the form of a software functional unit and used as an independent product, can be stored in a computer-readable storage medium. Based on such an understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Wherein, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium, etc.

[0262] The above are preferred embodiments of the present invention. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A conservative virtual synchronous generator impedance setting method, characterized in that: include: Obtaining control data of a grid-type converter; According to the control data, a first voltage reference value is obtained by establishing an open-loop voltage control model; Based on the open-loop voltage control model, a second voltage reference value is established by adding resistance and inductance of a virtual impedance; When a fault occurs and causes the current flowing through the grid-type converter to be less than the current limit, the voltage of the grid-type converter is adjusted to the first voltage reference value; otherwise, the voltage is adjusted to the second voltage reference value; Controlling the resistance and inductance of the virtual impedance within a conservative feasible domain; wherein the conservative feasible domain is based on the feasible domain of the virtual impedance resistance and the virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops; Among them, the feasible domain of the virtual impedance resistor and the virtual impedance inductor is: Among them, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

2. A conservative virtual synchronous generator impedance setting method as claimed in claim 1, characterized in that: According to the control data, an open-loop voltage control model is established to obtain a first voltage reference value, specifically: In the grid-type converter, based on the control data, a system model is established by equating the right circuit of the common coupling point to an equivalent circuit consisting of an infinite voltage source and a series reactance; wherein the system model represents the difference between the output voltage of the grid-type converter and the voltage at the common coupling point; Based on the system model, the open-loop voltage control model is established by controlling the voltage of the common coupling point to be parallel to the d-axis, and the first voltage reference value is obtained according to the open-loop voltage control model.

3. A conservative virtual synchronous generator impedance setting method as claimed in claim 1, characterized in that: The conservative feasible region is based on the feasible region of virtual impedance resistance and virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops, specifically: When the grid-side voltage drops, establishing a voltage equation at the common coupling point; In combination with the second voltage reference value and the voltage equation, a current equation is established by replacing the voltage and current in the second voltage reference value with the voltage and current when the fault occurs; By limiting the current in the current equation to not exceed a preset maximum threshold, a feasible domain of the virtual impedance resistor and the virtual impedance inductor that can meet the current limiting condition is established; Based on the feasible domains of the virtual impedance resistor and the virtual impedance inductor, the conservative feasible domain is established according to the voltage of the common coupling point when the grid-side voltage drops.

4. A conservative virtual synchronous generator impedance setting method as claimed in claim 3, characterized in that: Based on the feasible domain of the virtual impedance resistor and the virtual impedance inductor, the conservative feasible domain is established according to the voltage of the common coupling point when the grid side voltage drops, specifically: When the grid-side voltage drops, a first voltage limiting equation is established by controlling the voltage of the common coupling point to be not higher than the voltage modulus of the common coupling point in a steady state; The first voltage limiting equation is calculated by defining the voltage of the common coupling point on the d-axis when the grid-side voltage drops as the negative value of the voltage modulus to obtain a second voltage limiting equation; The conservative feasible region is established according to the feasible region of the virtual impedance resistor and the virtual impedance inductor, and the second voltage limiting equation.

5. A conservative virtual synchronous generator impedance setting method as claimed in claim 4, characterized in that: According to the feasible domain of the virtual impedance resistor and the virtual impedance inductor, and the second voltage limiting equation, the conservative feasible domain is established, specifically: The maximum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the second voltage limiting equation is defined as the minimum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the feasible domain of the virtual impedance resistor and the virtual impedance inductor, to obtain an initial conservative feasible domain; The frequency in the initial conservative feasible region is replaced by the minimum frequency of the grid-type converter to obtain the conservative feasible region.

6. A conservative virtual synchronous generator impedance setting method as claimed in claim 1, characterized in that: The conservative feasible region is specifically: Among them, R ν is the virtual impedance resistor, L ν is the virtual impedance inductor, ∑ min is the minimum frequency of the grid-type converter, U p is the voltage modulus, I max is the preset maximum current threshold.

7. A conservative virtual synchronous generator impedance setting device, characterized in that: It includes data module, model module, parameter module, adjustment module and control module; Wherein, the data module is used to obtain control data of the grid-type converter; The model module is used to obtain a first voltage reference value by establishing an open-loop voltage control model according to the control data; The parameter module is used to establish a second voltage reference value by adding resistance and inductance of a virtual impedance based on the open-loop voltage control model; The adjustment module is used to adjust the voltage of the meshed converter to the first voltage reference value when a fault occurs and causes the current flowing through the meshed converter to be less than the current limit, otherwise, adjust the voltage to the second voltage reference value; The control module is used to control the resistance and inductance of the virtual impedance within a conservative feasible domain; wherein the conservative feasible domain is based on the feasible domain of the virtual impedance resistance and the virtual impedance inductance, and is established according to the voltage of the common coupling point when the grid side voltage drops; Among them, the feasible domain of the virtual impedance resistor and the virtual impedance inductor is: Among them, U p is the voltage modulus of the common coupling point in steady state, and is the grid side voltage u s The voltage of the common coupling point on the d-axis and q-axis respectively during the drop, R ν and L ν are the resistance and inductance of the virtual impedance, ω is the angular frequency, I max is the preset maximum threshold value for current.

8. A conservative virtual synchronous generator impedance setting device as claimed in claim 7, characterized in that: The model module includes a model unit and a numerical unit; The model unit is used to establish a system model in the grid-type converter based on the control data by equating the right circuit of the common coupling point to an equivalent circuit consisting of an infinite voltage source and a series reactance; wherein the system model represents the difference between the output voltage of the grid-type converter and the voltage at the common coupling point; The numerical unit is used to establish the open-loop voltage control model based on the system model by controlling the voltage of the common coupling point to be parallel to the d-axis, and obtain the first voltage reference value according to the open-loop voltage control model.

9. A conservative virtual synchronous generator impedance setting device as claimed in claim 7, characterized in that: The control module includes a voltage unit, a current unit, a construction unit and a threshold unit; Wherein, the voltage unit is used to establish a voltage equation at the common coupling point when the grid-side voltage drops; The current unit is used to combine the second voltage reference value and the voltage equation to establish a current equation by replacing the voltage and current in the second voltage reference value with the voltage and current when a fault occurs; The construction unit is used to establish a feasible domain of the virtual impedance resistor and the virtual impedance inductor that can meet the current limiting condition by limiting the current in the current equation to not exceed a preset maximum threshold; The threshold unit is used to establish the conservative feasible region based on the feasible region of the virtual impedance resistor and the virtual impedance inductor and according to the voltage of the common coupling point when the grid side voltage drops.

10. A conservative virtual synchronous generator impedance setting device as claimed in claim 9, characterized in that: The threshold unit includes a voltage subunit, a limit subunit and a threshold subunit; The voltage subunit is used to establish a first voltage limiting equation by controlling the voltage of the common coupling point to be not higher than the voltage modulus of the common coupling point in a steady state when the grid side voltage drops; The limiting subunit is used to calculate the first voltage limiting equation by defining the voltage of the common coupling point on the d-axis when the grid-side voltage drops as the negative value of the voltage modulus to obtain a second voltage limiting equation; The threshold subunit is used to establish the conservative feasible domain according to the feasible domain of the virtual impedance resistor and the virtual impedance inductor, and the second voltage limit equation.

11. A conservative virtual synchronous generator impedance setting device as claimed in claim 10, characterized in that: The threshold subunit is specifically: The maximum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the second voltage limiting equation is defined as the minimum value of the comprehensive calculation result of the virtual impedance resistor and the virtual impedance inductor in the feasible domain of the virtual impedance resistor and the virtual impedance inductor, to obtain an initial conservative feasible domain; The frequency in the initial conservative feasible region is replaced by the minimum frequency of the grid-type converter to obtain the conservative feasible region.

12. A conservative virtual synchronous generator impedance setting device as claimed in claim 7, characterized in that: The conservative feasible region is specifically: Among them, R v is the virtual impedance resistor, L v is the virtual impedance inductor, ω min is the minimum frequency of the grid-type converter, U p is the voltage modulus, I max is the preset maximum current threshold.

13. A storage medium, characterized in that: The storage medium stores a computer program, which is called and executed by a computer to implement any conservative virtual synchronous generator impedance setting method as claimed in any one of claims 1 to 6.

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