CN108964138B - Synchronous grid connection method and system - Google Patents
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- CN108964138B CN108964138B CN201810839745.5A CN201810839745A CN108964138B CN 108964138 B CN108964138 B CN 108964138B CN 201810839745 A CN201810839745 A CN 201810839745A CN 108964138 B CN108964138 B CN 108964138B
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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
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/40—Synchronising a generator for connection to a network or to another generator
Abstract
The invention provides a synchronous grid connection method and system. The synchronous grid connection method comprises the following steps: the speed regulating device measures the frequency of the motor to be merged and judges whether the frequency of the motor to be merged meets a first grid-connected condition or not; when the frequency of the motor to be merged does not meet the first grid-connected condition, the speed regulating device regulates the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first grid-connected condition; the excitation adjusting device measures the excitation current of the motor to be merged and judges whether the excitation current of the motor to be merged meets a second merging condition; when the exciting current of the motor to be merged does not meet the second grid-connected condition, the exciting current of the motor to be merged is adjusted by the exciting adjusting device until the exciting current of the motor to be merged meets the second grid-connected condition; when the first grid-connected condition and the second grid-connected condition are met, the synchronous device outputs a breaker closing instruction, overshooting or undershooting can be avoided, the adjusting process is quicker, and the adjusting precision is greatly improved.
Description
Technical Field
The invention relates to the technical field of power grid parallel connection, in particular to a synchronous grid connection method and system.
Background
Modern power system power is generally composed of synchronous motors distributed in power plants in different regions and operated in parallel, so that different kinds of energy sources are economically and reasonably utilized, and the power system power comprises the following components: natural resources such as water energy, wind energy, nuclear energy, coal, natural gas and the like. The synchronous motor and the power grid are interconnected through the circuit breaker under the control of the synchronous device, so that the safe and reliable operation of the synchronous device is the premise of synchronization of the synchronous motor. In addition, when two different power grid systems are interconnected in an alternating current mode, a synchronization device is also needed to optimize the interconnection time and determine the optimal closing time.
With the continuous increase of the capacity of the put-in synchronous motor, the impact current generated by asynchronous switching-on can cause the damage of the motor under the action of huge electric power, and also cause huge impact on the power grid, thereby causing the stability of the power grid to be damaged. Therefore, modern synchronous motors are generally provided with intelligent synchronization devices, and synchronization points are predicted in an automatic quasi-synchronization mode, so that the motors can perform synchronous parallel operation under the condition of meeting certain pressure difference, frequency difference and angle difference.
From the principle of synchronization, when the synchronization device captures the synchronization point, the frequency difference between the grid frequency and the frequency of the synchronous motor must exist in order to capture the synchronization point. In the prior art, synchronous devices send adjusting instructions to an excitation adjusting device and a speed adjusting device, the adjusting instructions are superposed on the set values of the respective devices, and the corresponding devices respond to the adjusting instructions, so that overshoot or undershoot can be caused, the adjusting process is delayed, synchronous grid connection is delayed, and the adjusting precision is not high.
Disclosure of Invention
The embodiment of the invention mainly aims to provide a synchronous grid-connected method and system, which avoid overshoot or undershoot, have a quicker adjusting process and greatly improve the adjusting precision.
In order to achieve the above object, an embodiment of the present invention provides a synchronization grid connection method, including:
the speed regulating device measures the frequency of the motor to be merged and judges whether the frequency of the motor to be merged meets a first grid-connected condition or not;
when the frequency of the motor to be merged does not meet the first grid-connected condition, the speed regulating device regulates the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first grid-connected condition;
the excitation adjusting device measures the excitation current of the motor to be merged and judges whether the excitation current of the motor to be merged meets a second merging condition;
when the exciting current of the motor to be merged does not meet the second grid-connected condition, the exciting current of the motor to be merged is adjusted by the exciting adjusting device until the exciting current of the motor to be merged meets the second grid-connected condition;
and when the first grid-connected condition and the second grid-connected condition are simultaneously met, the synchronous device outputs a breaker closing instruction.
The embodiment of the present invention further provides a synchronous grid-connected system, including:
the speed regulating device is used for measuring the frequency of the to-be-merged motor and judging whether the frequency of the to-be-merged motor meets a first grid-connected condition or not; when the frequency of the motor to be merged does not meet the first grid-connection condition, adjusting the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first grid-connection condition;
the excitation adjusting device is used for measuring the excitation current of the motor to be merged and judging whether the excitation current of the motor to be merged meets a second merging condition or not; when the exciting current of the motor to be merged does not meet the second grid-connected condition, adjusting the exciting current of the motor to be merged until the exciting current of the motor to be merged meets the second grid-connected condition;
and the synchronization device is used for outputting a closing instruction of the circuit breaker when the first grid-connected condition and the second grid-connected condition are met simultaneously.
The speed regulating device of the synchronization grid-connected method and system of the embodiment of the invention measures the frequency of the motor to be combined and judges whether the frequency of the motor to be combined meets a first grid-connected condition; when the frequency of the motor to be merged does not meet the first grid-connected condition, the speed regulating device regulates the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first grid-connected condition; meanwhile, the excitation adjusting device measures the excitation current of the motor to be merged and judges whether the excitation current of the motor to be merged meets a second merging condition or not; when the exciting current of the motor to be merged does not meet the second grid-connected condition, the exciting current of the motor to be merged is adjusted by the exciting adjusting device until the exciting current of the motor to be merged meets the second grid-connected condition; when the first grid-connected condition and the second grid-connected condition are met, the synchronous device outputs a breaker closing instruction, overshooting or undershooting can be avoided, the adjusting process is quicker, and the adjusting precision is greatly improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a flow chart of a synchronization grid connection method in an embodiment of the invention;
fig. 2 is a structural block diagram of a synchronous grid-connected system in the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.
In view of the fact that synchronous devices in the prior art send adjusting instructions to an excitation adjusting device and a speed adjusting device, the adjusting instructions are superposed on the set values of the respective devices, and the corresponding devices respond to the adjusting instructions, so that overshoot or undershoot can be caused, the adjusting process is delayed, synchronous grid connection is delayed, and the adjusting precision is low. The present invention will be described in detail below with reference to the accompanying drawings.
Fig. 1 is a flowchart of a synchronization grid connection method in an embodiment of the present invention. As shown in fig. 1, the synchronization grid-connection method includes:
s101: the speed regulating device measures the frequency of the motor to be combined and judges whether the frequency of the motor to be combined meets a first grid-connected condition.
S102: when the frequency of the motor to be combined does not meet the first grid-connected condition, the speed regulating device regulates the rotating speed of the motor to be combined until the frequency of the motor to be combined meets the first grid-connected condition.
S201: and the excitation adjusting device measures the excitation current of the motor to be merged and judges whether the excitation current of the motor to be merged meets a second merging condition.
S202: when the exciting current of the motor to be combined does not meet the second grid-connected condition, the exciting current of the motor to be combined is adjusted by the exciting adjusting device until the exciting current of the motor to be combined meets the second grid-connected condition.
S301: and when the first grid-connected condition and the second grid-connected condition are simultaneously met, the synchronous device outputs a breaker closing instruction.
As can be seen from the flow shown in fig. 1, the speed adjusting device in the synchronization grid-connection method according to the embodiment of the present invention measures the frequency of the to-be-combined motor, and determines whether the frequency of the to-be-combined motor meets the first grid-connection condition; when the frequency of the motor to be merged does not meet the first grid-connected condition, the speed regulating device regulates the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first grid-connected condition; meanwhile, the excitation adjusting device measures the excitation current of the motor to be merged and judges whether the excitation current of the motor to be merged meets a second merging condition or not; when the exciting current of the motor to be merged does not meet the second grid-connected condition, the exciting current of the motor to be merged is adjusted by the exciting adjusting device until the exciting current of the motor to be merged meets the second grid-connected condition; when the first grid-connected condition and the second grid-connected condition are met, the synchronous device outputs a breaker closing instruction, overshooting or undershooting can be avoided, the adjusting process is quicker, and the adjusting precision is greatly improved.
In one embodiment, the first grid-connection condition is: the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged.
S102 specifically comprises the following steps: when the difference value between the frequency of the power grid and the frequency difference is larger than the frequency of the motor to be merged, the speed regulating device increases the rotating speed of the motor to be merged until the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged; when the difference value between the frequency of the power grid and the frequency difference is smaller than the frequency of the motor to be merged, the speed regulating device reduces the rotating speed of the motor to be merged until the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged. The frequency difference is determined by the grid-connected slip and is a preset fixed value.
The operation is closed-loop regulated by a speed regulating device, and the regulation mode can be carried out by adopting a proportional-integral-derivative (PID) algorithm so as to save the time of synchronization. The speed regulating device can be a speed regulator of a motor to be combined (the direction of a water turbine is connected to the grid), or a static frequency converter (the dragging mode of the static frequency converter is connected to the grid), or a speed regulator of an opposite unit (the direction of a water pump is connected to the grid in a back-to-back starting mode).
In an embodiment, the second grid-connection condition is: l VG/FG-KI│<σ；
Wherein, VGIs the effective value of the voltage of the power grid, FGThe frequency of the power grid is K, the proportionality coefficient is K, I is exciting current, and sigma is a preset value.
S202 specifically includes: when V isG/FG-KI>At sigma, excitationThe adjusting device increases the excitation current of the motor to be combined until | VG/FG-KI│<Sigma; when V isG/FG-KI<When sigma is minus, the excitation adjusting device reduces the excitation current of the motors to be combined until | VG/FG-KI│<σ。
Wherein KI is VU/FU，VUIs the effective value of the voltage of the motor to be merged, FUIs the frequency of the motor to be merged. The operation can be carried out by adopting a proportional-integral-derivative (PID) algorithm, the tracking target of the algorithm is the ratio of the effective value of the grid voltage to the frequency, and the difference adjusting dead zone is sigma.
Wherein the speed regulating device and the excitation regulating device simultaneously regulate the parameters, i.e. S101 to S102 and S201 to S202 are parallel.
In specific implementation, when the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged, the frequency difference (the difference value between the frequency of the power grid and the frequency of the motor to be merged) calculated by the synchronization device meets the first merging requirement; when-VG/FG-KI│<And sigma, the differential pressure (the difference between the effective voltage value of the power grid and the effective voltage value of the motor to be combined) calculated by the synchronization device meets a second grid-connection requirement. When the first grid-connected requirement and the second grid-connected requirement are met (the first grid-connected condition and the second grid-connected condition are met), the angle difference between the power grid and the motor to be connected meets the third grid-connected requirement, the synchronous device outputs a breaker switching-on instruction to the breaker, and the breaker is switched on.
In addition, a period of time elapses from when the synchronous device outputs a breaker closing instruction (closing pulse) until the breaker contact moves to the closing position, and the synchronous device needs to send a closing pulse before the synchronous time due to the time difference, which is referred to as lead time of the synchronous device. The lead time depends on the inherent mechanical action delay of the circuit breaker (the time that the moving contact of the circuit breaker passes through the full stroke), the action time of the auxiliary relay of the circuit breaker and the opening action time of the relay of the synchronous device. That is, the synchronization device outputs a breaker closing instruction, and after the lead time elapses, the breaker is closed.
The flow of an embodiment of the invention is as follows:
1. the speed regulating device measures the frequency of the motor to be merged; when the difference value between the frequency of the power grid and the frequency difference is larger than the frequency of the motor to be merged, the speed regulating device increases the rotating speed of the motor to be merged, and when the difference value between the frequency of the power grid and the frequency difference is smaller than the frequency of the motor to be merged, the speed regulating device decreases the rotating speed of the motor to be merged until the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged.
2. Meanwhile, the excitation adjusting device measures the excitation current of the motor to be merged; when V isG/FG-KI>When sigma is larger, the excitation regulator increases the excitation current of the motor to be combined, when V is largerG/FG-KI<When sigma is minus, the excitation adjusting device reduces the excitation current of the motors to be combined until | VG/FG-KI│<σ。
3. When the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged, the frequency difference obtained by calculation of the synchronization device meets the first merging requirement; when-VG/FG-KI│<And sigma, the pressure difference obtained by calculation of the synchronization device meets a second grid-connected requirement, the synchronization device outputs a breaker closing instruction to the breaker, and the breaker is closed after the lead time.
In summary, the synchronization grid-connected method of the embodiment of the invention has the following beneficial effects:
1. the existing synchronization device regulates the voltage of a to-be-combined power grid at intervals of a period of time (second level), so that the regulation is slow, the excitation regulation of the synchronization device is released from the synchronization device and is placed in the excitation regulation device, and closed-loop regulation is realized by tracking the ratio of the voltage effective value of the power grid to the frequency of the power grid, so that the regulation process is quicker (millisecond level), and the over-regulation of the excitation of the to-be-combined motor caused by low voltage due to low rotating speed is avoided; the voltage under-regulation of the motor to be merged caused by high voltage due to high rotating speed is avoided; and the frequent adjustment of the voltage amplitude value change caused by the change of the rotating speed is avoided, the adjustment precision of the voltage of the standby grid during synchronization is greatly improved, and the differential pressure is controlled within a reasonable range.
2. The frequency of the grid to be merged is adjusted at intervals of a period of time (second level) by the conventional synchronization device, so that the adjustment is slow, the frequency adjustment of the synchronization device is released from the synchronization device and transferred to a speed adjusting device, and the tracking and specifying frequency function is adopted, so that the adjustment process is quicker (millisecond level), the adjustment precision of the frequency of the grid to be merged during synchronization is greatly improved, and the difference value between the frequency of a motor to be merged and the frequency of the grid is a given frequency difference.
3. Greatly simplifying the function of the synchronous device. The synchronization device is only used for judging whether the synchronization requirement is met or not and sending a closing pulse according to the lead time, so that the problem of grid connection failure caused by the adjustment problem of the synchronization device is solved.
Based on the same inventive concept, the embodiment of the invention also provides a synchronous grid-connected system, and as the problem solving principle of the system is similar to that of a synchronous grid-connected method, the implementation of the system can refer to the implementation of the method, and repeated parts are not described again.
Fig. 2 is a structural block diagram of a synchronous grid-connected system in the embodiment of the present invention. As shown in fig. 2, the synchronization grid-connected system includes:
the speed regulating device is used for measuring the frequency of the to-be-merged motor and judging whether the frequency of the to-be-merged motor meets a first grid-connected condition or not; when the frequency of the motor to be merged does not meet the first grid-connection condition, adjusting the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first grid-connection condition;
the excitation adjusting device is used for measuring the excitation current of the motor to be merged and judging whether the excitation current of the motor to be merged meets a second merging condition or not; when the exciting current of the motor to be merged does not meet the second grid-connected condition, adjusting the exciting current of the motor to be merged until the exciting current of the motor to be merged meets the second grid-connected condition;
and the synchronization device is used for outputting a closing instruction of the circuit breaker when the first grid-connected condition and the second grid-connected condition are met simultaneously.
In one embodiment, the first grid-connection condition is:
the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged.
In one embodiment, the second grid-connection condition is:
│VG/FG-KI│<σ；
wherein, VGIs the effective value of the voltage of the power grid, FGThe frequency of the power grid is K, the proportionality coefficient is K, I is exciting current, and sigma is a preset value.
In one embodiment, the speed adjusting device is specifically configured to:
when the difference value between the frequency of the power grid and the frequency difference is larger than the frequency of the motor to be merged, increasing the rotating speed of the motor to be merged;
and when the difference value between the frequency of the power grid and the frequency difference is smaller than the frequency of the motor to be merged, reducing the rotating speed of the motor to be merged.
In one embodiment, the excitation adjusting device is specifically configured to:
when V isG/FG-KI>Increasing the exciting current of the motor to be merged when the sigma is larger;
when V isG/FG-KI<σ, the excitation current of the motor to be merged is reduced.
In summary, the synchronization grid-connected system of the embodiment of the invention has the following beneficial effects:
1. the existing synchronization device regulates the voltage of a to-be-combined power grid at intervals of a period of time (second level), so that the regulation is slow, the excitation regulation of the synchronization device is released from the synchronization device and is placed in the excitation regulation device, and closed-loop regulation is realized by tracking the ratio of the voltage effective value of the power grid to the frequency of the power grid, so that the regulation process is quicker (millisecond level), and the over-regulation of the excitation of the to-be-combined motor caused by low voltage due to low rotating speed is avoided; the voltage under-regulation of the motor to be merged caused by high voltage due to high rotating speed is avoided; and the frequent adjustment of the voltage amplitude value change caused by the change of the rotating speed is avoided, the adjustment precision of the voltage of the standby grid during synchronization is greatly improved, and the differential pressure is controlled within a reasonable range.
2. The frequency of the grid to be merged is adjusted at intervals of a period of time (second level) by the conventional synchronization device, so that the adjustment is slow, the frequency adjustment of the synchronization device is released from the synchronization device and transferred to a speed adjusting device, and the tracking and specifying frequency function is adopted, so that the adjustment process is quicker (millisecond level), the adjustment precision of the frequency of the grid to be merged during synchronization is greatly improved, and the difference value between the frequency of a motor to be merged and the frequency of the grid is a given frequency difference.
3. Greatly simplifying the function of the synchronous device. The synchronization device is only used for judging whether the synchronization requirement is met or not and sending a closing pulse according to the lead time, so that the problem of grid connection failure caused by the adjustment problem of the synchronization device is solved.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A synchronization grid-connection method is characterized by comprising the following steps:
the method comprises the steps that a speed regulating device measures the frequency of a to-be-merged motor and judges whether the frequency of the to-be-merged motor meets a first merging condition or not;
when the frequency of the motor to be merged does not meet the first grid-connected condition, the speed regulating device regulates the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first grid-connected condition;
the excitation adjusting device measures the excitation current of the motor to be combined and judges whether the excitation current of the motor to be combined meets a second grid-connected condition or not;
when the excitation current of the motor to be combined does not meet the second grid-connected condition, the excitation adjusting device adjusts the excitation current of the motor to be combined until the excitation current of the motor to be combined meets the second grid-connected condition;
when the first grid-connected condition and the second grid-connected condition are met simultaneously, the synchronous device outputs a breaker closing instruction;
the second grid-connected condition is as follows:
│VG/FG-KI│<σ；
wherein, VGIs the effective value of the voltage of the power grid, FGThe frequency of the power grid is K, the proportionality coefficient is K, I is exciting current, and sigma is a preset value.
2. The synchronization grid connection method according to claim 1, wherein the first grid connection condition is that:
and the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged.
3. The synchronous grid connection method according to claim 2, wherein the speed regulating device regulates the rotating speed of the to-be-connected motor, and comprises the following steps:
when the difference value between the frequency of the power grid and the frequency difference is larger than the frequency of the motor to be merged, the speed regulating device increases the rotating speed of the motor to be merged;
and when the difference value between the frequency of the power grid and the frequency difference is smaller than the frequency of the motor to be merged, the speed regulating device reduces the rotating speed of the motor to be merged.
4. The synchronous grid connection method according to claim 1, wherein the excitation adjusting device adjusts an excitation current of the to-be-combined motor, and comprises:
when V isG/FG-KI>When sigma is generated, the excitation adjusting device increases the excitation current of the motor to be combined;
when V isG/FG-KI<σ, the excitation adjusting device reduces the excitation current of the to-be-merged motor.
5. A synchronization grid-connected system is characterized by comprising:
the speed regulating device is used for measuring the frequency of the motor to be merged and judging whether the frequency of the motor to be merged meets a first merging condition or not; when the frequency of the motor to be merged does not meet the first merging condition, adjusting the rotating speed of the motor to be merged until the frequency of the motor to be merged meets the first merging condition;
the excitation adjusting device is used for measuring the excitation current of the motor to be combined and judging whether the excitation current of the motor to be combined meets a second grid-connected condition or not; when the exciting current of the motor to be combined does not meet the second grid-connected condition, adjusting the exciting current of the motor to be combined until the exciting current of the motor to be combined meets the second grid-connected condition;
the synchronization device is used for outputting a circuit breaker closing instruction when the first grid-connected condition and the second grid-connected condition are met simultaneously;
the second grid-connected condition is as follows:
│VG/FG-KI│<σ；
wherein, VGIs the effective value of the voltage of the power grid, FGThe frequency of the power grid is K, the proportionality coefficient is K, I is exciting current, and sigma is a preset value.
6. The contemporaneous grid-connection system according to claim 5, characterized in that the first grid-connection condition is:
and the difference value between the frequency of the power grid and the frequency difference is equal to the frequency of the motor to be merged.
7. The synchronous grid-connected system according to claim 6, wherein the speed regulating device is specifically configured to:
when the difference value between the frequency of the power grid and the frequency difference is larger than the frequency of the motor to be merged, increasing the rotating speed of the motor to be merged;
and when the difference value between the frequency of the power grid and the frequency difference is smaller than the frequency of the motor to be merged, reducing the rotating speed of the motor to be merged.
8. The synchronous grid-connected system according to claim 5, wherein the excitation adjusting device is specifically configured to:
when V isG/FG-KI>Increasing the exciting current of the motor to be combined when the sigma is larger than the preset value;
when V isG/FG-KI<- σ, reducing the excitation current of the machine to be merged.
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| CN101645607A (en) * | 2009-09-14 | 2010-02-10 | 华北电力大学（保定） | Quick ideal condition quasi-synchronization paralleling method of hydro-generator |
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