CN111725832B - Direct-current side voltage indirect control method of multi-terminal flexible power transmission system based on simplified offline algorithm - Google Patents
Direct-current side voltage indirect control method of multi-terminal flexible power transmission system based on simplified offline algorithm Download PDFInfo
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- CN111725832B CN111725832B CN202010507243.XA CN202010507243A CN111725832B CN 111725832 B CN111725832 B CN 111725832B CN 202010507243 A CN202010507243 A CN 202010507243A CN 111725832 B CN111725832 B CN 111725832B
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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
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
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Abstract
The invention discloses a simplified offline algorithm-based direct-current side voltage indirect control method for a multi-terminal flexible power transmission system, which comprises the following steps of: 1) replacing a direct-current side voltage controller in the rectifying side MMC control system by a total capacitance voltage controller; 2) according to the steady-state model, fixing the active power of the rectifying side MMC control system to be 0MW, and solving a voltage compensation signal of the rectifying side MMC control system under the condition of reactive power change in an off-line mode; 3) simplifying the voltage compensation signal obtained in the step 2), and fitting and converting the simplified voltage compensation signal into a linear function; 4) compensating the obtained voltage
And adding the voltage commands to the upper and lower bridge arms to obtain final voltage commands of the upper and lower bridge arms, and then controlling the direct-current side voltage of the multi-terminal flexible power transmission system according to the final voltage commands of the upper and lower bridge arms.
Description
Technical Field
The invention belongs to the technical field of modular multilevel converters in power electronics, and relates to a direct-current side voltage indirect control method of a multi-terminal flexible power transmission system based on a simplified offline algorithm.
Background
With the wide application of high-power electronic conversion devices, the multilevel conversion technology is rapidly developed. Modular Multilevel Converter (MMC) is a novel Multilevel voltage source Converter, which has been proposed since the beginning of 2000, because it has the advantages of Modular characteristics, easy expansion, convenient assembly, high quality output and high voltage level, and the like, it is a research hotspot in recent years, and it has obvious advantages in the field of medium and high voltage applications. At present, the MMC has been widely used in the field of High Voltage Direct Current (HVDC) transmission, and multiple lines have been put into operation, such as TransBayCable engineering in the united states, south australia three-terminal flexible dc transmission engineering in china, and a navian five-terminal flexible dc transmission system.
In order to maintain stable operation of the multi-terminal flexible power transmission system, the voltage on the direct current side of the multi-terminal flexible power transmission system must be well controlled. Currently, to control the dc side voltage, it relies on measuring the dc side voltage. In HVDC systems, the dc side voltage is typically up to several hundred kilovolts, and reliable measuring instruments are required to achieve voltage measurements. According to the national standard, a typical dc voltage measuring device of a high-voltage dc transmission system includes a dc voltage divider, a dc voltage measuring device, a converter, a transmission system, etc. It must meet the design requirements of digital quantity, external insulation requirements, painting and rust prevention requirements, electromagnetic compatibility requirements, radio interference voltage requirements and the like. Therefore, the whole direct-current voltage measuring system is complex and high in cost, and when the measuring system breaks down, the direct-current side voltage of the system cannot be effectively controlled.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a simplified offline algorithm-based direct-current side voltage indirect control method for a multi-terminal flexible power transmission system, which can realize effective control of the direct-current side voltage of the system and reduce the complexity and cost of the system.
In order to achieve the above object, the indirect control method for dc side voltage applied to a multi-terminal flexible power transmission system according to the present invention comprises the following steps:
1) replacing a direct-current side voltage controller in the rectifying side MMC control system by a total capacitance voltage controller;
2) according to the steady-state model, fixing the active power of the rectifying side MMC control system to be 0MW, and solving a voltage compensation signal of the rectifying side MMC control system under the condition of reactive power change in an off-line mode;
3) simplifying the voltage compensation signal obtained in the step 2), and fitting and converting the simplified voltage compensation signal into a linear function;
4) compensating the obtained voltage
And adding the voltage commands to the upper and lower bridge arms to obtain final voltage commands of the upper and lower bridge arms, and then controlling the direct-current side voltage of the multi-terminal flexible power transmission system according to the final voltage commands of the upper and lower bridge arms.
The specific operation of the step 2) is as follows:
21) setting step length, and discretizing all working conditions of the rectifying side MMC control system;
22) the active power of the rectifying side MMC control system is fixed to be 0 MW;
23) and according to the MMC steady-state analysis model, voltage compensation signals corresponding to the rectifying side MMC control system under the condition of reactive power change are calculated in an off-line mode.
The specific operation of the step 3) is as follows:
simplifying the voltage compensation signal obtained in the step 2) for the voltage compensation signal obtained in the step 2), and fitting and converting the voltage compensation signal into a linear function to obtain:
the specific operation of the step 4) is as follows:
the system reactive power obtained by real-time calculation is substituted into formula (1) to obtain a voltage compensation signal
Compensating the voltage signal
Switching function S acting on upper and lower bridge arms respectivelyU(t) and SL(t) and finally, efficient control of the dc side voltage is achieved, wherein,
compared with the existing control method, the method has the following beneficial effects:
the direct current side voltage indirect control method applied to the multi-terminal flexible power transmission system fixes the active power of the rectifying side MMC control system to be 0MW during specific operation, solves a voltage compensation signal of the rectifying side MMC control system under the condition of reactive power change in an off-line mode, fits and linearly processes the voltage compensation signal obtained under the off-line condition, and adds the voltage compensation signal to voltage instructions of an upper bridge arm and a lower bridge arm to control the direct current side voltage of the multi-terminal flexible power transmission system.
Drawings
FIG. 1 is a corresponding MMC control block diagram of the present invention;
FIG. 2 is a diagram of DC side voltage offset for a simulation system without DC side control;
FIG. 3 is a view of the axis Q-u of FIG. 2;
FIG. 4 is a graph of voltage compensation signals obtained by off-line calculation;
FIG. 5 is a diagram of DC side voltage waveforms when active power of the system dynamically changes according to the present invention;
FIG. 6 is a diagram of DC side voltage waveforms when the reactive power of the system dynamically changes according to the present invention;
fig. 7 is a voltage waveform diagram of the dc side when the active power and the reactive power of the system dynamically change simultaneously in the invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the invention discloses a direct-current side voltage indirect control method applied to a multi-terminal flexible power transmission system, which comprises the following steps of:
1) replacing a direct-current side voltage controller in the rectifying side MMC control system by a total capacitance voltage controller;
2) according to the steady-state model, fixing the active power of the rectifying side MMC control system to be 0MW, and solving a voltage compensation signal of the rectifying side MMC control system under the condition of reactive power change in an off-line mode;
3) simplifying the voltage compensation signal obtained in the step 2), and fitting and converting the voltage compensation signal into a linear function;
4) compensating the obtained voltage
And adding the voltage commands to the upper and lower bridge arms to obtain final voltage commands of the upper and lower bridge arms, and then controlling the direct-current side voltage of the multi-terminal flexible power transmission system according to the final voltage commands of the upper and lower bridge arms.
The specific operation of the step 1) is as follows:
in the present invention, the dc-side voltage controller in the existing rectifying-side MMC control system needs to measure the dc-side voltage of the system to realize control.
The specific operation of the step 2) is as follows:
21) setting a step length, discretizing all working conditions of the rectifying side MMC control system, and preferably setting the step length to be 1MVA, wherein the control effect is reduced by too large compensation, and the calculated amount is increased by too small step length.
22) By observation, it can be found that the voltage offset of the direct current side of the system is insensitive to active power variation, referring to fig. 3, in the process of offline calculation, the active power is fixed to be 0MW, and the offline calculation amount can be greatly reduced.
23) And according to the MMC steady-state analysis model, voltage compensation signals corresponding to the rectifying side MMC control system under the condition of reactive power change are calculated in an off-line mode.
The specific operation of the step 3) is as follows:
without loss of generality, the voltage compensation signal is found to be a linear function of the reactive power, and the obtained voltage compensation signal is fitted, namely:
the specific operation of the step 4) is as follows:
the system reactive power obtained by real-time calculation is substituted into formula (1) to obtain a voltage compensation signal
Compensating the voltage signal
Switching function S acting on upper and lower bridge arms respectivelyU(t) and SLIn (t), efficient control of the dc-side voltage is finally achieved.
Simulation experiment
The circuit parameter settings are shown in table 1:
TABLE 1
Fig. 2 shows the dc side voltage offset without dc side control applied to the system, and fig. 3 shows the Q-u axis view of fig. 2, where the voltage offset is found to be insensitive to active power variations. Fig. 4 shows the voltage compensation signal obtained off-line, which is approximated as a linear function of the reactive power.
Fig. 5 shows a voltage waveform diagram of the dc side of the system when the present invention is applied during the active power dynamic change process. Through comparison, the voltage on the direct current side is well kept at the rated value of 320kV by applying the method, and when the control is not carried out, the voltage on the direct current side has deviation. Fig. 6 shows a voltage waveform diagram of a dc side of a system when the present invention is applied in a dynamic reactive power change process of the system. After the invention is applied, the voltage of the direct current side is well kept at the rated value of 320kV, and when the control is not carried out, the voltage deviation of the direct current side is changed greatly. Fig. 7 shows a voltage waveform diagram of a dc side of a system when the present invention is applied in a process of dynamic change of active power and reactive power of the system. After the invention is applied, the voltage of the direct current side is well kept at the rated value of 320kV, and when the control is not carried out, the voltage deviation of the direct current side is changed greatly.
Claims (2)
1. A simplified offline algorithm-based direct-current side voltage indirect control method for a multi-terminal flexible power transmission system is characterized by comprising the following steps:
1) replacing a direct-current side voltage controller in the rectifying side MMC control system by a total capacitance voltage controller;
2) according to the steady-state model, fixing the active power of the rectifying side MMC control system to be 0MW, and solving a voltage compensation signal of the rectifying side MMC control system under the condition of reactive power change in an off-line mode;
3) simplifying the voltage compensation signal obtained in the step 2), and fitting and converting the simplified voltage compensation signal into a linear function;
4) compensating the obtained voltage
Adding the voltage commands to the upper and lower bridge arms to obtain final voltage commands of the upper and lower bridge arms, and then controlling the direct-current side voltage of the multi-terminal flexible power transmission system according to the final voltage commands of the upper and lower bridge arms;
the specific operation of the step 3) is as follows:
simplifying the voltage compensation signal obtained in the step 2) for the voltage compensation signal obtained in the step 2), and fitting and converting the voltage compensation signal into a linear function to obtain:
wherein the content of the first and second substances,
a voltage compensation signal; k is a linear function proportionality coefficient; d is a linear function intercept; and Q is the reactive power of the system.
2. The simplified offline algorithm-based direct-current side voltage indirect control method for the multi-terminal flexible power transmission system according to claim 1, wherein the specific operations in the step 2) are as follows:
21) setting step length, and discretizing all working conditions of the rectifying side MMC control system;
22) the active power of the rectifying side MMC control system is fixed to be 0 MW;
23) and according to the MMC steady-state analysis model, voltage compensation signals corresponding to the rectifying side MMC control system under the condition of reactive power change are calculated in an off-line mode.
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