Method and system for solving and reconstructing feasible region of grid-connected system of network-following hybrid converter

Abstract

The invention relates to a method and a system for solving and reconstructing a feasible region of a network-following hybrid converter grid-connected system. The method comprises the following steps of: acquiring parameters of the hybrid converter grid-connected system and parameters of an alternating-current power grid; the hybrid converter grid-connected system is simplified into a plurality of equivalent grid-following or grid-constructing converters through grouping and equivalent aggregation; theoretically solving a capacity feasible region meeting the overload capacity constraint and a static voltage stability feasible region meeting the static voltage stability constraint; discretizing the intersection of the capacity feasible region and the static voltage stability feasible region; judging whether the operation condition meets the broadband oscillation constraint point by point, if so, determining that the condition belongs to the operation feasible region of the hybrid converter grid-connected system, and finally obtaining the operation feasible region of the grid-following and grid-constructing hybrid converter grid-connected system; and carrying out expansion and reconstruction of an operation feasible region by configuring a network construction converter. According to the method, the difference between different converters and all possible working conditions of the converters are considered, and safe and stable operation of the converter grid-connected system can be guaranteed.

Description

Technical Field

[0001] The present invention belongs to the field of electric power technology, and in particular relates to a feasible domain solution and reconstruction method and system for a grid-connected hybrid converter system. Background Art

[0002] Wind power, photovoltaic and other converters are connected to the AC power grid through grid-following or grid-building converters. The randomness, volatility and intermittency of renewable energy output lead to complex and changeable converter operating conditions. When the operating conditions change, the converter operating characteristics (such as grid connection point voltage, oscillation characteristics, etc.) will also change accordingly. Under some operating conditions, the unit may face risks such as output current exceeding the limit, port voltage not meeting grid connection requirements, or broadband oscillation instability. Such risks make it difficult for the converter grid-connected system to operate safely and stably, and in severe cases may even cause equipment damage or disconnection from the grid. Therefore, it is necessary to clarify the operating feasible domain of the converter grid-connected system, guide the system to avoid risky operating conditions during operation, and thus ensure the safe and stable operation of the system. However, existing studies usually treat the hybrid converter grid-connected system as a converter, ignoring the differences between different converters. In addition, only a few typical conditions are analyzed when solving the operating feasible domain, and all 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 solution method of the operating feasible domain taking into account the differences between converters and all operating conditions. Summary of the invention

[0003] The object of the present invention is to provide a method and system for solving and reconstructing the feasible domain of a grid-connected hybrid converter system to solve the above-mentioned technical problems.

[0004] The present invention provides

[0005] A method for solving and reconstructing a feasible domain of a grid-connected hybrid converter system includes the following steps:

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

[0007] Step 2, simplifying the hybrid converter grid-connected system into multiple equal-value grid-following or grid-forming converters by means of a grouping method and an equal-value aggregation method;

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

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

[0010] Step 5, determine point by point whether the operating conditions in the discretized set meet the wide-band oscillation constraint. If so, the operating condition belongs to the feasible domain of the hybrid converter grid-connected system, and finally obtain the feasible domain of the grid-connected and grid-building hybrid converter grid-connected systems;

[0011] Step 6: Expand and reconstruct the feasible domain of operation by configuring the grid-connected converter.

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

[0013] Furthermore, the grouping method in step 2 includes: assigning the reactive compensation device to the converter, and dividing the converters of the same model, the same control parameters and the adjacent geographical locations into the same group. After the grouping is completed, it is assumed that all converters in the group have the same active and reactive power outputs, and the control strategies and parameters are consistent;

[0014] The equal value aggregation method comprises:

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

[0016] Furthermore, the step 3 comprises:

[0017] Assume that there are m equivalent converters in the hybrid converter grid-connected system, and each converter is connected to the grid connection point through an equivalent feeder and then connected to the AC power grid; the operating conditions in the hybrid converter grid-connected system are expressed as:

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

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

[0020] Capacity feasible region of hybrid converter grid-connected system Ω I The solution is:

[0021]

[0022] Feasible region of static voltage stability of hybrid converter grid-connected system Ω 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] Where: 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, and both are related to the input active power P of the equivalent converter. i and reactive Q i Function of

[0026] Known equivalent converter output power P i , Q i When , use the following formula to solve

[0027]

[0028] Where: is the output current of the ith equivalent converter; the superscript * indicates the conjugate of the complex number; Z i is the equivalent feeder impedance of the i-th equivalent converter; is the grid connection point voltage; R g , X g are the equivalent resistance and equivalent reactance of the AC power grid respectively.

[0029] Furthermore, the step 4 comprises:

[0030] The operating condition set Ω of the hybrid converter grid-connected system that simultaneously satisfies the overload capacity constraint, static voltage stability constraint and the inverter's own constraint I ∩Ω V Evenly divide and obtain a finite number of operating points, that is, I ∩Ω V Discretization of sets;

[0031] The discretized set is defined as Ω VI , the 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] Where: ΔP, ΔQ are active step length and reactive step length; k P,i , k Q,i is the discrete coefficient of the i-th equivalent converter.

[0035] Further, in step 5, if the damping of all oscillation modes is greater than zero, it is determined that the operating condition belongs to the feasible operation domain of the hybrid converter grid-connected system;

[0036] The steps of solving the oscillation mode damping are as follows:

[0037] a) Aggregate the impedance models of each device in the system to obtain the system aggregate impedance Z Σ ;

[0038] b) Solve the determinant D of the system aggregate impedance Σ

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

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

[0041] c) According to the equivalent resistance R Σ and equivalent reactance X Σ Solve for oscillation damping, including:

[0042] Equivalent reactance X ΣThe zero crossing point corresponds to an oscillation mode. Based on the properties of the zero crossing point, the oscillation damping σ and oscillation frequency ω corresponding to the oscillation mode are solved. The expression is:

[0043]

[0044] Where: 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; ω r is the frequency of the zero crossing.

[0045] Furthermore, the step 6 comprises:

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

[0047] (a) Select the node where the grid-connected converter is located that is the farthest away from the grid-connected point, and replace it with the grid-connected converter;

[0048] (b) Follow steps 2 to 4 to obtain the discretized set Ω VI ;

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

[0050] (d) Determine the discretized set Ω VI Whether it coincides with the feasible domain Ω of the hybrid converter grid-connected system operation, if so, the optimal number and configuration position of the grid-connected converter are obtained; if not, repeat steps (a) to (c).

[0051] The present invention also provides a feasible domain solving and reconstruction system for a grid-connected hybrid converter system, comprising:

[0052] An input unit, used for inputting hybrid converter grid-connected system parameters and AC power grid parameters;

[0053] An equal value aggregation unit is used to simplify the hybrid converter grid-connected system into multiple equal value grid-following or grid-forming converters by means of a grouping method and an equal value aggregation method;

[0054] Capacity and static voltage feasible region solving unit, used to theoretically solve the capacity feasible region that meets the overload capacity constraint and the static voltage stability feasible region that meets the static voltage stability constraint;

[0055] A feasible domain discretization unit is used to discretize the intersection of the capacity feasible domain and the static voltage stability feasible domain to obtain a discretized set;

[0056] The operation feasible domain solving unit is used to determine point by point whether the operating conditions in the discretized set meet the wide-band oscillation constraint. If so, the operating condition belongs to the operation feasible domain of the hybrid converter grid-connected system, and finally the operation feasible domain of the grid-following and grid-building hybrid converter grid-connected systems is obtained;

[0057] An operation feasible domain reconstruction unit is used to expand and reconstruct the operation feasible domain by configuring the grid-forming converter;

[0058] The output unit is used to output the operation feasible domain of the hybrid converter grid-connected system and the grid-connected converter configuration results.

[0059] The present invention also provides a non-transitory computer-readable storage medium, which stores computer instructions. When the computer instructions are executed by a processor, the method for solving and reconstructing the feasible domain of the grid-connected hybrid converter system is implemented.

[0060] The present invention also provides an electronic device, comprising:

[0061] A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the feasible domain solution and reconstruction method of the grid-connected hybrid converter system by executing the computer instructions.

[0062] Through the above scheme, by solving the feasible domain of the hybrid converter grid-connected system and reconstructing the method and system, considering the differences between different converters and all the working conditions that the converter may face, the safe and stable operation of the converter grid-connected system can be guaranteed.

[0063] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 is a circuit topology of a grid-connected converter system in an embodiment of the invention;

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

[0066] Figure 3 It is a flow chart of the invention and the method for solving and reconstructing the feasible domain of the grid-connected hybrid converter system.

[0067] Figure 4 It is a schematic diagram of the structure of the invention and the grid-connected hybrid converter system for solving the feasible domain and reconstructing the system;

[0068] Figure 5 It is a schematic diagram of the structure of an invented electronic device. DETAILED DESCRIPTION

[0069] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0070] The grid topology of the converter grid-connected system is as follows Figure 1 As shown, the converter control modes include two types: grid-following type and grid-forming type. Therefore, the system is also called a grid-following and grid-forming hybrid converter grid-connected system. Figure 1 There are n converters in total. Each converter is connected to the feeder through a 0.69 / 35kV step-up transformer, and then connected to the AC grid through the feeder. n are the feeder impedances corresponding to each converter respectively; the AC power grid is equivalent to an infinite power source with series impedance, where the power amplitude is V g , the series resistance is R g , the series reactance is X g In order to improve the system voltage stability, 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 reactive power Q output by the converter represents a certain operating condition. Then any operating condition Ω0 of the system can be expressed as

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

[0073] Where: P i , Q i is the output active and reactive power of the ith converter; n is the total number of converters.

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

[0075] The set of operating conditions that satisfy the overload capacity constraint is defined as the capacity feasible region Ω I Ω I It can be defined by the output power of the converter or by the output current of the converter. The specific expressions of the two definition methods are:

[0076]

[0077] Where: Smax Allowable overload capacity for the converter.

[0078]

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

[0080] The set of operating conditions that satisfy the static voltage stability constraint is defined as the static voltage stability feasible region Ω V , whose expression is:

[0081]

[0082] Where: V i is the effective value of the voltage on the high-voltage side of the boost transformer of the i-th converter, V i For the unit output active power P i and reactive Q i Function of V max 、V min They are respectively the maximum voltage RMS value and the minimum voltage RMS value that the converter port is allowed to withstand.

[0083] The set of operating conditions that satisfy the broadband oscillation stability constraint is defined as the broadband oscillation feasible domain Ω σ , whose expression is:

[0084]

[0085] Where: j is the oscillation damping corresponding to the jth oscillation mode of the hybrid converter grid-connected system, σ j It is a function of the active and reactive power output of all converters. There are a total of l oscillation modes in the system.

[0086] The operational feasible domain 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-band oscillation stability constraint. That is, the operational feasible domain Ω is the capacity feasible domain Ω. I , Static voltage stability feasible region Ω V and broadband oscillation feasible domain Ω σ The intersection of can be expressed as

[0087] Ω=Ω I ∩Ω V ∩Ω σ (6)

[0088] Ginseng Figure 3As shown in the figure, the steps of solving and reconstructing the feasible domain of the hybrid converter grid-connected system are as follows:

[0089] Step S1, obtaining the hybrid converter grid-connected system parameters and AC power grid parameters.

[0090] AC grid parameters include power amplitude V g Range, series resistance R g Interval, series reactance X g Interval, etc.

[0091] The parameters of the hybrid converter grid-connected system include the system circuit topology, the number of converters n, the installation position of the grid-following converter, the installation position of the grid-connecting converter, the corresponding feeder impedance of each converter (Z1, Z2, ..., Z n ) and boost impedance (Z T1 , Z T2 ,……,Z Tn ), impedance model of reactive compensation device, impedance model of each converter, etc.

[0092] Step S2, simplifying the hybrid converter grid-connected system into a plurality of equal-value grid-following or grid-forming converters by means of a grouping method and an equal-value aggregation method.

[0093] There are dozens or even hundreds of converters in the hybrid converter grid-connected system. If the potential operating conditions of all 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-connected system. This step first divides the hybrid converter grid-connected system into m groups with different numbers of units, and then aggregates all the units in a single group into a single grid-following or grid-forming converter. Therefore, this step can simplify the hybrid converter grid-connected system into m grid-following or grid-forming parallel converters, such as Figure 2 The following introduces the clustering and equal value aggregation methods in turn.

[0094] (a) Clustering method

[0095] Reactive compensation devices such as SVG and STATCOM are also classified as converters. Converters of the same model, same control parameters and close geographical locations (connected to the same grid-connected bus or close to the grid-connected bus) are divided into the same group. After the grouping is completed, it is assumed that all converters in the group have consistent active and reactive power outputs, and the control strategies and parameters are consistent. When the number of groups m is large, the equivalent accuracy is high, but the calculation efficiency is low; conversely, when m is small, the equivalent accuracy is low, but the calculation efficiency is high. Therefore, it is necessary to balance the equivalent accuracy and calculation efficiency when selecting m.

[0096] (c) Equivalue Aggregation Method

[0097] Equivalent aggregation is used to aggregate all units in the group into a single grid-following or grid-forming converter, which is connected to the grid-connected busbar via feeders. Equivalent aggregation requires solving three types of parameters, and the solution methods for each parameter include but are not limited to: 1) The impedance model of the equivalent converter is the same as that of the equivalent units in the group; 2) The output active / reactive power of the equivalent converter 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 solve the capacity feasible region Ω that satisfies the overload capacity constraint I , the feasible region of static voltage stability that satisfies the static voltage stability constraint Ω V .

[0099] There are m equivalent converters in the hybrid converter grid-connected system, and each converter is connected to the grid connection 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 expressed as:

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

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

[0102] Capacity feasible region of hybrid converter grid-connected system Ω I The solution is:

[0103]

[0104] Feasible region of static voltage stability of hybrid converter grid-connected system Ω V , whose expression is:

[0105]

[0106] Where: 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, and both are related to the input active power P of the equivalent converter. i and reactive Q i function.

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

[0108]

[0109] Where: is the output current of the ith equivalent converter; the superscript * indicates the conjugate of the complex number; Z i is the equivalent feeder impedance of the i-th equivalent converter; is the grid connection point voltage; R g , X g are the equivalent resistance and equivalent reactance of the AC power grid respectively.

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

[0111] Set Ω I ∩Ω V is the set of operating conditions for the hybrid inverter grid-connected system that simultaneously satisfies the overload capacity constraint, static voltage stability constraint and the inverter's own constraints. From a geometric point of view, the set Ω I ∩Ω V There are countless operating conditions. Analyzing the oscillation stability of massive operating conditions will be extremely time-consuming, so the set Ω I ∩Ω V Evenly divide and obtain a finite number of operating points, that is, I ∩Ω V The set is discretized. The discretized set is defined as Ω VI , the expression is:

[0112]

[0113] Where: ΔP, ΔQ are active step length and reactive step length; k P,i , k Q,i is the discrete coefficient of the i-th equivalent converter.

[0114] Step S5, determine the discretized set Ω point by point VI Whether the internal operating condition meets the wide-frequency oscillation constraint, if it does, the condition belongs to the feasible domain Ω of the hybrid converter grid-connected system operation, and finally the feasible domain Ω of the hybrid converter grid-connected system operation of the following grid and the building grid is obtained.

[0115] This step will determine Ω point by point VI Whether the operating condition satisfies the broadband oscillation constraint, if so, the condition belongs to the feasible operation domain Ω; otherwise, the operating condition does not belong to the feasible operation domain Ω.

[0116] For any hybrid converter grid-connected system operating condition [P1,Q1,…,Pi ,Q i ,…,P m ,Q m ], i = 1, 2, ..., m, when the equivalent converter parameters (operating conditions, control strategy, parameters), equivalent feeder impedance and AC grid parameters (equivalent impedance, grid topology) are known, the oscillation damping σ of all oscillation modes of the renewable energy grid-connected system can be calculated. j (j=1,2,…,l, l means that the system has l oscillation modes). If the damping of all oscillation modes is greater than zero, the operating condition belongs to the feasible operation domain. VI Whether all the operating conditions in the grid belong to the feasible operation domain, the feasible operation domain Ω of the hybrid converter grid-connected system is finally obtained.

[0117] Here is a brief description of the steps to solve the oscillation damping:

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

[0119] b) Solve the determinant D of the system aggregate impedance Σ

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

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

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

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

[0124]

[0125] Where: 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.

[0126] Step S6, expanding and reconstructing the feasible domain of operation by configuring the grid-connected converter (configuring the grid-connected converter so that the feasible domain Ω of the hybrid converter grid-connected system is expanded and reconstructed to ΩVI).

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

[0128] a) Select the node where the grid-following converter is located that is the farthest away from the grid connection point, and replace it with the grid-connecting converter;

[0129] b) Follow steps S2 to S4 to obtain the discretized set Ω VI ;

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

[0131] d) Determine the discretized set Ω VI Whether it coincides with the feasible domain Ω of the hybrid converter grid-connected system operation, if so, the optimal number and configuration position of the grid-connected converter are obtained; if not, repeat steps a) to c).

[0132] The feasible domain solution and reconstruction method of the grid-connected hybrid converter system takes into account the differences between different converters and all working conditions that the converter may face, and can ensure the safe and stable operation of the converter grid-connected system.

[0133] Ginseng Figure 4 As shown, this embodiment also provides a feasible domain solution and reconstruction system for a grid-connected hybrid converter system, including:

[0134] The input unit 310 is used to input the hybrid converter grid-connected system parameters and AC grid parameters. The unit input includes: 1) external input, i.e., initial hybrid converter grid-connected system parameters and AC grid parameters; 2) grid-connected converter configuration results and reconstructed hybrid converter grid-connected system parameters from the unit 360. The parameters from the unit 360 will update the initial parameters from the external input.

[0135] The equivalent aggregation unit 320 is used to simplify the hybrid converter grid-connected system into multiple equivalent grid-following or grid-forming converters by means of a grouping method and an equivalent aggregation method. The hybrid converter grid-connected system is grouped and equivalently aggregated, and the hybrid converter grid-connected system is simplified into multiple equivalent grid-following / grid-forming converters. Its input signal is from the unit 310, and its output signal is equivalent converter parameters, equivalent system parameters, etc.

[0136] The capacity and static voltage feasible domain solving unit 330 is used to theoretically solve the capacity feasible domain that satisfies the overload capacity constraint and the static voltage stability feasible domain that satisfies the static voltage stability constraint. Its input signal comes from unit 320, and its output signal is Ω I and Ω V .

[0137] The feasible domain discretization unit 340 is used to discretize the intersection of the capacity feasible domain and the static voltage stability feasible domain to obtain a discretized set. I ∩Ω V Discretization, only contains a finite set of operating points Ω VI Its input signal comes from unit 330, and its output signal is Ω VI .

[0138] The operation feasible domain solving unit 350 is used to determine point by point whether the operating conditions in the discretized set meet the wide-band oscillation constraint. If so, the operating condition belongs to the operation feasible domain of the hybrid converter grid-connected system, and finally the operation feasible domain of the grid-connected and grid-forming hybrid converter grid-connected systems is obtained. The operation feasible domain Ω of the grid-connected and grid-forming hybrid converter grid-connected systems is solved. Its input signal comes from unit 340, and the output signal is Ω VI .

[0139] The operation feasible domain reconstruction unit 360 is used to expand and reconstruct the operation feasible domain by configuring the grid-forming converter. When the system is required to only implement the operation feasible domain solution function, the function of this unit is locked. This unit is used to expand and reconstruct the operation feasible domain Ω into Ω VI , realizing the optimal configuration of the capacity and installation position of the grid-connected converter. Its input signal comes from unit 350, and its output signal is the operation feasible domain Ω, the grid-connected converter configuration result, and the reconstructed hybrid converter grid-connected system parameters.

[0140] Output unit 370 is used to output the hybrid converter grid-connected system operation feasible domain and grid-connected converter configuration results. When the system is required to only solve the operation feasible domain, the unit is used to output the operation feasible domain Ω from unit 350; when the device is required to solve and reconstruct the operation feasible domain, the unit is used to output the operation feasible domain Ω and grid-connected converter configuration results from unit 360.

[0141] This embodiment also provides a non-transitory computer-readable storage medium, which stores computer instructions. When the computer instructions are executed by a processor, the feasible domain solution and reconstruction method of the grid-connected hybrid converter system is implemented.

[0142] Ginseng Figure 5 As shown, this embodiment also provides an electronic device, including:

[0143] A memory 201 and a processor 202, wherein the memory 201 and the processor 202 are communicatively connected to each other, the memory 201 stores computer instructions, and the processor 202 executes the computer instructions to solve and reconstruct the feasible domain of the grid-connected hybrid converter system.

[0144] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for solving and reconstructing the feasible domain of a grid-connected hybrid converter system, characterized in that: The steps include: Step 1, obtaining the hybrid converter grid-connected system parameters and AC power grid parameters; Step 2, simplifying the hybrid converter grid-connected system into multiple equal-value grid-following or grid-forming converters by means of a grouping method and an equal-value aggregation method; Step 3, theoretically solving the capacity feasible region that satisfies the overload capacity constraint and the static voltage stability feasible region that satisfies the static voltage stability constraint; Step 4, discretize the intersection of the capacity feasible region and the static voltage stability feasible region to obtain a discretized set; Step 5, determine point by point whether the operating conditions in the discretized set meet the wide-band oscillation constraint. If so, the operating condition belongs to the feasible domain of the hybrid converter grid-connected system, and finally obtain the feasible domain of the grid-connected and grid-building hybrid converter grid-connected systems; Step 6: Expand and reconstruct the feasible domain of operation by configuring the grid-connected converter.

2. The method for solving and reconstructing the feasible domain of a grid-connected hybrid converter system according to claim 1 is characterized in that: The hybrid converter grid-connected system parameters described in step 1 include system circuit topology, the number of converters, the installation position of the grid-following converter, the installation position of the grid-forming converter, the feeder impedance and boost transformer impedance corresponding to each converter, the impedance model of the reactive compensation device, and the impedance model of each converter; the AC power 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 domain of the grid-connected hybrid converter system according to claim 2 is characterized in that: The grouping method in step 2 includes: assigning reactive power compensation devices to converters, and dividing converters of the same model, the same control parameters and close geographical locations into the same group. After the grouping is completed, it is assumed that all converters in the group have consistent active and reactive power outputs, and consistent control strategies and parameters. The equal value aggregation method comprises: All the units in the group are equivalently aggregated into a single grid-following or grid-forming converter, and the equivalent converter is connected to the grid-connected bus through the feeder; the equivalent aggregation solves three types of parameters, and the solution methods of each parameter include: 1) the impedance model of the equivalent converter is the same as that of the equivalent units in the group; 2) the active / reactive power output of the equivalent converter is the sum of the active / reactive power output of the equivalent units in 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 domain of the grid-connected hybrid converter system according to claim 3 is characterized in that: The step 3 comprises: Assume that there are m equivalent converters in the hybrid converter grid-connected system, and each converter is connected to the grid connection point through an equivalent feeder and then connected to the AC power grid; the operating conditions in the hybrid converter grid-connected system are expressed as: Ω0=[P1,Q1,…,P i ,Q i ,…,P m ,Q m ],i=1,2,…,m Where: P i , Q i is the output active and reactive power of the i-th equivalent converter; n is the total number of equivalent converters; Capacity feasible region of hybrid converter grid-connected system Ω I The solution is: Feasible region of static voltage stability of hybrid converter grid-connected system Ω V , whose expression is: Ω V ={(P1,Q1,…,P i ,Q i ,…,P m ,Q m )|0.9pu<V i <1.1pu,i=1,2,…,m} Where: 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, and both are related to the input active power P of the equivalent converter. i and reactive Q i Function of Known equivalent converter output power P i , Q i When , use the following formula to solve Where: is the output current of the ith equivalent converter; the superscript * indicates the conjugate of the complex number; Z i is the equivalent feeder impedance of the i-th equivalent converter; is the grid connection point voltage; R g , X g are the equivalent resistance and equivalent reactance of the AC power grid respectively.

5. The method for solving and reconstructing the feasible domain of the grid-connected hybrid converter system according to claim 4 is characterized in that: The step 4 comprises: The operating condition set Ω of the hybrid converter grid-connected system that simultaneously satisfies the overload capacity constraint, static voltage stability constraint and the inverter's own constraint I ∩Ω V Evenly divide and obtain a finite number of operating points, that is, I ∩Ω V Discretization of sets; The discretized set is defined as Ω VI , the expression is: 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 )} Where: ΔP, ΔQ are active step length and reactive step length; k P,i , k Q,i is the discrete coefficient of the i-th equivalent converter.

6. The method for solving and reconstructing the feasible domain of the grid-connected hybrid converter system according to claim 5 is characterized in that: In step 5, if the damping of all oscillation modes is greater than zero, it is determined that the operating condition belongs to the feasible operation domain of the hybrid converter grid-connected system; The steps of solving the oscillation mode damping are as follows: a) Aggregate the impedance models of each device in the system to obtain the system aggregate impedance Z Σ ; b) Solve the determinant D of the system aggregate impedance Σ D Σ (s)=R Σ +jX Σ =Z Σ11 (s)Z Σ22 (s)-Z Σ12 (s)Z Σ21 (s) Where: Z Σ11 , Z Σ12 , Z Σ21 and Z Σ22 Z Σ The four elements of D Σ The real part of (s) is defined as the equivalent resistance R Σ , the imaginary part is defined as the equivalent reactance X Σ ; c) According to the equivalent resistance R Σ and equivalent reactance X Σ Solve for oscillation damping, including: Equivalent reactance X Σ The zero crossing point corresponds to an oscillation mode. Based on the properties of the zero crossing point, the oscillation damping σ and oscillation frequency ω corresponding to the oscillation mode are solved. The expression is: Where: 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; ω r is the frequency of the zero crossing.

7. The method for solving and reconstructing the feasible domain of a grid-connected hybrid converter system according to claim 6 is characterized in that: The step 6 comprises: If all operating conditions in the discretized set do not satisfy that the oscillation mode damping is greater than zero, the proportion of grid-connected converters is increased until the discretized set coincides with the feasible domain of the hybrid converter grid-connected system; the steps for increasing the proportion of grid-connected converters are: (a) Select the node where the grid-connected converter is located that is the farthest away from the grid-connected point, and replace it with the grid-connected converter; (b) Follow steps 2 to 4 to obtain the discretized set Ω VI ; (c) Solve the hybrid converter grid-connected system operation feasible region Ω according to step 5; (d) Determine the discretized set Ω VI Whether it coincides with the feasible domain Ω of the hybrid converter grid-connected system operation, if so, the optimal number and configuration position of the grid-connected converter are obtained; if not, repeat steps (a) to (c).

8. A feasible domain solution and reconstruction system for a grid-connected hybrid converter system, characterized in that: include: An input unit, used for inputting hybrid converter grid-connected system parameters and AC power grid parameters; An equal value aggregation unit is used to simplify the hybrid converter grid-connected system into multiple equal value grid-following or grid-forming converters by means of a grouping method and an equal value aggregation method; Capacity and static voltage feasible region solving unit, used to theoretically solve the capacity feasible region that meets the overload capacity constraint and the static voltage stability feasible region that meets the static voltage stability constraint; A feasible domain discretization unit is used to discretize the intersection of the capacity feasible domain and the static voltage stability feasible domain to obtain a discretized set; The operation feasible domain solving unit is used to determine point by point whether the operating conditions in the discretized set meet the wide-band oscillation constraint. If so, the operating condition belongs to the operation feasible domain of the hybrid converter grid-connected system, and finally the operation feasible domain of the grid-following and grid-building hybrid converter grid-connected systems is obtained; An operation feasible domain reconstruction unit is used to expand and reconstruct the operation feasible domain by configuring the grid-forming converter; The output unit is used to output the operation feasible domain of the hybrid converter grid-connected system and the grid-connected converter configuration results.

9. A non-transitory computer-readable storage medium, characterized in that: The non-transitory computer-readable storage medium stores computer instructions, and when the computer instructions are executed by the processor, the feasible domain solution and reconstruction method of the grid-connected hybrid converter system according to any one of claims 1 to 7 is implemented.

10. An electronic device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the feasible domain solution and reconstruction method of the grid-connected hybrid converter system according to any one of claims 1 to 7 by executing the computer instructions.

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