An ac flexible loop closing topology and method based on ups starting

Abstract

This invention belongs to the field of active power distribution network operation and control technology, and discloses an AC flexible loop-closing topology and method based on UPS startup. The topology includes a UPS module, a monitoring module, a communication module, and a control module. The monitoring module monitors the status information of the loop-closing line and uploads it to the communication module. The communication module transmits the received status information to the control module. The control module includes a calculation unit, a modulation unit, and a capacitor. The calculation unit performs difference calculations based on the received status information to obtain a control target signal and sends the control target signal to the modulation unit. The modulation unit modulates the control target signal to obtain a balance control signal and outputs the balance control signal to complete the balance loop-closing operation. The UPS module is used to charge the capacitor. This invention improves the speed and stability of loop closing, meets the requirements for shock-free loop closing, and solves the problem of energy extraction by the loop-closing device when the pre-closing line is not energized.

Description

Technical Field

[0001] This invention belongs to the field of active power distribution network operation and control technology, specifically relating to an AC flexible loop topology and method based on UPS startup. Background Technology

[0002] In a power system, the distribution network plays a crucial role in precisely delivering electrical energy from the transmission network to end users. Traditionally, electrical energy flows in a unidirectional direction, directly from large power plants to users. However, with the rapid development and widespread adoption of renewable energy technologies, a large number of distributed energy resources, such as rooftop solar photovoltaic panels and small wind turbines, have gradually been integrated into the distribution network, forming an active distribution network. These networks can generate electricity independently and supply it directly or indirectly to users.

[0003] To address distribution faults and maintenance, loop closing is commonly used in distribution networks. This is an effective strategy to ensure uninterrupted power supply to users. Through loop closing, the load on faulty or under-maintenance lines can be transferred to fault-free lines, significantly improving the reliability and flexibility of power supply. However, traditional mechanical loop closing switches, due to their slow operating speed, are no longer sufficient to meet the rapid loop closing requirements of active distribution networks. Particularly complex is the possibility that when the two feeders in the loop come from different substations or different branches of the same substation, differences in voltage amplitude and phase angle on both sides of the tie switch can lead to malfunctions in protection systems, affecting the success rate of loop closing. This is especially true when distributed renewable energy sources with fluctuating output are connected to the distribution network; the amplitude and phase angle differences between feeders make shock-free flexible loop closing particularly difficult. Therefore, flexible loop closing technology has been introduced. This technology allows the grid to maintain continuous power supply while performing necessary adjustments or maintenance, ensuring grid stability and reliability. Flexible loop closing, as a special operating technique, aims to achieve shock-free and uninterrupted parallel operation or disconnection between two or more grid ring networks. Currently, flexible loop closure is typically achieved using two-port or multi-port AC / DC / AC converters or unified power flow controllers, both domestically and internationally. While these devices effectively address issues arising from voltage amplitude and phase angle differences, they are costly and their cost-effectiveness needs improvement. Furthermore, static series compensators (SLCs) are also used for flexible loop closure; however, the voltage source converters in these devices require energy from the line and must be rectified by the AC / DC converter to supply power to the DC capacitors. Besides being costly, they also suffer from the limitation of being unable to operate without an external power source. Summary of the Invention

[0004] Based on the aforementioned shortcomings and deficiencies in the existing technology, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the existing technology. In other words, one of the objectives of this invention is to provide an AC flexible loop-closing topology and method based on UPS startup that meets one or more of the aforementioned requirements, aiming to significantly improve the speed and stability reliability of loop closing in active distribution networks, so as to meet the impact-free loop closing requirements for the access of fluctuating distributed new energy to the distribution network, and to solve the problem of energy extraction by the loop-closing device when the pre-loop-closing line is not energized.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a topology for an AC flexible loop-closing device based on UPS startup, comprising a UPS module, a monitoring module, a communication module, and a control module; the monitoring module is used to monitor the status information of the loop-closing line and upload it to the communication module; the communication module is used to transmit the received status information to the control module; the control module includes a calculation unit, a modulation unit, and a capacitor; the calculation unit performs difference calculation based on the received status information to obtain a control target signal, and sends the control target signal to the modulation unit; the modulation unit modulates the control target signal to obtain a balance control signal, and outputs the balance control signal to complete the balance loop-closing operation; the capacitor is used to receive electrical energy from the UPS module and drive the topology to start flexible loop-closing; the UPS module includes a first charging unit and a second charging unit; the first charging unit is used to convert AC power obtained from an external power source into DC power and charge the capacitor and the second charging unit; the second charging unit is used to store the DC power provided by the first charging unit and charge the capacitor when the first charging unit has no external power source.

[0007] As a preferred embodiment, the control module further includes an instruction input unit; the instruction input unit is used for the loop closing operator to input a compensation loop closing instruction value and to send the compensation loop closing instruction to the modulation unit; the modulation unit modulates the control target signal and the compensation loop closing instruction to obtain a compensation control signal, and outputs the compensation control signal to complete the compensation loop closing operation.

[0008] Secondly, the present invention provides a flexible loop closure method based on the topology described in the first aspect, comprising the following steps:

[0009] S1. The UPS charges the voltage source converter capacitor directly from the external power supply or from the internal battery to initiate flexible loop operation.

[0010] S2. Obtain the status information of the closed loop line;

[0011] S3. Calculate the difference based on the state information to obtain the compensation value, thereby generating the control target signal;

[0012] S4. Modulate the control target signal to obtain a control signal, and output the control signal to complete the flexible loop closure.

[0013] As a preferred embodiment, the status information includes the voltage values ​​of the two lines that need to undergo loop closing operation, respectively. and

[0014] As a preferred embodiment, step S3, which involves calculating the difference based on the state information to obtain a compensation value, thereby generating a control target signal, includes the following steps:

[0015] Based on the above Obtain its d-axis component U Ad and q-axis component U Aq ;

[0016] Based on the above Obtain its d-axis component U Bd and q-axis component U Bq ;

[0017] Based on the U Ad and the U Bd The d-axis component U of the reference value of the voltage difference at the closing point is obtained by performing difference calculation. * ABd ;

[0018] Based on the U Aq and the U Bq The q-axis component U of the reference value of the voltage difference at the junction point is obtained by performing difference calculation. * ABq ;

[0019] Based on the above and stated Perform difference calculation to obtain the voltage difference at the closing point. and its d-axis component U ABd and q-axis component U ABq ;

[0020] Based on the voltage difference at the junction point Obtain the control target voltage reference value Thus, the control target signal is obtained.

[0021] As a preferred embodiment, step S4, which modulates the control target signal to obtain a control signal, includes the following steps:

[0022] Based on the d-axis component U of the voltage difference at the junction point ABd and q-axis component U ABq The d-axis component U of the control target voltage reference value is obtained. * FIDd With q-axis component U * FIDq ,Right now:

[0023]

[0024] Based on the d-axis component U of the control target voltage reference value * FIDd With q-axis component U * FIDq Inverter to control target voltage This results in the acquisition of control signals.

[0025] As a preferred embodiment, step S4 is preceded by the following step:

[0026] Obtain the compensation loop closing command for the flexible loop closing operation of the loop closing line, wherein the compensation loop closing command includes an inductive compensation command value or a capacitive compensation command value.

[0027] Step S4, which modulates the control target signal to obtain a control signal, specifically involves modulating the control target signal based on the inductive compensation command value or the capacitive compensation command value to obtain a control signal.

[0028] As a preferred embodiment, the modulation of the control target signal based on the inductive compensation command value or the capacitive compensation command value includes the following steps:

[0029] The inductive compensation command value or the capacitive compensation command value is recorded as the control target voltage reference value;

[0030] Based on the expression for the target voltage reference value, PI control is performed to obtain the d-axis component U of the target voltage reference value. * FIDd With q-axis component U * FIDq ;

[0031] Based on the d-axis component U of the control target voltage reference value * FIDd With q-axis component U * FIDq Inverter to control target voltage Thus, control signals are obtained;

[0032] The expression for the control target voltage reference value is:

[0033]

[0034] In the formula, K P1 K P2 K is the proportional gain of the PI controller. I1 K I2 This represents the integral coefficient of the PI controller.

[0035] As a preferred embodiment, step S1, where the UPS directly charges the voltage source converter capacitor based on an external power supply to initiate the flexible loop-closing operation, includes the following steps: establishing a connection with the external power supply; converting the AC power input from the external power supply into DC power U1 and then charging the voltage source converter capacitor until the voltage of the voltage source converter capacitor reaches the rated value U. dc .

[0036] As a preferred embodiment, step S1 of the UPS charging the voltage source converter capacitor based on the internal battery to initiate the flexible loop-closing operation includes the following steps: inverting the AC power input from the external power source into DC power U1 and storing it in the internal battery U2; charging the voltage source converter capacitor through the internal battery U2 until the voltage of the voltage source converter capacitor reaches the rated value U. dc .

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. Enhanced initial startup capability: By combining the UPS with a voltage source converter (VSC), this invention ensures that even when the pre-loop circuit is not energized, the UPS's DC power supply can quickly charge the VSC capacitor, enabling the device to rapidly reach initial startup conditions. This design significantly enhances the adaptability and reliability of the device, effectively avoiding startup obstacles caused by power supply issues.

[0039] 2. This invention achieves active, shock-free flexible loop closure. By determining the compensation value through differential calculation and using SPWM modulation technology, it can accurately compensate for the voltage difference between the closing points of two circuit breakers, achieving smooth, shock-free flexible loop closure. This technology not only reduces voltage and current surges during the loop closure process but also effectively protects power grid equipment and loads from damage, improving the overall stability and security of the power grid.

[0040] 3. Improved loop stability and reliability: Through precise voltage compensation and current control, this invention effectively reduces the current in the loop circuit, minimizing line losses and heat generation, thereby enhancing the stability and reliability of the loop. This characteristic is particularly important when fluctuating distributed renewable energy sources are integrated into the distribution network, providing a solid guarantee for the stable operation of the power grid under various complex conditions.

[0041] 4. This invention solves the energy extraction problem and optimizes energy management. Addressing the energy extraction issue of the loop-closing device when the pre-loop circuit is not energized, this invention innovatively utilizes the UPS's internal battery as a backup power source. After the UPS completes its initial charging task, and simultaneously after AC power is restored, it automatically starts the UPS charging mode to replenish the battery, achieving efficient energy recycling and intelligent management. This design extends battery life, reduces operating costs, and improves the overall system's economic efficiency.

[0042] Further or more detailed beneficial effects will be described in conjunction with specific embodiments in the detailed implementation. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0044] Figure 1 This is a schematic diagram illustrating the application scenario of the present invention.

[0045] Figure 2 This is a schematic diagram of the topology of the AC flexible loop closing device described in Embodiment 1 of the present invention.

[0046] Figure 3 This is a schematic flowchart of the AC flexible loop closing method described in Embodiment 2 of the present invention.

[0047] Figure 4 This is a schematic diagram illustrating the principle of an embodiment of the present invention.

[0048] Figure 5 This is a schematic diagram of the simulation results of Embodiment 3 of the present invention, where a is the voltage difference at the connection point of the two zone-connecting circuits, b is the effective value of the voltage difference at the connection point of the two zone-connecting circuits, c is the current value of the two zone-connecting loop lines, and d is the effective value of the current of the two zone-connecting loop lines. Detailed Implementation

[0049] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0050] In the following description, several embodiments of the present invention are provided. Different embodiments can be substituted or combined. Therefore, the present invention can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then the present invention should also be considered to include embodiments containing one or more other possible combinations of A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0051] The following description provides examples and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made to the function and arrangement of the described elements without departing from the scope of the invention. Various processes or components may be appropriately omitted, substituted, or added to the various examples. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Furthermore, features described with respect to some examples may be combined into other examples.

[0052] To facilitate a better understanding of the embodiments of the present invention, its application scenarios will be explained before providing a detailed explanation of the specific implementation methods.

[0053] Please see Figure 1 , Figure 1 This diagram illustrates the topology of an AC flexible loop-closing device based on UPS startup and its application scenario. The invention is applied to processes such as uninterrupted power switching, load transfer, and grid optimization in power systems. In these scenarios, the invention aims to ensure a smooth transition during loop-closing operations, reducing inrush currents, protecting grid equipment from damage, and ensuring power supply continuity and stability. This allows users to enjoy uninterrupted, high-quality power services, providing a superior user experience and reliable performance. Figure 1As can be seen, the topology of the AC flexible loop-closing device of the present invention can at least include a bypass switch, a single-phase full-bridge switch, a DC capacitor, a controller, a communication module, and a UPS. The UPS charges the voltage source converter capacitor to enable the topology of the AC flexible loop-closing device of the present invention to have initial startup capability. When one end of the line is normally powered, the UPS directly inverts the AC power input into DC power to charge the voltage source converter capacitor. When the voltage of the voltage source converter capacitor reaches its rated value, the voltage source converter outputs a voltage with the same amplitude and phase angle, completing the flexible loop closure. If the UPS cannot input AC power from both ends of the line, it charges the voltage source converter capacitor through the UPS internal battery to complete the flexible loop closure, solving the problem of energy extraction for the loop-closing device when the pre-loop-closing line is not energized. At this time, the UPS charging mode is activated to supplement the charging of the internal battery. During loop closure, the voltage on both sides of the flexible loop-closing device is collected by sensors. and Current and Information such as the positions of switches S1 and S2 is received. The controller receives signals from the communication module, feedback from the flexible loop closing device and line status information from the sensors, performs internal calculations, and then sends a trigger pulse control signal to the voltage source converter to achieve flexible loop closing.

[0054] Example 1:

[0055] like Figure 2 As shown, this embodiment provides a topology for an AC flexible loop-closing device based on UPS startup, including a UPS module, a monitoring module, a communication module, and a control module. The monitoring module monitors the status information of the loop-closing line and uploads it to the communication module. The communication module transmits the received status information to the control module. The control module includes a calculation unit, a modulation unit, and a capacitor. The calculation unit performs difference calculation based on the received status information to obtain a control target signal and sends the control target signal to the modulation unit. The modulation unit modulates the control target signal to obtain a balance control signal and outputs the balance control signal to complete the balance loop-closing operation. The capacitor receives power from the UPS module and drives the topology to start flexible loop-closing. The UPS module includes a first charging unit and a second charging unit. The first charging unit converts AC power obtained from an external power source into DC power and charges the capacitor and the second charging unit. The second charging unit stores the DC power provided by the first charging unit and charges the capacitor when the first charging unit has no external power source.

[0056] More specifically, the monitoring module can be configured with at least two sensors, each connected to one of the two lines requiring flexible loop closure. The modulation unit can be configured as a voltage source converter.

[0057] This embodiment combines a UPS with a voltage source converter (VSC). This invention ensures that even when the pre-loop circuit is not energized, the UPS's DC power supply can quickly charge the VSC capacitor, enabling the device to rapidly reach initial startup conditions. This design significantly enhances the device's adaptability and reliability, effectively avoiding startup obstacles caused by power supply issues.

[0058] Specifically, this embodiment provides a preferred implementation, wherein the control module further includes an instruction input unit; the instruction input unit is used to allow the loop closing operator to input a compensation loop closing instruction value and send the compensation loop closing instruction to the modulation unit; the modulation unit modulates the control target signal and the compensation loop closing instruction to obtain a compensation control signal, and outputs the compensation control signal to complete the compensation loop closing operation.

[0059] Combination Figure 1 and Figure 4 It is understood that the working principle of the topology described in this embodiment is to inject a voltage with controllable amplitude and phase angle into the controlled line, thereby changing the line impedance parameters to achieve system control. In the active distribution network loop-closing scenario, the voltage difference at different closing points is constantly changing based on the closing requirements. The closing requirements include balancing the deviation between the two lines, inductive compensation, and capacitive compensation. Inductive compensation refers to injecting voltage to make the equivalent impedance positive, reducing the line current and decreasing the line transmission power. Capacitive compensation refers to injecting voltage to make the equivalent impedance negative, increasing the line current and increasing the line transmission power. This embodiment, by setting the input unit shown, gives the loop-closing operator a high degree of flexibility and initiative, allowing them to input commands according to actual needs to achieve precise loop-closing control. This not only improves the efficiency and success rate of loop-closing operations but also greatly enhances the flexibility and reliability of the distribution network, providing users with a more stable and high-quality power supply.

[0060] Example 2:

[0061] like Figure 3 As shown, this embodiment provides a flexible loop closure method based on the topology described in Embodiment 1, including the following steps:

[0062] S1. The UPS charges the voltage source converter capacitor directly from the external power supply or from the internal battery to initiate flexible loop operation.

[0063] S2. Obtain the status information of the closed loop line;

[0064] S3. Calculate the difference based on the state information to obtain the compensation value, thereby generating the target signal;

[0065] S4. Modulate the control target signal to obtain a control signal, and output the control signal to complete the flexible loop closure.

[0066] Specifically, this embodiment provides a preferred implementation of step S1, wherein the UPS directly charges the voltage source converter capacitor based on an external power supply to initiate the flexible loop closing operation, including the following steps:

[0067] Establish connection with external power source;

[0068] After the external AC power input is inverted into DC power U1, the capacitor of the voltage source converter is charged until the voltage of the voltage source converter capacitor reaches the rated value U. dc .

[0069] Specifically, this embodiment provides a preferred implementation of step S1, wherein the UPS charges the voltage source converter capacitor based on its internal battery to initiate the flexible loop-closing operation, including the following steps:

[0070] The AC power input from the external power source is inverted into DC power U1 and then stored in the internal battery U2;

[0071] The voltage source converter capacitor is charged through the internal battery U2 until the voltage of the voltage source converter capacitor reaches the rated value U. dc .

[0072] It is understood that this embodiment, by combining with an uninterruptible power supply (UPS) system, effectively pre-charges the voltage source converter capacitor, thereby ensuring the smooth startup of the flexible loop-closing device. The two preferred implementation methods provided in this embodiment are applicable to different application scenarios. Specifically, when the external power supply is stable and reliable, the inverter charging method can be directly used to quickly start the loop-closing device; while when the external power supply is uncertain or a backup power supply is needed, the UPS internal battery can be used for charging, ensuring smooth startup of the loop-closing operation under any circumstances. This flexibility allows the flexible loop-closing device of this embodiment to adapt to a wider range of power grid environments and user needs. Both methods can quickly increase the voltage of the voltage source converter capacitor to its rated value, thereby greatly shortening the device startup time, improving overall operating efficiency, and ensuring the system reliability of the flexible loop-closing device.

[0073] It is understood that the aforementioned topology can be equivalent to a voltage source with adjustable amplitude and phase angle connected in series in the line, such as... Figure 4As shown in the diagram, this schematic represents the equivalent model of a series-type flexible control device in the controlled circuit. The flexible loop-closing device is equivalent to a voltage whose amplitude and phase angle can be adjusted. The voltage difference across line AB is given by , therefore the current flowing through the loop-closing line is given by . The above analysis shows that the voltage amplitude and phase angle generated by the series-type flexible control equipment are freely adjustable, and the voltage of the line system is [unclear - possibly related to voltage regulation]. A constant voltage can be generated by controlling the converter to produce a voltage with the same amplitude and phase angle as the line system voltage. To achieve shock-free loop closure.

[0074] Therefore, to meet the loop-closing requirement of balancing the deviations of the two lines as described in this specification, the control target of the output voltage of the flexible loop-closing device is to compensate for the voltage difference at the closing point, that is... To meet the closed-loop requirements of inductive and capacitive compensation as described in this specification, this embodiment provides an active distribution network closed-loop voltage tracking compensation control strategy based on a PI controller, that is, by using a compensation voltage reference value... and The measured value of the compensation voltage U from the feedback ABd and U ABq The difference is used to obtain the deviation signal, and the deviation signal is used by the PI controller to dynamically calculate the d-axis component U of the output voltage. FIDd Reference value With q-axis component U FIDq Reference value Finally, after PI controller and decoupling calculation, the quantity U of the modulation voltage of the single-phase control unit in the dq0 coordinate system is obtained. rd and U rq After single-phase reverse Park transformation, the modulated voltage in the abc three-phase stationary coordinate system is obtained. After SPWM modulation, the resulting trigger pulse is sent to the power electronic switch in the single-phase control unit to invert and produce the required output voltage. The above process can be implemented with reference to the following five preferred embodiments.

[0075] Specifically, this embodiment provides a preferred implementation, wherein the status information includes the voltage values ​​of the two lines that need to undergo loop closing operation, respectively. and

[0076] Specifically, this embodiment provides a preferred implementation of step S3, which involves calculating the difference based on the state information to obtain a compensation value, thereby generating a control target signal, and includes the following steps:

[0077] Based on the above Obtain its d-axis component U Ad and q-axis component U Aq ;

[0078] Based on the above Obtain its d-axis component U Bd and q-axis component U Bq ;

[0079] Based on the U Ad and the U Bd The d-axis component U of the reference value of the voltage difference at the closing point is obtained by performing difference calculation. * ABd ;

[0080] Based on the U Aq and the U Bq The q-axis component U of the reference value of the voltage difference at the junction point is obtained by performing difference calculation. * ABq ;

[0081] Based on the above and stated Perform difference calculation to obtain the voltage difference at the closing point. and its d-axis component U ABd and q-axis component U ABq ;

[0082] Based on the voltage difference at the junction point Obtain the control target voltage reference value Thus, the control target signal is obtained.

[0083] Specifically, this embodiment provides a preferred implementation of step S4, wherein modulating the control target signal to obtain a control signal includes the following steps:

[0084] Based on the d-axis component U of the voltage difference at the junction point ABd and q-axis component U ABq The d-axis component U of the control target voltage reference value is obtained. * FIDd With q-axis component U * FIDq ,Right now:

[0085]

[0086] Based on the d-axis component U of the control target voltage reference value * FIDd With q-axis component U * FIDq Inverter to control target voltage This results in the acquisition of control signals.

[0087] Specifically, this embodiment provides a preferred implementation, which includes the following step before step S4: obtaining a compensation loop closing instruction for the loop closing line to perform a flexible loop closing operation, wherein the compensation loop closing instruction includes an inductive compensation instruction value or a capacitive compensation instruction value.

[0088] Step S4, which modulates the control target signal to obtain a control signal, specifically involves modulating the control target signal based on the inductive compensation command value or the capacitive compensation command value to obtain a control signal.

[0089] Specifically, this embodiment provides a preferred implementation, wherein the modulation of the control target signal based on the inductive compensation command value or the capacitive compensation command value includes the following steps:

[0090] The inductive compensation command value or the capacitive compensation command value is recorded as the control target voltage reference value;

[0091] Based on the expression for the target voltage reference value, PI control is performed to obtain the d-axis component U of the target voltage reference value. * FIDd With q-axis component U * FIDq ;

[0092] Based on the d-axis component U of the control target voltage reference value * FIDd With q-axis component U * FIDq Inverter to control target voltage Thus, control signals are obtained;

[0093] The expression for the control target voltage reference value is:

[0094]

[0095] In the formula, K P1 K P2 K is the proportional gain of the PI controller. I1 K I2 This represents the integral coefficient of the PI controller.

[0096] Example 3:

[0097] To verify the effectiveness of the AC flexible loop-closing device topology and flexible loop-closing method based on UPS startup described in this specification, a simulation model was constructed in this embodiment, and a simulation cycle of 2 seconds was set. During the simulation, the two UPS units performed a loop-closing operation at 0.3 seconds. Simultaneously, the flexible loop-closing device was connected in series to the system, instantly generating a compensation voltage to achieve smooth loop closure. Immediately afterwards, at 0.5 seconds, the device autonomously activated its energy harvesting mechanism; and at 0.6 seconds, the UPS stopped charging the DC capacitor.

[0098] Figure 5 The experimental results based on the above simulation model are presented. Figure 5 In the diagram, 'a' represents the voltage difference at the connection point of the two junction stations. Figure 5 In the figure, b represents the effective value of the voltage difference at the point of closure between the two substations. During the period from 0s to 0.3s when the two substations are not closed, the voltage difference is 43.6V. After closure, during the period from 0.4s to 0.6s, the voltage difference between the two substations is compensated to 12.7V through the UPS and the flexible closure device, with the flexible closure device providing a compensation voltage of 30.9V. After 0.6s, the flexible closure device switches to self-powered operation, using a DC capacitor to provide DC voltage, resulting in a voltage difference of 35.7V between the two substations, with the flexible closure device providing a compensation voltage of 7.9V. Figure 5 In the figure, c represents the current value of the loop line connecting the two substations. Figure 5 In the figure, d represents the effective value of the loop current between the two transformer substations. During the period from 0s to 0.3s when the two substations are not in a loop, the current in the connecting line between the two substations is 0A. After the loop is closed, during the period from 0.4s to 0.6s, the current in the connecting line between the two substations via the UPS and the flexible loop closing device is 0.126A. After 0.6s, the flexible loop closing device switches to self-powered operation, with DC voltage provided by a DC capacitor, and the current in the connecting line between the two substations is 0.029A.

[0099] Based on the above, this embodiment verifies the effectiveness of the AC flexible loop closing device topology and flexible loop closing method based on UPS startup described in this specification.

[0100] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0101] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0102] The foregoing description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Those skilled in the art will readily conceive of other embodiments of this disclosure upon considering the specification and practicing the disclosure herein. This invention is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

Claims

1. A UPS-based AC flexible closing loop topology, comprising: a UPS module, a monitoring module, a communication module, and a control module; the monitoring module is configured to monitor state information of the closing loop and upload the state information to the communication module; the communication module is configured to transmit the received state information to the control module; the control module comprises a calculation unit, a modulation unit, and a capacitor; the calculation unit is configured to perform difference calculation based on the received state information to obtain a control target signal, and send the control target signal to the modulation unit; the modulation unit is configured to perform modulation based on the control target signal to obtain a balance control signal, and output the balance control signal to complete the balance closing loop operation; and the capacitor is configured to receive power from the UPS module and drive the topology to start the flexible closing loop; the UPS module comprises a first charging unit and a second charging unit; the first charging unit is configured to convert AC power obtained from an external power source into DC power, and charge the capacitor and the second charging unit; and the second charging unit is configured to store the DC power provided by the first charging unit, and charge the capacitor when the first charging unit has no external power source. 2.The UPS-based AC flexible closing loop topology of claim 1, wherein: the control module further comprises an instruction input unit; the instruction input unit is configured to input a compensation closing loop instruction value by a closing loop operator, and send the compensation closing loop instruction to the modulation unit; and the modulation unit is configured to perform modulation based on the control target signal and the compensation closing loop instruction to obtain a compensation control signal, and output the compensation control signal to complete the compensation closing loop operation. The method comprises the following steps: S1, the UPS charges the capacitor of the voltage source converter based on the external power source directly or based on the internal battery to start the flexible closing loop operation; S2, state information of the closing loop is obtained; S3, difference calculation is performed based on the state information to obtain a compensation value, thereby generating a control target signal; S4, modulation is performed on the control target signal to obtain a control signal, and the control signal is output to complete the flexible closing loop. 4.The flexible closing loop method of claim 3, wherein: the step S3 of performing difference calculation based on the state information to obtain a compensation value, thereby generating a control target signal, comprises the following steps: the step S4 of performing modulation on the control target signal to obtain a control signal comprises the following steps: before the step S4, a compensation closing loop instruction for the flexible closing loop operation of the closing loop is obtained, and the compensation closing loop instruction comprises an inductive compensation instruction value or a capacitive compensation instruction value; and the step S4 of performing modulation on the control target signal to obtain a control signal is specifically: performing modulation on the control target signal based on the inductive compensation instruction value or the capacitive compensation instruction value to obtain a control signal; and the step of performing modulation on the control target signal based on the inductive compensation instruction value or the capacitive compensation instruction value comprises the following steps: ​ ​ ​ ​ ​ ​ 3. A flexible ring closure method based on the topology of claim 2, characterized in that, ​ ​ ​ ​ ​ ​ The state information includes the voltage values of the two lines which need to be looped, respectively and 5. The flexible ring closure method of claim 4, wherein, ​ Based on the Obtaining the d-axis component U Ad and the q-axis component U Aq ; Based on the Obtaining the d-axis component U Bd And the q-axis component U Bq ; Based on the U Ad And the U Bd The difference calculation is carried out to obtain the d-axis component U * ABd ; Based on the U Aq and the U Bq The difference calculation is carried out to obtain the q-axis component U * ABq ; Based on the And the Difference calculation, get the voltage difference of the closing node And its d-axis component U ABd And q-axis component U ABq ; based on the ring closure node voltage difference obtaining a control target voltage reference value thus obtaining the control target signal.

6. The flexible ring closure method of claim 5, wherein, ​ a d-axis component U of the said closed loop node voltage difference ABd and a q-axis component U ABq a d-axis component U of the control target voltage reference value * FIDd and a q-axis component U * FIDq i.e.: a d-axis component U of the control target voltage reference value * FIDd a q-axis component U * FIDq inverted to obtain a control target voltage to obtain a control signal.

7. The flexible ring closure method of claim 5, wherein, ​ ​ 8. The flexible ring closure method of claim 7, wherein, ​ The inductive compensation instruction value or capacitive compensation instruction value is recorded as a control target voltage reference value; Based on the expression of the control target voltage reference value, PI control is performed to obtain a d-axis component U * FIDd and a q-axis component U * FIDq ; a d-axis component U of the control target voltage reference value * FIDd a q-axis component U * FIDq inverted to obtain a control target voltage to obtain a control signal; An expression of the control target voltage reference value is: where K P1 , K P2 , K I1 , and K I2 are the proportional and integral coefficients of the PI controller.

9. The flexible ring closure method according to any one of claims 3-8, wherein, The step S1 includes the following steps for the UPS to charge the voltage source converter capacitor based on the external power supply to start the flexible closed-loop operation: Establishing a connection with the external power supply; The AC power input from an external power source is inverted into DC power U1, and the voltage source inverter capacitor is charged until the voltage source inverter capacitor voltage reaches the rated value U dc .

10. The method of claim 3-8, wherein, The step S1 includes the following steps for the UPS to charge the voltage source converter capacitor based on the internal battery to start the flexible closed-loop operation: The AC power input from the external power supply is inverted into DC power U1 and then stored in the internal battery U2; The voltage source inverter capacitor is charged by the internal battery U2 until the voltage source inverter capacitor voltage reaches the rated value U dc .

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