Low-voltage treatment method and system based on multi-stage series direct-current remote supply device

Abstract

The invention discloses a low-voltage treatment method and system based on multistage series direct-current remote supply devices, and belongs to the technical field of low-voltage treatment, and the method comprises the steps: enabling a plurality of direct-current remote supply devices to be connected to a power transmission line at the tail end of a power grid in series, and enabling a load point on the power transmission line to be connected to the nearest direct-current remote supply device; wherein the load point comprises a plurality of end users; controlling the direct-current side voltage of the power transmission line within a preset direct-current voltage reference range through the host control of the direct-current remote supply device; and when the load on the load point changes, controlling the AC voltage of the end user within a preset AC voltage reference range through a slave of the DC remote power supply device. Therefore, by implementing the application, the problem in the prior art that the low-voltage treatment effect is relatively poor because the direct-current remote supply device can only improve the power utilization quality of part of users in the scene that the end users are relatively dispersed can be solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of low-voltage management, and particularly relates to a low-voltage management method and system based on a multi-stage series DC remote supply device. BACKGROUND

[0002] Low voltage at the end user will affect normal power consumption of residents. A traditional low-voltage management scheme is power grid reconstruction, which moves and thickens the transformer in the corresponding area of the low-voltage distribution network to reduce the power supply radius and thus reduce the line voltage drop. However, this scheme has high investment cost and long construction period. With the development of power technology, DC remote supply technology can now be used to transmit power in the form of DC power, and a DC line with a higher voltage level is used to replace the original AC line for power transmission, so as to reduce voltage drop by reducing line loss.

[0003] Common DC remote supply devices are single-stage parallel or single-stage series. The single-stage parallel DC remote supply device causes most of the current to flow through the DC line, and only part of the current flows through the AC line. If there are sporadic AC users distributed near the AC line, they will not get enough power. The single-stage series DC remote supply device uses DC power transmission and does not have an AC line. If sporadic AC users are distributed near the DC power transmission line, they cannot directly obtain AC power. Therefore, in remote mountainous areas and other areas where low-voltage distribution network end users are relatively dispersed, the DC remote supply device can only improve the voltage of part of the users and cannot improve the power quality of most users. SUMMARY

[0004] The application provides a low-voltage management method and system based on a multi-stage series DC remote supply device, which can solve the problem that the DC remote supply device can only improve the power quality of part of the users in the existing technology in the scenario where end users are relatively dispersed, resulting in poor low-voltage management effect.

[0005] The first aspect of the application provides a low-voltage management method based on a multi-stage series DC remote supply device, which comprises the following steps:

[0006] A plurality of DC remote supply devices are connected in series on a power transmission line at the end of the power grid, and a load point on the power transmission line is connected to the nearest DC remote supply device; wherein the load point comprises a plurality of end users;

[0007] The DC side voltage of the power transmission line is controlled within a preset DC voltage reference range by a host of the DC remote supply device;

[0008] When the load on the load point changes, the AC voltage of the end user is controlled within a preset AC voltage reference range by a slave of the DC remote supply device.

[0009] The scheme above connects multiple DC remote supply devices in series on a power transmission line, controls the voltage of one terminal load point in a specified range through one DC remote supply device, and realizes low voltage management of the dispersed load point. The DC remote supply device is divided into two parts, the host controls the DC side voltage, and the slave controls the AC side voltage. When the load of the load point changes, the voltage of the load point is still maintained in the specified AC voltage reference range through the voltage regulation of the AC user by the slave, which ensures the power quality of the users at the end of the low-voltage distribution network. Because one DC remote supply device is used for low voltage management of one load point, the DC remote supply device can be set and removed at any time according to the addition and cancellation of the load point, and the flexibility of low voltage management is realized.

[0010] In a possible implementation method of the first aspect, the load point and the DC remote supply device accessed by the load point, in particular:

[0011] For each of the load points and the DC remote supply devices accessed by the load points, the capacity of the load point is less than the capacity of the DC remote supply device accessed by the load point.

[0012] For a first load point and a second load point in the load points, the first load point accesses a first DC remote supply device, and the second load point accesses a second DC remote supply device, and the capacity of the first DC remote supply device is greater than the sum of the capacities of the first load point and the second load point; wherein the distance of the first load point at the end of the power grid is less than the distance of the second load point at the end of the power grid.

[0013] The scheme above limits the capacity of the multi-stage series DC remote supply device, so as to select a suitable type of DC remote supply device, ensure that the capacity of the DC remote supply device is sufficient to realize low voltage management of the load point, and improve the voltage stabilization effect.

[0014] In a possible implementation method of the first aspect, the voltage management between the first DC remote supply device and the second DC remote supply device, in particular:

[0015] The first DC remote supply device provides power to the first load point and the second DC remote supply device, and when the current flowing through the DC line of the first DC remote supply device is greater than the current flowing through the DC line of the second DC remote supply device, the voltage of the first DC remote supply device is increased.

[0016] The scheme above reduces line loss, improves the power transmission capacity of the line, and ensures the power supply quality when the currents flowing through the two DC remote supply devices are different, by increasing the voltage of the DC remote supply device with higher current.

[0017] In a possible implementation of the first aspect, the DC side voltage of the power transmission line is controlled within a preset DC voltage reference range by host control of the DC remote power supply device, specifically:

[0018] The host is operated in a rectification mode, and a DC voltage outer loop of the host processes the DC side voltage and a preset DC voltage reference value to obtain a first AC current reference value of a first AC current inner loop of the host.

[0019] The first AC current outer loop processes the acquired three-phase input current and the first AC current reference value, and signal modulates a processing result to obtain a first driving signal.

[0020] The operation of the switching device of the host is controlled according to the first driving signal, and the DC side voltage is controlled within the DC voltage reference range.

[0021] The above scheme performs double-loop control on the host of the DC remote power supply device, compares the acquired voltage and current data with the preset current voltage reference value through the DC voltage outer loop and the first AC current inner loop respectively, and obtains a driving signal that can keep the DC side voltage in a stable state, so as to realize voltage maintenance.

[0022] In a possible implementation of the first aspect, when the load at the load point changes, the AC voltage of the end user is controlled within a preset AC voltage reference range by a slave of the DC remote power supply device, specifically:

[0023] According to the low-voltage treatment requirement, an AC voltage reference value and a phase thereof are set;

[0024] The slave is operated in an inversion mode, and an AC voltage outer loop of the slave processes the AC voltage of the end user and the AC voltage reference value to obtain a second AC current reference value of a second AC current inner loop of the slave.

[0025] The second AC current inner loop processes the second AC current reference value and the acquired three-phase input current, and signal modulates a processing result to obtain a second driving signal.

[0026] The operation of the switching device of the slave is controlled according to the second driving signal, and the AC voltage is controlled within the AC voltage reference range.

[0027] In the above scheme, the slave of the DC remote power supply device is used to control the data on the AC side, and therefore the slave is double-loop controlled by using the AC voltage outer loop and the AC current inner loop, so as to obtain a driving signal that can keep the AC voltage of the end user in a set range, thereby realizing low-voltage treatment.

[0028] In one possible implementation of the first aspect, the controllers for the outer AC voltage loop and the inner AC current loop are both PI controllers based on the dq coordinate system, used to adjust the AC voltage reference range; the control logic for the slave device's outer AC voltage loop and inner AC current loop specifically includes:

[0029] When the controller switches to another coordinate system, only the AC voltage outer loop is used to control the AC voltage.

[0030] One possible implementation of the first aspect also includes:

[0031] When a new load point appears on the transmission line at the end of the power grid, a new DC remote power supply device is connected between the new load point and the transmission line.

[0032] When circulating current occurs between power modules, a droop control strategy is used to regulate the power modules; wherein, both the master and the slave are composed of several power modules connected in parallel.

[0033] When new, dispersed load points appear on the transmission line, the above solution can directly add a DC remote power supply device between the new load point and the transmission line to stabilize the voltage at that new load point, thus achieving flexibility in low-voltage management. Furthermore, considering that differences in the control parameters of the DC remote power supply devices can lead to circulating currents between power modules, potentially damaging equipment on the line, droop control is adopted to achieve coordinated operation between the power modules.

[0034] The second aspect of this application provides a low-voltage management system based on a multi-stage series DC remote power supply device, the system comprising: a device access module, a DC voltage control module, and an AC voltage control module;

[0035] The device access module is used to connect several DC remote power supply devices in series on the transmission line at the end of the power grid, and to connect the load point on the transmission line to the nearest DC remote power supply device; wherein, the load point includes several end users;

[0036] The DC voltage control module is used to control the DC side voltage of the transmission line within a preset DC voltage reference range through the main control of the DC remote power supply device.

[0037] The AC voltage control module is used to control the AC voltage of the end user within a preset AC voltage reference range through the slave unit of the DC remote power supply device when the load at the load point changes.

[0038] A third aspect of this application provides a terminal device, the device comprising: a terminal device including a processor and a memory, the memory storing a computer program, wherein the processor executes the computer program to implement the steps of the low voltage management method based on a multi-stage series DC remote power supply device as described in any one of the embodiments of this application.

[0039] A fourth aspect of this application provides a storage medium that stores computer-readable program code, which, when executed, implements the steps of a low-voltage management method based on a multi-stage series DC remote power supply device as described in any one of the embodiments of this application. Attached Figure Description

[0040] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 This is a schematic flowchart illustrating a low-voltage management method based on a multi-stage series DC remote power supply device according to an embodiment of this application.

[0042] Figure 2 This is a schematic diagram of a single-stage DC remote power supply device, which is a low-voltage management method based on a multi-stage series DC remote power supply device provided in an embodiment of this application.

[0043] Figure 3 This is a schematic diagram of a multi-stage series DC remote power supply device, which is a low voltage management method based on a multi-stage series DC remote power supply device according to an embodiment of this application.

[0044] Figure 4 This application provides an embodiment of a low-voltage management method based on a multi-stage series DC remote power supply device, including a DC remote power supply device and its electrical measurement diagram.

[0045] Figure 5 This is a control block diagram of a DC remote power supply device based on a low voltage management method for a multi-stage series DC remote power supply device provided in an embodiment of this application;

[0046] Figure 6 This is a structural diagram of a low-voltage management system based on a multi-stage series DC remote power supply device provided in one embodiment of this application;

[0047] Figure 7 This application provides a structural diagram of a terminal device according to one embodiment. Detailed Implementation

[0048] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0049] It should be understood that the step numbers used in the text are for ease of description only and are not intended to limit the order in which the steps are performed.

[0050] First Embodiment

[0051] At the end of a low-voltage distribution network, excessive AC transmission line losses can lead to low voltage for end users, affecting their normal electricity use. Existing low-voltage mitigation technologies primarily focus on centralized end users, using single-stage series or single-stage parallel back-to-back converters to reduce transmission line losses and thus improve end-user voltage. However, in remote mountainous areas and other locations with dispersed load points, single-stage DC remote power supply devices cannot effectively improve power quality for all end-user load points. Therefore, this application proposes a multi-stage series DC remote power supply device to address the problem of intermittent or continuous low voltage at multiple dispersed load points.

[0052] like Figure 1 As shown, to address the problem in existing technologies where DC remote power supply devices can only improve the power quality for some users in scenarios with dispersed end users, resulting in poor low-voltage management, the first embodiment of this application provides a detailed flowchart of a low-voltage management method based on a multi-stage series DC remote power supply device. This embodiment's low-voltage management method based on a multi-stage series DC remote power supply device includes steps S1 to S3, detailed below:

[0053] Step S1: Connect several DC remote power supply devices in series on the transmission line at the end of the power grid, and connect the load point on the transmission line to the nearest DC remote power supply device.

[0054] DC remote power supply technology utilizes back-to-back power electronic converters to transmit electrical energy in DC mode, replacing the original AC lines with higher voltage DC lines for power transmission, thus mitigating low voltage by reducing line losses. DC remote power supply devices primarily use AC / DC converters to convert AC to DC, with the electrical energy mainly transmitted via DC transmission lines. At the user side, DC / AC converters are installed to convert the transmitted DC energy back to AC energy for use. Common DC remote power supply devices are divided into single-stage series or single-stage parallel configurations, as detailed below. Figure 1 As shown.

[0055] exist Figure 1Figure (a) shows the topology of a single-stage parallel DC remote power supply device connected to the end user, and Figure (b) shows the topology of a single-stage series DC remote power supply device connected to the end user. In order to improve the voltage of the end user, the single-stage parallel DC remote power supply device ensures that most of the current in the transmission line flows through the DC line between the converters, with only a portion flowing through impedance Z. AC If there are distributed end users located near the AC line, sufficient power cannot be obtained. The single-stage series-type DC remote power supply device only uses DC transmission and cannot perform AC transmission (i.e., current only flows through impedance Z). DC Since these are located on DC lines, they can only supply power to end users near the DC lines. Therefore, neither of these two types of DC remote power supply devices can provide sufficient power to end users scattered across AC lines.

[0056] Among them, for Figure 1 The two diagrams show a 380V AC transmission line. Z1 represents the impedance between the AC / DC converter of the DC remote power supply unit and the AC line, while Z2 represents the AC line impedance between the DC / AC converter of the DC remote power supply unit and the end user. AC For AC line impedance, Z DC The impedance of the DC line between the converters.

[0057] Considering the dispersed nature of low-voltage distribution network end users in remote mountainous areas, using only single-stage series or single-stage parallel DC remote power supply devices for power transmission can only improve the voltage for a portion of users. To achieve voltage enhancement at multiple load points in remote areas, this application provides a multi-stage series DC remote power supply device connection scheme. Each load point is connected to the nearest DC remote power supply device, and these devices are connected in series on the transmission line, allowing one DC remote power supply device to manage low voltage at one load point. Since low-voltage distribution network end users are often scattered in small communities, each community containing multiple users located relatively close to each other, and different communities being geographically distant, the term "load point" is used as the collective name for end users within a community.

[0058] The topology of the multi-stage series-connected DC remote power supply device and the end user in this application embodiment is as follows: Figure 3 As shown. The application scenario presented in this application embodiment is that there are two dispersed end users at the end of the power grid. Therefore, a two-stage series-connected DC remote power supply device is used. End user 1 is connected to the end of the first-stage DC remote power supply device to perform low voltage management for end user 1; end user 2 is connected to the end of the second-stage DC remote power supply device to perform low voltage management for end user 2. Wherein, Z AC1 Z represents the AC line impedance between the primary DC remote power supply device and the transmission line. AC2Z represents the AC line impedance between the primary DC remote power supply unit and end user 1. AC3 Z represents the AC line impedance between the primary DC remote power supply unit and the secondary DC remote power supply unit. AC3 Z represents the AC line impedance between the secondary DC remote power supply unit and end user 2. DC1 Z DC2 These refer to the DC line impedance between the converters in the primary DC remote power supply unit and the secondary DC remote power supply unit, respectively.

[0059] Optionally, 380V AC voltage transmission is used in this embodiment, but in other embodiments, higher-level DC voltage transmission can be used to reduce line losses.

[0060] In addition to setting up the connection between the load point and the DC remote power supply device, the embodiments of this application also set the selection of the DC remote power supply device, including the selection of the device capacity. Specifically, the capacity selection criteria for each level of DC remote power supply device can be different, but the capacity of the DC remote power supply device should be slightly larger than the capacity of the connected load point.

[0061] For example, with Figure 3 Taking a two-stage series-connected DC remote power supply device as an example, the capacity of the second-stage DC remote power supply device should be slightly larger than the capacity of end user 2, and the capacity of the first-stage DC remote power supply device should be slightly larger than the sum of the capacities of end user 1 and end user 2.

[0062] Therefore, for any two load points that are close to each other on the transmission line, designated as the first load point and the second load point, the corresponding DC remote power supply devices are called the first DC remote power supply device and the second DC remote power supply device. The capacity of the first DC remote power supply device should be greater than the sum of the capacities of the first load point and the second load point in order to achieve the optimal voltage stabilization effect.

[0063] As an improvement to the above solution, this application embodiment also provides the selection of DC lines, where the DC lines refer to the lines between the converters of the DC remote power supply devices. Since the first DC remote power supply device needs to provide power to the first load point and the second DC remote power supply device, when the current flowing through the DC line of the first DC remote power supply device is greater than the current flowing through the DC line of the second DC remote power supply device, the voltage of the first DC remote power supply device can be appropriately increased to reduce line losses. For example, in this application embodiment, the DC voltage of the first-stage DC remote power supply device is ±400V, and the DC voltage of the second-stage DC remote power supply device is ±375V.

[0064] Furthermore, the embodiments of this application Figure 4 A more detailed diagram of the DC remote power supply device and its electrical measurement is provided. For ease of description, the N line is not shown in the diagram; only the three-phase lines are shown. Figure 4 andFigure 3 The impedance data in the two are basically the same, i a0 i b0 i c0 i represents the three-phase current on the input side of the primary DC remote power supply unit. a1 i b1 i c1 i represents the three-phase current on the output side of the primary DC remote power supply unit. az1 i bz1 i cz1 For the three-phase current at the input side of end user 1, i' a1 、i' b1 、i' c1 i represents the three-phase current on the input side of the primary DC remote power supply unit. a2 i b2 i c2 i represents the three-phase current on the output side of the secondary DC remote power supply unit. az2 i bz2 i cz2 For the three-phase current on the input side of end user 2; u an1 u bn1 u cn1 The three-phase voltage on the output side of the primary DC remote power supply unit, u an2 u bn2 u cn2 The three-phase voltage on the output side of the secondary DC remote power supply device, u DC1 The DC voltage of the primary DC remote power supply device, u DC2 This refers to the DC voltage of the secondary DC remote power supply device.

[0065] Step S2: The DC side voltage of the transmission line is controlled within a preset DC voltage reference range by the host control of the DC remote power supply device.

[0066] Furthermore, the embodiments of this application Figure 4 A more detailed diagram of the DC remote power supply device and its electrical measurement is provided. For ease of description, the N line is not shown in the diagram; only the three-phase lines are shown. Figure 4 and Figure 3 The impedance data in the two are basically the same, i a0 i b0 i c0 i represents the three-phase current on the input side of the primary DC remote power supply unit. a1 i b1 i c1 i represents the three-phase current on the output side of the primary DC remote power supply unit. az1 i bz1 i cz1 For the three-phase current at the input side of end user 1, i' a1 、i' b1 、i'c1 i represents the three-phase current on the input side of the primary DC remote power supply unit. a2 i b2 i c2 i represents the three-phase current on the output side of the secondary DC remote power supply unit. az2 i bz2 i cz2 For the three-phase current on the input side of end user 2; u an1 u bn1 u cn1 The three-phase voltage on the output side of the primary DC remote power supply unit, u an2 u bn2 u cn2 The three-phase voltage on the output side of the secondary DC remote power supply device, u DC1 The DC voltage of the primary DC remote power supply device, u DC2 This refers to the DC voltage of the secondary DC remote power supply device.

[0067] In a multi-stage series-connected DC remote power supply unit, the main unit controls the DC voltage, and the slave unit controls the AC voltage. Figure 4 As can be seen from the content, the AC voltage of end user 1 is controlled by slave device 1, and the AC voltage of end user 2 is controlled by slave device 2.

[0068] When the multi-stage series-connected DC remote power supply device is operating normally, the main unit operates in rectification mode and the slave unit operates in inverter mode.

[0069] Regarding the control strategy for the host, this embodiment of the application mainly employs a dual-loop control system consisting of a DC voltage outer loop and an AC current inner loop, as detailed below:

[0070] (1) Set the value of the DC voltage reference value, subtract the DC voltage reference value from the DC side voltage of the DC remote power supply device on the transmission line, and then pass through the DC voltage outer loop to obtain the AC current reference value of the AC current inner loop.

[0071] (2) The AC current reference value is subtracted from the collected three-phase input current and then passed through the AC current inner loop to obtain the modulation wave;

[0072] (3) The modulation wave is modulated using an SPWM or SVPWM modulation strategy to obtain a first drive signal that can drive the switching device of the host computer; the operation of the switching device of the host computer is controlled by the first drive signal to control the DC side voltage within the DC voltage reference range. Among them, SPWM is based on sinusoidal drive and changes the modulation pulse mode. The pulse width time duty cycle is arranged according to a sinusoidal law, so that the output waveform can be sinusoidal after appropriate filtering.

[0073] Optionally, in the embodiments of this application, the DC-side voltage is generally controlled near the DC voltage reference value.

[0074] For the main unit of the DC remote power supply device, the controller of its outer DC voltage loop is a PI controller based on the dq coordinate system, used to track the DC voltage reference value. The controller of its inner AC current loop is a PR controller based on either the dq or αβ coordinate system, used to track the AC current reference value.

[0075] Step S3: When the load at the load point changes, the AC voltage of the end user is controlled within a preset AC voltage reference range by the slave unit of the DC remote power supply device.

[0076] Based on the requirements for low voltage management, an AC voltage reference value and its phase are set. In this embodiment, it is set to 220V according to domestic standards.

[0077] Regarding the control strategy for the slave device, this embodiment of the application mainly employs a dual-loop control system consisting of an AC voltage outer loop and an AC current inner loop, as detailed below:

[0078] (1) Subtract the set AC voltage reference value from the collected AC voltage of the end user and pass it through the AC voltage outer loop of the slave device to obtain the AC current reference value of the AC current inner loop.

[0079] (2) The AC current reference value is subtracted from the three-phase input current obtained by sampling, and then passed through the AC current inner loop to obtain the modulation wave;

[0080] (3) The modulation wave is modulated using an SPWM or SVPWM modulation strategy to obtain a second drive signal that can drive the switching device of the slave device; the operation of the switching device of the slave device is controlled by the second drive signal to control the AC voltage within the AC voltage reference range.

[0081] Optionally, in the embodiments of this application, the AC voltage is generally controlled near the AC current reference value.

[0082] The slave unit of the DC remote power supply device uses a PI controller based on the dq coordinate system for its AC voltage outer loop controller to track the AC voltage reference value. Its AC current inner loop controller is also a PI controller based on the dq coordinate system, used to track the AC current reference value. When these controllers are switched to the αβ coordinate system, only the AC voltage outer loop is needed for effective AC voltage control.

[0083] As an improvement to the above solution, since both the host and the slave are composed of several power modules connected in parallel, under the above dual-loop control, due to differences in control parameters, circulating currents are prone to occur between the power modules, which will increase equipment losses and reduce power supply reliability. Therefore, a droop control strategy can also be used to regulate the power modules.

[0084] Figure 5 This is a control block diagram of a DC remote power supply device provided in an embodiment of this application. Its application background is as follows: Figure 4 The architecture in it. Figure 5 (a) is the control block diagram of the primary DC remote power supply device. Figure 5 (b) is the control block diagram of the secondary DC remote power supply device. For the main unit, u DC1ref u DC2ref These are the DC voltage reference values ​​for the primary and secondary DC remote power supply devices, respectively. DC1 u DC2 These are the DC-side voltages of the primary DC remote power supply unit and the secondary DC remote power supply unit, respectively; i a,b,c0ref 、i' a,b,c1ref These are the AC current reference values ​​for the inner loops of the AC current of the primary DC remote power supply device and the secondary DC remote power supply device, respectively. a,b,c0 、i' a,b,c1 These are the three-phase input currents of the inner loop of the AC current input to the primary and secondary DC remote power supply units, respectively. a,b,c1 u a,b,c2 These are the modulation waves of the main units of the primary DC remote power supply device and the secondary DC remote power supply device, respectively.

[0085] For the slave device, u a,b,cn1ref u a,b,cn2ref These are the AC voltage reference values ​​for the primary and secondary DC remote power supply devices, respectively. a,b,cn1 u a,b,cn2 The AC voltages collected at the primary DC remote power supply device and the secondary DC remote power supply device are respectively, i a,b,c1ref i a,b,c2ref These are the AC current reference values ​​for the inner loops of the AC current of the primary DC remote power supply device and the secondary DC remote power supply device, respectively. a,b,c1 、i' a,b,c2 These are the three-phase input currents of the slave AC current inner loops of the primary and secondary DC remote power supply devices, respectively; u' a,b,c1 、u' a,b,c2 These are the modulation waves of the slave devices of the primary DC remote power supply device and the secondary DC remote power supply device, respectively.

[0086] Therefore, when a new load point is added to the transmission line, it is only necessary to increase the number of stages of the DC remote power supply device to achieve low voltage management for all end users on the transmission line. Specifically, according to the on-site conditions of the transmission line, a new DC remote power supply device is added between the new load point and the transmission line, so that the new load point is connected to the end of the DC remote power supply device. The DC remote power supply device will be used to regulate the AC voltage of the new load point. If the original architecture is a three-stage series DC remote power supply device, then it is now a four-stage series DC remote power supply device.

[0087] This scheme enables flexibility in selecting DC remote power supply devices, and the converter topology of the DC remote power supply device is not limited to T-type three-level. Other architectures can also be selected in other embodiments. Furthermore, the number of converters in the DC remote power supply device is not limited to a single unit. In other embodiments, multiple converters can be connected in parallel.

[0088] Implementing the embodiments of this application has the following beneficial effects:

[0089] This application embodiment achieves low-voltage management for distributed load points by connecting multiple DC remote power supply devices in series on the transmission line, and using one DC remote power supply device to control the voltage of a single end load point within a specified range. The DC remote power supply device consists of two parts: a master unit controls the DC side voltage, and a slave unit controls the AC side voltage. When the load at the load point changes, the slave unit adjusts the voltage of the AC user, ensuring that the voltage at the load point remains within the specified AC voltage reference range, thus guaranteeing the power quality for users at the end of the low-voltage distribution network. Because one DC remote power supply device manages low voltage for one load point, it can be easily added and removed as load points are added or removed, achieving flexibility in low-voltage management.

[0090] Second Embodiment

[0091] Furthermore, in order to implement the low-voltage management system based on a multi-stage series DC remote power supply device corresponding to the above method embodiments, and to achieve the corresponding functions and technical effects, Figure 6 A structural diagram of a low-voltage mitigation system based on a multi-stage series DC remote power supply device is provided. For ease of explanation, only the parts relevant to this embodiment are shown. The low-voltage mitigation system based on a multi-stage series DC remote power supply device provided in this application embodiment includes:

[0092] The device access module 201 is used to connect several DC remote power supply devices in series on the transmission line at the end of the power grid, and to connect the load point on the transmission line to the nearest DC remote power supply device; wherein, the load point includes several end users.

[0093] In this embodiment of the application, for each load point and the DC remote power supply device connected to it, the capacity of the load point is less than the capacity of the DC remote power supply device connected to it.

[0094] For the first load point and the second load point among the load points, the first load point is connected to the first DC remote power supply device, and the second load point is connected to the second DC remote power supply device. Then, the capacity of the first DC remote power supply device is greater than the sum of the capacities of the first load point and the second load point; wherein, the distance of the first load point to the end of the power grid is less than the distance of the second load point to the end of the power grid.

[0095] The DC voltage control module 202 is used to control the DC side voltage of the transmission line within a preset DC voltage reference range through the host control of the DC remote power supply device.

[0096] In the embodiments of this application, the master unit of the multi-stage series-connected DC remote power supply device is used to control the DC voltage, and the slave unit is used to control the AC voltage. That is, the AC voltage of end user 1 is controlled by the slave unit of the first-stage DC remote power supply device, and the AC voltage of end user 2 is controlled by the slave unit of the second-stage DC remote power supply device.

[0097] When the multi-stage series-connected DC remote power supply device is operating normally, the main unit operates in rectification mode and the slave unit operates in inverter mode.

[0098] Regarding the control strategy for the host, this embodiment of the application mainly employs a dual-loop control system consisting of a DC voltage outer loop and an AC current inner loop, as detailed below:

[0099] (1) Set the value of the DC voltage reference value, subtract the DC voltage reference value from the DC side voltage of the DC remote power supply device on the transmission line, and then pass through the DC voltage outer loop to obtain the AC current reference value of the AC current inner loop.

[0100] (2) The AC current reference value is subtracted from the collected three-phase input current and then passed through the AC current inner loop to obtain the modulation wave;

[0101] (3) The modulation wave is modulated using an SPWM or SVPWM modulation strategy to obtain a first drive signal that can drive the switching device of the host computer; the operation of the switching device of the host computer is controlled by the first drive signal to control the DC side voltage within the DC voltage reference range. Among them, SPWM is based on sinusoidal drive and changes the modulation pulse mode. The pulse width time duty cycle is arranged according to a sinusoidal law, so that the output waveform can be sinusoidal after appropriate filtering.

[0102] Optionally, in the embodiments of this application, the DC-side voltage is generally controlled near the DC voltage reference value.

[0103] For the main unit of the DC remote power supply device, the controller of its outer DC voltage loop is a PI controller based on the dq coordinate system, used to track the DC voltage reference value. The controller of its inner AC current loop is a PR controller based on either the dq or αβ coordinate system, used to track the AC current reference value.

[0104] The AC voltage control module 203 is used to control the AC voltage of the end user within a preset AC voltage reference range through the slave unit of the DC remote power supply device when the load at the load point changes.

[0105] In this embodiment, an AC voltage reference value and its phase are set according to the low voltage management requirements. In this embodiment, it is set to 220V according to domestic standards.

[0106] Regarding the control strategy for the slave device, this embodiment of the application mainly employs a dual-loop control system consisting of an AC voltage outer loop and an AC current inner loop, as detailed below:

[0107] (1) Subtract the set AC voltage reference value from the collected AC voltage of the end user and pass it through the AC voltage outer loop of the slave device to obtain the AC current reference value of the AC current inner loop.

[0108] (2) The AC current reference value is subtracted from the three-phase input current obtained by sampling, and then passed through the AC current inner loop to obtain the modulation wave;

[0109] (3) The modulation wave is modulated using an SPWM or SVPWM modulation strategy to obtain a second drive signal that can drive the switching device of the slave device; the operation of the switching device of the slave device is controlled by the second drive signal to control the AC voltage within the AC voltage reference range.

[0110] Optionally, in the embodiments of this application, the AC voltage is generally controlled near the AC current reference value.

[0111] The slave unit of the DC remote power supply device uses a PI controller based on the dq coordinate system for its AC voltage outer loop controller to track the AC voltage reference value. Its AC current inner loop controller is also a PI controller based on the dq coordinate system, used to track the AC current reference value. When these controllers are switched to the αβ coordinate system, only the AC voltage outer loop is needed for effective AC voltage control.

[0112] As an improvement to the above solution, since both the host and the slave are composed of several power modules connected in parallel, under the above dual-loop control, due to differences in control parameters, circulating currents are prone to occur between the power modules, which will increase equipment losses and reduce power supply reliability. Therefore, a droop control strategy can also be used to regulate the power modules.

[0113] When a new load point is added to a transmission line, the low voltage management of all end users on the transmission line can be achieved simply by increasing the number of stages of the DC remote power supply device. Specifically, based on the site conditions of the transmission line, a new DC remote power supply device is added between the new load point and the transmission line, so that the new load point is connected to the end of the DC remote power supply device. This DC remote power supply device will be used to regulate the AC voltage of the new load point. If the original architecture was a three-stage series DC remote power supply device, it will now become a four-stage series DC remote power supply device.

[0114] This scheme enables flexibility in selecting DC remote power supply devices, and the converter topology of the DC remote power supply device is not limited to T-type three-level. Other architectures can also be selected in other embodiments. Furthermore, the number of converters in the DC remote power supply device is not limited to a single unit. In other embodiments, multiple converters can be connected in parallel.

[0115] In some embodiments, the device access module 201 is specifically:

[0116] DC remote power supply technology utilizes back-to-back power electronic converters to transmit electrical energy in DC mode, replacing the original AC lines with higher voltage DC lines for power transmission, thus mitigating low voltage by reducing line losses. DC remote power supply devices primarily use AC / DC converters to convert AC to DC, with the electrical energy mainly transmitted via DC transmission lines. At the user side, DC / AC converters are installed to convert the transmitted DC energy back to AC energy for use. Common DC remote power supply devices are either single-stage series or single-stage parallel.

[0117] In single-stage parallel DC remote power supply devices, to increase the voltage for end users, most of the current in the transmission line flows through the DC lines between the converters, with only a portion flowing through the AC lines. If there are dispersed end users located near AC lines, sufficient power cannot be obtained. The single-stage series DC remote power supply device only uses DC transmission and cannot transmit AC power; therefore, it can only supply power to end users near the DC lines. Thus, neither of these two types of DC remote power supply devices can provide sufficient power to end users dispersed along AC lines.

[0118] Considering the dispersed nature of low-voltage distribution network end users in remote mountainous areas, using only single-stage series or single-stage parallel DC remote power supply devices for power transmission can only improve the voltage for a portion of users. To achieve voltage enhancement at multiple load points in remote areas, this application provides a multi-stage series DC remote power supply device connection scheme. Each load point is connected to the nearest DC remote power supply device, and these devices are connected in series on the transmission line, allowing one DC remote power supply device to manage low voltage at one load point. Since low-voltage distribution network end users are often scattered in small communities, each community containing multiple users located relatively close to each other, and different communities being geographically distant, the term "load point" is used as the collective name for end users within a community.

[0119] The application scenario described in this application is that there are two dispersed end users at the end of the power grid. Therefore, a two-stage series DC remote power supply device is used. End user 1 is connected to the end of the first-stage DC remote power supply device to perform low voltage management for end user 1; end user 2 is connected to the end of the second-stage DC remote power supply device to perform low voltage management for end user 2.

[0120] Optionally, 380V AC voltage transmission is used in this embodiment, but in other embodiments, higher-level DC voltage transmission can be used to reduce line losses.

[0121] In addition to setting up the connection between the load point and the DC remote power supply device, the embodiments of this application also set the selection of the DC remote power supply device, including the selection of the device capacity. Specifically, the capacity selection criteria for each level of DC remote power supply device can be different, but the capacity of the DC remote power supply device should be slightly larger than the capacity of the connected load point.

[0122] For any two load points that are close to each other on a transmission line, designated as the first load point and the second load point, the corresponding DC remote power supply devices connected to them are called the first DC remote power supply device and the second DC remote power supply device. The capacity of the first DC remote power supply device should be greater than the sum of the capacities of the first load point and the second load point in order to achieve the optimal voltage stabilization effect.

[0123] As an improvement to the above solution, this application embodiment also provides the selection of DC lines, where the DC lines refer to the lines between the converters of the DC remote power supply devices. Since the first DC remote power supply device needs to provide power to the first load point and the second DC remote power supply device, when the current flowing through the DC line of the first DC remote power supply device is greater than the current flowing through the DC line of the second DC remote power supply device, the voltage of the first DC remote power supply device can be appropriately increased to reduce line losses. For example, in this application embodiment, the DC voltage of the first-stage DC remote power supply device is ±400V, and the DC voltage of the second-stage DC remote power supply device is ±375V.

[0124] Implementing the embodiments of this application has the following beneficial effects:

[0125] This application embodiment achieves low-voltage management for distributed load points by connecting multiple DC remote power supply devices in series on the transmission line, and using one DC remote power supply device to control the voltage of a single end load point within a specified range. The DC remote power supply device consists of two parts: a master unit controls the DC side voltage, and a slave unit controls the AC side voltage. When the load at the load point changes, the slave unit adjusts the voltage of the AC user, ensuring that the voltage at the load point remains within the specified AC voltage reference range, thus guaranteeing the power quality for users at the end of the low-voltage distribution network. Because one DC remote power supply device manages low voltage for one load point, it can be easily added and removed as load points are added or removed, achieving flexibility in low-voltage management.

[0126] Furthermore, Figure 7 This is a structural diagram of a terminal device provided in one embodiment of this application. Figure 7 As shown, the terminal device 3 of this embodiment includes: at least one processor 30 (in... Figure 7 (Only one is shown in the present invention) and a memory 31 and a computer program 32 stored in the memory 31 and executable on the at least one processor, wherein when the processor 30 executes the computer program 32, it can implement the steps of a low voltage management method for a multi-stage series DC remote power supply device according to any one of the embodiments of the present application.

[0127] The terminal device 3 may be a computing device such as a desktop computer, a cloud server, or a laptop computer, and the computing device may include, but is not limited to, a processor 30 and a memory 31. Figure 7 This is merely an example of terminal device 3 and does not constitute a limitation on terminal device 3. It may include more or fewer components than those shown in the figure.

[0128] This application provides a storage medium that stores computer-readable program code. When the computer-readable program code is executed, it implements the steps of the low-voltage management method of a multi-stage series DC remote power supply device described above.

[0129] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. In particular, it should be noted that any modifications, equivalent substitutions, or improvements made by those skilled in the art within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A low-voltage management method based on a multi-stage series DC remote power supply device, characterized in that, include: Several DC remote power supply devices are connected in series on the transmission line at the end of the power grid, and the load points on the transmission line are connected to the nearest DC remote power supply device; wherein, the load points include several end users; The DC-side voltage of the transmission line is controlled within a preset DC voltage reference range by the main control unit of the DC remote power supply device. When the load at the load point changes, the slave unit of the DC remote power supply device controls the AC voltage of the end user within a preset AC voltage reference range.

2. The low-voltage management method based on a multi-stage series DC remote power supply device according to claim 1, characterized in that, The load point and the DC remote power supply device connected to the load point are specifically as follows: For each load point and its connected DC remote power supply device, the capacity of the load point is less than the capacity of the connected DC remote power supply device. For the first load point and the second load point among the load points, the first load point is connected to the first DC remote power supply device, and the second load point is connected to the second DC remote power supply device. Then, the capacity of the first DC remote power supply device is greater than the sum of the capacities of the first load point and the second load point; wherein, the distance of the first load point to the end of the power grid is less than the distance of the second load point to the end of the power grid.

3. The low-voltage management method based on a multi-stage series DC remote power supply device according to claim 2, characterized in that, The voltage regulation between the first DC remote power supply device and the second DC remote power supply device is specifically as follows: The first DC remote power supply device provides power to the first load point and the second DC remote power supply device. When the current flowing through the DC line of the first DC remote power supply device is greater than the current flowing through the DC line of the second DC remote power supply device, the voltage of the first DC remote power supply device is increased.

4. The low-voltage management method based on a multi-stage series DC remote power supply device according to claim 1, characterized in that, The process of controlling the DC-side voltage of the transmission line within a preset DC voltage reference range via the main unit control of the DC remote power supply device specifically involves: When the host operates in rectification mode, the DC side voltage and the preset DC voltage reference value are processed by the DC voltage outer loop of the host to obtain the first AC current reference value of the first AC current inner loop of the host. The first AC current outer loop processes the collected three-phase input current and the first AC current reference value, and modulates the processing result to obtain the first drive signal. The operation of the switching device of the host is controlled according to the first drive signal, and the DC side voltage is controlled within the DC voltage reference range.

5. The low-voltage management method based on a multi-stage series DC remote power supply device according to claim 1, characterized in that, When the load at the load point changes, the slave unit of the DC remote power supply device controls the AC voltage of the end user within a preset AC voltage reference range, specifically as follows: Based on the requirements for low voltage management, set the AC voltage reference value and its phase; The slave device operates in inverter mode, and processes the AC voltage of the end user and the AC voltage reference value through the AC voltage outer loop of the slave device to obtain the second AC current reference value of the second AC current inner loop of the slave device. The second AC current reference value and the collected three-phase input current are processed through the second AC current inner loop, and the processing result is modulated to obtain the second drive signal; The operation of the slave switching device is controlled according to the second drive signal to control the AC voltage within the AC voltage reference range.

6. The low-voltage management method based on a multi-stage series DC remote power supply device according to claim 5, characterized in that, The controllers for the AC voltage outer loop and the second AC current inner loop are both PI controllers based on the dq coordinate system, used to adjust the AC voltage reference range; the control logic for the slave device's AC voltage outer loop and second AC current inner loop is as follows: When the controller switches to another coordinate system, only the AC voltage outer loop is used to control the AC voltage.

7. The low-voltage management method based on a multi-stage series DC remote power supply device according to any one of claims 1 to 6, characterized in that, Also includes: When a new load point appears on the transmission line at the end of the power grid, a new DC remote power supply device is connected between the new load point and the transmission line. When circulating current occurs between power modules, a droop control strategy is used to regulate the power modules; wherein, both the master and the slave are composed of several power modules connected in parallel.

8. A low-voltage management system based on a multi-stage series DC remote power supply device, characterized in that, include: The device includes an access module, a DC voltage control module, and an AC voltage control module. The device access module is used to connect several DC remote power supply devices in series on the transmission line at the end of the power grid, and to connect the load point on the transmission line to the nearest DC remote power supply device; wherein, the load point includes several end users; The DC voltage control module is used to control the DC side voltage of the transmission line within a preset DC voltage reference range through the main control of the DC remote power supply device. The AC voltage control module is used to control the AC voltage of the end user within a preset AC voltage reference range through the slave unit of the DC remote power supply device when the load at the load point changes.

9. A terminal device, characterized in that, It includes a processor and a memory, the memory storing a computer program, and the processor executing the computer program to implement the steps of the low voltage management method based on a multi-stage series DC remote power supply device according to any one of claims 1 to 7.

10. A storage medium, characterized in that, The storage medium stores computer-readable program code, which, when executed, implements the steps of the low-voltage management method based on a multi-stage series DC remote power supply device as described in any one of claims 1 to 7.

Images