Closed-loop impulse current regulation and control method, system, equipment and medium

Abstract

The invention provides a closed-loop impulse current regulation and control method, system and device and a medium, and the method comprises the steps: calculating the closed-loop impulse current through employing the Thevenin theorem based on the electrical quantity of a power distribution network when the power distribution network is not connected with a distributed photovoltaic system; substituting the closed-loop impact current target value after the distribution network is connected with the distributed photovoltaic, the closed-loop impact current when the distribution network is not connected with the distributed photovoltaic and the electrical quantity of the distribution network into an expression of the closed-loop impact current target value determined by using a superposition theorem to calculate the power of the distributed photovoltaic connected with the distribution network; regulating and controlling the closed-loop impact current of the power distribution network based on the power of the distributed photovoltaic connected to the power distribution network; the loop closing circuit is subjected to equivalence through the superposition theorem to obtain the distributed photovoltaic access power, and the process is clear; the closed-loop impulse current is regulated and controlled by adjusting the size of the distributed photovoltaic access power, the adjustable capacity of the distributed photovoltaic is fully utilized, and the effects of low cost, safety and reliability are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power distribution, and in particular relates to a closed-loop impulse current control method, system, equipment and medium. Background Art

[0002] The proportion of distributed power sources and flexible loads connected to the distribution network has increased year by year, and the source-load structure of the distribution network has become more complex. The distribution network that adopts "closed-loop design and open-loop operation" is difficult to meet the increasingly diverse power supply needs. At the same time, problems such as uneven source-load distribution, uncertainty on both sides of supply and demand, and complex power flow trends have further reduced the reliability of power supply in the distribution network. Closing-loop load reversal operation can significantly reduce the power outage time of users and meet the increasingly demanding power supply needs. However, if the voltage difference on both sides of the closing loop is more obvious, a large circulating current will be generated in the distribution network after the closing loop, and a large impact current will be generated at the moment of closing the loop, which may trigger the action of relay protection, thereby affecting the safe and stable operation of the distribution network.

[0003] In order to effectively reduce the impact current generated by the closing operation and improve the safety and reliability of the closing operation, most existing studies have adopted means such as distribution transformer tap adjustment and capacitor switching to improve the voltage on both sides of the closing point. The former changes the impedance distribution of the closing network by adjusting the tap position of the distribution transformer; the latter changes the node voltage on the feeder by switching the capacitor bank at the 10kV low-voltage bus of the substation, thereby achieving the effect of suppressing the closing impact current. With the access of highly random distributed photovoltaics, the voltage of the distribution network is constantly changing, which is easy to cause frequent operation of taps and capacitors, thereby causing transformer or switchgear failures, limiting the number of adjustments and adjustment capabilities of transformers and capacitors. In view of the above reasons, existing research has been unable to efficiently regulate the closing current. Distributed photovoltaics are flexible and controllable, so how to make full use of the controllability of distributed photovoltaics that have been connected to the distribution network to regulate the closing current has become the main direction of such research. Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present invention proposes a closed-loop impulse current control method, comprising:

[0005] Based on the acquired electrical quantity of the medium-voltage distribution network, the closing-loop impact current when the medium-voltage distribution network is not connected to distributed photovoltaics is calculated using the Thevenin theorem;

[0006] Substitute the set target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the electrical quantity of the medium-voltage distribution network into the predetermined expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, and calculate the power of the distributed photovoltaic connected to the medium-voltage distribution network;

[0007] Based on the power of the distributed photovoltaic connected to the medium-voltage distribution network, regulating the closed-loop impact current of the medium-voltage distribution network;

[0008] Among them, the expression of the target value of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is determined by using the superposition theorem based on the closed-loop inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

[0009] Preferably, the determination of the expression of the target value of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic includes:

[0010] The voltage drop of the medium-voltage distribution network after the distributed photovoltaic is connected is equivalent to adding a reverse voltage source between every two nodes of the medium-voltage distribution network, and based on the reverse voltage source, the superposition theorem is used to construct a closed-loop impulse current equivalent circuit in the medium-voltage distribution network;

[0011] According to the closed-loop impulse current equivalent circuit, by constructing and solving the voltage time-domain differential equation of the reverse voltage source, an expression of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is obtained;

[0012] The expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic are superimposed using the superposition theorem to obtain the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic;

[0013] Among them, the difference between the expression of the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic and the expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic is the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic; the voltage drop of the medium-voltage distribution network after the connection to the distributed photovoltaic is determined based on the electrical quantities of the medium-voltage distribution network; the electrical quantities of the medium-voltage distribution network include voltage, power, resistance, inductance and reactance.

[0014] Preferably, the expression of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is expressed as follows:

[0015]

[0016] Where i(t)” is the closing-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, R is the equivalent total resistance of the line before the closing port of the medium-voltage distribution network, L is the equivalent total inductance of the line before the closing port of the medium-voltage distribution network, and u is the voltage of the reverse voltage source;

[0017] Wherein, the voltage u of the reverse voltage source is expressed as follows:

[0018]

[0019] Where N a is the closing point in the medium voltage distribution network line A, a is the node of the medium voltage distribution network line A, P s is the active power of distributed photovoltaic connected to the medium voltage distribution network, Q s is the reactive power of distributed photovoltaic connected to the medium voltage distribution network, P a is the active power of node a, Q a is the reactive power of node a, R a is the resistance at node a, X a is the reactance at node a, U a is the rated voltage at node a, U a ' is the voltage at node a after the distributed photovoltaic is connected, N b is the closing point in the medium voltage distribution network line B, b is the node of the medium voltage distribution network line B, P b is the active power of node b, Q b is the reactive power of node b, R b is the resistance at node b, X b is the reactance at node b, U b is the rated voltage at node b, U b ' is the voltage at node b after the distributed photovoltaic is connected.

[0020] Preferably, the method of calculating the loop-closing inrush current when the medium-voltage distribution network is not connected to distributed photovoltaics based on the acquired electrical quantity of the medium-voltage distribution network and using the Thevenin theorem includes:

[0021] Based on the electrical quantity of the medium-voltage distribution network and in combination with the structural characteristics of the medium-voltage distribution network, the Thevenin equivalent is performed to obtain the Thevenin equivalent total impedance of the line before the ring-closing port of the medium-voltage distribution network;

[0022] In the case of three-phase symmetry, the single-phase voltage of the medium-voltage distribution network is obtained by calculating the voltage difference between the two sides of the tie switch based on the electrical quantity of the medium-voltage distribution network;

[0023] Based on the single-phase voltage of the medium-voltage distribution network and the Thevenin equivalent total impedance of the line before the closing port of the medium-voltage distribution network, the Thevenin equivalent circuit is obtained by performing Thevenin equivalent on both sides of the tie switch;

[0024] Based on the Thevenin equivalent circuit, the voltage time-domain differential equation when the distributed photovoltaic is not connected is constructed and solved to obtain the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

[0025] Preferably, the loop-closing inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic is calculated as follows:

[0026]

[0027] Where i(t)' is the loop impact current when the medium voltage distribution network is not connected to the distributed photovoltaic, I m is the amplitude of the periodic component of the closing-loop impulse current, ω is the angular velocity, t is the time, α is the initial phase angle of the single-phase voltage of the medium-voltage distribution network at the closing moment, is the impedance angle of the closed-loop network, e is the Euler number, T a is the decay time constant of the closed-loop impulse current;

[0028] The periodic component amplitude of the closed-loop impulse current is m , calculated as follows:

[0029]

[0030] In the formula, E m is the amplitude of the single-phase voltage of the medium voltage distribution network, R is the equivalent total resistance of the line before the closing port of the medium voltage distribution network, and L is the equivalent total inductance of the line before the closing port of the medium voltage distribution network;

[0031] The decay time constant T of the closed-loop impulse current a , calculated as follows:

[0032] T a =L / R.

[0033] Preferably, the target value of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic system is set based on the current margin limit of the lines, tie switches and load rated currents in the medium-voltage distribution network.

[0034] Preferably, the regulating the closed-loop impact current of the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network includes:

[0035] Based on the power of the distributed photovoltaic connected to the medium-voltage distribution network, the closed-loop impact current of the medium-voltage distribution network is reduced by increasing the power of the distributed photovoltaic connected to the medium-voltage distribution network.

[0036] Based on the same inventive concept, the present invention also provides a closed-loop impulse current control system, comprising: a first calculation module, a second calculation module and a control module;

[0037] The first calculation module is used to calculate the loop-closing inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic system based on the acquired electrical quantity of the medium-voltage distribution network and using the Thevenin theorem;

[0038] The second calculation module is used to substitute the set target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the electrical quantity of the medium-voltage distribution network into the predetermined expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, and calculate the power of the distributed photovoltaic connected to the medium-voltage distribution network;

[0039] The control module is used to control the closed-loop impulse current of the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network;

[0040] Among them, the expression of the target value of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is determined by using the superposition theorem based on the closed-loop inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

[0041] Preferably, the second calculation module is specifically used for:

[0042] The voltage drop of the medium-voltage distribution network after the distributed photovoltaic is connected is equivalent to adding a reverse voltage source between every two nodes of the medium-voltage distribution network, and based on the reverse voltage source, the superposition theorem is used to construct a closed-loop impulse current equivalent circuit in the medium-voltage distribution network;

[0043] According to the closed-loop impulse current equivalent circuit, by constructing and solving the voltage time-domain differential equation of the reverse voltage source, an expression of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is obtained;

[0044] The expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic are superimposed using the superposition theorem to obtain the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic;

[0045] Among them, the difference between the expression of the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic and the expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic is the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic; the voltage drop of the medium-voltage distribution network after the connection to the distributed photovoltaic is determined based on the electrical quantities of the medium-voltage distribution network; the electrical quantities of the medium-voltage distribution network include voltage, power, resistance, inductance and reactance.

[0046] Preferably, the expression of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is expressed as follows:

[0047]

[0048] Where i(t)” is the closing-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, R is the equivalent total resistance of the line before the closing port of the medium-voltage distribution network, L is the equivalent total inductance of the line before the closing port of the medium-voltage distribution network, and u is the voltage of the reverse voltage source;

[0049] Wherein, the voltage u of the reverse voltage source is expressed as follows:

[0050]

[0051] Where N a is the closing point in the medium voltage distribution network line A, a is the node of the medium voltage distribution network line A, P s is the active power of distributed photovoltaic connected to the medium voltage distribution network, Q s is the reactive power of distributed photovoltaic connected to the medium voltage distribution network, P a is the active power of node a, Q a is the reactive power of node a, R a is the resistance at node a, X a is the reactance at node a, U a is the rated voltage at node a, U a ' is the voltage at node a after the distributed photovoltaic is connected, N b is the closing point in the medium voltage distribution network line B, b is the node of the medium voltage distribution network line B, P b is the active power of node b, Q b is the reactive power of node b, R b is the resistance at node b, X b is the reactance at node b, U b is the rated voltage at node b, U b ' is the voltage at node b after the distributed photovoltaic is connected.

[0052] Preferably, the first calculation module is specifically used to:

[0053] Based on the electrical quantity of the medium-voltage distribution network and in combination with the structural characteristics of the medium-voltage distribution network, the Thevenin equivalent is performed to obtain the Thevenin equivalent total impedance of the line before the ring-closing port of the medium-voltage distribution network;

[0054] In the case of three-phase symmetry, the single-phase voltage of the medium-voltage distribution network is obtained by calculating the voltage difference between the two sides of the tie switch based on the electrical quantity of the medium-voltage distribution network;

[0055] Based on the single-phase voltage of the medium-voltage distribution network and the Thevenin equivalent total impedance of the line before the closing port of the medium-voltage distribution network, the Thevenin equivalent circuit is obtained by performing Thevenin equivalent on both sides of the tie switch;

[0056] Based on the Thevenin equivalent circuit, the voltage time-domain differential equation when the distributed photovoltaic is not connected is constructed and solved to obtain the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

[0057] Preferably, the loop-closing inrush current when the medium-voltage distribution network in the first calculation module is not connected to the distributed photovoltaic is calculated according to the following formula:

[0058]

[0059] Where i(t)' is the loop impact current when the medium voltage distribution network is not connected to the distributed photovoltaic, I m is the amplitude of the periodic component of the closing-loop impulse current, ω is the angular velocity, t is the time, α is the initial phase angle of the single-phase voltage of the medium-voltage distribution network at the closing moment, is the impedance angle of the closed-loop network, e is the Euler number, T a is the decay time constant of the closed-loop impulse current;

[0060] The periodic component amplitude of the closed-loop impulse current is m , calculated as follows:

[0061]

[0062] In the formula, E m is the amplitude of the single-phase voltage of the medium voltage distribution network, R is the equivalent total resistance of the line before the closing port of the medium voltage distribution network, and L is the equivalent total inductance of the line before the closing port of the medium voltage distribution network;

[0063] The decay time constant T of the closed-loop impulse current a , calculated as follows:

[0064] T a =L / R.

[0065] Preferably, the target value of the closed-loop inrush current after the medium-voltage distribution network in the second calculation module is connected to the distributed photovoltaic system is set based on the current margin limit of the lines, tie switches and load rated currents in the medium-voltage distribution network.

[0066] Preferably, the control module is specifically used to reduce the closed-loop impact current of the medium-voltage distribution network by increasing the power of the distributed photovoltaic connected to the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network.

[0067] Based on the same inventive concept, the present invention also provides a computer device, including:

[0068] one or more processors;

[0069] A memory for storing one or more programs;

[0070] When the one or more programs are executed by the one or more processors, the closed-loop impulse current control method is implemented.

[0071] Based on the same inventive concept, the present invention also provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed, the closed-loop impulse current control method is implemented.

[0072] Compared with the closest prior art, the present invention has the following beneficial effects:

[0073] 1. The present invention provides a closed-loop inrush current control method and system, comprising: obtaining and calculating the closed-loop inrush current when the medium-voltage distribution network is not connected to distributed photovoltaics based on the electrical quantity of the medium-voltage distribution network using the Thevenin theorem; substituting the set closed-loop inrush current target value after the medium-voltage distribution network is connected to distributed photovoltaics, the closed-loop inrush current when the medium-voltage distribution network is not connected to distributed photovoltaics, and the electrical quantity of the medium-voltage distribution network into the predetermined expression of the closed-loop inrush current target value after the medium-voltage distribution network is connected to distributed photovoltaics, and calculating the power of the distributed photovoltaics connected to the medium-voltage distribution network; based on the distributed photovoltaics connected to the medium-voltage distribution network Power, the closed-loop impulse current of the medium-voltage distribution network is regulated; wherein, the expression of the target value of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is determined by the superposition theorem based on the closed-loop impulse current when the medium-voltage distribution network is not connected to the distributed photovoltaic; the present invention uses the Thevenin theorem and the superposition theorem to obtain an equivalent circuit for the closed-loop circuit of the medium-voltage distribution network, and constructs an expression of the target value of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic on the basis of the equivalent circuit, and solves the expression to obtain the power of the distributed photovoltaic connected to the medium-voltage distribution network, the analysis process is clear, and the calculation process is simplified;

[0074] 2. The present invention is based on obtaining the power of distributed photovoltaics connected to the medium-voltage distribution network. By adjusting the power of the distributed photovoltaics that have been connected to the medium-voltage distribution network during the closing of the loop, the voltage on both sides of the closing loop is improved to meet the closing conditions, and the closing loop impact current regulation is realized, thereby making full use of the adjustable power capacity of distributed photovoltaics. Compared with the existing control methods, the method provided by the present invention does not require the change of additional equipment, and can achieve the effect of low cost, small impact, safety and reliability, thereby avoiding the problem that the existing control methods are prone to cause transformer or switch equipment failures. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 A schematic flow chart of a closed-loop impulse current control method provided by the present invention;

[0076] Figure 2A schematic diagram of the distributed photovoltaic access to the power distribution network provided by the present invention;

[0077] Figure 3 A schematic diagram of the Thevenin equivalent circuit when the distributed photovoltaic power generation provided by the present invention is not connected to a medium voltage distribution network;

[0078] Figure 4 A schematic diagram of an equivalent circuit of a closed-loop impulse current after a distributed photovoltaic system provided by the present invention is connected to a medium-voltage distribution network;

[0079] Figure 5 A schematic diagram of the closed-loop topology of the distributed photovoltaic access to the medium-voltage distribution network provided by the present invention;

[0080] Figure 6 A schematic diagram of a closed-loop topology after the distributed photovoltaic is equivalent to a reverse voltage source provided by the present invention;

[0081] Figure 7 A schematic diagram of the basic structure of a closed-loop impulse current control system provided by the present invention. DETAILED DESCRIPTION

[0082] As the penetration rate of distributed photovoltaic power continues to increase, its random intermittent impact on the distribution network is becoming more and more profound, and the impact of voltage fluctuations is becoming more and more obvious. The voltage difference on both sides of the closed loop changes accordingly, which undoubtedly has a great impact on the closed loop operation of the distribution network. The closed loop current control method proposed in the present invention can make full use of the adjustable power capacity of distributed photovoltaics, and improve the voltage on both sides of the closed loop by adjusting the access power of distributed power sources, so that it meets the closed loop conditions and realizes the closed loop impact current control. The present invention can be implemented through the following technical solutions: Taking distributed photovoltaic power sources as an example, the impact of distributed photovoltaic access to the distribution network on the voltage drop of the distribution network is analyzed, and the voltage source equivalence is adopted. The Thevenin theorem and the superposition theorem are used to derive the equivalent single-phase equivalent circuit diagram of the closed loop impact current of the distribution network after the distributed photovoltaic access, and then the current formula is derived. According to the influencing factors of the current shown in the formula, a method for regulating the closed loop impact current by changing the access power of the distributed photovoltaics connected to the medium voltage distribution network is proposed.

[0083] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0084] Embodiment 1:

[0085] The present invention provides a closed-loop impulse current control method, the flow chart of which is as follows: Figure 1 As shown, including:

[0086] Step 1: Based on the acquired electrical quantity of the medium-voltage distribution network, the closing-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic is calculated using the Thevenin theorem;

[0087] Step 2: Substitute the target value of the closed-loop impact current after connecting the set medium-voltage distribution network to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the electrical quantities of the medium-voltage distribution network into the expression of the target value of the closed-loop impact current after connecting the distributed photovoltaic to the medium-voltage distribution network determined in advance, and calculate the power of the distributed photovoltaic connected to the medium-voltage distribution network;

[0088] Step 3: Regulate the closed-loop impact current of the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network;

[0089] Among them, the expression of the target value of the closed-loop impact current after connecting the distributed photovoltaic to the medium-voltage distribution network is determined by using the superposition theorem based on the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

[0090] Before performing Step 1, the present invention first analyzes the voltage change situation of each node of the distribution network according to the access position of the distributed photovoltaic, as Figure 2 shown in the schematic diagram of the distributed photovoltaic accessing the distribution network. After a distributed photovoltaic PV accesses any node of the distribution network, the positional relationship between any node m (i.e., S m ) in the distribution network and its previous node m-1 (i.e., S m-1 ) is marked. The current between S m and S m-1 is I m , U0 is the rated output voltage of the medium-voltage distribution network, and the other nodes and currents are类推.

[0091] Analyze the voltage drop situation of each node of the medium-voltage distribution network after connecting the distributed photovoltaic to the medium-voltage distribution network. Assume that the distributed photovoltaic accesses the medium-voltage distribution network at point p, and its access power is P s +jQ s . According to different access points p, the voltage drop between node m and node m-1 in the medium-voltage distribution network can be discussed as follows:

[0092] When the access point p is after node m (0 < m < p), the voltage drop ΔU bm between node m and node m-1 after connecting the distributed photovoltaic is:

[0093]

[0094] In the formula, P s is the active power of the distributed photovoltaic connected to the medium-voltage distribution network, Q s is the reactive power of the distributed photovoltaic connected to the medium-voltage distribution network, P m is the active power of node m, Q m is the reactive power of node m, and R mis the resistance at node m, X m is the reactance at node m, U m ’ is the voltage at node m after the access of distributed PV.

[0095] When the access point p is before node m (0 < p < m), the voltage drop ΔU between node m and node m - 1 after the access of distributed PV fm is:

[0096]

[0097] It can be seen from the formula that after the access of distributed PV in the medium - voltage distribution network, the overall voltage distribution of the medium - voltage distribution network increases.

[0098] Secondly, analyze the voltage drop difference U of the medium - voltage distribution network in two scenarios: with and without the access of distributed PV change . When the medium - voltage distribution network does not access distributed PV, the voltage drop ΔU between node m and node m - 1 m is:

[0099]

[0100] In the formula, U m is the voltage at node m before the access of distributed PV;

[0101] When the access point p is after node m (0 < m < p), by taking the difference, the voltage drop difference U bchange is:

[0102]

[0103] When the access point p is before node m (0 < p < m), by taking the difference, the voltage drop difference U fchange is:

[0104]

[0105] From the above formula, it can be obtained that after the medium - voltage distribution network accesses distributed PV, the change amount U of the voltage drop at the nodes before the access point change is negative, and the voltage drop at the nodes after the access point is the same as that before the access, which also verifies the conclusion that the overall voltage of each node in the medium - voltage distribution network increases.

[0106] On the basis of the above analysis, step 1 is executed, which specifically includes:

[0107] First, in the case of three - phase symmetry, the phase voltage of this phase is obtained through the voltage difference on both sides of the closed - loop switch, and the phase voltage is transformed into the time - domain form to solve the voltage values before and after the access of distributed PV;

[0108] The equivalent calculation circuit of the closing-loop impact current is analyzed when the medium-voltage distribution network is not connected to distributed photovoltaics. Assume that the voltage difference on both sides of the tie switch before closing the loop is The corresponding single-phase voltage for:

[0109]

[0110] Convert the above equation from phasor form to time domain form:

[0111] e(t)=E m sin(ωt+α) (7)

[0112] ω is the angular velocity, E m is the amplitude of the single-phase voltage of the medium voltage distribution network, t is the time, e(t) is the time domain form of the single-phase voltage, and α is the closing time The initial phase angle.

[0113] Then, according to the medium-voltage distribution network architecture and resource type, the equivalent impedance of the distribution network before the ring closing is calculated, and the Thevenin equivalent circuit before the ring closing switch port is obtained. Based on the distribution network voltage analysis results before connecting to photovoltaic power, the ring closing impact current when distributed photovoltaic power is not connected is calculated;

[0114] Considering that most medium-voltage distribution networks are overhead lines, the susceptance can be ignored, and the Thevenin equivalent total impedance Z = R + jX of all components in the closed-loop network before the closed-loop port is calculated;

[0115] Based on the single-phase voltage of the medium-voltage distribution network and the total impedance of the line Thevenin equivalent before the closing port of the medium-voltage distribution network, the Thevenin equivalent circuit is obtained by performing Thevenin equivalent on both sides of the tie switch, as shown in Figure 3 As shown, the voltage of the voltage source in the figure can be expressed by formula (7);

[0116] Based on the Thevenin equivalent circuit, the voltage time-domain differential equation when the distributed photovoltaic is not connected is constructed and solved to obtain the loop-closing impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic;

[0117] Depend on Figure 3 The differential equation can be written as follows:

[0118]

[0119] In the formula, R is the resistance and L is the inductance;

[0120] Solving the non-homogeneous first-order differential equation about i(t)', the instantaneous value of the impact current (i.e., the closed-loop impact current when the medium-voltage distribution network is not connected to distributed photovoltaics) is expressed as:

[0121]

[0122] Where i(t)' is the loop impact current when the medium voltage distribution network is not connected to the distributed photovoltaic, I m is the amplitude of the periodic component of the closing-loop impulse current, ω is the angular velocity, t is the time, α is the initial phase angle of the single-phase voltage of the medium-voltage distribution network at the closing moment, is the impedance angle of the closed-loop network, e is the Euler number, T a is the decay time constant of the closed-loop impulse current, and T a =L / R;

[0123] Formula (9) consists of periodic components and non-periodic components. When the non-periodic component reaches its maximum value, there is a maximum impact current. The analytical expression shows that the instantaneous value of the impulse current is the largest when t is equal to 0, but in actual situations, it often reaches the maximum value around t = 0.01s. This maximum instantaneous value i m It can be expressed as:

[0124]

[0125] Among them, I m The expression is:

[0126]

[0127] Where R is the total equivalent resistance of the line before the closing port of the medium voltage distribution network, and L is the total equivalent inductance of the line before the closing port of the medium voltage distribution network.

[0128] It can be obtained from the above formula that when distributed photovoltaics are not connected, the impact current generated by the closing of the distribution network is affected by the voltage difference on both sides of the closing switch as well as the equivalent resistance and equivalent inductance.

[0129] In step 2, the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic is determined, specifically, according to the closed-loop equivalent circuit after the photovoltaic is connected, the differential equation when the distributed photovoltaic acts alone is derived, and the differential equation is solved to obtain the instantaneous value expression of the closed-loop current when the distributed photovoltaic acts alone, and then the total instantaneous value expression of the closed-loop current after the distributed photovoltaic is connected to the distribution network is obtained (that is, the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic), including:

[0130] The voltage drop of the medium-voltage distribution network after the distributed photovoltaic is connected is equivalent to adding a reverse voltage source between every two nodes of the medium-voltage distribution network, and based on the reverse voltage source, the superposition theorem is used to construct a closed-loop impulse current equivalent circuit in the medium-voltage distribution network;

[0131] Due to the access of distributed photovoltaics, the voltage drop of the medium voltage distribution network is reduced by U changeTherefore, the distributed photovoltaic access can be equivalent to adding a reverse voltage source U between every two nodes. change-m , whose expression is:

[0132]

[0133] Using the superposition theorem, a new circuit for calculating the closed-loop impulse current can be obtained: Figure 4 As shown, the voltage drop value of the medium-voltage distribution network after the distributed photovoltaic access is equivalent to adding a voltage source in the opposite direction between every two nodes. According to the superposition theorem, the equivalent circuit of the closed-loop impulse current is obtained. The voltage drop value of the medium-voltage distribution network after the distributed photovoltaic access is determined based on the electrical quantities of the medium-voltage distribution network; the electrical quantities of the medium-voltage distribution network include voltage, power, resistance, inductance and reactance.

[0134] According to the closed-loop impulse current equivalent circuit, by constructing the voltage time-domain differential equation of the reverse voltage source and solving it, the expression of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is obtained, that is, Figure 4 The differential equation can be written as follows:

[0135]

[0136] Where u is the voltage of the reverse voltage source (controlled source), and i(t) is the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic.

[0137] When the controlled source voltage u acts alone, it satisfies the differential equation f(P s +jQ s ):

[0138]

[0139] In the formula, i(t)” is the loop impact current after the medium voltage distribution network is connected to the distributed photovoltaic, and j is an imaginary number;

[0140] Solving this homogeneous second-order differential equation yields:

[0141]

[0142] or

[0143]

[0144] Since this value needs to be greater than 0, the first solution is retained, that is, equation (15) is the expression of the closed-loop inrush current after the medium-voltage distribution network is connected to distributed photovoltaics.

[0145] The expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic are superimposed using the superposition theorem to obtain the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic;

[0146] When e(t) acts alone, the closed-loop impact current when the medium-voltage distribution network is not connected to distributed photovoltaics has been obtained as shown in formula (9). According to the superposition theorem, the expression of the closed-loop impact current target value after the medium-voltage distribution network is connected to distributed photovoltaics is:

[0147]

[0148] Wherein, i(t)' is the loop impact current when the medium voltage distribution network is not connected to the distributed photovoltaic; i(t) is set based on the current margin limit of the line, tie switch and load rated current in the medium voltage distribution network, and the value should not exceed the minimum current margin value;

[0149] From equations (12) and (14), the voltage u of the reverse voltage source can be obtained as:

[0150]

[0151] Where N a is the closing point in the medium voltage distribution network line A, a is the node of the medium voltage distribution network line A, P s is the active power of distributed photovoltaic connected to the medium voltage distribution network, Q s is the reactive power of distributed photovoltaic connected to the medium voltage distribution network, P a is the active power of node a, Q a is the reactive power of node a, R a is the resistance at node a, X a is the reactance at node a, U a is the rated voltage at node a, U a ' is the voltage at node a after the distributed photovoltaic is connected, N b is the closing point in the medium voltage distribution network line B, b is the node of the medium voltage distribution network line B, P b is the active power of node b, Q b is the reactive power of node b, R b is the resistance at node b, X b is the reactance at node b, U b is the rated voltage at node b, U b ' is the voltage at node b after the distributed photovoltaic is connected.

[0152] It can be seen from the above equations that the impact current generated by the closing of the medium-voltage distribution network is also affected by the active power P of the distributed photovoltaic connected to the medium-voltage distribution network. s and the reactive power Q of distributed photovoltaic connected to the medium voltage distribution network s The influence of P is changed by changing P in the closed loop under the original circuit conditions. s With Q s The closed-loop impact current i can be reduced, thereby achieving the purpose of reducing the closed-loop impact current.

[0153] According to the expression of the target value of the closing-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the factors affecting the closing-loop impact current of the medium-voltage distribution network considering the access of distributed photovoltaic are analyzed, and the correlation between the access power of distributed photovoltaic power sources and the corresponding current components is analyzed. The increase and decrease relationship between the access power of distributed photovoltaic and the closing-loop current components is obtained, that is, the total closing-loop current is negatively correlated with the current component corresponding to the distributed photovoltaic. Then, by increasing the power of the connected distributed photovoltaic, the closing-loop impact current is reduced.

[0154] Compared with the existing method of changing the transformer ratio and switching capacitor groups, the method provided by the present invention can utilize the distribution network itself to control the size of the distributed photovoltaic access power when closing the loop, thereby realizing the suppression of the distribution network closing-loop impact current under the background of large-scale distributed photovoltaic access distribution network, and the method has low cost and small impact; the present invention uses the Thevenin theorem and the superposition theorem to obtain an equivalent circuit for the closing-loop circuit of the medium-voltage distribution network, and constructs an expression for the target value of the closing-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic on the basis of the equivalent circuit, and solves the expression to obtain the power of the distributed photovoltaic connected to the medium-voltage distribution network, and the analysis process is clear, which simplifies the calculation process.

[0155] Embodiment 2:

[0156] This embodiment introduces a specific implementation process of a closed-loop impulse current control method, including:

[0157] 1) First, calculate the loop impact current i(t)' when the medium voltage distribution network is not connected to the distributed photovoltaic;

[0158] 2) Secondly, according to the current margin limit of the line, tie switch, load rated current, etc., set the target value i(t) of the loop impact current after the medium voltage distribution network is connected to the distributed photovoltaic, which should not exceed the minimum current margin value;

[0159] 3) Then, according to the superposition theorem, the closed-loop impact current i(t)″ after the medium-voltage distribution network is connected to the distributed photovoltaic is calculated. The calculation formula is: i(t)″=i(t)'-i(t);

[0160] 4) Finally, according to the above formula, by calculating i(t)”, the active power P of the distributed photovoltaic connected to the medium voltage distribution network is solved. s and the reactive power Q of distributed photovoltaic connected to the medium voltage distribution network s , in P s and Q s It is increased on the basis of the above, thereby reducing the loop impact current.

[0161] In such Figure 5 In the medium-voltage distribution network ring topology diagram shown in the figure, distributed photovoltaics are connected. The closing points are node 2 on the left line and node 5 on the right line. Distributed photovoltaics are connected to node 2 and node 5 respectively. Z2 is the impedance between node 1 and node 2, and the others are similar. In addition, it should be noted that Figure 5 It is a special case of the present invention. The present invention realizes the closed-loop current regulation by calculating and adjusting the power of distributed photovoltaics after the distributed photovoltaics have been connected to the medium-voltage distribution network. Therefore, the location where the distributed photovoltaics are connected, whether both lines need to be connected to the distributed photovoltaics, etc., are not within the scope of consideration of the present invention.

[0162] Will Figure 5 The distributed photovoltaic equivalent in is to add a reverse voltage source between every two nodes, and we can get the following: Figure 6 The distributed photovoltaic is equivalent to a closed-loop topology diagram of a reverse voltage source. The reverse voltage source between each two nodes is shown in the figure. change1 -U change5 shown; for Figure 6 The reverse voltage source shown in FIG. 1 can be obtained according to formula (18) as follows:

[0163]

[0164] Where 2 and 5 represent the closing point, x is any node before the closing point in the line where node 2 is located in the medium voltage distribution network, y is any node before the closing point in the line where node 5 is located in the medium voltage distribution network, P s is the active power of distributed photovoltaic connected to the medium voltage distribution network, Q s is the reactive power of distributed photovoltaic connected to the medium voltage distribution network, P x is the active power of node x, Q x is the reactive power of node x, R x is the resistance at node x, X x is the reactance at node x, U x is the rated voltage at the x node, U x ' is the voltage at node x after the distributed photovoltaic is connected, P y is the active power of node y, Q y is the reactive power of node y, Ry is the resistance at node y, X y is the reactance at node y, U y is the rated voltage at the y node, U y ' is the voltage at node y after distributed photovoltaic access.

[0165] Then, substituting the above formula into formula (17), we can calculate P s and Q s , and then according to P s and Q s Adjust the power of distributed photovoltaic access when closing the loop to suppress the loop impact current.

[0166] Compared with changing the transformer ratio and switching capacitor groups, the present invention, in the context of medium-voltage distribution networks with large-scale distributed photovoltaic access, utilizes the medium-voltage distribution network itself to control the size of the distributed photovoltaic access power when the loop is closed, thereby suppressing the closing-loop impact current of the distribution network. This method has low cost and small impact. The method utilizes the superposition theorem to construct an equivalent circuit for the closing-loop impact current, separates the influence of the distributed photovoltaic and the original distribution network power supply on the closing-loop impact current, and the analysis is independent, simplifying the analysis process.

[0167] Embodiment 3:

[0168] Based on the same inventive concept, the present invention also provides a closed-loop impulse current control system, the basic structural diagram of which is shown in FIG. Figure 7 As shown, it includes: a first calculation module, a second calculation module and a control module;

[0169] The first calculation module is used to calculate the loop-closing inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic system based on the acquired electrical quantity of the medium-voltage distribution network and using the Thevenin theorem;

[0170] The second calculation module is used to substitute the set target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the electrical quantity of the medium-voltage distribution network into the predetermined expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, and calculate the power of the distributed photovoltaic connected to the medium-voltage distribution network;

[0171] The control module is used to control the closed-loop impulse current of the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network;

[0172] Among them, the expression of the target value of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is determined by using the superposition theorem based on the closed-loop inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

[0173] Preferably, the second calculation module is specifically used for:

[0174] The voltage drop of the medium-voltage distribution network after the distributed photovoltaic is connected is equivalent to adding a reverse voltage source between every two nodes of the medium-voltage distribution network, and based on the reverse voltage source, the superposition theorem is used to construct a closed-loop impulse current equivalent circuit in the medium-voltage distribution network;

[0175] According to the closed-loop impulse current equivalent circuit, by constructing and solving the voltage time-domain differential equation of the reverse voltage source, an expression of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is obtained;

[0176] The expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic are superimposed using the superposition theorem to obtain the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic;

[0177] Among them, the difference between the expression of the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic and the expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic is the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic; the voltage drop of the medium-voltage distribution network after the connection to the distributed photovoltaic is determined based on the electrical quantities of the medium-voltage distribution network; the electrical quantities of the medium-voltage distribution network include voltage, power, resistance, inductance and reactance.

[0178] Preferably, the expression of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is expressed as follows:

[0179]

[0180] Where i(t)” is the closing-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, R is the equivalent total resistance of the line before the closing port of the medium-voltage distribution network, L is the equivalent total inductance of the line before the closing port of the medium-voltage distribution network, and u is the voltage of the reverse voltage source;

[0181] Wherein, the voltage u of the reverse voltage source is expressed as follows:

[0182]

[0183] Where N a is the closing point in the medium voltage distribution network line A, a is the node of the medium voltage distribution network line A, P s is the active power of distributed photovoltaic connected to the medium voltage distribution network, Q s is the reactive power of distributed photovoltaic connected to the medium voltage distribution network, P ais the active power of node a, Q a is the reactive power of node a, R a is the resistance at node a, X a is the reactance at node a, U a is the rated voltage at node a, U a ' is the voltage at node a after the distributed photovoltaic is connected, N b is the closing point in the medium voltage distribution network line B, b is the node of the medium voltage distribution network line B, P b is the active power of node b, Q b is the reactive power of node b, R b is the resistance at node b, X b is the reactance at node b, U b is the rated voltage at node b, U b ' is the voltage at node b after the distributed photovoltaic is connected.

[0184] Preferably, the first calculation module is specifically used to:

[0185] Based on the electrical quantity of the medium-voltage distribution network and in combination with the structural characteristics of the medium-voltage distribution network, the Thevenin equivalent is performed to obtain the Thevenin equivalent total impedance of the line before the ring-closing port of the medium-voltage distribution network;

[0186] In the case of three-phase symmetry, the single-phase voltage of the medium-voltage distribution network is obtained by calculating the voltage difference between the two sides of the tie switch based on the electrical quantity of the medium-voltage distribution network;

[0187] Based on the single-phase voltage of the medium-voltage distribution network and the Thevenin equivalent total impedance of the line before the closing port of the medium-voltage distribution network, the Thevenin equivalent circuit is obtained by performing Thevenin equivalent on both sides of the tie switch;

[0188] Based on the Thevenin equivalent circuit, the voltage time-domain differential equation when the distributed photovoltaic is not connected is constructed and solved to obtain the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

[0189] Preferably, the loop-closing inrush current when the medium-voltage distribution network in the first calculation module is not connected to the distributed photovoltaic is calculated according to the following formula:

[0190]

[0191] Where i(t)' is the loop impact current when the medium voltage distribution network is not connected to the distributed photovoltaic, I m is the amplitude of the periodic component of the closing-loop impulse current, ω is the angular velocity, t is the time, α is the initial phase angle of the single-phase voltage of the medium-voltage distribution network at the closing moment, is the impedance angle of the closed-loop network, e is the Euler number, T a is the decay time constant of the closed-loop impulse current;

[0192] The periodic component amplitude of the closed-loop impulse current is m , calculated as follows:

[0193]

[0194] In the formula, E m is the amplitude of the single-phase voltage of the medium voltage distribution network, R is the equivalent total resistance of the line before the closing port of the medium voltage distribution network, and L is the equivalent total inductance of the line before the closing port of the medium voltage distribution network;

[0195] The decay time constant T of the closed-loop impulse current a , calculated as follows:

[0196] T a =L / R.

[0197] Preferably, the target value of the closed-loop inrush current after the medium-voltage distribution network in the second calculation module is connected to the distributed photovoltaic system is set based on the current margin limit of the lines, tie switches and load rated currents in the medium-voltage distribution network.

[0198] Preferably, the control module is specifically used to reduce the closed-loop impact current of the medium-voltage distribution network by increasing the power of the distributed photovoltaic connected to the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network.

[0199] The present invention obtains an equivalent circuit by equating the closing circuit of the medium-voltage distribution network through the Thevenin theorem and the superposition theorem, and constructs an expression for the target value of the closing-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic on the basis of the equivalent circuit, and solves the expression to obtain the power of the distributed photovoltaic connected to the medium-voltage distribution network. The analysis process is clear and the calculation process is simplified. The present invention is based on obtaining the power of the distributed photovoltaic connected to the medium-voltage distribution network, and improves the voltage on both sides of the closing loop by adjusting the power size of the distributed photovoltaic connected to the medium-voltage distribution network when closing the loop, so that the closing loop conditions are met, and the closing loop impulse current regulation is realized, and the adjustable power capacity of the distributed photovoltaic is fully utilized. Compared with the existing control method, the method provided by the present invention does not require changing additional equipment, and can achieve the effects of low cost, small impact, safety and reliability, and avoids the problem that the existing control method is easy to cause transformer or switch equipment failure.

[0200] Embodiment 4:

[0201] Based on the same inventive concept, the present invention also provides a computer device, which includes a processor and a memory, wherein the memory is used to store a computer program, the computer program includes program instructions, and the processor is used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc. It is the computing core and control core of the terminal, which is suitable for implementing one or more instructions, and is specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding function, so as to implement the steps of a closed-loop impulse current control method in the above embodiment.

[0202] By means of the computer device provided in this embodiment, a closed-loop impulse current control method is implemented. The closed-loop circuit of the medium-voltage distribution network is equivalently obtained by the Thevenin theorem and the superposition theorem to obtain an equivalent circuit. Based on the equivalent circuit, an expression for the target value of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is constructed. The power of the distributed photovoltaic connected to the medium-voltage distribution network is obtained by solving the expression. The analysis process is clear and the calculation process is simplified. Based on the power of the distributed photovoltaic connected to the medium-voltage distribution network, the power of the distributed photovoltaic connected to the medium-voltage distribution network is adjusted to improve the voltage on both sides of the closed loop so that the closed loop conditions are met. The closed-loop impulse current control is implemented, and the adjustable power capacity of the distributed photovoltaic is fully utilized. Compared with the existing control method, there is no need to change additional equipment, and the effect of low cost, small impact, safety and reliability can be achieved, avoiding the problem that the existing control method easily causes transformer or switch equipment failure.

[0203] Embodiment 5:

[0204] Based on the same inventive concept, the present invention also provides a storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It can be understood that the computer-readable storage medium here can include both built-in storage media in a computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space, which stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space, and these instructions can be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium here can be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor can load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of a closed-loop impulse current control method in the above embodiment.

[0205] Through the storage medium provided in this embodiment, a closed-loop impulse current control method is implemented. The closed-loop circuit of the medium-voltage distribution network is equivalently obtained by the Thevenin theorem and the superposition theorem to obtain an equivalent circuit, and an expression for the closed-loop impulse current target value after the medium-voltage distribution network is connected to the distributed photovoltaic is constructed on the basis of the equivalent circuit. The power of the distributed photovoltaic connected to the medium-voltage distribution network is obtained by solving the expression. The analysis process is clear and the calculation process is simplified. Based on the power of the distributed photovoltaic connected to the medium-voltage distribution network, the power size of the distributed photovoltaic connected to the medium-voltage distribution network is adjusted to improve the voltage on both sides of the closed loop so that it meets the closed loop conditions, and the closed-loop impulse current control is implemented, which makes full use of the adjustable power capacity of the distributed photovoltaic. Compared with the existing control method, there is no need to change additional equipment, and the effect of low cost, small impact, safety and reliability can be achieved, avoiding the problem that the existing control method easily causes transformer or switch equipment failure.

[0206] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0207] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0208] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0209] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0210] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit its protection scope. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that after reading the present invention, those skilled in the art can still make various changes, modifications or equivalent substitutions to the specific implementation methods of the invention, but these changes, modifications or equivalent substitutions are all within the protection scope of the pending claims of the invention.

Claims

1. A closed-loop impulse current control method, characterized in that: include: Based on the acquired electrical quantity of the medium-voltage distribution network, the closing-loop impact current when the medium-voltage distribution network is not connected to distributed photovoltaics is calculated using the Thevenin theorem; Substitute the set target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the electrical quantity of the medium-voltage distribution network into the predetermined expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, and calculate the power of the distributed photovoltaic connected to the medium-voltage distribution network; Based on the power of the distributed photovoltaic connected to the medium-voltage distribution network, regulating the closed-loop impact current of the medium-voltage distribution network; Among them, the expression of the target value of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is determined by using the superposition theorem based on the closed-loop inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

2. The method according to claim 1, characterized in that The determination of the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic includes: The voltage drop of the medium-voltage distribution network after the distributed photovoltaic is connected is equivalent to adding a reverse voltage source between every two nodes of the medium-voltage distribution network, and based on the reverse voltage source, the superposition theorem is used to construct a closed-loop impulse current equivalent circuit in the medium-voltage distribution network; According to the closed-loop impulse current equivalent circuit, by constructing and solving the voltage time-domain differential equation of the reverse voltage source, an expression of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is obtained; The expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic are superimposed using the superposition theorem to obtain the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic; Among them, the difference between the expression of the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic and the expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic is the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic; the voltage drop of the medium-voltage distribution network after the connection to the distributed photovoltaic is determined based on the electrical quantities of the medium-voltage distribution network; the electrical quantities of the medium-voltage distribution network include voltage, power, resistance, inductance and reactance.

3. The method according to claim 2, characterized in that The expression of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is expressed as follows: Where i(t)” is the closing-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic system, R is the total resistance equivalent to the line before the closing port of the medium-voltage distribution network, L is the total inductance equivalent to the line before the closing port of the medium-voltage distribution network, and u is the voltage of the reverse voltage source; Wherein, the voltage u of the reverse voltage source is expressed as follows: Where N a is the closing point in the medium voltage distribution network line A, a is the node of the medium voltage distribution network line A, P s is the active power of distributed photovoltaic connected to the medium voltage distribution network, Q s is the reactive power of distributed photovoltaic connected to the medium voltage distribution network, P a is the active power of node a, Q a is the reactive power of node a, R a is the resistance at node a, X a is the reactance at node a, U a is the rated voltage at node a, U a ' is the voltage at node a after the distributed photovoltaic is connected, N b is the closing point in the medium voltage distribution network line B, b is the node of the medium voltage distribution network line B, P b is the active power of node b, Q b is the reactive power of node b, R b is the resistance at node b, X b is the reactance at node b, U b is the rated voltage at node b, U b ' is the voltage at node b after the distributed photovoltaic is connected.

4. The method according to claim 1, characterized in that The method of calculating the loop-closing inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic power generation based on the acquired electrical quantity of the medium-voltage distribution network using the Thevenin theorem includes: Based on the electrical quantity of the medium-voltage distribution network and in combination with the structural characteristics of the medium-voltage distribution network, the Thevenin equivalent is performed to obtain the Thevenin equivalent total impedance of the line before the ring-closing port of the medium-voltage distribution network; In the case of three-phase symmetry, the single-phase voltage of the medium-voltage distribution network is obtained by calculating the voltage difference between the two sides of the tie switch based on the electrical quantity of the medium-voltage distribution network; Based on the single-phase voltage of the medium-voltage distribution network and the Thevenin equivalent total impedance of the line before the closing port of the medium-voltage distribution network, the Thevenin equivalent circuit is obtained by performing Thevenin equivalent on both sides of the tie switch; Based on the Thevenin equivalent circuit, the voltage time-domain differential equation when the distributed photovoltaic is not connected is constructed and solved to obtain the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

5. The method according to claim 4, characterized in that When the medium voltage distribution network is not connected to the distributed photovoltaic power generation, the loop-closing inrush current is calculated as follows: Where i(t)' is the loop impact current when the medium voltage distribution network is not connected to the distributed photovoltaic, I m is the amplitude of the periodic component of the closing-loop impulse current, ω is the angular velocity, t is the time, α is the initial phase angle of the single-phase voltage of the medium-voltage distribution network at the closing moment, is the impedance angle of the closed-loop network, e is the Euler number, T a is the decay time constant of the closed-loop impulse current; The periodic component amplitude of the closed-loop impulse current is m , calculated as follows: In the formula, E m is the amplitude of the single-phase voltage of the medium voltage distribution network, R is the equivalent total resistance of the line before the closing port of the medium voltage distribution network, and L is the equivalent total inductance of the line before the closing port of the medium voltage distribution network; The decay time constant T of the closed-loop impulse current a , calculated as follows: T a =L / R。 6. The method according to claim 1, characterized in that The target value of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic system is set based on the current margin limit of the lines, tie switches and load rated currents in the medium-voltage distribution network.

7. The method according to claim 1, characterized in that The method of regulating the closed-loop impact current of the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network includes: Based on the power of the distributed photovoltaic connected to the medium-voltage distribution network, the closed-loop impact current of the medium-voltage distribution network is reduced by increasing the power of the distributed photovoltaic connected to the medium-voltage distribution network.

8. A closed-loop impulse current control system, characterized in that: include: A first calculation module, a second calculation module and a control module; The first calculation module is used to calculate the loop-closing inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic system based on the acquired electrical quantity of the medium-voltage distribution network and using the Thevenin theorem; The second calculation module is used to substitute the set target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the electrical quantity of the medium-voltage distribution network into the predetermined expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, and calculate the power of the distributed photovoltaic connected to the medium-voltage distribution network; The control module is used to control the closed-loop impulse current of the medium-voltage distribution network based on the power of the distributed photovoltaic connected to the medium-voltage distribution network; Among them, the expression of the target value of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is determined by using the superposition theorem based on the closed-loop inrush current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

9. The system according to claim 8, characterized in that The second calculation module is specifically used to: convert the voltage drop of the medium-voltage distribution network after connecting to the distributed photovoltaic power generation into the equivalent of adding a reverse voltage source between every two nodes of the medium-voltage distribution network, and construct a closed-loop impulse current equivalent circuit in the medium-voltage distribution network based on the reverse voltage source using the superposition theorem; According to the closed-loop impulse current equivalent circuit, by constructing and solving the voltage time-domain differential equation of the reverse voltage source, an expression of the closed-loop impulse current after the medium-voltage distribution network is connected to the distributed photovoltaic is obtained; The expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic, and the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic are superimposed using the superposition theorem to obtain the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic; Among them, the difference between the expression of the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic and the expression of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic is the expression of the target value of the closed-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic; the voltage drop of the medium-voltage distribution network after the connection to the distributed photovoltaic is determined based on the electrical quantities of the medium-voltage distribution network; the electrical quantities of the medium-voltage distribution network include voltage, power, resistance, inductance and reactance.

10. The system according to claim 9, characterized in that The expression of the closed-loop inrush current after the medium-voltage distribution network is connected to the distributed photovoltaic is expressed as follows: Where i(t)” is the closing-loop impact current after the medium-voltage distribution network is connected to the distributed photovoltaic, R is the equivalent total resistance of the line before the closing port of the medium-voltage distribution network, L is the equivalent total inductance of the line before the closing port of the medium-voltage distribution network, and u is the voltage of the reverse voltage source; Wherein, the voltage u of the reverse voltage source is expressed as follows: Where N a is the closing point in the medium voltage distribution network line A, a is the node of the medium voltage distribution network line A, P s is the active power of distributed photovoltaic connected to the medium voltage distribution network, Q s is the reactive power of distributed photovoltaic connected to the medium voltage distribution network, P a is the active power of node a, Q a is the reactive power of node a, R a is the resistance at node a, X a is the reactance at node a, U a is the rated voltage at node a, U a ' is the voltage at node a after the distributed photovoltaic is connected, N b is the closing point in the medium voltage distribution network line B, b is the node of the medium voltage distribution network line B, P b is the active power of node b, Q b is the reactive power of node b, R b is the resistance at node b, X b is the reactance at node b, U b is the rated voltage at node b, U b ' is the voltage at node b after the distributed photovoltaic is connected.

11. The system according to claim 8, characterized in that The first calculation module is specifically used for: Based on the electrical quantity of the medium-voltage distribution network and in combination with the structural characteristics of the medium-voltage distribution network, the Thevenin equivalent is performed to obtain the Thevenin equivalent total impedance of the line before the ring-closing port of the medium-voltage distribution network; In the case of three-phase symmetry, the single-phase voltage of the medium-voltage distribution network is obtained by calculating the voltage difference between the two sides of the tie switch based on the electrical quantity of the medium-voltage distribution network; Based on the single-phase voltage of the medium-voltage distribution network and the Thevenin equivalent total impedance of the line before the closing port of the medium-voltage distribution network, the Thevenin equivalent circuit is obtained by performing Thevenin equivalent on both sides of the tie switch; Based on the Thevenin equivalent circuit, the voltage time-domain differential equation when the distributed photovoltaic is not connected is constructed and solved to obtain the closed-loop impact current when the medium-voltage distribution network is not connected to the distributed photovoltaic.

12. The system according to claim 11, characterized in that The loop-closing inrush current when the medium-voltage distribution network in the first calculation module is not connected to the distributed photovoltaic is calculated as follows: Where i(t)' is the loop impact current when the medium voltage distribution network is not connected to the distributed photovoltaic, I m is the amplitude of the periodic component of the closing-loop impulse current, ω is the angular velocity, t is the time, α is the initial phase angle of the single-phase voltage of the medium-voltage distribution network at the closing moment, is the impedance angle of the closed-loop network, e is the Euler number, T a is the decay time constant of the closed-loop impulse current; The periodic component amplitude of the closed-loop impulse current is m , calculated as follows: In the formula, E m is the amplitude of the single-phase voltage of the medium voltage distribution network, R is the equivalent total resistance of the line before the closing port of the medium voltage distribution network, and L is the equivalent total inductance of the line before the closing port of the medium voltage distribution network; The decay time constant T of the closed-loop impulse current a , calculated as follows: T a =L / R。 13. A computer device, characterized in that: include: one or more processors; A memory for storing one or more programs; When the one or more programs are executed by the one or more processors, a closed-loop impulse current control method as claimed in any one of claims 1 to 7 is implemented.

14. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed, a closed-loop impulse current control method as claimed in any one of claims 1 to 7 is implemented.

Images