CN107612013B - Direct-current power grid voltage range control method - Google Patents
Direct-current power grid voltage range control method Download PDFInfo
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- CN107612013B CN107612013B CN201710822374.5A CN201710822374A CN107612013B CN 107612013 B CN107612013 B CN 107612013B CN 201710822374 A CN201710822374 A CN 201710822374A CN 107612013 B CN107612013 B CN 107612013B
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Abstract
The invention relates to a direct current power grid voltage range control method, and belongs to the field of direct current power transmission. The converter stations of the flexible direct current power grid are usually interconnected by long lines, the voltage drop at two ends of each line is large, and in order to prevent one end of each direct current line from generating steady overvoltage or undervoltage during operation, the direct current voltage of the whole grid needs to be controlled within a designed operation range. The invention is mainly arranged in a converter station control system with fixed direct-current voltage, collects the bus voltage of each converter station on a direct-current power grid, and controls the direct-current bus voltage of the fixed voltage station in a proper interval through a direct-current power grid operation range control strategy so as to ensure that the direct-current bus voltage of each converter station of the direct-current power grid operates in a designed voltage range. The method has important guiding significance for ensuring the voltage stability of the whole direct-current power grid.
Description
Technical Field
The invention belongs to the technical field of flexible direct current transmission of a power system, and particularly relates to a direct current power grid voltage range control method.
Background
Under the same direct current network frame, a multi-end converter station system consisting of more than two converter stations can form a direct current power grid capable of realizing multi-power supply and multi-drop point power receiving, and has higher economical efficiency and flexibility. The important premise for stable operation of a direct-current power grid formed by a multi-terminal converter system is that the voltage stability of the direct-current power grid is very important as the frequency stability in an alternating-current system. The existing system-level direct-current voltage controller mainly includes two types of control with communication and control without communication, when the whole direct-current power grid operates stably, the control strategy of the fixed direct-current voltage station needs to ensure that the direct-current voltage of the converter station is stable, and also needs to ensure that the direct-current bus voltage of each converter station on the whole direct-current power grid operates in an allowable range, so that the direct-current voltage of each non-fixed-voltage converter station needs to be coordinated.
Considering that the converter stations of the direct current power grid are interconnected through long lines, the voltage drop at two ends of the lines is large, and in order to prevent one end of the direct current line from generating steady overvoltage or undervoltage during operation and ensure that the direct current voltage of the whole grid is within the designed operation range, a direct current power grid voltage range control method suitable for engineering application needs to be provided.
Disclosure of Invention
The invention aims to provide a direct current power grid voltage range control method which is generally arranged at a converter station with fixed direct current voltage, and the direct current bus voltage of the fixed voltage station is controlled in a proper interval by utilizing inter-station communication or upper-layer communication equipment to acquire the bus voltage of each converter station on a direct current power grid and through a direct current power grid operation range control strategy so as to ensure that the direct current bus voltage of each converter station of the direct current power grid operates in a designed range.
In order to achieve the purpose, the invention adopts the following technical scheme: a voltage range control method for a direct current power grid is characterized in that the direct current power grid is a multi-terminal converter station system formed by more than two converter stations, and the converter stations are mutually connected through direct current lines to form a direct current network;
The control method comprises the steps of setting a converter station controlled by a fixed direct-current voltage, and collecting the voltage of a direct-current bus where each converter station of a direct-current power grid is located; according to the direct current bus voltage and the direct current voltage set value U of each converter station dcrefObtaining a direct current voltage instruction deviation correction value; according to the DC voltage command deviation correction value and the DC voltage set value U dcrefAnd adjusting the reference value of the constant voltage station in real time so as to enable the voltage of the whole network to be within a reasonable range.
Further, the method specifically comprises the following steps:
1) Collecting voltage U of direct current bus where each converter station of direct current power grid is located dcmean1、Udcmean2～UdcmeanN(ii) a N is the total number of converter stations in the direct current power grid; the Nth converter station is a fixed direct-current voltage station, and the direct-current bus voltage of the station is U dcmeanN；
2) Alternating current three-phase voltage U of fixed direct current voltage station is gathered L，ABCAC three-phase current I L，ABCAn AC side voltage frequency f, and obtaining a voltage reference phase theta according to the AC side voltage frequency f ref；
3) Processing the collected DC bus voltage U of each converter station by adopting a DC voltage operation range control algorithm dcmean1、Udcmean2～UdcmeanNAnd a DC voltage set value U dcrefObtaining a direct current voltage command deviation correction value delta U dcref；
4) Processing DC voltage command deviation correction value delta U dcrefAnd a DC voltage set value U dcrefObtaining an active current reference value I dref；
5) Obtaining a reactive current reference value I by controlling the electric quantity collected in the step 2) through alternating voltage or reactive power qref；
6) Reference value I of active current drefReference value of reactive current I qrefAnd system voltage phase reference value theta refAs converter control signal to each converter, the output active current of each converter follows the reference value of active current I drefAnd the reactive current follows the reactive current reference value I qref。
Further, the control system collects the voltage of a direct current bus where each converter station of the direct current power grid is located through inter-station communication or upper-layer communication equipment.
Further, the direct current voltage set value U of the direct current voltage station is determined dcrefProvided by an upper level control device or other external means, or manually set.
Further, a direct-current voltage operation range control algorithm is adopted in the step 3), and pole-bus voltage deviation delta U between each converter station with non-constant direct-current voltage and each converter station with constant direct-current voltage is calculated dcmeankWherein k is more than or equal to 1 and less than or equal to N-1, and the calculation expression is as follows:
ΔUdcmean1＝UdcmeanN-Udcmean1
ΔUdcmean2＝UdcmeanN-Udcmean2
……
ΔUdcmeank＝UdcmeanN-Udcmeank
Taking Delta U dcmeankMaximum value of (1) Δ U dcmean_maxAnd used as direct current voltage command deviation correction value delta U dcref。
Further, the direct current voltage set value U of the direct current voltage station is determined dcrefOne of the following set values is selected:
a) Selecting the highest operation voltage of the whole network as a set value;
b) Selecting the lowest operation voltage of the whole network as a set value;
c) The selected set value is lower than the maximum voltage limit value of the whole network and higher than the minimum voltage limit value of the whole network.
Further, the specific operation of step 4) is as follows: correcting voltage command deviation value delta U dcrefAnd a DC voltage set value U dcrefThe deviation delta U is subjected to proportional-integral adjustment to obtain an active current reference value I drefAnd the active current reference value I is ensured through an amplitude limiting link drefWithout exceeding the limit, wherein:
ΔU＝Udcref-ΔUdcref。
Furthermore, in the multi-terminal converter station system, the number of the fixed direct-current voltage stations is one, and the direct-current bus is a positive bus or a negative bus.
Further, the reference value of active current I drefNon-out-of-limit refers to the active current reference value I drefAt minimum value of active current I allowed to operate dminAnd maximum value of active current I dmaxNamely:
Idmin≤Idref≤Idmax。
Further, any converter in each converter in the step 6) adopts current vector control.
The invention has the beneficial effects that:
(1) The method utilizes the control of the converter stations with the fixed voltage, can realize the coordination of the voltage of the whole direct current power grid by monitoring and processing the direct current bus voltage of each converter station of the whole direct current power grid, avoids any direct current bus voltage on the direct current power grid from exceeding the designed operation range, and has important guiding significance for maintaining the voltage stability of the whole direct current power grid.
(2) The method has the advantages of simple control algorithm, high reliability and suitability for engineering application.
Drawings
FIG. 1 is an exemplary diagram of a DC power grid topology;
FIG. 2 is a block diagram of a DC voltage operating range control strategy;
Fig. 3 is a block diagram of a control strategy for a constant dc voltage converter station.
Detailed Description
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a schematic topology diagram of a DC power grid, which is composed of N converter stations forming a "multi-port" structure, and sets the converter stations S1-S (N-1) as the converter stations under non-constant voltage control, SN as the converter station under constant voltage control, and records that the DC bus voltages of S1, S2-SN converter stations are U dcmean1、Udcmean2～UdcmeanN。
FIG. 2 is a DC voltage A block diagram of an operating range control strategy. The control strategy can be applied to the dc power grid topology illustrated in fig. 1, and the voltage U of the dc bus where each converter station of the dc power grid is located is firstly acquired by the upper layer communication equipment dcmean1、Udcmean2～UdcmeanNN is the total number of converter stations in the direct current power grid; the Nth converter station is designed as a fixed direct-current voltage station and the direct-current bus voltage is U dcmeanN. Calculating a pole-to-bus voltage deviation Δ U between each non-constant DC voltage converter station and a constant DC voltage converter station using voltage range control logic dcmeankThe specific calculation expression is as follows, wherein k is more than or equal to 1 and less than or equal to N-1:
ΔUdcmean1＝UdcmeanN-Udcmean1
ΔUdcmean2＝UdcmeanN-Udcmean2
……
ΔUdcmeank＝UdcmeanN-Udcmeank
Taking Delta U dcmeankMaximum value of (1) Δ U dcmean_maxAs a correction value delta U for the command deviation received by the fixed DC voltage station dcref。
Then the operator provides a set value U of the DC voltage of the fixed DC voltage station dcrefD.c. voltage set value U dcrefThe maximum operation voltage of the whole network is set. Calculating voltage command deviation correction value delta U dcrefAnd a DC voltage set value U dcrefVoltage deviation Δ U of (1), where Δ U ═ U dcref-ΔUdcref. Carrying out proportional integral adjustment on the voltage deviation delta U to obtain an active current reference value I drefAnd the active current reference value I is ensured through an amplitude limiting link drefWithout going beyond the limit, namely: i is dmin≤Idref≤Idmax。
FIG. 3 shows an overall control strategy of a fixed DC voltage converter station, wherein a control system collects AC three-phase voltage U in a unified manner L，ABCAC three-phase current I L，ABCAC side voltage frequency f, DC pole bus voltage U dcmeanObtaining a voltage reference phase theta according to the frequency f of the AC side voltage ref. From the figure 2 obtaining an active current reference value I by constant voltage range control drefThen obtaining a reactive current reference value I by constant alternating voltage control or reactive power control qref. Reference value I of active current drefReference value of reactive current I qrefAnd system voltage phase reference value theta refAnd as the input of the direct current inner loop vector control, the control of the fixed direct current voltage converter station is completed by the control method.
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 (10)
1. A voltage range control method for a direct current power grid is characterized in that the direct current power grid is a multi-terminal converter station system formed by more than two converter stations, and the converter stations are mutually connected through direct current lines to form a direct current network; the control method is characterized in that the control method sets a converter station controlled by fixed direct-current voltage, and collects the voltage of a direct-current bus where each converter station of a direct-current power grid is located; calculating the voltage deviation of a pole bus between the converter station of each non-constant direct current voltage and the constant direct current voltage converter station, and taking the maximum value in the voltage deviation of the pole bus as a direct current voltage command deviation correction value; according to the DC voltage command deviation correction value and the DC voltage set value U dcrefAnd adjusting the reference value of the constant voltage station in real time so as to enable the voltage of the whole network to be within a reasonable range.
2. The method according to claim 1, characterized in that the method comprises the following steps:
1) Collecting voltage U of direct current bus where each converter station of direct current power grid is located dcmean1、Udcmean2～UdcmeanN(ii) a N is the total number of converter stations in the direct current power grid; the Nth converter station is a fixed direct-current voltage station, and the direct-current bus voltage of the station is U dcmeanN；
2) Alternating current three-phase voltage U of fixed direct current voltage station is gathered L，ABCAC three-phase current I L，ABCAn AC side voltage frequency f, and obtaining a voltage reference phase theta according to the AC side voltage frequency f ref；
3) Processing the collected DC bus voltage U of each converter station by adopting a DC voltage operation range control algorithm dcmean1、Udcmean2～UdcmeanNAnd a DC voltage set value U dcrefObtaining a direct current voltage command deviation correction value delta U dcref；
4) Processing DC voltage command deviation correction value delta U dcrefAnd a DC voltage set value U dcrefObtaining an active current reference value I dref；
5) Obtaining a reactive current reference value I by controlling the electric quantity collected in the step 2) through alternating voltage or reactive power qref；
6) Reference value I of active current drefReference value of reactive current I qrefAnd system voltage phase reference value theta refAs converter control signal to each converter, the output active current of each converter follows the reference value of active current I drefAnd the reactive current follows the reactive current reference value I qref。
3. The direct current network voltage range control method according to claim 1 or 2, characterized in that the control system collects the voltage of the direct current bus where each converter station of the direct current network is located through inter-station communication or through upper communication equipment.
4. A method according to claim 1 or 2, characterized by fixing the dc voltage set-point U of the dc voltage station dcrefProvided by an upper level control device or other external means, or manually set.
5. The method according to claim 2, wherein a dc voltage operation range control algorithm is used in step 3) to calculate the converter station and the fixed dc voltage of each non-fixed dc voltage Pole-to-bus voltage deviation DeltaU between DC voltage converter stations dcmeankWherein k is more than or equal to 1 and less than or equal to N-1, and the calculation expression is as follows:
Taking Delta U dcmeankMaximum value of (1) Δ U dcmean_maxAnd used as direct current voltage command deviation correction value delta U dcref。
6. A method according to claim 1 or 2, characterized by fixing the dc voltage set-point U of the dc voltage station dcrefOne of the following set values is selected:
a) Selecting the highest operation voltage of the whole network as a set value;
b) Selecting the lowest operation voltage of the whole network as a set value;
c) The selected set value is lower than the maximum voltage limit value of the whole network and higher than the minimum voltage limit value of the whole network.
7. The dc grid voltage range control method according to claim 2, wherein the specific operation of step 4) is: correcting voltage command deviation value delta U dcrefAnd a DC voltage set value U dcrefThe deviation delta U is subjected to proportional-integral adjustment to obtain an active current reference value I drefAnd the active current reference value I is ensured through an amplitude limiting link drefWithout exceeding the limit, wherein:
ΔU＝Udcref-ΔUdcref。
8. The method according to claim 1 or 2, wherein the number of the fixed dc voltage stations in the multi-terminal converter station system is one, and the dc bus is a positive bus or a negative bus.
9. A method according to claim 7, characterized in that the active current is the active current Reference value I drefNon-out-of-limit refers to the active current reference value I drefAt minimum value of active current I allowed to operate dminAnd maximum value of active current I dmaxNamely:
Idmin≤Idref≤Idmax。
10. A dc network voltage range control method according to claim 2, wherein in step 6) any of said converters is controlled using current vectors.
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| CN105071372A (en) * | 2015-07-20 | 2015-11-18 | 清华大学 | Voltage control method applied to flexible DC power distribution network |
| CN105552946A (en) * | 2015-12-30 | 2016-05-04 | 国网辽宁省电力有限公司电力科学研究院 | DC voltage control method of flexible ring network controller and control system thereof |
| CN106451572A (en) * | 2016-10-18 | 2017-02-22 | 许继集团有限公司 | AC/DC hybrid microgrid power balance control method |
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| CN105071372A (en) * | 2015-07-20 | 2015-11-18 | 清华大学 | Voltage control method applied to flexible DC power distribution network |
| CN105552946A (en) * | 2015-12-30 | 2016-05-04 | 国网辽宁省电力有限公司电力科学研究院 | DC voltage control method of flexible ring network controller and control system thereof |
| CN106451572A (en) * | 2016-10-18 | 2017-02-22 | 许继集团有限公司 | AC/DC hybrid microgrid power balance control method |
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