CN115800340A - Amplitude limiting control method and system for enhancing transient stability of network-type VSC (Voltage Source converter) - Google Patents
Amplitude limiting control method and system for enhancing transient stability of network-type VSC (Voltage Source converter) Download PDFInfo
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Abstract
The invention discloses an amplitude limiting control method and system for enhancing transient stability of a network VSC, wherein the method comprises the following steps: determining a power outer ring output phase based on a maximum power fluctuation value under a system steady state; determining a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value; and improving the amplitude limiting link based on the current distribution coefficient, determining an inner loop current reference value output by the amplitude limiting link, and controlling the inner loop current reference value output by the amplitude limiting link to enhance the transient stability of the VSC. According to the invention, on the basis of defining the influence of an amplitude limiting link which is easy to trigger under large disturbance on transient stability, the distribution of d-axis and q-axis currents after amplitude limiting is changed by adding a current distribution coefficient method, and the transient stability characteristic of a GFM-VSC system can be effectively improved.
Description
Technical Field
The invention relates to the technical field of a network-type converter, in particular to an amplitude limiting control method and system for enhancing transient stability of a network-type VSC.
Background
With the continuous development of new energy power generation, the power structure of a power system in China is remarkably changed, the proportion of traditional synchronous power generation equipment is gradually reduced, the permeability of a power electronic power supply with a Voltage Source Converter (VSC) interface is continuously increased, the potential of the VSC-based power electronic power supply is further developed, and the future power grid development is urgently needed. In recent years, a Grid Forming (GFM) technique has been attracting attention as a feasible solution for system transformation. Different from the network-following control, the GFM control is essentially a Voltage Control Mode (VCM), and by a power synchronization method, a port voltage amplitude and phase are autonomously formed, and power required by the system is output, thereby implementing grid-connected synchronous operation. The idea of modeling the grid-connected characteristic of the synchronous machine improves the active supporting capability of a power electronic power supply with a VSC interface, ensures the continuation of a power system stability research system, and cannot avoid the transient stability problem under the traditional large disturbance.
Considering the hardware overcurrent capacity of power electronic equipment, the operation of an actual GFM-VSC system under large disturbance is easily influenced by an amplitude limiting link, and the transient stability characteristic of the GFM-VSC with the amplitude limiting link is urgently needed to be analyzed and a method for improving the transient stability is provided.
Disclosure of Invention
The invention provides an amplitude limiting control method and system for enhancing transient stability of a network VSC (voltage source converter), and aims to solve the problem of how to improve an amplitude limiting link so as to improve the transient stability of the system.
In order to solve the above problem, according to an aspect of the present invention, there is provided a clipping control method for enhancing transient stability of mesh-type VSC, the method including:
determining a power outer ring output phase based on a maximum power fluctuation value under a system steady state;
determining a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value;
and controlling the amplitude limiting link based on the current distribution coefficient, and determining an inner loop current reference value output by the amplitude limiting link so as to enhance the transient stability of the VSC based on the inner loop current reference value output by the amplitude limiting link.
Preferably, the determining the power outer loop output phase based on the maximum power fluctuation value in the system steady state includes:
wherein, delta 0 Outputting the phase for the power outer loop; u shape g Is the grid voltage amplitude; u shape VSC,VCM The port voltage magnitude in voltage source control mode VCM; x L Is a line inductance; PMAX is the system maximum power fluctuation value.
Preferably, wherein the determining a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value comprises:
wherein, P T,CCM * The transmission power under the CCM constraint of the current control mode is obtained; u shape VSC,CCM * The port voltage amplitude under the improved CCM is obtained; rho is a power grid voltage fault degree coefficient; u shape g Is the grid voltage amplitude; delta CCM * The port voltage phase under the CCM is improved; x L Is a line inductance; i is max To allow maximum current amplitude; k is a radical of d Distributing coefficients for the currents; delta. For the preparation of a coating 0 The phase is output for the power outer loop.
Preferably, the controlling the amplitude limiting element based on the current distribution coefficient and determining the inner-loop current reference value output by the amplitude limiting element includes:
wherein k is d Distributing coefficients for the currents; i all right angle Lref,d * And i Lref,q * Respectively are inner ring current reference values output by the amplitude limiting link after the amplitude limiting link under the dq axis; i is max To allow maximum current amplitude; i.e. i Lref,d And i Lref,q And the reference values of the current inner ring under the dq axis before passing through the amplitude limiting link are respectively.
According to another aspect of the present invention, there is provided a clipping control system for enhancing transient stability of mesh-type VSCs, the system comprising:
the power outer ring output phase determining unit is used for determining the power outer ring output phase based on the maximum power fluctuation value under the system steady state;
a current distribution coefficient determination unit for determining a current distribution coefficient based on the power outer loop output phase and a maximum power fluctuation value;
and the amplitude limiting control unit is used for controlling the amplitude limiting link based on the current distribution coefficient, determining an inner loop current reference value output by the amplitude limiting link, and enhancing the transient stability of the VSC based on the inner loop current reference value output by the amplitude limiting link.
Preferably, the determining unit of the power outer loop output phase determines the power outer loop output phase based on the maximum power fluctuation value in the system steady state, and includes:
wherein, delta 0 Outputting the phase for the power outer loop; u shape g Is the grid voltage amplitude; u shape VSC,VCM Is a voltagePort voltage magnitude in source control mode VCM; x L Is a line inductance; PMAX is the system maximum power fluctuation value.
Preferably, the current distribution coefficient determining unit, which determines the current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value, includes:
wherein, P T,CCM * The transmission power under the CCM constraint of the current control mode; u shape VSC,CCM * The port voltage amplitude under the CCM is improved; rho is a power grid voltage fault degree coefficient; u shape g Is the grid voltage amplitude; delta CCM * The port voltage phase under the CCM is improved; x L Is a line inductance; i is max To allow maximum current amplitude; k is a radical of d Distributing coefficients for the currents; delta. For the preparation of a coating 0 The phase is output for the power outer loop.
Preferably, the amplitude limiting control unit controls the amplitude limiting element based on the current distribution coefficient, and determines the reference value of the inner loop current output by the amplitude limiting element, including:
wherein k is d Distributing coefficients for the currents; i.e. i Lref,d * And i Lref,q * Respectively are inner ring current reference values output by the amplitude limiting link after the amplitude limiting link under the dq axis; i is max To allow maximum current amplitude; i all right angle Lref,d And i Lref,q And the reference values of the current inner ring under the dq axis before passing through the amplitude limiting link are respectively.
Based on another aspect of the invention, the invention provides a computer readable storage medium having stored thereon a computer program which, when being executed by a processor, carries out the steps of any one of the clipping control methods of enhancing mesh-type VSC transient stability.
Based on another aspect of the present invention, the present invention provides an electronic device comprising:
the computer-readable storage medium described above; and
one or more processors to execute the program in the computer-readable storage medium.
The invention provides an amplitude limiting control method and system for enhancing transient stability of a network VSC, which comprises the following steps: determining a power outer ring output phase based on a maximum power fluctuation value under a system steady state; determining a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value; and controlling the amplitude limiting link based on the current distribution coefficient, and determining an inner loop current reference value output by the amplitude limiting link so as to enhance the transient stability of the VSC based on the inner loop current reference value output by the amplitude limiting link. According to the invention, on the basis of defining the influence of an amplitude limiting link which is easy to trigger under large disturbance on transient stability, the distribution of d-axis and q-axis currents after amplitude limiting is changed by adding a current distribution coefficient method, and the transient stability characteristic of a GFM-VSC system can be effectively improved.
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A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
fig. 1 is a flow diagram of a method 100 for limiting transient stability of an enhanced mesh VSC in accordance with an embodiment of the present invention;
fig. 2 is a schematic diagram of a topology structure and a control strategy of a network-forming VSC system according to an embodiment of the present invention;
FIG. 3 is a block diagram of a network-based control strategy according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a current inner loop response process under a large disturbance according to an embodiment of the invention;
FIG. 5 is a P-delta plot of a GFM-VSC system that accounts for clipping effects, according to an embodiment of the invention;
FIG. 6 is a schematic diagram illustrating the effect of dq-axis current sharing on the transient process of a GFM-VSC system according to an embodiment of the present invention;
fig. 7 is a schematic diagram illustrating the influence of different current distribution coefficients kd on the transmission power of the system after amplitude limiting according to the embodiment of the present invention;
FIG. 8 is a simulated waveform comparing GFM-VSC transient stability characteristics under conventional and improved strategies in accordance with an embodiment of the present invention;
FIG. 9 is a simulated waveform comparing GFM-VSC power fluctuation characteristics under conventional and improved strategies in accordance with an embodiment of the invention;
fig. 10 is a schematic diagram of a structure of an amplitude-limiting control system 1000 for enhancing the transient stability of the network VSC according to an embodiment of the present invention.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In addition, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their context in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Considering the hardware overcurrent capacity of power electronic equipment, the operation of an actual GFM-VSC system under large disturbance is easily affected by amplitude limiting, so that the transient stability characteristic of the GFM-VSC with an amplitude limiting link needs to be analyzed urgently and a method for improving the transient stability is provided. Therefore, the invention analyzes the reason of transient instability of the system caused by the amplitude limiting link, and provides an improved amplitude limiting method with current distribution coefficients by utilizing the influence mechanism of dq axis current distribution under faults, thereby effectively enhancing the transient stability of the system.
Fig. 1 is a flowchart of a clipping control method 100 for enhancing network VSC transient stability according to an embodiment of the present invention. As shown in fig. 1, according to the amplitude limiting control method for enhancing the transient stability of the network-based VSC provided in the embodiment of the present invention, on the basis of a mechanism that the transient stability is affected by an amplitude limiting link that is easily triggered under a large disturbance, the distribution of d-axis and q-axis currents after amplitude limiting is changed by a method of adding a current distribution coefficient, so that the transient stability characteristic of the GFM-VSC system can be effectively improved. The amplitude limiting control method 100 for enhancing the transient stability of the network-enhanced VSC provided in the embodiment of the present invention starts from step 101, and determines a power outer loop output phase based on a maximum power fluctuation value in a system steady state in step 101.
Preferably, the determining the power outer loop output phase based on the maximum power fluctuation value in the system steady state includes:
wherein, delta 0 Outputting the phase for the power outer loop; u shape g Is the grid voltage amplitude; u shape VSC,VCM The port voltage magnitude in voltage source control mode VCM; x L Is a line inductance; PMAX is the system maximum power fluctuation value.
In step 102, a current distribution coefficient is determined based on the power outer loop output phase and the maximum power fluctuation value.
Preferably, wherein the determining a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value comprises:
wherein, P T,CCM * The transmission power under the CCM constraint of the current control mode; u shape VSC,CCM * The port voltage amplitude under the improved CCM is obtained; rho is a power grid voltage fault degree coefficient; u shape g Is the grid voltage amplitude; delta CCM * The port voltage phase under the CCM is improved; x L For line electricityFeeling; i is max To allow maximum current amplitude; k is a radical of d Distributing coefficients for the currents; delta 0 The phase is output for the power outer loop.
In step 103, the clipping link is controlled based on the current distribution coefficient, and an inner loop current reference value output by the clipping link is determined, so as to enhance the transient stability of the VSC based on the inner loop current reference value output by the clipping link.
Preferably, the controlling the amplitude limiting element based on the current distribution coefficient and determining the inner-loop current reference value output by the amplitude limiting element includes:
wherein k is d Distributing coefficients for the currents; i.e. i Lref,d * And i Lref,q * Respectively are inner ring current reference values output by the amplitude limiting link after the amplitude limiting link under the dq axis; i is max To allow maximum current amplitude; i.e. i Lref,d And i Lref,q And the reference values of the current inner ring before passing through the amplitude limiting link under the dq axis are respectively.
The present invention will be described in further detail by taking the actual network VSC system shown in fig. 2 as an example. As shown in fig. 2, the VSC system specifically includes three parts, i.e., an ac side grid and transmission line, a grid type converter, and a DC side DC/DC and energy storage device. In said fig. 1, the circuit topology: u. u g ,i g Respectively, the network side voltage and the current; u. of VSC ,i VSC The output voltage and the current of the VSC are respectively; e is the internal potential of the VSC; i.e. i L Is a filter inductor current; u. of dc ,i dc Respectively direct current voltage and current; z Line Transmitting an impedance for the line; l is 1 ,R 1 And C 1 Respectively outputting filter parameters for the VSC; c dc Is a DC bus capacitor; l is a radical of an alcohol 2 ,C 2 And C 3 Respectively DC/DC converter parameters; p DC 、P C Direct current input power and direct current capacitance power are respectively; p is AC 、Q AC Respectively outputting active power and reactive power for VSCRate; p T 、Q T Active and reactive power is transmitted for the line, respectively. The control system part: p N1 ,Q N1 Respectively VSC rated power; u. of ref ,δ,U ref Respectively outputting reference voltage and corresponding phase and amplitude for the VSC; i.e. i Lref Is a VSC inner loop current reference value; p N2 Is an energy storage rated power reference value; u. of dcN Rated voltage for the direct current bus; u. u dcref ,i dcref Respectively are a direct current side voltage and a current reference value; e.g. of a cylinder ref1 ,e ref2 The modulation waves are respectively corresponding to the VSC and the DC/DC converter.
Based on the topology and control strategy of the GFM-VSC system shown in fig. 2 and the block diagram of the control strategy of the specific GFM-VSC shown in fig. 3, the power injected by the line impedance of the GFM-VSC system and the control equation of the GFM-VSC system can be derived, including:
step 1-1: as shown in FIG. 2, the GFM-VSC system injects active power P into the grid through line impedance T And according to the simplification that the inductance in the impedance of the power transmission line is far larger than the resistance, the method can obtain:
in the formula: delta is the phase difference between the voltage of the VSC port and the voltage of the network side, and can be called as a virtual power angle; theta is the phase of the line impedance; u shape VSC And U g Respectively are VSC port voltage and grid voltage amplitude; x L Is the line inductance.
Step 1-2: based on the control strategy of the GFM-VSC system as shown in FIG. 3, the control equation of the GFM-VSC system is derived as follows:
in the formula: omega ref And omega g Respectively are VSC virtual angular frequency and network side angular frequency; d P Is a damping coefficient; j. the design is a square vir Is a virtual inertia coefficient; k P Is the active frequency coefficient; k is Q Is reactive-voltage amplitudeA value coefficient; p is N1 ,Q N1 Respectively VSC rated power; u shape AC,N Is a rated voltage amplitude; defining the AC regulation factor K AC ＝K P +D P 。
And 2, step: and deducing the dq axis current of the inner ring of the GFM-VSC and providing a typical amplitude limiting link based on the model obtained in the previous step and the inner ring control of the GFM-VSC system, wherein the typical amplitude limiting link is as follows:
step 2-1: the inner loop dq axis current of the GFM-VSC is derived as follows:
in the formula: i all right angle L,d And i L,q Is the filter inductance dq axis current; i.e. i VSC,d And i VSC,q Outputting dq axis current for the VSC; filter capacitor C of VSC 1 Smaller and negligible.
The transient response process of the current inner loop dq axis current under a specific large disturbance is shown in fig. 3. In said FIG. 3, initial state (i) L,d ,i L,q ) At steady state point O; after disturbance (i) L,d ,i L,q ) Varying according to the solid line in the figure. The clipping segment is a boundary circle in the figure, and can be seen along with I max Due to the reduction of the voltage limiting value, under disturbance, the GFM-VSC may trigger a limiting link at the moment of or during a fault, so that the GFM-VSC cannot output the reference current according to the VCM constraint and is switched to the limiting current value under the CCM constraint to operate.
Step 2-2: based on the maximum value of the current allowed by the device, the existing typical clipping steps are given as follows:
in the formula: i.e. i Lref,d ,i Lref,q Respectively are reference values of an inner current ring before passing through an amplitude limiting link; i.e. i Lref,d * ,i Lref,q * Respectively are reference values of the current inner ring after passing through the amplitude limiting link; i is max To allow for maximum current amplitude.
And step 3: transmission power P of GFM-VSC under constraint of Voltage Control Mode (VCM) T,VCM The following are:
in the formula: u shape VSC,VCM ,δ VSC,VCM Respectively, port voltage amplitude and phase under VCM; delta. For the preparation of a coating 0 Outputting the phase for the power outer loop; and rho is a power grid voltage fault degree coefficient.
And 4, step 4: after further deducing and triggering the amplitude limiting link, the transmission power P of GFM-VSC is changed from VCM to CCM T,CCM The following are:
in the formula: u shape VSC,CCM ,δ VSC,CCM Respectively is the amplitude and the phase of the port voltage under CCM; delta 0 Outputting the phase for the power outer loop; and rho is a power grid voltage fault degree coefficient.
And 5: based on the equation 5 obtained in the previous step, an active-power angle curve of the GFM-VSC system, which is affected by the clipping step, is analyzed and calculated, as shown in fig. 5.
Said fig. 5 shows the P-delta curve of the GFM-VSC system obtained from equation 5, taking into account the effect of the clipping element, the solid line P tN, And the dotted line P tF Respectively representing VCM transmission power curves in a rated state and a disturbance state; solid line P tN,CCM And the dotted line P tF,CCM The transmission power curves of CCM under rated and disturbed states are respectively expressed, and analysis is carried out at different stages to know that:
1) And (5) fault instant: the system is started from an initial operation point t 0 Dropping to P under VCM tF T on the curve 1 ；
2) And (3) fault continuation: the control system increases omega due to the sudden drop in transmission power ref ，δ ref Rises so that P is tF T on the curve 1 Run to t 2 (ii) a At this time, the amplitude limiting link is triggeredLine transmission power is from P tF Curve conversion to P in CCM tF,CCM A curve; if the fault is not cleared, the system will follow P tF,CCM The curve oscillates continuously;
3) Fault clearing and recovery:
(1) if the fault is in UEP 1 Front-clearing and VSC input power at UEP 1 Before returning to rated power, δ ref Will return to t 5 Back, along P tN Curve back to SEP 1 (ii) a If VSC output power is in UEP 1 Before the rated power is restored, δ ref Will cross the UEP 1 In CCM under P tN,CCM The curve runs and is finally attracted by an Abnormal State Point (ASP) and destabilized.
(2) If the fault is in UEP 1 Post-clearing of the fault, also due to the fault being cleared, P tN,CCM The curve is already below the rated power, so ω ref Will further accelerate, will be attracted by ASP point and then destabilized too; but when the fault clearing time is extended to SEP 2 And UEP 3 E.g. t 7 Time), as in the above analysis, δ ref Will return to t 8 Back, along P tN Curve back to periodic equilibrium point SEP 2 。
In conclusion, the transient stability of GFM-VSC is greatly weakened under the influence of the limited link, and only in SEP 1 ～UEP 1 And the subsequent period interval may be guaranteed to be stable; once the above interval is crossed, the signal is attracted by ASP under CCM, resulting in transient instability.
Therefore, in the present invention, another degree of freedom of control of the clipping element is introduced: the distribution of the d-axis and q-axis currents in the amplitude limiting link obtains the influence of the d-axis and q-axis currents on the transient response of the GFM-VSC system under large disturbance, as shown in fig. 6 specifically;
the figure 6 shows the influence of dq-axis current allocation on transient response of the GFM-VSC system under large disturbance. As can be seen from fig. 6, I is the clipping element max Determining the radius of the boundary circle, namely the magnitude of the effective value of the current; and the dq-axis current sharing may affect the phase between the output current and the voltage in the current control mode.
Therefore, the invention designs an improved method with a current distribution coefficient based on an influence mechanism of d-axis and q-axis currents in an amplitude limiting link on transient response of a GFM-VSC system under large disturbance, and the method comprises the following steps:
in the formula: k is a radical of d Distributing coefficients for the currents; i.e. i Lref,d * And i Lref,q * The reference values of the inner ring current output by the amplitude limiting link after the amplitude limiting link under the dq axis are respectively; I.C. A max To allow maximum current amplitude; i.e. i Lref,d And i Lref,q And the reference values of the current inner ring under the dq axis before passing through the amplitude limiting link are respectively.
Combining equations 5 and 6, obtaining equation 7 as follows, and analyzing the influence of the improved clipping method on the system power transmission curve under different current distribution coefficients based on equation 7, as shown in fig. 7;
in the formula: u shape VSC,CCM * ,δ VSC,CCM * Respectively the port voltage amplitude and the phase under the improved CCM; delta 0 Outputting the phase for the power outer loop; u shape g Is the grid voltage amplitude; rho is a power grid voltage fault degree coefficient; i is max To allow for maximum current amplitude.
Said FIG. 7 shows the current distribution coefficient k d Influence on the system transmission power curve in the current control mode. As can be seen from FIG. 7, k is added d Only the phase of the transmission power in CCM is influenced, and the effective value is not influenced; with k d Increase of (UEP) 1 The system can move rightwards, and the system stability interval is increased; fault point ASP also moves to period balance point SEP 2 Approaching; at this time, the q-axis current is additionally distributed, so that the input power P under the action of the control system is caused VSC Entering the transmission power curve under VCM and then recovering to SEP 2 And the stable operation of the system is ensured.
As can be seen from equation 7 and the analysis of fig. 7, as kd increases, the transmission power curve in CCM shifts to the right, increasing the transient stability interval of the system; meanwhile, the requirement of meeting the steady-state power fluctuation of the system is considered, namely the transmission power curve of the GFM-VSC under the CCM constraint and the VCM constraint is intersected at the maximum power point P MAX The following can be obtained:
in the formula: p MAX The maximum power fluctuation value of the system under the steady state; delta MAX For maximum power point P under VCM constraint MAX Corresponding power angle position.
Therefore, in the present invention, first, the maximum fluctuation power value P is based on the system MAX Determination of delta 0 Is then based on P T,CCM * ＝P MAX 、δ 0 K is obtained in parallel with equation 7 d To improve the clipping step based on the current distribution coefficient. Wherein, k is d Substituting the formula 6 to obtain the inner loop current reference value with improved amplitude limit
In the present invention, specific simulation waveforms are shown in fig. 8 and 9. Said figure 8 compares the transient stability characteristics of GFM-VSCs under a conventional clipping strategy with an improved clipping strategy. As can be seen from fig. 8 (c 1) shown in the figure, after the 1.1s fault is cleared, the GFM-VSC system is attracted to the ASP under CCM in the foregoing analysis, and although the output active power is adjusted to 20kW, a large amount of idle power is output at the same time, the amplitude of the port voltage even rises to 1.6pu, the clipping link cannot be exited, and the system is unstable in transient state. Comparing with the fig. 8 (c 2), it can be seen that after the fault is cleared, the GFM-VSC system under the improved strategy can be switched from the CCM state to the VCM state to operate back to the cycle balance point; as can also be seen from fig. 8 (b 2) and (f 2), the port voltage and the output power of the VSC are both returned to the rated state.
The fig. 9 compares the conventional clipping strategy with the improved clipping strategy, and the transient response process of the system is performed under the condition that the power grid is normal and the output power fluctuates. The system operating conditions are shown in fig. 9 (a 1): setting VSC reference power of 20kW at the stage of 1.0s-2.0 s; in the stage of 2.0s-3.0s, the step of the output rated power is 28kW; in the 3.0s-4.0s stage, the system recovers. As can be seen from fig. 9 (b 1), when the conventional active current priority strategy is adopted, the system is attracted by the ASP after entering the amplitude limiting mode, so that the system is unstable and cannot normally operate; compared with fig. 9 (b 2), after a certain reactive current is distributed by adopting an improved strategy, the system can bear the set power fluctuation, and further, the VCM operation is continuously maintained.
The invention clarifies the mechanism of degrading GFM-VSC transient stability for the amplitude limiting link which is easy to trigger under large disturbance. On the basis, the distribution of d-axis and q-axis currents after amplitude limiting is changed only by a method of adding a current distribution coefficient, and the transient stability characteristic of the GFM-VSC system is improved.
Fig. 10 is a schematic diagram of a structure of a clipping control system 1000 for enhancing the transient stability of the mesh VSC according to an embodiment of the present invention. As shown in fig. 10, the amplitude limiting control system 1000 for enhancing the transient stability of the mesh VSC according to the embodiment of the present invention includes: a power outer loop output phase determination unit 1001, a current distribution coefficient determination unit 1002, and a clipping control unit 1003.
Preferably, the power outer loop output phase determining unit 1001 is configured to determine the power outer loop output phase based on a maximum power fluctuation value in a system steady state.
Preferably, the determining unit 1001 for determining the power outer loop output phase based on the maximum power fluctuation value in the system steady state includes:
wherein, delta 0 Outputting the phase for the power outer loop; u shape g Is the grid voltage amplitude; u shape VSC,VCM The port voltage magnitude in voltage source control mode VCM; x L Is a line inductance; PMAX is the system maximum power fluctuation value.
Preferably, the current distribution coefficient determining unit 1002 is configured to determine a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value.
Preferably, the current distribution coefficient determining unit 1002, determining a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value, includes:
wherein, P T,CCM * The transmission power under the CCM constraint of the current control mode; u shape VSC,CCM * The port voltage amplitude under the improved CCM is obtained; rho is a power grid voltage fault degree coefficient; u shape g Is the grid voltage amplitude; delta CCM * The port voltage phase under the CCM is improved; x L Is a line inductance; i is max To allow maximum current amplitude; k is a radical of d Distributing coefficients for the currents; delta 0 The phase is output for the power outer loop.
Preferably, the amplitude limiting control unit 1003 is configured to control the amplitude limiting link based on the current distribution coefficient, and determine an inner-loop current reference value output by the amplitude limiting link, so as to enhance the transient stability of the VSC based on the inner-loop current reference value output by the amplitude limiting link.
Preferably, the limiting control unit 1003 controls the limiting element based on the current distribution coefficient, and determines the inner-loop current reference value output by the limiting element, including:
wherein k is d Distributing coefficients for the currents; i.e. i Lref,d * And i Lref,q * Respectively are inner ring current reference values output by the amplitude limiting link after the amplitude limiting link under the dq axis; i is max To allow maximum current amplitude; i all right angle Lref,d And i Lref,q And the reference values of the current inner ring under the dq axis before passing through the amplitude limiting link are respectively.
The amplitude limiting control system 1000 for enhancing the transient stability of the mesh VSC according to the embodiment of the present invention corresponds to the amplitude limiting control method 100 for enhancing the transient stability of the mesh VSC according to another embodiment of the present invention, and is not described herein again.
Based on another aspect of the invention, the invention provides a computer readable storage medium having stored thereon a computer program which, when being executed by a processor, carries out the steps of any one of the clipping control methods of enhancing mesh-type VSC transient stability.
Based on another aspect of the present invention, the present invention provides an electronic device comprising:
the computer-readable storage medium described above; and
one or more processors to execute the program in the computer-readable storage medium.
The invention has been described with reference to a few embodiments. However, other embodiments of the invention than the one disclosed above are equally possible within the scope of the invention, as would be apparent to a person skilled in the art from the appended patent claims.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
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 is 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 (10)
1. A clipping control method for enhancing mesh VSC transient stability, the method comprising:
determining a power outer ring output phase based on a maximum power fluctuation value under a system steady state;
determining a current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value;
and improving the amplitude limiting link based on the current distribution coefficient, determining an inner-loop current reference value output by the amplitude limiting link, and controlling the inner-loop current reference value output by the amplitude limiting link to enhance the transient stability of the VSC.
2. The method of claim 1, wherein determining the power outer loop output phase based on the maximum power fluctuation value in the system steady state comprises:
wherein, delta 0 Outputting the phase for the power outer loop; u shape g Is the grid voltage amplitude; u shape VSC,VCM The port voltage magnitude in voltage source control mode VCM; x L Is a line inductance; PMAX is the system maximum power fluctuation value.
3. The method of claim 1, wherein determining a current distribution coefficient based on the power outer loop output phase and a maximum power fluctuation value comprises:
wherein, P T,CCM * The transmission power under the CCM constraint of the current control mode; u shape VSC,CCM * The port voltage amplitude under the improved CCM is obtained; rho is a power grid voltage fault degree coefficient; u shape g Is the grid voltage amplitude; delta CCM * The port voltage phase under the CCM is improved; x L Is a line inductance; i is max To allow maximum current amplitude; k is a radical of d Distributing coefficients for the currents; delta 0 The phase is output for the power outer loop.
4. The method of claim 1, wherein the controlling the clipping element based on the current distribution coefficient to determine the inner-loop current reference value of the clipping element output comprises:
wherein k is d Distributing coefficients for the currents; i.e. i Lref,d * And i Lref,q * Respectively are inner ring current reference values output by the amplitude limiting link after the amplitude limiting link under the dq axis; i is max To allow maximum current amplitude; i.e. i Lref,d And i Lref,q And the reference values of the current inner ring under the dq axis before passing through the amplitude limiting link are respectively.
5. A clipping control system for enhancing mesh VSC transient stability, the system comprising:
the power outer ring output phase determining unit is used for determining the power outer ring output phase based on the maximum power fluctuation value under the system steady state;
a current distribution coefficient determination unit for determining a current distribution coefficient based on the power outer loop output phase and a maximum power fluctuation value;
and the amplitude limiting control unit is used for controlling the amplitude limiting link based on the current distribution coefficient, determining an inner-loop current reference value output by the amplitude limiting link and enhancing the transient stability of the VSC based on the inner-loop current reference value output by the amplitude limiting link.
6. The system of claim 5, wherein the power outer loop output phase determining unit determines the power outer loop output phase based on a maximum power fluctuation value in a system steady state, and comprises:
wherein, delta 0 Outputting the phase for the power outer loop; u shape g Is the grid voltage amplitude; u shape VSC,VCM The port voltage magnitude in voltage source control mode VCM; x L Is a line inductance; PMAX is the system maximum power fluctuation value.
7. The system of claim 5, wherein the current distribution coefficient determining unit determines the current distribution coefficient based on the power outer loop output phase and the maximum power fluctuation value, comprising:
wherein, P T,CCM * The transmission power under the CCM constraint of the current control mode; u shape VSC,CCM * The port voltage amplitude under the improved CCM is obtained; rho is a power grid voltage fault degree coefficient; u shape g Is the grid voltage amplitude; delta CCM * The port voltage phase under the CCM is improved; x L Is a line inductance; i is max To allow maximum current amplitude; k is a radical of d Distributing coefficients for the currents; delta 0 The phase is output for the power outer loop.
8. The system of claim 5, wherein the clipping control unit controls the clipping element based on the current distribution coefficient to determine an inner-loop current reference value output by the clipping element, and comprises:
wherein k is d Distributing coefficients for the currents; i.e. i Lref,d * And i Lref,q * Respectively are inner ring current reference values output by the amplitude limiting link after the amplitude limiting link under the dq axis; i is max To allow maximum current amplitude; i all right angle Lref,d And i Lref,q And the reference values of the current inner ring under the dq axis before passing through the amplitude limiting link are respectively.
9. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 4.
10. An electronic device, comprising:
the computer-readable storage medium recited in claim 9; and
one or more processors to execute the program in the computer-readable storage medium.
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