CN106875127B - Unified power flow controller reliability modeling and access power grid reliability assessment method thereof - Google Patents
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Abstract
A unified power flow controller reliability modeling and access power grid reliability assessment method is provided, which starts from a UPFC physical structure, analyzes the functional characteristics and the logic relationship of the constituent elements, decomposes the UPFC into 5 subsystems, establishes the reliability model of each subsystem, and finally obtains the reliability model and the reliability parameters of the UPFC device by adopting a series-parallel analysis method. On the basis, the influence of the UPFC on the bus voltage and the line load flow of the power grid after being accessed is analyzed, the magnitude of the voltage out-of-limit load and the line load flow out-of-limit load is calculated and eliminated, and the power grid reliability evaluation method considering the UPFC is provided. The method can be applied to the power grid planning and operation stages, has important significance for analyzing the influence of novel equipment on the reliability of the power grid and then guiding the later-stage upgrading and reconstruction of the power grid.
Description
Technical Field
The invention relates to a reliability modeling method for a unified tidal current controller in a power system and a reliability evaluation method for accessing the unified tidal current controller into a power grid, belonging to the field of reliability evaluation of the power system.
Background
Along with the continuous increase of the power demand, the load of the power transmission line is larger and larger, and in addition, the power supply and the load center are not distributed uniformly, so that long-distance and ultrahigh-voltage power transmission needs to be matched. The problems of voltage fluctuation, power backflow, power bypass and the like generated by the method influence the safe and stable operation of the power grid. How to ensure the safe and stable operation of a large power grid and research of related electrical devices become the research focus of the power industry.
A Unified Power Flow Controller (UPFC) has attracted attention as a hybrid alternating Current transmission systems (FACTS) device with the strongest Power Flow regulation capability. The UPFC realizes a voltage source connected in series in a circuit by utilizing a power electronic switch principle, plays the roles of circuit parameter compensation, independent reactive compensation and circuit power flow control, has excellent power flow control performance and can perform quick dynamic response on the change of power flow. The method is the most effective one of a plurality of power flow control methods, and can control by changing and compensating parameters such as voltage amplitude, power angle and line impedance. However, the UPFC has a complex structure, and includes links such as a series transformer, a parallel transformer, a Voltage Source Converter (VSC) or a Modular Multilevel Converter (MMC), a dc line, a dc capacitor, and a control and protection system, and detailed modeling work for reliability of the UPFC has not been performed yet, so that the reliability of a power grid including the UPFC is not influenced.
Therefore, in order to more effectively evaluate the influence of the UPFC on the reliability of the power grid and further guide the subsequent upgrading and reconstruction of the power grid, the working mechanism of the UPFC needs to be deeply analyzed, and a UPFC refined reliability model which is suitable for the evaluation requirement of the power grid is established through the analysis of the logical relationship among the components; on the basis, the regulation capacity of the UPFC on the voltage and the line current of the power grid after being accessed is analyzed, a load shedding strategy which accords with the control characteristics of the UPFC is researched, and the evaluation of the influence of the UPFC access on the reliability of the power grid is important.
Disclosure of Invention
In view of the above problems, the present invention aims to provide a unified power flow controller reliability modeling method, and on this basis, provide a power grid reliability evaluation method including a UPFC, so as to qualitatively and quantitatively evaluate the influence of UPFC access on the reliability of the power grid, and further guide the later-stage upgrading and reconstruction of the power grid.
The technical scheme of the invention is as follows:
a unified power flow controller reliability modeling method is characterized by comprising the following steps:
1) dividing the unified power flow controller into five subsystems, namely a transformer subsystem, a converter bridge subsystem, a pole equipment subsystem, a direct current line subsystem and a control and protection subsystem, according to the functional characteristics of the components of the unified power flow controller;
2) in each subsystem, determining the logical relationship among the components in each subsystem according to the realized established function, and establishing a reliability fault model of each subsystem;
3) according to the logic relation among the subsystems and the series relation of the elements, a series equivalent formula is used for solving two state models and corresponding reliability parameters of the unified power flow controller:
in the formula: lambda [ alpha ]eqiAnd mueqiRespectively the equivalent failure rate and the equivalent repair rate, r, of each subsystemiRepair time for equivalent failure of each subsystem, lambdaUPFCIs the equivalent failure rate, r, of the unified power flow controllerUPFCIs the mean time to repair per failure, μUPFCIs the equivalent repair rate; assuming that the fault probability of the unified power flow controller obeys exponential distribution, the normal working probability of the unified power flow controller is obtained as
Probability of failure of
Among the above-mentioned technical scheme, its characterized in that: the transformer subsystem comprises a single-phase three-winding converter transformer and an alternating-current side circuit breaker; the converter bridge subsystem comprises a converter valve group, converter valve cooling equipment and a protection device; the pole equipment subsystem comprises a neutral point grounding branch and a related switch element; the direct-current line subsystem comprises a direct-current circuit breaker, a direct-current reactance and a direct-current transmission line.
In the technical scheme of the invention, the step 2) of determining the logical relationship among the components in each subsystem, and establishing the reliability fault model of each subsystem adopts at least one of a series equivalent model, a parallel equivalent model, a non-standby component reliability model, a cold standby reliability model and a hot standby reliability model.
The invention also provides a method for evaluating the reliability of the power grid with the unified power flow controller, which is characterized by comprising the following steps of:
1) simulating the system running state by a Monte Carlo simulation method, and establishing a state space S, wherein each element in the state space represents a system state SiThe probability of the system state is pi；
2) For the system state SiAnalyzing whether a voltage out-of-limit bus and a tide out-of-limit circuit are included in the current running state, and recording the out-of-limit bus as BiThe out-of-limit line is recorded as Lij；
3) For the system state SiIn each out-of-limit bus BiAnalyzing the current out-of-limit bus BiWhether a unified power flow controller is accessed:
i) if the unified power flow controller is accessed, generating a random number of 0-1 and connecting the random number with the out-of-limit bus BiProbability of failure q ofUPFCAnd (3) comparison:
a. if the random number is less than or equal to the fault probability of the unified power flow controller under the current bus, the current unified power flow controller has faults, and the load is reduced to α -load to eliminate voltage out-of-limiti,1Calculating the load shedding probability p in the current statei×qUPFC；
b. If the random number is larger than the fault probability under the current bus, the unified power flow controller works normally, the injection amount of the unified power flow controller is adjusted, the bus voltage out-of-limit is eliminated, the load is reduced to be 0, and the load shedding probability is 0; if the voltage threshold cannot be eliminated after the adjustment,the load size still needs to be reduced β -loadi,1Calculating the load shedding probability p in the current statei×pUPFC；
Ii) if there is no unified power flow controller, to eliminate voltage out-of-limit, reduce loadi,1Calculating the load shedding probability p in the current statei，1＝pi；
4) For the system state SiEach of which is an out-of-limit line LijAnalyzing the current out-of-limit line LijWhether a unified power flow controller is accessed:
i) if the unified power flow controller is accessed, generating a random number and connecting the random number with the line LijProbability of failure q ofUPFCAnd (3) comparison:
a, if the random number is less than or equal to the fault probability of the current line, the current line has a fault and cannot work, and the load is reduced to α -load to eliminate line out-of-limiti,2Calculating the load shedding probability p in the current statei×qUPFC；
b. If the random number is larger than the fault probability of the current line, the method works normally, injection amount of the unified power flow controller is adjusted, line out-of-limit is eliminated, the load is reduced to be 0, the load shedding probability is 0, and if the line out-of-limit cannot be eliminated after the unified power flow controller is adjusted, the load is reduced to β -loadi,2Calculating the load shedding probability p in the current statei×pUPFC；
Ii) if there is no unified power flow controller, load is reducedi,2Calculating the load shedding probability p in the current statei,2＝pi；
5) And (4) after the calculation is finished, counting the system load shedding probability and the load shedding amount caused by bus voltage out-of-limit and line load flow out-of-limit to obtain the reliability index.
The invention has the following advantages and prominent technical effects: the UPFC reliability modeling and access power grid reliability evaluation method provided by the invention analyzes the functional characteristics and the logical relationship of the constituent elements from the physical structure of the UPFC, decomposes the UPFC into 5 subsystems, then establishes the reliability model of the subsystems, and finally obtains the reliability model and the reliability parameters of the UPFC device through a series-parallel analysis method. On the basis, the influence of the UPFC on the bus voltage and the line tide of the power grid after being accessed is analyzed, the size of the voltage out-of-limit load and the size of the line tide out-of-limit load are calculated and eliminated, the power grid reliability assessment method considering the UPFC is provided, the problems that the UPFC modeling of a novel power electronic device applied to the power grid is difficult and the influence of the UPFC on the reliability of the accessed power grid is not detailed at present are solved, the method has important significance on analyzing the influence of novel equipment on the reliability of the power grid and then guiding the later upgrading and transformation of the power grid, and the method can be applied to the power grid.
Drawings
Fig. 1 is a division diagram of the structure of the unified power flow controller and its subsystems.
Wherein, 1-a transformer subsystem; 2-converter bridge subsystem; a 3-pole device subsystem; 4-dc line subsystem.
Fig. 2 is a state space diagram of the unified power flow controller.
Fig. 3 is a working schematic diagram of the unified power flow controller accessing to the power grid.
Fig. 4 is an equivalent diagram of the unified power flow controller accessing to the power grid.
Fig. 5 is a schematic diagram of an access point after a failure of the unified power flow controller.
Fig. 6 is a flow of a method for evaluating reliability of a power grid including a unified power flow controller.
Detailed Description
The principles and embodiments of this invention will be further explained with reference to the drawings and detailed description, and other objects and results of the invention will be more clearly understood and appreciated as the invention becomes more fully understood.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details.
The invention provides a unified power flow controller reliability modeling and access power grid reliability evaluation method, which is used for solving the problems that a novel power electronic device applied in the current power grid is difficult to model UPFC and the influence of the access power grid reliability is unknown, and developing the UPFC reliability modeling and the access power grid reliability evaluation work. The invention analyzes the functional characteristics and the logical relationship of the constituent elements from the physical structure of the UPFC, decomposes the UPFC into 5 subsystems, establishes the reliability model of the subsystems and finally obtains the reliability model and the reliability parameters of the UPFC device by a series-parallel analysis method. On the basis, the influence of the UPFC on the bus voltage and the line load flow of the power grid after being accessed is analyzed, the magnitude of the voltage out-of-limit load shedding and the line load flow out-of-limit load shedding is calculated and eliminated, and the power grid reliability evaluation method considering the UPFC is provided and specifically comprises the following steps:
firstly, establishing a reliability model of a unified power flow controller:
1. according to the functional characteristics of the constituent elements of the UPFC, the UPFC is divided into the following five subsystems: the transformer subsystem comprises a single-phase three-winding converter transformer, an alternating-current side circuit breaker and the like; the converter bridge subsystem mainly comprises a converter valve group, converter valve cooling equipment, a protection device and the like; a pole equipment subsystem including a neutral grounding branch and associated switching elements; the direct-current line subsystem mainly comprises a direct-current circuit breaker, a direct-current reactor and a direct-current transmission line; a control and protection subsystem. As shown in fig. 1.
2. In each subsystem, the logic relation between the components in the subsystem is analyzed to realize the given function, and the reliability parameters of the components in each subsystem are determined according to the logic relation. The logic relation and corresponding reliability parameter calculation method adopts at least one of a series equivalent model, a parallel equivalent model, a no-standby element reliability model, a cold standby reliability model and a hot standby reliability model.
If n elements are connected in series, any one element fails, the system fails, and only when all the elements are repaired, the system can be recovered to be normal; if n elements are connected in parallel, the system will fail only if all elements fail, but the system will return to normal as long as any element is repaired.
In the unified power flow controller, the direct current line subsystem is not easy to replace after the direct current line fails, so that the direct current line subsystem is mainly repaired after the direct current line subsystem fails, and a reliability model without a spare element can be adopted. When the spare components are not considered, the state transition diagram is used for simulating 3 random processes of running, overhauling and installing the components. The transformer subsystem and the pole equipment subsystem have high voltage level, large volume, high manufacturing cost and difficult replacement, but compared with the repair process, the replacement process has relatively short time, and a cold spare element is usually prepared. The main components of the converter bridge subsystem, namely the MMC converter valve and the components of the control and protection subsystem have relatively low voltage levels, small size and easy replacement, and a plurality of spare components can be arranged. When the operation element fails, the spare element can quickly replace the failed element, and the equivalence can be carried out by using a k/n (G) model.
3. Calculating reliability parameters of unified power flow controller
All 5 subsystems of the unified power flow controller have important influence on the normal operation of the whole device, and if any submodule fails, the system is required to exit the operation state, so that the reliability evaluation model of the whole device can be regarded as a series connection of the reliability evaluation models of the 5 subsystems, and the model of the whole device is obtained, and a state space diagram is shown in fig. 2. In the figure lambdaeqiAnd mueqiThe equivalent failure rate and the equivalent restoration rate of each subsystem are respectively obtained by the following methods (1) to (3).
According to the relation of element series, the series equivalent formula can be used to obtain the two-state model of the UPFC and the corresponding reliability parameters:
in the formula: lambda [ alpha ]eqiAnd riRespectively the equivalent failure rate and the equivalent failure repair time, lambda, of each subsystemUPFCIs the equivalent failure rate of UPFC, rUPFCIs the mean time to repair per failure, μUPFCIs the equivalent repair rate. Assuming that the fault probability of the unified power flow controller obeys the exponential distribution, the normal working probability of the unified power flow controller can be obtained as
Probability of failure of
3.1) establishing a fault model of the UPFC access power grid: in order to simplify the fault mode analysis of the UPFC access power grid, a two-state fault model of the UPFC is established, namely an operation state and a fault state. The available capacity of the UPFC in the two states is 100% capacity and 0 capacity, respectively. It should be noted that the UPFC at 100% capacity indicates that the UPFC can work normally, and the output can be adjusted between 0% and 100% according to the power grid regulation requirement.
3.2) establishing an equivalent load model of the UPFC access power grid. According to the working principle of the UPFC, the UPFC of the access point can be equivalent to a series voltage source and a parallel current source. The voltage and the tidal current threshold value can be reduced to the maximum extent through the adjustment of the injection amount, so that the load loss of a power grid is reduced. The operating principle of the UPFC is shown in FIG. 3:
therefore, without considering the loss of the UPFC itself, the effect of the UPFC can be equivalent to the injected power across the line where it is located, as shown in fig. 4:
in the figure, Δ PiAnd Δ QiIs the equivalent adjustable active and reactive power of the access point i, delta PjAnd Δ QjThe equivalent adjustable active and reactive sizes of the access point j.
When the UPFC is in fault, the power grid loses the power flow regulation and reactive power regulation capacity of the UPFC. At this time, the UPFC access point is consistent with the conventional bus and transmission line, as shown in fig. 5:
secondly, evaluating the reliability of the power grid containing the UPFC:
the invention provides a method for evaluating the reliability of a power grid with UPFC, which comprises the following steps (see figure 6)
1) Simulating the system running state by a Monte Carlo simulation method, and establishing a state space S, wherein each element in the state space represents a system state SiThe probability of the system state is pi；
2) For the system state SiAnalyzing whether a voltage out-of-limit bus and a tide out-of-limit circuit are included in the current running state, and recording the out-of-limit bus as BiThe out-of-limit line is recorded as Lij；
3) For the system state SiIn each out-of-limit bus BiAnalyzing the current out-of-limit bus BiWhether a unified power flow controller is accessed:
i) if the unified power flow controller is accessed, generating a random number of 0-1 and connecting the random number with the out-of-limit bus BiProbability of failure q ofUPFCAnd (3) comparison:
a. if the random number is less than or equal to the fault probability of the unified power flow controller under the current bus, the current unified power flow controller has faults, and the load is reduced to α -load to eliminate voltage out-of-limiti,1Calculating the load shedding probability p in the current statei×qUPFC；
b. If the random number is larger than the fault probability under the current bus, the operation is normal, the injection amount of the unified power flow controller is adjusted, the bus voltage out-of-limit is eliminated, the load is reduced to 0, the load shedding probability is 0, and if the voltage out-of-limit cannot be eliminated after adjustment, the load size is still required to be reduced to β -loadi,1Calculating the load shedding probability p in the current statei×pUPFC；
Ii) if there is no unified power flow controller, to eliminate voltage out-of-limit, reduce loadi,1Calculating the load shedding probability p in the current statei，1＝pi；
4) For the system state SiEach of which is an out-of-limit line LijAnalyzing the current out-of-limit line LijWhether there is unified tidal flow controlThe system access:
i) if the unified power flow controller is accessed, generating a random number and connecting the random number with the line LijProbability of failure q ofUPFCAnd (3) comparison:
a, if the random number is less than or equal to the fault probability of the current line, the current line has a fault and cannot work, and the load is reduced to α -load to eliminate line out-of-limiti,2Calculating the load shedding probability p in the current statei×qUPFC；
b. If the random number is larger than the fault probability of the current line, the method works normally, injection amount of the unified power flow controller is adjusted, line out-of-limit is eliminated, the load is reduced to be 0, the load shedding probability is 0, and if the line out-of-limit cannot be eliminated after the unified power flow controller is adjusted, the load is reduced to β -loadi,2Calculating the load shedding probability p in the current statei×pUPFC；
Ii) if there is no unified power flow controller, load is reducedi,2Calculating the load shedding probability p in the current statei,2＝pi；
5) And (4) after the calculation is finished, counting the system load shedding probability and the load shedding amount caused by bus voltage out-of-limit and line load flow out-of-limit to obtain the reliability index.
The UPFC reliability modeling and access grid reliability evaluation method proposed by the present invention is described above with reference to the accompanying drawings and embodiments. However, it should be understood by those skilled in the art that various modifications can be made to the UPFC reliability modeling and access grid reliability evaluation method provided by the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should be determined by the contents of the appended claims.
Claims (3)
1. A power grid reliability assessment method based on unified power flow controller reliability modeling is characterized by comprising the following steps:
1) dividing the unified power flow controller into five subsystems, namely a transformer subsystem, a converter bridge subsystem, a pole equipment subsystem, a direct current line subsystem and a control and protection subsystem, according to the functional characteristics of the components of the unified power flow controller;
2) in each subsystem, determining the logical relationship among the components in each subsystem according to the realized established function, and establishing a reliability fault model of each subsystem;
3) according to the logic relation among the subsystems and the series relation of the elements, a series equivalent formula is used for solving two state models and corresponding reliability parameters of the unified power flow controller:
in the formula: lambda [ alpha ]eqiFor the equivalent failure rate of each subsystem, riRepair time for equivalent failure of each subsystem, lambdaUPFCIs the equivalent failure rate, r, of the unified power flow controllerUPFCIs the mean time to repair per failure, μUPFCIs the equivalent repair rate; assuming that the fault probability of the unified power flow controller obeys exponential distribution, the normal working probability of the unified power flow controller is obtained as
Probability of failure of
4) And evaluating the reliability of the power grid containing the unified power flow controller according to the reliability parameters, wherein the evaluation method comprises the following steps:
I) simulating the system running state by a Monte Carlo simulation method, and establishing a state space S, a state spaceEach element in the set representing a system state SiThe probability of the system state is pi；
II) for the System State SiAnalyzing whether a voltage out-of-limit bus and a tide out-of-limit circuit are included in the current running state, and recording the out-of-limit bus as BiThe out-of-limit line is recorded as Lij；
III) for the System State SiIn each out-of-limit bus BiAnalyzing the current out-of-limit bus BiWhether a unified power flow controller is accessed:
i) if the unified power flow controller is accessed, a random number of 0-1 is generated and is connected with the out-of-limit bus BiProbability of failure q ofUPFCAnd (3) comparison:
a. if the random number is less than or equal to the fault probability of the unified power flow controller under the current bus, the current unified power flow controller has faults, and the load is reduced to α -load to eliminate voltage out-of-limiti，1Calculating the load shedding probability p in the current statei×qUPFC；
b. If the random number is larger than the fault probability under the current bus, the operation is normal, the injection amount of the unified power flow controller is adjusted, the bus voltage out-of-limit is eliminated, the load is reduced to 0, the load shedding probability is 0, and if the voltage out-of-limit cannot be eliminated after adjustment, the load size is still required to be reduced to β -loadi，1Calculating the load shedding probability p in the current statei×pUPFC；
ii) if there is no unified power flow controller, to eliminate voltage out-of-limit, reduce loadi，1Calculating the load shedding probability p in the current statei，1＝pi；
IV) for the System State SiEach of which is an out-of-limit line LijAnalyzing the current out-of-limit line LijWhether a unified power flow controller is accessed:
i) if the unified power flow controller is accessed, a random number is generated and is connected with the line LijProbability of failure q ofUPFCAnd (3) comparison:
a. if the random number is less than or equal to the fault probability of the current line, thenAt present, the circuit is out of order and the load is reduced to α -load to eliminate the line out-of-limiti，2Calculating the load shedding probability p in the current statei×qUPFC；
b. If the random number is larger than the fault probability of the current line, the method works normally, injection amount of the unified power flow controller is adjusted, line out-of-limit is eliminated, the load is reduced to be 0, the load shedding probability is 0, and if the line out-of-limit cannot be eliminated after the unified power flow controller is adjusted, the load is reduced to β -loadi，2Calculating the load shedding probability p in the current statei×pUPFC；
ii) if there is no unified power flow controller, load is reducedi，2Calculating the load shedding probability p in the current statei，2＝pi；
And V) calculating, and counting the system load shedding probability and load shedding amount caused by bus voltage out-of-limit and line power flow out-of-limit to obtain a reliability index.
2. The method for evaluating the reliability of the power grid based on the unified power flow controller reliability modeling as claimed in claim 1, wherein: the transformer subsystem comprises a single-phase three-winding converter transformer and an alternating-current side circuit breaker; the converter bridge subsystem comprises a converter valve group, converter valve cooling equipment and a protection device; the pole equipment subsystem comprises a neutral point grounding branch and a related switch element; the direct-current line subsystem comprises a direct-current circuit breaker, a direct-current reactance and a direct-current transmission line.
3. The method for evaluating the reliability of the power grid based on the reliability modeling of the unified power flow controller according to claim 1 or 2, wherein: and 2) determining the logical relationship among the components in each subsystem, establishing a reliability fault model of each subsystem, and adopting at least one of a series equivalent model, a parallel equivalent model, a non-standby component reliability model, a cold standby reliability model and a hot standby reliability model.
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| CN102255307A (en) * | 2011-06-09 | 2011-11-23 | 重庆大学 | Layering equivalence method for reliability estimation of distribution network |
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