Grid-connected system feasible region solving and reconstruction method and system for hybrid grid-connected converter

Abstract

The present application relates to a method and system for solving and reconstructing the feasible region of a grid-connected system of grid-following and grid-forming hybrid converters, which comprises: obtaining parameters of the grid-connected system of hybrid converters and parameters of an AC power grid; simplifying the grid-connected system of hybrid converters into multiple equivalent grid-following or grid-forming converters through grouping and equivalent aggregation; theoretically solving the capacity feasible region satisfying the overload capability constraint and the static voltage stability feasible region satisfying the static voltage stability constraint; discretizing the intersection of the capacity feasible region and the static voltage stability feasible region; judging whether the operating condition satisfies the wide-area oscillation constraint point by point, and if it does, the condition belongs to the operating feasible region of the grid-connected system of hybrid converters, and finally obtaining the operating feasible region of the grid-following and grid-forming hybrid converter grid-connected system; and expanding and reconstructing the operating feasible region by configuring the grid-forming converter. The present application takes into account the differences between different converters and all operating conditions that the converters may face, and can ensure the safe and stable operation of the converter grid-connected system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electric power, and particularly relates to a follow-network hybrid converter grid-connected system feasible region solving and reconstruction method and system. BACKGROUND

[0002] Wind power, photovoltaic and other converters are connected to the alternating current power grid through follow-network or network-construction converters. The randomness, volatility and intermittency of new energy output lead to complex and variable operating conditions of the converters. When the operating conditions change, the operating characteristics of the converters (such as grid-connected point voltage, oscillation characteristics, etc.) will also change. Under some operating conditions, the unit may face the risk of output current exceeding the limit, port voltage not meeting the grid-connected requirements or wideband oscillation instability. Such risks make it difficult for the converter grid-connected system to operate safely and stably, and in serious cases may even cause equipment damage or disconnection. Therefore, it is necessary to clarify the operating feasible region of the converter grid-connected system to guide the system to avoid risky operating conditions during operation and thus ensure the safe and stable operation of the system. However, existing researches usually equate the hybrid converter grid-connected system to a single converter, ignoring the differences between different converters. In addition, when solving the operating feasible region, only a few typical operating conditions are analyzed, and all operating conditions that the converter may face are not fully considered. In order to ensure the safe and stable operation of the converter grid-connected system, it is necessary to study the operating feasible region solving method considering the differences between converters and all operating conditions. SUMMARY

[0003] The purpose of the present application is to provide a follow-network hybrid converter grid-connected system feasible region solving and reconstruction method and system to solve the above technical problems.

[0004] The present application provides

[0005] A follow-network hybrid converter grid-connected system feasible region solving and reconstruction method, comprising the following steps:

[0006] Step 1, obtaining the parameters of the hybrid converter grid-connected system and the parameters of the alternating current power grid;

[0007] Step 2, simplifying the hybrid converter grid-connected system into multiple equivalent follow-network or network-construction converters through the grouping method and the equivalent aggregation method;

[0008] Step 3, theoretically solving the capacity feasible region meeting the overload capacity constraint and the static voltage stability feasible region meeting the static voltage stability constraint;

[0009] Step 4, discretizing the intersection of the capacity feasible region and the static voltage stability feasible region to obtain the discretized set;

[0010] Step 5, judging whether the operating condition in the discretized set meets the wide frequency oscillation constraint point by point, if yes, the operating condition belongs to the operation feasible region of the hybrid converter grid-connected system, and finally the operation feasible region of the hybrid converter grid-connected system is obtained;

[0011] Step 6, extending and reconstructing the operation feasible region by configuring the grid-forming converter.

[0012] Further, the parameters of the hybrid converter grid-connected system in step 1 include system circuit topology, number of converters, installation position of the grid-following converter, installation position of the grid-forming converter, corresponding feeder impedance and step-up impedance of each converter, impedance model of the reactive power compensation device, and impedance model of each converter; the parameters of the AC power grid include power source amplitude range, series resistance interval, and series reactance interval.

[0013] Further, the grouping method in step 2 includes: attributing the reactive power compensation device to the converter, dividing the converters of the same model, the same control parameters and the adjacent geographical position into the same group, and after the grouping is completed, defaulting that the outputs of all the converters in the group are consistent, and the control strategy and parameters are consistent;

[0014] The equivalent aggregation method includes:

[0015] All the units in the group are aggregated into a single grid-following or grid-forming converter, and the equivalent converter is connected to the grid bus through the feeder; three types of parameters are solved by the equivalent aggregation, and the solving method of each parameter includes: 1) the equivalent converter impedance model is the same as the equivalent units in the group; 2) the output active power / reactive power of the equivalent converter is the sum of the output active power / reactive power of the equivalent units in the group; 3) the equivalent feeder impedance is solved based on the consistent power loss principle.

[0016] Further, the step 3 includes:

[0017] There are m equivalent converters in the hybrid converter grid-connected system, and each converter is connected to the grid point through the equivalent feeder, and then connected to the AC power grid; the operating condition of the hybrid converter grid-connected system is represented as:

[0018] Ω0=[P1,Q1,…,P i ,Q i ,…,P m ,Q m ],i=1,2,…,m

[0019] In the formula, P i , Q i are the output active power and reactive power of the i-th equivalent converter; n is the total number of equivalent converters;

[0020] The capacity feasible region Ω I of the hybrid converter grid-connected system is solved by the following method:

[0021]

[0022] Static voltage stability feasible region Ω of hybrid converter grid-connected system V , whose expression is:

[0023] Ω V = {(P1, Q1, …, P i , Q i , …, P m , Q m ) | 0.9pu < V i < 1.1pu, i = 1, 2, …, m}

[0024]

[0025] In the formula, V i is the effective value of the high-voltage side voltage of the voltage-boosting transformer of the i-th equivalent converter, is the high-voltage side voltage of the voltage-boosting transformer of the i-th equivalent converter, both of which are functions of the input active power P i and the input reactive power Q i of the equivalent converter;

[0026] When the output power P i and Q i of the equivalent converter are known, the following formula is used to solve

[0027]

[0028] In the formula, I is the output current of the i-th equivalent converter; the superscript * represents the conjugate of a complex number; Z i is the equivalent feeder impedance of the i-th equivalent converter; is the grid-connected point voltage; R g and X g are the equivalent resistance and the equivalent reactance of the AC power grid, respectively.

[0029] Further, the step 4 comprises:

[0030] The operation condition set Ω I ∩Ω V of the hybrid converter grid-connected system satisfying the overload capability constraint, the static voltage stability constraint and the inverter self-constraint simultaneously is uniformly divided to obtain a finite number of operation working points, i.e., the set Ω I ∩Ω V is discretized;

[0031] The discretized set is defined as Ω VI , and its expression is:

[0032] Ω VI = {(k P,1 ΔP,k P,1 ΔQ,…,k P,i ΔP,k Q,i ΔQ,…,k P,m ΔP,k Q,m ΔQ)∈(Ω I ∩Ω V )}

[0033]

[0034] wherein: ΔP, ΔQ are active step length and reactive step length; k P,i , k Q,i are discrete coefficients of the ith equivalent converter.

[0035] Further, in step 5, if all the oscillation mode dampings are greater than zero, it is judged that the operating condition belongs to the feasible region of the hybrid converter grid-connected system operation;

[0036] The oscillation mode damping solving step is as follows:

[0037] a) aggregating the impedance models of all devices in the system to obtain the system aggregated impedance Z Σ ;

[0038] b) solving the determinant D Σ of the system aggregated impedance

[0039] D Σ (s) = R Σ +jX Σ = Z Σ11 (s)Z Σ22 (s)-Z Σ12 (s)Z Σ21 (s)

[0040] wherein: Z Σ11 , Z Σ12 , Z Σ21 and Z Σ22 are four elements of Z Σ ; the real part of D Σ (s) is defined as the equivalent resistance R Σ , and the imaginary part is defined as the equivalent reactance X Σ ;

[0041] c) solving the oscillation damping according to the equivalent resistance R Σ and the equivalent reactance X Σ , including:

[0042] the equivalent reactance X ΣThe zero-crossing point corresponds to an oscillation mode, and the oscillation damping σ and the oscillation frequency ω corresponding to the oscillation mode are solved according to the properties of the zero-crossing point, and the expression is:

[0043]

[0044] In the formula, k R and k X are the slopes of the equivalent resistance curve and the equivalent reactance curve respectively; R Σ is the equivalent resistance; and ω r is the frequency of the zero-crossing point.

[0045] Further, the step 6 comprises:

[0046] If all operating conditions in the discretized set do not satisfy that the damping of the oscillation mode is greater than zero, the proportion of the grid-connected converter is increased until the discretized set coincides with the operating feasible region of the hybrid converter grid-connected system; the step of increasing the proportion of the grid-connected converter is:

[0047] (a) selecting the node where the grid-following converter farthest from the grid point is located, and replacing it with a grid-connected converter;

[0048] (b) sequentially solving the discretized set Ω VI according to steps 2 to 4;

[0049] (c) solving the operating feasible region Ω of the hybrid converter grid-connected system according to step 5;

[0050] (d) judging whether the discretized set Ω VI coincides with the operating feasible region Ω of the hybrid converter grid-connected system, if yes, the optimal configuration number and configuration position of the grid-connected converter are obtained, and if no, steps (a) to (c) are repeated.

[0051] The application further provides a hybrid converter grid-connected system feasible region solving and reconstruction system, comprising:

[0052] an input unit configured to input hybrid converter grid-connected system parameters and alternating current grid parameters;

[0053] an equivalent aggregation unit configured to simplify the hybrid converter grid-connected system into multiple equivalent grid-following or grid-connected converters by using a grouping method and an equivalent aggregation method;

[0054] a capacity and static voltage feasible region solving unit configured to theoretically solve a capacity feasible region meeting an overload capacity constraint and a static voltage stability feasible region meeting a static voltage stability constraint;

[0055] a feasible region discretization unit configured to discretize the intersection of the capacity feasible region and the static voltage stability feasible region to obtain a discretized set.

[0056] The operation feasible region solving unit is used for judging whether the operation condition in the discretized set meets the wide-frequency oscillation constraint point by point, and if yes, the condition belongs to the operation feasible region of the hybrid converter grid-connected system, and finally the operation feasible region of the hybrid converter grid-connected system is obtained.

[0057] The operation feasible region reconstruction unit is used for expanding and reconstructing the operation feasible region by configuring the grid-connected converter.

[0058] The output unit is used for outputting the operation feasible region of the hybrid converter grid-connected system and the configuration result of the grid-connected converter.

[0059] The application further provides a non-transitory computer readable storage medium storing computer instructions, which are executed by a processor to implement the hybrid converter grid-connected system feasible region solving and reconstructing method.

[0060] The application further provides an electronic device, which comprises:

[0061] The memory and the processor are communicatively connected, and the memory stores computer instructions, and the processor executes the computer instructions to implement the hybrid converter grid-connected system feasible region solving and reconstructing method.

[0062] By the hybrid converter grid-connected system feasible region solving and reconstructing method and system, the differences between different converters and all possible operation conditions of the converters are considered, and the safe and stable operation of the converter grid-connected system is ensured.

[0063] The above description is only a summary of the technical scheme of the application, in order to more clearly understand the technical means of the application, and the application can be implemented according to the content of the description, as follows. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 is the circuit topology of the converter grid-connected system in the first embodiment of the application;

[0065] Figure 2 is the equivalent circuit topology of the new energy grid-connected system in the first embodiment of the application;

[0066] Figure 3 is the flowchart of the hybrid converter grid-connected system feasible region solving and reconstructing method.

[0067] Figure 4 is the structural schematic diagram of the hybrid converter grid-connected system feasible region solving and reconstructing system;

[0068] Figure 5 is a structural schematic diagram of an electronic device. DETAILED DESCRIPTION

[0069] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present application, but are not used to limit the scope of the present application.

[0070] The grid topology of the converter grid-connected system is shown in Figure 1 The converter control mode includes two types of grid-following and grid-forming, so the system is also called a grid-following and grid-forming hybrid converter grid-connected system. Figure 1 There are n converters in the system, each of which is connected to the feeder through a 0.69 / 35 kV booster, and then connected to the AC grid through the feeder. Z1, Z2, …, Z n are the feeder impedances corresponding to each converter, respectively; the AC grid is equivalent to an infinite source with series impedance, where the source amplitude is V g , the series resistance is R g , and the series reactance is X g . To improve the voltage stability of the system, reactive power compensation devices are usually installed in the system, including but not limited to SVG, STATCOM, etc.

[0071] The combination of the active power P and the reactive power Q output by the converter represents a certain operating condition, and then any operating condition Ω0 of the system can be represented as

[0072] Ω0=[P1,Q1,…,P i ,Q i ,…,P n ,Q n ],i=1,2,…,n (1)

[0073] In the formula, P i and Q i are the output active power and reactive power of the i-th converter, respectively, and n is the total number of converters.

[0074] During the operation of the hybrid converter grid-connected system, the converter overload capability constraint, the static voltage stability constraint and the wide frequency oscillation stability constraint need to be met to ensure the safe and stable operation of the system.

[0075] The set of operating conditions that meet the overload capability constraint is defined as the capacity feasible region Ω I . Ω I can be defined using the output power of the converter, or using the output current of the converter. The specific expressions of the two types of definition methods are as follows:

[0076]

[0077] In the formula, Smax is the allowable overload capacity of the converter.

[0078]

[0079] Where: I max is the allowable overload current of the converter; I i is the output current of the i-th converter, I i is a function of the active power P i and reactive power Q i of the unit output.

[0080] Define the set of operating conditions that satisfy the static voltage stability constraint as the static voltage stability feasible region Ω V , and its expression is:

[0081]

[0082] Where: V i is the effective value of the voltage on the high-voltage side of the step-up transformer of the i-th converter, V i is a function of the active power P i and reactive power Q i of the unit output; V max , V min are the maximum and minimum effective values of the voltage that the converter port can withstand, respectively.

[0083] Define the set of operating conditions that satisfy the wide-frequency oscillation stability constraint as the wide-frequency oscillation feasible region Ω σ , and its expression is:

[0084] <00,00372>

[0085] Where: σ j is the oscillation damping corresponding to the j-th oscillation mode of the hybrid converter grid-connected system, σ j is a function of the active and reactive powers output by all converters, and there are l oscillation modes in the system.

[0086] The operating feasible region Ω of the hybrid converter grid-connected system represents the set of all operating conditions that satisfy the overload capacity constraint, static voltage stability constraint, and wide-frequency oscillation stability constraint. That is, the operating feasible region Ω is the intersection of the capacity feasible region Ω I , the static voltage stability feasible region Ω V and the wide-frequency oscillation feasible region Ω σ , and can be expressed as

[0087] Ω = Ω I ∩Ω V ∩Ω σ (6) <00,00379>Ref Figure 3As shown, the steps of the grid-connection system feasible region solving and reconstruction method of the grid-following and grid-forming hybrid converter are as follows:

[0089] In step S1, the parameters of the hybrid converter grid-connection system and the AC power grid are obtained. The parameters of the hybrid converter grid-connection system include the system circuit topology, the number of converters n, the installation positions of the grid-following converters, the installation positions of the grid-forming converters, the corresponding feeder impedance (Z1, Z2, …, Z n ) of each converter, the step-up impedance (Z T1 , Z T2 , …, Z Tn ), the impedance model of the reactive power compensation device, and the impedance model of each converter.

[0090] The AC power grid parameters include the power source amplitude V g , the range of the series resistance R g , the range of the series reactance X g , and the like.

[0091] The parameters of the hybrid converter grid-connection system include the system circuit topology, the number of converters n, the installation positions of the grid-following converters, the installation positions of the grid-forming converters, the corresponding feeder impedance (Z1, Z2, …, Z n ) of each converter, the step-up impedance (Z T1 , Z T2 , …, Z Tn ), the impedance model of the reactive power compensation device, and the impedance model of each converter.

[0092] In step S2, the hybrid converter grid-connection system is simplified into multiple equivalent grid-following or grid-forming converters by the grouping method and the equivalent aggregation method.

[0093] There are dozens or even hundreds of converters in the hybrid converter grid-connection system. If the potential operating conditions of all the converters are considered, it will be extremely difficult to solve. In order to improve the calculation efficiency, it is necessary to simplify the hybrid converter grid-connection system. In this step, the hybrid converter grid-connection system is first divided into m groups containing different numbers of units, and then all the units in a single group are aggregated into a single grid-following or grid-forming converter. Therefore, the hybrid converter grid-connection system can be simplified into m grid-following or grid-forming parallel converters, as shown in Figure 2 The grouping and equivalent aggregation methods are introduced in turn.

[0094] (a) Grouping method

[0095] The SVG, STATCOM, and other reactive power compensation devices are also attributed to the converter. Converters of the same model, the same control parameters, and close geographical location (connected to the same grid bus or adjacent to the grid bus) are divided into the same group. After grouping, the output active and reactive power of all the converters in the group are consistent, and the control strategy and parameters are consistent. When the number of groups m is large, the equivalent accuracy is high, but the calculation efficiency is low; on the contrary, when m is small, the equivalent accuracy is low, but the calculation efficiency is relatively high. Therefore, when selecting m, the equivalent accuracy and calculation efficiency need to be balanced.

[0096] (c) Equivalent aggregation method

[0097] The equivalent aggregation is used to aggregate all the units in the group into a single equivalent grid-connected or grid-forming converter, which is connected to the grid bus through a feeder. The equivalent aggregation needs to solve three types of parameters, and the solving methods of each parameter include but are not limited to: 1) the equivalent converter impedance model is the same as the equivalent units in the group; 2) the equivalent converter output active / reactive power is the sum of the output active / reactive power of the equivalent units in the group; 3) the equivalent feeder impedance can be solved based on the principle of consistent power loss.

[0098] Step S3, theoretically solving the capacity feasible region Ω satisfying the overload capability constraint I , the static voltage stability feasible region Ω satisfying the static voltage stability constraint V .

[0099] There are m equivalent converters in the hybrid converter grid-connected system, and each converter is connected to the grid point through an equivalent feeder and then connected to the AC power grid. The operating conditions in the hybrid converter grid-connected system can be represented as:

[0100] Ω0=[P1,Q1,…,P i ,Q i ,…,P m ,Q m ],i=1,2,…,m (7)

[0101] In the formula: P i , Q i is the output active / reactive power of the i-th equivalent converter; n is the total number of equivalent converters.

[0102] The capacity feasible region Ω of the hybrid converter grid-connected system I The solving method is:

[0103]

[0104] The static voltage stability feasible region Ω of the hybrid converter grid-connected system V , and its expression is:

[0105]

[0106] In the formula: V i is the effective value of the high-voltage side voltage of the step-up transformer of the i-th equivalent converter, is the high-voltage side voltage of the step-up transformer of the i-th equivalent converter, both of which are functions of the input active power P i and the input reactive power Q i of the equivalent converter.

[0107] Given the output power P i , Q i of the equivalent converter, the following formula can be used to solve

[0108]

[0109] In the formula: is the output current of the i-th equivalent converter; the superscript * represents the conjugate of a complex number; Z i is the equivalent feeder impedance of the i-th equivalent converter; is the grid-connected point voltage; R g , X g are the equivalent resistance and the equivalent reactance of the alternating current grid, respectively.

[0110] Step S4: discretize the intersection of the capacity feasible region Ω I and the static voltage stability feasible region Ω V to obtain the discretized set Ω VI .

[0111] The set Ω I ∩ Ω V is the set of operating conditions of the hybrid converter grid-connected system that simultaneously satisfy the overload capability constraint, the static voltage stability constraint and the constraint of the inverter itself. From a geometric point of view, the set Ω I ∩ Ω V contains an infinite number of operating conditions. Analyzing the oscillation stability of the massive operating conditions will result in extremely time-consuming, and therefore, the set Ω I ∩ Ω V can be uniformly divided to obtain a limited number of operating points, i.e., the set Ω I ∩ Ω V is discretized. The discretized set is defined as Ω VI , and the expression is as follows:

[0112]

[0113] In the formula: ΔP and ΔQ are the active step size and the reactive step size; k P,i and k Q,i are the discretization coefficients of the i-th equivalent converter.

[0114] Step S5: point-by-point judge whether the operating conditions in the discretized set Ω VI satisfy the wide-frequency oscillation constraint. If yes, the operating condition belongs to the operating feasible region Ω of the hybrid converter grid-connected system, and finally, the operating feasible region Ω of the hybrid converter grid-connected system is obtained.

[0115] In this step, it is judged whether the operating conditions in Ω VI satisfy the wide-frequency oscillation constraint. If yes, the operating condition belongs to the operating feasible region Ω; otherwise, the operating condition does not belong to the operating feasible region Ω.

[0116] For any operating condition [P1, Q1, …, Pn, Qn] of the hybrid converter grid-connected system, if the operating condition satisfies the wide-frequency oscillation constraint, the operating condition belongs to the operating feasible region Ω of the hybrid converter grid-connected system.i Q i ,…,P m Q m For i = 1, 2, ..., m, given the equivalent converter parameters (operating conditions, control strategy, parameters), equivalent feeder impedance, and AC grid parameters (equivalent impedance, grid topology), the oscillation damping σ for all oscillation modes of the renewable energy grid-connected system can be calculated. j (j = 1, 2, ..., l, where l represents the existence of l oscillation modes in the system). If the damping of all oscillation modes is greater than zero, then the operating condition belongs to the feasible region. Ω is determined point by point. VI Whether all operating conditions within the system belong to the feasible operating region is determined, and the feasible operating region Ω of the hybrid converter grid-connected system is finally obtained.

[0117] The steps for solving oscillation damping are briefly described here:

[0118] a) Aggregate the impedance models of each device in the system to obtain the aggregated system impedance Z. Σ ;

[0119] b) Solve for the determinant D of the system's pooling impedance. Σ

[0120] D Σ (s)=R Σ +jX Σ =Z Σ11 (s)Z Σ22 (s)-Z Σ12 (s)Z Σ21 (s) (12)

[0121] In the formula: Z Σ11 Z Σ12 Z Σ21 and Z Σ22 Z Σ The four elements; D Σ (s) The real part is defined as the equivalent resistance R. Σ The imaginary part is defined as the equivalent reactance X. Σ .

[0122] c) Based on the equivalent resistance R Σ and equivalent reactance X Σ Solve for the oscillation damping.

[0123] Equivalent reactance X Σ A zero-crossing point corresponds to an oscillation mode. Based on the properties of this zero-crossing point, the oscillation damping σ and oscillation frequency ω corresponding to this oscillation mode can be solved, and the expression is:

[0124]

[0125] In the formula: kR and k X are the slopes of the equivalent resistance curve and the equivalent reactance curve respectively; R Σ is the equivalent resistance; ω r is the frequency of the zero crossing point.

[0126] Step S6, expand and reconstruct the operation feasible region by configuring the network-forming converter (configure the network-forming converter to expand and reconstruct the operation feasible region Ω of the hybrid converter grid-connected system into ΩVI).

[0127] If all operating conditions in the discretized set ΩVI do not satisfy that the oscillation mode damping is greater than zero, increase the proportion of the network-forming converter until the discretized set ΩVI coincides with the operation feasible region Ω of the hybrid converter grid-connected system. The steps to increase the proportion of the network-forming converter are as follows:

[0128] a) Select the node where the grid-following converter with the farthest electrical distance from the grid connection point is located, and replace it with a network-forming converter;

[0129] b) Solve the discretized set Ω in sequence according to steps S2 - S4 VI ;

[0130] c) Solve the operation feasible region Ω of the hybrid converter grid-connected system according to step S5;

[0131] d) Determine whether the discretized set Ω VI coincides with the operation feasible region Ω of the hybrid converter grid-connected system. If it coincides, obtain the optimal number of configured network-forming converters and the configuration positions; if not, repeat steps a) - c).

[0132] The method for solving and reconstructing the feasible region of the grid-connected system of the grid-following and network-forming hybrid converter takes into account the differences between different converters and all possible operating conditions that the converter may face, and can ensure the safe and stable operation of the converter grid-connected system.

[0133] Refer Figure 4 As shown, this embodiment also provides a system for solving and reconstructing the feasible region of the grid-connected system of the grid-following and network-forming hybrid converter, including:

[0134] An input unit 310, used to input the parameters of the hybrid converter grid-connected system and the parameters of the AC power grid. The inputs of this unit include: 1) External input, that is, the initial parameters of the hybrid converter grid-connected system and the parameters of the AC power grid; 2) The configuration results of the network-forming converter and the parameters of the reconstructed hybrid converter grid-connected system from unit 360. The parameters from unit 360 will update the initial parameters from the external input.

[0135] An equivalent aggregation unit 320 is configured to simplify the hybrid converter grid-connected system into multiple equivalent grid-following or grid-forming converters by using a grouping method and an equivalent aggregation method. The grouping and equivalent aggregation of the hybrid converter grid-connected system are implemented to simplify the hybrid converter grid-connected system into multiple equivalent grid-following / grid-forming converters. The input signal of the equivalent aggregation unit 320 is from the unit 310, and the output signal is equivalent converter parameters, equivalent system parameters, and the like.

[0136] A capacity and static voltage feasible region solving unit 330 is configured to theoretically solve a capacity feasible region satisfying an overload capability constraint and a static voltage stability feasible region satisfying a static voltage stability constraint. The input signal of the capacity and static voltage feasible region solving unit 330 is from the unit 320, and the output signal is Ω I and Ω V .

[0137] A feasible region discretization unit 340 is configured to discretize the intersection of the capacity feasible region and the static voltage stability feasible region to obtain a discretized set. The intersection of the capacity feasible region and the static voltage feasible region Ω I ∩Ω V is discretized to obtain a discretized set Ω VI containing only a finite set of operating points. The input signal of the feasible region discretization unit 340 is from the unit 330, and the output signal is Ω VI .

[0138] An operating feasible region solving unit 350 is configured to determine whether an operating condition in the discretized set satisfies a wide-frequency oscillation constraint point by point, and if the operating condition satisfies the wide-frequency oscillation constraint, the operating condition belongs to the operating feasible region of the hybrid converter grid-connected system. The operating feasible region of the grid-following / grid-forming hybrid converter grid-connected system is finally obtained. The operating feasible region of the grid-following / grid-forming hybrid converter grid-connected system Ω is solved. The input signal of the operating feasible region solving unit 350 is from the unit 340, and the output signal is Ω VI .

[0139] An operating feasible region reconstruction unit 360 is configured to expand and reconstruct the operating feasible region by configuring the grid-forming converter. When the system is required to only implement the operating feasible region solving function, the unit is functionally locked. The unit is configured to expand and reconstruct the operating feasible region Ω into Ω VI , so as to realize the optimal configuration of the capacity and installation position of the grid-forming converter. The input signal of the operating feasible region reconstruction unit 360 is from the unit 350, and the output signal is the operating feasible region Ω, the configuration result of the grid-forming converter, and the parameter of the reconstructed hybrid converter grid-connected system.

[0140] An output unit 370 is configured to output the operating feasible region of the hybrid converter grid-connected system and the configuration result of the grid-forming converter. When the system is required to only implement the operating feasible region solving function, the output unit 370 is configured to output the operating feasible region Ω from the unit 350; when the device is required to implement the operating feasible region solving and reconstruction, the output unit 370 is configured to output the operating feasible region Ω from the unit 360 and the configuration result of the grid-forming converter.

[0141] The embodiment further provides a non-transitory computer readable storage medium storing computer instructions, which, when executed by a processor, implement the feasible region solving and reconstructing method for the grid-connected system of the grid-forming hybrid converter.

[0142] Referring to Figure 5 The embodiment further provides an electronic device, which comprises:

[0143] The memory 201 and the processor 202 are in communication connection with each other, the memory 201 stores computer instructions, and the processor 202 executes the computer instructions to perform the feasible region solving and reconstructing method for the grid-connected system of the grid-forming hybrid converter.

[0144] The above merely describes the preferred embodiments of the present application and is not used to limit the present application, and it should be noted that, for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A method for solving and reconstructing the feasible region of a grid-connected system with a hybrid converter, characterized in that, Includes the following steps: Step 1: Obtain the parameters of the hybrid converter grid-connected system and the AC grid parameters; Step 2: The hybrid converter grid-connected system is simplified into multiple equivalent grid-connected or grid-connected converters by using the grouping method and the equivalent aggregation method. Step 3: Theoretically solve for the capacity feasible region satisfying the overload capacity constraint and the static voltage stability feasible region satisfying the static voltage stability constraint, including: Suppose that there are m equivalent converters in the hybrid converter grid-connected system, and each converter is connected to the grid connection point via an equivalent feeder, and then connected to the AC power grid; the operating conditions of the hybrid converter grid-connected system are represented as follows: Ω0=[P1,Q1,…,P i ,Q i ,…,P m ,Q m ],i=1,2,…,m In the formula: P i Q i Let i be the active and reactive power outputs of the i-th equivalent converter; Capacity feasible range (Ω) for hybrid converter grid-connected systems I The solution method is as follows: Static voltage stability feasible range (Ω) for hybrid converter grid-connected systems V Its expression is: Ω V ={(P1,Q1,…,P i ,Q i ,…,P m ,Q m )|0.9pu<V i <1.1pu,i=1,2,…,m} In the formula: V i Let be the effective value of the high-voltage side voltage of the step-up transformer of the i-th equivalent converter. Let P be the voltage on the step-up transformer of the i-th equivalent converter, and both are related to the active power input P of the equivalent converter. i and no Q i The function; Given the equivalent converter output power P i Q i When, use the following formula to solve. In the formula: Z represents the output current of the i-th equivalent converter; the superscript * indicates the conjugate of the complex number; Z i Let be the equivalent feeder impedance of the i-th equivalent converter; R is the grid connection point voltage; g X g These are the equivalent resistance and equivalent reactance of the AC power grid, respectively. Step 4: Discretize the intersection of the capacity feasible region and the static voltage stability feasible region to obtain the discretized set; Step 5: Determine whether the operating conditions within the discretized set satisfy the wideband oscillation constraint point by point. If they do, the operating condition belongs to the feasible operating region of the hybrid converter grid-connected system. Finally, the feasible operating region of the grid-connected hybrid converter system with and without grid connection is obtained. Step 6: Expand and reconfigure the operational feasible domain by configuring the network converter.

2. The method for solving and reconstructing the feasible region of a grid-connected hybrid converter system according to claim 1, characterized in that, The parameters of the hybrid converter grid-connected system mentioned in step 1 include the system circuit topology, the number of converters, the installation location of the grid-connected converters, the installation location of the grid-connected converters, the corresponding feeder impedance and step-up transformer impedance of each converter, the impedance model of the reactive power compensation device, and the impedance model of each converter; the AC grid parameters include the power supply amplitude range, the series resistance range, and the series reactance range.

3. The method for solving and reconstructing the feasible region of a grid-connected hybrid converter system according to claim 2, characterized in that, The grouping method described in step 2 includes: classifying reactive power compensation devices as converters, grouping converters of the same model, with the same control parameters and geographical proximity into the same group, and by default, all converters in the group have the same active and reactive power outputs, and the same control strategies and parameters. The equivalent aggregation method includes: All units within the group are equivalently aggregated into a single grid-connected or grid-connected converter, and the equivalent converter is connected to the grid bus via a feeder. Three types of parameters are solved for the equivalent aggregation. The solution methods for each parameter include: 1) The impedance model of the equivalent converter is the same as that of the equivalent units within the group; 2) The active / reactive power output of the equivalent converter is the sum of the active / reactive power outputs of the equivalent units within the group; 3) The equivalent feeder impedance is solved based on the principle of consistent power loss.

4. The method for solving and reconstructing the feasible region of a grid-connected hybrid converter system according to claim 3, characterized in that, Step 4 includes: The set of operating conditions for a hybrid converter grid-connected system that simultaneously meets overload capacity constraints, static voltage stability constraints, and inverter self-constraints Ω I ∩Ω V By uniformly dividing the Ω region, a finite number of operating points are obtained, which is Ω. I ∩Ω V Discretization of sets; The discretized set is defined as Ω. VI The expression is: In the formula: ΔP and ΔQ are the active step size and reactive step size, respectively; k P,i k Q,i Let be the discrete coefficient of the i-th equivalent converter.

5. The method for solving and reconstructing the feasible region of a grid-connected hybrid converter system according to claim 4, characterized in that, In step 5, if the damping of all oscillation modes is greater than zero, then the operating condition is determined to be within the feasible operating range of the hybrid converter grid-connected system. The steps for solving the damping of the oscillation mode are as follows: a) Aggregate the impedance models of each device in the system to obtain the aggregated system impedance Z. Σ ; b) Solve for the determinant D of the system's aggregation impedance. Σ D Σ (s)=R Σ +jX Σ =Z Σ11 (s)Z Σ22 (s)-Z Σ12 (s)Z Σ21 (s) In the formula: Z Σ11 Z Σ12 Z Σ21 and Z Σ22 Z Σ The four elements; D Σ (s) The real part is defined as the equivalent resistance R. Σ The imaginary part is defined as the equivalent reactance X. Σ ; c) Based on the equivalent resistance R Σ and equivalent reactance X Σ Solving for oscillation damping includes: Equivalent reactance X Σ A zero-crossing point corresponds to an oscillation mode. Based on the properties of this zero-crossing point, the oscillation damping σ and oscillation frequency ω corresponding to this oscillation mode can be solved using the following expression: In the formula: k R and k X R represents the slope of the equivalent resistance curve and the equivalent reactance curve, respectively. Σ ω is the equivalent resistance; r The frequency that crosses zero.

6. The method for solving and reconstructing the feasible region of a grid-connected hybrid converter system according to claim 5, characterized in that, Step 6 includes: If all operating conditions within the discretized set do not satisfy the condition that the oscillation mode damping is greater than zero, then the proportion of grid-connected converters is increased until the discretized set coincides with the feasible operating region of the hybrid converter grid-connected system; the steps for increasing the proportion of grid-connected converters are as follows: (a) Select the node where the grid-connected converter is located, which is the farthest from the grid connection point in terms of electrical distance, and replace it with the grid-connected converter; (b) Solve step 2 through step 4 in sequence to obtain the discretized set Ω. VI ; (c) Solve for the feasible operating domain Ω of the hybrid converter grid-connected system according to step 5; (d) Determine the discretized set Ω VI If the feasible region Ω of the grid-connected system with the hybrid converter overlaps, the optimal number and location of the grid-connected converters are obtained; if they do not overlap, steps (a) to (c) are repeated.

7. A feasible domain solution and reconfiguration system for a grid-connected hybrid converter system, characterized in that, Performing the method of claim 1, comprising: The input unit is used to input the parameters of the hybrid converter grid-connected system and the AC grid parameters; Equivalent aggregation unit is used to simplify a hybrid converter grid-connected system into multiple equivalent grid-connected or grid-forming converters through grouping and equivalent aggregation methods. Capacity and static voltage feasible region solution unit, used to theoretically solve the capacity feasible region that satisfies overload capacity constraints and the static voltage stability feasible region that satisfies static voltage stability constraints; The feasible region discretization unit is used to discretize the intersection of the capacity feasible region and the static voltage stability feasible region to obtain the discretized set. The feasible region solution unit is used to determine point by point whether the operating conditions within the discretized set meet the wideband oscillation constraint. If they do, the operating condition belongs to the feasible region of the hybrid converter grid-connected system, and finally the feasible region of the grid-connected hybrid converter system with and without grid connection is obtained. The operational feasible domain reconfiguration unit is used to expand and reconfigure the operational feasible domain by configuring the network converter; The output unit is used to output the operational feasibility domain of the hybrid converter grid-connected system and the configuration results of the grid-connected converter.

8. A non-transitory computer-readable storage medium, characterized in that, The non-transitory computer-readable storage medium stores computer instructions, which, when executed by a processor, implement the feasible domain solution and reconfiguration method for a grid-connected hybrid converter system as described in any one of claims 1-6.

9. An electronic device, characterized in that, include: The system includes a memory and a processor, which are interconnected. The memory stores computer instructions, and the processor executes the computer instructions to perform the feasible domain solution and reconfiguration method for a grid-connected hybrid converter system as described in any one of claims 1-6.

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