Distribution network line closing method based on distributed power flow controller

Abstract

The present invention discloses a distribution network line closing method based on a distributed flow controller, wherein a distributed flow controller is connected to the closing line, and the distributed flow controller includes: a plurality of converter valve modules and a bypass switch CB1; wherein the plurality of converter valve modules are connected in series, and the bypass switch CB1 is connected in parallel with the plurality of converter valve modules as a whole; and each converter valve module has a built-in bypass switch. First, unlock the size of the closed-loop flow of a single valve module to adjust the closed-loop flow, and judge the number of valve modules that need to be put into operation for the flow target value control. At the same time, the current of the closed-loop line shall not be lower than the minimum operating current of the valve module. The method judges the number of valve modules put into operation and the working state according to the real-time current of the closed-loop line, and can realize flexible flow control of the closed-loop line of the distribution network. At the same time, during the fault period, the valve module can be instantly locked and exited, and restored to the closed-loop operation state of the AC line. It will not affect the relay protection setting of the AC system.

Description

Technical Field

[0001] The invention relates to a distribution network line closing method based on a distributed power flow controller, and belongs to the technical field of distribution networks. Background Art

[0002] With the large-scale access of distributed renewable energy, the structural form of the distribution network is also changing. Under the traditional single-side feeder network structure, with the access of distributed renewable energy, the problems of frequent flow reversal and equipment overload have become prominent. In some local areas, safety constraints have been imposed on the consumption of renewable energy, and the traditional regional distribution network is difficult to adapt to the task of renewable energy consumption. On the one hand, the existing distribution network cannot fully utilize the renewable energy consumption capacity of the regional power grid due to the mismatch of source-grid-load resource distribution, uncontrollable grid flow, and uncoordinated operation of source-load-storage, which affects the local low-energy consumption of renewable energy and the development efficiency of the power grid. On the other hand, the power grids in various regions operate relatively independently, and the scope of local consumption of renewable energy is limited. A large number of renewable energy sources have to be boosted to the main grid, causing congestion in the transmission flow of the main grid, which seriously restricts the carrying capacity of the regional power grid and the level of renewable energy consumption. Therefore, it is worth conducting in-depth research on how to improve the efficiency of renewable energy consumption under the existing network form without the regulation of new lines. It is a feasible technical solution to consider the closed-loop operation of the distribution network in some areas where the development of renewable energy is uneven. However, if AC lines are directly closed in a loop, it is difficult to control the power flow of the power grid, and it is easy to cause problems such as increased equipment complexity and difficulty in power flow control during the fluctuation of new energy. Therefore, realizing flexible power flow control of distribution network lines after closing the loop is a key issue in the closed loop operation of the distribution network. Summary of the invention

[0003] In view of the above problems, the present invention proposes a distribution network line closing method based on a distributed power flow controller. The method mainly detects the electrical quantities of the closing points on both sides of the distribution line, controls the switches of the closing line, the number of closing valve modules to be put into use and the operating status. The distributed power flow controller controls the power flow of the line after closing to be within the target range.

[0004] In order to achieve the above object, the solution of the present invention is:

[0005] A distribution network line closing method based on a distributed power flow controller, wherein a distributed power flow controller is connected to the closed-loop line, and the distributed power flow controller includes:

[0006] Multiple converter valve modules and a bypass switch CB1; wherein the multiple converter valve modules are connected in series, and the bypass switch CB1 is connected in parallel with the multiple converter valve modules as a whole; each converter valve module has a built-in bypass switch, and when any converter valve module fails, it will be bypassed through the bypass switch without affecting the operation of other converter valve modules;

[0007] The distribution network line closing method includes the following steps:

[0008] S1. Detect the phase angle and amplitude of the closed-loop bus voltage on both sides of the closed-loop line, calculate the closed-loop impact current and steady-state operation current through the electrical parameters of the closed-loop line, and judge whether the steady-state operation current is less than the minimum starting current Iq of the converter valve module of the distributed power flow controller. If the steady-state operation current is less than the minimum starting current Iq of the converter valve module, the closed-loop operation condition is not met. If it is greater than the minimum starting current Iq, execute the next step;

[0009] S2. According to the steady-state operating power Ps of the line after closing the loop, the target value Pt of the closing loop line to be controlled, and the power direction, determine whether the converter valve module operates in a capacitive mode or an inductive mode;

[0010] S3. After determining the operation mode of the converter valve module, close the AC switches on both sides of the original line of the closed-loop line, unlock the converter valve module of the distributed power flow controller at the same time, and put a single converter valve module into operation: if it operates in the capacitive mode, the converter valve module performs a power increase operation; if it operates in the inductive mode, the converter valve module performs a power reduction operation;

[0011] S4, obtaining the maximum change ΔP1 of the line power after a single converter valve module is put into operation;

[0012] S5, continue to unlock the nth converter valve module, and obtain the maximum variable of the line power change is ΔPn;

[0013] S6. When the total change in line power caused by the put-in-service converter valve modules reaches the control target value Pt, it indicates that the power flow control target of the distributed power flow controller has been achieved.

[0014] Specifically, in S1, the phase angle and amplitude of the closed-loop bus voltage on both sides of the closed-loop line are detected, and the closed-loop impact current and steady-state operating current are calculated by the electrical parameters of the closed-loop line. The specific steps are as follows:

[0015] The impedance values ​​of the lines on both sides of the closing point are Z1=R1+jX1 and Z2=R2+jX2 respectively; the voltage angles on both sides of the interconnection line (the two sides of the interconnection line are the closing line bus A and the closing line bus B) are θ1 and θ2 respectively when the maximum phase angle difference θmax is reached, that is, θmax=θ1-θ2; the voltage amplitudes at both ends of the interconnection line are u1 and u2 respectively; let x=u1cosθ1-u2cosθ2, y=u1sinθ1-u2sinθ2. The steady-state closing current amplitude is obtained as Closed loop impulse current I max =I m (1+e -0.0R1L / ), the final R, L are the equivalent resistance and inductance of the closed loop circuit, R = R1 + R2, X = X1 + X2.

[0016] Preferably, when operating in capacity mode or inductive mode, it is necessary to determine the steady-state operating power Ps and power direction after the loop is closed, as well as the target value Pt and power direction of the control after the loop is closed:

[0017] If the target value Pt of the control after the loop is closed needs to be greater than the steady-state power Ps, it operates in the capacitive mode; if the target value Pt of the control after the loop is closed needs to be less than the steady-state power Ps, it operates in the inductive mode.

[0018] The structure of each converter valve module is as follows: DC capacitor, IGBT1 and IGBT2 are connected in series and then connected in parallel on both sides of the DC capacitor, IGBT3 and IGBT4 are connected in series and then connected in parallel on both sides of the DC capacitor, one side of the outgoing line is led between IGBT1 and IGBT2, and the other side of the outgoing line is led between IGBT3 and IGBT4; the two outgoing lines are respectively connected in parallel with a resistor, a thyristor fast bypass switch, a mechanical switch, a filter circuit, and a lightning arrester, the PT is connected in parallel on both sides of the DC capacitor, and a measurement CT and an energy extraction CT are connected in series in the main circuit.

[0019] The present invention is suitable for situations where the power of the closed-loop line needs to be adjusted frequently, but cannot be used for situations where the power flow of the closed-loop line is reversed.

[0020] Beneficial Effects of the Invention

[0021] The present invention first unlocks the size of the closed-loop current of a single valve module and determines the number of valve modules that need to be put into operation to control the target value of the current. At the same time, the current of the closed-loop circuit must not be lower than the minimum operating current of the valve module. The method determines the number of valve modules put into operation and the working state according to the real-time current of the closed-loop circuit, and can realize flexible current control of the closed-loop circuit of the distribution network. At the same time, during a fault, the valve module can be instantly locked and exited, and restored to the closed-loop operation state of the AC line. It will not affect the relay protection setting of the AC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the basic structure of a distribution network line closing device based on a distributed power flow controller in a specific implementation manner of the present invention.

[0023] Figure 2 This is the basic structure of a single converter valve module of the device in a specific implementation manner of the present invention.

[0024] Figure 3 The present invention provides a basic control process of a distribution network line closing method based on a distributed power flow controller. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with embodiments, but the protection scope of the present invention is not limited thereto:

[0026] The basic structure of a distribution network line closing device based on a distributed power flow controller is as follows: Figure 1 As shown in the figure, the distributed flow controller consists of multiple converter valve modules connected in series. The basic structure of a single converter valve module is as follows: Figure 2 As shown: DC capacitor, IGBT1 and IGBT2 are connected in series and then connected in parallel on both sides of the DC capacitor, IGBT3 and IGBT4 are connected in series and then connected in parallel on both sides of the DC capacitor, one side of the outgoing line is drawn between IGBT1 and IGBT2, and the other side of the outgoing line is drawn between IGBT3 and IGBT4; the two outgoing lines are respectively connected in parallel with resistors, parallel thyristor fast bypass switches, parallel mechanical switches, parallel filter circuits, and parallel lightning arresters, PT is connected in parallel on both sides of the DC capacitor, and the measurement CT and energy extraction CT are connected in series in the main circuit. . The distributed power flow controller proposed in this case is composed of multiple converter valve modules in series, and the parameters and dimensions of each converter valve module are the same. After any converter valve module fails, it will be bypassed through the bypass switch and will not cause the operation of other converter valve modules. During the period when the grounding fault occurs in the AC power grid near the device, when the converter valve overcurrent protection setting value is reached, the converter valve module will be quickly bypassed, and the power flow of the closed-loop line is not controlled at this time. The AC protection setting value is not affected. At the same time, since it is necessary to obtain energy from the line to maintain the operation of the device, the minimum operating current of the line must not be lower than the minimum allowable current of the device. Therefore, it cannot be used in situations where the current of the closed-loop line is reversed.

[0027] This case proposes a distribution network line closing method based on a distributed power flow controller. This method mainly controls the switch of the closing line, the number of closing valve modules to be put into use, and the operating status by detecting the electrical quantities of the closing points on both sides of the distribution line. Figure 3 , the method mainly includes the following steps:

[0028] S1: Detect the phase angle, amplitude, and R1+jX1 of the voltage of the closed-loop bus A and the closed-loop bus B on both sides of the closed-loop line, calculate the closed-loop impact current and steady-state operation current through the electrical parameters such as the impedance of the closed-loop line, and judge whether the steady-state operation current is less than the minimum starting current of the converter valve module of the distributed power flow controller. If the steady-state operation current is less than the minimum starting current Iq of the converter valve module, no specific closed-loop operation condition is required. If it is greater than the minimum starting current, execute the next step;

[0029] S2. According to the steady-state operating power Ps of the line after closing the loop, the target value Pt of the closing loop line to be controlled, and the power direction, determine whether the converter valve module operates in a capacitive mode or an inductive mode;

[0030] S3. After determining the operation mode of the converter valve module, close the AC switch of the closed-loop line, unlock the converter valve module of the distributed power flow controller, and put a single converter valve module into operation: if it is operating in the capacitive mode, the converter valve module performs a power increase operation; if it is operating in the inductive mode, the converter valve module performs a power reduction operation;

[0031] S4, obtaining the maximum change ΔP1 of the line power after a single converter valve module is put into operation;

[0032] S5, continue to unlock the nth converter valve module, and obtain the maximum variable of the line power change is ΔPn;

[0033] S6. When the total change in line power caused by the put-in-service converter valve modules reaches the control target value Pt, it indicates that the power flow control target of the distributed power flow controller has been achieved.

[0034] The present invention first unlocks the size of the closed-loop current of a single valve module and determines the number of valve modules that need to be put into operation to control the target value of the current. At the same time, the current of the closed-loop circuit must not be lower than the minimum operating current of the valve module. The method determines the number of valve modules put into operation and the working state according to the real-time current of the closed-loop circuit, and can realize flexible current control of the closed-loop circuit of the distribution network. At the same time, during a fault, the valve module can be instantly locked and exited, and restored to the closed-loop operation state of the AC line. It will not affect the relay protection setting of the AC system.

[0035] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A distribution network line closing method based on a distributed power flow controller, characterized in that A distributed power flow controller is connected to the closed loop line, wherein the distributed power flow controller comprises: Multiple converter valve modules and a bypass switch CB1; wherein the multiple converter valve modules are connected in series, and the bypass switch CB1 is connected in parallel with the multiple converter valve modules as a whole; each converter valve module has a built-in bypass switch, and when any converter valve module fails, it will be bypassed through the bypass switch without affecting the operation of other converter valve modules; The distribution network line closing method includes the following steps: S1. Detect the phase angle and amplitude of the closed-loop bus voltage on both sides of the closed-loop line, calculate the closed-loop impact current and steady-state operation current through the electrical parameters of the closed-loop line, and judge whether the steady-state operation current is less than the minimum starting current Iq of the converter valve module of the distributed power flow controller. If the steady-state operation current is less than the minimum starting current Iq of the converter valve module, the closed-loop operation condition is not met. If it is greater than the minimum starting current Iq, execute the next step; S2. According to the steady-state operating power Ps of the line after closing the loop, the target value Pt of the closing loop line to be controlled, and the power direction, determine whether the converter valve module operates in a capacitive mode or an inductive mode; S3. After determining the operation mode of the converter valve module, close the AC switch of the closed-loop line, unlock the converter valve module of the distributed power flow controller, and put a single converter valve module into operation: if it is operating in the capacitive mode, the converter valve module performs a power increase operation; if it is operating in the inductive mode, the converter valve module performs a power reduction operation; S4, obtaining the maximum change ΔP1 of the line power after a single converter valve module is put into operation; S5, continue to unlock the nth converter valve module, and obtain the maximum variable of the line power change is ΔPn; S6. When the total change in line power caused by the put-in-service converter valve modules reaches the control target value Pt, it indicates that the power flow control target of the distributed power flow controller has been achieved.

2. The method according to claim 1, characterized in that In S1, the phase angle and amplitude of the closed-loop bus voltage on both sides of the closed-loop line are detected, and the closed-loop impact current and steady-state operating current are calculated by the electrical parameters of the closed-loop line. The specific steps are as follows: The impedance values ​​of the lines on both sides of the closing point are Z1=R1+jX1 and Z2=R2+jX2 respectively; the voltage angles on both sides of the interconnection line are θ1 and θ2 respectively when the maximum phase angle difference θmax is reached, that is, θmax=θ1-θ2; the voltage amplitudes at both ends of the interconnection line are u1 and u2 respectively; let the intermediate value x=u1cosθ1-u2cosθ2, y=u1sinθ1-u2sinθ 2； The steady-state closed-loop current amplitude is Closed loop impulse current I max =I m (1+e -0.01R / L ), the final R, L are the equivalent resistance and inductance of the closed loop circuit, R = R1 + R2, X = X1 + X2.

3. The method according to claim 1, characterized in that: If the target value Pt of the control after the loop is closed needs to be greater than the steady-state power Ps, it operates in the capacitive mode; if the target value Pt of the control after the loop is closed needs to be less than the steady-state power Ps, it operates in the inductive mode.

4. The method according to claim 1, characterized in that The structure of each converter valve module is as follows: DC capacitor, IGBT1 and IGBT2 are connected in series and then connected in parallel on both sides of the DC capacitor, IGBT3 and IGBT4 are connected in series and then connected in parallel on both sides of the DC capacitor, one side of the outgoing line is led between IGBT1 and IGBT2, and the other side of the outgoing line is led between IGBT3 and IGBT4; the two outgoing lines are respectively connected in parallel with a resistor, a thyristor fast bypass switch, a mechanical switch, a filter circuit, and a lightning arrester, the PT is connected in parallel on both sides of the DC capacitor, and a measurement CT and an energy extraction CT are connected in series in the main circuit.

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