A voltage control method for low-voltage distribution networks based on flexible interconnection devices

Abstract

This invention discloses a voltage control method for low-voltage distribution networks based on flexible interconnection devices, comprising: achieving flexible interconnection between low-voltage distribution networks; measuring relevant data; adjusting the voltage of feeder PCC nodes; and controlling the normal operation of PCC node voltages. This method establishes power corridors between different feeders through flexible interconnection devices, improves the power quality of other feeders, achieves power mutual assistance, and enhances the reliability and resilience of the distribution network. Compared to active power regulation and reactive power regulation, this method can reduce the apparent power dispatched by the device under the same voltage regulation demand.

Description

Technical Field

[0001] This invention relates to the field of AC power grid flexible interconnection technology, and in particular to a voltage control method for low-voltage distribution networks based on flexible interconnection devices. Background Technology

[0002] With the increasing prominence of climate change and the energy crisis, renewable energy has become a development trend, among which solar photovoltaic (PV) power generation is an important form of renewable energy utilization. Depending on the capacity, solar PV power generation is divided into two grid connection methods: one is connected to the transmission grid via medium- and high-voltage lines; the other is connected to the distribution grid via low-voltage lines. The second type is mostly rural rooftop PV power generation, i.e., distributed PV power generation. Because distributed PV connected to the distribution grid will change the traditional radial distribution mode of the distribution network, it will also have many adverse effects on the operation of the distribution network, including unbalanced voltage feeder loads, low voltage quality at the end of the lines, poor power supply reliability, and insufficient renewable energy absorption capacity.

[0003] To address the issue of excessively high voltage or even voltage exceeding limits at the feeder ends of distribution networks caused by the large-scale integration of distributed energy resources, traditional solutions mainly fall into four categories: adding voltage and reactive power compensation devices, adding on-load voltage regulators for voltage control, expanding and upgrading distribution network lines, and disconnecting loads / reducing load power / reducing the penetration of distributed energy resources. Among these, reactive power compensation devices are mainly divided into two types: centralized reactive power compensation and distributed reactive power compensation. The former, while addressing voltage exceeding limits, injects reactive power into the feeder, increasing line losses and causing undervoltage at the feeder headend, resulting in a low power factor at the feeder headend transformer. The latter requires good communication conditions and significant investment costs. On-load voltage regulators adjust the voltage at the feeder headend by changing the taps of the distribution transformer, thereby indirectly controlling the feeder headend voltage and feeder load power. This method is simple to control and low in cost, but its control performance is poor, the adjustment range is small, and it cannot achieve continuous voltage regulation. Similar to the first method, while reducing the voltage level at the feeder headend, it can also cause undervoltage at the feeder headend. Expanding or upgrading distribution network lines requires significant investment in cables and transformers, making it inefficient. Disconnecting loads / reducing load power / decreasing distributed energy penetration comes at the cost of sacrificing power supply to some users or reducing renewable energy generation, and cannot be used as a conventional method for voltage regulation. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the current low-voltage distribution network voltage control methods based on flexible interconnection devices, this invention is proposed.

[0006] Therefore, the purpose of this invention is to provide a low-voltage distribution network voltage control method based on a flexible interconnection device.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solutions: enabling flexible interconnection between low-voltage distribution networks; measuring relevant data; adjusting PCC node voltage; and controlling the normal operation of PCC node voltage.

[0008] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection device described in this invention, the voltage source converter is connected to the ends of different feeders of the low-voltage distribution network, and flexible interconnection between low-voltage distribution feeders is realized by using DC lines.

[0009] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection device described in this invention, wherein: the voltage U at the beginning of feeder n is measured. S.n Feeder impedance R n X n Feeder load P L.n Q L.n Distributed power supply output power P DG.n ;

[0010] In order to increase the penetration rate of distributed power sources, it is designed to have a unity power factor output.

[0011] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection device described in this invention, wherein: the voltage U at the beginning of feeder n S.n The expression is:

[0012]

[0013] Where, p c.n q c.n The active and reactive power provided to feeder n, U P.n P is the voltage at the PCC node. p.n Q represents the active power flowing from feeder n into the PCC node. P.n Let be the reactive power flowing into the PCC node from feeder n, and j represent the imaginary part.

[0014] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection device described in this invention, wherein: for power grids with voltage levels of 110kV and below, the horizontal component of voltage drop is ignored, and the imaginary part in equation (1) is ignored, then the PCC node voltage U P.n The expression is:

[0015]

[0016] Among them, the first-terminal voltage U S.n Feeder impedance R n X n Feeder load P L.n Q L.n Distributed power supply output power P DG.n The voltage at the PCC node will not change drastically in a short period of time and can be considered a constant. The active and reactive power provided to feeder n by the flexible interconnection device can be adjusted.

[0017] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection device described in this invention, when the voltage of the PCC node exceeds the upper limit, the voltage is restored to the upper limit value using the flexible interconnection device.

[0018] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection device described in this invention, wherein: if the distributed power source P of feeder n DG.n Excessive output leads to PCC node voltage U P.n Greater than the node voltage limit u p.n.max At that time, in order to restore the PCC node voltage to the upper limit value u p.n.max The active power p that the port converter of the flexible interconnect device connects to feeder n needs to regulate. c.n and reactive power q c.n The following relationship must be satisfied:

[0019] q c.n =A n -B n p c.n

[0020] in:

[0021] Among them, active power p c.n and reactive power q c.n There exists a linear functional relationship, A n B is the intercept of the function. n The slope of the function is denoted by , and the magnitudes of both are determined by the local information of the PCC node.

[0022] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection devices described in this invention, the active power p is represented by a relationship diagram. c.n and the reactive power q c.n The numerical relationship, the apparent power vector adjusted by the flexible interconnect device. Determine the PCC node voltage U of feeder n P.nWhether it has recovered to a reasonable level.

[0023] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection devices described in this invention, wherein: if active power and reactive power regulation are used simultaneously, the apparent power required for scheduling by the port converter is... for:

[0024]

[0025] in, This refers to the apparent power that the port converter needs to schedule when both active and reactive power regulation are used simultaneously.

[0026] As a preferred embodiment of the low-voltage distribution network voltage control method based on flexible interconnection devices described in this invention, wherein: if the active power p regulated by the flexible interconnection device... c.n and reactive power q c.n The voltage regulation capability of the device can be improved when the following formula is satisfied:

[0027]

[0028] If there is active power regulation p c.n and reactive power regulation q c.n When the following formula is used, the flexible interconnect device utilizes minimal apparent power to restore the over-voltage PCC node to the upper voltage limit.

[0029]

[0030] in

[0031] The beneficial effects of this invention are: 1. By establishing a power corridor between different feeders through a flexible interconnection device, the power quality of other feeders is improved, power mutual assistance is achieved, and the reliability and resilience of the distribution network are enhanced.

[0032] 2. Compared with active voltage regulation and reactive voltage regulation, this method can reduce the apparent power of device scheduling under the same voltage regulation requirements. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0034] Figure 1 This is a flexible interconnected distribution network architecture based on flexible interconnection devices.

[0035] Figure 2 This is a graph showing the numerical relationship between active power regulation and reactive power regulation.

[0036] Figure 3 Apparent power required to adjust the port converter for connecting feeder n to a flexible interconnect device Active power p regulated by the converter c.n A diagram showing the relationships between them.

[0037] Figure 4 It is a low-voltage distribution network based on two-port flexible interconnection.

[0038] Figure 5 This is a simulation waveform diagram. Detailed Implementation

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0041] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0042] Secondly, the present invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not according to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0043] Example 1

[0044] Reference Figures 1-3 A low-voltage distribution network voltage control method based on flexible interconnection devices includes:

[0045] S1: Enables flexible interconnection between low-voltage distribution networks. It should be noted that:

[0046] The flexible interconnection device uses a voltage source converter to connect to the ends of different feeders in the low-voltage distribution network, and uses DC lines to realize flexible interconnection between low-voltage distribution feeders.

[0047] S2: Data measurement. It should be noted that:

[0048] Figure 1 For a flexible interconnected distribution network architecture based on flexible interconnection devices, the node connecting the flexible interconnection device and the feeder is designated as the point of common coupling (PCC). Measured grid parameters include the head-end voltage U. S.n Feeder impedance R n X n Feeder load P L.n Q L.n Distributed power supply output power P DG.n (To increase the penetration rate of distributed power sources, it is designed to have a unity power factor output).

[0049] S3: Adjust the voltage at the PCC node of the feeder. It should be noted that:

[0050] p c.n q c.n Defined as a flexible interconnect device Figure 1 The active and reactive power provided by the feeder n, and the voltage at the PCC node are U. P.n From the power flow equations of the power system, the expression for the feeder head voltage can be obtained as follows (j represents the imaginary part):

[0051]

[0052] For power grids with voltage levels of 110kV and below, the horizontal component of voltage drop can be ignored. Therefore, ignoring the imaginary part in equation (1), we obtain the voltage relationship of the PCC node:

[0053]

[0054] Among them, P p.n Q represents the active power flowing from feeder n into the PCC node. P.n Let n be the reactive power flowing into the PCC node from feeder n.

[0055] Due to the voltage at the beginning U S.n Feeder impedance R n X n Feeder load P L.n Q L.n Distributed power supply output power P DG.n Neither of these will change drastically, so they can be considered constants. Therefore, the PCC node voltage can be adjusted by the active and reactive power supplied to feeder n through the flexible interconnection device.

[0056] S4: Controls the normal operation of the PCC node voltage. It should be noted that:

[0057] In a power system, PCC nodes need to operate normally within a certain voltage range (the voltage range of low-voltage distribution network feeders is 0.93pu-1.07pu). When the voltage of a PCC node exceeds the upper limit, a flexible interconnection device is used to restore the voltage to the upper limit value.

[0058] If the distributed power source P of feeder n DG.n Excessive output leads to PCC node voltage U P.n Greater than the node voltage limit u p.n.max As can be seen from equation (2), in order to restore the PCC node voltage to the upper limit value u p.n.max The active power p that the port converter of the flexible interconnect device connects to feeder n needs to regulate. c.n and reactive power q c.n The following relationship must be satisfied:

[0059] q c.n =A n -B n p c.n (3)

[0060] in:

[0061] From the above formula, it can be seen that the active power p c.n and reactive power q c.n There exists a linear functional relationship, where A n B is the intercept of the function. n The slope of the function is denoted by , and the magnitudes of both are determined by the local information of the PCC node.

[0062] Figure 2 The graph represents the numerical relationship between active power regulation and reactive power regulation, where equation (3) divides the coordinate graph into U... P.n >u p.n.max and U P.n ≤u p.n.max Two parts.

[0063] If the apparent power vector adjusted by the flexible interconnect device If the endpoint falls in region I, it means that the power regulation of the flexible interconnect device is insufficient to make the PCC node voltage U of feeder n reach the specified value. P.n Return to a reasonable level.

[0064] If the apparent power vector adjusted by the flexible interconnect device If the endpoint falls in region II, it means that the power regulated by the flexible interconnect device can make the PCC node voltage U of feeder n so that... P.n Return to a reasonable level.

[0065] further, Figure 2It also demonstrates how flexible interconnect devices can be used to restore the PCC node voltage to u. p.n.max Different working methods at different times. It should be noted that:

[0066] Currently, the main methods for adjusting feeder node voltage are reactive power voltage regulation and active power voltage regulation.

[0067] Among them, reactive power voltage regulation mainly uses static var compensators, switching capacitors, etc. This method adjusts the voltage by only changing the reactive power flow in the feeder. Its principle can be equivalent to using only the reactive power compensation of flexible interconnection devices for voltage regulation.

[0068] When the PCC node voltage U of feeder n P.n Greater than the upper limit of voltage u p.n.max At that time, in order to restore the PCC node voltage to the upper limit value u p.n.max ,like Figure 2 middle The reactive power q required to be regulated by the converter of the flexible interconnect device connected to feeder n c.n With PCC node voltage u p.n.max The relationship is:

[0069]

[0070] At this point, the apparent power required to be adjusted by the port converter of the flexible interconnect device connected to feeder n is Equation (5):

[0071]

[0072] For active power regulation in distribution networks, energy storage is mainly used to transfer surplus active power in feeders to energy storage devices, i.e., voltage regulation is achieved by only changing the active power flow in the feeders; the principle can also be equivalent to voltage regulation using only active power compensation from flexible interconnection devices; when the PCC node voltage U of feeder n... P.n Greater than the upper limit of voltage u p.n.max At that time, in order to restore the PCC node voltage to the upper limit value u p.n.max ,like Figure 2 middle The active power p that the port converter of the flexible interconnect device connects to feeder n needs to regulate. c.n With PCC node voltage u p.n.max The relationship is:

[0073]

[0074] At this point, the apparent power that the port converter of the flexible interconnect device connected to feeder n needs to adjust is:

[0075]

[0076] If both active and reactive power regulation are used simultaneously, the apparent power that the port converter needs to schedule is given by equation (8):

[0077]

[0078] As shown in (8), under the same voltage regulation requirement, with the increase of active power p c.n The apparent power that the port converter needs to schedule varies depending on the output power.

[0079] If the apparent power regulated by the flexible interconnect device is perpendicular to equation (3) (e.g.) If the apparent power needs to be adjusted, then... It is the minimum, and at this time the active power and reactive power regulated by the flexible interconnection device satisfy equation (9).

[0080]

[0081] Furthermore, combining equations (3) and (9), when the active power regulation p c.n and reactive power regulation q c.n When it is (10), the flexible interconnect device uses the minimum apparent power to restore the overvoltage PCC node to the upper voltage limit.

[0082]

[0083] in

[0084] Comparing equations (5), (7), and (8), it can be seen that when p c.n When q = 0 (only reactive voltage regulation is used), equations (5) and (8) represent the same operating condition. c.n When =0 (only active voltage regulation is used), equations (7) and (8) are the same operating condition.

[0085] When feeder local information A n and B n When determined, it can be concluded that in order to restore the PCC node voltage to the upper limit value u p.n.max , Figure 3 Apparent power required to adjust the port converter for connecting feeder n to a flexible interconnect device Active power p regulated by the converter c.n A diagram showing the relationships between them.

[0086] Depend on Figure 3 It can be seen that the ability of the flexible interconnect device to jointly regulate active and reactive power proposed in this patent can reduce the apparent power regulated by the port converter in the flexible interconnect device under the same voltage regulation requirements.

[0087] This method utilizes a flexible interconnecting switch to open a power corridor, enabling bidirectional flow of active power between different feeders. This invention employs a novel method for controlling active and reactive power, using minimal apparent power to restore voltage levels to feeders that have exceeded their limits, while simultaneously reducing system losses and improving energy utilization.

[0088] Example 2

[0089] This embodiment is the second embodiment of the present invention. Unlike the first embodiment, this embodiment provides a verification test of a low-voltage distribution network voltage control method based on a flexible interconnection device, and verifies and explains the technical effects used in this method.

[0090] like Figure 4 As shown, this is a low-voltage distribution network based on a two-port flexible interconnection, in which the ends of the two feeders of the low-voltage distribution network are connected together through a flexible interconnection device to realize bidirectional power transmission, thereby addressing the problem of voltage exceeding limits.

[0091] Set up Figure 4 The simulation model shown assumes that the PCC node of the feeder experiences a voltage overshoot of 417V (1.1 pu). This simulation utilizes different voltage regulation methods of the flexible interconnect device to restore the PCC node voltage of feeder 1 to 400V (1.05 pu). The simulation platform is Matlab / Simulink.

[0092] The following table shows the specific parameters of the simulation model:

[0093] Table 1: Simulation Model Parameters

[0094]

[0095] Simulated waveforms such as Figure 5 As shown, in the following timeframes: 0-0.1s: the flexible interconnect device does not participate in voltage regulation; 0.1-0.3s: the flexible interconnect device uses reactive power voltage regulation; 0.3-0.5s: the flexible interconnect device uses active power voltage regulation; 0.5-0.7s: the flexible interconnect device uses the voltage regulation method proposed in this patent; waveform (a) represents the PCC node voltage of feeder 1; waveform (b) represents the apparent power dispatched by the flexible interconnect device at the feeder 1 port. Table 2 shows the theoretically calculated values ​​of the apparent power dispatched by the flexible interconnect device of feeder 1, which are basically consistent with the simulation waveforms.

[0096] More preferably, by Figure 5 As shown in Table 2, the method of using the active and reactive power to jointly regulate voltage in the flexible interconnection device proposed in this patent can enable the flexible interconnection device to restore the node voltage level with less apparent power.

[0097] The table below shows the compensation effects under different compensation strategies.

[0098] Table 2: Theoretical Calculations of Apparent Power for Flexible Interconnected Device Scheduling

[0099]

[0100] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for voltage control of a low voltage distribution network based on flexible interconnection devices, characterized in that: Comprising, Flexible interconnection between low-voltage distribution networks is realized; Measuring relevant data; Adjusting the voltage of PCC node; And, Control PCC node voltage normal operation, PCC node voltage U P.n When exceeding the upper limit, use flexible interconnection device to restore voltage to the upper limit value, if the distributed power P DG.n of feeder n is too large to cause PCC node voltage U P.n > node voltage upper limit u p.n.max , in order to restore PCC node voltage to the upper limit value u p.n.max , the active power p c.n and reactive power q c.n required for the port converter of the flexible interconnection device connected to feeder n to adjust need to meet the following relationship: q c.n = A n - B n p c.n wherein: wherein the active power p c.n and the reactive power q c.n there is a linear function relationship, A n is the intercept of the function, B n is the slope of the function, the size of both is determined by the local information of the PCC node, U P.n is the PCC node voltage, the head voltage U S.n , feeder impedance R n , X n , feeder load P L.n , Q L.n , distributed power output P DG.n In a short time, neither of them will change dramatically, and they are considered constant.

2. The flexible interconnection device based low voltage distribution network voltage control method of claim 1, wherein: The voltage source converter is connected to the end of different feeders of low-voltage distribution network, and flexible interconnection between low-voltage distribution feeders is realized by using DC line.

3. The flexible interconnection device based low voltage distribution network voltage control method of claim 1, wherein: measuring the head-end voltage U of the feeder n S.n , the feeder impedance R n , X n , the feeder load P L.n , Q L.n , the distributed power output P DG.n ; In order to improve the penetration rate of distributed power supply, it is required to output unit power factor.

4. The method of claim 3, wherein the method further comprises: determining a voltage at the first node of the first distribution circuit; and determining a voltage at the second node of the second distribution circuit. The head end voltage U of the feeder n S.n The expression is: where p c.n , q c.n are the active and reactive power provided by feeder n, U P.n is the PCC node voltage, P p.n is the active power flowing from feeder n into the PCC node, Q P.n is the reactive power flowing from feeder n into the PCC node, and j denotes the imaginary part.

5. The method of claim 4, wherein the method further comprises: determining a voltage at the first node; and determining a voltage at the second node. For power networks of 110 kV and below voltage class, the horizontal component of voltage drop is ignored, and the imaginary part in (1) is ignored, the PCC node voltage U P.n The expression is: Wherein, the head voltage U S.n , the feeder impedance R n , X n , the feeder load P L.n , Q L.n , the distributed power output P DG.n In a short time, it will not change sharply, and it is considered as a constant, and the PCC node voltage can be adjusted by the active power p c.n and the reactive power q c.n provided by the flexible interconnection device for the feeder n.

6. The flexible interconnection device based low voltage distribution network voltage control method of claim 1, wherein: The active power p is represented by a relation graph c.n and the reactive power q c.n The apparent power vector adjusted by the flexible interconnection device is determined by the numerical relation of the active power p and the reactive power q. P.n whether the PCC node voltage U of the feeder n is restored to a reasonable level.

7. The method of claim 6, wherein the method further comprises: determining a voltage at the first node; and determining a voltage at the second node. If both active power and reactive power regulation is used, the apparent power that needs to be scheduled for the port converter is P = V * I wherein, Qreq is the required apparent power for the dispatch of the port converter when both active power and reactive power regulation is employed.

8. The method of claim 7, wherein the method further comprises: determining a voltage at the first node; and determining a voltage at the second node. If the flexible interconnection device regulates the active power p c.n and the reactive power q c.n The voltage regulating capability of the device can be improved if the following equation is satisfied: If the active regulation amount p c.n and the reactive regulation amount q c.n is of the following form, the flexible interconnection device utilizes the least apparent power to restore the PCC node with voltage excursion to the upper voltage limit value wherein

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