Reactive automatic compensation device applied to medium-voltage distribution line

Abstract

The invention provides a reactive automatic compensation device applied to a medium-voltage distribution line. The reactive automatic compensation device comprises a line compensation control unit and a line compensation unit, the uplink of the line compensation control unit is connected with the medium-voltage distribution line, and the downlink is connected with the line compensation unit; the line compensation control unit is used for acquiring the compensation capacitor capacity of the line compensation unit and calculating the reactive power of the line, and when the reactive power is greater than the compensation capacitor capacity, the capacitor of the line compensation unit is put into use by sending a closing command to the switch driving terminal in the line compensation unit with the least switch action times; when the reactive power of the line is less than zero, an opening command is sent to the switch driving terminal of the line compensation unit with the most switch action times, and the capacitor of the line compensation unit is cut off; and calculating the opening and closing time of each phase of switch at the current temperature through parabola interpolation. According to the invention, the reactive compensation capacity of the medium-voltage distribution line can be freely expanded without limitation, and the compensation effect is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of reactive power compensation, and in particular relates to an automatic reactive power compensation device applied to a medium voltage distribution line. Background Art

[0002] Reactive power compensation devices can play the following roles in the power grid: reduce reactive power flow, reduce power grid losses, improve system power factor, reduce equipment configuration capacity, and stabilize the voltage at the receiving end and the power grid side. Therefore, reactive power compensation devices have become essential equipment in the power grid. According to the principle of reactive power hierarchical and regional balance, the deployment principles of reactive power compensation devices in regional power grids are generally divided into three levels: high-voltage reactive power compensation devices in substations, reactive power compensation devices in medium-voltage distribution lines, and reactive power compensation devices in distribution low-voltage areas.

[0003] Medium-voltage distribution lines generally refer to 6-10kV distribution lines from substations. The poles of such lines are generally single-pole erected at heights of 12 meters, 15 meters, and 18 meters. In real scenarios, some low-voltage areas have insufficient reactive capacity for various reasons, and some substations that were built a long time ago do not reserve space for reactive compensation devices. In these cases, the capacity of the line compensation device needs to be increased. The current mainstream line compensation device is equipped with two sets of capacitors, plus switches, cabinets, etc. If the compensation capacity reaches 600kvar, the weight of the device will reach more than 300 kilograms. In order to ensure a safe distance from the ground, the line compensation device is generally more than 4 meters above the ground. Due to the limitations of pole load-bearing and wind load, the capacity of a single line compensation device is bound to be difficult to increase, and the compensation effect is poor, resulting in some line losses seriously exceeding the standard, and the corresponding grid voltage is unqualified, affecting economic and social development. In addition, the current capacitor-specific high-voltage switching switch, its opening and closing action time is greatly affected by the coil drive voltage and ambient temperature. However, the current dedicated zero-crossing switching switches generally assume that the opening and closing action time is constant, and these two factors are rarely considered. Traditionally, if the zero-crossing switching of the reactive power compensation device is to be realized, it is necessary to introduce the three-phase system voltage and the three-phase capacitor current to find the zero-crossing point of these signals. Since the high voltage and high current must be converted into signals that can be processed by electronic circuits, it is necessary to install three-phase high-voltage voltage transformers and three-phase high-voltage current transformers, and introduce the secondary side signals of the high-voltage transformers into the intelligent processing module for processing. The intelligent processing module also needs to be equipped with small voltage transformers, current transformers and subsequent processing circuits, and the system design is very complicated. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a reactive power automatic compensation device applied to a medium voltage distribution line, which realizes that the reactive power compensation capacity can be arbitrarily expanded without restriction, thereby greatly improving the compensation effect.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A reactive power automatic compensation device applied to a medium voltage distribution line comprises a line compensation control unit and a line compensation unit;

[0007] The uplink of the line compensation control unit is connected to the medium voltage distribution line, and the downlink of the line compensation control unit is connected to the line compensation unit;

[0008] The line compensation control unit is used to obtain the compensation capacitor capacity of the line compensation unit and calculate the line reactive power. When the line reactive power is greater than the compensation capacitor capacity, a closing command is sent to the switch drive terminal in the line compensation unit with the least number of switch actions, and the capacitor of this line compensation unit is put into use; when the line reactive power is less than zero, an opening command is sent to the switch drive terminal of the line compensation unit with the most number of switch actions, and the capacitor of this line compensation unit is cut off; and the opening and closing time of each phase switch at the current temperature is calculated by parabolic interpolation.

[0009] Furthermore, in the automatic reactive power compensation device, when the line reactive power is greater than zero and less than the capacity of the compensation capacitor, the status quo is maintained and no compensation is required.

[0010] Furthermore, the line compensation unit is one or more;

[0011] When there is one line compensation unit, the line compensation control unit is directly connected to the line compensation unit;

[0012] When there are multiple line compensation units, the line compensation control unit is connected to the nearest line compensation unit; and the line compensation units are cascaded.

[0013] Further, the line compensation control unit includes: a CPU module, a signal conditioning circuit, a first power supply module, a first communication module, a first voltage transformer, a first current transformer, a second voltage transformer and a second current transformer;

[0014] The primary side of the first voltage transformer and the primary side of the first current transformer are both connected to the medium voltage distribution line; the secondary side of the first voltage transformer is connected to the primary side of the second voltage transformer and the first power module; the secondary side of the first current transformer is connected to the primary side of the second current transformer; the secondary side of the second voltage transformer and the secondary side of the second current transformer are both connected to the signal conditioning circuit; the first power module is also respectively connected to the CPU module, the signal conditioning circuit and the first communication module;

[0015] The signal conditioning circuit converts the current signal sent by the second current transformer and the voltage signal sent by the second voltage transformer into signals that can be processed by the CPU module; the CPU module is used to calculate the system reactive power based on the processable signals.

[0016] Furthermore, the process of calculating the line reactive power includes:

[0017]

[0018] Among them, Q s is the line reactive power; U AB is the line voltage of phase A and phase B of the medium voltage distribution line; I C is the C phase current of the medium voltage distribution line; ψ is U AB with I C The angle between.

[0019] Further, the line compensation unit includes a third voltage transformer, an energy storage module, a voltage stabilizing module, a switching switch, a switch drive terminal and a power capacitor;

[0020] The primary side and the switching switch of the third voltage transformer are respectively connected to the medium voltage distribution line; the secondary side of the third voltage transformer is connected to the energy storage module and the switch drive terminal; the voltage stabilizing module is connected to the energy storage module, the switching switch and the switch drive terminal; the switching switch is also connected to the switch drive terminal and the power capacitor;

[0021] The energy storage module is used to convert the AC power supply on the secondary side of the third voltage transformer into a DC unregulated power supply; the voltage stabilization module is used to convert the DC unregulated power supply into a DC high-precision regulated power supply;

[0022] The energy storage module and the voltage stabilizing module are used together to store the energy transmitted by the third voltage transformer and provide a DC driving voltage when the switch is opened or closed.

[0023] Furthermore, the process of calculating the opening time of each phase switch at the current temperature by parabolic interpolation includes:

[0024]

[0025] Among them, t fd is the opening action time of the phase switch under the current ambient temperature T;

[0026] t f1 is the opening action time of the phase switch at temperature T1; t f2 is the opening action time of the phase switch at temperature T2; t f3 It is the opening action time of the phase switch at temperature T3.

[0027] Furthermore, the process of calculating the closing time of each phase switch at the current temperature by parabolic interpolation includes:

[0028]

[0029] Among them, t hd is the closing action time of the phase switch under the current ambient temperature T; t h1 is the closing action time of the phase switch at temperature T1; t h2 is the closing action time of the phase switch at temperature T2; t h3 It is the closing action time of the phase switch at temperature T3.

[0030] Furthermore, when the line compensation unit receives the capacitor injection command sent by the line compensation control unit, the action sequence of the three-phase switch is:

[0031] The A-phase closing drive module immediately drives the A-phase switch closing coil to close; after the switch drive terminal detects that the A-phase switch is closed successfully at time t1, it predicts U ab The next zero-crossing time t2, according to the closing action time t of the B-phase switch at the current temperature hd·b , the best time to drive the B phase closing coil is: t qhb =t1+(t2-t1-t hd·b ), ensure that when the B phase switch is closed, U ab It is at the moment of crossing zero;

[0032] After the switch driver detects that the B phase switch is closed successfully, the U ab and C phase voltage U c relationship, predicting U c The next zero-crossing time t3, according to the closing action time t of the C-phase switch at the current temperature hd·c , the best time to drive the C phase closing coil is: t qhc =t2+(t3-t2-t hd·c ), ensure that when the C phase switch is closed, U c It is at the moment of zero o'clock.

[0033] Further, when the switch driving terminal receives the capacitor cutting command from the line compensation control unit at time t4, the switch driving terminal firstly switches to the capacitor cutting state through U ab Predict the phase C capacitor current I C·C The next zero-crossing time t5, according to the current temperature, the C-phase switch opening action time t fd·c , determine the time to drive the C phase opening coil: t qfc =t4+(t5-t4-t fd·c ), ensuring that the C-phase switch is disconnected when the C-phase capacitor current passes through zero;

[0034] After the switch driver detects that the C phase switch is successfully opened, it will pass U ab Predict the capacitive current I between phases A and B C·ab The zero-crossing time t6, according to the current temperature B phase switch opening action time t fd·b , the best time to drive the B phase opening coil is: t qfb =t5+(t6-t5-t fd·b ), ensure that the B phase switch is at I C·ab It is disconnected when crossing the zero point; after the switch driving terminal detects that the B-phase switch is successfully opened, it drives the A-phase switch opening coil to open the A-phase switch without judging the zero point.

[0035] The effects provided in the content of the invention are only the effects of the embodiments, not all the effects of the invention. One of the above technical solutions has the following advantages or beneficial effects:

[0036] The present invention proposes a reactive power automatic compensation device applied to a medium-voltage distribution line, comprising a line compensation control unit and a line compensation unit; the uplink of the line compensation control unit is connected to the medium-voltage distribution line, and the downlink of the line compensation control unit is connected to the line compensation unit; the line compensation control unit is used to obtain the compensation capacitance of the line compensation unit, and calculate the reactive power of the line. When the reactive power of the line is greater than the compensation capacitance, a closing command is sent to the switch drive terminal in the line compensation unit with the least number of switch actions, and the capacitor of this line compensation unit is put into operation; when the reactive power of the line is less than zero, an opening command is sent to the switch drive terminal of the line compensation unit with the most number of switch actions, and the capacitor of this line compensation unit is cut off; and the opening and closing time of each phase switch at the current temperature is calculated by parabolic interpolation. The present invention realizes that the reactive power compensation capacity of the medium-voltage distribution line can be arbitrarily expanded without restriction, greatly improves the compensation effect, expands the product application occasions, and makes up for the shortcomings of existing products. The current transformer and the line compensation control unit can be shared in the reactive power automatic compensation device, reducing repeated arrangement and reducing the weight of the line compensation device.

[0037] The present invention takes into account the influence of ambient temperature and the driving voltage of the opening and closing coil on the switching action time, and can reduce the error of the predicted switch action time to an extremely small range, greatly improving the prediction accuracy of the switch opening and closing time, and also improving the accuracy of zero-crossing opening and closing.

[0038] The present invention utilizes the corresponding relationship between the line voltage and the voltages of each phase, and between the line voltage and the phase of the capacitor current of each phase. Only one line voltage needs to be connected to determine the zero-crossing point of the voltage or current required for switching the capacitors of each phase, thereby reducing the wiring complexity, saving costs, and simplifying the product design of the line compensation device. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a connection diagram of a reactive power automatic compensation device applied to a medium voltage distribution line proposed in Embodiment 1 of the present invention;

[0040] Figure 2 This is a schematic diagram of a line compensation control unit proposed in Embodiment 1 of the present invention;

[0041] Figure 3 This is a schematic diagram of a line compensation unit proposed in Embodiment 1 of the present invention;

[0042] Figure 4 This is a schematic diagram of the energy storage module proposed in Example 1 of the present invention;

[0043] Figure 5 This is a schematic diagram of a voltage stabilizing module according to Embodiment 1 of the present invention;

[0044] Figure 6 This is an overall structural diagram of the switch driving terminal proposed in Embodiment 1 of the present invention;

[0045] Figure 7 This is a three-phase switch closing waveform diagram proposed in Embodiment 1 of the present invention;

[0046] Figure 8 This is a three-phase switch opening waveform diagram proposed in Example 1 of the present invention. DETAILED DESCRIPTION

[0047] In order to clearly illustrate the technical features of the present solution, the present invention is described in detail below through specific implementation methods and in conjunction with the accompanying drawings. The disclosure below provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. In addition, the present invention may repeat reference numbers and / or letters in different examples. This repetition is for the purpose of simplification and clarity, and does not itself indicate the relationship between the various embodiments and / or settings discussed. It should be noted that the components illustrated in the accompanying drawings are not necessarily drawn to scale. The present invention omits the description of known components and processing techniques and processes to avoid unnecessary limitations on the present invention.

[0048] Example 1

[0049] Embodiment 1 of the present invention proposes a reactive power automatic compensation device for medium-voltage distribution lines, which is used to solve the problem that the capacity of the reactive power automatic compensation device in the current medium-voltage distribution lines cannot be expanded due to objective factors, as well as the problem that the action time of the zero-crossing switching scheme of the switch is inaccurate and too much information needs to be accessed and processed.

[0050] Figure 1This is a connection diagram of a reactive power automatic compensation device applied to a medium voltage distribution line proposed in Embodiment 1 of the present invention; the device includes a line compensation control unit and a line compensation unit;

[0051] The uplink of the line compensation control unit is connected to the medium voltage distribution line, and the downlink of the line compensation control unit is connected to the line compensation unit;

[0052] The line compensation control unit is used to obtain the compensation capacitor capacity of the line compensation unit and calculate the line reactive power. When the line reactive power is greater than the compensation capacitor capacity, a closing command is sent to the switch drive terminal in the line compensation unit with the least number of switch actions, and the capacitor of this line compensation unit is put into operation; when the line reactive power is less than zero, an opening command is sent to the switch drive terminal of the line compensation unit with the largest number of switch actions, and the capacitor of this line compensation unit is cut off; and the opening and closing time of each phase switch at the current temperature is calculated by parabolic interpolation.

[0053] Figure 2 A schematic diagram of a line compensation control unit proposed in Example 1 of the present invention; the line compensation control unit includes: a CPU module, a signal conditioning circuit, a first power module, a first communication module, a first voltage transformer, a first current transformer, a second voltage transformer and a second current transformer; the primary side of the first voltage transformer and the primary side of the first current transformer are both connected to a medium voltage distribution line; the secondary side of the first voltage transformer is connected to the primary side of the second voltage transformer and the first power module; the secondary side of the first current transformer is connected to the primary side of the second current transformer; the secondary side of the second voltage transformer and the secondary side of the second current transformer are both connected to the signal conditioning circuit; the first power module is also connected to the CPU module, the signal conditioning circuit and the first communication module, respectively; the signal conditioning circuit converts the current signal sent by the second current transformer and the voltage signal sent by the second voltage transformer into signals that can be processed by the CPU module; the CPU module is used to calculate the system reactive power based on the processable signals.

[0054] Figure 3Schematic diagram of the line compensation unit proposed in Example 1 of the present invention; the line compensation unit includes a third voltage transformer, an energy storage module, a voltage stabilizing module, a switching switch, a switch drive terminal and a power capacitor; the primary side of the third voltage transformer and the switching switch are respectively connected to the medium voltage distribution line; the secondary side of the third voltage transformer is connected to the energy storage module and the switch drive terminal; the voltage stabilizing module is connected to the energy storage module, the switching switch and the switch drive terminal; the switching switch is also connected to the switch drive terminal and the power capacitor; the energy storage module is used to convert the AC power supply on the secondary side of the third voltage transformer into a DC unregulated power supply; the voltage stabilizing module is used to convert the DC unregulated power supply into a DC high-precision regulated power supply; the energy storage module and the voltage stabilizing module are jointly used to store the energy transmitted by the third voltage transformer and provide a DC drive voltage when the switch is opened and closed.

[0055] The third voltage transformer in the line compensation unit is a high-voltage voltage transformer, and its secondary side is connected to the energy storage module and the switch drive terminal. Since the energy required in the switch opening and closing process is relatively large, and the secondary power of the high-voltage voltage transformer is relatively small, in order to solve this contradiction, an energy storage module must be used. Figure 4 Schematic diagram of the energy storage module proposed in Example 1 of the present invention; It is composed of a protection circuit, a first rectifier circuit and an energy storage circuit, the protection circuit is connected to the rectifier circuit, and the first rectifier circuit is connected to the energy storage circuit. The protection circuit is used to suppress transient overvoltage and high-frequency interference, the first rectifier circuit is composed of a single-phase full-bridge rectifier circuit, and the energy storage circuit is composed of a single large-capacity electrolytic capacitor (such as an electrolytic capacitor of 10000uF / 450V). Due to the release of energy in the electrolytic capacitor during the opening and closing process, the terminal voltage of the capacitor will continue to decrease, and the opening and closing time of the switch is highly related to the driving voltage, and the system voltage of the medium-voltage distribution line changes at any time, so the driving voltage of the switch cannot remain stable and cannot be predicted, resulting in the unpredictable opening and closing time of the switch each time.

[0056] Taking a 10kV medium-voltage distribution line as an example, the transformation ratio of the first voltage transformer of the line compensation control unit and the third voltage transformer in the line compensation unit are both 10kV / 220V, the primary side of the first current transformer is selected according to the on-site current conditions (generally 100A to 1000A), and the secondary side is generally 5A. Since the voltage of the medium-voltage distribution line is generally between 8 and 11kV, the secondary side of the first voltage transformer generally fluctuates between 176V and 242V.

[0057] The voltage stabilizing module in the line compensation unit is composed of an inverter circuit, a second rectifier circuit and a filter circuit; Figure 5This is a schematic diagram of the voltage stabilizing module proposed in Example 1 of the present invention; the inverter circuit is connected to the second rectifier circuit, and the second rectifier circuit is connected to the filter circuit; the inverter circuit is used to convert the DC non-regulated power supply into a high-frequency square wave power supply, the second rectifier circuit re-regulates the high-frequency square wave power supply into DC, and the filter circuit is used to eliminate high-order harmonics and improve the quality of DC power. The non-regulated DC power of the energy storage module is converted into high-precision regulated DC power (voltage is stabilized at DC220V±1V) through the voltage stabilizing module, because the influence of the unstable driving voltage on the switch action time will be significantly reduced, and the switch opening and closing action time is more predictable. The energy storage module and the voltage stabilizing module are used together to store the energy transmitted by the high-voltage transformer and provide a high-precision, instantaneous large-current DC drive voltage when the switch is opened and closed.

[0058] The switch drive terminal in the line compensation unit includes a fourth voltage transformer, an input module, a signal shaping circuit, a second power module, a processor, a second communication module, a drive module and an ambient temperature sensor module. The input end of the second power module and the primary side of the fourth voltage transformer are both connected to the secondary side of the third voltage transformer, the output end of the second power module is connected to the signal shaping circuit, the ambient temperature sensor module, the processor and the second communication module, the secondary side of the fourth voltage transformer is connected to the signal shaping circuit, the processor is connected to the signal shaping circuit, the input module, the second communication module, the ambient temperature sensor module and the drive module; each phase is configured with a switch-on and switch-off drive module, a total of six. Figure 6 This is an overall structural diagram of the switch driving terminal proposed in Example 1 of the present invention.

[0059] The first communication module of the line compensation control unit includes an HRF master module and a Bluetooth Mesh master module, and the second communication module in the switch driving terminal of the line compensation unit includes an HRF slave module and a Bluetooth Mesh slave module. Whether it is HRF communication or Bluetooth Mesh communication, communication can be established between the master module and the slave module of the same communication mode, and the slave modules of the same communication mode can also be cascaded. In this way, the line compensation control unit can establish a connection relationship with any line compensation unit through HRF or Bluetooth Mesh respectively, and when one of the communication modes cannot achieve communication capabilities, it will immediately switch to the other.

[0060] The first voltage transformer in the line compensation control unit and the third voltage transformer in the line compensation unit are both connected to the line voltage U of the A phase and the B phase of the medium voltage distribution line. AB , the first current transformer senses the C phase current I of the medium voltage distribution line c ; The line compensation control unit obtains the compensation capacity Q of the line compensation unit through wireless communication C and the number of actions, by collecting the line voltage U AB and current data I c , calculate the line reactive power Q according to the formulaS :

[0061]

[0062] Where ψ is U AB and I c The angle between S >Q C , then it is necessary to put the capacitor in again. At this time, the line compensation control unit sends a closing command to the switch drive terminal in the line compensation unit with the least number of switch actions, and the capacitor in the line compensation unit is put in; if 0 S C , then maintain the status quo; if Q S <0, at least one group of capacitors needs to be removed. At this time, the line compensation control unit sends a trip command to the switch drive module of the line compensation unit with the largest number of switch actions, and the capacitors in the line compensation unit are removed. If the number of actions is the same, a trip command is sent to the line compensation unit with the longest closing time.

[0063] In order to realize the input of capacitors at the voltage zero point and the removal of capacitors at the capacitor current zero point, it is necessary to first determine the action time of the switch when opening and closing. By setting the voltage stabilization module, the influence of the driving voltage fluctuation on the switch action time can be eliminated. Another influencing factor is temperature. Since the line compensation device works outdoors, the operating temperature is in the wide span range of -40℃~+45℃. The action time of the switch at the two extreme temperatures of -40℃ and +45℃ is very different. Before the device leaves the factory, the opening action time and closing action time of the switch can be tested every 5℃ under the condition of stable DC drive voltage (DC220V±1V), and the action time data is stored in the switch drive terminal. The selected temperature points are: -40℃, -35℃, -30℃, -25℃, ┄, +35℃, +40℃, +45℃. The on-site ambient temperature may be different from these selected specific temperature values, and the switch opening and closing time at the current temperature needs to be calculated by parabolic interpolation.

[0064] Assume that the current temperature T is 3°C, and the selected points closest to 3°C include 0°C, 5°C and 10°C.

[0065] Assume that the opening and closing action time of the switch at T1 = 0°C is t f1 ,t h1 , the opening and closing action time at T2 = 5℃ is t f2 ,t h2 , the opening and closing action time at T3 = 10℃ is t f3 ,t h3 .

[0066] ​​The process of calculating the opening time of each phase switch at the current temperature by parabolic interpolation includes:

[0067]

[0068] Among them, t fd is the opening action time of the phase switch at the current ambient temperature T; t f1 is the opening action time of the phase switch at temperature T1; t f2 is the opening action time of the phase switch at temperature T2; t f3 It is the opening action time of the phase switch at temperature T3.

[0069] The process of calculating the closing time of each phase switch at the current temperature by parabolic interpolation includes:

[0070]

[0071] Among them, t hd is the closing action time of the phase switch under the current ambient temperature T; t h1 is the closing action time of the phase switch at temperature T1; t h2 is the closing action time of the phase switch at temperature T2; t h3 It is the closing action time of the phase switch at temperature T3.

[0072] The line compensation control unit calculates the reactive power of the medium-voltage distribution line and determines whether to switch on and off the capacitor. Since the capacitor capacity in each line compensation unit is the same, in order to improve the overall operating life of the reactive automatic compensation device, the balancing method is used to control the switching of the capacitor. If it is necessary to continue to add capacitors to the system, a closing command is sent to the line compensation unit with the least number of switch actions; if it is necessary to remove the capacitor, an opening command is sent to the line compensation unit with the most number of switch actions. If the number of actions is the same, an opening command is sent to the line compensation unit with the longest operating time.

[0073] Figure 7 This is a three-phase switch closing waveform diagram proposed in Embodiment 1 of the present invention; when the line compensation unit receives a command to put the capacitor in from the line compensation control unit, the action sequence of the three-phase switch is:

[0074] The A-phase closing drive module immediately drives the A-phase switch closing coil to close; after the switch drive terminal detects that the A-phase switch is closed successfully at time t1, it predicts U ab The next zero-crossing time t2, according to the closing action time t of the B-phase switch at the current temperature hd·b , the best time to drive the B phase closing coil is: t qhb =t1+(t2-t1-t hd·b), ensure that when the B phase switch is closed, U ab It is at the moment of zero.

[0075] After the switch driver detects that the B phase switch is closed successfully, the U ab and C phase voltage U c relationship, predicting U c The next zero-crossing time t3, according to the closing action time t of the C-phase switch at the current temperature hd·c , the best time to drive the C phase closing coil is: t qhc =t2+(t3-t2-t hd·c ), ensure that when the C phase switch is closed, U c It is at the moment of zero o'clock.

[0076] Assume that the closing action time of the three-phase switches A, B, and C are t hd·a =22ms,t hd·b =23ms,t hd·c =21ms. Figure 7 As shown, the square wave signal is the line voltage U ab After shaping, the grid frequency is 50Hz, with a rising or falling edge every 10ms, corresponding to a zero crossing point. When the switch drive terminal receives the command to cast the capacitor from the line compensation control unit, the A-phase closing drive module drives the A-phase switch closing coil to act first at 2ms. After the A-phase switch is successfully closed at 24ms, since the A-phase closing does not form a loop after the successful closing, there is no capacitive current flowing in the A-phase capacitor. Therefore, the closing time of the A-phase does not need to judge the zero crossing point; after the switch drive terminal receives the return signal of the successful closing of the A-phase, the voltage U ab The zero-crossing moment after the B-phase switch is reached, and according to the closing action time of the B-phase switch, the B-phase closing coil is finally driven at 27ms. Since the closing action time of the B-phase switch is 23ms, the closing time of the B-phase switch is 50ms. At this time, U ab It is at the zero point; after the B phase is closed successfully, according to U ab Predicted C phase voltage U c The subsequent zero crossing point (U c with U ab The voltage angle is 90 degrees, 360 degrees corresponds to 20ms, so U c The zero crossing point lags behind or leads U ab The zero crossing point is 5ms). According to the action time of the C-phase switch at the current temperature, the C-phase closing drive module finally drives the C-phase closing coil at 54ms. The C-phase switch closes successfully at 75ms. At this time, U c It is at the moment of zero.

[0077] Figure 8The three-phase switch opening waveform diagram proposed in Embodiment 1 of the present invention; when the switch driving terminal receives the capacitor cutting command sent by the line compensation control unit at time t4, firstly, U ab Predict the phase C capacitor current I C·C The next zero-crossing time t5, according to the current temperature, the C-phase switch opening action time t fd·c , determine the time to drive the C phase opening coil: t qfc =t4+(t5-t4-t fd·c ) to ensure that the C-phase switch is disconnected when the C-phase capacitor current passes through zero.

[0078] After the switch driver detects that the C phase switch is successfully opened, it will pass U ab Predict the capacitive current I between phases A and B c·ab The zero-crossing time t6, according to the current temperature B phase switch opening action time t fd·b , the best time to drive the B phase opening coil is: t qfb =t5+(t6-t5-t fd·b ), ensure that the B phase switch is at I c·ab It is disconnected when crossing the zero point; after the switch driving terminal detects that the B-phase switch is successfully opened, it drives the A-phase switch opening coil to open the A-phase switch without judging the zero point.

[0079] Assume that the current opening action times of the three-phase switches A, B, and C are t fd·a =14ms,t fd·b =16ms,t fd·c =15ms.

[0080] When the switch drive terminal receives the capacitor cut command from the line compensation control unit, it firstly ab Predict the phase C capacitor current I c·c The subsequent zero crossing point (I c·c with U ab According to the opening action time of the C-phase switch at the current temperature, it is finally determined that the C-phase opening coil is driven at 5ms, and the C-phase capacitor is at 20ms (at this time U ab and I c·c After the switch driver receives the signal that the C phase is successfully opened, it will then ab Determine the capacitance current I between phases A and B c·ab The zero crossing point (I c·ab The zero crossing point of U is ahead or behind ab The zero crossing point is 5ms), and according to the opening action time of the B-phase switch at the current temperature, it is determined that the B-phase opening coil is driven at 29ms, and the B-phase switch is at 45ms (at this time I c·abAfter the B and C phase switches are opened, the A phase switch needs to be disconnected as soon as possible without judging the zero point. It is determined that the A phase opening coil is driven in 48ms and the opening action is completed in 62ms.

[0081] The reactive power automatic compensation device applied to the medium voltage distribution line proposed in the first embodiment of the present invention realizes that the reactive power compensation capacity of the medium voltage distribution line can be arbitrarily expanded without restriction, greatly improves the compensation effect, expands the product application occasions, and makes up for the shortcomings of existing products. The current transformer and the line compensation control unit can be shared in the reactive power automatic compensation device, which reduces repeated arrangement and also reduces the weight of the line compensation device.

[0082] In an automatic reactive power compensation device applied to a medium-voltage distribution line proposed in Example 1 of the present invention, the influence of ambient temperature and the driving voltage of the opening and closing coil on the action time of the switching switch is taken into account, and the error of the predicted switching action time can be reduced to an extremely small range, thereby greatly improving the prediction accuracy of the switch opening and closing time, and also improving the accuracy of the zero-crossing opening and closing.

[0083] Embodiment 1 of the present invention proposes an automatic reactive power compensation device for medium-voltage distribution lines. It utilizes the corresponding relationship between the line voltage and the voltages of each phase, and between the line voltage and the phase of the capacitor current of each phase. Only one line voltage needs to be connected to determine the zero-crossing point of the voltage or current required for switching on and off the capacitors of each phase, thereby reducing the complexity of wiring, saving costs, and simplifying the product design of the line compensation device.

[0084] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "include", "comprise" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment that includes a series of elements are inherent to the elements. In the absence of more restrictions, the elements limited by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or equipment that includes the elements. In addition, the above-mentioned technical solution provided in the embodiment of the present application is consistent with the corresponding technical solution in the prior art in principle, and the part is not described in detail, so as not to repeat too much.

[0085] Although the above describes the specific implementation of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. For those skilled in the art, other different forms of modifications or deformations can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here. On the basis of the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative work are still within the scope of protection of the present invention.

Claims

1. A reactive power automatic compensation device applied to a medium voltage distribution line, characterized in that: It includes a line compensation control unit and a line compensation unit; The uplink of the line compensation control unit is connected to the medium voltage distribution line, and the downlink of the line compensation control unit is connected to the line compensation unit; The line compensation control unit is used to obtain the compensation capacitor capacity of the line compensation unit and calculate the line reactive power. When the line reactive power is greater than the compensation capacitor capacity, a closing command is sent to the switch drive terminal in the line compensation unit with the least number of switch actions, and the capacitor of this line compensation unit is put into operation; When the line reactive power is less than zero, a switch-off command is sent to the switch drive terminal of the line compensation unit with the most switch actions, and the capacitor of this line compensation unit is removed; And the opening and closing time of each phase switch under the current temperature is calculated by parabolic interpolation.

2. The reactive power automatic compensation device applied to a medium voltage distribution line according to claim 1, characterized in that: In the reactive power automatic compensation device, when the line reactive power is greater than zero and less than the capacity of the compensation capacitor, the status quo is maintained and no compensation is required.

3. The reactive power automatic compensation device applied to a medium voltage distribution line according to claim 1, characterized in that: The number of the line compensation units is one or more; When there is one line compensation unit, the line compensation control unit is directly connected to the line compensation unit; When there are multiple line compensation units, the line compensation control unit is connected to the nearest line compensation unit; The line compensation units are cascaded.

4. The reactive power automatic compensation device for medium voltage distribution lines according to claim 1, characterized in that: The line compensation control unit includes: a CPU module, a signal conditioning circuit, a first power supply module, a first communication module, a first voltage transformer, a first current transformer, a second voltage transformer and a second current transformer; The primary side of the first voltage transformer and the primary side of the first current transformer are both connected to the medium voltage distribution line; the secondary side of the first voltage transformer is connected to the primary side of the second voltage transformer and the first power module; the secondary side of the first current transformer is connected to the primary side of the second current transformer; the secondary side of the second voltage transformer and the secondary side of the second current transformer are both connected to the signal conditioning circuit; the first power module is also respectively connected to the CPU module, the signal conditioning circuit and the first communication module; The signal conditioning circuit converts the current signal sent by the second current transformer and the voltage signal sent by the second voltage transformer into signals that can be processed by the CPU module; the CPU module is used to calculate the system reactive power based on the processable signals.

5. The reactive power automatic compensation device applied to a medium voltage distribution line according to claim 4, characterized in that: The process of calculating the line reactive power includes: Among them, Q s is the line reactive power; U AB is the line voltage of phase A and phase B of the medium voltage distribution line; I C is the C phase current of the medium voltage distribution line; ψ is U AB with I C The angle between.

6. The reactive power automatic compensation device for medium voltage distribution lines according to claim 1, characterized in that: The line compensation unit includes a third voltage transformer, an energy storage module, a voltage stabilizing module, a switching switch, a switch driving terminal and a power capacitor; The primary side and the switching switch of the third voltage transformer are respectively connected to the medium voltage distribution line; the secondary side of the third voltage transformer is connected to the energy storage module and the switch drive terminal; the voltage stabilizing module is connected to the energy storage module, the switching switch and the switch drive terminal; the switching switch is also connected to the switch drive terminal and the power capacitor; The energy storage module is used to convert the AC power supply on the secondary side of the third voltage transformer into a DC unregulated power supply; the voltage stabilization module is used to convert the DC unregulated power supply into a DC high-precision regulated power supply; The energy storage module and the voltage stabilizing module are used together to store the energy transmitted by the third voltage transformer and provide a DC driving voltage when the switch is opened or closed.

7. The reactive power automatic compensation device applied to a medium voltage distribution line according to claim 6, characterized in that: The process of calculating the opening time of each phase switch at the current temperature by parabolic interpolation includes: Among them, t fd is the opening action time of the phase switch under the current ambient temperature T; t f1 is the opening action time of the phase switch at temperature T1; t f2 is the opening action time of the phase switch at temperature T2; t f3 It is the opening action time of the phase switch at temperature T3.

8. The reactive power automatic compensation device for medium voltage distribution lines according to claim 6, characterized in that: The process of calculating the closing time of each phase switch at the current temperature by parabolic interpolation includes: Among them, t hd is the closing action time of the phase switch under the current ambient temperature T; t h1 is the closing action time of the phase switch at temperature T1; t h2 is the closing action time of the phase switch at temperature T2; t h3 It is the closing action time of the phase switch at temperature T3.

9. The reactive power automatic compensation device applied to a medium voltage distribution line according to claim 8, characterized in that: When the line compensation unit receives the capacitor injection command sent by the line compensation control unit, the action sequence of the three-phase switch is: The A-phase closing drive module immediately drives the A-phase switch closing coil to close; after the switch drive terminal detects that the A-phase switch is closed successfully at time t1, it predicts U ab The next zero-crossing time t2, according to the closing action time t of the B-phase switch at the current temperature hd·b , the best time to drive the B phase closing coil is: t qhb =t1+(t2-t1-t hd·b ), ensure that when the B phase switch is closed, U ab It is at the moment of zero crossing; After the switch driver detects that the B phase switch is closed successfully, the U ab and C phase voltage U c relationship, predicting U c The next zero-crossing time t3, according to the closing action time t of the C-phase switch at the current temperature hd·c , the best time to drive the C phase closing coil is: t qhc =t2+(t3-t2-t hd·c ), ensure that when the C phase switch is closed, U c It is at the moment of zero o'clock.

10. The reactive power automatic compensation device applied to a medium voltage distribution line according to claim 9, characterized in that: When the switch driving terminal receives the capacitor cutting command from the line compensation control unit at time t4, the U ab Predict the phase C capacitor current I C·C The next zero-crossing time t5, according to the current temperature, the C-phase switch opening action time t fd·c , determine the time to drive the C phase opening coil: t qfc =t4+(t5-t4-t fd·c ), ensuring that the C-phase switch is disconnected when the C-phase capacitor current passes through zero; After the switch driver detects that the C phase switch is successfully opened, it will pass U ab Predict the capacitive current I between phases A and B C·ab The zero-crossing time t6, according to the current temperature B phase switch opening action time t fd·b , the best time to drive the B phase opening coil is: t qfb =t5+(t6-t5-t fd·b ), ensure that the B phase switch is at I C·ab It is disconnected when crossing the zero point; after the switch driving terminal detects that the B-phase switch is successfully opened, it drives the A-phase switch opening coil to open the A-phase switch without judging the zero point.

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