CN113901756B - Converter synchronous stability margin evaluation method, electronic device and storage medium - Google Patents
Converter synchronous stability margin evaluation method, electronic device and storage medium Download PDFInfo
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Abstract
The invention provides a converter synchronous stability margin evaluation method, electronic equipment and a storage medium. The method comprises the following steps: the method comprises the steps of defining a synchronous stability static margin index of a grid-connected converter, calculating a synchronous stability static margin value of each grid-connected converter, determining a synchronous stability static margin value of a multi-grid-connected converter system formed by each grid-connected converter, and carrying out quantitative synchronous stability evaluation on the multi-grid-connected converter system according to the synchronous stability static margin value of the multi-grid-connected converter system, wherein the larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the synchronous stability of the multi-grid-connected converter system is. And defining and quantizing the synchronous stability static margin value of the grid-connected converter, and intuitively reflecting the specific information of the synchronous stability static margin. The method is suitable for various operating environments of the power system and high in universality. The method is suitable for a multi-converter system, and can calculate the influence of the output current of the converter and the active and reactive components on the synchronization stability under the actual working condition.
Description
Technical Field
The present disclosure relates to the field of power system technologies, and in particular, to a converter synchronization stability margin evaluation method, an electronic device, and a storage medium.
Background
In modern power systems, a power electronic grid-connected converter is widely used as a grid-connected interface of equipment such as a new energy power generation system, a flexible direct current transmission system, an energy storage system, a static var generator and the like. In order to realize stable power exchange between the grid-connected converter and the power grid, frequency synchronization between the grid-connected converter and the power grid needs to be ensured, and the property is called synchronization stability. The basic control methods of the grid-connected converter can be divided into two categories, namely a current control type and a voltage control type, wherein the current control type grid-connected converter is most widely applied and is generally synchronized with a power grid by a phase-locked loop. In order to ensure reliable operation of the grid, grid operators need to know the synchronous and stable static tolerance value of the grid-connected converter. However, for a new power system in the future, in terms of the synchronous stability of the grid-connected converter, a simple and effective static margin evaluation index and a method which can be used for engineering are lacked at present, and particularly for a multi-grid-connected converter system.
In the related art, whether a single grid-connected converter system is synchronous and stable or not can only be judged, and specific information of synchronous and stable static margin cannot be provided, and the method cannot be applied to a multi-grid-connected converter system.
Disclosure of Invention
The embodiment of the invention provides a converter synchronous stability margin evaluation method, electronic equipment and a storage medium, aiming at solving the problems existing in the special conditions.
In order to solve the technical problem, the invention is realized as follows:
in a first aspect, an embodiment of the present invention provides a method for evaluating a synchronous stability margin of a converter, where the method includes:
the synchronous stability static margin index of the grid-connected converter is defined as follows:
in the formula, λ k For synchronous stabilization of the static margin value, Δ u, of the grid-connected converter kq For the impedance drop, U, produced by the current output by the grid-connected converter on the grid impedance g Is the grid voltage amplitude;
calculating the synchronous stable static margin value of each grid-connected converter;
determining the synchronous stable static margin value of a multi-grid-connected converter system consisting of all the grid-connected converters according to the synchronous stable static margin value of each grid-connected converter;
and quantitatively evaluating the synchronous stability of the multi-grid-connected converter system according to the synchronous stability static margin value of the multi-grid-connected converter system, wherein the larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the synchronous stability of the multi-grid-connected converter system is.
Optionally, the obtaining process of the impedance voltage drop generated by the grid-connected converter output current on the grid impedance includes:
under the condition that the power system normally operates, calculating the machine end voltage phasor of the grid-connected converter according to the angle difference between the output angle of the phase-locked loop and the voltage phase angle of a power grid, the output current phasor of the grid-connected converter, the impedance of the power grid, the current collection network impedance, the leakage impedance of the transformer and the voltage amplitude of the power grid;
decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and a quadrature-axis component in a phase-locked loop coordinate system to obtain a quadrature-axis component of the terminal voltage component of the grid-connected converter;
and determining the impedance voltage drop of the output current of the grid-connected converter on the power grid impedance according to the quadrature axis component of the voltage phasor at the machine end of the grid-connected converter.
Optionally, the calculation formula of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula (I), the compound is shown in the specification,
terminal voltage component, U, of the grid-connected converter k g For the grid voltage amplitude, delta j ,δ k Is the angle difference, Z, between the phase angle of the output of the phase-locked loop and the phase angle of the mains voltage g As impedance of the grid, Z i Is the collector network impedance, Z kt Is the leakage impedance of the terminal transformer of the grid-connected inverter k,
is the output current phasor of the grid-connected converter,
to make the current phasor
And transforming a phase-locked loop coordinate system of the grid-connected converter j into a phase-locked loop coordinate system of a grid-connected converter k, wherein N is the total number of converters in the multi-grid-connected converter system, and N is the number of converters on a branch where the kth converter is located.
Optionally, the calculation formula of the quadrature axis component of the machine-side voltage phasor of the grid-connected converter is as follows:
in the formula u kq The quadrature axis component of the machine end voltage phasor of the grid-connected converter is represented by Im, the imaginary part is taken for operation,
and the impedance voltage drop generated on the grid impedance for the output current of the grid-connected converter.
Optionally, in the case of a power system fault, calculating a terminal voltage magnitude of the grid-connected converter according to an output current phasor of the grid-connected converter, a grid impedance, a collection network impedance, a transformer leakage impedance and a grid voltage magnitude;
decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and a quadrature-axis component in a phase-locked loop coordinate system, thereby obtaining the quadrature-axis component of the terminal voltage component of the grid-connected converter;
determining impedance voltage drop generated by output current of the grid-connected converter on the power grid impedance according to quadrature axis component of the voltage phasor at the machine end of the grid-connected converter;
the approximate calculation formula of the quadrature axis component of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula u kq The quadrature axis component of the machine end voltage phasor of the grid-connected converter is represented by Im, the imaginary part is taken for operation,
and the impedance voltage drop generated on the grid impedance for the output current of the grid-connected converter.
Optionally, the minimum value of the synchronous stable static margin values of the grid-connected converters is used as the synchronous stable static margin value of the multi-grid-connected converter system composed of the grid-connected converters.
Optionally, the evaluating the synchronous stability of the multi-grid-connected converter system according to the synchronous stable static margin value of the multi-grid-connected converter system includes:
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 1, the system has the maximum synchronous stability margin;
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 0, the synchronous stability margin of the system is zero, namely the system is in a critical stable state;
if the synchronous stability static tolerance value of the multi-grid-connected converter system is smaller than 0, the system does not have a balance point, and the system cannot keep synchronous stability.
A second aspect of the embodiments of the present invention provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, where the computer program is executed by the processor, so as to implement the method steps set forth in the first aspect of the embodiments of the present invention.
A third aspect of the embodiments of the present invention provides a computer-readable storage medium, on which a computer program is stored, which, when executed by a processor, implements the method as set forth in the first aspect of the embodiments of the present invention.
The embodiment of the invention has the following advantages: according to the method and the device, the synchronous stability static margin index of each grid-connected converter is defined through the impedance voltage drop and the grid voltage amplitude of the output current of each grid-connected converter on the grid impedance, the synchronous stability static margin value of a multi-grid-connected converter system composed of each grid-connected converter is determined according to the synchronous stability static margin value of each grid-connected converter, and then the synchronous stability of the multi-grid-connected converter system can be evaluated according to the synchronous stability static margin value of the multi-grid-connected converter system. The larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the synchronous stability of the multi-grid-connected converter system is. Therefore, the method and the device not only realize the judgment of whether the multi-grid-connected converter system is synchronous and stable, but also can quantitatively evaluate the stability of the system according to the synchronous and stable static tolerance value of the multi-grid-connected converter system compared with the prior art; for example, the specific difference and the strength relation of the synchronous stability between the multi-grid-connected converter systems in the strong power grid environment and the weak power grid environment can be evaluated quantitatively, and the specific numerical difference of the synchronous stability between the multi-grid-connected converter systems belonging to the strong power grid environment or the weak power grid environment can be evaluated.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a flowchart illustrating steps of a method for evaluating a synchronous stability margin of a converter according to an embodiment of the present invention;
FIG. 2 is a system circuit diagram and a typical control block diagram of a grid-connected inverter with multiple current control types according to an embodiment of the present invention;
FIG. 3 is a schematic view of a wind farm topology in an embodiment of the present invention;
FIG. 4 is a schematic diagram of a stability margin calculation result of a wind farm in an embodiment of the invention;
FIG. 5 is a schematic diagram of stability margin simulation of a wind farm in an embodiment of the invention;
FIG. 6 is a schematic diagram of functional modules of a synchronous stability margin evaluation system of a converter according to an embodiment of the present invention;
fig. 7 is a functional block diagram of an electronic device according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
In the related art, for the current control type grid-connected converter, under the background of a strong power grid, the synchronization stability of the current control type grid-connected converter is strong. However, in a weak grid background (especially when grid characteristics are weakened during grid failure), the problem of synchronization stability of the current control type grid-connected converter is very serious. The strength of the power grid is usually judged based on a Short Circuit Ratio (SCR) index, and the short circuit ratio index is a general index, which can only take the rated output current of the converter under the short circuit working condition of the power grid into consideration, and cannot take the influence of the output current and the current components (namely active and reactive current components) under the actual working condition into consideration. The short circuit ratio is characterized by dividing the short circuit capacity of the system by the capacity of the equipment, so when the short circuit ratio is large, the equipment is connected into a strong system, and the switching of the equipment has little influence on the system. That is, the larger the value of the short-circuit ratio, the stronger the corresponding grid strength, and the stronger the corresponding synchronization stability. Namely, the current power grid can only be distinguished as a strong power grid or a weak power grid by using the short-circuit ratio index, so that the synchronous stability of the converter is reflected by using the positive correlation of the power grid strength and the synchronous stability. And the specific numerical difference of the synchronization stability of the multi-grid-connected converter system in the power grid environment cannot be specifically judged, so that the quantitative analysis of the synchronization stability of the multi-grid-connected converter system cannot be realized.
On the other hand, the static stability margin index of the grid-connected converter is very important in the system planning stage, and for example, the index can provide a reference for the establishment of a grid connection scheme. In the actual operation stage, the index has important significance for offline stability verification or online stability evaluation. In addition, the stability margin index can also provide important reference for making and revising the grid guide rule specification and controlling the stability of the grid-connected converter equipment. From the above engineering point of view, a simple and effective stability margin index and a convenient and practical evaluation method are very necessary.
The inventor finds that the existing means can only judge the synchronous stability static margin of a single grid-connected converter system, cannot give specific information of the synchronous stability static margin, and cannot be applied to a multi-grid-connected converter system. Based on this, the core technical idea of the application is proposed: and defining the static margin index of the synchronous stability of the converter according to the relative ratio of the impedance voltage drop contained in the cross-axis component of the voltage at the converter end to the voltage of the power grid. And then the synchronous stable static margin value of a multi-grid-connected converter system consisting of a plurality of grid-connected converters is determined based on the synchronous stable static margin of the grid-connected converters, and finally the synchronous stability evaluation of the multi-grid-connected converter system under each power grid environment is realized.
The embodiment of the invention provides a method for evaluating a synchronous stability margin of a converter, and referring to fig. 1, fig. 1 shows a flow chart of steps of the method for evaluating the synchronous stability margin of the converter in the embodiment of the application, and the method comprises the following steps:
step S101:
the synchronous stability static margin index of the grid-connected converter is defined as follows:
in the formula, λ k For synchronous stabilization of the static margin value, Δ u, of the grid-connected converter kq For the impedance drop, U, produced by the current output by the grid-connected converter on the grid impedance g Is the grid voltage amplitude;
taking fig. 2 as an example, fig. 2 shows a system circuit diagram and a typical control block diagram of a grid-connected converter with a plurality of current control types. The system is assumed to contain N grid-connected converters, wherein N are located on the illustrated branches, and the rest N-N are located in other branches or other stations. If the synchronous stable static tolerance value of any grid-connected converter is required to be calculated, the impedance voltage drop delta u caused by impedance in the power system needs to be calculated kq 。
The method for determining the impedance voltage drop generated by the output current of any one grid-connected converter in the N grid-connected converters on the grid impedance specifically comprises the following steps:
step S101-1: under the condition that the power system normally operates, the machine end voltage phasor of the grid-connected converter is calculated according to the angle difference between the output angle of the phase-locked loop and the voltage phase angle of the power grid, the output current phasor of the grid-connected converter, the impedance of the power grid, the current collection network impedance, the leakage impedance of the transformer and the voltage amplitude of the power grid.
Step S101-2: and decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and a quadrature-axis component in a phase-locked loop coordinate system, thereby obtaining the quadrature-axis component of the terminal voltage component of the grid-connected converter.
Step S101-3: and determining the impedance voltage drop of the output current of the grid-connected converter on the power grid impedance according to the quadrature axis component of the voltage phasor at the machine end of the grid-connected converter.
In the present embodiment, taking the system circuit diagram of fig. 2 as an example, for any grid-connected converter k,
neglecting the electromagnetic transient state of the circuit, under the quasi-steady state condition, the terminal voltage phasor of any grid-connected converter k is not difficult to obtain according to the circuit equation
The symbols in the formula have the following meanings:
in the formula (I), the compound is shown in the specification,
terminal voltage component, U, of the grid-connected converter k g To the grid voltage amplitude, δ j ,δ k Is the angle difference between the phase-locked loop output angle and the grid voltage phase angle, Z g As impedance of the grid, Z i Is the collector network impedance, Z kt Is the leakage impedance of the terminal transformer of the grid-connected inverter k,
is the output current phasor of the grid-connected converter,
to make the current phasor
Transformation of the phase-locked loop coordinate system by a grid-connected converter jIn a phase-locked loop coordinate system of a grid-connected converter k, N is the total number of converters in a multi-grid-connected converter system, and N is the number of converters on a branch where the kth converter is located.
According to the formula, the terminal voltage component of any grid-connected converter k can be calculated
Then, by mixing
The direct axis (d) and quadrature axis (q) components are decomposed in a phase-locked loop coordinate system of a grid-connected converter k, and the quadrature axis component can be obtained as
In the formula, im represents the operation of taking an imaginary part, the second term on the right side of the equal sign represents the total voltage drop of the output current of the grid-connected converter on the impedance of a power grid, the impedance of a collecting line and the leakage impedance of a transformer, namely the impedance voltage drop of a grid-connected converter k, and the term is abbreviated as delta u kq I.e. by
And the impedance voltage drop generated on the grid impedance for the output current of the grid-connected converter. Then there is u kq ＝-U g sinδ k +Δu kq . Synchronization requirement u of grid-connected converter and power grid kq =0, voltage drop Δ u due to impedance kq Presence of terminal voltage u kq The synchronous stability of the grid-connected converter is influenced to a certain degree. In particular, if Δ u kq If 0, then u kq Regarding delta k The curve of (1) is a standard sine curve, and the synchronous stabilization has the maximum static margin.
And S102, calculating synchronous stable static tolerance values of all grid-connected converters.
When the impedance voltage drop generated by the output current of each grid-connected converter on the grid impedance is calculatedΔu kq And then, calculating the synchronous stable static margin value of each grid-connected converter by combining the voltage amplitude of the power grid through a synchronous stable static margin value definition formula, thereby providing a corresponding data basis for determining the synchronous stable static margin value of the whole system.
And S103, determining the synchronous stable static margin value of the multi-grid-connected converter system consisting of the grid-connected converters according to the synchronous stable static margin value of each grid-connected converter.
And S104, evaluating the synchronous stability of the multi-grid-connected converter system according to the synchronous stability static margin value of the multi-grid-connected converter system, wherein the larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the synchronous stability of the multi-grid-connected converter system is.
In the embodiment, the converter synchronous stability static margin index is defined according to the relative ratio of the impedance voltage drop contained in the cross-axis component of the converter terminal voltage to the grid voltage, so that the converter synchronous stability static margin is quantized. According to the definition formula of the impedance voltage drop generated by the output current of the grid-connected converter on the power grid impedance, in order to realize the accurate calculation of the stability margin, the relative angle delta of the phase-locked loop needs to be known 1 ,δ 2 ,…,δ N Current output of grid-connected converter
Grid impedance Z g Collector network impedance and transformer leakage impedance Z 1 ,Z 2 ,…,Z N ,Z 1t ,Z 1t ,…,Z Nt And the amplitude of the grid voltage. The grid impedance and voltage can be calculated by off-line equivalence (such as Thevenin equivalence) or identified on-line, and the parameters of the collecting network impedance and the transformer leakage impedance can be provided by a station owner. Under the normal operation condition, the information of the relative angle of the phase-locked loop and the current output of the grid-connected converter can be acquired by the on-line collection of the integrated controller of the station, and accordingly, the synchronous stable static tolerance value of each grid-connected converter in the multi-grid-connected converter system can be calculated on line, and the synchronous stable static tolerance value of each grid-connected converter in the multi-grid-connected converter system can be calculatedThe synchronous stability evaluation of a multi-grid-connected converter system consisting of a plurality of grid-connected converters is realized, so that the method is suitable for the multi-converter system. Under the background of a strong power grid, the strength relation of the synchronization stability between the systems can be displayed more intuitively through the synchronous stability static margin value, namely the larger the synchronous stability static margin value is, the higher the system synchronization stability is. Compared with the traditional short-circuit ratio index, the index does not need to reversely deduce whether the power grid belongs to a strong power grid or a weak power grid based on the short-circuit ratio index, and the influence of the output current and the component on the synchronization stability under the actual working condition can be calculated.
In a possible embodiment, in case of a power system fault, calculating a terminal voltage magnitude of the grid-connected converter according to an output current phasor of the grid-connected converter, a grid impedance, a collection network impedance, a transformer leakage impedance and a grid voltage magnitude;
decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and a quadrature-axis component in a phase-locked loop coordinate system, thereby obtaining the quadrature-axis component of the terminal voltage component of the grid-connected converter;
determining impedance voltage drop generated by output current of the grid-connected converter on the power grid impedance according to quadrature axis component of the voltage phasor at the machine end of the grid-connected converter;
the approximate calculation formula of the quadrature axis component of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula u kq The quadrature axis component of the machine end voltage phasor of the grid-connected converter is represented by Im, the imaginary part is taken for operation,
and the impedance voltage drop generated on the grid impedance for the output current of the grid-connected converter.
In the embodiment, the synchronization stability of the grid-connected converter is still very important in case of power system failure, and the grid failure occursUnder the condition of the fault condition, in order to ensure the synchronous stability of the grid-connected converter during the grid fault, the synchronous stability margins of the system under different fault conditions, network parameters and current injection need to be evaluated in advance, and therefore off-line calculation and verification are generally needed. In an off-line mode, the accurate calculation of the stability margin needs to firstly solve the steady-state operating point of the grid-connected converter during the fault period so as to obtain the relative angle information of the phase-locked loop. However, the solution of the steady-state operating point is computationally expensive, wherein high-dimensional operations are involved, in order to avoid the high-dimensional operations. In this embodiment, a simplified impedance voltage drop calculation method is provided, and under a normal working condition, because the working conditions of each grid-connected converter are similar, the phase-locked loop angles of the grid-connected converters have similar values when a steady state is achieved. Therefore, the difference of the phase-locked loop angles of any two grid-connected converters is ignored, namely, the phase-locked loop angles are approximately regarded as delta j ≈δ k That is to say
Accordingly, the impedance drop in the stability margin indicator definition can be simplified to
In the case of a power grid fault, the calculation of the synchronous stable static margin value does not require the angle information of the known phase-locked loop, and other required information is easy to obtain (similar to the acquisition under the normal working condition). Therefore, for the offline application of the stability margin index, the approximate assumption of the angle difference of the phase-locked loop of the converter is provided, and the calculation of the stability margin index is simplified based on the approximate assumption.
In one possible embodiment, the minimum value of the synchronous stability static margin values of the grid-connected converters is used as the synchronous stability static margin value of the multi-grid-connected converter system composed of the grid-connected converters.
In the present embodiment, after the synchronous static margin value of each grid-connected converter is calculated, the synchronous static margin value of the grid-connected converter system composed of a plurality of grid-connected converters is set as the synchronous static margin value of the multi-grid-connected converter system based on the barrel effect of the system, that is, the grid-connected converter having the smallest synchronous static margin value in the system is the short plate of the synchronous stability margin of the whole system.
In a possible embodiment, the performing of the synchronous stability evaluation on the multi-grid-connected converter system according to the synchronous stability static margin value of the multi-grid-connected converter system comprises:
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 1, the system has the maximum synchronous stability margin;
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 0, the synchronous stability margin of the system is 0;
if the synchronous stability static tolerance value of the multi-grid-connected converter system is smaller than 0, the system does not have a balance point, and the system cannot keep synchronous stability;
the larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the stability of the multi-grid-connected converter system is.
In this embodiment, after the synchronization stability static margin value of the whole system is determined, the synchronization stability of the system is evaluated according to the synchronization stability static margin value of the system:
if lambda is equal to 1, the impedance voltage drop is zero, and the system has the maximum synchronous stability margin;
if lambda is equal to 0, the impedance voltage drop is equal to the power grid voltage, namely the power grid voltage information is just submerged by the impedance voltage drop, the synchronous stability margin of the system is zero, and the system does not have any anti-interference capability;
if λ is less than 0, it means that the impedance drop is greater than the grid voltage, i.e. u kq If there is no solution, i.e. the system does not have an equilibrium point, the system cannot keep the synchronization stable.
In practice, the static margin for the synchronization stability of the system is between 0 and 1, with greater margin for higher stability.
Based on the above method, taking an actual wind farm as an example, the scheme of the present application is explained again, and taking the wind farm topology and the length of the power collection line shown in fig. 3 as an example, where the line inductance is 1.05mH/km, the line resistance is 0.1153 Ω/km, and the per-unit value of the grid impedance is 0.02+ j0.12 pu (per-unit). The leakage impedance of the transformer at the end of the fan is 0.05/30 j0.05pu, the voltage level is 690V/35kV, and each fan outputs 0.6-j0.8 pu current according to the capacity of each fan. Furthermore, consider a grid voltage sag at two different depths, ug, dip =0.10pu,0.09pu, where Ug, dip represent the value after the grid voltage sag. The synchronous stable static margin value of each fan can be calculated by the following formula:
it is thus possible to determine the stability margin of the entire wind farm, consisting of
Given in the formula, where wpp Representing the stability margin of the entire wind farm.
Fig. 4 shows the stability margin calculation results for each wind turbine and the whole wind farm, where (a) and (b) are the results of the grid voltage dropping to 0.10pu and 0.09pu, respectively. It can be seen that at grid voltage drops, the stability margin of the wind farm is very low, approaching the critical condition of zero margin. The simulation results are shown in fig. 5, where the phase locked loop for fan No. 11 (WT 11) in fig. 5 (a) has the largest steady state angle, thus resulting in the smallest stability margin, consistent with the prediction of the results in fig. 4 (a). Therefore, WT11 becomes a short board of the entire wind farm synchronization stability margin. Looking at the layout of the wind farm in FIG. 3, WT11 may be considered the least synchronous-stable wind turbine, and therefore is most susceptible to synchronous instability. In fig. 4 (b), under more severe grid voltage drop, the stability margin predicted by the provided index is less than zero, which indicates that the system does not have a balance point, and therefore, the whole wind farm cannot keep synchronous stability. As shown in the simulation verification in fig. 5 (b), after the grid voltage drops at 1s, the wind farm is subjected to synchronous instability, and the validity of the stability margin index is verified.
The embodiment of the invention also provides a converter synchronous stability margin evaluation system, and referring to fig. 6, a functional module diagram of a first embodiment of the grid-connected converter synchronous stability margin evaluation system of the invention is shown, and the system may include the following modules:
the first calculation module 601 is used for calculating synchronous stable static tolerance values of all grid-connected converters;
a second calculating module 602, configured to determine, according to the synchronous stable static margin value of each grid-connected converter, a synchronous stable static margin value of a multi-grid-connected converter system formed by the grid-connected converters;
the evaluation module 603 is configured to perform synchronous stability evaluation on the multi-grid-connected converter system according to the synchronous stability static margin value of the multi-grid-connected converter system, where the larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the synchronous stability of the multi-grid-connected converter system is.
In one possible implementation, the first calculation module 601 includes:
the terminal voltage phasor calculation unit is used for calculating the terminal voltage phasor of the grid-connected converter according to the angle difference between the output angle of the phase-locked loop and the voltage phase angle of the power grid, the output current phasor of the grid-connected converter, the power grid impedance, the current collection network impedance, the transformer leakage impedance and the voltage amplitude of the power grid under the condition that the power system normally operates;
the quadrature component calculation unit is used for decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and a quadrature-axis component in a phase-locked loop coordinate system to obtain the quadrature-axis component of the terminal voltage component of the grid-connected converter;
and the impedance voltage drop calculation unit is used for determining the impedance voltage drop generated by the output current of the grid-connected converter on the impedance of the power grid according to the quadrature component of the voltage phasor at the machine end of the grid-connected converter.
The embodiment of the present invention further provides an electronic device, as shown in fig. 7, which includes a processor 71, a communication interface 72, a memory 73 and a communication bus 74, where the processor 71, the communication interface 72, and the memory 73 complete mutual communication through the communication bus 74,
a memory 73 for storing a computer program;
the processor 71, when executing the program stored in the memory 73, implements the following steps:
the synchronous stability static margin index of the grid-connected converter is defined as follows:
in the formula, λ k For synchronous stabilization of the static margin value, Δ u, of the grid-connected converter kq For the impedance drop, U, produced by the current output by the grid-connected converter on the grid impedance g Is the grid voltage amplitude;
calculating the synchronous stable static margin value of each grid-connected converter;
determining the synchronous stable static margin value of a multi-grid-connected converter system consisting of all the grid-connected converters according to the synchronous stable static margin value of each grid-connected converter;
and according to the synchronous stability static margin value of the multi-grid-connected converter system, carrying out synchronous stability evaluation on the multi-grid-connected converter system, wherein the larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the synchronous stability of the multi-grid-connected converter system is.
The process for determining the impedance voltage drop generated by the output current of the grid-connected converter on the impedance of the power grid comprises the following steps:
under the condition that the power system normally runs, calculating the terminal voltage magnitude of the grid-connected converter according to the phase-locked loop output angle, the angle difference between grid voltage phase angles, the output current phasor of the grid-connected converter, the grid impedance, the current collection network impedance, the transformer leakage impedance and the grid voltage amplitude;
decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and an alternate-axis component in a phase-locked loop coordinate system to obtain the alternate-axis component of the terminal voltage component of the grid-connected converter;
and determining the impedance voltage drop of the output current of the grid-connected converter on the impedance of the power grid according to the quadrature component of the voltage phasor at the machine end of the grid-connected converter.
The calculation formula of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula (I), the compound is shown in the specification,
terminal voltage component, U, of the grid-connected converter k g For the grid voltage amplitude, delta j ,δ k Is the angle difference between the phase-locked loop output angle and the grid voltage phase angle, Z g As impedance of the grid, Z i Is the collector network impedance, Z kt The leakage impedance of the terminal transformer of the grid-connected inverter k,
is the output current phasor of the grid-connected converter,
to make the current phasor
And transforming a phase-locked loop coordinate system of the grid-connected converter j into a phase-locked loop coordinate system of a grid-connected converter k, wherein N is the total number of converters in the multi-grid-connected converter system, and N is the number of converters on a branch where the kth converter is located.
The calculation formula of the quadrature axis component of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula u kq The quadrature axis component of the machine end voltage phasor of the grid-connected converter is represented by Im, the imaginary part is taken for operation,
and the impedance voltage drop generated on the grid impedance for the output current of the grid-connected converter.
Under the condition of a power system fault, calculating the terminal voltage magnitude of the grid-connected converter according to the output current phasor, the grid impedance, the current collection network impedance, the transformer leakage impedance and the grid voltage amplitude of the grid-connected converter;
decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and a quadrature-axis component in a phase-locked loop coordinate system, thereby obtaining the quadrature-axis component of the terminal voltage component of the grid-connected converter;
determining impedance voltage drop generated by output current of the grid-connected converter on the power grid impedance according to quadrature axis component of the voltage phasor at the machine end of the grid-connected converter;
the approximate calculation formula of the quadrature axis component of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula u kq The quadrature axis component of the machine end voltage phasor of the grid-connected converter is represented by Im, the imaginary part is taken for operation,
And taking the minimum value of the synchronous stable static tolerance value of each grid-connected converter as the synchronous stable static tolerance value of the multi-grid-connected converter system formed by each grid-connected converter.
The synchronous stability evaluation of the multi-grid-connected converter system according to the synchronous stability static tolerance value of the multi-grid-connected converter system comprises the following steps:
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 1, the system has the maximum synchronous stability margin;
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 0, the synchronous stability margin of the system is 0;
if the synchronous stability static tolerance value of the multi-grid-connected converter system is smaller than 0, the system does not have a balance point, and the system cannot keep synchronous stability.
If the synchronous stability static tolerance value of the multi-grid-connected converter system is smaller than 0, the system does not have a balance point, and the system cannot keep synchronous stability.
The communication bus mentioned in the above terminal may be a Peripheral Component Interconnect (PCI) bus, an Extended Industry Standard Architecture (EISA) bus, or the like. The communication bus may be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, only one thick line is shown, but this does not mean that there is only one bus or one type of bus.
The communication interface is used for communication between the terminal and other equipment.
The Memory may include a Random Access Memory (RAM) or a non-volatile Memory (non-volatile Memory), such as at least one disk Memory. Optionally, the memory may also be at least one memory device located remotely from the processor.
The Processor may be a general-purpose Processor, and includes a Central Processing Unit (CPU), a Network Processor (NP), and the like; the Integrated Circuit may also be a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other Programmable logic device, a discrete Gate or transistor logic device, or a discrete hardware component.
In another embodiment of the present invention, a computer-readable storage medium is further provided, where instructions are stored in the computer-readable storage medium, and when the instructions are executed on a computer, the computer is caused to perform the method for evaluating the synchronous stability margin of the grid-connected converter described in any one of the above embodiments.
The embodiments in the present specification are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, apparatus, or computer program product. Accordingly, embodiments of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, embodiments of the present invention 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, and the like) having computer-usable program code embodied therein.
Embodiments of the present invention are described with reference to flowchart illustrations and/or block diagrams of methods, terminal devices (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing terminal to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing terminal, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing terminal to cause a series of operational steps to be performed on the computer or other programmable terminal to produce a computer implemented process such that the instructions which execute on the computer or other programmable terminal provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should also be noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. "and/or" means that either one or both of them can be selected. Also, the terms "include", "including" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or terminal device including a series of elements includes not only those elements but also other elements not explicitly listed or inherent to such process, method, article, or terminal device. Without further limitation, an element defined by the phrase "comprising a … …" does not exclude the presence of another identical element in a process, method, article, or terminal apparatus that comprises the element.
The converter synchronization stability margin evaluation method, system, device and storage medium provided by the invention are introduced in detail, and a specific example is applied in the text to explain the principle and the implementation of the invention, and the description of the above embodiment is only used to help understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
Claims (9)
1. A method for evaluating a synchronous stability margin of a converter is characterized by comprising the following steps:
the synchronous stability static margin index of the grid-connected converter is defined as follows:
in the formula, λ k For the synchronous stabilization of the static margin value, Δ u, of the grid-connected converter kq For the impedance drop, U, produced by the output current of the grid-connected converter on the grid impedance g Is the grid voltage amplitude;
calculating the synchronous stable static margin value of each grid-connected converter;
determining the synchronous stable static margin value of a multi-grid-connected converter system consisting of all grid-connected converters according to the synchronous stable static margin value of all the grid-connected converters;
and carrying out quantitative evaluation on the synchronous stability of the multi-grid-connected converter system according to the synchronous stability static margin value of the multi-grid-connected converter system, wherein the larger the synchronous stability static margin value of the multi-grid-connected converter system is, the higher the synchronous stability of the multi-grid-connected converter system is.
2. The method according to claim 1, wherein the obtaining of the impedance drop generated by the grid-connected converter output current on the grid impedance comprises:
under the condition that the power system normally operates, calculating the machine end voltage phasor of the grid-connected converter according to the angle difference between the output angle of the phase-locked loop and the voltage phase angle of a power grid, the output current phasor of the grid-connected converter, the impedance of the power grid, the current collection network impedance, the leakage impedance of the transformer and the voltage amplitude of the power grid;
decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and an alternate-axis component in a phase-locked loop coordinate system to obtain the alternate-axis component of the terminal voltage component of the grid-connected converter;
and determining the impedance voltage drop of the output current of the grid-connected converter on the power grid impedance according to the quadrature axis component of the voltage phasor at the machine end of the grid-connected converter.
3. The method according to claim 2, wherein the calculation formula of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula (I), the compound is shown in the specification,
terminal voltage component, U, of the grid-connected converter k g For the grid voltage amplitude, delta j ,δ k Is the angle difference between the phase-locked loop output angle and the grid voltage phase angle, Z g As impedance of the grid, Z i Is the collector network impedance, Z kt Is the leakage impedance of the terminal transformer of the grid-connected inverter k,
is the output current phasor of the grid-connected converter,
to make the current phasor
And transforming a phase-locked loop coordinate system of the grid-connected converter j into a phase-locked loop coordinate system of a grid-connected converter k, wherein N is the total number of converters in the multi-grid-connected converter system, and N is the number of converters on a branch where the kth converter is located.
4. The method according to claim 2, wherein the quadrature component of the machine-side voltage phasor of the grid-connected converter is calculated by the following formula:
in the formula u kq The quadrature axis component of the machine end voltage phasor of the grid-connected converter is represented by Im, the imaginary part is taken for operation,
and the impedance voltage drop generated on the grid impedance for the output current of the grid-connected converter.
5. The method of claim 2, further comprising, in case of a power system fault, calculating a grid-side voltage magnitude of the grid-connected converter from the output current phasor of the grid-connected converter, the grid impedance, the collection network impedance, the transformer leakage impedance, and the grid voltage magnitude;
decomposing the terminal voltage component of the grid-connected converter into a direct-axis component and a quadrature-axis component in a phase-locked loop coordinate system, thereby obtaining the quadrature-axis component of the terminal voltage component of the grid-connected converter;
determining the impedance voltage drop of the output current of the grid-connected converter on the impedance of the power grid according to the quadrature component of the voltage phasor at the machine end of the grid-connected converter;
the approximate calculation formula of the quadrature axis component of the machine end voltage phasor of the grid-connected converter is as follows:
in the formula u kq The quadrature axis component of the machine end voltage phasor of the grid-connected converter is represented by Im, the imaginary part is taken for operation,
and the impedance voltage drop generated on the grid impedance for the output current of the grid-connected converter.
6. The method according to claim 1, characterized in that the minimum value of the synchronous stable static margin values of the grid-connected converters is used as the synchronous stable static margin value of the multi-grid-connected converter system consisting of the grid-connected converters.
7. The method according to claim 1, wherein the performing the synchronous stability assessment on the multi-grid-connected converter system according to the synchronous stability static margin value of the multi-grid-connected converter system comprises:
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 1, the system has the maximum synchronous stability margin;
if the synchronous stability static margin value of the multi-grid-connected converter system is equal to 0, the synchronous stability margin of the system is zero, namely the system is in a critical stable state;
if the synchronous stability static tolerance value of the multi-grid-connected converter system is smaller than 0, the system does not have a balance point, and the system cannot keep synchronous stability.
8. An electronic device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the steps of the method according to any of claims 1 to 7 are implemented when the computer program is executed by the processor.
9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 7.
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