CN110808595B - Method for coordinately optimizing transient stability and dynamic stability of excitation gain - Google Patents
Method for coordinately optimizing transient stability and dynamic stability of excitation gain Download PDFInfo
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Abstract
本发明公开一种励磁增益对暂态稳定及动态稳定的协调优化方法，应用于动稳制约系统，包括：确定待优化区域；计算待优化区域内励磁控制系统的静稳极限、暂稳极限和动稳极限；基于计算得到的静稳极限、暂稳极限和动稳极限，确定待优化的主要参与机组；调整主要参与机组的PSS增益参数至最优；调整励磁增益参数，使静稳极限、暂稳极限和动稳极限中的最小值最大。本发明通过调整励磁增益来协调系统动态稳定和暂态稳定的关系，有效抑制系统低频振荡现象，提高整体输电能力。
The invention discloses a coordinated optimization method of excitation gain for transient stability and dynamic stability, which is applied to a dynamic stability control system, comprising: determining an area to be optimized; calculating the static stability limit, temporary stability limit and Dynamic stability limit; based on the calculated static stability limit, temporary stability limit and dynamic stability limit, determine the main participating units to be optimized; adjust the PSS gain parameters of the main participating units to the optimum; adjust the excitation gain parameters so that the static stability limit, The minimum value of the transient stability limit and the dynamic stability limit is the largest. The present invention coordinates the relationship between the dynamic stability and the transient stability of the system by adjusting the excitation gain, effectively suppresses the low-frequency oscillation phenomenon of the system, and improves the overall power transmission capacity.
Description
Technical Field
The invention belongs to the field of Power systems, and particularly relates to a method for coordinately controlling excitation gain and Power System Stabilizer (PSS) gain, in particular to a method for coordinately optimizing transient stability and dynamic stability by excitation gain.
Background
In recent years, with the increase of loads, the construction of extra-high voltage grid frames and the import of direct current, the power receiving proportion of a power grid is higher and higher, the application of a strip-shaped power transmission mode is wider and wider, the transient stability of a power system is enhanced, but the problem of inter-area low-frequency oscillation is more and more prominent. At the present stage, the main measure for suppressing the low-frequency oscillation of the system is to add a PSS device, which is an additional control link of the excitation system of the generator set and can effectively reduce the negative damping torque brought by the high gain of excitation, but the PSS device is limited by the critical gain, and the effect of compensating the positive damping cannot be infinitely increased.
The excitation system is used as a main control link of the generator and has the task of maintaining the voltage of the generator at a given value level and improving the running stability of the power system, wherein the influence of the excitation system on the system stability is mainly reflected on static stability, transient stability and dynamic stability. In practical engineering applications, the excitation system generally adopts high-gain control to improve the power transmission capacity and the system stability level, but the dynamic stability level of the system is also reduced. Aiming at the current grid subjected to dynamic stability, the excitation gain can be properly reduced so as to coordinate the relationship between the dynamic stability and the transient stability of the system and improve the whole power transmission capacity.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a method for coordinating and optimizing transient stability and dynamic stability by excitation gain.
In order to achieve the purpose, the invention adopts the technical scheme that:
a coordinated optimization method of excitation gain to transient stability and dynamic stability is applied to a dynamic stability restriction system, and comprises the following steps:
determining a region to be optimized;
calculating a static stability limit, a transient stability limit and a dynamic stability limit of an excitation control system in a region to be optimized;
determining a main participating unit to be optimized based on the statically stable limit, the temporarily stable limit and the dynamically stable limit obtained by calculation;
adjusting PSS gain parameters of main participating units to be optimal;
and when the dynamic stability limit is still greatly lower than the transient stability limit, adjusting the excitation gain parameter to maximize the minimum value among the static stability limit, the transient stability limit and the dynamic stability limit.
Preferably, the dynamic stability constraint system is a system in which the dynamic stability limit is smaller than the transient stability limit and the static stability limit.
Preferably, the determining the region to be optimized further comprises: and dividing important power transmission sections according to the research scale and the partition condition, and counting the installed load and power balance condition in the area to be optimized.
Preferably, the calculating the instability limit, the transient stability limit and the dynamic stability limit of the excitation control system in the area to be optimized further comprises: the static stability limit is that the maximum transmission power of the transmission line or the section is obtained by gradually increasing the power of the sending end unit and correspondingly reducing the power of the receiving end unit or increasing the load of the receiving end; the transient stability limit is a stability limit which enables any two units in the same system not to have periodic desynchronizing relative angle through starting and stopping the receiving end units; the dynamic stability limit is a stability limit which enables the system not to generate divergent oscillation after being disturbed by increasing section power.
Preferably, determining the main participating group to be optimized further comprises: and calculating limit modes of a static stability limit, a transient stability limit and a dynamic stability limit by using an SSAP small interference analysis program in the BPA, determining a mode with the oscillation frequency within 0.1-1.0 Hz and the minimum damping as a dominant oscillation mode, and taking a main participating unit in the mode as an object to be optimized.
Preferably, the adjusting the PSS gain parameter of the main participating unit to the optimal further comprises: the PSS gain is increased.
Preferably, adjusting the excitation gain parameter to maximize the minimum of the stationarity limit, the transient stability limit, and the dynamic stability limit further comprises: and when the dynamic stability limit is still greatly lower than the transient stability limit after the PSS gain parameter is adjusted, the dynamic stability level is improved by adjusting the excitation gain, and the minimum value among the dynamic stability limit, the transient stability limit and the static stability limit is the largest.
Preferably, the value range of the direct-axis transient open-circuit time constant of the excitation control system is 6-10.
Compared with the prior art, the invention has the beneficial effects that: according to the control principle and parameter requirements of the excitation system, the influence of the excitation gain on the static stability limit, the transient stability limit and the dynamic stability limit of the system is analyzed, and the adjustment range of the excitation gain under the condition of safety and stability is determined; by coordinating the excitation gain and the PSS gain parameters, the transient stability limit and the dynamic stability limit of the system are both at a higher level, and the system transmission capacity is increased.
Drawings
FIG. 1 is a schematic diagram of a typical excitation system and generator connection according to an embodiment of the invention;
FIG. 2 is a model of a generator according to an embodiment of the invention;
FIG. 3 is an exemplary self shunt excitation system model according to an embodiment of the present invention;
FIG. 4 shows T according to an embodiment of the present inventiond'oThe distribution condition of parameters;
FIG. 5 is a simplified diagram of an excitation system transfer function according to an embodiment of the invention;
FIG. 6 is a schematic diagram of a stand-alone infinity bus according to an embodiment of the present invention;
FIG. 7 is a diagram illustrating a standalone infinity system according to an embodiment of the present invention;
FIG. 8 is a schematic diagram illustrating the effect of excitation transient gain on system damping ratio according to an embodiment of the present invention;
FIG. 9 is a Huazhong power grid partition diagram according to an embodiment of the present invention;
FIG. 10 is a graph of post city bus voltage before and after PSS parameter adjustment according to an embodiment of the present invention;
FIG. 11 is a graph of active power curves of lines from Xiang Bao City to Hu Song Bao according to the PSS parameter adjustment of the embodiment of the present invention;
fig. 12 is a schematic diagram illustrating an effect of excitation gain variation on line power of songba-sentry city according to an embodiment of the present invention;
fig. 13 is a schematic diagram illustrating an influence of an excitation gain on a frequency change of a kumquat set according to an embodiment of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. 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.
The invention provides a coordinated optimization method of transient stability and dynamic stability by excitation gain, which comprises the following steps:
1) determining the study area and calculating the boundary.
Determining research scale and partition conditions, dividing important power transmission sections, and counting installed load, load and power balance conditions in the area;
2) and calculating the static stability limit, the transient stability limit and the dynamic stability limit of the system.
And adjusting the current of the important power transmission section by starting and stopping the unit operation and the like so that the system reaches the corresponding stable limit. The static stability limit can obtain the maximum transmission power of a transmission line or a section by gradually increasing the power of a sending end unit and correspondingly reducing the power of a receiving end unit or increasing the load of the receiving end, and is only used for theoretical calculation and does not count the stability restriction problem; the transient stability limit can be a stability limit that any two units in the same system do not periodically lose step relative to the angle by starting and stopping the receiving end unit; and the dynamic stability limit can be a stability limit which can prevent the system from generating divergent oscillation after being disturbed by increasing the section power. The invention does not make any correction for the system with transient stability restriction. For a system with dynamic stability restriction, namely the dynamic stability limit is smaller than the transient stability limit and the static stability limit, the optimization can be carried out by adjusting the PSS parameter and the excitation parameter;
3) the low-frequency oscillation mainly participates in the selection of the unit.
And (3) calculating the limit mode in the last step by using an SSAP small interference analysis program in the BPA, and taking the mode with the oscillation frequency within 0.1-1.0 Hz (the oscillation mode in the area with great harm) and the minimum damping as a dominant oscillation mode, wherein the main participating machine set in the mode is the current participating optimization object.
4) And adjusting the PSS parameters to be optimal so as to improve the dynamic stability level of the system.
The most effective method for suppressing the low-frequency oscillation is to add a PSS device, and for the generator with the PSS installed, the dynamic stability limit can be improved by adjusting the PSS parameters (such as increasing the gain of the PSS);
5) and determining an excitation gain adjustment range, and properly adjusting excitation parameters to enable the stability limit to be at a higher level.
When the dynamic stability limit is still greatly lower than the transient stability limit after the PSS parameters are adjusted, the dynamic stability level can be improved by properly adjusting the excitation gain, the minimum value among the dynamic stability limit, the transient stability limit and the static stability limit is maximized, and the system transmission capacity is increased.
The invention researches the influence of the excitation gain on the static stability limit, the transient stability limit and the dynamic stability limit of the system by analyzing the control principle and the parameter requirement of the excitation system, and determines the adjustment range of the excitation gain under the condition of safety and stability; then, taking a single-machine infinite system and a certain actual power grid as an example, by coordinating excitation gain and PSS gain parameters, the transient stability limit and the dynamic stability limit of the system are both at a higher level, and the effectiveness of the excitation gain on the regulation of the power transmission capacity of the system is verified.
In the implementation of the invention, the excitation control system mainly has the following functions:
the excitation control system of a synchronous generator, especially a large synchronous generator, has an important influence on the safe and stable operation of a power system. The task of the field control system, although many, is to maintain the voltage of the generator (or other control point such as the high-side bus of the plant) at a given value and to improve the stability of the operation of the power system (on the premise of high reliability).
The synchronous generator excitation control system can accomplish many tasks, but the most basic and important task among them is to maintain the generator-side (or designated control point) voltage at a given level. The national standard of China stipulates that the automatic voltage regulator should ensure that the terminal voltage static difference rate of the synchronous generator is less than 1%. This requires that the open loop gain (steady state gain) of the excitation control system be no less than 100p.u (for hydro-generators) or 200p.u (for turbo-generators). Maintaining the generator terminal voltage at a given voltage level is the most fundamental primary task of an excitation control system for three main reasons.
Firstly, the safety of the power system operation equipment is ensured. Devices operating in the power system all have their rated operating voltage and maximum operating voltage. The voltage level of the generator is the basis of the operating voltage levels of all points of the power system, the voltage of the generator end is ensured to be at the allowable level, and the voltage level of the generator end is one of the basic conditions for ensuring the voltage of the generator and the voltage of all points of the system to be at the allowable level, namely one of the basic conditions for ensuring the safe operation of the generator and the power system equipment, so that the generator excitation system is required to be not only in a static state, but also be capable of ensuring the voltage level of the generator to be at the given allowable level in a stable state after large disturbance. The generator operation regulations stipulate that the normal variation range of the operation voltage of the large synchronous generator is 5%, and the maximum voltage cannot be higher than 110% of a rated value.
Second, the economy of generator operation is guaranteed. It is most economical for the generator to operate near the rated value. When the generator voltage drops, the stator current required to output the same power rises, increasing losses. When the voltage of the generator drops too much, the output of the generator will be limited due to the limitation of the stator current. Therefore, the generator operating regulations stipulate that the large generator operating voltage cannot be below 90% of the rated value, and when the generator voltage is below 95%, the generator should be operated with limited load, which is also a problem for other electrical equipment.
Third, the need to increase the ability to maintain generator voltage and the need to increase power system stability are consistent in many respects. It can be seen from subsequent analysis that the static stability and transient stability level of the power system are improved while the capability of the excitation control system to maintain the voltage level of the generator is improved.
Further, the gain adjustment range of the excitation control system is analyzed as follows:
the connection relationship between the excitation system and the generator is shown in fig. 1.The six-winding model (dq0 coordinate system) of the generator is shown in fig. 2, wherein x and y are damping windings, f is an excitation winding, and g is a short-circuit damping coil formed in a q-axis iron core. Excitation system model as shown in FIG. 3, VERRAs a voltage deviation signal, VSIs a reference voltage signal, K is a regulator gain, T1、T2、T3、T4To adjust the time constant, KVAdjusting the selection factor, K, for proportional integralA、TAIs the gain and time constant of the voltage regulator, KFTF is the gain and time constant of the voltage regulator stable loop, VHFor low excitation limiting signal, VL2For overdriving the limiting signal, EFDAnd the signals are output at the speed of excitation.
It can be seen from fig. 1 and 2 that the excitation system mainly acts through the excitation winding of the generator set, and the main parameter of the excitation winding is a direct-axis transient open-circuit time constant T'doThe influence of the parameter on the open-loop amplification factor of the excitation system is large, because the excitation system needs to keep enough open-loop amplification factors in order to meet the requirements of the excitation system on static stability, dynamic stability and generator quality regulation, and the requirements on two aspects are mainly as follows:
1) the voltage regulation precision is generally 0.5 percent, and the steady state amplification factor of the excitation system is required to be more than 200 times;
the step response of the generator under no load: the step quantity is 5% of rated voltage of the generator, the overshoot is not more than 30% of the step quantity, the oscillation frequency is not more than 3 times, the rising time is not more than 0.6s, and the adjusting time is not more than 5 s. The index requires that the excitation system has enough open-loop amplification factor to match with different generator set parameters to meet the performance index.
According to the 2019 year calculation database of the state network, the total number of the 1200 left and right generator parameters T 'in the database'doThe distribution of (2) is shown in fig. 4.
As can be seen from FIG. 4, most of the generators T'doBetween 6 and 10. Therefore, T 'in the invention'doThe value range is 6-10. As a mechanism study, the excitation system employs a simplified transfer function:
wherein K is the excitation steady-state gain, T1、T2Is the voltage regulator time constant. Considering the generator field winding, the whole field system can be simplified into a transfer function block diagram as shown in fig. 5.
The closed loop transfer function is then:
the general differentiation is simplified as follows:
finishing to obtain:
further simplification obtains:
considering that K is much greater than 1, there are:
1+ K ≈ K, substituting into the above formula:
let the denominator factorize:
then the following results are obtained:
if T isxIf the above two equations are satisfied simultaneously, the transfer function can be simplified as follows:
to meet the requirement of the step response of the generator in no-load time, especially the requirement of 0.6s of rise time, the generator is composed of
The result of the function is known, then requires:
2.3×Tx＜0.6 (9)
namely:
Tx＜0.26 (10)
belt 7, gives:
considering 6 ≦ T'doLess than or equal to 10, obtaining
And analyzing the amplification factor of the excitation system meeting the no-load requirement of the single machine. Consider a typical excitation system transfer function:
in the classical control theory, the method is generally divided into a steady-state gain and a transient-state gain, wherein the steady-state gain is s → 0 time gain and is K; the transient gain is a gain at s → ∞ and is
Consider that there is generally T1≈10T2Then bring in
The following can be obtained:
232≤K≤384 (13)
further consider T2＝1,T1When 10, the transient gain of the excitation system is:
the above results show that T is more than or equal to 6d'oAnd the minimum value of the transient gain of the excitation system is less than or equal to 10. The specific calculation for out-of-range excitation systems can be based on equation 11.
Further, the influence of the excitation control system on the stability is reflected in:
1) effect of synchronous motor excitation control system on improving static stability of electric power system
FIG. 6 is a single machine infinity system wherein Xd＝Xq1.5 is generator AC and DC reactance, X'd0.3 is the transient reactance of the generator direct axis, XT1＝XT20.1 is equivalent reactance of transformer on two sides, XL0.8 is the equivalent reactance of the line, EqFor generator synchronous potential amplitude, E' for transient potential amplitude, UtWhen the voltage at the system side is taken as the reference value as the amplitude of the generator-end voltage, the power angles of the generators are delta respectivelyEq、δE’、δUt，UsInfinite system side voltage amplitude. Based on the synchronous potential, transient potential and generator terminal voltage U of the generatortThe generator delivers power PECan be expressed as:
is provided with a Ut＝1.0,UsWhen the voltage of the generator is equal to 1.0, an operator does not adjust excitation manually after the generator is connected to the grid, and the static stability limit in the absence of a voltage regulator, the limit in the presence of a voltage regulator capable of maintaining constant E' and the voltage U at the end of the generator can be maintainedtThe static stability limits for a constant voltage regulator are: 0.4, 0.77 and 1.0. It can be seen that when the automatic voltage regulator is able to maintain the generator voltage constant, the quiescent stability limit reaches the line limit, increasing it by about 30% over the regulator that maintains E' constant. The requirement to maintain the generator voltage level is consistent with and compatible with the requirement to raise the static stability limit of the power system. And when the excitation control system can maintain the voltage of the generator at a constant value, the static stability limit can reach the line limit no matter the fast excitation system or the conventional excitation system.
2) Synchronous motor excitation control system for improving transient stability of power system
Transient stability is the stability of a power system after a large disturbance. The effect of the excitation control system on improving the transient stability of the power system is mainly determined by three factors.
The strong excitation top value multiple of the excitation system. The transient stability of the power system can be improved by improving the forced excitation multiple of the excitation system. The requirement of improving the forced excitation multiple of the excitation system is compatible with the requirement of improving the voltage regulation precision without contradiction.
And secondly, excitation system top voltage response ratio. The larger the excitation system top voltage response ratio is, the shorter the time for the excitation system output voltage to reach the top value is, and the more beneficial the transient stability is to be improved. The top voltage response ratio is mainly determined by the type of the excitation system, but the control law and parameters of the excitation controller may also have a significant influence on the voltage response ratio. The excitation control system with excellent control law and parameters can transform a slow excitation into a high-starting excitation system close to a fast excitation system, and the excitation control device with unreasonable law and parameters can also change a fast excitation system into a slow excitation system. Under the same control law, the open-loop gain of the excitation control system is increased, so that the response ratio of the excitation voltage can be improved, and the voltage regulation precision is also improved.
And utilizing degree of strong excitation multiple of the excitation system. The strong excitation times of the excitation system are fully utilized, and the strong excitation times are also an important factor for improving the transient stability of the excitation system. If the output voltage of the excitation system does not reach the top value or the time for maintaining the top value is short when the power system fails, and the generator voltage is not forced when the voltage of the generator is not restored to the value before the failure, the forced excitation multiple of the generator is not well exerted, and the effect of improving the transient stability is not good. One of the measures of fully utilizing the top voltage of the excitation system is to improve the open-loop gain of the excitation control system, the larger the open-loop gain is, the more fully the strong excitation multiple is utilized, and the higher the voltage regulation precision is, so that the transient stability of the power system is better improved.
Therefore, the capability of the excitation control system for maintaining the terminal voltage level is improved, and the transient stability of the power system is consistent and compatible.
3) Effect of synchronous motor excitation control system on improving dynamic stability of electric power system
The dynamic stability problem of the power system can be understood as the damping problem of the electromechanical oscillation of the power system, and the automatic voltage regulation function in the excitation control system is one of the most important reasons for weakening (even becoming negative) the damping of the electromechanical oscillation of the power system. Under a certain operation mode and excitation system parameters, the voltage regulation function can generate a negative damping function while maintaining the voltage of the generator constant. Many studies have shown that, within normal practical limits, the negative damping of the excitation voltage regulator increases with increasing open loop gain. The requirements for improved voltage regulation accuracy and improved dynamic stability are therefore incompatible. The solutions to this incompatibility are:
firstly, a dynamic gain attenuation link is added in a voltage regulation channel. The method can achieve two purposes of not only keeping the voltage regulation precision, but also reducing the negative damping action of the voltage regulation channel. However, this link reduces the response ratio of the excitation voltage, which is not preferable because it is not favorable for transient stability.
Secondly, in the excitation control system, an additional excitation control channel is added to solve the effective measure of contradiction between voltage regulation precision and dynamic stability, and other control signals are added in the excitation control system. Such control signals may provide a positive damping effect such that the damping provided by the overall excitation control system is positive, while the dynamic stability limit level reaches and exceeds the transient and static stability levels. Such control signals do not affect the voltage regulation function of the voltage regulation channels and the ability to maintain the voltage level at the generator terminals, changing their primary control position. But limited by critical gain, have limited ability to raise the dynamic stability limit.
In addition, there is another method of suppressing low frequency oscillation: under the allowable conditions of static stability and transient stability, the requirement of voltage regulation precision is properly reduced, and the open-loop gain of an excitation control system is reduced so as to improve the dynamic stability. Although the static stability level and the transient stability level are reduced, the adjusted limit value is not less than the dynamic stability limit, and the transmission capacity of the entire system can be increased.
Example 1
The present embodiment is exemplified by a single machine infinity. A certain generator in an actual power grid is introduced, a single-machine infinite system shown in fig. 7 is built, the inertia time of the generator is tried to be 11.15 seconds, the transient open-circuit time constant of a direct axis is 8.72, excitation is a typical self-shunt excitation static excitation system, the excitation steady-state gain is 377p.u., the equivalent excitation time constants T1 and T2 are 0.3 and 0.06, and the transient gain is 75 p.u.; the PSS is a PSS2B type with the speed deviation and the acceleration power input together, and the PSS initial gain is 1.0p.u.
Under the fault of three permanent N-1 of a bus 1-bus 2 line, the system has the dynamic stability problem, the oscillation frequency is 0.747Hz, and the damping ratio is-0.0162; the output condition of the generator is adjusted to obtain that the static stability limit of the system is 1850MW, the transient stability limit is 1235MW, and the dynamic stability limit is 1100 MW.
Given that the PSS of the PSS2B type has a critical gain of one third to one half, assuming that the initial gain of the PSS is one third, the PSS gain can be adjusted from 1.0 to 1.5 at most, and the system dynamic stability limit is increased to 1170MW, which is a difference of 65MW from the transient stability limit.
As can be seen from the system excitation parameters and equation 11, the minimum value of the excitation gain K is 168p.u. In order to continuously improve the power transmission capacity of the system, the variation condition of the system stability limit is shown in table 1 after the excitation gain K is reduced from 377p.u. to 352p.u. As can be seen from the table, the excitation transient gain of the generator is reduced, the transient stability limit of the system is reduced to 1190MW, the dynamic stability limit is increased to 1185MW, the dynamic stability limit and the transient stability limit are basically equal, and the overall power transmission capacity is increased by 85MW (8%) compared with the original parameter.
TABLE 1 Effect of excitation gain on System transport Limit
Fig. 8 shows the active power change of the other circuit after the failure of three permanent N-1 of the bus 1 to the bus 2, the adjustment of the parameter of the PSS, and the adjustment of the parameter of the PSS and the excitation parameter under the same 1100MW transmission power. The low-frequency oscillation phenomenon of the system is effectively inhibited, the transient stability problem does not occur, and the effectiveness of the method is verified.
Example 2
The present embodiment is exemplified by the chinese power grid. Fig. 9 is a geographical wiring diagram of the chinese power grid for a year, and the scale of each provincial power grid and the power of each tie line are marked in the diagram. The mode is a north Henan-Hunan hedging mode with summer, large load and large power generation, the power transmitted from the Hunan is 1000MW, the power transmitted from the North Henan is 3600MW, and the mode is limited by the benefit of the north Henan outgoing line to Jia single Yong N-1 and is under the dynamic stability limit transmission power. The transient stability limit of the northern Henan delivery section is 7250MW, and the static stability limit is 9400 MW. The system needs to coordinate the dynamic stability and the transient stability of the system by adjusting the excitation gain.
Table 2 shows the small interference analysis results of the operation mode set, and it can be known that the damping ratio of the north-south africa oscillation mode system is the minimum, and the system is the dominant oscillation mode.
TABLE 2 analysis table of small interference in initial operation mode
Statistics is conducted on the main participating unit in the dominant oscillation mode, 60 generators meeting the conditions are provided, 8 PSS devices are of a PSS1A type, the rest 52 PSS devices are of a PSS2B type, excitation is a typical self-shunt excitation static excitation system, and the main oscillation mode part participating unit is shown in table 3.
Table 3 mode 1 oscillation mode part of north-south yunnan participating units
The PSS gain of all the main participating units meets the setting requirement and is one third of the critical gain. In order to improve the dynamic stability limit of the system, the PSS gain is now increased to 1.5 times of the original value, i.e. one half of the critical gain, and fig. 10 and 11 are graphs for adjusting the bus voltage of the post city and the active power curve of the post city-Song sentry lines before and after the PSS, so that the problem of low-frequency oscillation is effectively suppressed. After the PSS is adjusted, the dynamic stability limit of the North Henan section is increased to 5800MW, and the dynamic stability limit of the North Henan section is 1450MW from the temporary stability limit 7250 MW.
In order to further improve the power transmission capacity of the system, excitation parameters of main participating units are properly adjusted.
The direct-axis transient open-circuit time constant, the excitation steady-state gain and the excitation transient gain of the main participating units are given in table 3, and the minimum value of the excitation gain of each unit can be known by combining formula 11. And uniformly adjusting the parameters of the main participating units by taking the current excitation steady-state gain and the minimum excitation gain as boundaries and taking the adjustable excitation gain ratio as a variable.
Table 4 shows the effect of excitation gain on the transmission capacity of the north-Henan section. As can be seen from the table, when the excitation gain is reduced to 80%, the dynamic stability limit and the transient stability limit of the north-seeking section are basically the same, and the maximum power transmission capacity of the system is 6200MW at the moment, which is increased by 400MW compared with that before the excitation gain is adjusted; fig. 12 and 13 are graphs showing the change curves of the frequency of the jinzhushan unit and the active power of the line from the songhba dam to the sentry city when a huji-gain singleton N-1 fault occurs in 5800MW outgoing before and after the adjustment of excitation, so that the dynamic stability of the system is improved to a certain extent, and the effectiveness of the method is verified.
TABLE 4 influence of excitation gain variation on transmission capacity of North Henan section (unit: MW)
| Excitation gain adjustment ratio | Dynamic stability limit of north Henan section | Temporary stability limit of north Henan fracture surface | Difference value between dynamic stability limit and temporary stability limit |
| 100％ | 5800 | 7250 | -1450 |
| 95％ | 5890 | 6910 | -1020 |
| 90％ | 6000 | 6670 | -670 |
| 85％ | 6110 | 6440 | -330 |
| 80％ | 6200 | 6220 | -20 |
| 75％ | - | 6010 | - |
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
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