CN108011378B - Receiving end layered access extra-high voltage direct current low-load reactive power control method and control device - Google Patents
Receiving end layered access extra-high voltage direct current low-load reactive power control method and control device Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
本发明公开一种受端分层接入特高压直流低负荷无功控制方法及控制装置，用于实现对受端分层接入特高压直流系统低负荷运行方式下受端两个交流电网无功功率的独立控制。在双极层控制，通过实时检测受端两个交流电网中交直流系统的无功交换值，将其作为反馈量分别送入两个独立的低负荷无功控制器，分别计算得到用于控制高端和低端阀组无功损耗的触发角或熄弧角参考值；在换流器层控制，通过换流变分接头控制、换流器触发控制及阀组均压控制的协调控制，实现对高、低端阀组无功损耗的独立控制。此种技术方案不仅能实现对受端站两个交流电网中交直流无功交换值的独立控制，同时具有平滑投入、自动平滑退出的特点。
The invention discloses a low-load reactive power control method and a control device for a receiving end layered access to an ultra-high voltage direct current system, which are used to realize the low-load operation mode of the receiving end layered access to an ultra-high voltage direct current system. Independent control of power. In the bipolar layer control, the reactive power exchange value of the AC-DC system in the two AC power grids at the receiving end is detected in real time, and it is sent to two independent low-load reactive power controllers as a feedback value, respectively, and calculated and used for control. The trigger angle or arc extinction angle reference value of the reactive power loss of the high-end and low-end valve groups; controlled at the converter layer, through the coordinated control of the converter tap control, the inverter trigger control and the valve group pressure equalization control, to achieve Independent control of reactive power loss of high and low-end valve groups. This technical solution can not only realize the independent control of the AC/DC reactive power exchange value in the two AC power grids of the receiving station, but also has the characteristics of smooth input and automatic smooth exit.
Description
Technical Field
The invention belongs to the field of extra-high voltage direct current transmission, and particularly relates to a receiving end layered access extra-high voltage direct current low-load reactive power control method and a control device.
Background
When a conventional extra-high voltage direct current system operates in a low-load operation mode, due to the limitation of switching of an absolute minimum filter, the reactive power consumed by a converter is far less than the reactive power compensated by an alternating current filter, so that a large amount of surplus reactive power is injected into an alternating current system by a direct current converter station, and the voltage of an alternating current power grid is easily high. Compared with a conventional extra-high voltage direct current system, a receiving end is connected into the extra-high voltage direct current system in a layered mode, a high-end valve group and a low-end valve group of a receiving end station are respectively connected into two alternating current power grids with different voltage levels, and two independent alternating current filter fields are respectively configured on the two alternating current power grids. Under a low-load operation mode, a receiving end is connected to an alternating current power grid connected to an extra-high voltage direct current system receiving end station in a layered mode, reactive power consumed by a converter is only half of that of conventional direct current, reactive power compensated by an alternating current filter is limited by switching of an absolute minimum filter, and the value of the reactive power is close to that of the conventional direct current, so that excessive reactive power injected into the alternating current system by the receiving end converter station is further increased, the voltage of the alternating current power grid is easily caused to be higher, and stable operation of the alternating current power grid of the receiving end station is affected.
The reactive power consumed by the converter can be adjusted by adjusting the trigger angle or the arc-extinguishing angle of the converter (or the valve bank), so that the reactive power exchanged between the converter station and the alternating current system can be adjusted. Based on the principle, the current low-load reactive power control method mainly comprises direct-current voltage direct control type low-load reactive power control and reactive power exchange direct type low-load reactive power control. The direct-current voltage direct control type low-load reactive power control is to calculate a direct-current reference voltage of the operation of the direct-current system according to the power value of the operation of the direct-current system, and adjust a trigger angle or an arc extinguishing angle of the converter by controlling the direct-current voltage of the direct-current system. Because the change of the DC pole line voltage can affect the control of the transmitting end station and the receiving end station at the same time, the method cannot realize the independent control of the reactive power of the transmitting end converter station and the receiving end converter station. The reactive power exchange direct type low-load reactive power control directly controls the reactive power exchanged between the converter station and the alternating current system as feedback quantity, the adjustment of the trigger angle or the arc-extinguishing angle of the two stations is relatively independent, and the independent control of the reactive power of the two stations can be realized.
At present, two existing low-load reactive power control methods are mainly used for a conventional non-hierarchical ultra-high voltage direct current system. In a conventional extra-high voltage direct current system, when a transmitting end converter station or a receiving end converter station is subjected to low-load reactive power control, because two high-end valve banks and two low-end valve banks in each converter station are connected to the same power grid and the model parameters of the high-end valve banks and the low-end valve banks and the converter transformer are consistent, the adjusting processes of a trigger angle (or an arc extinguishing angle) and a converter transformer tap between different valve banks are completely consistent, the coordination action among the converter transformer tap control, the converter trigger control and the valve bank voltage-sharing control between the high-end valve banks and the low-end valve banks does not need to be considered, and the control mode.
Different from a conventional extra-high voltage direct current system, a receiving end is connected into the extra-high voltage direct current system in a layered mode, model parameters of a high-end valve group, a low-end valve group and a converter transformer are not consistent, and meanwhile, because the high-end valve group and the low-end valve group in each pole are in a series connection relationship, under a direct-current low-load reactive control mode, the adjustment of a trigger angle (or an arc extinguishing angle) of one valve group can influence the control of the valve group connected in series, and further influence the reactive control of another power grid. Therefore, under the direct-current low-load operation mode, how to realize the independent control of reactive power between two alternating-current power grids connected to the receiving end of an extra-high voltage direct-current system in a layered mode at the receiving end by coordinating the control of a converter transformer tap, the control of a converter trigger and the control of valve bank voltage-sharing between a high-end valve bank and a low-end valve bank is a subject worthy of research.
Disclosure of Invention
The invention aims to provide a receiving end layered access extra-high voltage direct current low-load reactive power control method and a control device, which can realize independent control of reactive power exchanged between a receiving end layered access extra-high voltage direct current receiving end station and different alternating current power grids in a low-load operation mode by controlling a trigger angle (or an arc-extinguishing angle) of a receiving end valve group and a converter transformer tap gear.
In order to achieve the above purpose, the solution of the invention is:
a receiving end layered access extra-high voltage direct current low-load reactive power control method comprises the following steps:
step 1, reactive power Control of a converter station is set to be in an automatic Q-Control mode, and gear Control of a converter transformer tap is set to be in an automatic mode;
step 2, the receiving end station is put into low-load reactive power control, the bipolar layer control host respectively uses alternating current-direct current reactive power exchange values accessed into a power grid by the high-end valve bank and the low-end valve bank as feedback quantities, an auxiliary trigger angle or an auxiliary arc-quenching angle for adjusting the reactive power loss of the high-end valve bank and the low-end valve bank of the receiving end station is respectively obtained through calculation by the low-load reactive power controller, then the auxiliary trigger angle and the auxiliary arc-quenching angle are superposed on an initially set trigger angle reference value and an initially set arc-quenching angle reference value, and a trigger angle reference value or an arc-quenching angle reference value of the valve bank is obtained and sent to the valve layer control host;
step 3, the receiving terminal station valve layer control host takes the trigger angle reference value or the extinction angle reference value as a control target, and realizes the adjustment of the actual value of the trigger angle or the extinction angle of the valve group and finally realizes the adjustment of the reactive loss of the valve group through the coordination control of the converter transformer tap control, the converter trigger control and the valve group voltage-sharing control;
and 4, when the active power transmitted by the direct current system is greater than a set value, the low-load reactive power control automatically and smoothly exits after a certain time delay.
In the step 1, the contents of the setting of the gear control of the converter transformer tap to the automatic mode are as follows: when the receiving end station operates as a rectifying station, the trigger angle is adjusted through gear control cooperation of the converter transformer tap; when the receiving terminal station operates as an inverter station, the adjustment of the direct-current voltage is realized through the gear control cooperation of the converter transformer tap.
In the step 2, the low-load reactive controller takes the difference value between the alternating current-direct current reactive power exchange value and the reference value thereof as an input quantity, the input quantity is sent to the PI controller after being processed by the amplitude limiting function and the dead zone function, and the PI controller outputs an auxiliary trigger angle or an auxiliary arc-quenching angle for adjusting the reactive loss of the valve bank.
In the step 4, the automatic smooth exit means that when the low-load reactive power control is turned on and the dc transmission power is greater than the set value, the low-load reactive power control on/off enable signal is set to zero, so that the input value of the low-pass filter changes from 1 to 0, the output value of the low-pass filter changes gradually from 1 to 0, and the actual auxiliary trigger angle or extinction angle changes gradually to zero after the output value of the low-pass filter is multiplied by the output value of the PI controller in the low-load reactive power controller.
In the step 2, when the receiving end station operates as a rectifier station, the sum of the auxiliary trigger angle and the trigger angle reference value which is initially set is used as an actual trigger angle reference value; and when the receiving terminal station operates as an inverter station, the sum of the auxiliary arc-quenching angle and the initially set arc-quenching angle reference value is used as an actual arc-quenching angle reference value.
Valve bank pressure equalizing control is adopted between the high-end valve bank and the low-end valve bank of the receiving end station; when the receiving end station operates as a rectifying station, the high-end valve controls current for the main control valve group, the trigger angle of the high-end valve is directly obtained by triggering and controlling the converter, the low-end valve realizes valve group voltage balance control for the slave control valve group through the voltage balance controller, and the trigger angle of the low-end valve is the sum of the trigger angle of the high-end valve and the output value of the valve group voltage-sharing controller; when the receiving end station is used as an inverter station, the voltage control of the high-end converter transformer tap and the low-end converter transformer tap both take the direct-current voltage at the two ends of the converter plus half of the line voltage drop as a controlled object and take the half of the rated voltage of the rectifier station as a control target to adjust the gear of the converter transformer tap, so that the balance control between the high-end valve bank and the low-end valve bank is realized.
A receiving end layered access extra-high voltage direct current low-load reactive power control device is used for independently adjusting alternating current-direct current reactive power exchange values of a receiving end layered access extra-high voltage direct current system receiving end station high-end valve group and a receiving end valve group accessed in an alternating current power grid; the device comprises:
the detection unit is used for detecting the voltage of an alternating current system, the trigger angle or the arc-quenching angle of the converter, the current flowing through the direct current neutral bus, the voltage of a direct current pole bus, the gear of the converter transformer substation and the group capacity and the number of the alternating current filter field filter;
the power grid alternating current-direct current reactive power exchange quantity calculation unit is used for calculating reactive power generated by the alternating current filter based on an alternating current voltage value of an alternating current power grid, group capacity and quantity input by a filter in the converter station, calculating reactive loss of the valve group based on a trigger angle or an arc extinguishing angle of the converter and current flowing through a direct current neutral bus, and subtracting the reactive loss of the converter from the reactive power generated by the alternating current filter to obtain an alternating current-direct current reactive power exchange value accessed into the power grid by the valve group; and the number of the first and second groups,
the control unit of the AC/DC reactive exchange quantity of the power grid takes the AC/DC reactive exchange value accessed into the power grid by the high-end valve bank and the low-end valve bank of the receiving end station as a feedback quantity, respectively calculates the auxiliary trigger angle or the auxiliary arc-quenching angle of the high-end valve bank and the low-end valve bank of the receiving end converter station through the low-load reactive controller, and superposes the auxiliary trigger angle and the auxiliary arc-quenching angle on the initially set trigger angle reference value and the initially set arc-quenching angle reference value as the actual trigger angle reference value and the actual arc-quenching angle reference value of the valve bank; the receiving end station valve layer control host takes the trigger angle reference value or the extinction angle reference value as a control target, and realizes the adjustment of the actual value of the trigger angle or the extinction angle of the valve group through the coordination control of the converter transformer tap control, the converter trigger control and the valve group voltage-sharing control, and finally realizes the adjustment of the reactive power exchanged between the converter station and the alternating current system.
After the scheme is adopted, compared with the prior art, the invention realizes the independent control of the reactive power loss of the high-end and low-end valve banks of the receiving-end layered access extra-high voltage direct current receiving end station by setting two independent low-load controllers and simultaneously coordinating the control of the converter transformer tap, the trigger control of the converter and the pressure equalizing control of the valve banks between the high-end and low-end valve banks, thereby realizing the independent control of the reactive power exchanged between the receiving-end layered access extra-high voltage direct current receiving end station and different alternating current power grids in a low-load operation mode; by adding the smooth switching-in and switching-out logic in the low-load reactive power controller, the functions of smooth switching-in and automatic smooth switching-out of the low-load reactive power control are realized, and the impact on an alternating current power grid caused by the switching-in or switching-out of the low-load reactive power control is avoided.
Drawings
FIG. 1 is a schematic diagram of a single-converter main loop of a conventional extra-high voltage DC power transmission system with high and low end valve banks connected to the same AC power grid;
FIG. 2 is a schematic diagram of a single current conversion station main loop of a layered access extra-high voltage DC power transmission system with high and low end valve banks respectively accessed to different AC power grids;
FIG. 3 is a hierarchical control structure diagram of the low load reactive control of the present invention;
FIG. 4 is a schematic diagram of the implementation of the low load reactive control of the present invention;
FIG. 5 is a block diagram of the low-load reactive power control principle of the present invention when the receiving end station operates as a rectifying station;
FIG. 6 is a block diagram of the low-load reactive power control principle when the receiving station of the present invention operates as an inverter station;
fig. 7 is a schematic structural diagram of the control device of the present invention.
Reference numerals: 1. an alternating current grid; 1a, an alternating current power grid I; 1b, an alternating current power grid II; 2. an AC filter; 3. a high-end converter transformer; 4. a low-side converter transformer; 5. a high-end valve bank; 6. a low end valve bank; 7. A direct current smoothing reactor; 8. a DC filter; 9. a direct current pole bus; 10. a neutral bus; 11. and a grounding electrode.
Detailed Description
The technical scheme of the invention is explained in detail in the following with the accompanying drawings.
The main loops of a receiving end station of a conventional extra-high voltage direct current system and a receiving end hierarchically accessed extra-high voltage direct current system are respectively shown in fig. 1 and fig. 2. In fig. 1, a conventional extra-high voltage dc system includes a high-end valve bank 5 and a low-end valve bank 6 on each pole, each valve bank being a 12-pulse inverter. The high-voltage end of the high-end valve group 5 is connected with a polar direct-current line, the low-voltage end is connected with the high-voltage end of the low-end valve group 6, and the low-voltage end of the low-end valve group 6 is connected with a neutral bus 10. The alternating current sides of all the valve groups in the converter station are connected to the same alternating current power grid 1 through converter transformers (3, 4), and the types and parameters of the converter transformers adopted by each valve group are consistent. In fig. 2, different from fig. 1, the ac sides of the high-side and low-side valve banks of the two poles are respectively connected to two ac power grids (1a, 1b) with different voltage levels through different types of converter transformers, the two ac power grids are respectively configured with independent ac filter fields, and the dc pole control system needs to implement independent control of reactive power of the two ac power grids through two independent application programs.
In order to realize independent control of ac/dc reactive power exchange values in a power grid to which high and low valves of a receiving end station of a layered access ultra-high voltage direct current system are accessed under a low-load operation mode, independent low-load reactive power controllers need to be respectively configured for two power grids in bipolar layer control, and the principle structure of the controller is shown in fig. 3. In fig. 3, the bipolar layer control host calculates the ac/dc reactive power exchange amounts of the ac power grid I1 a and the ac power grid II 1b connected to the high-side and low-side valve banks, respectively, through the ac/dc system reactive power exchange amount calculation modules 31 and 32, and then sends the results to the corresponding low-load reactive power controllers 33 and 34 for control.
The calculation expression of the reactive power exchanged between the alternating current and direct current systems is as follows:
Qex＝Qfilter-Qd
in the formula, QdThe expression for the reactive power consumed by the direct current system is as follows:
in the formula, QconviThe reactive loss of the ith 12-pulse converter, and m is the number of the converters.
When the inverter is operated in the rectifying state,
in the formula IdFor direct current through the inverter, Udi0For an ideal no-load direct-current voltage of each 6-pulse converter, alpha is a trigger angle, and mu is a commutation angle.
When the converter is operated in the inverter state,
wherein γ is the extinction angle.
QfilterReactive power provided to the ac filter in the ac filter field is expressed by:
in which n is the number of AC filter groups in the AC filter field, UacIs the effective value of the AC bus voltage in the AC field, facFor the frequency, Q, of an AC systemfilteriNFor the rated capacity of the ith subgroup of ac filters, the subscript N represents the rated value.
After the reactive power exchange value of the alternating current-direct current system is obtained, the high-end valve bank and the low-end valve bank respectively calculate a triggering angle or a extinction angle reference value for valve layer control through two independent low-load reactive power controllers according to respective reactive power reference values. And then, the valve layer control host machine realizes the control of the actual trigger angle and the actual extinction angle of the converter based on the reference value.
The high-end and low-end valve group low-load reactive power controllers have the same structure, and are specifically shown in fig. 4. In fig. 4, the low load reactive controller mainly includes three modules, i.e., a commissioning/decommissioning enabling operation 41, an auxiliary firing angle or auxiliary extinction angle calculation 42, and a firing angle or extinction angle reference value calculation 43. The switching enabling operation module mainly realizes the functions of smooth switching and smooth exiting of low-load reactive power control, and comprises two parts of low-load reactive power control switching enabling and exiting enabling. Four conditions need to be met when the drop enable signal is active: the low-load reactive power Control in the background monitoring system is already put into use, the reactive power Control is automatic Control, the reactive power Control is in a Q-Control mode, and the direct current power transmitted by the high-end or low-end valve bank of the receiving terminal station is smaller than the threshold value. The de-enable is active as long as the dc power delivered by the high-side or low-side bank of terminals is greater than its threshold and the hold time is greater than T1. The input/output enable signal is the AND of the input/output enable signal and the output/output enable signal after negation. When the switching enable signal is 1, the low-load reactive power control is in an effective switching state, and when the switching enable signal is 0, the low-load reactive power control is in an effective exiting state. In the operation of switching on and off, the low-load reactive power control smooth switching on and switching off is realized through a first-order filtering link. Although the control mode of the converter transformer tap position does not affect the enabling operation of the low-load reactive power control, because both the adjustment of the trigger angle of the rectifier station and the adjustment of the direct-current voltage of the inverter station need to be realized by adjusting the converter transformer tap, the gear control of the converter transformer tap position needs to be set to be an automatic control mode in the low-load reactive power control process.
The auxiliary trigger angle or extinction angle calculation module firstly exchanges the reference value Q with the reactive powerQPC_refReactive power Q exchanged by the converter station with the AC system as a reference valueexAnd calculating a reactive power deviation value delta Q for the feedback quantity. And the power deviation value delta Q is sent to a PI controller after being processed by an amplitude limiting function and a dead zone operation function, and an auxiliary triggering angle delta alpha or an auxiliary extinction angle delta gamma for regulating the reactive loss of the valve bank is obtained by calculation of the PI controller. The amplitude limiting function module mainly prevents the reactive deviation value input into the PI controller from being too large, so that the regulation speed of the PI controller is prevented from being too high; the dead zone function module mainly avoids the condition that the low-load reactive power controller still frequently adjusts when the reactive power exchange value of the alternating current and direct current system is close to the reference value of the low-load reactive power controller.
In a trigger angle or extinction angle reference value calculation module, an auxiliary trigger angle delta alpha or an auxiliary extinction angle delta gamma is firstly multiplied by an output signal of a first-order filter in an on-off enabling operation module, and then the result is respectively superposed to an initial trigger angle alpharef0And the extinction angle gammaref0Obtaining a trigger angle reference value alpha on the reference valuerefAnd the reference value gamma of the extinction angleref. In extra-high voltage DC engineering, alpharef0And gammaref0The values of the reference angle alpha are respectively 15 degrees and 17 degrees, and the reference value alpha of the trigger angle is adopted during the rectification operationrefControl is carried out, and the reference value gamma of the arc extinguishing angle is adopted during the inversion operationrefAnd (5) controlling.
In the low-load reactive power control process, the control principles are different when the receiving end station of the layered access extra-high voltage direct current system is used as a rectifying station and an inverter station, and the two are respectively shown in fig. 5 and fig. 6.
In fig. 5, when the receiving end station operates as a rectifying station, the converter transformer tap angle control module 51 adjusts the converter transformer tap gear with the trigger angle reference value as a target, so as to change the ideal no-load voltage value of the converter. The inverter firing control module 52 then keeps the dc current constant by adjusting the firing angle of the inverter. When the high-end valve set and the low-end valve set are operated simultaneously, the low-end valve set also has the function of balancing the voltage of the high-end valve set and the low-end valve set. At this time, the high-end valve set is a master control valve, and the firing angle instruction value is directly calculated by the inverter firing control module 52. The low-end valve set is a slave control valve, and the firing angle instruction value of the low-end valve set is the sum of the firing angle instruction value of the high-end valve set and the output value of the inverter voltage balance control 53. The valve block control finally converts the firing angle command into an ignition pulse and sends the ignition pulse to the firing pulse controller 37 to realize the actual control of the valve block.
When the receiving end station operates as a rectifying station, the regulation principle of the operation of the receiving end station of the layered access extra-high voltage direct current system as the rectifying station is described by taking a high-end valve bank and a low-end valve bank for low-load reactive power control as examples. When the high-end valve bank is put into low-load reactive power control, the AC/DC reactive power exchange value of the high-end valve bank connected into the power grid is supposed to be far larger than the reactive power reference value before the low-load reactive power control is put into operation. After the high-end valve bank is put into low-load reactive power control, firstly, in the bipolar layer control host, the low-load reactive power controller can increase the trigger angle reference value of the high-end valve bank. Then, in the high-end valve group control main machine, because the actual valve group firing angle value is smaller than the firing angle reference value, the converter transformer tap angle control can raise the tap position. The converter transformer gear is increased to cause the ideal no-load voltage value of the converter to be increased, and at the moment, in order to keep the direct current constant, the trigger controller of the high-end valve group can increase the trigger angle instruction value of the converter. For the low-end valve group, the gear of the converter transformer tap is kept unchanged, the firing angle instruction transmitted to the low-end valve group by the high-end valve group is increased, the voltage of the low-end valve group is reduced, at the moment, the converter voltage balance controller outputs a negative angle, and the low-end valve group and the converter voltage balance controller are overlapped to keep the actual firing angle instruction of the low-end valve group unchanged. Finally, the reactive loss of the high-end converter is increased due to the fact that the trigger angle of the high-end valve group is increased, and therefore the reactive power exchanged by the alternating current and direct current system is reduced; the low-end valve group keeps the gear and the trigger angle of the converter transformer tap unchanged, so that the reactive power exchanged by an alternating current and direct current system is not influenced, and the reactive independent control of the alternating current system where the high-end valve group of the converter station is located is realized.
When the low-end valve bank is put into low-load reactive power control, the AC/DC reactive power exchange value of the low-end valve bank connected to the power grid is supposed to be far larger than the reactive power reference value before the low-load reactive power control is put into operation. After the low-end valve bank is put into low-load reactive power control, firstly, in the bipolar layer control host, the low-load reactive power controller can increase the trigger angle reference value of the low-end valve bank. Then, in the low-end valve group control main machine, since the actual valve group firing angle value is smaller than the firing angle reference value, the converter transformer tap angle control can raise the tap gear. The converter transformer gear is increased to increase the ideal no-load voltage value of the converter, so that the voltage of the low-end valve bank is increased, at the moment, the converter voltage balance controller outputs a positive angle, and the value is superposed with a firing angle instruction transmitted to the low-end valve bank by the high-end valve bank to increase the actual firing angle instruction of the low-end valve bank. For the high-end valve group, the gear and the trigger angle of the converter transformer tap are kept unchanged, so that the influence of low-load reactive power control investment of the low-end valve group is avoided, and reactive power independent control of an alternating current system where the low-end valve group of the converter station is located is realized.
In fig. 6, when the receiving end station operates as an inverter station, the firing angles and tap positions of the high-pressure and low-pressure valve banks are independently controlled. The converter trigger control 52 directly adjusts the trigger angle of the converter by taking the reference value of the arc extinguishing angle as a target, and the converter transformer tap voltage control 61 adjusts the gear of the converter transformer tap by taking the direct-current voltage at two ends of the converter plus half of the line voltage drop as a controlled object and taking half of the rated voltage of the rectifier station as a control target, so as to realize the balance of the high-low valve group voltage as far as possible.
When the receiving end station operates as an inverter station, the regulation principle that the receiving end station of the layered access extra-high voltage direct current system operates as the inverter station is described by taking the high-end valve bank and the low-end valve bank to input low-load reactive power control as examples. When the high-end valve group is put into low-load reactive power control, the reactive power exchanged between the alternating current power grid where the high-end valve group is located and the converter station is far larger than a reactive reference value before the low-load reactive power control is put into operation. After the high-end valve bank is put into low-load reactive power control, firstly, in the bipolar layer control host, the low-load reactive power controller can increase the reference value of the extinction angle of the high-end valve bank. And then in the high-end valve bank control host, the converter trigger control directly increases the arc-quenching angle of the converter by taking the arc-quenching angle reference value as a target. The increase of the extinction angle of the high-end valve bank can cause the voltage of the valve bank to be reduced, and the voltage control of the converter transformer tap can increase the tap at the moment, so that the voltage of the valve bank is increased. Generally, due to the limitation of the voltage stress protection of the valve group, the range of the gear rise of the converter transformer tap is limited, and the voltage of the high-end valve group and the voltage of the low-end valve group cannot be the same. At this time, because the voltage of the high-end valve set and the low-end valve set are regulated independently, the gear of the low-end valve set converter transformer tapping connector is still unchanged. Finally, the arc extinguishing angle of the high-end valve group is increased, so that the reactive loss of the converter is increased, and the reactive power exchanged by the alternating current and direct current system is reduced; the arc extinguishing angle and the converter transformer tap gear of the low-end valve group are kept unchanged, so that the reactive power exchanged by an alternating current and direct current system is not influenced, and the reactive independent control of the converter station is realized. The reduction of the voltage of the high-end valve bank can lead to the reduction of the voltage of the direct-current line to a certain degree. But because the drop amplitude of the direct current line voltage is smaller, the normal operation of the sending end station cannot be influenced.
Similarly, when the low-end valve bank is put into low-load reactive power control, the reactive power exchanged between the alternating current power grid where the low-end valve bank is located and the converter station is far greater than the reactive reference value before the low-load reactive power control is put into operation. After the low-end valve bank is subjected to low-load reactive power control, firstly, in the bipolar layer control host, the low-load reactive power controller can increase the reference value of the extinction angle of the low-end valve bank. And then in the low-end valve bank control host, the converter trigger control directly increases the arc-extinguishing angle of the converter by taking the arc-extinguishing angle reference value as a target. The increase of the extinction angle of the low-end valve bank can cause the voltage of the valve bank to be reduced, and the voltage control of the converter transformer tap can increase the tap at the moment, so that the voltage of the valve bank is increased. Generally, due to the limitation of the voltage stress protection of the valve group, the range of the gear rise of the converter transformer tap is limited, and the voltage of the low-end valve group cannot be the same as that of the high-end valve group. At this time, because the voltage of the high-end valve set and the low-end valve set are regulated independently, the gear of the high-end valve set converter transformer tapping head still remains unchanged. Finally, the arc extinguishing angle of the low-end valve bank is increased, so that the reactive loss of the converter is increased, and the reactive power exchanged by the alternating current and direct current system is reduced; the arc extinguishing angle and the converter transformer tap gear of the high-end valve group are kept unchanged, so that the reactive power exchanged by an alternating current and direct current system is not influenced, and the reactive independent control of the converter station is realized. The reduction in the low side bank voltage will result in a certain reduction in the dc line voltage. But because the drop amplitude of the direct current line voltage is smaller, the normal operation of the sending end station cannot be influenced.
The invention provides a receiving end layered access extra-high voltage direct current low-load reactive power control device 7, the structural principle of which is shown in figure 7, and the device specifically comprises the following components:
(1) the detection unit 71 detects an ac voltage, a trigger angle or an arc-quenching angle of the ac power grid, a current flowing through the neutral bus, a pole bus voltage, a converter transformer tap position, and a group capacity and a number of the ac filter field filters.
(2) The grid ac/dc reactive power exchange amount calculation unit 72 calculates the reactive power generated by the ac filter according to the ac voltage of the ac grid, the group capacity and the amount of the ac filtering field filter, calculates the reactive power consumed by the inverter according to the trigger angle or the extinction angle of the inverter and the current flowing through the neutral bus, and subtracts the reactive power consumed by the inverter from the reactive power generated by the ac filter to obtain the reactive power exchanged between the converter station and the ac system.
(3) The grid ac/dc reactive power exchange control unit 73 uses reactive power exchanged between the converter station and the ac system in the grid to which the high-end and low-end valve banks of the receiving end station are connected as feedback quantity, calculates an auxiliary firing angle or an auxiliary arc-quenching angle used for adjusting the reactive power consumed by the valve banks by the high-end and low-end valve banks of the receiving end station through a low-load reactive power controller, and superimposes the auxiliary firing angle and the auxiliary arc-quenching angle on an initially set firing angle reference value and an initially set arc-quenching angle reference value to be used as an actual firing angle reference value and an actual arc-quenching angle reference value of the valve banks for control; meanwhile, the rectification station realizes the adjustment of the trigger angle through the control coordination of the converter transformer tap, and the inverter station realizes the minimum reduction amplitude of the direct-current voltage through the control coordination of the converter transformer tap.
In summary, the invention discloses a receiving end layered access extra-high voltage direct current low-load reactive power control method and a control device, which are used for realizing independent control of reactive power of two receiving end alternating current power grids under a receiving end layered access extra-high voltage direct current system low-load operation mode. In the bipolar layer control, reactive power exchange values of an alternating current system and a direct current system in two alternating current power grids at a receiving end are detected in real time and are respectively sent to two independent low-load reactive power controllers as feedback quantities, and trigger angles or extinction angle reference values for controlling reactive power losses of a high-end valve bank and a low-end valve bank are respectively calculated; and in the converter layer control, the independent control of the reactive loss of the high-end valve group and the low-end valve group is realized through the coordination control of the converter transformer tap control, the converter trigger control and the valve group voltage-sharing control. The method can realize independent control of the AC/DC reactive power exchange values in the two AC power grids of the receiving terminal station, and has the characteristics of smooth input and automatic smooth exit. The method and the device effectively realize the independent control of the alternating current and direct current reactive power exchange quantity in the two alternating current power grids of the receiving end station in the mode that the receiving end is connected into the extra-high voltage direct current low-load operation in a layered mode, and meanwhile, the normal operation of the transmitting end station is not influenced by the input of the low-load reactive power control of the receiving end converter station.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.
Claims (7)
1. A receiving end layered access extra-high voltage direct current low-load reactive power control method is characterized by comprising the following steps:
step 1, reactive power Control of a converter station is set to be in an automatic Q-Control mode, and gear Control of a converter transformer tap is set to be in an automatic mode;
step 2, the receiving end station is subjected to low-load reactive power control, when the receiving end station operates as a rectifier station, the bipolar layer control host respectively uses alternating current-direct current reactive power exchange values of a power grid connected with the high-end valve group and the low-end valve group as feedback quantities, an auxiliary trigger angle for adjusting the reactive power loss of the high-end valve group and the low-end valve group of the receiving end station is respectively obtained through calculation by a low-load reactive power controller, and then a trigger angle reference value of the valve group is obtained through calculation and sent to the valve layer control host based on the auxiliary trigger angle and an initially set trigger angle reference value; when the receiving terminal station operates as an inverter station, the bipolar layer control host respectively uses alternating current-direct current reactive power exchange values accessed into a power grid by the high-end valve bank and the low-end valve bank as feedback quantities, respectively calculates and obtains an auxiliary extinction angle for adjusting the reactive power loss of the high-end valve bank and the low-end valve bank of the receiving terminal station through the low-load reactive power controller, then calculates and obtains an extinction angle reference value of the valve bank based on the auxiliary extinction angle and an initially set extinction angle reference value, and sends the extinction angle reference value to the valve layer control host;
step 3, the receiving terminal station valve layer control host takes the trigger angle reference value or the extinction angle reference value as a control target, and realizes the adjustment of the actual value of the trigger angle or the extinction angle of the valve group and finally realizes the adjustment of the reactive loss of the valve group through the coordination control of the converter transformer tap control, the converter trigger control and the valve group voltage-sharing control;
and 4, when the active power transmitted by the direct current system is greater than a set value, the low-load reactive power control automatically and smoothly exits after a certain time delay.
2. The receiving-end layered access extra-high voltage direct current low-load reactive power control method according to claim 1, characterized in that: in the step 1, the content of setting the gear control of the converter transformer tap to the automatic mode is as follows: when the receiving end station operates as a rectifying station, the trigger angle is adjusted through gear control cooperation of the converter transformer tap; when the receiving terminal station operates as an inverter station, the adjustment of the direct-current voltage is realized through the gear control cooperation of the converter transformer tap.
3. The receiving-end layered access extra-high voltage direct current low-load reactive power control method according to claim 1, characterized in that: in the step 2, the low-load reactive controller takes the difference value between the alternating current-direct current reactive power exchange value and the reference value thereof as an input quantity, the input quantity is sent to the PI controller after being processed by the amplitude limiting function and the dead zone function, and the PI controller outputs an auxiliary trigger angle or an auxiliary arc-quenching angle for adjusting the reactive loss of the valve bank.
4. The receiving-end layered access extra-high voltage direct current low-load reactive power control method according to claim 3, characterized in that: in the step 4, the automatic smooth exit means that when the low-load reactive power control is put in and the direct-current transmission power is greater than the set value, the low-load reactive power control put-in/out enable signal is set to zero, so that the input value of the low-pass filter is changed from 1 to 0, the output value of the low-pass filter is gradually changed from 1 to 0, and after the output value of the low-pass filter is multiplied by the output value of the PI controller in the low-load reactive power controller, the actual auxiliary trigger angle or extinction angle is gradually changed to zero.
5. The receiving-end layered access extra-high voltage direct current low-load reactive power control method according to claim 1, characterized in that: in the step 2, when the receiving end station operates as a rectifier station, the sum of the auxiliary trigger angle and the trigger angle reference value which is initially set is used as an actual trigger angle reference value; and when the receiving terminal station operates as an inverter station, the sum of the auxiliary arc-quenching angle and the initially set arc-quenching angle reference value is used as an actual arc-quenching angle reference value.
6. The receiving-end layered access extra-high voltage direct current low-load reactive power control method according to claim 1, characterized in that: valve bank pressure equalizing control is adopted between the high-end valve bank and the low-end valve bank of the receiving end station; when the receiving end station operates as a rectifying station, the high-end valve is a master control valve group and controls current, the trigger angle of the high-end valve is directly obtained by triggering and controlling a current converter, the low-end valve is a slave control valve group and realizes valve group voltage balance control through a voltage balance controller, and the trigger angle of the low-end valve is the sum of the trigger angle of the high-end valve and the output value of a valve group voltage-sharing controller; when the receiving end station is used as an inverter station, the voltage control of the high-end converter transformer tap and the low-end converter transformer tap both take the direct-current voltage at the two ends of the converter plus half of the line voltage drop as a controlled object and take the half of the rated voltage of the rectifier station as a control target to adjust the gear of the converter transformer tap, so that the balance control between the high-end valve bank and the low-end valve bank is realized.
7. A receiving end layered access extra-high voltage direct current low-load reactive power control device is used for independently adjusting alternating current-direct current reactive power exchange values of a receiving end layered access extra-high voltage direct current system receiving end station high-end valve group and a receiving end valve group accessed in an alternating current power grid; characterized in that said device comprises:
the detection unit is used for detecting the voltage of an alternating current system, the trigger angle or the arc-quenching angle of the converter, the current flowing through the direct current neutral bus, the voltage of a direct current pole bus, the gear of the converter transformer substation and the group capacity and the number of the alternating current filter field filter;
the power grid alternating current-direct current reactive power exchange quantity calculation unit is used for calculating reactive power generated by the alternating current filter based on an alternating current voltage value of an alternating current power grid, group capacity and quantity input by a filter in the converter station, calculating reactive loss of the valve group based on a trigger angle or an arc extinguishing angle of the converter and current flowing through a direct current neutral bus, and subtracting the reactive loss of the converter from the reactive power generated by the alternating current filter to obtain an alternating current-direct current reactive power exchange value accessed into the power grid by the valve group; and the number of the first and second groups,
when the receiving end station operates as a rectifier station, the AC/DC reactive exchange value accessed into the power grid by the receiving end station high-end valve group and the receiving end station low-end valve group is taken as a feedback quantity, the auxiliary trigger angles of the receiving end converter station high-end valve group and the receiving end converter station low-end valve group are respectively calculated through the low-load reactive controller, and the auxiliary trigger angles are superposed on the initially set trigger angle reference value to be taken as the actual trigger angle reference value of the valve group; when the receiving end station operates as an inverter station, taking an alternating current-direct current reactive power exchange value in a power grid accessed by a high-end valve bank and a low-end valve bank of the receiving end station as a feedback quantity, respectively calculating auxiliary arc-quenching angles of the high-end valve bank and the low-end valve bank of the receiving end converter station through a low-load reactive power controller, and superposing the auxiliary arc-quenching angles on an initially set arc-quenching angle reference value to serve as an actual arc-quenching angle reference value of the valve bank; the receiving end station valve layer control host takes the trigger angle reference value or the extinction angle reference value as a control target, and realizes the adjustment of the actual value of the trigger angle or the extinction angle of the valve group through the coordination control of the converter transformer tap control, the converter trigger control and the valve group voltage-sharing control, and finally realizes the adjustment of the reactive power exchanged between the converter station and the alternating current system.
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| CN109802424B (en) * | 2019-03-08 | 2022-07-22 | 南京南瑞继保电气有限公司 | Hybrid direct current transmission system converter input coordination method and device |
| CN109861268B (en) * | 2019-03-29 | 2020-08-18 | 西安交通大学 | Nonlinear control method for layered access of extra-high voltage direct current transmission system |
| CN110137999B (en) * | 2019-05-28 | 2023-03-28 | 国网江西省电力有限公司电力科学研究院 | Direct-current power coordination control method and system with participation of receiving-end wind power plant |
| CN111509712B (en) * | 2020-05-15 | 2021-09-03 | 南方电网科学研究院有限责任公司 | Multi-terminal main loop transformation method of direct current transmission system |
| CN112202193B (en) * | 2020-07-24 | 2022-05-31 | 国网江苏省电力有限公司检修分公司 | Method, system and storage medium for on-line input of valve group of UHV layered access system |
| CN112968460B (en) * | 2021-02-05 | 2023-05-23 | 国网山西省电力公司检修分公司 | Converter transformer tap control method based on ALPHA-VDIO_R coordination control |
| CN112968459B (en) * | 2021-02-05 | 2023-05-23 | 国网山西省电力公司检修分公司 | Tap control method based on homopolar converter transformer tap fixed deviation alternating control |
| CN115296333B (en) * | 2022-07-20 | 2024-03-26 | 四川大学 | Voltage balance control method based on LCC converter station at the transmission end of UHV DC transmission system |
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