CN114884052A - Control optimization method of flexible loop closing system - Google Patents
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
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Abstract
The invention discloses a control optimization method of a flexible loop closing system, which comprises the following steps: step 1: calculating the impedance of two alternating current sides of the flexible loop closing system under the voltage disturbance of different frequencies; step 2: constructing a function model of impedance-frequency characteristic curves of two alternating current sides, and calculating an actual damping value corresponding to each zero point of the function model; when the actual damping value is larger than the standard damping value, the optimization process is completed; when the actual damping value is less than or equal to the standard damping value, resetting the reference damping value, and executing the step 3-4; and step 3: optimizing parameters in the multi-oscillation mode controller according to the set reference damping value; and 4, step 4: and (3) collecting the voltage and the current of the grid-connected point, remodeling the impedance of the two alternating current sides through the optimized multi-oscillation mode controller according to the frequency of the weak damping oscillation mode of the flexible loop closing system, and returning to execute the step 1. The invention does not depend on the specific parameters of the flexible loop closing system and has higher reliability and disturbance resistance.
Description
Technical Field
The invention relates to the technical field of power converters, in particular to a control optimization method of a flexible loop closing system.
Background
With the gradual upgrade of the electric power industry in China and the continuous improvement of the living standard of people, the requirements of national economic construction and resident users on the quality of electric energy and the reliability of power supply are higher and higher, and even if the power failure in a short time is caused, the production and the life of the users are greatly inconvenient. The power distribution network in China is developed and constructed for a long time, and the power distribution network structure mainly adopts a closed-loop design and open-loop operation at present.
In order to effectively improve the electric energy quality and the flexible reliability of power supply, the power distribution network needs to select a proper power supply path to transfer load through a loop closing operation, the uninterrupted power supply transfer of the power distribution network is realized, meanwhile, the operation can also reduce the power supply loss, the user satisfaction degree is improved, and a foundation is laid for the intelligent development of the power distribution network. However, the loop closing operation also brings certain risks and problems, if the two sides of the loop closing point have different pressure difference and short-circuit impedance, the loop closing moment can generate larger impact current, and loop current can be generated after the loop closing. And the overlarge impact current can cause relay protection action, so that the power failure range is further expanded, and even the safe and stable operation of the system can be directly influenced. In the stability control strategy of a part of flexible loop closing systems, the system flow is controlled by adjusting a transformer tap and adopting methods such as reactive compensation and the like, but the methods cannot adjust the phase difference between voltages, so that the multi-power-supply long-term stable loop closing operation is difficult to realize. In addition, two nodes with the minimum voltage difference can be found by optimizing and are used as the optimal ring closing node in the power distribution network, the stability of ring closing can be guaranteed to the maximum extent, but the method changes the position and the operation mode of a ring network, and the structure of the distribution network can also be changed.
The stability control strategy of the existing flexible loop closing system is very dependent on the accuracy of system parameters aiming at the analysis of the system stability. The stability of the system is very sensitive to the change of the parameters of the controller, and the damping of the system is easily reduced to generate oscillation, so that the stability of the system is reduced.
Disclosure of Invention
The invention provides a control optimization method of a flexible loop closing system, which aims to solve the problems of loop impact generated after loop closing, incapability of adjusting voltage phase difference and low accuracy of system parameters in the prior art.
The invention provides a control optimization method of a flexible loop closing system, which comprises the following steps:
step 1: respectively obtaining the variable quantities of voltage and current at two alternating current sides of the flexible loop closing system, and respectively calculating the impedance of the two alternating current sides of the flexible loop closing system under the voltage disturbance of different frequencies;
step 2: respectively constructing function models of impedance-frequency characteristic curves of two alternating current sides according to the relation between the impedance and the frequency obtained in the step 1 and combining with a transfer function, and calculating actual damping values corresponding to all zeros of the function models;
when the actual damping value is larger than the standard damping value, the flexible closed-loop system is in an optimal control state, and the optimization process is completed;
when the actual damping value is less than or equal to the standard damping value, resetting the reference damping value, and executing the step 3-4;
and step 3: optimizing parameters in the multi-oscillation mode controller according to the set reference damping value, so that the amplitude-frequency and phase-frequency characteristics of the multi-oscillation mode controller meet the operation requirement of the flexible closed-loop system;
the multi-oscillation mode controller comprises a plurality of branches which are connected in parallel and have the same structure, and each branch comprises a band-pass filter, a lead-lag compensator and a proportional amplifier which are connected in series; the branch circuit corresponds to a weak damping oscillation mode of the flexible loop closing system; the current output by the multi-oscillation mode controller is used as the input of a current inner ring in the flexible closed-loop system;
and 4, step 4: and (3) collecting the voltage and the current of the grid-connected point, remodeling the impedance of the two alternating current sides of the flexible loop-closing system through the multi-oscillation mode controller optimized in the step (3) according to the frequency of the weak damping oscillation mode of the flexible loop-closing system, and returning to execute the step (1).
Further, the standard damping value is a damping value according to actual requirements of actual conditions; and the reference damping value is greater than or equal to the standard damping value, and when the reference damping value is reset every time, the reset reference damping value is greater than the previously set reference damping value.
Further, the specific steps of respectively calculating the impedances of the two ac sides of the flexible loop closing system under the voltage disturbance with different frequencies in the step 1 are as follows:
step 11: respectively injecting series voltages with different frequencies into the alternating current side of the flexible loop closing system;
step 12: acquiring response current of an alternating current side of the flexible loop closing system under series voltage disturbance;
step 13: calculating the impedance of the AC side of the flexible loop closing system according to the following formula:
wherein Z represents an impedance matrix of a certain AC side of the flexible loop closing system under a dq coordinate system, and Z dd And Z qq Dq impedance, Z, representing the ratio of voltage to current on the d-and q-axes, respectively dq And Z qd Representing the equivalent impedance resulting from the coupling between the dq axes.
Further, in the step 2, according to the relationship between the impedance and the frequency obtained in the step 1, in combination with the transfer function, function models of impedance-frequency characteristic curves of two ac sides are respectively constructed, specifically:
respectively drawing a curve graph of the real part and the imaginary part of the determinant of the impedance matrix along with the change of frequency, and fitting a transfer function and the curve graph to obtain an expression of the determinant of the impedance matrix:
D(s)＝det(Z)＝Z dd Z qq -Z dq Z qd
wherein D(s) represents the impedance matrix determinant of the impedance matrix Z, i.e. the function model, Z dd And Z qq Dq impedance, Z, representing the ratio of voltage to current on the d-and q-axes, respectively dq And Z qd Representing the equivalent impedance resulting from the coupling between the dq axes.
Further, the specific steps of step 3 are as follows:
step 31: setting parameter T i1 、T i2 、K gi Given a boundary of T i1 、T i2 、K gi The initial value of (a) is,
wherein, T i1 Time constant of leading element, T i2 Time constant of lag element, K gi Is in proportionThe amplification factor of the amplification controller;
step 32: for T i1 、T i2 、K gi Optimizing to obtain the optimal T within the boundary range i1 、T i2 、K gi 。
Further, the specific steps of step 4 are as follows:
step 41: collecting voltages at two alternating current side feeders of a flexible closed loop system as input signals u of a multi-oscillation mode controller sa ，u sb ；
Step 42: the band-pass filter extracts an oscillation signal in an input signal as an input signal of a phase compensation unit through the following expression:
in the formula G bi (s) is an oscillating signal; omega i For the center frequency of the ith bandpass filter, equal to the frequency of the ith oscillation mode; xi is the damping coefficient of the band-pass filter; s is a laplace operator;
step 43: the lead-lag compensator performs phase compensation on the extracted oscillation signal, the expression of the lead-lag compensator is as follows, and the output signal of the lead-lag compensator is the input signal of the proportional amplification controller:
in the formula G gi (s) is the oscillation signal after phase compensation; t is i1 And T i2 Respectively time constants of an advance link and a lag link; s is the laplace operator.
Step 44: the proportional amplification controller is based on the amplification factor K gi And adjusting the current output by the multi-oscillation mode controller, and returning to execute the step 1.
The invention has the beneficial effects that:
the invention relates to a control optimization method of a flexible loop closing system, which comprises the following steps of 1, adjusting the damping of the flexible loop closing system through a novel multi-oscillation mode controller without depending on specific parameters of the flexible loop closing system, and having higher reliability and interference resistance; 2. the stability of the flexible interconnection device is improved through parameter optimization design, and the dynamic and steady-state performance of the system is not influenced; 3. the control optimization method can simultaneously improve the stability of the system in the full frequency band and is simple and convenient to implement.
Drawings
The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:
FIG. 1 is a schematic view of a flexible ring closure system;
FIG. 2 is a schematic diagram of a multi-mode oscillation controller;
FIG. 3 is a graph showing the amplitude-frequency characteristics of a band-pass filter according to an embodiment of the present invention;
FIG. 4 is a graph illustrating the phase-frequency characteristics of the lead-lag compensator in accordance with an embodiment of the present invention;
FIG. 5 is a flow chart illustrating an embodiment of the present invention.
Detailed Description
In order to make the objects, 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 with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. 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 invention.
As shown in fig. 1, the flexible loop closing system includes a VSC-a side current inner loop, a dc voltage outer loop and corresponding modules including the method of the present invention, and a VSC-B side current inner loop, a power outer loop and corresponding modules including the method of the present invention, where the current inner loop, the voltage outer loop, and the power outer loop are not different from the conventional VSC control, and the control optimization method is described in detail in this specific embodiment:
a control optimization method of a flexible loop closing system comprises the following steps:
step 1: respectively obtaining the variable quantities of voltage and current at two alternating current sides of the flexible loop closing system, and respectively calculating the impedance of the two alternating current sides of the flexible loop closing system under the voltage disturbance of different frequencies;
the method comprises the following specific steps:
step 11: respectively injecting series voltages with different frequencies into the alternating current side of the flexible loop closing system;
step 12: acquiring response current of an alternating current side of the flexible loop closing system under series voltage disturbance;
step 13: calculating the impedance of the AC side of the flexible loop closing system according to the following formula:
wherein Z represents an impedance matrix of a certain AC side of the flexible loop closing system under a dq coordinate system, and Z dd And Z qq Dq impedance, Z, representing the ratio of voltage to current on the d-and q-axes, respectively dq And Z qd Representing the equivalent impedance resulting from the coupling between the dq axes.
Step 2: respectively constructing function models of impedance-frequency characteristic curves of two alternating current sides according to the relation between the impedance and the frequency obtained in the step 1 and combining with a transfer function, and calculating actual damping values corresponding to all zeros of the function models;
the specific method comprises the following steps:
respectively drawing a curve graph of the real part and the imaginary part of the determinant of the impedance matrix along with the change of frequency, and fitting a transfer function and the curve graph to obtain an expression of the determinant of the impedance matrix:
D(s)＝det(Z)＝Z dd Z qq -Z dq Z qd
wherein D(s) represents the impedance matrix determinant of the impedance matrix Z, i.e. the function model, Z dd And Z qq Dq impedance, Z, representing the ratio of voltage to current on the d-and q-axes, respectively dq And Z qd Represents the equivalent impedance resulting from the coupling between the dq axes;
when the actual damping value is larger than the standard damping value, the flexible loop closing system is in an optimal control state, and the optimization process is completed;
when the actual damping value is less than or equal to the standard damping value, resetting the reference damping value, and executing the step 3-4;
and step 3: optimizing parameters in the multi-oscillation mode controller according to the set reference damping value, so that the amplitude-frequency and phase-frequency characteristics of the multi-oscillation mode controller meet the operation requirement of the flexible closed-loop system;
the multi-oscillation mode controller comprises a plurality of parallel branches with the same structure, wherein each branch comprises a band-pass filter, a lead-lag compensator and a proportional amplifier which are connected in series; the branch circuit corresponds to a weak damping oscillation mode of the flexible loop closing system; the current output by the multi-oscillation mode controller is used as the input of a current inner ring in the flexible loop closing system;
the method comprises the following specific steps:
step 31: setting parameter T i1 、T i2 、K gi Given a boundary of T i1 、T i2 、K gi The initial value of (a) is,
wherein, T i1 Time constant of leading element, T i2 Time constant of lag element, K gi The amplification factor of the proportional amplification controller;
step 32: for T i1 、T i2 、K gi Optimizing to obtain the optimal T within the boundary range i1 、T i2 、K gi 。
And 4, step 4: collecting the voltage and current of a grid-connected point, remodeling the impedance of two alternating current sides of the flexible loop closing system through the multi-oscillation mode controller optimized in the step 3 according to the frequency of the weak damping oscillation mode of the flexible loop closing system, and returning to execute the step 1;
the method comprises the following specific steps:
step 41: collecting voltages at two alternating current side feeders of a flexible closed loop system as input signals u of a multi-oscillation mode controller sa ，u sb ；
Step 42: the band-pass filter extracts an oscillation signal in an input signal as an input signal of a phase compensation unit through the following expression:
in the formula G bi (s) is an oscillating signal; omega i For the center frequency of the ith bandpass filter, equal to the frequency of the ith oscillation mode; xi is the damping coefficient of the band-pass filter; s is a laplace operator;
step 43: the lead-lag compensator performs phase compensation on the extracted oscillation signal, the expression of the lead-lag compensator is as follows, and the output signal of the lead-lag compensator is the input signal of the proportional amplification controller:
in the formula G gi (s) is the oscillation signal after phase compensation; t is i1 And T i2 Respectively time constants of an advance link and a lag link; s is the laplace operator.
Step 44: the proportional amplification controller is based on the amplification factor K gi And adjusting the voltage and the current output by the multi-oscillation mode controller, and returning to execute the step 1.
The standard damping value is a damping value according to actual requirements of actual conditions; the reference damping value is greater than or equal to the standard damping value, and when the reference damping value is reset every time, the reset reference damping value is greater than the previously set reference damping value.
Practical examples are as follows:
firstly, considering a method for calculating the impedance of a flexible closed-loop system under different voltage disturbance frequencies, taking the VSC-A side of the flexible closed-loop system as an example, measuring the three-phase voltage and current at the VSC-A AC side in a steady state, and obtaining the flexible closed-loop system under a dq rotation coordinate system in the steady state in advance through Clark conversion and Park conversionVoltage V of VSC-A alternating side of closed loop system under rated state d0 、V q0 And current I d0 、I q0 Hereinafter, measurement and analysis are mainly performed under dq rotation coordinate system. Under the condition of stable operation of the flexible closed-loop system, series voltage disturbance delta v of a certain frequency is injected into the VSC-A alternating current side d When let Δ v q Obtaining a group of response current data i of the voltage disturbance at the frequency by using a measuring device as 0 d1 And i q1 Is compared with a stable value I d0 、I q0 The difference is made to obtain the current variation delta i d1 And Δ i q1 (ii) a Reinjection of voltage disturbances Deltav of the same frequency q When let Δ v d Obtaining a set of response current data i of the voltage disturbance at the frequency by using a measuring device d2 And i q2 Is compared with a stable value I d0 、 I q0 The difference is made to obtain the current variation delta i d2 And Δ i q2 . For example, when the ac feeder voltage is 10kV, the disturbance voltage is set to 500V, the frequency of the disturbance voltage is changed, the frequency of the voltage disturbance is set at intervals of 0.1Hz, continuous measurement is performed from 1Hz to 500Hz, and the data of the response current is measured to obtain a set of corresponding data of the disturbance voltage frequency and the response current, the measurement data result on the VSC-a ac side is partially listed in the following table 1, and table 1 is a partial measurement data result on the VSC-a side:
| disturbance frequency f r /Hz | Current Δ i d1max /A | Current Δ i q1max /A | Current Δ i d2max /A | Current Δ i q2max /A |
| 50 | 0.214 | 4.78×10 -5 | 0.075 | 3.63 |
| 55 | 0.190 | 4.22×10 -5 | 0.064 | 3.39 |
| 60 | 0.174 | 4.00×10 -5 | 0.053 | 3.15 |
| 65 | 0.159 | 3.80×10 -5 | 0.044 | 2.94 |
| 70 | 0.149 | 3.63×10 -5 | 0.036 | 2.74 |
| 75 | 0.139 | 3.41×10 -5 | 0.030 | 2.56 |
| 80 | 0.130 | 3.24×10 -5 | 0.025 | 2.40 |
| 85 | 0.122 | 3.10×10 -5 | 0.021 | 2.25 |
| 90 | 0.115 | 2.97×10 -5 | 0.017 | 2.13 |
| 95 | 0.109 | 2.87×10 -5 | 0.014 | 2.00 |
| 100 | 0.103 | 2.83×10 -5 | 0.012 | 1.90 |
TABLE 1
Based on this data, according to formula (1)To calculate the impedance Z of VSC-A AC side in the flexible closed-loop system A ：
In the formula Z A Representing the impedance matrix, Z, on the AC side of the VSC-A dd-A 、Z qq-A 、Z dq-A 、Z qd-A Respectively represents Z A 4 elements under dq synchronous rotation coordinate system.
From the partial measurement data of VSC-A side of Table 1, Z can be calculated A As shown in table 2, table 2 shows the impedance measurement results of the VSC-a side:
TABLE 2
Obtaining the impedance matrix Z of the VSC-B AC side of the flexible loop closing system B 。
According to formula (2), according to Z obtained A And Z B Calculating impedance model determinants of the VSC-A and the VSC-B:
according to the determinant D of the obtained impedance model under different voltage disturbance frequencies 1 (s) and D 2 (s) respectively drawing a curve graph of which the real part and the imaginary part change along with the frequency, and further fitting the data points by using a function fitting method according to the data points on the curve graph to obtain D 1 (s) and D 2 Expression of(s). And calculating the distribution of the zero points by using the expression of the impedance model determinant, and analyzing the damping and the frequency of the oscillation mode corresponding to each zero point.
At this time, although the damping is set according to the standard damping, the actual damping may be smaller than the standard damping due to the actual condition of the flexible loop closing system, and the damping needs to be reset to be remolded;
the invention adds a multi-oscillation mode controller in the control system, as shown in fig. 2, and further adjusts the damping by using the output current. Before adjustment, each parameter of the multi-oscillation mode controller is adjusted according to the set reference damping, and the damping is adjusted through the adjusted multi-oscillation mode controller. The multi-oscillation mode controller comprises a plurality of branches which are connected in parallel and have the same structure, wherein each branch comprises a band-pass filter (used for oscillation signal acquisition), a lead-lag compensator (used for phase compensation) and a proportional amplifier which are connected in series; the branch circuit corresponds to a weak damping oscillation mode of the flexible loop closing system; the current output by the multi-oscillation mode controller is used as the input of a current inner ring in the flexible closed-loop system.
The damping provided by the multi-mode oscillation controller is further adjusted by a proportional amplification controller in accordance with a reference damping. And after the output signals of all the branches are superposed, generating a total output signal of the stable controller, and respectively injecting the total output signal into the current inner ring control link.
According to reference damping, parameters of the multi-oscillation mode controller are designed and optimized by adopting an optimization tool box of software MATLAB, so that the overall amplitude-frequency and phase-frequency characteristics of the multi-oscillation mode controller meet requirements, wherein the amplitude-frequency requirements are to amplify the amplitude of a frequency signal to be extracted and attenuate signals of other frequencies; the phase frequency needs to be reserved with a certain phase margin, the control requirements are different for different controls, the phase margin is small when the control speed is high, the phase margin is small when the stability is high, and the optimization parameters comprise T i1 、T i2 And K gi The design flow is shown in fig. 5. The method comprises the following specific steps: first, setting parameter T i1 、T i2 And K gi At the boundary of (2), where T i1 、T i2 And K gi Are respectively set to [0, 0.1 ]]、[0，0.1]And [0, 10]Calculating the parameter T according to the set optimization target of the amplitude frequency and the phase frequency i1 、T i2 、K gi An initial value of (d); second step optimization of toolkit pair T using MATLAB i1 、T i2 、K gi Optimizing the initial value of (A) to obtain T i1 、T i2 、K gi The optimum value of (d); thirdly, according to the parameters of the stable controllers on the two sides, which are obtained through the design, the impedance of the alternating current side of the flexible interconnection device and the stability characteristics of the two sides are re-analyzed and evaluated, whether the stability meets the requirements needs to be checked again, and if the stability does not meet the requirements, the boundaries of the parameters are reset to obtain new optimal values of the parameters; and fourthly, analyzing and evaluating the voltage fluctuation of the direct current side of the flexible interconnection device and the steady state and dynamic performance of voltage/power closed-loop control according to the obtained parameters of the stable controllers on the two sides, if the parameters do not meet the requirements, adjusting the damping standard of each oscillation mode, and carrying out optimization design on the parameters of the controller again until the parameters of the controller meet the required requirements.
After the parameter optimization of the multi-oscillation mode controller is completed, the damping can be adjusted through the multi-oscillation mode controller, and the specific process is as follows: collecting voltages at two alternating sides of a flexible closed loop system as input signals u of a multi-oscillation mode stable controller sa ，u sb Then, a band-pass filter shown in formula (3) is adopted to extract the oscillation signal in the input voltage, and the output signal is the input signal of the phase compensation link.
In the formula, ω i For the center frequency of the ith bandpass filter, equal to the frequency of the ith oscillation mode; omega i Is the damping coefficient of the band pass filter. For example, when the calculated weakly damped oscillation mode frequency is 200Hz, ω i Take 1256.6rad/s, and ω i Then 0.707 may be taken, and the amplitude-frequency characteristic of the bandpass filter is shown in fig. 3.
And performing phase compensation on the extracted oscillation signal by adopting a lead-lag compensator, wherein an output signal of the lead-lag compensator is an input signal of a proportional amplification link:
in the formula, T i1 And T i2 The time constants of the lead link and the lag link are respectively. For example here T i1 It may be taken to be 0.001, T i2 It may take 0.0005 for the lead-lag compensator to have a phase-frequency characteristic as shown in fig. 4.
After the adjustment is completed, in the step of returning to the beginning, the actual damping is obtained again, because the optimized multi-oscillation mode controller is the set reference damping and is only a reference value, the actual damping of the adjusted damping of the flexible closed-loop system is not necessarily the same as the reference damping and may be smaller than the standard damping, and at the moment, the reference damping needs to be adjusted to optimize the multi-oscillation mode controller again until the actual damping is larger than the standard damping.
Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.
Claims (6)
1. A control optimization method of a flexible loop closing system is characterized by comprising the following steps:
step 1: respectively obtaining the variable quantities of voltage and current at two alternating current sides of the flexible loop closing system, and respectively calculating the impedance of the two alternating current sides of the flexible loop closing system under the voltage disturbance of different frequencies;
and 2, step: respectively constructing function models of impedance-frequency characteristic curves of two alternating current sides according to the relation between the impedance and the frequency obtained in the step 1 and combining with a transfer function, and calculating actual damping values corresponding to all zeros of the function models;
when the actual damping value is larger than the standard damping value, the flexible closed-loop system is in an optimal control state, and the optimization process is completed;
when the actual damping value is less than or equal to the standard damping value, resetting the reference damping value, and executing the step 3-4;
and step 3: optimizing parameters in the multi-oscillation mode controller according to the set reference damping value, so that the amplitude-frequency and phase-frequency characteristics of the multi-oscillation mode controller meet the operation requirement of the flexible closed-loop system;
the multi-oscillation mode controller comprises a plurality of branches which are connected in parallel and have the same structure, and each branch comprises a band-pass filter, a lead-lag compensator and a proportional amplifier which are connected in series; the branch circuit corresponds to a weak damping oscillation mode of the flexible loop closing system; the current output by the multi-oscillation mode controller is used as the input of a current inner ring in the flexible closed-loop system;
and 4, step 4: and (3) collecting the voltage and the current of the grid-connected point, remodeling the impedance of the two alternating current sides of the flexible loop-closing system through the multi-oscillation mode controller optimized in the step (3) according to the frequency of the weak damping oscillation mode of the flexible loop-closing system, and returning to execute the step (1).
2. The method for controlling and optimizing a flexible loop closing system according to claim 1, wherein the standard damping value is a damping value according to actual requirements of actual conditions; and when the reference damping value is reset every time, resetting the reference damping value to be larger than the reference damping value set last time.
3. The method for controlling and optimizing the flexible loop closing system according to claim 1, wherein the specific steps of calculating the impedances of the two ac sides of the flexible loop closing system under the voltage disturbance with different frequencies in step 1 are as follows:
step 11: respectively injecting series voltages with different frequencies into the alternating current side of the flexible loop closing system;
step 12: acquiring response current of an alternating current side of the flexible loop closing system under series voltage disturbance;
step 13: calculating the impedance of the AC side of the flexible loop closing system according to the following formula:
wherein Z represents an impedance matrix of a certain alternating current side of the flexible loop closing system under a dq coordinate system, Z dd And Z qq Dq impedance, Z, representing the ratio of voltage to current on the d-and q-axes, respectively dq And Z qd Representing the equivalent impedance resulting from the coupling between the dq axes.
4. The method for controlling and optimizing the flexible loop closing system according to claim 1, wherein in the step 2, according to the relationship between the impedance and the frequency obtained in the step 1, a function model of impedance-frequency characteristic curves of two ac sides is respectively constructed by combining a transfer function, specifically:
respectively drawing a curve graph of the real part and the imaginary part of the determinant of the impedance matrix along with the change of frequency, and fitting a transfer function and the curve graph to obtain an expression of the determinant of the impedance matrix:
D(s)＝det(Z)＝Z dd Z qq -Z dq Z qd
wherein D(s) represents the impedance matrix determinant of the impedance matrix Z, i.e. the function model, Z dd And Z qq Dq impedance, Z, representing the ratio of voltage to current on the d-and q-axes, respectively dq And Z qd Representing the equivalent impedance resulting from the coupling between the dq axes.
5. The method for controlling and optimizing a flexible loop system according to claim 1 or 2, wherein the specific steps of the step 3 are as follows:
step 31: setting parameter T i1 、T i2 、K gi Given a boundary of T i1 、T i2 、K gi The initial value of (a) is,
wherein, T i1 Time constant of leading element, T i2 Time constant of lag element, K gi The amplification factor of the proportional amplification controller;
step 32: for T i1 、T i2 、K gi Optimizing to obtain boundary rangeOptimum T inside the enclosure i1 、T i2 、K gi 。
6. The method for controlling and optimizing a flexible loop closing system according to claim 1, wherein the specific steps of the step 4 are as follows:
step 41: collecting voltages at two alternating current side feeders of a flexible closed loop system as input signals u of a multi-oscillation mode controller sa ，u sb ；
Step 42: the band-pass filter extracts an oscillation signal in an input signal as an input signal of a phase compensation unit through the following expression:
in the formula G bi (s) is an oscillating signal; i for the center frequency of the ith bandpass filter, equal to the frequency of the ith oscillation mode; xi is the damping coefficient of the band-pass filter; s is a laplace operator;
step 43: the lead-lag compensator performs phase compensation on the extracted oscillation signal, the expression of the lead-lag compensator is as follows, and the output signal of the lead-lag compensator is the input signal of the proportional amplification controller:
in the formula G gi (s) is the oscillation signal after phase compensation; t is i1 And T i2 Respectively time constants of an advance link and a lag link; s is the laplace operator.
And step 44: the proportional amplification controller is based on the amplification factor K gi And adjusting the current output by the multi-oscillation mode controller, and returning to execute the step 1.
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| CN113162069A (en) * | 2021-04-22 | 2021-07-23 | 武汉大学 | Method for inhibiting high-frequency oscillation of flexible direct current transmission system by active/passive damping |
| CN113595123A (en) * | 2021-06-15 | 2021-11-02 | 中电普瑞电力工程有限公司 | High-frequency impedance calculation method and device of modular multilevel converter |
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