CN116388224A - Dynamic decoupling control method based on self-adaptive virtual synchronous impedance - Google Patents
Dynamic decoupling control method based on self-adaptive virtual synchronous impedance Download PDFInfo
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Abstract
The invention discloses a dynamic decoupling control method based on self-adaptive virtual synchronous impedance, which belongs to the technical field of virtual synchronous machines and comprises the following steps: constructing a VSG grid-connected equivalent circuit, and calculating a single-machine wide-frequency-domain dynamic small signal model of the virtual synchronous machine taking the dynamic process of the system into consideration after virtual impedance is added; comprehensively considering the influence of a large power angle and high line impedance ratio under a weak current network on VSG coupling characteristics, and solving a wide-frequency-domain dynamic small-signal model with a virtual resistor and a virtual inductor as adjusting variables by adopting a self-adaptive virtual synchronous impedance decoupling strategy based on a dynamic model; the method comprises the steps of adopting a diagonal array decoupling method, eliminating power coupling in a dynamic process of a VSG disturbed system through self-adaptive adjustment of virtual impedance, calculating a virtual impedance instruction value and sending the virtual impedance instruction value into a virtual impedance loop for control; the stability and dynamic response performance of the system before and after decoupling control are compared and analyzed, and the method is verified to be capable of improving the dynamic response performance of the system and enhancing the stability of the VSG grid-connected system.
Description
Technical Field
The invention belongs to the technical field of virtual synchronous machines, and particularly relates to a dynamic decoupling control method based on self-adaptive virtual synchronous impedance.
Background
With the development of new energy technology, the permeability of distributed power sources such as wind power, photovoltaic and the like in a power system is continuously improved. The large-scale new energy unit is integrated into a power grid through power electronic equipment, has the advantages of flexible control, quick response and the like, but also brings the problems of insufficient inertia and damping of the power grid, weakened supporting capacity of voltage and frequency and the like, and the power system is easily affected by power fluctuation and system faults to induce stability problems of system voltage, frequency and the like. The virtual synchronous generator technology (virtual synchronous generator, VSG) provides inertia and damping support for the system by simulating the rotor equation of a conventional synchronous generator, and enables good frequency, voltage support and regulation after distributed power is connected to the power grid by power control. However, VSG allows for automatic independent adjustment of frequency and voltage through droop control, and thus the power coupling problem in conventional droop control still exists.
In the control analysis of the relevant VSG, the transmission line between the converter and the grid-connected point is assumed to be nearly pure, and the system works under the approximate condition of a small power angle in a steady state, so that the power coupling degree is not obvious, and the coupling effect is often ignored to analyze the problem. In an actual system, on one hand, the power grid strength further shows a descending trend after large-scale new energy is accessed, and on the other hand, when the new energy is located in a remote area and is connected to a main network through a long line, a power grid background of a weak power grid is formed. When the VSG works under the conditions of weak network and even extremely weak network, the power angle value at the steady-state working point is usually larger and does not meet the constraint of small power angle approximation, and meanwhile, when the distributed power supply is connected into a medium-low voltage network, the line impedance ratio R/X is larger, so that serious coupling exists between the power, the oscillation amplitude of the system after being disturbed is large, the adjusting time is long, the power control performance is deteriorated, and the system instability is caused by oscillation divergence in serious conditions, so that the power coupling problem needs to be focused.
The power decoupling control is widely applied and mature at present and is a virtual impedance technology, and the output impedance of the system can be simply and flexibly changed by adding virtual impedance in a control link, so that the aim of decoupling is achieved, and therefore, the power decoupling control is also widely focused by students at home and abroad, such as a virtual negative impedance decoupling strategy, a self-adaptive virtual impedance decoupling strategy and the like. In fact, decoupling control needs to take into account, on the one hand, the complete elimination of the coupling action between the power loops and the lack of constraints such as small power angle constraints, and, on the other hand, needs to be built on a dynamic model of the system, taking into account the system dynamics.
In the prior art, various virtual impedance technologies are mostly based on a quasi-steady state model, a static transfer function (the parameter is a constant) is used for representing the coupling relation, and mostly only the impedance ratio requirement is considered, so that the control effect is poor due to the fact that the small power angle constraint condition is met, the large power angle under a weak power grid cannot be comprehensively considered, and the influence of high line impedance ratio on the VSG coupling characteristic is not comprehensively considered.
Therefore, a dynamic decoupling control method based on self-adaptive virtual synchronous impedance is needed, the influence of a large power angle under a weak power grid and the influence of high line impedance on VSG coupling characteristics can be comprehensively considered, a self-adaptive virtual synchronous impedance decoupling strategy based on a dynamic model is adopted, power coupling in the dynamic process of a system after VSG interference is eliminated through self-adaptive adjustment of virtual impedance, the dynamic response performance of the system is improved, and the stability of a VSG grid-connected system is enhanced.
Disclosure of Invention
The invention aims to provide a dynamic decoupling control method based on self-adaptive virtual synchronous impedance, which is characterized by comprising the following steps:
s1: constructing a VSG grid-connected equivalent circuit, calculating a VSG output current I and a VSG actual output active power P which are added with virtual impedance and considered in a system dynamic process o And reactive power Q o Constructing a wide-frequency domain dynamic model containing a virtual impedance control link;
s2: the wide-frequency dynamic model is set at the steady-state working point (delta) 0 ,E 0 ) Linearizing the nonlinear system at the position to obtain a linearized wide-frequency-domain dynamic small signal model, and using a virtual resistor R v And virtual inductance L v To adjust the variables, solve for the steady state operating point (delta 0 ,E 0 ) A wide frequency domain dynamic small signal model;
s3: self-adaptive dynamic virtual synchronous impedance decoupling is carried out by adopting a diagonal array decoupling method, and steady-state working point (delta) of the virtual synchronous machine is eliminated 0 ,E 0 ) Power coupling of the wide-frequency-domain dynamic small signal model;
s4: and comparing the data before and after decoupling control, and performing decoupling control validity verification.
The wide frequency domain dynamic model in the S1 is as follows:
wherein E and delta are the virtual internal potential and the power angle of VSG; u (U) o And theta o The voltage amplitude and phase angle of the VSG output end are; x is X v And R is v For VSG virtual inductance and virtual resistance value, U g Is the voltage amplitude of the power grid; r is R g And X g L is the equivalent line resistance and reactance between the inverter and the grid g Is equivalent inductance;
wherein,,
for the actual output complex power of the virtual synchronous machine, P o And Q o Actually outputs active power and reactive power for VSG, R vc As virtual resistance steady-state component, R in steady-state v =R vc R is the total equivalent resistance, the value r=r g +R vc ，X vc For virtual reactance steady-state component, X in steady-state v ＝X vc X is the total equivalent reactance, the value x=x g +X vc 。
The linearized wide-frequency-domain dynamic small signal model in the S2 is as follows:
wherein:
G v (s) is a system transfer function matrix containing coupling after considering virtual impedance, wherein each element in the system transfer function matrix is a transfer function containing dynamic process, and delta P, delta Q, delta and delta E are disturbance components of active power, reactive power, a work angle and virtual internal potential respectively.
The steady-state operating point (delta) in S2 0 ,E 0 ) The wide frequency domain dynamic small signal model is:
wherein:
B(s)＝R vc (EU g cosδ-U g 2 )+(R g +sL g )(E 2 -EU g cosδ)+XEU g sinδ
C(s)＝X vc (EU g cosδ-U g 2 )+X g (E 2 -EU g cosδ)-(R+sL g )EU g sinδ
ΔL v 、ΔR v adjustment increment omega of virtual inductance and virtual resistance respectively 0 Rated for VSG frequency.
The specific step of self-adaptive dynamic virtual synchronous impedance decoupling in the step S3 is as follows:
s31: determining the running condition of a system, and detecting the real-time running states of the voltage E and the power angle delta;
s32: calculating the power coupling quantity and calculating the P-E coupling quantity delta P in the dynamic process E-P And Q-delta coupling amount DeltaQ δ-Q ，
S33: calculating a virtual impedance command value, including a virtual inductance command value and a virtual resistance command value;
the virtual inductance command value and the virtual resistance command value satisfy the following formula:
wherein DeltaL v * And DeltaR v * The virtual inductance command value and the virtual resistance command value are VSG;
the virtual inductance command value and the virtual resistance command value are obtained by the equation (6):
sending the virtual impedance command value into the virtual impedance ring to finger the virtual impedanceChanging the value and dynamically eliminating the coupling; ensuring steady-state operating point (delta) of virtual synchronous machine 0 ,E 0 ) The wide-frequency dynamic small signal model meets the input-output relation after decoupling the diagonal array;
the virtual resistance and virtual inductance of the virtual impedance control link satisfy the calculation formula:
wherein L is vc And R is vc The virtual inductance steady state value and the virtual resistance steady state value are VSG.
And in the step S4, the data before and after decoupling control are compared, and the step of verifying the effectiveness of the decoupling control is as follows:
s41: setting parameters to compare and analyze the stability influence of the system before and after decoupling control, and analyzing and comparing the frequency domain characteristics of the system;
s42: and setting simulation contrast analysis system decoupling control dynamic response performance influence under different running conditions, and analyzing and comparing the system response performance indexes.
The invention has the beneficial effects that:
in the practical system, on one hand, the power grid strength further shows a descending trend after large-scale new energy is accessed, and on the other hand, when the new energy is located in a remote area and is connected to a main network through a long line, a power grid background of a weak power grid is formed. When the VSG works under the conditions of weak network and even extremely weak network, the power angle value at the steady-state working point is usually larger, the constraint of small power angle approximation is not satisfied, meanwhile, when the distributed power supply is connected to a medium-low voltage network, the line impedance ratio R/X is considered to be larger, so that serious coupling exists between the power, the oscillation amplitude of the system after being disturbed is large, the adjusting time is long, the power control performance is deteriorated, and the instability of the system is caused by oscillation divergence in serious.
In the prior art, various virtual impedance technologies are mostly based on a quasi-steady state model, a static transfer function (the parameter is a constant) is used for representing the coupling relation, and mostly only the impedance ratio requirement is considered, the constraint condition of a small power angle is ignored, the large power angle under a weak power network cannot be comprehensively considered, and the influence of high line impedance ratio on the VSG coupling characteristic is not considered, so that the control effect is poor.
The invention discloses a dynamic decoupling control method based on self-adaptive virtual synchronous impedance, which comprehensively considers the influence of a large power angle under a weak current network and high line impedance ratio on VSG coupling characteristics, adopts a self-adaptive virtual synchronous impedance decoupling strategy based on a dynamic model, eliminates power coupling in the dynamic process of a system after VSG is disturbed through self-adaptive adjustment of virtual impedance, improves the dynamic response performance of the system, and enhances the stability of a VSG grid-connected system.
Drawings
FIG. 1 is a flow chart of a dynamic decoupling control method based on adaptive virtual synchronous impedance according to an embodiment of the present invention;
FIG. 2 is a block diagram of a single-machine grid-connected system of a virtual synchronous generator in the invention;
FIG. 3 is a schematic diagram of an equivalent circuit of the virtual impedance-containing VSG connected to an AC power grid;
FIG. 4 is a schematic diagram of a VSG wide-frequency-domain dynamic small signal model with adaptive virtual impedance according to the present invention;
FIG. 5 is a schematic flow chart of the adaptive dynamic virtual synchronous impedance decoupling implementation according to the present invention;
FIG. 6 is a diagram of a wide-frequency-domain dynamic small-signal model of a control system reconstructed into two single-input single-output by a VSG system before decoupling provided by the invention;
FIG. 7 shows the real power open loop transfer function with reactive parameter J after the adaptive decoupling method is adopted without considering decoupling q A modified bode plot;
FIG. 8 is a schematic diagram of the change curves of the active P and reactive Q output by the VSG after the active command value is stepped according to the embodiment provided by the invention;
fig. 9 is a schematic diagram of a change curve of the active P and reactive Q output by the VSG after a step of the reactive command value according to the embodiment provided by the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
The embodiment of the invention as shown in fig. 1 discloses a dynamic decoupling control method based on self-adaptive virtual synchronous impedance, which comprises the following steps:
s1: constructing a VSG grid-connected equivalent circuit, calculating a VSG output current I and a VSG actual output active power P which are added with virtual impedance and considered in a system dynamic process o And reactive power Q o Constructing a wide-frequency domain dynamic model containing a virtual impedance control link;
as shown in fig. 3, an equivalent circuit diagram of the virtual impedance VSG connected to the ac power grid is shown, wherein the grid-connected inverter is simplified into a controllable voltage source with adjustable amplitude and phase angle. E is the virtual internal potential amplitude of VSG; delta is the internal potential E of VSG and the voltage amplitude U of the power grid g The phase difference, i.e., the power angle; r is R g And X g The equivalent resistance and reactance of the line are respectively the impedance of the power grid;
p, Q are the complex power, active power and reactive power actually output by the virtual synchronous machine respectively.
Comprehensively considering the dynamic process of the system, and establishing a wide-frequency-domain dynamic model of the system including the VSG.
The wide frequency domain dynamic model in the S1 is as follows:
wherein E and delta are the virtual internal potential and the power angle of VSG; u (U) o And theta o The voltage amplitude and phase angle of the VSG output end are; x is X v And R is v For VSG virtual inductance and virtual resistance value, U g Is the voltage amplitude of the power grid; r is R g And X g L is the equivalent line resistance and reactance between the inverter and the grid g Is equivalent inductance;
wherein,,
for the actual output complex power of the virtual synchronous machine, P o And Q o Actually outputs active power and reactive power for VSG, R vc As virtual resistance steady-state component, R in steady-state v ＝R vc R is the total equivalent resistance, the value r=r g +R vc ，X vc For virtual reactance steady-state component, X in steady-state v ＝X vc X is the total equivalent reactance, the value x=x g +X vc ；
S2: the wide-frequency dynamic model is set at the steady-state working point (delta) 0 ,E 0 ) Linearizing the nonlinear system at the position to obtain a linearized wide-frequency-domain dynamic small signal model, and using a virtual resistor R v And virtual inductance L v To adjust the variables, solve for the steady state operating point (delta 0 ,E 0 ) A wide frequency domain dynamic small signal model;
the linearized wide-frequency-domain dynamic small signal model in the S2 is as follows:
wherein:
G v (s) is a system transfer function matrix containing coupling after virtual impedance is considered, each element in the system transfer function matrix is a transfer function containing a dynamic process, and delta P, delta Q, delta and delta E are disturbance components of active power, reactive power, a work angle and virtual internal potential respectively, and the rest components are steady-state components.
With virtual resistance R v And virtual inductance L v To adjust the variables, R is adjusted in real time v And L v Size, active power in self-adaptive compensation dynamic processCoupling component between power and reactive power. However, the changes of the virtual resistor and the virtual inductor affect the active power and the reactive power, so that the change relation between the virtual impedance and the power needs to be obtained. At the working point (delta) by the formula (2) 0 ,E 0 ) And linearizing to obtain a wide-frequency-domain dynamic small-signal model with the virtual resistor and the virtual inductor as adjusting variables.
The steady-state operating point (delta) in S2 0 ,E 0 ) The wide frequency domain dynamic small signal model is:
wherein:
ΔL v 、ΔR v the adjustment increment of the virtual inductor and the virtual resistor are respectively carried out, and the rest components are steady-state components; omega 0 Rated for VSG frequency;
s3: self-adaptive dynamic virtual synchronous impedance decoupling is carried out by adopting a diagonal array decoupling method, and steady-state working point (delta) of the virtual synchronous machine is eliminated 0 ,E 0 ) Power coupling of the wide-frequency-domain dynamic small signal model;
fig. 4 is a schematic diagram of a VSG small signal model with adaptive virtual impedance according to the present invention. To simultaneously eliminate P-E coupling quantity DeltaP in dynamic process E-P And Q-delta coupling amount DeltaQ δ-Q The original forward channel gain is not changed, and the reverse compensation of-delta P to the system in real time is needed E-P and-DeltaQ δ-Q Dynamic power of (a) is provided. Thus compensating for magnitude- ΔP in dynamic process by adaptive variation of virtual impedance E-P and-DeltaQ δ-Q The dynamic coupling power of the power control link is eliminated, so that the power small signal model meets the input-output relation after decoupling the diagonal array.
In this embodiment, as shown in fig. 5, the specific steps of performing adaptive dynamic virtual synchronization impedance decoupling in S3 are as follows:
s31: determining the running condition of a system, and detecting the real-time running states of the voltage E and the power angle delta;
s32: calculating the power coupling quantity and calculating the P-E coupling quantity delta P in the dynamic process E-P And Q-delta coupling amount DeltaQ δ-Q ，
Calculating the coupling amount of power, detecting the real-time running states of the voltage E and the power angle delta, and calculating the P-E coupling amount delta P in the dynamic process by the formula (2) E-P And Q-delta coupling amount DeltaQ δ-Q The method comprises the following steps:
ΔP E-P ＝ΔEG (v)P-E (s)
ΔQ δ-Q ＝ΔδG (v)Q-δ (s) (5)
s33: calculating a virtual impedance command value, including a virtual inductance command value and a virtual resistance command value;
the virtual impedance changes according to the calculated instruction value, and the self-adaptive change of the virtual impedance reversely compensates the system with delta P in the dynamic process E-P and-DeltaQ δ-Q The dynamic coupling power of the virtual inductance instruction value and the virtual resistance instruction value meet the following formula:
wherein DeltaL v * And DeltaR v * The virtual inductance command value and the virtual resistance command value are VSG;
the virtual inductance command value and the virtual resistance command value are obtained by the equation (6):
sending the instruction value into a virtual impedance ring to enable the virtual impedance to change according to the instruction value, and dynamically eliminating coupling; ensuring steady-state operating point (delta) of virtual synchronous machine 0 ,E 0 ) The wide-frequency dynamic small signal model meets the input-output relation after decoupling the diagonal array;
the virtual resistance and virtual inductance of the virtual impedance control link satisfy the calculation formula:
wherein L is vc And R is vc The initial values of the VSG virtual inductance steady-state value and the virtual resistance steady-state value can be set according to the system, and the initial values are generally 0 if no special condition exists.
S4: comparing the data before and after decoupling control, and verifying the effectiveness of decoupling control;
the method comprises the following specific steps:
s41: setting parameters to compare and analyze the stability influence of the system before and after decoupling control, and analyzing and comparing the frequency domain characteristics of the system;
fig. 6 is a diagram of a small signal model of a control system reconstructed into two single-input single-output control systems before decoupling, wherein fig. 6 (a) shows an active power control loop and fig. 6 (b) shows a reactive power control loop. Consider that the VSG system is a multiple-input multiple-output (MIMO) nonlinear coupling system when the decoupling control strategy is not employed. The stability of a MIMO system is a system-inherent property, irrespective of the number and number of its input and output signals. Thus, a single input to single output loop stability analysis may be focused to simplify the stability analysis of the VSG coupling system.
And constructing a VSG wide-frequency-domain dynamic small signal model before and after decoupling control in MATLAB/Simulink, wherein main simulation parameters are shown in table 1.
Table 1 simulation parameter table
As can be seen from the small signal model diagrams before and after decoupling, when decoupling is not considered, due to the fact that coupling exists in the control links, power oscillation in the dynamic process is conducted in the two control links through the coupling loop, meanwhile, the parameter stability of the two control links is also affected mutually through the coupling loop, and therefore the stability margin of the system is reduced.
FIG. 7 shows the open loop transfer function of active power with reactive parameter J without considering decoupling and after adopting the adaptive decoupling method q A modified bode plot. It can be seen from the figure that when the decoupling method is not employed, the coupling is followed by J q Gradually generating a resonance spike at a frequency of around 300rad/s and introducing a 180 deg. phase lag. The phase lag reduces the active control link phase margin of the VSG system. By adopting the self-adaptive decoupling method, the influence of power coupling on system oscillation is eliminated, meanwhile, the mutual influence of control link parameter changes is avoided, and the stability of the system is enhanced.
S42: and setting simulation contrast analysis system decoupling control dynamic response performance influence under different running conditions, and analyzing and comparing the system response performance indexes.
In the embodiment, the simulation contrast analysis system is arranged in the PSCAD/EMTDC to decouple the dynamic response performance influence under different running conditions before and after control.
(1): active command value step 0.02MW (reactive power sag control)
Fig. 8 is a schematic diagram of the change curves of the active P and reactive Q output by the VSG after the active command value is stepped before and after the decoupling control is adopted. In the initial state set in the simulation, the VSG stably feeds active power of 0.15MW and reactive power of 0.0004Mvar to the power grid, and at the moment, the steady-state power angle delta n The impedance ratio R/x=0.3, which corresponds to the steady state operating condition of "large power angle, high impedance ratio". Wherein some of the modification and addition parameters are shown in table 2 below and the remaining parameters are unchanged as shown in table 1. And setting the active command value to be 0.02MW in 0.5s, and keeping the reactive command unchanged.
Table 2 partial modification parameter table
Fig. 8 (a) is a schematic diagram of an active change curve of the VSG output before and after decoupling control, and it can be seen from the active response waveform that the system operates in an under-damped state at this time, and the oscillation is more intense. After the decoupling control strategy is adopted, the power coupling between the active power and the reactive power is reduced, so that the damping ratio of the system is increased, the oscillation damping speed is increased, and the adjusting time is shortened. The effect of active power control on reactive coupling is further evident from the reactive response waveforms, and the specific reactive response performance indicators are shown in table 3.
TABLE 3 reactive response index Table
Fig. 8 (b) is a schematic diagram of a reactive power change curve of VSG output before and after decoupling control, and it can be seen from a reactive response waveform that, after a step of a VSG active command without decoupling strategy, active power oscillation is conducted to a reactive loop through coupling due to severe coupling between active power and reactive power, so that the reactive power output also generates relatively severe oscillation. From the graph, the maximum deviation of reactive oscillation in the dynamic process reaches 0.0114Mvar, the oscillation duration is long, and after the system is stabilized again, the reactive deviation point reaches 0.00486Mvar at the moment, and the deviation value is larger. And after self-adaptive decoupling is adopted, the power coupling phenomenon is obviously improved. At this time, the reactive power deviation is 0 in the steady state, the improvement is more obvious in the dynamic process of the system, the oscillation deviation value is lower, the maximum deviation is only 0.0003Mvar, the adjusting time is shorter, the decoupling effect is more obvious, and the coupling between the power control links can be effectively solved.
(2): reactive command value step 0.005Mvar (reactive constant power control)
Fig. 9 shows the VSG output active P and reactive Q line intent after an active command value step before and after decoupling control is employed. In order to intuitively embody the influence of VSG reactive power fluctuation on active power, the reactive power loop is changed from the previous droop control to constant power control. In the initial setting state in simulation, the VSG stably feeds active power of 0.15MW and reactive power of 0Mvar to the power grid, and a reactive power command value step of 0.005Mvar is set at 0.5s, so that the active command is unchanged. Some of the modified parameter maps are shown in table 4 below, with the remaining parameters unchanged as shown in table 1.
Table 4 partial modification parameter table
Fig. 9 (b) is a schematic diagram of a reactive change curve of VSG output before and after decoupling control, and it can be seen from reactive response waveforms that when the reactive power of the system is controlled by constant power, each reactive steady-state error is 0 during steady operation, but a dynamic oscillation process exists in reactive step response. After the decoupling scheme is adopted, reactive dynamic oscillation is weakened, stability can be achieved more quickly, and dynamic response performance of reactive power is improved better.
Fig. 9 (a) is a schematic diagram of an active change curve of VSG output before and after decoupling control, and the influence of reactive power control on active coupling can be further seen from the active power response waveform, and specific active response indexes are shown in table 5.
TABLE 5 active response index Table
When the VSG without decoupling measures is used for power control, as the active power control is a dead control, the coupling does not cause steady-state deviation of the active power, but the reactive power influences the active power output through the coupling, so that the active power output generates an oscillation process, the maximum deviation in the dynamic process is 0.0058Mw (3.8%), and the adjustment time is about 0.3s. When the decoupling method is added, the active power coupling is weakened, at the moment, the maximum active deviation in the dynamic process is only 0.0008Mw (0.5%), meanwhile, the adjusting time is also reduced to 0.19s, the dynamic response of the active power is improved, and the accuracy of the decoupling control is reflected.
In order to better verify the dynamic decoupling control method based on the self-adaptive virtual synchronous impedance, the invention also discloses a VSG control system, and the dynamic decoupling control method based on the self-adaptive virtual synchronous impedance disclosed by the embodiment is applied.
FIG. 2 is a block diagram of a single-machine grid-connected system of a virtual synchronous generator in the invention. As shown in fig. 2, the VSG control system of the present disclosure includes a power control loop, a virtual impedance loop, and a voltage-current dual loop. The power control loop comprises an active power control loop simulating rotor inertia and damping, as shown in the following formula (8); a droop controlled reactive power control loop, as in equation (9) below. The virtual impedance loop corrects the output voltage reference by introducing output current feedback to the voltage drop of the output current across the virtual impedance, as shown in equation (10). The voltage and current double loop adopts a classical double closed loop structure. The output voltage reference value passing through the virtual impedance loop realizes the rapid tracking and adjustment of VSG output voltage and current change through a voltage-current double loop, and the output of the double loop, namely the modulation wave, is sent into a PWM link to be modulated and drive a switching tube, so that the corresponding output is finally obtained.
Wherein P is ref And P e The method comprises the steps of respectively outputting active power instructions and the actual active power of the inverter; q (Q) ref And Q e Reactive power instructions and actual output reactive power of the inverter are respectively provided; e (E) r Simulating the internal potential of the synchronous generator for the virtual internal potential of the VSG; omega r Angular frequency being the virtual internal potential; j (J) p And D p VSG virtual moment of inertia and virtual damping coefficient respectively; k (K) ω Is active power-a frequency primary modulation factor; omega n And omega 0 The rated frequency of the power grid and the rated frequency of the VSG are respectively; j (J) q And K v The reactive integration coefficient and the reactive droop coefficient of VSG are respectively; u (U) n And U is VSG output rated voltage and output voltage respectively. R is R v And X v The virtual resistance and the virtual reactance value in the virtual impedance control link are calculated; u (u) odref ，u oqref Command values of d-q axis components of the output voltage respectively; i.e gd ，i gq The d-q axis components of the grid-tied output current, respectively.
The embodiment of the invention comprehensively considers the large power angle under a weak current network and the influence of high line impedance on VSG coupling characteristics, constructs a VSG grid-connected equivalent circuit, calculates a single-machine wide-frequency domain dynamic small signal model of the virtual synchronous machine taking the dynamic process of the system into consideration after adding virtual impedance, selects an adaptive virtual synchronous impedance decoupling strategy based on the dynamic model, eliminates power coupling by a diagonal array decoupling method, solves the power small signal model taking the virtual resistor and the virtual inductor as adjusting variables on the basis, obtains a virtual impedance command value through calculation, sends the command value into a virtual impedance ring for decoupling control, and verifies the dynamic response performance of the system under different running conditions before and after decoupling control by comparing and verifying that the provided decoupling control strategy not only can effectively eliminate the coupling between the power, but also can play the roles of improving the dynamic response performance of the system and enhancing the stability of the VSG system.
Claims (6)
1. The dynamic decoupling control method based on the self-adaptive virtual synchronous impedance is characterized by comprising the following steps of:
s1: constructing a VSG grid-connected equivalent circuit, calculating a VSG output current I and a VSG actual output active power P which are added with virtual impedance and considered in a system dynamic process o And reactive power Q o Constructing a wide-frequency domain dynamic model containing a virtual impedance control link;
s2: the wide-frequency dynamic model is set at the steady-state working point (delta) 0 ,E 0 ) Linearizing the nonlinear system at the position to obtain a linearized wide-frequency domain motionA small state signal model with virtual resistance R v And virtual inductance L v To adjust the variables, solve for the steady state operating point (delta 0 ,E 0 ) A wide frequency domain dynamic small signal model;
s3: self-adaptive dynamic virtual synchronous impedance decoupling is carried out by adopting a diagonal array decoupling method, and steady-state working point (delta) of the virtual synchronous machine is eliminated 0 ,E 0 ) Power coupling of the wide-frequency-domain dynamic small signal model;
s4: and comparing the data before and after decoupling control, and performing decoupling control validity verification.
2. The method for dynamic decoupling control based on adaptive virtual synchronous impedance according to claim 1, wherein the wide frequency domain dynamic model in S1 is:
wherein E and delta are the virtual internal potential and the power angle of VSG; u (U) o And theta o The voltage amplitude and phase angle of the VSG output end are; x is X v And R is v For VSG virtual inductance and virtual resistance value, U g Is the voltage amplitude of the power grid; r is R g And X g L is the equivalent line resistance and reactance between the inverter and the grid g Is equivalent inductance.
Wherein,,
for the actual output complex power of the virtual synchronous machine, P o And Q o Actually outputs active power and reactive power for VSG, R vc As virtual resistance steady-state component, R in steady-state v ＝R vc R is the total equivalent resistance, the value r=r g +R vc ，X vc For virtual reactance steady-state component, X in steady-state v ＝X vc X is the total equivalent reactance, the value x=x g +X vc 。
3. The method for controlling dynamic decoupling based on adaptive virtual synchronous impedance according to claim 2, wherein the wide-frequency-domain dynamic small signal model linearized in S2 is:
wherein:
G v (s) is a system transfer function matrix containing coupling after considering virtual impedance, wherein each element in the system transfer function matrix is a transfer function containing dynamic process, and delta P, delta Q, delta and delta E are disturbance components of active power, reactive power, a work angle and virtual internal potential respectively.
4. A method of dynamic decoupling control based on adaptive virtual synchronous impedance as claimed in claim 3, wherein the steady state operating point (δ 0 ,E 0 ) The wide frequency domain dynamic small signal model is:
wherein:
B(s)＝R vc (EU g cosδ-U g 2 )+(R g +sL g )(E 2 -EU g cosδ)+XEU g sinδ
C(s)＝X vc (EU g cosδ-U g 2 )+X g (E 2 -EU g cos-)-(R+sL g )EU g sinδ
ΔL v 、ΔR v adjustment increment omega of virtual inductance and virtual resistance respectively 0 Rated for VSG frequency.
5. The method for controlling dynamic decoupling based on adaptive virtual synchronous impedance according to claim 4, wherein the specific steps of performing adaptive dynamic virtual synchronous impedance decoupling in S3 are as follows:
s31: determining the running condition of a system, and detecting the real-time running states of the voltage E and the power angle delta;
s32: calculating the power coupling quantity and calculating the P-E coupling quantity delta P in the dynamic process E-P And Q-delta coupling amount DeltaQ δ-Q ，
S33: calculating a virtual impedance command value, including a virtual inductance command value and a virtual resistance command value;
the virtual inductance command value and the virtual resistance command value satisfy the following formula:
wherein DeltaL v * And DeltaR v * The virtual inductance command value and the virtual resistance command value are VSG;
the virtual inductance command value and the virtual resistance command value are obtained by the equation (6):
sending the virtual impedance command value into a virtual impedance ring, so that the virtual impedance is changed according to the command value, and dynamically eliminating coupling; ensuring steady-state operating point (delta) of virtual synchronous machine 0 ,E 0 ) The wide-frequency dynamic small signal model meets the input-output relation after decoupling the diagonal array;
the virtual resistance and virtual inductance of the virtual impedance control link satisfy the calculation formula:
wherein L is vc And R is vc The virtual inductance steady state value and the virtual resistance steady state value are VSG.
6. The method for dynamic decoupling control based on adaptive virtual synchronous impedance according to claim 1, wherein the step of verifying the validity of the decoupling control by comparing the data before and after the decoupling control in S4 is as follows:
s41: setting parameters to compare and analyze the stability influence of the system before and after decoupling control, and analyzing and comparing the frequency domain characteristics of the system;
s42: and setting simulation contrast analysis system decoupling control dynamic response performance influence under different running conditions, and analyzing and comparing the system response performance indexes.
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