CN116316708B - Adaptive control method, device and system for flexible direct-current power grid - Google Patents

Abstract

The invention provides an adaptive control method, device and system for a flexible DC power grid. The method includes: calculating the steady-state error of the active power of the flexible DC network at both ends under adaptive control, and obtaining the difference between the DC current error and the steady-state error of the active power relationship; calculate the steady-state error of the active power of the multi-terminal flexible DC network under adaptive control, and obtain the influence of the DC line impedance on the steady-state error of active power; based on the relationship between the DC current error and the steady-state error of active power and the obtained To describe the influence of DC line impedance on the steady-state error of active power, the droop characteristic curve of the converter is translated to the intersection point of the volt-ampere characteristic curve and the reference value of DC current, so that the actual DC current of each converter is always consistent with the reference value . In the present invention, without changing the slope of the drooping characteristic curve, the dynamic performance of the network will not deteriorate while significantly reducing the steady-state error.

Description

A flexible DC power grid adaptive control method, device and system

technical field

The invention relates to the field of DC power grid stability and control, in particular to an adaptive control method, device and system for a flexible DC power grid.

Background technique

Multi-terminal flexible direct current (VSC-HVDC) networks are technologies for large-scale integrated renewable energy power transmission. Compared with traditional AC power transmission, multi-terminal VSC-HVDC network has the advantages of high transmission efficiency and compensation of reactive power of AC system. From the perspective of active power, the control methods of multi-terminal flexible DC networks interconnected across regions and long distances are worthy of further study. The existing control methods of flexible DC networks mainly include the following types:

1. Master/slave control method: The master/slave control method is widely used in point-to-point high-voltage flexible DC systems, and can also be applied to multi-terminal high-voltage flexible DC networks. The master/slave control algorithm is simple and can accurately control the power flow.

2. Adaptive control method: Adaptive control is a widely accepted method based on voltage droop control, document [C.D. Barker, and R.S.Whitehouse, 'Further Developments in AutonomousConverter Control in a Multi-Terminal HVDC System', in ALSTOM Grid, PowerElectronics Activities, Stafford, UK] introduced the principle of adaptive control, which allows each converter to meet the overall power balance requirements by independently adjusting its DC voltage. The DC voltage reference of each converter can be automatically adjusted by measuring the droop characteristic curve generated by the DC current and voltage. It is first applied to the distribution of microgrids, and then further applied to multi-terminal high-voltage flexible DC transmission networks. Literature [Y. Zhang, L. Wang and W. Li, "Autonomous DC Line Power Flow Regulation Using Adaptive Droop Control in HVDCGrid," in IEEE Transactions on Power Delivery, vol. 36, no. 6, pp. 3550-3560, Dec. 2021, doi: 10.1109/TPWRD.2020.3044978.] describes the application of adaptive control methods to multi-terminal HVDC flexible DC transmission networks.

3. Correction method for increasing the slope of the droop characteristic curve: [Gyusub Lee, Dohoon Kwon, Seungil Moon. DC Current and Voltage Droop Control Method of Hybrid HVDC Systems for an Offshore Wind Farm Connection to Enhance AC Voltage Stability[J]. IEEETransactions on Energy Conversion,2020,PP(99).] proposed a correction method for droop control, trying to reduce the steady-state error by increasing the slope of the droop characteristic curve.

The prior art has the following defects:

(1) The master/slave control method puts too much pressure on the balance node and relies heavily on communication, so it cannot be well adapted to more complex HVDC transmission networks;

(2) The influence of impedance on the operation of multi-terminal VSC-HVDC has not been analyzed in detail in traditional adaptive control;

(3) The correction method of increasing the slope of the droop characteristic curve will reduce the damping of the power receiving converter and reduce the dynamic stability of the network, while the steady-state error is still large.

Contents of the invention

The invention provides an adaptive control method, device and system for a flexible DC power grid. The invention combines the advantages of voltage droop control and master/slave control not relying on communication, the average stress of each converter and accurate active power distribution, and realizes The steady-state error of the network is significantly reduced without changing the slope of the droop characteristic curve, and the dynamic performance of the network will not deteriorate.

A method for adaptive control of a flexible DC power grid, comprising the steps of:

Calculate the steady-state error of the active power of the flexible DC network at both ends under adaptive control, and obtain the relationship between the DC current error and the steady-state error of active power;

Calculate the steady-state error of the active power of the multi-terminal flexible DC network under adaptive control, and obtain the influence of the DC line impedance on the steady-state error of the active power;

Based on the relationship between the DC current error and the steady-state error of active power and the influence of the DC line impedance on the steady-state error of active power, the droop characteristic curve of the converter is shifted to the volt-ampere characteristic curve and the DC current reference value so that the actual DC current of each converter is always consistent with the reference value.

Further, the calculation of the steady-state error of the active power of the flexible DC network at both ends under adaptive control obtains the relationship between the DC current error and the steady-state error of the active power, including:

The volt-ampere characteristic curve expressions and droop characteristic curve expressions of the two-end flexible DC grid converters A and B under simultaneous adaptive control, the intersection point is obtained as the actual operating point of the converter, and then through the converter's Calculate the active power steady-state error expression at the actual operating point, and finally analyze the active power steady-state error expression to obtain the relationship between the DC current error and the active power steady-state error: the active power steady-state error caused by the line impedance is determined by the DC current error , and when the slope k of the voltage droop control curve increases within the allowable range, the steady-state error decreases.

Furthermore, in the two-terminal VSC-HVDC system, the calculation of the steady-state error of active power needs to determine the actual operating points of two converters: P _A (I ^' _dc , U _dca ) and P _B (I ^' _dc , U _dcb ), where I ^' _dc is the actual DC current, U _dca and U _dcb are the actual operating voltages of converter A and converter B respectively, and the actual operating point of the converter is the difference between the volt-ampere characteristic curve and the droop characteristic curve intersection point, where the droop characteristic curve expression is:

;

In the formula, k is the slope of the voltage droop control curve, I _dc represents the changing DC current, U _s represents the change of the DC voltage at the sending end relative to I _dc , U _r represents the change of the DC voltage at the receiving end relative to I _dc , U ^* _dca and U ^* _dcb represent the intercept of the above curve;

_Udc0 represents the normal working voltage of the entire HVDC network set by the dispatch center, and the relationship between its value and the voltage droop characteristic curve is expressed as:

;

The DC current reference value I _dc0 is the current when the converter works at the reference point P ₀ :

;

The expression of the volt-ampere characteristic curve is:

;

In the formula, _Udca and _Udcb represent the actual DC voltage of converter A and converter B, and _R0 is the resistance between converter A and converter B;

The relationship between the value of U _dc0 and the volt-ampere characteristic curve is expressed as:

;

Combined with the expression of the volt-ampere characteristic curve and the expression of the droop characteristic curve, the actual operating point of the converter is obtained by paralleling the vertical (3), formula (4), and formula (7):

;

The calculation expression of active power steady-state error is:

;

From the formula, it can be concluded that the steady-state error of active power caused by line impedance can almost be expressed by the DC current error, and when the steady-state increases within the allowable range, the steady-state error decreases.

Further, the calculation of the steady-state error of the active power of the multi-terminal flexible DC network under adaptive control, to obtain the influence of the DC line impedance on the steady-state error of the active power, includes:

The expression of the volt-ampere characteristic curve and the expression of the droop characteristic curve of each converter in the simultaneous multi-terminal system are obtained to obtain the actual operating point of each converter, and then the active power steady-state error expression is calculated through the actual operating point of the converter, Finally, the influence of the DC line impedance on the steady-state error of active power is obtained: In the long-distance interconnected multi-terminal VSC-HVDC system, the influence of the DC line impedance cannot be ignored, and the steady-state error of the active power of the converter is mainly reflected in the DC current On the error.

Furthermore, in a multi-terminal network, the steady-state error of active power is calculated by determining the actual operating point of each converter. For an N-terminal system, the voltage at the central connection point is U _t , and the ith converter

The relationship between the DC voltage _Udci and the voltage at the central connection point of the device is expressed as:

;

In the formula, I _dci is the DC current flowing from the i-th converter to the central connection point, and R _it is the impedance between the i-th converter and the central connection point;

The DC current relationship of each converter is expressed as:

;

Simultaneous formula (13) and formula (14), the voltage at the central connection point is obtained as: ;

In the formula, Y _it is the admittance between the i-th converter and the central connection point;

The volt-ampere characteristic curves of each converter are described as follows:

;

In the formula, U _s1 ~ U _sN are the changes of the DC voltage of each converter;

The droop characteristic curve of each converter is described as:

;

Where U ^* _dc1 ~U ^* _dcN is the intercept of the characteristic curve, k ₁ ~k _N is the slope;

In this multi-terminal system, the relationship between _Udc0 and the voltage droop curve is expressed as:

;

U _dci represents the actual DC voltage of the i-th converter, and I _dci0 represents the DC reference current of the i-th converter;

The relationship of the DC current reference value of each converter is expressed as:

;

Simultaneous volt-ampere characteristic expression and droop characteristic expression combined with formula (18) and formula (19), the actual working point of the i-th converter is:

;

In the formula, I ^' _dci is the actual DC current of the i-th converter when it is working, U ^* _dci is the intercept of the droop characteristic curve of the i-th converter, Y _it is the distance between the i-th converter and the central connection point The admittance between , U _dc0 represents the normal working voltage of the entire HVDC network set by the dispatching center, _ki is the slope of the i-th converter droop characteristic curve, and I _dci0 represents the DC reference current of the i-th converter;

;

where U _dci represents the actual DC voltage of the i-th converter, I _dci0 represents the DC reference current of the i-th converter, k _i is the slope of the droop characteristic curve of the i-th converter, and U _dc0 represents the dispatching center The normal operating voltage of the entire HVDC network is set;

The calculation expression of converter active power steady-state error ΔP _i is:

;

where P _i is the active power of the i-th converter, U ^* _dci is the intercept of the droop characteristic curve of the i-th converter, Y _it is the admittance between the i-th converter and the central connection point , _Udc0 represents the normal working voltage of the entire HVDC network set by the dispatch center, _ki is the slope of the droop characteristic curve of the ith converter, and _Idci0 represents the DC reference current of the ith converter;

;

where ΔPi is the active power steady-state error of the i-th converter, U ^* _dci is the intercept of the droop characteristic curve of the i-th converter, Y _it is the distance between the i-th converter and the central connection point Admittance, _Udc0 represents the normal operating voltage of the entire HVDC network set by the dispatch center, _ki is the slope of the droop characteristic curve of the ith converter, and _Idci0 represents the DC reference current of the ith converter.

Further, the step is based on the relationship between the DC current error and the active power steady-state error and the influence of the DC line impedance on the active power steady-state error, shifting the droop characteristic curve of the converter to the volt-ampere characteristic curve The point of intersection of the curve with the reference value of the DC current so that the actual DC current of each converter always corresponds to the reference value, including:

Based on the relationship between the DC current error and the steady-state error of active power and the influence of the DC line impedance on the steady-state error of active power, the steady-state error of active power is reduced without changing the slope k of the voltage droop control curve. state error:

The DC current reference value _Idci0 of the ith converter is expressed as:

;

In the formula, U ^* _dci is the intercept of the i-th converter droop characteristic curve, U _dc0 is the normal working voltage of the entire HVDC network set by the dispatching center, k _i is the slope of the i-th converter droop characteristic curve, I _dci0 represents the DC reference current of the i-th converter;

Translate the droop characteristic curve of each converter so that the curve passes through the intersection point of the volt-ampere characteristic curve and the corresponding DC current reference value to obtain the final position of the droop characteristic curve. The droop curve of each converter is expressed as:

;

where Y _it is the admittance between the i-th converter and the central connection point, _ki is the slope of the droop characteristic curve of the i-th converter, I _dci0 is the DC reference current of the i-th converter, U _dci represents the actual DC voltage of the i-th converter, I _dci represents the changed DC current of the i-th converter, _{and U'si} ^is the new DC voltage of the converter i relative to the change of I _dci .

A flexible DC power grid adaptive control device, comprising:

The first steady-state error calculation module is used to calculate the steady-state error of the active power of the flexible DC network at both ends under adaptive control, and obtain the relationship between the DC current error and the active power steady-state error;

The second steady-state error calculation module is used to calculate the steady-state error of the active power of the multi-terminal flexible DC network under adaptive control, and obtain the influence of the DC line impedance on the steady-state error of the active power;

an adaptive control module, configured to translate the droop characteristic curve of the converter to volt-amperes based on the relationship between the DC current error and the steady-state error of active power and the influence of the DC link impedance on the steady-state error of active power The point of intersection of the characteristic curve and the reference value of the DC current, so that the actual DC current of each converter is always consistent with the reference value.

Further, the first steady-state error calculation module is specifically used for

The volt-ampere characteristic curve expressions and droop characteristic curve expressions of the two-end flexible DC grid converters A and B under simultaneous adaptive control, the intersection point is obtained as the actual operating point of the converter, and then through the converter's Calculate the active power steady-state error expression at the actual operating point, and finally analyze the active power steady-state error expression to obtain the relationship between the DC current error and the active power steady-state error: the active power steady-state error caused by the line impedance is determined by the DC current error , and when the slope k of the voltage droop control curve increases within the allowable range, the steady-state error decreases.

Further, the second steady-state error calculation module is specifically used for

The expression of the volt-ampere characteristic curve and the expression of the droop characteristic curve of each converter in the simultaneous multi-terminal system are obtained to obtain the actual operating point of each converter, and then the active power steady-state error expression is calculated through the actual operating point of the converter, Finally, the influence of the DC line impedance on the steady-state error of active power is obtained: In the long-distance interconnected multi-terminal VSC-HVDC system, the influence of the DC line impedance cannot be ignored, and the steady-state error of the active power of the converter is mainly reflected in the DC current On the error.

A flexible direct current grid adaptive control system includes a memory, a processor, and a computer program stored on the memory and operable on the processor. When the processor executes the computer program, the above flexible direct current grid adaptive control method is realized.

The invention combines the advantages of voltage droop control and master/slave control not relying on communication, stress averaging and active power distribution of each converter, and achieves a significant reduction in network stability without changing the slope of the droop characteristic curve. state error, and the dynamic performance of the network will not deteriorate.

Description of drawings

Figure 1 is the control scheme of the converter C;

Figure 2 is the main circuit of the system at both ends;

(a) in Fig. 3 is a broken line diagram of power flow from converter A to converter B under ideal operating conditions, and (b) in Fig. 3 is a line diagram of power flow flowing from converter A to converter B under actual operating conditions line chart of

Figure 4 is a simplified circuit diagram of a multi-terminal HVDC network;

Fig. 5 is a droop characteristic curve of the converter C after using the improved adaptive control method of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

An embodiment of the present invention provides an adaptive control method for a flexible direct current grid; the steps are as follows:

Step (1): Calculate the steady-state error of the active power of the flexible DC network at both ends under adaptive control, and analyze the relationship between the DC current error and the active power steady-state error: the active power steady-state error caused by the line impedance is determined by the DC current Error, and when the slope k of the voltage droop control curve increases within the allowable range, the steady-state error decreases.

The traditional adaptive control method is more suitable when the influence of transmission line impedance is ignored, but when the transmission line is long enough, the operating point of each converter will change, and the impedance of the transmission line cannot be ignored at this time.

Taking a two-terminal VSC-HVDC system as an example, the control scheme of the converter is shown in Figure 1, and the main circuit of the two-terminal system is shown in Figure 2. To calculate the steady-state error of active power, it is necessary to determine the actual operating point P of the two converters _A (I ^' _dc , U _dca ) and P _B (I ^' _dc , U _dcb ), I ^' _dc is the actual DC current, U _dca and U _dcb are the actual working voltages of converter A and converter B respectively. The actual working point of the converter is the intersection of the volt-ampere characteristic curve and the droop characteristic curve, where the expression of the droop characteristic curve is:

;

In the formula, k is the slope of the voltage droop control, I _dc represents the changing DC current, U _s represents the change of the sending end DC voltage relative to I _dc , U _r represents the change of the receiving end DC voltage relative to I _dc , U ^* _dca and U ^* _dcb denote the intercept of the above curve.

_Udc0 represents the normal working voltage of the entire HVDC network set by the dispatch center, and the relationship between its value and the voltage droop curve is expressed as:

;

(b) in Figure 3 is a line diagram of the power flow flowing from converter A to converter B under actual operating conditions, and the DC current reference value I _dc0 is the point P ₀ in (b) in Figure 3 (P ₀ point is the reference operating point of the converter):

;

The volt-ampere characteristic expression is:

;

In the formula, _Udca and _Udcb represent the actual DC voltages of converter A and converter B, and R ₀ is the resistance between converter A and converter B.

The relationship between the value of U _dc0 and the volt-ampere characteristic curve is expressed as:

;

Combining the volt-ampere characteristic expression and the droop characteristic expression, the parallel vertical type (3), formula (4), and formula (7) get the actual working point of the converter as:

;

The calculation expression of active power steady-state error is:

;

From the formula, it can be concluded that the active power error caused by the line impedance can almost be expressed by the steady-state error of the DC current, and when the slope k increases within the allowable range, the steady-state error decreases.

Step (2): Calculate the steady-state error of the active power of the multi-terminal flexible DC network under adaptive control, and reveal the influence of the DC line impedance on the steady-state error of the active power: In the long-distance interconnected multi-terminal VSC-HVDC system, the line impedance The impact cannot be ignored. Some of the actual active power of the converter increase, some decrease, and the steady-state error of the active power of the converter is mainly reflected in the error of the DC current.

Similar to step (1), in a multi-terminal network, the steady-state error of active power can also be calculated by determining the actual operating point of each converter. For an N-terminal system, its simplified circuit diagram is shown in Fig. 4, the voltage at the central connection point is U _t , and the relationship between the DC voltage _Udci of the i-th converter and the voltage at the central connection point is expressed as:

;

In the formula, I _dci is the DC current flowing from the i-th converter to the central connection point, and R _it is the impedance between the i-th converter and the central connection point;

The DC current relationship of each converter is expressed as:

;

Simultaneous formula (13) and formula (14), the voltage at the central connection point is obtained as:

;

where Y _it is the admittance between the i-th converter flow and the central connection point;

The volt-ampere characteristic curves of each converter are described as follows:

;

In the formula, U _s1 ~ U _sN are the changes of the DC voltage of each converter;

The droop characteristic curve of each converter is described as:

;

Where U ^* _dc1 ~U ^* _dcN is the intercept of the characteristic curve, k ₁ ~k _N is the slope;

In this multi-terminal system, the relationship between _Udc0 and the voltage droop curve is expressed as:

;

_Udci represents the actual DC voltage of the i-th converter, and _Idci0 represents the DC reference current of the i-th converter.

The relationship of the DC current reference value of each converter is expressed as:

;

Simultaneous volt-ampere characteristic expression and droop characteristic expression combined with formula (43) and formula (44), the actual working point of each converter is:

;

In the formula, I ^' _dci is the actual DC current of the i-th converter when it is working, U ^* _dci is the intercept of the droop characteristic curve of the i-th converter, Y _it is the distance between the i-th converter and the central connection point The admittance between , U _dc0 represents the normal working voltage of the entire HVDC network set by the dispatching center, _ki is the slope of the i-th converter droop characteristic curve, and I _dci0 represents the DC reference current of the i-th converter;

;

where U _dci represents the actual DC voltage of the i-th converter, I _dci0 represents the DC reference current of the i-th converter, k _i is the slope of the droop characteristic curve of the i-th converter, and U _dc0 represents the dispatching center The normal operating voltage of the entire HVDC network is set;

The calculation expression of converter active power steady-state error ΔP _i is:

;

where P _i is the active power of the i-th converter, U ^* _dci is the intercept of the droop characteristic curve of the i-th converter, Y _it is the admittance between the i-th converter and the central connection point , _Udc0 represents the normal working voltage of the entire HVDC network set by the dispatch center, _ki is the slope of the droop characteristic curve of the ith converter, and _Idci0 represents the DC reference current of the ith converter;

;

where ΔP _i is the active power steady-state error of the i-th converter, U ^* _dci is the intercept of the droop characteristic curve of the i-th converter, Y _it is the distance between the i-th converter and the central connection point The admittance of , U _dc0 represents the normal working voltage of the entire HVDC network set by the dispatch center, _ki is the slope of the droop characteristic curve of the i-th converter, and I _dci0 represents the DC reference current of the i-th converter;

Table 1 shows the actual working points of each converter in a four-terminal network:

Table 1

It can be concluded from Table 1 that in the long-distance interconnected multi-terminal VSC-HVDC system, the influence of line impedance cannot be ignored. The actual active power of the converter increases in some cases and decreases in others, and the steady-state error of active power is mainly reflected in the error of DC current.

Step (3): An adaptive control method for steady-state error correction is proposed: the droop characteristic curve of the converter is translated to the intersection point of the volt-ampere characteristic curve and the DC current reference value, so that the actual DC current of each converter is always consistent with The reference value is the same.

Based on the analysis results of step (1) and step (2), this step proposes an improved adaptive control method, which reduces the steady-state error of active power without changing the slope k. The DC current reference value I _dci0 of the converter is expressed as:

;

The droop characteristic curve of each converter is shifted so that the curve passes through the intersection of the volt-ampere characteristic curve and the corresponding DC current reference value to obtain the final position of the droop characteristic curve. The droop characteristic curve of the nth converter c after using the improved adaptive control method is shown in Fig. 5 .

The droop curve of each converter can be expressed as:

;

where ^U'si is the new DC voltage of converter i relative to _Idci variation; this control method can effectively eliminate the steady-state error of active power, because the actual DC current of each converter is always consistent _with the reference value .

An embodiment of the present invention provides an adaptive control method for a flexible DC power grid, which combines the advantages of voltage droop control and master/slave control not relying on communication, stress averaging of each converter and accurate active power distribution, without changing In the case of the slope of the drooping characteristic curve, the steady-state error of the network is significantly reduced, and the dynamic performance of the network will not deteriorate.

An embodiment of the present invention also provides an adaptive control device for a flexible direct current grid, including:

The first steady-state error calculation module is used to calculate the steady-state error of the active power of the flexible DC network at both ends under adaptive control, and obtain the relationship between the DC current error and the active power steady-state error;

The second steady-state error calculation module is used to calculate the steady-state error of the active power of the multi-terminal flexible DC network under adaptive control, and obtain the influence of the DC line impedance on the steady-state error of the active power;

an adaptive control module, configured to translate the droop characteristic curve of the converter to volt-amperes based on the relationship between the DC current error and the steady-state error of active power and the influence of the DC link impedance on the steady-state error of active power The point of intersection of the characteristic curve and the reference value of the DC current, so that the actual DC current of each converter is always consistent with the reference value.

Another embodiment of the present invention provides an adaptive control system for a flexible direct current grid, including: a computer-readable storage medium and a processor;

The computer-readable storage medium is used to store executable instructions;

The processor is configured to read the executable instructions stored in the computer-readable storage medium, and execute the adaptive control method for the flexible direct current grid described in the first aspect.

Another embodiment of the present invention provides a non-transitory computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the adaptive control method for the flexible direct current grid described in the first aspect is implemented.

Those skilled in the art should understand that the embodiments of the present application may be provided as methods, systems, or computer program products. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) having computer-usable program code embodied therein.

The present application is described with reference to flowcharts and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each procedure and/or block in the flowchart and/or block diagram, and combinations of procedures and/or blocks in the flowchart and/or block diagram can be realized by computer program instructions. These computer program instructions may be provided to a general purpose computer, special purpose computer, embedded processor, or processor of other programmable data processing equipment to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing equipment produce a Means for realizing the functions specified in one or more steps of the flowchart and/or one or more blocks of the block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to operate in a specific manner, such that the instructions stored in the computer-readable memory produce an article of manufacture comprising instruction means, the instructions The device realizes the function specified in one or more procedures of the flowchart and/or one or more blocks of the block diagram.

These computer program instructions can also be loaded onto a computer or other programmable data processing device, causing a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process, thereby The instructions provide steps for implementing the functions specified in the flow chart flow or flows and/or block diagram block or blocks.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall fall within the protection scope of the claims of the present invention.

Claims (5)

1. A flexible direct current power grid self-adaptive control method is characterized in that: the method comprises the following steps:

calculating steady-state errors of active power of the flexible direct current networks at two ends under self-adaptive control to obtain a relation between the direct current errors and the steady-state errors of the active power;

calculating the steady-state error of the active power of the multi-terminal flexible direct current network under the self-adaptive control to obtain the influence of the direct current line impedance on the steady-state error of the active power;

based on the relation between the DC current error and the active power steady-state error and the influence of the DC line impedance on the active power steady-state error, translating a sagging characteristic curve of the converters to an intersection point of the volt-ampere characteristic curve and a DC current reference value, so that the actual DC current of each converter is consistent with the reference value all the time;

calculating steady-state errors of active power of the flexible direct current networks at two ends under self-adaptive control to obtain a relation between the direct current errors and the steady-state errors of the active power, wherein the calculating steady-state errors comprise the following steps:

the method comprises the steps of obtaining an intersection point which is an actual working point of a converter through volt-ampere characteristic curve expression and sagging characteristic curve expression of flexible direct current grid converters A and B at two ends under simultaneous self-adaptive control, calculating an active power steady-state error expression through the actual working point of the converter, and finally analyzing the active power steady-state error expression to obtain the relation between a direct current error and an active power steady-state error: the active power steady-state error caused by the line impedance is represented by a direct current error, and decreases when the slope k of the voltage droop control curve increases within an allowable range;

calculating the steady-state error of the active power of the multi-terminal flexible direct current network under the self-adaptive control to obtain the influence of the direct current line impedance on the steady-state error of the active power, wherein the method comprises the following steps:

the method comprises the steps of obtaining the actual working points of all converters by volt-ampere characteristic curve expression and sagging characteristic curve expression of all converters of a simultaneous multi-terminal system, calculating an active power steady-state error expression through the actual working points of the converters, and finally obtaining the influence of direct current line impedance on the active power steady-state error: in a long-distance interconnected multi-terminal VSC-HVDC system, the influence of the impedance of a direct current line cannot be ignored, and the steady-state error of the active power of the converter is reflected on the direct current error;

in a multi-terminal network, the steady-state error of active power is calculated by determining the actual operating point of each converter, and for an N-terminal system, the voltage at the central connection point is U _t I-th converter DC voltage

U _dci The relationship with the voltage at the center junction is expressed as:

；

wherein I is _dci For the direct current of the ith converter flowing to the central connection point, R _it Is the impedance between the ith current transformer flow and the center connection point;

the dc current relationship of each converter is expressed as:

；

combining (13) with (14), solving for the voltage at the center junction to be:；

wherein Y is _it Is admittance between the ith converter and the central connection point;

the volt-ampere characteristic of each converter is described as follows:

；

in U _s1 ~U _sN The direct current voltage of each converter is changed;

the sag characteristic curves of the converters are described as follows:

；

wherein U is ^* _dc1 ~U ^* _dcN Is the intercept, k, of the characteristic curve ₁ ~k _N Is the slope;

in this multi-terminal system, U _dc0 The relationship with the voltage sag curve is expressed as:

；

U _dci representing the actual DC voltage of the ith converter, I _dci0 Representing the direct current reference current of the ith converter;

the relationship between the DC reference values of the converters is expressed as:

；

the practical operating point of the ith converter is obtained by combining the simultaneous volt-ampere characteristic expression and the sagging characteristic expression and combining the expression (18) and the expression (19):

；

in which I ^’ _dci For the actual DC current of the ith converter in operation, U ^* _dci Is the intercept of the sagging characteristic curve of the ith converter, Y _it U is admittance between the ith converter and the central connection point _dc0 Representing the normal operating voltage, k, of the entire HVDC network set by the dispatch center _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Representing the direct current reference current of the ith converter;

；

u in _dci Representing the actual DC voltage of the ith converter, I _dci0 Representing the direct reference current, k, of the ith converter _i For the slope of the sagging characteristic curve of the ith converter, U _dc0 Representing the normal operating voltage of the entire HVDC network set by the dispatch center;

active power steady state error ΔP of converter _i The computational expression is:

；

p in the formula _i Is the active power of the ith converter, U ^* _dci Is the intercept of the sagging characteristic curve of the ith converter, Y _it U is admittance between the ith converter and the central connection point _dc0 Representing the normal operating voltage, k, of the entire HVDC network set by the dispatch center _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Representing the direct current reference current of the ith converter;

；

in DeltaP _i Is the steady state error of the active power of the ith converter, U ^* _dci Is the intercept of the sagging characteristic curve of the ith converter, Y _it U is admittance between the ith converter and the central connection point _dc0 Representing the normal operating voltage, k, of the entire HVDC network set by the dispatch center _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Representing the dc reference current of the i-th converter.

2. The flexible direct current power grid adaptive control method according to claim 1, wherein:

in a two-terminal VSC-HVDC system, calculating the steady state error of the active power requires determining the actual operating point of the two converters: p (P) _A (I ^’ _dc ,U _dca ) And P _B (I ^’ _dc ,U _dcb ) Wherein I ^’ _dc For actual DC current, U _dca And U _dcb The actual working voltages of the current transformer A and the current transformer B are respectively, the actual working point of the current transformer is the intersection point of a volt-ampere characteristic curve and a sagging characteristic curve, and the sagging characteristic curve has the expression:

；

wherein k is the slope of the voltage sag control curve, I _dc Indicating varying DC current, U _s Indicating the DC voltage at the transmitting end relative to I _dc Variation of U _r Representing the direct current voltage at the receiving end relative to I _dc Variation of U ^* _dca And U ^* _dcb Represents the intercept of the curve;

U _dc0 representing the normal operating voltage of the whole HVDC network set by the dispatch center, the relation of the value and the voltage sag characteristic curve is expressed as follows:

；

DC reference value I _dc0 Is that the converter works at the reference work P ₀ Current at point:

；

the voltammetric characteristic curve expression is:

；

u in _dca And U _dcb Representing the actual DC voltages of converter A and converter B, R ₀ The resistor is between the current transformer A and the current transformer B;

U _dc0 the relation of the values of (2) to the voltammetric characteristic is expressed as:

；

combining the volt-ampere characteristic curve expression and the sagging characteristic curve expression, and obtaining the actual working points of the converter by the vertical type (3), the formula (4) and the formula (7) in parallel is as follows:

；

the active power steady state error calculation expression is:

。

3. the flexible direct current power grid adaptive control method according to claim 1, wherein: based on the relation between the DC current error and the active power steady-state error and the influence of the DC line impedance on the active power steady-state error, translating the sagging characteristic curve of the converters to the intersection point of the volt-ampere characteristic curve and the DC current reference value, so that the actual DC current of each converter is consistent with the reference value all the time, and the method comprises the following steps:

based on the relationship between the DC current error and the active power steady state error and the effect of the DC line impedance on the active power steady state error, the steady state error of the active power is reduced without changing the slope k of the voltage droop control curve:

DC reference value I of the ith converter _dci0 Expressed as:

；

u in ^* _dci For the intercept of the sagging characteristic curve of the ith converter, U _dc0 Representing the normal operating voltage, k, of the entire HVDC network set by the dispatch center _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Representing the direct current reference current of the ith converter;

translating the sagging characteristic curve of each converter to enable the curve to pass through the intersection point of the volt-ampere characteristic curve and the corresponding direct current reference value, and obtaining the final position of the sagging characteristic curve, wherein the sagging curve of each converter is expressed as:

；

wherein Y is _it Is the admittance, k between the ith converter and the central connection point _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Indicating the direct reference current of the ith converter, U _dci Representing the actual DC voltage of the ith converter, I _dci DC current representing variation of ith converter, U ^’ _si Is the current transformer I relative to I _dci A new dc voltage that changes.

4. The utility model provides a flexible direct current electric wire netting self-adaptation controlling means which characterized in that includes:

the first steady-state error calculation module is used for calculating steady-state errors of active power of the flexible direct current networks at two ends under self-adaptive control to obtain a relation between the direct current errors and the steady-state errors of the active power;

the second steady-state error calculation module is used for calculating steady-state errors of active power of the multi-terminal flexible direct current network under self-adaptive control to obtain the influence of direct current line impedance on the steady-state errors of the active power;

the self-adaptive control module is used for translating the sagging characteristic curve of the current transformers to the intersection point of the volt-ampere characteristic curve and the direct current reference value based on the relation between the direct current error and the active power steady-state error and the influence of the direct current line impedance on the active power steady-state error, so that the actual direct current of each current transformer is consistent with the reference value all the time;

the first steady-state error calculation module is specifically used for obtaining the intersection point, namely the actual working point of the converter, by combining the volt-ampere characteristic curve expression and the sagging characteristic curve expression of the flexible direct-current power grid converters A and B under the self-adaptive control, calculating the steady-state error expression of the active power by the actual working point of the converter, and finally analyzing the steady-state error expression of the active power to obtain the relation between the direct-current error and the steady-state error of the active power: the active power steady-state error caused by the line impedance is represented by a direct current error, and decreases when the slope k of the voltage droop control curve increases within an allowable range;

the second steady-state error calculation module is specifically used for solving the actual working points of the converters by combining the volt-ampere characteristic curve expression and the sagging characteristic curve expression of each converter of the multi-terminal system, calculating the steady-state error expression of the active power by the actual working points of the converters, and finally obtaining the influence of the impedance of the direct-current circuit on the steady-state error of the active power: in a long-distance interconnected multi-terminal VSC-HVDC system, the influence of the impedance of a direct current line cannot be ignored, and the steady-state error of the active power of the converter is reflected on the direct current error;

in a multi-terminal network, the steady-state error of active power is calculated by determining the actual operating point of each converter, for an N-terminal systemThe voltage of the core connection point is U _t I-th converter DC voltage

U _dci The relationship with the voltage at the center junction is expressed as:

；

wherein I is _dci For the direct current of the ith converter flowing to the central connection point, R _it Is the impedance between the ith current transformer flow and the center connection point;

the dc current relationship of each converter is expressed as:

；

combining (13) with (14), solving for the voltage at the center junction to be:；

wherein Y is _it Is admittance between the ith converter and the central connection point;

the volt-ampere characteristic of each converter is described as follows:

；

in U _s1 ~U _sN The direct current voltage of each converter is changed;

the sag characteristic curves of the converters are described as follows:

；

wherein U is ^* _dc1 ~U ^* _dcN Is the intercept, k, of the characteristic curve ₁ ~k _N Is the slope;

in this multi-terminal system, U _dc0 The relationship with the voltage sag curve is expressed as:

；

U _dci representing the actual DC voltage of the ith converter, I _dci0 Representing the direct current reference current of the ith converter;

the relationship between the DC reference values of the converters is expressed as:

；

the practical operating point of the ith converter is obtained by combining the simultaneous volt-ampere characteristic expression and the sagging characteristic expression and combining the expression (18) and the expression (19):

；

in which I ^’ _dci For the actual DC current of the ith converter in operation, U ^* _dci Is the intercept of the sagging characteristic curve of the ith converter, Y _it U is admittance between the ith converter and the central connection point _dc0 Representing the normal operating voltage, k, of the entire HVDC network set by the dispatch center _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Representing the direct current reference current of the ith converter;

；

u in _dci Representing the actual DC voltage of the ith converter, I _dci0 Representing the direct reference current, k, of the ith converter _i For the slope of the sagging characteristic curve of the ith converter, U _dc0 Representing the normal operating voltage of the entire HVDC network set by the dispatch center;

active power steady state error ΔP of converter _i The computational expression is:

；

p in the formula _i Is the active power of the ith converter, U ^* _dci Is the intercept of the sagging characteristic curve of the ith converter, Y _it U is admittance between the ith converter and the central connection point _dc0 Representing the normal operating voltage, k, of the entire HVDC network set by the dispatch center _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Representing the direct current reference current of the ith converter;

；

in DeltaP _i Is the steady state error of the active power of the ith converter, U ^* _dci Is the intercept of the sagging characteristic curve of the ith converter, Y _it U is admittance between the ith converter and the central connection point _dc0 Representing the normal operating voltage, k, of the entire HVDC network set by the dispatch center _i For the slope of the sagging characteristic curve of the ith converter, I _dci0 Representing the dc reference current of the i-th converter.

5. A flexible direct current electric wire netting self-adaptation control system, its characterized in that: a computer program comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the flexible direct current network adaptive control method according to any one of claims 1-3 when the computer program is executed by the processor.