CN109546673A - A kind of impedance stability evaluation method of new energy three-terminal flexible direct-current power transmission system - Google Patents
A kind of impedance stability evaluation method of new energy three-terminal flexible direct-current power transmission system 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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
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Abstract
The present invention relates to a kind of impedance stability evaluation methods of new energy three-terminal flexible direct-current power transmission system, impedance stability evaluation method is applied to Multi-end flexible direct current transmission system by this method, and for instructing attitude conirol, comprising the following steps: step 1: establishing the Equivalent DC impedance model of each inverter in the three-terminal flexible direct-current power transmission system under dq coordinate system；Step 2: converting equivalent small signal impedance model for Equivalent DC impedance model；Step 3: the determination of stability under different parameters being carried out to equivalent small signal impedance model, obtains and determines result；Step 4: building three-terminal flexible direct-current power transmission system simulation model, verifying determines result.Compared with prior art, the present invention has many advantages, such as effectively differentiate the stability of Multi-end flexible direct current transmission system, and directly instructs the adjusting of controller parameter.
Description
Technical field
The present invention relates to field of power electronics, more particularly, to a kind of resistance of new energy three-terminal flexible direct-current power transmission system
Anti- method for estimating stability.
Background technique
As converters develop, flexible DC transmission (Voltage Source Converter Based
High Voltage Direct Current, VSC-HVDC) it has received widespread attention, modeling has also obtained extensively with control
Using.Both ends VSC-HVDC engineering includes two converter stations, is the most common flexible HVDC transmission system, but in each load
The heart and power supply all need a set of transmission facility, insufficient in economy and flexibility.Multiterminal based on voltage source converter are soft
Property DC transmission system (Voltage Source Converter in Multi-terminal High Voltage Direct
Current, VSC-MTDC) it is the flexible HVDC transmission system being made of 3 and the above VSC and DC line, it can be and regard as
The extension of both ends VSC-HVDC.VSC-MTDC not only has the advantages that both ends VSC-HVDC, but also can connect multiple and different positions
The distributed generation resource set is powered to multiple load centers, is conducive to system and is received with intermittent, power long-time random wave
The renewable energy of dynamic property has a extensive future in terms of passive load power supply, city.In flexible DC transmission
In research field, operation stability is always the project being concerned.
Method for analyzing stability based on impedance is that a kind of analysis Complex Power electronic system stability is simple and effective
Method.This method models system impedance according to converter Control mode, judges entire system using Nyquist stability criteria
The stability of system, and it is based on the potential resonance frequency of control theory forecasting system and stability margin.In addition, this method also can be used
Exist at present in the influence of analysis major loop and controller parameter to system stability to provide guidance for System Parameter Design
Relatively broad application is obtained in the HVDC system of both ends.Wen B et al. is in IEEE Transactions on Power
" the Small-Signal Stability Analysis of Three-Phase AC Systems delivered on Electronics
in the Presence of Constant Power Loads Based on Measured d-q Frame
Impedances " stability of constant power load three-phase alternating current system studied using the method for exchange end equivalent impedance；Amin
The Impedance-based that M et al. is delivered in IEEE Energy Conversion Congress and Exposition
And eigenvalue based stability assessment compared in VSC-HVDC system compares resistance
Analysis resistant method and the superiority and inferiority based on eigenvalue Method.In Multi-end flexible direct current transmission system, usual inverter should conduct
Rectifier operation, is used as invertor operation again, and controller parameter can cause large effect to the stability of system.This
The attitude conirol of class inverter is particularly important to the stable operation of system.However rarely have document application impedance to comment at present
Valence analytic approach carries out estimation of stability analysis to Multi-end flexible direct current transmission system.
Summary of the invention
It is an object of the present invention to overcome the above-mentioned drawbacks of the prior art and provide a kind of three end of new energy is soft
The impedance stability evaluation method of property DC transmission system.
The purpose of the present invention can be achieved through the following technical solutions:
A kind of impedance stability evaluation method of new energy three-terminal flexible direct-current power transmission system, this method is by impedance stabilization
Property evaluation method be applied to Multi-end flexible direct current transmission system, and for instructing attitude conirol, comprising the following steps:
Step 1: establishing the Equivalent DC resistance of each inverter in the three-terminal flexible direct-current power transmission system under dq coordinate system
Anti- model；
Step 2: converting equivalent small signal impedance model for Equivalent DC impedance model；
Step 3: the determination of stability under different parameters being carried out to equivalent small signal impedance model, obtains and determines result；
Step 4: building three-terminal flexible direct-current power transmission system simulation model, verifying determines result.
Further, the Equivalent DC impedance model in the step 1, specific formula are as follows:
In formula, LcAnd RcCorrespond to the inductance and resistance of inverter, CfFor filter capacitor, ωbFor the basic angular frequency of power grid,
ωgFor the per unit value of mains frequency, icAnd vcCorrespond to the electric current and voltage of inverter inverter side, isAnd vsCorrespond to grid-connected place
Electric current and voltage, LgAnd RgCorrespond to the inductance and resistance of inverter, vgFor network voltage, j is imaginary number.
Further, the step 1 include it is following step by step:
Step 11: drawing the control of the power control inverter and DC voltage control inverter including PLL phaselocked loop
Block diagram processed；
Step 12: the voltage and current component under a, b and c three-phase static coordinate system is transformed into dq rotation by Park transformation
Turn under coordinate system；
Step 13: according to converter Control block diagram, voltage-current relationship and PLL phaselocked loop dynamic effects, deriving and establish often
The Equivalent DC impedance model of a inverter.
Further, the power control inverter in the step S11 and DC voltage control inverter are all made of double close
Ring control, the inner ring of the double-closed-loop control of the power control inverter use current control, and outer ring uses wattful power surely
Rate control, the inner ring of the DC voltage control inverter use current control, and outer ring uses constant DC voltage control.
Further, the PLL phaselocked loop dynamic effects in the step S13 are required phase angle theta in inverter control loop
To the dynamically track of PCC points of common connection voltage phase angle θ ', specific representation formula are as follows:
In formula, TΔθFor the spin matrix of Δ θ, Δ θ is that required phase angle theta is commonly connected to PCC in inverter control loop
The dynamically track respective value of point voltage phase angle θ ',For set of integers.
Further, the step 2 include it is following step by step:
Step 21: deriving that three inverters include the equivalent impedance formula of DC line capacitor；
Step 22: establishing the equivalent small signal impedance model of whole system and abbreviation obtains active power source impedance and bears
Carry impedance.
Further, the equivalent impedance formula of the step 21 are as follows:
In formula, ZVSC1(s)、ZVSC2(s) and ZVSC3(s) the first inverter VSC1, the second inverter VSC2 and are corresponded to
The equivalent impedance of three inverter VSC3, ZPIt (s) is the direct current equivalent impedance of power control inverter, ZV(s) voltage-controlled for direct current
The direct current equivalent impedance of inverter processed, CdcFor DC line capacitor, s is complex variable.
Further, the active power source impedance and load impedance of the step 22, specific formula are as follows:
Zr(s)=Zdccable+ZVSC1(s)
In formula, ZrIt (s) is active power source impedance, ZlIt (s) is load impedance, ZdccableFor direct current cables impedance.
Further, the determination of stability in the step 3 is the ratio for examining active power source impedance and load impedance
Whether corresponding Nyquist curve meets Nyquist stability criterion, if the Nyquist stability criterion is the wattful power
Nyquist curve corresponding to the ratio of rate source impedance and load impedance does not include point (- 1, j0), then is determined as that system is stablized,
If Nyquist curve corresponding to the ratio of the active power source impedance and load impedance includes point (- 1, j0), then determine
For system unstability.
Further, component library used by the three-terminal flexible direct-current power transmission system simulation model in the step 4 is
MATLAB/simulink component library, the input frequency of the three-terminal flexible direct-current power transmission system simulation model be 1HZ~
1kHz, the voltage and current analysis tool of the three-terminal flexible direct-current power transmission system simulation model are Fourier transformation tool.
Compared with prior art, the invention has the following advantages that
(1) present invention by using impedance evaluation assessment to flexible HVDC transmission system carry out estimation of stability analysis when,
The way traffic of inverter is required in Multi-end flexible direct current transmission system, system is established suitable for bidirectional power
The small signal impedance model of flowing, model setting parameter more adapt to actual running environment, simulate effect closer to reality.
(2) present invention is by carrying out Nyquist stability criterion using the ratio to active power source impedance and load impedance
It examines, since its controller parameter has larger impact to system stability, simulation analysis has been carried out to the adjusting of its parameter and has been commented
Valence, the judgement result obtained is more reliable, and accuracy is higher,
(3) present invention establishes three-terminal flexible direct-current power transmission system emulation by using MATLAB/simulink component library
Model, model foundation is more simple, and data visualization is convenient for the subsequent adjusting for instructing controller parameter.
Detailed description of the invention
Fig. 1 is three-terminal flexible direct-current power transmission system structure chart；
Fig. 2 is converter station analysis model figure；
Fig. 3 is power control converter Control structure chart；
Fig. 4 is DC voltage control converter Control structure chart；
Fig. 5 is the PLL dynamic model figure in the present invention under synchronous rotating frame；
Fig. 6 is two rotating coordinate systems phase angle difference schematic diagram of the present invention；
Fig. 7 is the equivalent small signal impedance illustraton of model of three-terminal flexible direct-current power transmission system of the present invention；
Fig. 8 is the simplification equivalent impedance illustraton of model of three-terminal flexible direct-current power transmission system；
Fig. 9 is the impedance model proof diagram of three-terminal flexible direct-current power transmission system；
Figure 10 is impedance model verification result figure, and wherein Figure 10 (a) is active power source impedance model verification result figure,
Figure 10 (b) is load impedance model verification result figure；
Figure 11 is the stabilization of DC voltage controller system under the conditions of outer ring DC voltage initial control parameter 1+3/s
Property analysis chart, wherein Figure 11 (a) is the impedance frequency response of load impedance and active power source impedance, and Figure 11 (b) is wattful power
The Nyquist curve of the ratio of rate source impedance and load impedance；
Figure 12 is the stability of DC voltage controller system under the conditions of outer ring DC voltage control parameter 0.1+3/s
Analysis chart, wherein Figure 12 (a) is the impedance frequency response of load impedance and active power source impedance, and Figure 12 (b) is active power
The Nyquist curve of the ratio of source impedance and load impedance；
Figure 13 is the stability of DC voltage controller system under the conditions of outer ring DC voltage control parameter 3.5+3/s
Analysis chart, wherein Figure 13 (a) is the impedance frequency response of load impedance and active power source impedance, and Figure 13 (b) is active power
The Nyquist curve of the ratio of source impedance and load impedance；
Figure 14 is DC voltage controller simulation result diagram under the conditions of outer ring DC voltage initial control parameter 1+3/s,
Wherein Figure 14 (a) is that VSC1 exchanges side voltage, and Figure 14 (b) is active power source and the DC voltage v for loading junctiondc；
Figure 15 is DC voltage controller simulation result diagram under the conditions of outer ring DC voltage control parameter 0.1+3/s,
Middle Figure 15 (a) is that VSC1 exchanges side voltage, and Figure 15 (b) is active power source and the DC voltage v for loading junctiondc, Figure 15
It (c) is the spectrum analysis figure of VSC1 DC side electric current；
Figure 16 is DC voltage controller simulation result diagram under the conditions of outer ring DC voltage control parameter 3.5+3/s,
Middle Figure 16 (a) is that VSC1 exchanges side voltage, and Figure 16 (b) is active power source and the DC voltage v for loading junctiondc；
Figure 17 is overall flow schematic diagram of the invention.
Specific embodiment
Following will be combined with the drawings in the embodiments of the present invention, and technical solution in the embodiment of the present invention carries out clear, complete
Site preparation description, it is clear that described embodiment is a part of the embodiments of the present invention, rather than whole embodiments.Based on this hair
Embodiment in bright, those of ordinary skill in the art are obtained every other without making creative work
Embodiment all should belong to the scope of protection of the invention.
Embodiment
It is as shown in figure 17 overall flow schematic diagram of the invention, impedance stability analysis method is applied to by this method
Multi-end flexible direct current transmission system, and for instructing attitude conirol, comprising the following steps:
Step 1: establishing the Equivalent DC resistance of each inverter in the three-terminal flexible direct-current power transmission system under dq coordinate system
Anti- model；
Step 2: converting equivalent small signal impedance model for Equivalent DC impedance model, power control inverter is used
Equivalent circuit substitution, DC voltage control inverter are substituted with thevenin equivalent circuit, establish the equivalent small of whole system
Signal impedance model；
Step 3: to equivalent small signal impedance model carry out different parameters under determination of stability, obtain determine as a result,
The Nyquist figure that the ratio of active power source impedance and load impedance under different controller parameters is drawn in MATLAB, passes through inspection
Whether the ratio Nyquist figure for testing active power source impedance and load impedance meets Nyquist stability criterion, carrys out forecasting system
Stability, if the Nyquist curve of the ratio Nyquist figure of active power source impedance and load impedance do not include point (- 1,
J0), then system is stablized, otherwise system unstability；
Step 4: building three-terminal flexible direct-current power transmission system simulation model, verifying determines as a result, in MATLAB/
It is steady to system to probe into DC voltage control inverter for the simulation model that three-terminal flexible direct-current power transmission system is built in simulink
It qualitatively influences, and verifies impedance model proposed in this paper and sentence the validity and accuracy of steady method.
In above four steps, step 1 include it is following step by step:
Step 11: drawing the control of the power control inverter and DC voltage control inverter including PLL phaselocked loop
Block diagram processed；
Step 12: the voltage and current component under a, b and c three-phase static coordinate system is transformed into dq rotation by Park transformation
Turn under coordinate system；
Step 13: according to converter Control block diagram, voltage-current relationship and PLL phaselocked loop dynamic effects, deriving and establish often
The Equivalent DC impedance model of a inverter；
Step 2 include it is following step by step:
Step 21: deriving that three converter stations include the equivalent impedance formula of DC line capacitor；
Step 22: establishing the equivalent small signal impedance model of whole system and abbreviation obtains active power source impedance and bears
Carry impedance.
Three-terminal flexible direct-current power transmission system is as shown in Figure 1, and system is made of three inverters: VSC1, VSC2, VSC3,
Wherein VSC1 connects active electric network with VSC2, and VSC3 connection constant power load (Constant power load, CPL), three are changed
Stream device is all made of double-closed-loop control, and inner ring is that active power controller is determined in the outer ring use of current control, wherein VSC1 and VSC3,
VSC1 injects active power, rectification operation to direct current system, and VSC3 absorbs active power, and the outer ring of inverter operation, VSC2 uses
Constant DC voltage control, working condition depend on the size of VSC1 output power, when VSC1 active power of output is greater than CPL
Power consumption, VSC2 absorbs active power from direct current system, and inverter operation is on the contrary then rectify operation, both operating conditions can be with
Active power by changing VSC1, which gives, to be converted.
Three inverters use identical structure, and model is as shown in Fig. 2, modeling, analysis and the control of system are all same
It carries out under step reference frame (synchronous reference frame, SRF), is become using the equal Park of amplitude
It changes, the corresponding Equivalent DC impedance model of total, specific formula are as follows:
In formula, LcAnd RcCorrespond to the inductance and resistance of inverter, CfFor filter capacitor, ωbFor the basic angular frequency of power grid,
ωgFor the per unit value of mains frequency, icAnd vcCorrespond to the electric current and voltage of inverter inverter side, isAnd vsCorrespond to grid-connected place
Electric current and voltage, LgAnd RgCorrespond to the inductance and resistance of inverter, vgFor network voltage, j is imaginary number.
Current inner loop controller is widely used SFR proportional integration (PI) controller of VSC, and with decoupling item, VSC1
Outer ring with VSC3 is all using active power controller is determined, and d axis reference current is provided by outer ring PI controller, q shaft current reference value
Constant, specially 0, control structure such as Fig. 3 institute of power control inverter VSC1 and VSC3 are set as according to reactive power demand
Show, Hp(s)=kpp+kip/ s is the transmission function of power controller, wherein kppAnd kipRespectively indicate the ratio of power controller
Gain and integral gain, VSC2 determine direct current as shown in figure 4, outer ring uses as the control structure of DC voltage control inverter
The PI of voltage is controlled, Hdc(s)=kpdc+kidc/ s is the transmission function of voltage controller, kpdcAnd kidcIt is PI controller respectively
Proportional gain and integral gain, vdc,refIt is direct voltage reference value.
PLL dynamic model is as shown in Figure 5 under synchronous coordinate system.The effect of PLL is to realize institute in inverter control loop
Need phase angle theta to the dynamically track of PCC voltage phase angle θ ', as shown in fig. 6, its specific representation formula are as follows:
In formula, TΔθFor the spin matrix of Δ θ, Δ θ is that required phase angle theta is commonly connected to PCC in inverter control loop
The dynamically track respective value of point voltage phase angle θ ',For set of integers.
Stability analysis is carried out using system of the Impedance Analysis to Fig. 1, the equivalent small signal resistance of whole system need to be established
Anti- model, according to document " Impedance-Based Stability Criterion for Grid-Connected
Inverters " in equivalence principle, VSC1 and VSC3 can be substituted with equivalent circuit, is i.e. an ideal current source and waited
The circuit for imitating impedance parallel connection, can substitute VSC2 with thevenin equivalent circuit, i.e. an ideal voltage source and equivalent impedance series connection
Circuit, equivalent small signal impedance model is as shown in fig. 7, direct current cables is indicated with π type equivalent circuit, in such a system, VSC1
Active power is absorbed to DC line active power of output, VSC2 and VSC3 from DC line as active power source, as negative
It carries, therefore, the equivalent impedance of three converter stations (including DC line capacitor) is as follows:
In formula, ZVSC1(s)、ZVSC2(s) and ZVSC3(s) the first inverter VSC1, the second inverter VSC2 and are corresponded to
The equivalent impedance of three inverter VSC3, ZPIt (s) is the direct current equivalent impedance of power control inverter, ZV(s) voltage-controlled for direct current
The direct current equivalent impedance of inverter processed, CdcFor DC line capacitor, s is complex variable.
After active power source and load has been determined, the equivalent model of Fig. 7 can be converted to the equivalent model such as Fig. 8, schemed
In 7, corresponding includes active power source impedance and load impedance, specific formula are as follows:
Zr(s)=Zdccable+ZVSC1(s)
In formula, ZrIt (s) is active power source impedance, ZlIt (s) is load impedance, ZdccableFor direct current cables impedance, I is straight
Galvanic electricity stream, Vs2For the voltage source voltage of the second inverter VSC2, Is3For the current source current of third inverter VSC3.
Detailed system simulation model is built, in MATLAB/simulink to verify inverter expressed by above formula
The correctness of impedance model, as shown in figure 9, (nominal DC is steady for the current perturbation not waited to system injection 1Hz~1kHz frequency
The 1% of state electric current), the voltage and current under different frequency is analyzed with Fourier transformation tool (FFT), is used at each frequency
Voltage obtains respective impedance divided by electric current, the active power source impedance and load impedance such as Figure 10 that theory analysis and emulation obtain
(a) and shown in Figure 10 (b), solid line is the theoretical analysis result of impedance, and blue dot indicates simulation result, theory analysis and emulation
As a result consistent, the correctness that impedance model derives is verified.
After the correctness for demonstrating impedance model, carry out system stability analysis, active power source shown in Fig. 8 and load
The DC current I of junction may be expressed as:
In formula, Is1For the current source current of the first inverter VSC1.
Above formula is similar to a closed loop transfer function, can pass through the ratio of inspection active power source impedance and load impedance
Whether the corresponding Nyquist curve of value meets Nyquist stability criterion, if the Nyquist stability criterion is described active
Nyquist curve corresponding to the ratio of power source impedance and load impedance does not include point (- 1, j0), then is determined as that system is steady
It is fixed, if Nyquist curve corresponding to the ratio of the active power source impedance and load impedance includes point (- 1, j0), then sentence
It is set to system unstability, can realizes that adjustment is changed by adjusting the parameter of inverter passive element and the parameter tuning of controller
The parameter for flowing device passive element is clearly worthless, therefore, usually increases load impedance by attitude conirol,
Due to the second inverter VSC2 often rectification and reversals switching, controller parameter system is stablized it is most important,
It being referred in the article of some analysis both ends HVDC stability, the bandwidth for reducing DC voltage controller can increase impedance, from
And system stability is improved, reducing controller bandwidth can be realized by reducing its proportionality coefficient.
Load impedance and active power source are drawn under the conditions of the initial control parameter of outer ring DC voltage is 1+3/s first
The Bode diagram of impedance, as shown in Figure 11 (a), Figure 11 (b) is the active power source impedance drawn with this condition and load impedance
The Nyquist curve graph of ratio, it can be seen that Nyquist curve is located in unit circle, do not include point (- 1, j0), judge be
The outer ring DC voltage control parameter of VSC2 can be changed to 0.1+3/s, other parameters are constant, draw at this time with stable operation by system
Load impedance and the Bode diagram of active power source impedance such as Figure 12 (a) are shown, with subtracting for DC voltage controller proportionality coefficient
Small, the amplitude of load impedance becomes larger, and Figure 12 (b) is the active power source impedance drawn under this condition and load impedance ratio
Nyquist curve, curve do not include point (- 1, j0), illustrate that system still can be with stable operation, frequency of the curve in 3.89Hz
Intersect under rate with unit circle, at this time phase margin very little, only about 25 °, judges that system will appear low frequency in 3.89Hz or so
The outer ring DC voltage control parameter of VSC2, is changed to 3.5+3/s by oscillation, and other parameters are constant, draws load impedance and active
Shown in the Bode diagram of power source impedance such as Figure 13 (a), it can be seen that the amplitude of load impedance becomes smaller, so that in all frequencies
Under, the amplitude of load impedance is both less than active power source impedance, and Figure 13 (b) is the active power source impedance drawn under this condition
With the Nyquist curve of load impedance ratio, curve includes point (- 1, j0) at this time, judges that system is unable to operate stably.
Simulation result diagram under initial outer ring DC voltage control parameter 1+3/s is as shown in figure 14, and Figure 14 (a) is VSC1
Side voltage is exchanged, Figure 14 (b) is active power source and the DC voltage v for loading junctiondc, it can be seen that system stable operation,
And operating status is good, and it is consistent with the stability prediction result of Figure 11, when outer ring DC voltage control parameter is adjusted to 0.1+
3/s carries out time-domain-simulation at this time, and simulation result is as shown in figure 15, and Figure 15 (a) is VSC1 exchange side voltage under this condition, figure
15 (b) be the DC voltage v in active power source and load junction under this conditiondc, Figure 15 (c) is VSC1 under this condition
The spectrum analysis figure of DC side electric current, as Figure 12 (b) is judged, system overall trend is stablized, but 4Hz occur or so
Low-frequency oscillation, when outer ring DC voltage control parameter is changed to 3.5+3/s, Figure 16 (a) is that VSC1 under this condition exchanges side
Voltage, Figure 16 (b) are the DC voltage v in active power source and load junction under this conditiondc, system can not at this time
There is different harmonic pollutions, v in stable operation, VSC1 exchange side voltagedcAlso there is the oscillation of different frequency, this emulation
As a result also consistent with the result of Figure 13 prediction.
It can be seen that the amplitude of load impedance can become smaller, and cause when the proportionality coefficient of DC voltage controller increases
There is unstable situation in system, and proportionality coefficient is too small, and since phase margin is inadequate, system will appear low-frequency oscillation, is selecting
When proportionality coefficient, these two aspects is combined, selects the value of a rational.
In conclusion the present invention gives a kind of differentiation Multi-end flexible direct current transmission system from the angle of impedance analysis
The method for stability of uniting, and the adjusting of controller parameter can be effectively instructed, convenient for being promoted and applied in practice in engineering.
The above description is merely a specific embodiment, but scope of protection of the present invention is not limited thereto, appoints
What those familiar with the art in the technical scope disclosed by the present invention, can readily occur in various equivalent modifications
Or replacement, these modifications or substitutions should be covered by the protection scope of the present invention.Therefore, protection scope of the present invention is answered
It is subject to the protection scope in claims.
Claims (10)
1. a kind of impedance stability evaluation method of new energy three-terminal flexible direct-current power transmission system, this method comment impedance stability
Valence method is applied to Multi-end flexible direct current transmission system, and for instructing attitude conirol, which is characterized in that including following
Step:
Step 1: establishing the Equivalent DC modulus of impedance of each inverter in the three-terminal flexible direct-current power transmission system under dq coordinate system
Type；
Step 2: converting equivalent small signal impedance model for Equivalent DC impedance model；
Step 3: the determination of stability under different parameters being carried out to equivalent small signal impedance model, obtains and determines result；
Step 4: building three-terminal flexible direct-current power transmission system simulation model, verifying determines result.
2. a kind of impedance stability evaluation method according to claim 1, which is characterized in that in the step 1 etc.
Imitate DC impedance model, specific formula are as follows:
In formula, LcAnd RcCorrespond to the inductance and resistance of inverter, CfFor filter capacitor, ωbFor the basic angular frequency of power grid, ωgFor
The per unit value of mains frequency, icAnd vcCorrespond to the electric current and voltage of inverter inverter side, isAnd vsCorrespond to the electric current at grid-connected place
And voltage, LgAnd RgCorrespond to the inductance and resistance of inverter, vgFor network voltage, j is imaginary number.
3. a kind of impedance stability evaluation method according to claim 1, which is characterized in that the step 1 include with
Under step by step:
Step 11: drawing the controller chassis of the power control inverter and DC voltage control inverter including PLL phaselocked loop
Figure；
Step 12: the voltage and current component under a, b and c three-phase static coordinate system is transformed into dq rotational coordinates by Park transformation
Under system；
Step 13: according to converter Control block diagram, voltage-current relationship and PLL phaselocked loop dynamic effects, deriving to establish and each change
Flow the Equivalent DC impedance model of device.
4. a kind of impedance stability evaluation method according to claim 3, which is characterized in that the function in the step S11
Rate control inverter and DC voltage control inverter are all made of double-closed-loop control, the two close cycles control of the power control inverter
The inner ring of system uses current control, and outer ring uses active power controller, the inner ring of the DC voltage control inverter surely
Using current control, outer ring uses constant DC voltage control.
5. a kind of impedance stability evaluation method according to claim 3, which is characterized in that the PLL in the step S13
Phaselocked loop dynamic effects be in inverter control loop required phase angle theta to the dynamically track of PCC points of common connection voltage phase angle θ ',
Its specific representation formula are as follows:
In formula, TΔθFor the spin matrix of Δ θ, Δ θ is required phase angle theta in inverter control loop to PCC points of common connection voltage
Phase angle theta ' dynamically track respective value,For set of integers.
6. a kind of impedance stability evaluation method according to claim 1, which is characterized in that the step 2 include with
Under step by step:
Step 21: deriving that three inverters include the equivalent impedance formula of DC line capacitor；
Step 22: establishing the equivalent small signal impedance model of whole system and abbreviation obtains active power source impedance and load resistance
It is anti-.
7. a kind of impedance stability evaluation method according to claim 6, which is characterized in that the step 21 it is equivalent
Formula of impedance are as follows:
In formula, ZVSC1(s)、ZVSC2(s) and ZVSC3(s) the first inverter VSC1, the second inverter VSC2 and the third change of current are corresponded to
The equivalent impedance of device VSC3, ZPIt (s) is the direct current equivalent impedance of power control inverter, ZVIt (s) is DC voltage control inverter
Direct current equivalent impedance, CdcFor DC line capacitor, s is complex variable.
8. a kind of impedance stability evaluation method according to claim 6, which is characterized in that the step 22 it is active
Power source impedance and load impedance, specific formula are as follows:
Zr(s)=Zdccable+ZVSC1(s)
In formula, ZrIt (s) is active power source impedance, ZlIt (s) is load impedance, ZdccableFor direct current cables impedance.
9. a kind of impedance stability evaluation method according to claim 1, which is characterized in that the stabilization in the step 3
Sex determination is to examine whether Nyquist curve corresponding to the ratio of active power source impedance and load impedance meets Nyquist
Stability criterion, if the Nyquist stability criterion is corresponding to the ratio of the active power source impedance and load impedance
Nyquist curve does not include point (- 1, j0), then is determined as that system is stablized, if the active power source impedance and load impedance
Nyquist curve corresponding to ratio includes point (- 1, j0), then is determined as system unstability.
10. a kind of impedance stability evaluation method according to claim 1, which is characterized in that three ends in the step 4
Component library used by flexible HVDC transmission system simulation model is MATLAB/simulink component library, and three ends are flexible
The input frequency of DC transmission system simulation model is 1HZ~1kHz, the three-terminal flexible direct-current power transmission system simulation model
Voltage and current analysis tool be Fourier transformation tool.
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