CN115603377B - Method and system for improving weak network stability of grid-connected inverter - Google Patents
Method and system for improving weak network stability of grid-connected inverter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- 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
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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
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
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Abstract
The invention discloses a method and a system for improving the stability of a grid-connected inverter weak grid, belonging to the technical field of inverters, wherein the method comprises the steps of introducing a virtual inductor to obtain a virtual voltage after the virtual inductor is connected with a grid-side impedance in series; performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage; after the virtual voltage is connected with the grid-connected point voltage through the virtual inductor, calculating a phase angle difference between a grid-connected point voltage vector and the virtual voltage vector; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the grid-connected point voltage; and taking the phase angle of the voltage of the grid-connected point as a synchronous reference to transmit power to a power grid. The influence of the impedance of the power grid is counteracted by building the virtual voltage, then the phase locking is carried out on the built virtual voltage, and finally the phase angle difference caused by the virtual voltage is compensated, so that the stability of the weak grid of the grid-connected inverter is improved.
Description
Technical Field
The invention relates to the technical field of power supply or power distribution, in particular to a method and a system for improving the stability of a weak grid of a grid-connected inverter.
Background
More and more attention is paid to circuit devices or systems for power supply or distribution, particularly to the development of new energy technology, and more power supply types are added to a power grid. With the improvement of the proportion of the distributed new energy, the number of grid-connected power stations at the tail end of a power grid is increased, and the power grid impedance of the equivalent impedance is increased continuously; short circuit capacity ratio (of grid-connected point) of corresponding power stationSCR,short circuit ratio) And is constantly decreasing, presenting a very weak grid environment. The dynamic performance of the access voltage is deteriorated under the influence of a weak power grid environment, and the traditional grid-connected inverter based on phase-locked loop control is difficult to perfectly synchronize the access system.
In the prior art, a model of inverter output impedance is established, and a phase-locked loop can introduce negative resistance to cause system synchronous instability in an extremely weak power grid environment; to improve system stability, this negative resistance characteristic is counteracted by a given feed forward of the current loop, providing a strategic assumptionqThe shaft current is zero and the actual inverter shouldIn use, in order to keep the voltage of the output port of the inverter constant under the extremely weak power grid environment, the inverter is generally required to be usedqThe shaft outputs current, maintaining a constant port voltage through the reactive current.
In the prior art, an improved feedforward strategy is introduced into an inverter current loop to weaken the negative resistance characteristic, so that the stability of a phase-locked loop in a weak power grid environment is improved. However, in an extremely weak grid environment, the scheme still has certain limitations.
Disclosure of Invention
In order to overcome the problem of insufficient stability of the grid-connected inverter in the extremely weak grid environment in the prior art, the invention provides the method and the system for improving the stability of the grid-connected inverter in the weak grid environment.
In order to achieve the purpose, the invention provides the following technical scheme:
a method for improving the stability of a grid-connected inverter weak grid comprises the following steps:
introducing a virtual inductor to obtain a virtual voltage after the virtual inductor is connected with a network side impedance in series;
performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
after the virtual voltage and the grid-connected point voltage are connected through the virtual inductor, calculating a phase angle difference between a grid-connected point voltage vector and the virtual voltage vector; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the grid-connected point voltage;
and taking the phase angle of the voltage of the grid-connected point as a synchronous reference to transmit power to a power grid.
As a further improvement of the present invention, the method for obtaining the virtual voltage after the virtual inductor is connected in series with the network side impedance comprises:
wherein, V s Is a virtual voltage vector in a stationary coordinate system, E s Is a grid-connected point voltage vector under a static coordinate system，i s Is a grid-connected current vector under a static coordinate system,L v in order to be a virtual inductance value,sω s1 /(s+ω s1 ) In order to be an incomplete differential term,ω s1 is the cut-off frequency of the filter,sis a complex frequency.
As a further improvement of the present invention, the virtual inductance value is:
L v =0.6~0.8L g
wherein,L g is the grid impedance.
As a further improvement of the invention, the phase locking of the virtual voltage is performed by selecting a q-axis virtual voltage under a synchronous reference coordinate.
As a further improvement of the present invention, the method for obtaining the phase-locked angle of the virtual voltage comprises:
wherein,φis the phase locking angle of the virtual voltage, V is the virtual voltage vector under the synchronous rotating coordinate system,ω 1 is the angular frequency of the power frequency side,k pi 、k ii respectively proportional gain and integral gain of the phase locked loop,sis a complex frequency.
As a further improvement of the present invention, calculating the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector comprises:
the active power transmitted between the grid-connected point voltage vector and the virtual voltage vector is calculated, and then the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector is calculated.
As a further improvement of the invention, the active power transmitted between the grid-connected point voltage vector and the virtual voltage vector is calculated firstly, and the method comprises the following steps:
wherein,Pis active power, E s Is a grid-connected point voltage vector i under a static coordinate system s* The method comprises the following steps that (1) Re { } represents a real part of a complex number, wherein the complex number is the conjugate of a grid-connected current vector under a static coordinate system;
and then combining the active power transmitted between the grid-connected point voltage vector E under the synchronous rotating coordinate system and the virtual voltage vector V under the synchronous rotating coordinate system as follows:
wherein,δis the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector,ω 1 is the angular frequency of the power frequency side,L v is a virtual inductance value;
the method comprises the following steps that a low-pass filter is connected in series with an output end to obtain a phase angle difference between a grid-connected point voltage vector and a virtual voltage vector, and the method comprises the following steps:
wherein,ω s2 is the cut-off frequency of the low-pass filter,sand E is a complex frequency, E is a grid-connected point voltage vector under a synchronous rotating coordinate system, and V is a virtual voltage vector under the synchronous rotating coordinate system.
As a further improvement of the present invention, the phase angle difference is superimposed on the phase-locked angle to obtain a corrected phase angle, and the corrected phase angle is used as a phase angle of the voltage of the grid-connected point, and the method comprises:
θ=φ+δ
wherein,θthe phase angle of the grid-connected point voltage vector,φis the phase-locked angle of the virtual voltage,δis the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector.
A system for improving the stability of a weak grid of a grid-connected inverter comprises:
the building module is used for introducing a virtual inductor and building to obtain a virtual voltage formed by connecting the virtual inductor and the network side impedance in series;
the phase locking module is used for performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
the correction module is used for calculating the phase angle difference between the voltage vector of the grid-connected point and the virtual voltage vector after the virtual voltage is connected with the grid-connected point voltage through the virtual inductor; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the grid-connected point voltage;
and the transmission module is used for transmitting power to a power grid by taking the phase angle of the grid-connected point voltage as a synchronous reference.
In the correction module, calculating a phase angle difference between a grid-connected point voltage vector and a virtual voltage vector, including:
the active power transmitted between the grid-connected point voltage vector and the virtual voltage vector is calculated, and then the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector is calculated.
Compared with the prior art, the invention has the following beneficial effects:
according to the method for improving the stability of the grid-connected inverter weak grid, the virtual inductor is introduced to offset the positive feedback effect of the grid impedance, further the virtual voltage is introduced, the virtual voltage is constructed for phase locking, the influence of the grid impedance is offset by constructing the virtual voltage, the constructed virtual voltage is phase-locked, and finally the phase angle difference caused by the virtual voltage is compensated, so that the stability of the grid-connected inverter weak grid is improved.
Drawings
Fig. 1 is a flowchart of a method for improving the stability of a grid-connected inverter weak grid according to the present invention;
fig. 2 is a main circuit diagram of a grid-connected inverter;
FIG. 3 is a control block diagram of the phase-locked loop strategy of the present invention;
FIG. 4 is an equivalent circuit diagram and phasor diagram of a grid-connected point voltage vector E and a virtual voltage vector V of the present invention, where (a) is the equivalent circuit diagram of E and V, and (b) is the phasor diagram of E and V;
fig. 5 is a comparison graph of the short-circuit coefficient =3.2 based on the control of the conventional pll and the control of the novel pll, where (a 1), (a 2), (a 3) are test graphs of the short-circuit coefficient =3.2 based on the control current, voltage and active power of the conventional pll, respectively, and (b 1), (b 2), (b 3) are test graphs of the short-circuit coefficient =3.2 based on the control current, voltage and active power of the pll according to the present invention, respectively;
FIG. 6 is a block diagram of a system for improving the stability of a weak grid of a grid-connected inverter according to the present invention;
fig. 7 is a schematic diagram of an electronic device according to the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, 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.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
As shown in fig. 1, the present invention provides a method for improving grid-connected inverter weak grid stability, including:
introducing a virtual inductor to obtain a virtual voltage after the virtual inductor is connected with a network side impedance in series;
performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
after the virtual voltage and the grid-connected point voltage are connected through the virtual inductor, calculating a phase angle difference between a grid-connected point voltage vector and the virtual voltage vector; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the grid-connected point voltage;
and taking the phase angle of the voltage of the grid-connected point as a synchronous reference to transmit power to a power grid.
According to the invention, the virtual inductor is introduced to offset the positive feedback effect of the power grid impedance, so that the synchronization stability of the grid-connected inverter is improved.
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
The invention provides a method for improving the stability of a weak grid of a grid-connected inverter, which counteracts the positive feedback effect of the impedance of a power grid by introducing a virtual inductor and improves the synchronous stability of the grid-connected inverter. Wherein the method comprises the following steps: constructing virtual voltage for phase locking, and offsetting the influence of power grid impedance by constructing virtual voltage; the phase locking is carried out by adopting a q-axis component of a virtual voltage; the phase correction is carried out according to the power frequency phase angle difference introduced by the virtual voltage.
The main circuit topology of the grid-connected inverter is shown in fig. 2, and the dc side is usually connected to a preceding stage boost circuit or a photovoltaic module. Connected to AC via inverter bridgeLCLAnd (4) a filter.L f Is a machine side alternating current filter inductor,C f is a machine side AC filter capacitor. Usually the grid equivalent impedance consists of the leakage inductance of the transformer and the impedance of the transmission line.
According to the practical application scenario of the inverter, it can be assumed that in the very weak grid environment, the grid-side impedance is pure inductance and the inductance value isL g ，
、E s Respectively are the grid voltage and the grid-connected point voltage vector under the static coordinate. i all right angle s And the grid-connected current vector is under a static coordinate. After the transformation of the coordinates, the obtained object is processed by coordinate transformation,
，E s and i s Can be respectively converted into vectors u under synchronous rotation coordinates g E and i.
In the practical application of the grid-connected inverter, the grid-connected point voltage vector E is often adopted s For phase locking. From FIG. 2, it can be seen that the grid-connected point voltage vector E in the stationary coordinate system s Expressed as:
from the equation (1), the voltage vector E of the grid-connected point under the static coordinate system can be seen s Impedance of power receiving networkL g The influence of (c).
In order to counteract the influence of the grid impedance on the phase-locked loop, the invention provides a phase-locked loop strategy based on virtual inductance cancellation, and a control block diagram of the phase-locked loop strategy is shown in fig. 3. The method specifically comprises the following steps:
the method comprises the following steps: a virtual voltage is constructed for phase locking.
Introducing a virtual inductance valueL v Generally selectL v =0.6~0.8L g . The introduced virtual inductor is connected in series with the network side impedance, and the virtual voltage V under the static coordinate system after the series connection is selected s For phase locking. E s And V s The relationship of (a) to (b) is as follows:
in the above formula, V s Is a virtual voltage in a stationary coordinate system, E s Is a voltage vector of a grid-connected point under a static coordinate system，i s Is a grid-connected current vector under a static coordinate system,L v in order to be a virtual inductance value,sω s1 /(s+ω s1 ) Is an incomplete differential term and consists of a pure differential link and a first-order low-pass filter,ω s1 the cut-off frequency of the filter, mainly to suppress the amplification of high frequency noise by the differentiation term,sis a complex frequency.
Step two: phase locking of the virtual voltage.
In the embodiment of the invention, any form of phase-locked loop structure can be adopted, and particularly, the phase-locked loop structure under synchronous reference coordinates can be selectedqThe axis virtual voltage is phase locked and is shown outside the dashed box in fig. 3. Phase-locked angle of virtual voltageφComprises the following steps:
in the formula,φis the phase locking angle of the virtual voltage, V is the virtual voltage vector under the synchronous reference coordinate system,ω 1 is the angular frequency of the power frequency side,k pi ，k ii respectively proportional gain and integral gain of the phase locked loop,sis a complex frequency.
In fig. 3, LPF denotes a low pass filter, park denotes a complex number, and Re denotes a real part of one complex number.
Step three: and obtaining the phase angle difference.
Calculating a phase angle difference between the grid-connected point voltage vector and the virtual voltage vector, specifically comprising:
the active power transmitted between the grid-connected point voltage vector and the virtual voltage vector is calculated firstly, and the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector is obtained.
In actual loop control, the grid-connected point voltage vector E under a static coordinate system is always used s Is used as a synchronous reference, and power is transmitted to the power grid. Therefore, the phase angle difference of the two power frequencies needs to be compensated. Grid voltage vector E under synchronous reference coordinate system and virtual voltage vector V under synchronous reference coordinate system pass through virtual inductorL v Connection ofAs shown in fig. 4 (a); the corresponding phasor relationship diagram is shown in fig. 4 (b). The phase angle difference between E and V isδAs can be seen from fig. 4 (b), the active power transmitted between E and V is:
wherein,Pactive power, E is a grid voltage vector under a synchronous reference coordinate system, V is a virtual voltage vector under the synchronous reference coordinate system,δis the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector,ω 1 is the angular frequency of the power frequency side,L v is a virtual inductance value.
Again based on the instantaneous power theory, the active power can be expressed as:
in addition, in the case of the present invention,sinδcan be approximated byδ. In addition, high-frequency noise is prevented from being introduced, and the final output end is connected with a low-pass filter in series. Thereby, the deviceδCan be expressed as:
in the formula,δis the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector, E s Is a grid-connected point voltage vector i under a static coordinate system s* Is the conjugate of the grid-connected current vector under the static coordinate system,ω 1 is the angular frequency of the power frequency side,L v in order to be a virtual inductance value,ω s2 is the cut-off frequency of the low-pass filter,sand E is a complex frequency, E is a power grid voltage vector under a synchronous reference coordinate system, and V is a virtual voltage vector under the synchronous reference coordinate system. In addition, the above formula phase angle differenceδThe acquisition of the phase angle is similar to the acquisition of the phase angle in the power synchronous control, and the system weak network stability is improved.
In the figure, j denotes the imaginary unit.
Final phase lock angleθComprises the following steps:
θ=φ+δ (7)
wherein,θthe phase angle of the grid-connected point voltage vector,φis the phase-lock angle of the virtual voltage,δis the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector.
The invention is further described below with reference to specific examples.
Fig. 2 shows a topology of a grid-connected inverter according to the present invention. The rated capacity is 228 kW, and the rated line voltage is 800V. In engineering practice, the short circuit coefficient is often used to describe the grid strength and the grid impedance. The definition is as follows:
FIG. 5 shows the weak grid condition with short circuit coefficient =3.2, using E s Conventional phase locked loop with voltage phase lock and method using V s And comparing the active step response of the novel phase-locked loop of the virtual voltage phase lock. At 0.4 s, 0.8 s, 1.2 s and 1.6 s, the active settings were 70 kW, 140 kW,205 kW and 23 kW, respectively. As can be seen from (a 1), (a 2), and (a 3) in fig. 5, when the conventional phase-locked loop is used, low-frequency oscillation occurs in both the grid current and the voltage of the public grid-connected point. In contrast, as shown in fig. 5 (b 1), (b 2), and (b 3), the phase-locked loop of the present invention does not have such oscillation phenomenon.
As shown in fig. 6, the present invention further provides a system for improving the stability of the grid-connected inverter weak grid, including:
the device comprises a construction module, a detection module and a control module, wherein the construction module is used for introducing a virtual inductor and constructing to obtain a virtual voltage formed by connecting the virtual inductor and a network side impedance in series;
the phase locking module is used for performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
the correction module is used for calculating the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector after the virtual voltage and the grid-connected point voltage are connected through the virtual inductor; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the grid-connected point voltage;
and the transmission module is used for transmitting power to a power grid by taking the phase angle of the grid-connected point voltage as a synchronous reference.
As shown in fig. 7, the present invention provides an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the method for improving grid-connected inverter weak grid stability when executing the computer program.
The method for improving the stability of the grid-connected inverter weak grid comprises the following steps:
introducing a virtual inductor to obtain a virtual voltage after the virtual inductor is connected with a network side impedance in series;
performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
after the virtual voltage is connected with the grid-connected point voltage through the virtual inductor, calculating a phase angle difference between a grid-connected point voltage vector and the virtual voltage vector; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the voltage of the grid-connected point;
and taking the phase angle of the voltage of the grid-connected point as a synchronous reference to transmit power to a power grid.
The invention also provides a computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the steps of the method for improving the stability of a grid-connected inverter weak grid.
The method for improving the stability of the grid-connected inverter weak grid comprises the following steps:
introducing a virtual inductor to obtain a virtual voltage after the virtual inductor is connected with a network side impedance in series;
performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
after the virtual voltage and the grid-connected point voltage are connected through the virtual inductor, calculating a phase angle difference between a grid-connected point voltage vector and the virtual voltage vector; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the grid-connected point voltage;
and taking the phase angle of the voltage of the grid-connected point as a synchronous reference to transmit power to a power grid.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention has been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (8)
1. A method for improving the stability of a grid-connected inverter weak grid is characterized by comprising the following steps:
introducing a virtual inductor to obtain a virtual voltage after the virtual inductor is connected with a network side impedance in series;
performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
after the virtual voltage and the grid-connected point voltage are connected through the virtual inductor, calculating a phase angle difference between a grid-connected point voltage vector and the virtual voltage vector; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the voltage of the grid-connected point;
taking the phase angle of the grid-connected point voltage as a synchronous reference, and transmitting power to a power grid;
wherein, calculate the phase angle difference between grid-connected point voltage vector and the virtual voltage vector, include:
calculating active power transmitted between a grid-connected point voltage vector and a virtual voltage vector, and then calculating a phase angle difference between the grid-connected point voltage vector and the virtual voltage vector;
the active power transmitted between the voltage vector of the grid-connected point and the virtual voltage vector is calculated firstly, and the method comprises the following steps:
wherein,Pis active power, E s Is a grid-connected point voltage vector i under a static coordinate system s* The method comprises the following steps that (1) Re { } represents a real part of a complex number, wherein the complex number is the conjugate of a grid-connected current vector under a static coordinate system;
and then the active power transmitted between the grid-connected point voltage vector E under the synchronous rotating coordinate system and the virtual voltage vector V under the synchronous rotating coordinate system is combined as follows:
wherein,δas the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector,ω 1 is the angular frequency of the power frequency side,L v is a virtual inductance value;
the method comprises the following steps that a low-pass filter is connected in series with an output end to obtain a phase angle difference between a grid-connected point voltage vector and a virtual voltage vector, and the method comprises the following steps:
wherein,ω s2 is the cut-off frequency of the low-pass filter,sand E is complex frequency, the voltage vector of the grid-connected point under the synchronous rotating coordinate system, and V is a virtual voltage vector under the synchronous rotating coordinate system.
2. The method for improving the stability of the grid-connected inverter weak grid according to claim 1, wherein the method for obtaining the virtual voltage after the virtual inductor is connected in series with the grid-side impedance comprises the following steps:
wherein，V s Is a virtual voltage vector in a stationary coordinate system, E s Is a grid-connected point voltage vector under a static coordinate system，i s Is a grid-connected current vector under a static coordinate system,L v in order to be a virtual inductance value,sω s1 /(s+ω s1 ) In order to be an incomplete differential term,ω s1 is the cut-off frequency of the filter,sis a complex frequency.
3. The method for improving the grid-connected inverter weak grid stability according to claim 2, wherein the virtual inductance value is:
L v =0.6~0.8L g
wherein,L g is the grid impedance.
4. The method for improving the stability of the grid-connected inverter weak grid according to claim 1, wherein the step of phase-locking the virtual voltage is performed by using a synchronous reference coordinateqThe axis virtual voltage is phase locked.
5. The method for improving the stability of the grid-connected inverter weak grid according to claim 1 or 4, wherein the method for obtaining the phase-locked angle of the virtual voltage comprises the following steps:
wherein,φis the phase locking angle of the virtual voltage, V is the virtual voltage vector under the synchronous rotating coordinate system,ω 1 is the angular frequency of the power frequency side,k pi 、k ii respectively the proportional gain and the integral gain of the phase locked loop,sis a complex frequency.
6. The method for improving the stability of the grid-connected inverter weak grid according to claim 1, wherein the phase angle difference is superposed with the phase locking angle to obtain a corrected phase angle, and the corrected phase angle is used as a phase angle of a grid-connected point voltage, and the method comprises the following steps:
θ=φ+δ
wherein,θthe phase angle of the grid-connected point voltage vector,φis the phase-lock angle of the virtual voltage,δis the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector.
7. A grid-connected inverter weak grid stability improving system based on any one of claims 1 to 6 is characterized by comprising the following steps:
the device comprises a construction module, a detection module and a control module, wherein the construction module is used for introducing a virtual inductor and constructing to obtain a virtual voltage formed by connecting the virtual inductor and a network side impedance in series;
the phase locking module is used for performing phase locking on the virtual voltage to obtain a phase locking angle of the virtual voltage;
the correction module is used for calculating the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector after the virtual voltage and the grid-connected point voltage are connected through the virtual inductor; superposing the phase angle difference on the phase locking angle to obtain a corrected phase angle, and taking the corrected phase angle as the phase angle of the grid-connected point voltage;
and the transmission module is used for transmitting power to a power grid by taking the phase angle of the grid-connected point voltage as a synchronous reference.
8. The system for improving the stability of the grid-connected inverter weak grid according to claim 7, wherein the calculating, in the correction module, a phase angle difference between the grid-connected point voltage vector and the virtual voltage vector includes:
the active power transmitted between the grid-connected point voltage vector and the virtual voltage vector is calculated first, and then the phase angle difference between the grid-connected point voltage vector and the virtual voltage vector is calculated.
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