CN116961031A - High-frequency oscillation frequency division suppression and parameter design method for flexible direct-current transmission system - Google Patents
High-frequency oscillation frequency division suppression and parameter design method for flexible direct-current transmission system Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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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
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- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses a method for restraining high-frequency oscillation frequency division and designing parameters of a flexible direct current transmission system, which comprises the following steps: obtaining an ac system impedance Z at a PCC point ac And a minimum phase theta acmin Flexible DC converter station impedance Z mmc The method comprises the steps of carrying out a first treatment on the surface of the Determining the number of high-frequency oscillation risk areas H res And the frequency interval value thereof, and then determining the number N of the parallel frequency division damping controllers damp The method comprises the steps of carrying out a first treatment on the surface of the Acquiring d-axis and q-axis input quantities of the frequency division damping controller; calculating and designing parameters of the frequency division damping controller; checking parameters of the frequency division damping controller; output compensating voltage e generated by frequency division damping controller isd And e isq And finally, the current is overlapped to the current inner loop controller to realize frequency division damping control and inhibit high-frequency oscillation. The invention has the advantages of detailed steps, higher precision, no need of adding additional passive damping filter, not only being capable of inhibiting a plurality of high-frequency oscillations, but also being suitable for medium-low frequency andthe subsynchronous oscillation has wide applicability and can effectively improve the running stability of the system.
Description
Technical neighborhood
The invention relates to the application fields of flexible direct current transmission (high voltage direct current, HVDC) systems and VSCs (voltage source converter) based on modularized multi-level converters (modular multilevel converter, MMC), which comprise application scenes such as connection of a flexible direct current converter station to an active alternating current power grid, a new energy station and the like, in particular to a high-frequency oscillation frequency division suppression and parameter design method of a flexible direct current transmission system.
Background
The flexible direct current transmission technology (high voltage direct current, HVDC) based on voltage source converters (voltage source converter, VSC), in particular modular multilevel converters (modular multilevel converter, MMC), provides a highly flexible and controllable solution for weak/passive alternating current grid voltage support, offshore wind power, cross-region interconnection, urban power supply and other application scenarios. However, link delay caused by measurement, transmission, calculation, execution, triggering and the like related to a digital control system of high-power electronic equipment is a root cause of high-frequency oscillation of flexible direct-current transmission engineering in recent years. After high-frequency oscillation, if the high-frequency harmonic cannot be eliminated in time in a period of time, an alternating current system is excited to generate high-frequency harmonic with larger amplitude, alternating voltage and alternating current are severely distorted, the running loss of the system is increased, and even electric equipment is broken down once to stop the system, so that great economic loss is caused, and the normal running of the power system is influenced.
The high-frequency oscillation suppression strategy is developed mainly from two aspects of an active damping suppression strategy and a passive damping suppression strategy, and the active damping suppression strategy can realize damping control through self-detected voltage and current without introducing an external circuit. However, the active damping controller with a single structure cannot eliminate the negative damping effect, and has certain difficulty in remodeling damping characteristics of a plurality of frequency intervals in a high frequency range, so that the suppression requirement of a plurality of high-frequency oscillation risk areas is difficult to realize. Therefore, the method has the defect of low adaptability in the case of coping with the variable operation conditions of the alternating current system. The passive suppression method has the advantage of completely eliminating the negative damping effect of the impedance high-frequency band, is generally configured at a common coupling point (point of common coupling, PCC), and has a structure of A type, second order, C type and the like. However, the passive filter introduces fundamental wave loss and fundamental wave reactive power, increases system equipment and operation and maintenance cost, and is relatively suitable for occasions with uncertain running modes of an alternating current system, uncertain external influence factors and higher reliability requirements. If the operation condition of the alternating current system connected with the flexible direct current transmission system is simpler and the number of the capacitive impedances of the alternating current system is smaller, the active damping suppression strategy has better competitiveness.
Therefore, aiming at the defects of simple structure, low applicability and power loss and reactive compensation introduced by the passive damping scheme in the existing single damping scheme, the invention provides a frequency division active damping suppression idea, a control strategy implementation mode and a parameter analysis calculation and design method thereof. According to the scheme, a plurality of active damping suppressors connected in parallel are adopted, each active damping suppressor connected in parallel remodels the impedance characteristic of a converter station in a frequency section, according to the high-frequency oscillation suppression requirements of a plurality of areas, an analytical calculation expression of a part of parameter selection range is provided, and the rest related parameters are optimally designed.
Disclosure of Invention
The invention aims at improving the damping characteristics of the flexible direct current converter station in a high-frequency range aiming at a plurality of high-frequency oscillation risk areas of an alternating current system on the basis of not influencing the control protection architecture of the original flexible direct current power transmission system and the parameters of the control system, enhancing the damping characteristics of the converter station in the high-frequency oscillation risk areas, inhibiting the occurrence of high-frequency oscillation and improving the running stability of the flexible direct current power transmission system.
The invention provides a method for restraining high-frequency oscillation frequency division and parameter design of a flexible direct current transmission system, which comprises the following steps:
s1, acquiring the impedance Z of an alternating current system at a PCC point ac And a minimum phase theta acmin ；
S2, obtaining the impedance Z of the flexible direct current converter station at the PCC point mmc ；
S3, determining the number H of high-frequency oscillation risk areas res And its frequency interval value;
s4, determining the number N of parallel frequency division damping controllers damp ；
S5, acquiring input quantity of a frequency division damping controller;
s6, calculating and designing parameters of the frequency division damping controller;
s7, checking parameters of the frequency division damping controller;
S8.output compensating voltage e generated by frequency division damping controller isd And e isq 。
Step S1 of obtaining the AC System impedance Z at the PCC Point ac And a minimum phase theta acmin The method is characterized by comprising the following steps:
acquiring an alternating current system Z at a PCC point ac The impedance characteristic curve of (2) is divided into two main types, namely a scanning method and a calculation method: the scanning method is to build an alternating current system in simulation software, input three-phase symmetrical alternating current voltage sources with different frequencies into PCC points, obtain current response conditions under all possible operation modes, calculate impedance values of each frequency of the PCC points, and form a scanning curve Z ac . According to the distributed parameter model or a plurality of pi series equivalent models, the calculation method calculates the equivalent impedance Z of the alternating current system by adopting a node voltage method or a one-by-one iteration method ac . The frequency-dependent characteristic and the coupling effect of the circuit are difficult to consider by the calculation method, the universality is relatively poor, the calculated impedance characteristic curve is relatively strict, and the parameter calculation result of the frequency division damping controller is more conservative than that of the scanning method.
Further, the communication system Z is plotted in all possible permissible operating modes within the frequency range of interest ac Impedance characteristic curve, including amplitude-frequency characteristic curve and phase-frequency characteristic curve, on which the minimum value theta of impedance phase of AC system is found acmin . This value is negative and is typically expressed in radians or in angular values over the first ac system capacitive frequency range.
Step S2 of obtaining the impedance Z of the flexible direct current converter station at the PCC point mmc The method is characterized by comprising the following steps:
obtaining the impedance Z of a flexible DC converter station mmc Scanning methods and calculations may also be used. The impedance scanning method of the flexible direct current converter station is the same as the impedance scanning of the alternating current system, and the method is very suitable for a scene that a converter station control system model is not disclosed outside, namely a 'black box' converter station, and can consider the transmission process of actual link delay. The calculation rule is to calculate the relation between the voltage and the current at the PCC by adopting a linearization method according to the operation principle of the flexible direct current converter station. The calculation method can clearly know the replacementThe key influence link and the influence rule of the flow station impedance lay a theoretical foundation for the proposal of the frequency division damping controller. Also, in the frequency range of interest, with Z ac Overlapping together, plotting Z of a flexible DC converter station at different operating power levels mmc The impedance characteristic curve comprises an amplitude-frequency characteristic curve and a phase-frequency characteristic curve.
Determining the number H of the high-frequency oscillation risk areas in step S3 res And its frequency interval values, specifically as follows:
based on Z obtained in step S1 and step S2 ac And Z mmc Amplitude-frequency characteristic curve and phase-frequency characteristic curve, find all possible Z in each capacitive frequency interval range of AC system ac And Z mmc Amplitude-frequency characteristic curve intersection frequency. Determining each Z ac And Z mmc Taking the maximum value of the number as the number H of the high-frequency oscillation risk areas res . At the same time, at 1 st to H res Recording the minimum and maximum values of the frequency of each interval within the range of the risk interval of the high-frequency oscillation, namely [ f ] min1 ,f max1 ]、[f min2 ,f max2 ]、[f min3 ,f max3 ]、…，[f minHres ,f maxHres ]Each recorded interval value is slightly larger than the actual intersection frequency range, e.g. a relative relaxation of 1% of the frequency error.
Step S4 of determining the number N of parallel frequency-division damping controllers damp The method is characterized by comprising the following steps:
the suppression of the high-frequency oscillation is realized by considering the frequency division, each frequency division is dominated by a frequency division damping controller, and the number H of the high-frequency oscillation risk areas is determined according to the step S3 res Step S4 may initially select the number N of frequency-divided damping controllers damp ≥H res Suggesting selection of N damp ＝H res Or N damp ＝H res +1。
The input quantity of the frequency division damping controller is obtained in the step S5, and the input quantity is specifically as follows:
and (3) acquiring d-axis and q-axis voltages or currents on the alternating-current side of the converter station based on the number of the frequency division damping controllers obtained in the step (S4), and inputting the voltages or currents to each frequency division damping controller, wherein three-phase voltage or current input quantities are converted into a dq coordinate system through Park conversion, and the d-axis and q-axis input quantities are obtained. When negative sequence control is considered, the input quantity of the positive sequence element damping controller is positive sequence d-axis and q-axis voltages or currents, and the negative sequence element is negative sequence d-axis and q-axis voltages or currents.
The parameters of the frequency division damping controller are calculated and designed in the step S6, and the parameters are specifically as follows:
based on impedance Z of flexible DC converter station after considering frequency-dividing damping controller mmc The expression is used for calculating or designing the frequency division damping controller parameters from the first high-frequency oscillation risk area one by one. The implementation steps of the constraint conditions adopted in parameter calculation or design are shown in FIG. 5, and the impedance real part cosine function phase curve is in the high-frequency oscillation risk interval [ f ] min1 ,f max1 ]、[f min2 ,f max2 ]、[f min3 ,f max3 ]、…，[f minHres ,f maxHres ]The internal damping range is as wide as possible, namely [360 DEG k-90 DEG, 360 DEG k+90 DEG]Within the range, especially the first [ f min1 ,f max1 ]And a second interval [ f min2 ,f max2 ]The third interval and above are satisfied, and high-frequency oscillation does not occur and further check is needed.
The checking of the parameters of the frequency division damping controller in step S7 is specifically as follows:
and in the parameter range calculated in the step S6, proper values are selected to carry out positive sequence and negative sequence impedance characteristic curve checking, namely whether the calculated or designed frequency division damping controller parameters can keep the stability of the system is verified.
The compensation voltage e generated by the output frequency division damping controller in the step S8 isd And e isq The method is characterized by comprising the following steps:
setting compensation voltage output limit value E is_lim After the obtained input quantity passes through the frequency division damping controller, a compensation voltage e is generated isd And e isq The method comprises the steps of carrying out a first treatment on the surface of the Will compensate voltage e isd And e isq And the limiting value E is_lim In contrast, if the d-axis (q-axis) divided damping controller output value is at + -E is_lim In, directly outputting; otherwise, output limiting value E is_lim or-E is_lim . The output value is compared with the original current inner loop output valueAnd->And (5) superposing the materials and sending the materials to a valve control link.
Compared with the prior art, the invention has the beneficial effects that:
the high-frequency oscillation frequency division suppression and parameter design method for the flexible direct-current power transmission system is suitable for occasions with relatively determined running modes of the alternating-current system, does not need to add an additional passive damping filter, does not generate additional fundamental wave loss and fundamental wave reactive power, and does not need the operation and maintenance cost of additional equipment; the control strategy has clear logic and detailed steps, and the damping characteristics of the converter stations in the corresponding areas can be respectively improved aiming at a plurality of high-frequency oscillation risk areas, so that a plurality of high-frequency oscillations are accurately restrained, and the running stability of the system is improved; in addition, the frequency division damping control is suitable for high-frequency oscillation, medium-low frequency and subsynchronous/supersynchronous oscillation, and has wide applicability.
Drawings
Fig. 1 is a schematic diagram of an equivalent main circuit of a flexible dc power transmission system.
Fig. 2 is a schematic diagram of a flexible dc converter station inner loop control architecture taking into account a crossover damping controller.
Fig. 3 is a schematic diagram of an overall implementation of the frequency division damping control strategy.
Fig. 4 is a schematic diagram of a frequency division damping control strategy implementation flow proposed in the present invention.
FIG. 5 is a schematic diagram of the implementation steps for obtaining the parameter constraints of the frequency-divided active damping controller.
FIG. 6 is a specific example of a frequency division damping controller parameter constraint.
Detailed Description
Fig. 4 shows a method for suppressing high-frequency oscillation frequency division and designing parameters of a flexible direct current transmission system, which comprises the following steps:
s1, acquiring the impedance Z of an alternating current system at a PCC point ac And a minimum phase theta acmin ：
Obtaining an ac system impedance Z at a PCC point ac There are two main categories, scanning and calculation. Examples of the present patent theoretical calculation analysis was performed according to the equivalent main circuit of the flexible DC power transmission system shown in FIG. 1, in which the equivalent impedance of the AC system was calculated using L g This value is indicative of the intensity of the ac system in different modes of operation and will vary according to the change in mode of operation.
Based on dq impedance modeling, a dq impedance matrix of the alternating current system can be obtained as follows under the condition of a plurality of pi series connection
Wherein the method comprises the steps of
In N num Is pi number and L in series length The length of the line is r is equivalent resistance of the unit length of the alternating current line, c is equivalent capacitance of the unit length of the alternating current line, and l is equivalent inductance of the unit length of the alternating current line. Adopting orthogonal transformation to transform dq impedance matrix of alternating current system into positive and negative sequence impedance matrix
Wherein j is an imaginary unit, and the positive sequence impedance Z in the formula (4) is taken ac_pn (1,1)Impedance Z for AC system ac The stability of the negative sequence impedance will be checked at the end. Let s=jω, ω=2pi f, i.e. the frequency range of interest, be substituted into Z ac In (a) and (b); drawing different effective impedances L g In the case of (a), the impedance Z of the AC system ac Taking the minimum phase value of all possible curves as theta acmin 。
S2, obtaining the impedance Z of the flexible direct current converter station at the PCC point mmc ：
Obtaining the impedance Z of a flexible DC converter station mmc Scanning and calculation methods may also be employed. The positive sequence impedance Z of the flexible direct current converter station in the high frequency range can be obtained by adopting the calculation method mmc Is that
Initially without frequency-dividing damping controller, i.e. Z vir Let s=jω, ω=2pi f, f be the frequency range of interest, e.g. [1,5000 ]]In the Hz range, obtain Z mmc The amplitude-frequency characteristic and the phase-frequency characteristic of (2) are plotted together with the graph of step 1 in this example.
S3, determining the number H of high-frequency oscillation risk areas res And its frequency interval value:
z obtained based on actual operation cases step 1 and step 2 ac And Z mmc The amplitude-frequency characteristic curve and the phase-frequency characteristic curve find all possible Z in the range of each capacitive frequency interval of the alternating current system ac And Z mmc Amplitude-frequency characteristic curve intersection frequency. Determining each Z ac And Z mmc Taking the maximum value of the number as the number H of the high-frequency oscillation risk areas res . At the same time, at 1 st to H res Within the range of risk intervals of high-frequency oscillation, the minimum and maximum values of the frequency of each interval are recorded, for example [ f ] in the middle of FIG. 6 min1 ,f max1 ]、[f min2 ,f max2 ]、[f min3 ,f max3 ]、…，[f minHres ,f maxHres ]The interval value of each record is slightly more thanThe actual intersection frequency range is a little larger, for example a frequency that is relatively relaxed by 1%. For example, the three risk regions of the main circuit structure of FIG. 1 in the first diagram of FIG. 6 may be initially represented as [310,710 ]]Hz、[1320,1840]Hz sum [2510,3055 ]]Hz, at this time, is considered to be H res ＝3。
S4, determining the number N of parallel frequency division damping controllers damp ：
The suppression of the high-frequency oscillation is realized by considering the frequency division, each frequency division is dominated by a frequency division damping controller, and the number H of the high-frequency oscillation risk areas is determined according to the step 3 of the specific case res =3, in this embodiment step 4 preliminary selection of N damp ＝H res ＝3。
S5, acquiring input quantity of a frequency division damping controller:
the input is voltage or current, this example being current. Collecting three-phase instantaneous current i of alternating-current side of flexible direct-current converter station sabc Using phase theta of phase-locked loop output pll Realizing Park conversion and calculating to obtain d-axis current i sd And q-axis current i sq Wherein the Park transform formula is as follows:
in the formula (6), u sa 、u sb And u sc Instantaneous phase voltages, θ, of the ABC phases respectively pll Is the phase-locked loop output value, t is time. The formula is transformed in the time domain, the subsequent analysis is in the s domain, namely the variable contains(s) Laplains transformation values representing the corresponding time domain physical quantity in the s domain, and the two values are in one-to-one correspondence, namelyThe remaining variables are similar and will not be described in detail. If the negative sequence control link is considered, the input quantity of the input damping controller is positive sequence d-axis current, positive sequence q-axis current, negative sequence d-axis current and negative sequence q-axis current.
S6, calculating and designing parameters of the frequency division damping controller:
the single frequency division damping controller is selected in various forms, such as a first-order high-pass filter, a second-order band-pass filter, a third-order band-pass filter, etc., and the example uses the second-order band-pass filter as the frequency division damping controller, and then
In the formula (7), N damp Is the number k of second-order band-pass damping controllers viri 、ξ viri And omega viri ＝2πf viri Gain, damping ratio and undamped oscillation angular frequency corresponding to the ith second-order frequency division damping controller, f viri Is the i-th undamped oscillation frequency.
Based on the formula (5), the relevant links are substituted to obtain
Wherein T is de A is the delay of the link 3 And b 3 Can be expressed as
Beta has the expression of
Phase expression (ωT) of the impedance real part cosine function in equation (8) de -beta) is the place of great concern
Based on impedance Z of flexible DC converter station after considering frequency-dividing damping controller mmc The expression is used for calculating or designing the frequency division damping controller parameters from the first high-frequency oscillation risk area one by one. The implementation steps of constraints adopted by parameter calculation or design are shown in fig. 5, and the parameter constraints of this example are shown in fig. 6.
Impedance real part cosine function phase curve in high-frequency oscillation risk interval [ f min1 ,f max1 ]、[f min2 ,f max2 ]、[f min3 ,f max3 ]、…，[f minHres ,f maxHres ]The internal damping range is as wide as possible, namely [360 DEG k-90 DEG, 360 DEG k+90 DEG]Within the range, especially the first [ f min1 ,f max1 ]And a second interval [ f min2 ,f max2 ]The third interval and above are satisfied, and high-frequency oscillation does not occur and further check is needed. For the three oscillation risk regions in this case, in the first two risk regions, the impedance real part cosine function phase expression (ωt de - β) should satisfy equation (11) and the minimum frequency of the third risk zone should satisfy equation (12).
The idea of the calculation is based on frequency division suppression, firstly, for the first high-frequency oscillation risk area, only the first frequency division damping controller 1 acts, and according to the phase increment possibly generated in the range of the link delay, the range which is closer to [360 DEG k-90 DEG, 360 DEG k+90 DEG ] is judged, and the phase jump possibly occurs as shown in the third sub-graph of fig. 6, but the damping characteristic is not affected. In order to remodel the phase of the frequency band within the range, a set of inequality can be obtained, constraint conditions of the inequality are solved, and a parameter constraint range of the first damping controller 1 can be obtained, iteration parameters are reasonably selected in the constraint range, intermediate parameters are selected to be initially used as parameters of the first damping controller 1 after one iteration is completed, and the parameters can be properly fine-tuned in the follow-up process.
Secondly, after the first frequency division damping controller 1 is calculated or designed, the second frequency division damping controller 2 is selected, and after the first damping controller is considered according to the impedance real part cosine function phase curve, the range which is closer to [360 DEG k-90 DEG, 360 DEG k+90 DEG ] is judged, so that a group of inequality can be obtained, and the constraint relation between the parameters of the second frequency division damping controller 2 and other parameters can be solved. By reasonably selecting the parameters of the iteration within this constraint, an intermediate parameter preliminary is selected as the parameter of the second damping controller 2 after completion of one iteration, which parameter may be suitably fine-tuned in the following. And (3) checking whether the maximum phase of the impedance of the converter station and the phase difference of the impedance of the alternating current system are within a range of 180 degrees from the second parameter calculation, and if so, carrying out subsequent parameter calculation of the high-frequency oscillation risk area frequency division damping controller.
Again, the calculation and design according to the above steps is continued until the maximum phase of the converter station impedance and the ac system impedance phase difference are within 180 ° or all risk areas have met the positive damping requirement. In general, the maximum phase of the converter station impedance and the phase difference of the ac system impedance are preferably satisfied within a range of 180 °.
S7, checking parameters of the frequency division damping controller:
and selecting proper values to carry out positive sequence and negative sequence impedance characteristic curve checking, namely verifying whether the calculated or designed frequency division damping controller parameters can keep the stability of the system.
According to initial constraint 0<f vir1 <f min1 Preliminary let f vir1 Belonging to [200,280 ]]Hz, gain coefficient k vir1 Initial range of [250,140 ]]Calculate and select damping ratio ζ vir1 Is in the range of [0.59,1.51 ]]The parameter range limits for the first iteration are obtained thus far. Second iteration to f vir1 ∈[200,280]Hz and damping ratio ζ vir1 ∈[0.59,1.51]Taking the gain coefficient k as a reference to solve vir1 Upper range of the gain coefficient k vir1 Damping ratios greater than 250 are mostly greater than 0.8. In view of the fact that an excessively large gain factor results in a very large variation in the impedance amplitude, the gain factor should be as close to the upper limit value as possible in order to reduce the influence. Selectable increaseCoefficient of benefit k vir1 =200, damping ratio ζ vir1 =1.0, undamped oscillation frequency f vir1 =260 Hz as a parameter of the first divided active damping controller 1.
To make the real part and the imaginary part of the second damping controller show monotone property, the undamped oscillation frequency f is selected vir2 =1250 Hz, substituting the first damping controller parameter and the original controller parameter into the second damping controller parameter constraint relation obtained in the previous step, and preferably satisfying f min2 Under the condition of the constraint relation between the damping ratio and the gain coefficient, the damping ratio xi of the second damping controller is obtained vir2 < 0.35. This range of parameters does not take into account the influence of the first high-frequency oscillation risk region, it is recommended to choose a smaller damping ratio, for example ζ vir2 =0.1, and k can be calculated vir2 Should be greater than 143.3, select k vir2 =160. If Yubei engineering alternating current system minimum phase theta acmin Checking inequality (12) yields 0.0652 < 0.0699, which indicates that high frequency oscillations do not occur above 2.5kHz if the actual engineering parameters are 86 pi/180 pi 1.5. However, this example considers more severe conditions, tan (0.5pi+θ acmin ) =0.0087, inequality (12) does not hold, and there is a risk of high-frequency oscillation above 2.5kHz in this example.
In order to eliminate the influence, based on the reduction of the influence of the two previous risk frequency bands, a third frequency division damping controller 3 is designed to be added with a parameter k vir3 ＝50、ξ vir3 ＝0.02、f vir3 Check meets stability requirements =2500 Hz.
S8, outputting compensation voltage e generated by the frequency division damping controller isd And e isq ：
Setting compensation voltage output limit value E is_lim . I to be acquired sd And i sq After passing through the frequency division damping controller, a compensation voltage e is generated isd And e isq The method comprises the steps of carrying out a first treatment on the surface of the Will compensate voltage e isd And e isq And the limiting value E is_lim In contrast, if the d-axis (q-axis) divided damping controller output value is at + -E is_lim In, directly outputting; otherwise, output clippingValue E is_lim or-E is_lim Specifically, the formula (13) and the formula (14) are shown.
Wherein E is is_lim 2% of the rated ac voltage may be taken.
Will output value e isd And e isq And the original current inner loop output valueAnd->And (5) superposing the materials and sending the materials to a valve control link. The implementation of the patent specific case of the invention is completed.
Claims (9)
1. A method for suppressing high-frequency oscillation frequency division and designing parameters of a flexible direct current transmission system is characterized by comprising the following steps:
s1, acquiring the impedance Z of an alternating current system at a PCC point ac And a minimum phase theta acmin ；
S2, obtaining the impedance Z of the flexible direct current converter station at the PCC point mmc ；
S3, determining the number H of high-frequency oscillation risk areas res And its frequency interval value;
s4, determining the number N of parallel frequency division damping controllers damp ；
S5, acquiring input quantity of a frequency division damping controller;
s6, calculating and designing parameters of the frequency division damping controller;
s7, checking parameters of the frequency division damping controller;
s8, outputting compensation voltage e generated by the frequency division damping controller isd And e isq 。
2. The method for suppressing and designing parameters of high-frequency oscillation frequency division of a flexible DC power transmission system according to claim 1, wherein step S1 is performed by obtaining an impedance Z of an AC system at a PCC point ac And a minimum phase theta acmin ：
Obtaining an ac system impedance Z at a PCC point ac Two major types are a scanning method and a calculation method, wherein the scanning method is to build an alternating current system in simulation software, input three-phase symmetrical alternating current voltage sources with different frequencies into PCC points, obtain current response conditions under all possible operation modes, calculate impedance values of each frequency of the PCC points and form a scanning curve Z ac According to the distributed parameter model or a plurality of pi series equivalent models, the calculation method calculates the equivalent impedance Z of the alternating current system by adopting a node voltage method or a one-by-one iteration method ac However, the frequency-dependent characteristic and the coupling effect of the circuit are difficult to consider in the calculation method, the universality is relatively poor, the calculated impedance characteristic curve is relatively strict, and the parameter calculation result of the frequency division damping controller is more conservative than that of the scanning method; at the same time, the communication system Z is plotted in all possible permissible operating modes in the frequency range of interest ac Impedance characteristic curve, including amplitude-frequency characteristic curve and phase-frequency characteristic curve, on which the minimum value theta of impedance phase of AC system is found acmin The representation may be in radians or in angular values.
3. The method for suppressing and designing parameters for high-frequency oscillation frequency division of a flexible direct current transmission system according to claim 1, wherein step S2 is performed by obtaining the impedance Z of the flexible direct current converter station at the PCC point mmc ：
Further, the impedance Z of the flexible direct current converter station is obtained mmc The method is very suitable for the situation that the control system model of the converter station is not disclosed outside, namely a black box converter station, can consider the transmission process of actual link delay, and the calculation rule is based on the operation principle of the flexible direct current converter station,the relation between the voltage and the current at the PCC is calculated by adopting a linearization method, so that the key influence links of the impedance of the converter station and the influence rules thereof can be clearly known, and a theoretical basis is laid for the provision of the frequency division damping controller; also, in the frequency range of interest, with Z ac Overlapping together, plotting Z of a flexible DC converter station at different operating power levels mmc The impedance characteristic curve comprises an amplitude-frequency characteristic curve and a phase-frequency characteristic curve.
4. The method for suppressing and designing parameters of high-frequency oscillation frequency division of a flexible direct current transmission system according to claim 3, wherein the step S3 is characterized in that the number H of the risk areas of high-frequency oscillation is determined res And its frequency interval value:
further, Z is obtained based on step S1 and step S2 ac And Z mmc Amplitude-frequency characteristic curve and phase-frequency characteristic curve, find all possible Z in each capacitive frequency interval range of AC system ac And Z mmc Determining each Z by the cross point frequency of the amplitude-frequency characteristic curve ac And Z mmc Taking the maximum value of the number as the number H of the high-frequency oscillation risk areas res The method comprises the steps of carrying out a first treatment on the surface of the At the same time, at 1 st to H res Recording the minimum and maximum values of the frequency of each interval within the range of the risk interval of the high-frequency oscillation, namely [ f ] min1 ,f max1 ]、[f min2 ,f max2 ]、[f min3 ,f max3 ]、…，[f minHres ,f maxHres ]Each recorded interval value is slightly larger than the actual intersection frequency range, e.g. a relative relaxation of 1% of the frequency error.
5. The method for suppressing and designing parameters of high-frequency oscillation frequency division of a flexible DC power transmission system as defined in claim 4, wherein the step S4 is characterized by determining the number N of parallel frequency division damping controllers damp ：
Further, considering that the frequency division frequency bands realize the suppression of the high-frequency oscillation and each frequency band is dominated by a frequency division damping controller, the number H of the high-frequency oscillation risk areas is determined according to the step S3 res Preliminary selection of the number N of frequency-dividing damping controllers damp ≥H res Suggesting selection of N damp ＝H res Or N damp ＝H res +1。
6. The method for suppressing and designing parameters of high-frequency oscillation frequency division of a flexible direct current transmission system according to claim 5, wherein the step S5 is characterized in that the input quantity of the frequency division damping controller is obtained:
further, the input may be voltage or current. Converting three-phase voltage or current input quantity into dq coordinate system by Park conversion to obtain d-axis and q-axis input quantity, when taking negative sequence control into consideration, the positive sequence damping controller input quantity is positive sequence d-axis and q-axis voltage or current, the negative sequence is negative sequence d-axis and q-axis voltage or current, and the d-axis and q-axis input quantity is input into N damp And the frequency division damping controllers.
7. The method for suppressing and designing parameters for high-frequency oscillation frequency division of a flexible direct current transmission system according to claim 6, wherein the parameters of the frequency division damping controller are calculated and designed in step S6:
after the d-axis input quantity property and the q-axis input quantity property are determined, the impedance Z of the flexible direct current converter after the frequency division damping controller is considered is determined mmc The expression is used for calculating or designing parameters of the frequency division damping controller from a first high-frequency oscillation risk region one by one, and constraint conditions adopted by parameter calculation or design are mainly found through stability criteria, namely, the phase curve of the impedance real part cosine function is in the high-frequency oscillation risk region [ f ] min1 ,f max1 ]、[f min2 ,f max2 ]、[f min3 ,f max3 ]、…，[f minHres ,f maxHres ]The internal damping range is as wide as possible, namely [360 DEG k-90 DEG, 360 DEG k+90 DEG]And in the range, obtaining the parameter constraint condition of the frequency division damping controller through the condition, and determining the parameter selection range.
8. The method for suppressing and designing parameters of high-frequency oscillation frequency division of a flexible direct current transmission system according to claim 7, wherein the step S7 is characterized in that:
further, in the parameter selection range calculated in step S6, proper values are selected to perform positive sequence and negative sequence impedance characteristic curve checking, i.e. to verify whether the calculated or designed frequency division damping controller parameters can maintain the stability of the system.
9. The method for suppressing and designing parameters of high-frequency oscillation frequency division of a flexible DC power transmission system according to claim 8, wherein the compensation voltage e generated by said output frequency division damping controller in step S8 isd And e isq ：
Setting compensation voltage output limit value E is_lim The method comprises the steps of carrying out a first treatment on the surface of the After the obtained input quantity passes through the frequency division damping controller, a compensation voltage e is generated isd And e isq The method comprises the steps of carrying out a first treatment on the surface of the Will compensate voltage e isd And e isq And the limiting value E is_lim In contrast, if the d-axis (q-axis) divided damping controller output value is at + -E is_lim In, directly outputting; otherwise, output limiting value E is_lim or-E is_lim The method comprises the steps of carrying out a first treatment on the surface of the The output value is compared with the original current inner loop output valueAnd->And (5) superposing the materials and sending the materials to a valve control link.
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