Electric energy quality treatment method and system based on direct current remote supply parallel device

Abstract

The invention discloses an electric energy quality treatment method and system based on a direct current remote supply parallel device. The method comprises the following steps: collecting line operation data of a line tail end monitoring point; according to the line operation data, outputting a first current through a direct current remote supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value; and when the tail end voltage is higher than a preset voltage threshold upper limit, charging an energy storage device of the direct current remote supply parallel device until the tail end voltage is lower than the voltage threshold upper limit. According to different working conditions, the direct-current remote supply parallel device is adopted to output current for harmonic suppression, so that the stability of terminal voltage is maintained to improve the electric energy quality, and the operation stability of a power transmission line is realized.

Description

Technical Field

[0001] The present application belongs to the field of power electronics technology, and specifically relates to a method and system for managing power quality based on a DC remote power supply parallel device. Background Art

[0002] Modern society has entered a period of rapid development, and the demand for electric energy is constantly increasing. Proper operation and maintenance of distribution networks and ensuring power supply are the key to the sound development of the economy and society. At the end of the low-voltage distribution network, a DC remote supply parallel solution is often used to solve the low voltage problem of end users due to long lines through power electronic converters. However, due to the large increase in nonlinear loads such as power electronic equipment in recent years, the additional harmonic currents have a negative impact on the current quality in power quality.

[0003] Active power filters are commonly used to generate harmonic currents with opposite phases and the same magnitude to offset the harmonic currents generated by nonlinear loads. However, the current mainstream DC remote supply parallel solution will only start after low voltage is detected, and will be in shutdown or standby mode at other times. The low voltage problem of end users will be periodic after connecting to new energy sources such as photovoltaics. It will only start when the terminal voltage is detected to be too low, and will be idle when the terminal voltage is too high. It cannot give full play to the advantages of the equipment and cannot perform harmonic control under various working conditions. Summary of the invention

[0004] The present application proposes a power quality control method and system based on a DC remote power supply parallel device. According to different working conditions, the output current of the DC remote power supply parallel device is used to control harmonics, maintain the terminal voltage stability to improve the power quality and achieve the stability of transmission line operation.

[0005] The first aspect of the present application provides a method for controlling power quality based on a DC remote power supply parallel device, the method comprising:

[0006] Collecting line operation data of the monitoring point at the end of the line; wherein the line operation data includes the end voltage, the end current and the harmonic current;

[0007] According to the line operation data, output a first current to the transmission line through a DC remote supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value; wherein the first current is determined by the terminal current or the harmonic current;

[0008] When the terminal voltage is higher than a preset voltage threshold upper limit, the energy storage device of the DC remote power supply parallel device is charged until the terminal voltage is lower than the voltage threshold upper limit.

[0009] The above scheme first collects current, voltage and harmonic data at several monitoring points on the user side of the transmission line, and then determines whether the voltage at the user's terminal is currently lower than or higher than the safety threshold based on these data. When the terminal voltage is too low, the DC remote supply parallel device enters the low voltage management mode, and increases the terminal voltage by inputting additional current into the line to keep the terminal voltage within a safe range; when the terminal current is too high due to the influence of harmonics, the DC remote supply parallel device enters the harmonic management mode, and offsets the harmonic current generated by the nonlinear load by inputting a current in the opposite direction of the harmonic into the line, so that the terminal current is within a safe range. When the terminal voltage is too high, a charging operation is performed so that part of the current on the line flows into the energy storage device, reducing the terminal voltage to a safe range. Therefore, according to different working conditions, the DC remote supply parallel device outputs current or shares current, and the terminal voltage can be within a safe range for a long time, which improves the power quality of the user-side terminal and realizes the stability of transmission line operation.

[0010] In a possible implementation method of the first aspect, collecting line operation data of a monitoring point at the end of the line is specifically:

[0011] When it is detected that the DC remote power supply parallel device has not received a shutdown instruction and a fault instruction, the DC remote power supply parallel device is set to an electric energy monitoring mode, and the line operation data is collected;

[0012] When it is detected that the DC remote power supply parallel device receives a shutdown command or a fault command, the DC remote power supply parallel device is set to a shutdown mode.

[0013] In the above scheme, when the DC remote parallel supply device fails or needs to be shut down for repair for some reason, the device will not be used for power monitoring to extend the service life of the equipment. However, when the DC remote parallel supply device is normal, power monitoring can be started.

[0014] In a possible implementation method of the first aspect, according to the line operation data, a first current is output to the transmission line through a DC remote power supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value, specifically:

[0015] When the terminal voltage is lower than the voltage threshold lower limit, the DC remote supply parallel device is set to a low voltage management mode;

[0016] When the terminal voltage is not lower than the voltage threshold lower limit, if the terminal current is higher than the preset current threshold upper limit, the DC remote power supply parallel device is set to the harmonic control mode; otherwise, the DC remote power supply parallel device is set to the standby mode;

[0017] In the low voltage management mode, a first current is output to the transmission line through a DC remote supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit; wherein the value of the first current depends on the current terminal current;

[0018] In the harmonic control mode, a first current is output to the transmission line through a DC remote power supply parallel device until the harmonic current is lower than a preset harmonic rated value; wherein the value of the first current depends on the current harmonic current.

[0019] In the above scheme, when the terminal voltage is too low, the DC remote supply parallel device enters the low voltage control mode, and determines the size of the first current to be input to the line according to the size of the terminal current. The first current can increase the voltage at the user side terminal as a compensation current, so that the low terminal voltage returns to a safe range; when the terminal current is too high, considering that the harmonics generated by the nonlinear load have an impact on the terminal current, the DC remote supply parallel device enters the harmonic control mode, and outputs the first current opposite to the harmonic current to the line to offset the negative impact of the harmonic current and return the terminal current to a safe range.

[0020] In a possible implementation method of the first aspect, in the low voltage management mode, outputting a first current to the transmission line through a DC remote power supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit is specifically as follows:

[0021] determining a value of the first current according to the terminal current; wherein the smaller the terminal current is, the larger the first current is;

[0022] The DC remote power supply parallel device outputs the first current to the transmission line to increase the terminal voltage, and when the terminal voltage is higher than the lower limit of the voltage threshold, the low voltage management mode is exited.

[0023] In a possible implementation method of the first aspect, in the harmonic control mode, outputting a first current through a DC remote power supply parallel device until the harmonic current is lower than a preset harmonic rated value is specifically as follows:

[0024] Setting the first current to a negative value of the harmonic current;

[0025] The first current is output to the transmission line through a DC remote power supply parallel device to offset the harmonic current, and when the harmonic current is lower than the harmonic rated value, the harmonic control mode is exited.

[0026] In a possible implementation method of the first aspect, when the terminal voltage is higher than a preset voltage threshold upper limit, charging the energy storage device of the DC remote power supply parallel device is performed until the terminal voltage is lower than the voltage threshold upper limit, specifically:

[0027] When the terminal voltage is higher than a preset voltage threshold upper limit, the DC remote supply parallel device is set to a high voltage management mode;

[0028] In the high voltage management mode, the energy storage device is charged to reduce the terminal voltage; wherein the energy storage device can provide the first current in the low voltage management mode or the harmonic management mode;

[0029] When the terminal voltage is lower than the upper voltage threshold, the high voltage management mode is exited; wherein, the high voltage management mode can only be entered when the energy storage device exists in the DC remote power supply parallel device.

[0030] In the above scheme, because the access of new energy and the consumption of distributed energy affect the voltage stability of the distribution network, the user-side terminal may also have the problem of excessive voltage. Therefore, the energy storage device is introduced to share part of the current on the transmission line through charging, thereby reducing the terminal voltage to a safe range. After charging, the energy storage device can also output the first current in the low voltage control mode or harmonic control mode, so as to fully utilize the electric energy for circulation control and save energy.

[0031] In a possible implementation method of the first aspect, the method further includes:

[0032] When the transmission line is connected to a new energy source, an energy storage device is introduced into the DC remote supply parallel device;

[0033] When the DC remote power supply parallel device is set to a low voltage management mode and the power of the energy storage device is higher than a preset value, the energy storage device is used to perform a power supply operation to provide the first current;

[0034] When the DC remote power supply parallel device is set to the harmonic control mode and the power of the energy storage device is higher than a preset value, the energy storage device performs a power supply operation to provide the first current.

[0035] When the transmission line is connected to a new energy source and the energy storage device has enough electricity to supply mechanical energy to the transmission line, the above scheme will provide the first current to the transmission line through the energy storage device, which can save electricity resources while achieving the operational stability of the power grid and improving the power quality of end users.

[0036] The second aspect of the present application provides a power quality management system based on a DC remote power supply parallel device, the system comprising: a data acquisition module, a current feedback module and a high voltage management module;

[0037] The data acquisition module is used to collect line operation data of the monitoring point at the end of the line; wherein the line operation data includes the end voltage, the end current and the harmonic current;

[0038] The current feedback module is used to output a first current to the transmission line through a DC remote supply parallel device according to the line operation data until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value; wherein the first current is determined by the terminal current or the harmonic current;

[0039] The high voltage management module is used to charge the energy storage device of the DC remote supply parallel device when the terminal voltage is higher than the preset voltage threshold upper limit, until the terminal voltage is lower than the voltage threshold upper limit.

[0040] The third aspect of the present application provides a terminal device, which includes: a terminal device including a processor and a memory, the memory storing a computer program, and the processor implementing the steps of a power quality management method for a DC remote power supply parallel device described in any one of the embodiments of the present application when executing the computer program.

[0041] In a fourth aspect, the present application provides a storage medium, which stores computer-readable program code. When the computer-readable program code is executed, the steps of a method for power quality management of a DC remote power supply parallel device described in any one of the embodiments of the present application are implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the implementation manner will be briefly introduced below. Obviously, the drawings described below are only some implementation manners of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 It is a specific flow chart of a method for controlling power quality of a DC remote power supply parallel device provided in a certain embodiment of the present application;

[0044] Figure 2 It is a diagram of a DC remote supply series device of a power quality control method of a DC remote supply parallel device provided in a certain embodiment of the present application;

[0045] Figure 3 It is a diagram of a DC remote power supply parallel device according to a method for controlling power quality of a DC remote power supply parallel device provided in a certain embodiment of the present application;

[0046] Figure 4 It is a topological diagram of a DC remote power supply parallel device according to a method for controlling power quality of a DC remote power supply parallel device provided in a certain embodiment of the present application;

[0047] Figure 5This is a power monitoring diagram in a typical scenario of a power quality management method for a DC remote power supply parallel device provided in a certain embodiment of the present application;

[0048] Figure 6 This is a power monitoring diagram in a non-typical scenario of a power quality management method for a DC remote power supply parallel device provided in a certain embodiment of the present application;

[0049] Figure 7 It is a specific structural diagram of a method for controlling power quality of a DC remote power supply parallel device provided in a certain embodiment of the present application;

[0050] Figure 8 A structural diagram of a terminal device provided for a certain embodiment of the present application. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0052] It should be understood that the step numbers used in this article are only for the convenience of description and are not intended to limit the order in which the steps are executed.

[0053] First embodiment

[0054] In order to cope with the harmonic impact caused by the increase in nonlinear loads, active power filters are often used to generate harmonic currents with opposite phases and the same magnitude to offset the harmonic currents generated by the loads. Active power filters are divided into series and parallel types, of which the topology of the series-parallel type is consistent with the topology of the DC remote supply parallel device. Therefore, making full use of the topological advantages of the device, the DC remote supply parallel device often combines the filter to generate current to offset the harmonic current, achieve voltage boost and harmonic control at the end of the station area, and improve the power quality.

[0055] like Figure 1 As shown, Figure 1 A specific flow chart of a method for controlling the power quality of a DC remote power supply parallel device is provided for a certain embodiment of the present application. The method for controlling the power quality of a DC remote power supply parallel device of the present embodiment includes steps S1 to S3, which are described in detail as follows:

[0056] Step S1, collecting line operation data of the monitoring point at the end of the line.

[0057] In the embodiment of the present application, the DC remote supply device uses a power electronic converter to convert the original AC transmission of electric energy into DC transmission and increase the DC voltage level, thereby reducing line losses. Common DC remote supply devices are divided into series type and parallel type, such as Figure 2 and Figure 3 shown. Figure 2 This is a schematic diagram of a DC remote supply series device, in which the rectifier AC / DC and the converter DC / AC are connected in series with the user-side terminal. Figure 3 It is a schematic diagram of a DC remote supply parallel device, in which the rectifier AC / DC and the converter DC / AC are connected in parallel with the user-side end, which can adjust the three-phase voltage and current on the transmission line respectively.

[0058] In addition, Figure 4 In the paper, a schematic diagram of a DC remote power supply parallel device based on a T-type three-level topology is also provided. The T-type three-level topology can provide a higher quality output voltage waveform and higher efficiency, and is currently a commonly used DC remote power supply parallel device topology and active power filter topology.

[0059] Optionally, an embodiment of the present application is to perform power quality management based on a DC remote supply parallel device with a T-type three-level topology.

[0060] When the DC remote parallel supply device is turned on, first monitor whether the device receives a shutdown command or a fault command. If a shutdown command or a fault command is received, it means that the current DC remote parallel supply device needs maintenance due to a fault or urgent maintenance. In order to extend the service life of the equipment, the device will be shut down directly without power monitoring.

[0061] If no shutdown command or fault command is received, the device is set to power monitoring mode. Among them, power quality monitoring mainly includes collecting and analyzing the voltage and current of each phase at the set monitoring point. When the voltage amplitude is lower than the set value, the device outputs current until the voltage at the monitoring point returns to the rated value. When the voltage amplitude is higher than the set value but the current harmonic component is higher than the set value, the device outputs a current with the same magnitude and opposite phase as the current harmonic component, thereby achieving harmonic suppression. When the voltage amplitude is higher than the set value and the current harmonic component is lower than the set value, the end user can achieve normal power consumption and the device is in standby mode. The standby mode will continue to monitor fault signals and shutdown commands, and enter voltage / current modulation again when the conditions are met.

[0062] Specifically, after the DC remote supply parallel device enters the power monitoring mode, it starts to collect the three-phase voltage and current on the user-side terminal transmission line. Figure 5 The power monitoring diagram in a typical scenario is provided. As shown in the figure, several monitoring points are set at the place where the converter is connected in parallel with the three-phase, and the line operation data is collected at these monitoring points. 2Ais the voltage of phase A at the monitoring point, u 2B is the voltage of phase B at the monitoring point, u 2C is the voltage of phase C at the monitoring point; i 2A is the current of the AC transmission line in phase A, i 2B is the current of the AC transmission line in phase B, i 2C is the current of the AC transmission line in phase C; i 2kA is the current output by the converter in phase A, i 2kB is the current output by the converter in phase B, i 2kC is the current output by the converter in phase C; i LA is the load current of the end user in phase A, i LB is the load current of the end user in phase B, i LC is the load current of the end user on phase C.

[0063] In the embodiment of the present application, the typical scenario refers to the situation where the distribution network is not connected to new energy sources such as photovoltaics. At this time, no energy storage device is introduced into the DC remote supply parallel device.

[0064] The line operation data mainly include terminal voltage, terminal current and harmonic current. Figure 5 In the example, the terminal current is i LA 、i LB , and i LC The first current output by the DC remote supply parallel device is i 2kA 、i 2kB and i 2kC ; The terminal voltage is u 2A 、u 2B and u 2C .

[0065] When the voltage or current of these three items of the end user exceeds the safe range, the quality of the power used by the end user will deteriorate. Therefore, it is necessary to use a DC remote supply parallel device to manage the power on the line where the end user is located.

[0066] Step S2: outputting a first current to the transmission line through a DC remote power supply parallel device according to the line operation data, until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value.

[0067] In an embodiment of the present application, after the DC remote supply parallel device enters the power monitoring mode, it determines whether the voltage or current of the current end user is too low or too high based on the collected line operation data, and enters the corresponding mode to modulate the load current or voltage on the transmission line.

[0068] First, the terminal voltage is determined. When the terminal voltage is lower than the preset voltage threshold, it means that the terminal voltage is too low and the power provided to the terminal user is insufficient. At this time, the DC remote power supply parallel device is set to a low voltage management mode.

[0069] In the low voltage management mode, the DC remote supply parallel device is equivalent to the current source output, the rectifier in the device is controlled by the voltage loop, and the converter is controlled by the current loop. When the terminal voltage is lower than the lower limit of the voltage threshold, the reference value of the current loop gradually increases, and the converter will output the first current according to the reference value, and the load current of the end user, that is, the end current increases, thereby increasing the terminal voltage; when the terminal voltage is higher than the lower limit of the voltage threshold, the device exits the low voltage management mode. Among them, the change of the reference value is related to the change of the terminal current.

[0070] If the terminal voltage is not lower than the lower limit of the voltage threshold, but the terminal current is higher than the preset upper limit of the current threshold, it means that the harmonic current generated by the nonlinear load affects the current stability of the transmission line. At this time, the harmonic current has exceeded the set harmonic rated value, causing the current of the end user to exceed the safety range. At this time, the DC remote power supply parallel device is set to the harmonic control mode; otherwise, the DC remote power supply parallel device is set to the standby mode.

[0071] In the harmonic control mode, the rectifier of the DC remote supply parallel device adopts voltage loop control, the converter adopts current loop control, and the reference value of the converter is set to the negative value of the harmonic current, that is, the current with opposite phase but same magnitude as the harmonic current. The first current is output according to the reference value to offset the load current harmonics of the end user. When the harmonic current is lower than the harmonic rated value due to the compliance change, the harmonic control mode is exited.

[0072] In standby mode, because the terminal voltage is higher than the lower threshold and the harmonic current is lower than the set harmonic rated value, it means that the end user can use electricity normally. The DC remote supply parallel device is in standby state and will continue to monitor whether the device receives fault signals and shutdown signals.

[0073] The above-mentioned processing procedures for the low voltage control mode and the harmonic control mode are based on typical scenarios. No energy storage device is introduced in the DC remote supply parallel device, so the rectifier is used for power supply. In atypical scenarios, because the distribution network is connected to new energy sources such as photovoltaics, the resulting consumption of distributed energy affects the voltage stability of the distribution network. The distribution network has period-type photovoltaic reverse power transmission. The end users of the low-voltage distribution network will not only have low voltage problems due to the long power supply radius, but may also have period-type overvoltage problems. This scenario will seriously affect the user's power quality under the trend of large-scale access of new energy to the distribution network. Therefore, in the embodiment of the present application, an energy storage device is introduced to solve the problem of excessive terminal voltage, and low voltage control and harmonic control for end users are achieved when the energy storage device is charged to a certain value.

[0074] Optionally, even if it is not due to the access to new energy, when the terminal voltage is too high, it can be considered an atypical scenario.

[0075] like Figure 6 This is an electric energy monitoring diagram for an atypical scenario provided in an embodiment of the present application. Figure 6 There are several monitoring points, among which u 2A is the voltage of phase A at the monitoring point, u 2B is the voltage of phase B at the monitoring point, u 2C is the voltage of phase C at the monitoring point; i 2A is the current of the AC transmission line in phase A, i 2B is the current of the AC transmission line in phase B, i 2C is the current of the AC transmission line in phase C; i 2kA is the current output by the converter in phase A, i 2kB is the current output by the converter in phase B, i 2kC is the current output by the converter in phase C; i LA is the load current of the end user in phase A, i LB is the load current of the end user in phase B, i LC It is the load current of the end user in phase C. A battery is added between the rectifier and the converter as an energy storage device, which is responsible for charging in high voltage management mode, discharging in harmonic management mode or low voltage management mode, and providing the first current.

[0076] In atypical scenarios, when the DC remote power supply parallel device is set to low voltage management mode and the power of the energy storage device is higher than the preset value, the battery is used for power supply; when the power of the energy storage device is lower than the preset value, the rectifier is still used for power supply, and the converter is still controlled by current loop.

[0077] In atypical scenarios, when the DC remote power supply parallel device is set to the harmonic control mode and the power of the energy storage device is higher than the preset value, the battery is used for power supply; when the power of the energy storage device is lower than the preset value, the rectifier is still used for power supply, and the converter is still controlled by the current loop.

[0078] Therefore, the difference between the low-voltage management mode and the harmonic management mode in typical scenarios and atypical scenarios is that when certain conditions are met in atypical scenarios, the energy storage device can be used to power the device and provide the first current, thereby making full use of electrical energy for circulation management and saving electricity resources.

[0079] Step S3, when the terminal voltage is higher than a preset voltage threshold upper limit, charging the energy storage device of the DC remote power supply parallel device until the terminal voltage is lower than the voltage threshold upper limit.

[0080] In the embodiment of the present application, the terminal voltage may be too high in the distribution network connected to the new energy, so a DC remote supply parallel device containing an energy storage device is used to control the high voltage.

[0081] When the terminal voltage is higher than a preset voltage threshold upper limit, the DC remote supply parallel device is set to a high voltage management mode.

[0082] In the high voltage management mode, the converter side of the device performs PWM blocking, and the rectifier side still uses DC voltage control to start charging the energy storage device, so that part of the current on the transmission line flows into the energy storage device through the rectifier, causing the terminal voltage to drop. When the terminal voltage is lower than the upper voltage threshold, the high voltage management mode is exited.

[0083] The electricity stored in the energy storage device can power the converter and provide the first current in a low voltage management mode or a harmonic management mode, thereby making full use of the electric energy for circulation management.

[0084] Implementing the embodiments of the present application has the following beneficial effects:

[0085] The embodiment of the present application first collects current, voltage and harmonic data at several monitoring points on the user side of the transmission line, and then determines whether the voltage at the user terminal is currently lower than or higher than the safety threshold based on these data. When the terminal voltage is too low, the DC remote supply parallel device enters the low voltage management mode, and increases the terminal voltage by inputting additional current into the line, so that the terminal voltage is within a safe range; when the terminal current is too high due to the influence of harmonics, the DC remote supply parallel device enters the harmonic management mode, and offsets the harmonic current generated by the nonlinear load by inputting a current in the opposite direction of the harmonic into the line, so that the terminal current is within a safe range. When the terminal voltage is too high, a charging operation is performed so that part of the current on the line flows into the energy storage device, reducing the terminal voltage to a safe range. Therefore, according to different working conditions, the DC remote supply parallel device outputs current or shares current, and the terminal voltage can be within a safe range for a long time, thereby improving the power quality of the user-side terminal and achieving the stability of transmission line operation.

[0086] Second embodiment

[0087] Furthermore, in order to execute the power quality management system based on the DC remote power supply parallel device corresponding to the above method embodiment to achieve corresponding functions and technical effects, Figure 7 A structural diagram of a power quality management system based on a DC remote power supply parallel device is provided. For ease of description, only the parts related to this embodiment are shown. The power quality management system based on a DC remote power supply parallel device provided in the embodiment of the present application includes:

[0088] The data acquisition module 201 is used to collect line operation data of a monitoring point at the end of the line; wherein the line operation data includes the end voltage, the end current and the harmonic current.

[0089] In the embodiment of the present application, when it is detected that the DC remote supply parallel device has not received a shutdown instruction and a fault instruction, the DC remote supply parallel device is set to a power monitoring mode, and the line operation data is collected;

[0090] When it is detected that the DC remote power supply parallel device receives a shutdown command or a fault command, the DC remote power supply parallel device is set to a shutdown mode.

[0091] The current feedback module 202 is used to output a first current to the transmission line through a DC remote supply parallel device according to the line operation data until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value; wherein the first current is determined by the terminal current or the harmonic current.

[0092] In the embodiment of the present application, when the terminal voltage is lower than the lower limit of the voltage threshold, the DC remote supply parallel device is set to a low voltage management mode;

[0093] When the terminal voltage is not lower than the voltage threshold lower limit, if the terminal current is higher than the preset current threshold upper limit, the DC remote power supply parallel device is set to the harmonic control mode; otherwise, the DC remote power supply parallel device is set to the standby mode;

[0094] In the low voltage management mode, a first current is output to the transmission line through a DC remote supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit; wherein the value of the first current depends on the current terminal current;

[0095] In the harmonic control mode, a first current is output to the transmission line through a DC remote power supply parallel device until the harmonic current is lower than a preset harmonic rated value; wherein the value of the first current depends on the current harmonic current.

[0096] The high voltage management module 203 is used to charge the energy storage device of the DC remote supply parallel device when the terminal voltage is higher than the preset voltage threshold upper limit, until the terminal voltage is lower than the voltage threshold upper limit.

[0097] In the embodiment of the present application, when the terminal voltage is higher than the preset voltage threshold upper limit, the DC remote supply parallel device is set to a high voltage management mode;

[0098] In the high voltage management mode, the energy storage device is charged to reduce the terminal voltage; wherein the energy storage device can provide the first current in the low voltage management mode or the harmonic management mode;

[0099] When the terminal voltage is lower than the upper voltage threshold, the high voltage management mode is exited; wherein, the high voltage management mode can only be entered when the energy storage device exists in the DC remote power supply parallel device.

[0100] In some embodiments, the data acquisition module 201 further includes:

[0101] The embodiment of the present application is to manage power quality based on a DC remote supply parallel device with a T-type three-level topology.

[0102] When the DC remote parallel supply device is turned on, first monitor whether the device receives a shutdown command or a fault command. If a shutdown command or a fault command is received, it means that the current DC remote parallel supply device needs maintenance due to a fault or urgent maintenance. In order to extend the service life of the equipment, the device will be shut down directly without power monitoring.

[0103] If no shutdown command or fault command is received, the device is set to power monitoring mode. Among them, power quality monitoring mainly includes collecting and analyzing the voltage and current of each phase at the set monitoring point. When the voltage amplitude is lower than the set value, the device outputs current until the voltage at the monitoring point returns to the rated value. When the voltage amplitude is higher than the set value but the current harmonic component is higher than the set value, the device outputs a current with the same magnitude and opposite phase as the current harmonic component, thereby achieving harmonic suppression. When the voltage amplitude is higher than the set value and the current harmonic component is lower than the set value, the end user can achieve normal power consumption and the device is in standby mode. The standby mode will continue to monitor fault signals and shutdown commands, and enter voltage / current modulation again when the conditions are met.

[0104] Specifically, after the DC remote power supply parallel device enters the power monitoring mode, it starts to collect the three-phase voltage and current on the user-side terminal transmission line. Among them, several monitoring points are set at the three-phase parallel connection between the converter and the transmission line, and the line operation data is collected at these monitoring points.

[0105] The line operation data mainly includes terminal voltage, terminal current and harmonic current. The terminal current can be the load current of the end user in phases A, B and C; the first current output by the DC remote supply parallel device can be the current output by the converter in phases A, B and C; the terminal voltage is the voltage of phases A, B and C at the monitoring point.

[0106] When the voltage or current of these three items of the end user exceeds the safe range, the quality of the power used by the end user will deteriorate. Therefore, it is necessary to use a DC remote supply parallel device to manage the power on the line where the end user is located.

[0107] In some embodiments, the current feedback module 202 further includes:

[0108] In an embodiment of the present application, after the DC remote supply parallel device enters the power monitoring mode, it determines whether the voltage or current of the current end user is too low or too high based on the collected line operation data, and enters the corresponding mode to modulate the load current or voltage on the transmission line.

[0109] First, the terminal voltage is determined. When the terminal voltage is lower than the preset voltage threshold, it means that the terminal voltage is too low and the power provided to the terminal user is insufficient. At this time, the DC remote power supply parallel device is set to a low voltage management mode.

[0110] In the low voltage management mode, the DC remote supply parallel device is equivalent to the current source output, the rectifier in the device is controlled by the voltage loop, and the converter is controlled by the current loop. When the terminal voltage is lower than the lower limit of the voltage threshold, the reference value of the current loop gradually increases, and the converter will output the first current according to the reference value, and the load current of the end user, that is, the end current increases, thereby increasing the terminal voltage; when the terminal voltage is higher than the lower limit of the voltage threshold, the device exits the low voltage management mode. Among them, the change of the reference value is related to the change of the terminal current.

[0111] If the terminal voltage is not lower than the lower limit of the voltage threshold, but the terminal current is higher than the preset upper limit of the current threshold, it means that the harmonic current generated by the nonlinear load affects the current stability of the transmission line. At this time, the harmonic current has exceeded the set harmonic rated value, causing the current of the end user to exceed the safety range. At this time, the DC remote power supply parallel device is set to the harmonic control mode; otherwise, the DC remote power supply parallel device is set to the standby mode.

[0112] In the harmonic control mode, the rectifier of the DC remote supply parallel device adopts voltage loop control, the converter adopts current loop control, and the reference value of the converter is set to the negative value of the harmonic current, that is, the current with opposite phase but same magnitude as the harmonic current. The first current is output according to the reference value to offset the load current harmonics of the end user. When the harmonic current is lower than the harmonic rated value due to the compliance change, the harmonic control mode is exited.

[0113] In standby mode, because the terminal voltage is higher than the lower threshold and the harmonic current is lower than the set harmonic rated value, it means that the end user can use electricity normally. The DC remote supply parallel device is in standby state and will continue to monitor whether the device receives fault signals and shutdown signals.

[0114] The above-mentioned processing procedures for the low voltage control mode and the harmonic control mode are based on typical scenarios. No energy storage device is introduced in the DC remote supply parallel device, so the rectifier is used for power supply. In atypical scenarios, because the distribution network is connected to new energy sources such as photovoltaics, the resulting consumption of distributed energy affects the voltage stability of the distribution network. The distribution network has period-type photovoltaic reverse power transmission. The end users of the low-voltage distribution network will not only have low voltage problems due to the long power supply radius, but may also have period-type overvoltage problems. This scenario will seriously affect the user's power quality under the trend of large-scale access of new energy to the distribution network. Therefore, in the embodiment of the present application, an energy storage device is introduced to solve the problem of excessive terminal voltage, and low voltage control and harmonic control for end users are achieved when the energy storage device is charged to a certain value.

[0115] In atypical scenarios, when the DC remote power supply parallel device is set to low voltage management mode and the power of the energy storage device is higher than the preset value, the battery is used for power supply; when the power of the energy storage device is lower than the preset value, the rectifier is still used for power supply, and the converter is still controlled by current loop.

[0116] In atypical scenarios, when the DC remote power supply parallel device is set to the harmonic control mode and the power of the energy storage device is higher than the preset value, the battery is used for power supply; when the power of the energy storage device is lower than the preset value, the rectifier is still used for power supply, and the converter is still controlled by the current loop.

[0117] Therefore, the difference between the low-voltage management mode and the harmonic management mode in typical scenarios and atypical scenarios is that when certain conditions are met in atypical scenarios, the energy storage device can be used to power the device and provide the first current, thereby making full use of electrical energy for circulation management and saving electricity resources.

[0118] In some embodiments, the high voltage management module 203 further includes:

[0119] In the embodiment of the present application, the terminal voltage may be too high in the distribution network connected to the new energy, so a DC remote supply parallel device containing an energy storage device is used to control the high voltage.

[0120] When the terminal voltage is higher than a preset voltage threshold upper limit, the DC remote supply parallel device is set to a high voltage management mode.

[0121] In the high voltage management mode, the converter side of the device performs PWM blocking, and the rectifier side still uses DC voltage control to start charging the energy storage device, so that part of the current on the transmission line flows into the energy storage device through the rectifier, causing the terminal voltage to drop. When the terminal voltage is lower than the upper voltage threshold, the high voltage management mode is exited.

[0122] The electricity stored in the energy storage device can power the converter and provide the first current in a low voltage management mode or a harmonic management mode, thereby making full use of the electric energy for circulation management.

[0123] Implementing the embodiments of the present application has the following beneficial effects:

[0124] The embodiment of the present application first collects current, voltage and harmonic data at several monitoring points on the user side of the transmission line, and then determines whether the voltage at the user terminal is currently lower than or higher than the safety threshold based on these data. When the terminal voltage is too low, the DC remote supply parallel device enters the low voltage management mode, and increases the terminal voltage by inputting additional current into the line, so that the terminal voltage is within a safe range; when the terminal current is too high due to the influence of harmonics, the DC remote supply parallel device enters the harmonic management mode, and offsets the harmonic current generated by the nonlinear load by inputting a current in the opposite direction of the harmonic into the line, so that the terminal current is within a safe range. When the terminal voltage is too high, a charging operation is performed so that part of the current on the line flows into the energy storage device, reducing the terminal voltage to a safe range. Therefore, according to different working conditions, the DC remote supply parallel device outputs current or shares current, and the terminal voltage can be within a safe range for a long time, thereby improving the power quality of the user-side terminal and achieving the stability of transmission line operation.

[0125] Furthermore, Figure 8 This is a structural diagram of a terminal device provided in one embodiment of the present application. Figure 8 As shown, the terminal device 3 of this embodiment includes: at least one processor 30 (in Figure 8 Only one is shown) and a memory 31 and a computer program 32 stored in the memory 31 and executable on the at least one processor. When the processor 30 executes the computer program 32, the steps of a power quality management method based on a DC remote power supply parallel device described in any one of the embodiments of the present application can be implemented.

[0126] The terminal device 3 may be a computing device such as a desktop computer, a cloud server, or a laptop computer. The computing device may include but is not limited to a processor 30 and a memory 31 . Figure 8 This is merely an example of the terminal device 3 and does not constitute a limitation on the terminal device 3 , which may include more or fewer components than those shown in the figure.

[0127] An embodiment of the present application provides a storage medium, which stores computer-readable program codes. When the computer-readable program codes are executed, the steps of the above-mentioned power quality management method based on a DC remote power supply parallel device are implemented.

[0128] The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the scope of protection of the present application. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of protection of the present application.

Claims

1. A method for controlling power quality based on a DC remote power supply parallel device, characterized in that: include: Collecting line operation data of the monitoring point at the end of the line; wherein the line operation data includes the end voltage, the end current and the harmonic current; According to the line operation data, output a first current to the transmission line through a DC remote supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value; wherein the first current is determined by the terminal current or the harmonic current; When the terminal voltage is higher than a preset voltage threshold upper limit, the energy storage device of the DC remote power supply parallel device is charged until the terminal voltage is lower than the voltage threshold upper limit.

2. The power quality control method based on the DC remote supply parallel device according to claim 1 is characterized in that: The line operation data of the monitoring point at the end of the line is collected as follows: When it is detected that the DC remote power supply parallel device has not received a shutdown instruction and a fault instruction, the DC remote power supply parallel device is set to an electric energy monitoring mode, and the line operation data is collected; When it is detected that the DC remote power supply parallel device receives a shutdown command or a fault command, the DC remote power supply parallel device is set to a shutdown mode.

3. The power quality control method based on the DC remote supply parallel device according to claim 1 is characterized in that: The outputting of the first current to the transmission line through the DC remote supply parallel device according to the line operation data until the terminal voltage is higher than the preset voltage threshold lower limit or the harmonic current is lower than the preset harmonic rated value is specifically as follows: When the terminal voltage is lower than the lower limit of the voltage threshold, the DC remote supply parallel device is set to a low voltage management mode; When the terminal voltage is not lower than the voltage threshold lower limit, if the terminal current is higher than the preset current threshold upper limit, the DC remote power supply parallel device is set to the harmonic control mode; otherwise, the DC remote power supply parallel device is set to the standby mode; In the low voltage management mode, a first current is output to the transmission line through a DC remote supply parallel device until the terminal voltage is higher than a preset voltage threshold lower limit; wherein the value of the first current depends on the current terminal current; In the harmonic control mode, a first current is output to the transmission line through a DC remote power supply parallel device until the harmonic current is lower than a preset harmonic rated value; wherein the value of the first current depends on the current harmonic current.

4. The power quality control method based on the DC remote supply parallel device according to claim 3 is characterized in that: In the low voltage management mode, the first current is output to the transmission line through the DC remote supply parallel device until the terminal voltage is higher than the preset voltage threshold lower limit, specifically: Determining a value of the first current according to the terminal current; wherein the smaller the terminal current is, the larger the first current is; The DC remote power supply parallel device outputs the first current to the transmission line to increase the terminal voltage, and when the terminal voltage is higher than the lower limit of the voltage threshold, the low voltage management mode is exited.

5. The power quality control method based on the DC remote supply parallel device according to claim 3 is characterized in that: In the harmonic control mode, the first current is output through the DC remote supply parallel device until the harmonic current is lower than the preset harmonic rated value, specifically: Setting the first current to a negative value of the harmonic current; The first current is output to the transmission line through a DC remote power supply parallel device to offset the harmonic current, and when the harmonic current is lower than the harmonic rated value, the harmonic control mode is exited.

6. The power quality control method based on the DC remote supply parallel device according to claim 1 is characterized in that: When the terminal voltage is higher than the preset voltage threshold upper limit, the energy storage device of the DC remote supply parallel device is charged until the terminal voltage is lower than the voltage threshold upper limit, specifically: When the terminal voltage is higher than a preset voltage threshold upper limit, the DC remote supply parallel device is set to a high voltage management mode; In the high voltage management mode, the energy storage device is charged to reduce the terminal voltage; wherein the energy storage device can provide the first current in the low voltage management mode or the harmonic management mode; When the terminal voltage is lower than the upper voltage threshold, the high voltage management mode is exited; wherein, the high voltage management mode can only be entered when the energy storage device exists in the DC remote power supply parallel device.

7. The power quality control method based on the DC remote power supply parallel device according to any one of claims 1 to 6, characterized in that: Also includes: When the transmission line is connected to a new energy source, an energy storage device is introduced into the DC remote supply parallel device; When the DC remote power supply parallel device is set to a low voltage management mode and the power of the energy storage device is higher than a preset value, the energy storage device is used to perform a power supply operation to provide the first current; When the DC remote power supply parallel device is set to the harmonic control mode and the power of the energy storage device is higher than a preset value, the energy storage device performs a power supply operation to provide the first current.

8. A power quality management system based on a DC remote supply parallel device, characterized in that: include: Data acquisition module, current feedback module and high voltage management module; The data acquisition module is used to collect line operation data of the monitoring point at the end of the line; wherein the line operation data includes the end voltage, the end current and the harmonic current; The current feedback module is used to output a first current to the transmission line through a DC remote supply parallel device according to the line operation data until the terminal voltage is higher than a preset voltage threshold lower limit or the harmonic current is lower than a preset harmonic rated value; wherein the first current is determined by the terminal current or the harmonic current; The high voltage management module is used to charge the energy storage device of the DC remote supply parallel device when the terminal voltage is higher than the preset voltage threshold upper limit, until the terminal voltage is lower than the voltage threshold upper limit.

9. A terminal device, characterized in that: It comprises a processor and a memory, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of a power quality control method based on a DC remote power supply parallel device as described in any one of claims 1 to 7 are implemented.

10. A storage medium, characterized in that: The storage medium stores computer-readable program codes, which, when executed, implement the steps of a method for power quality management based on a DC remote power supply parallel device as described in any one of claims 1 to 7.

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