CN116760108B - LCL-SAPF stability control method based on unified stability constraint - Google Patents
LCL-SAPF stability control method based on unified stability constraint Download PDFInfo
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Abstract
The invention relates to a LCL-SAPF stability control method based on unified stability constraint and applicable to a multi-current strategy, which comprises the steps of firstly evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on a virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as the segmentation basis of an LCL initial resonance frequency range; secondly, aiming at the condition that the LCL initial resonance frequency is located in different frequency bands, utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each condition; and finally, carrying out line impedance universality control parameter correction design according to the gain curve or curved surface with the unified stability constraint. The beneficial effects of the invention are as follows: the invention is suitable for various LCL-SAPF current strategies, and can realize stable operation of the system when a new energy power station is connected in a large amount to cause line impedance change, so that the system has excellent fluctuation universality and harmonic compensation performance.
Description
Technical Field
The invention relates to the technical field of stability control of new energy power stations, in particular to a LCL-SAPF stability control method based on unified stability constraint.
Background
The development of solar photovoltaic power generation and wind power generation is rapid, the construction scale of new energy power stations based on solar energy and wind energy is continuously enlarged, and the installed capacity is continuously increased. The novel energy power station is limited by the reverse distribution of solar energy, wind energy resources and electric loads, is mostly developed and built in a large scale and high concentration mode, and is connected into a modern power grid through long-distance transmission. Because the grid-connected power generation of the new energy power station mainly depends on power electronic conversion equipment, a brand new power electronic characteristic appears in a power grid, and the power grid is typically expressed as follows: the access point line impedance has large dynamic fluctuation, and the access point voltage/current has broadband oscillation and harmonic pollution. The LCL type parallel active power filter is a flexible conversion device for managing the power quality of grid-connected points, can rapidly and flexibly realize multiple functions such as harmonic suppression, reactive compensation, damping promotion, energy consumption reduction and the like, is effectively applied to a medium-low voltage distribution network side at the present stage, and is applied and expanded in the field of high-voltage power transmission and transformation of new energy power stations.
LCL-SAPF is usually realized by adopting a digital control mode, but nonlinear links such as control delay and the like are inevitably introduced, so that the original active damping characteristic of the system is greatly changed, and current oscillation and divergence instability are easy to occur when the impedance of an access line fluctuates. The existing solution thought mainly comprises two types of improvement of a pulse width modulation process and an insertion delay compensation link, but the improvement effect is limited by frequency spectrum signal aliasing and sampling conversion rate, and brings new problems of control complexity increase and high-frequency noise amplification. In fact, both methods achieve an extension of the application range of the single stability constraint by increasing the active damping boundary frequency, while essentially limiting the initial resonant frequency of the LCL to a certain frequency range.
In addition, LCL-SAPF may employ different current strategies, where the control loop often includes multiple active damping loops with varying damping characteristics, where the damping characteristics of the system, stability constraints at different LCL initial resonant frequencies, and control conditions at different line impedances are difficult to determine. The existing literature generally only considers the single active damping condition, and lacks specific researches on a multi-current strategy and a system control and design method under the coexistence of the multiple active damping. In summary, there is a need to further explore a stability-enabling control technique and a parameter design method of LCL-SAPF, so that improvement of initial resonance frequency of any LCL, universality of system impedance fluctuation and harmonic compensation performance under various current strategies can be achieved without increasing control complexity.
Disclosure of Invention
The invention aims at overcoming the defects of the prior art and provides an LCL-SAPF stability control method based on unified stability constraint.
In a first aspect, there is provided an LCL-SAPF stability control method based on a unified stability constraint, comprising:
step 1, evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on a virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as a segmentation basis of an LCL initial resonance frequency range; the virtual admittance model is equivalent to a feedback or feedforward loop which generates active damping effect in a forward channel of the system;
step 2, aiming at the condition that the LCL initial resonance frequency is located in different frequency bands, utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each condition;
and step 3, carrying out line impedance universality control parameter correction design according to the gain curve or curved surface which is realized by the unified stability constraint.
Preferably, in step 1, by drawing different linesAmplitude frequency curve of conductance part and susceptance part in virtual admittance under path impedance, and maximum active damping boundary frequency is estimatedf adbmax Positive and negative damping characteristics before and after the boundary.
Preferably, the maximum active damping boundary frequencyf adbmax Is the maximum frequency value of the intersection of the amplitude-frequency curve of the conductance part in the virtual admittance and the zero-coordinate transverse axis, and the maximum active damping boundary frequencyf adbmax Full band before boundary frequencyG ad (ω)>0. The frequency band is partially located after the boundary frequencyG ad (ω)<And is considered valid at 0; wherein,G ad (ω) Representing the conductance fraction in the virtual admittance;
the LCL initial resonant frequency range is classified by using the maximum active damping boundary frequencyf adbmax Initial resonant frequency of LCLf r_ini The value range of (2) is divided into (0),f adbmax ) Or%f adbmax ,f s 2) two cases, whereinf s And/2 is the Nyquist frequency.
Preferably, step 3 includes:
step 3.1, determining based on the system parameters and current strategy adopted by LCL-SAPFf r_ini A frequency range in which the frequency is located;
step 3.2, determiningL line_b Taking a value;L line_b to make forward channel transfer functionL(z) Line impedance corresponding to first constraint of forward inner loop root track is not satisfiedL line A maximum value;
step 3.3, a gain curve or a curved surface with an embodied unified stability constraint;
step 3.4, determining the proportional gain and the unified stable value range of the current feedback controller, and selecting the value of the proportional gain;
step 3.5, judging the crossing frequencyf cros Whether the highest harmonic compensation frequency of LCL-SAPF can be covered; if the voltage of the power grid of the access point cannot be met, reducing the feedforward controller of the power grid voltage of the access pointG uff (ω) Representing control parameters of the bandwidth and repeating step 3.2;
and 3.6, optimally designing the control parameters of each harmonic suppression unit so that the control parameters of a final system can meet the normal requirement of a stability margin.
Preferably, in step 2, the first constraint of the forward inner loop root track is applied tof r_ini ∈(0,f adbmax ) Andf r_ini ∈(f adbmax ,f s and/2) two cases.
Preferably, in step 3.1, the current strategy includes: the current strategy of sampling the grid current and the inversion side current, the current strategy of sampling the load current and the inversion side current and the current strategy of sampling the load current and the filter capacitor current are adopted, and the default current strategy is introduced into the access point grid voltage feedforward.
In a second aspect, there is provided an LCL-SAPF stability control system based on a unified stability constraint and applying a multi-current strategy, for performing any one of the LCL-SAPF stability control methods based on a unified stability constraint of the first aspect, comprising:
the evaluation module is used for evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on the virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as the segmentation basis of the LCL initial resonance frequency range; the virtual admittance model is equivalent to a feedback or feedforward loop which generates active damping effect in a forward channel of the system;
the induction module is used for aiming at the situation that the LCL initial resonant frequency is located in different frequency bands, and utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each situation;
and the correction module is used for carrying out line impedance universality control parameter correction design according to the gain curve or curved surface which is realized by the unified stability constraint.
In a third aspect, an electronic device is provided that includes a memory and a processor; the memory stores an executable program; the processor is configured to run the program, where the program executes any one of the LCL-SAPF stability-enabling control methods based on the unified stability constraint of the first aspect.
In a fourth aspect, a computer readable storage medium is provided, where the computer readable storage medium includes a stored executable program, where when the executable program runs, the device in which the computer readable storage medium is controlled to execute the LCL-SAPF stability-enabling control method based on the unified stability constraint according to any one of the first aspects.
The beneficial effects of the invention are as follows: firstly, evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on a virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as a segmentation basis of an LCL initial resonance frequency range; secondly, aiming at the condition that the LCL initial resonance frequency is located in different frequency bands, utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each condition; and finally, carrying out line impedance universality control parameter correction design according to the gain curve or curved surface with the unified stability constraint. The invention is suitable for various LCL-SAPF current strategies, and can realize stable operation of the system when a new energy power station is connected in a large amount to cause line impedance change, so that the system has excellent fluctuation universality and harmonic compensation performance.
Drawings
FIG. 1 is a flow chart of a LCL-SAPF stability-enabling control method based on unified stability constraints;
FIG. 2 is a schematic diagram of an LCL-SAPF current strategy for sampling grid current and inverter side current;
FIG. 3 shows a different embodimentL line Conductivity part in virtual admittance under working conditionG ad (ω) Is a frequency curve of (a);
FIG. 4 shows a different embodimentL line Susceptance portion in virtual admittance under working conditionB ad (ω) Is a frequency curve of (a);
FIG. 5 shows a different embodimentL line Under working conditionsf r_ini ∈(0,f s 3) the corresponding inversion side current feedback loop closed-loop root track;
FIG. 6 shows a different embodimentL line Under working conditionsf r_ini ∈(f s /3,f s 2) corresponding inversion side current feedback loop closed loop root track;
FIG. 7 is a different viewL line Under working conditionsf r_ini ∈(0,f s 3) corresponding forward open loop frequency characteristics;
FIG. 8 shows a different embodimentL line Under working conditionsf r_ini ∈(f s /3,f s 2) corresponding forward open loop frequency characteristics;
FIG. 9 is directed tof r_ini ∈(0,f s In the case of the/3) of the above-mentioned materials,L line different when=0K ifb Take the value ofAndis a gain curve of (2);
FIG. 10 is directed tof r_ini ∈(f s /3,f s In the case of/2), differentK ifb AndL line take the value ofAndis a gain curve of (a);
FIG. 11 is a flow chart of a line impedance universality control parameter correction design;
FIG. 12 is a diagram off r_ini ∈(0,f s 3) andL line when the temperature is increased from 0 to approximately 1mH, adopting the LCL-SAPF experimental result corresponding to the corrected control parameter;
FIG. 13 is a diagram off r_ini ∈(0,f s 3) andL line when=0, control parametersK ifb Increasing the corrected numerical value to an LCL-SAPF experimental result which does not meet the corresponding unified stability constraint;
FIG. 14 is a diagram off r_ini ∈(f s /3,f s 2) andL line when the temperature is increased from 0 to approximately 1mH, adopting the LCL-SAPF experimental result corresponding to the corrected control parameter;
FIG. 15 is a diagram off r_ini ∈(f s /3,f s 2) andL line and when the temperature is increased to approximately 300 mu H from 0, adopting an LCL-SAPF experimental result corresponding to the control parameter before correction.
Detailed Description
The invention is further described below with reference to examples. The following examples are presented only to aid in the understanding of the invention. It should be noted that it will be apparent to those skilled in the art that modifications can be made to the present invention without departing from the principles of the invention, and such modifications and adaptations are intended to be within the scope of the invention as defined in the following claims.
Example 1:
in this embodiment, the LCL-SAPF current strategy for sampling grid current and inverter side current is taken as an example, and the system and control block diagram thereof are shown in fig. 2. Power grid current controllerG ih (z) Inverter-side current controller for suppressing harmonic components of grid currentG ifb (z) The fundamental component of the current at the inversion side is regulated, and meanwhile, the active damping effect of the current feedback at the inversion side is introduced.
Power grid current controllerG ih (z) The expression is that after the pre-modified Tustin transformation discretization treatment, the typical proportional gain and harmonic resonance unit is adopted
Wherein,K ih is the proportional gain of the grid current controller,K rn is thatnThe gain factor of the subharmonic resonance unit,ϕ n is thatnThe compensation phase of the subharmonic resonance unit,ω n is thatnThe angular frequency of the subharmonic wave,ω n =nω 1 ，ω 1 for the fundamental angular frequency of the wave,n=6k±1，k∈[1,2,3,4]，T s is the sampling period.
Inverter-side current controllerG ifb (z) The same adopts the proportional gain and fundamental wave resonance unit to form, and after the pre-modified Tustin transformation discretization treatment, the expression is as follows
Wherein,K ifb for the proportional gain of the inverter-side current feedback controller,K r1 is the gain factor of the fundamental resonance unit,ϕ 1 and compensating phase for the fundamental resonance unit.
Access point grid voltage feedforward controllerG uff (ω) The most common proportional gain is adopted, and the output quantity is added to the total output of the power grid current controller and the inversion side current feedback controller, the expression is
Wherein,K uff for the proportional gain of the access point grid voltage feedforward controller, 0 is typically selected<K uff ≤1/K pwm 。
Table 1 lists two sets of LCL-SAPF system parameters used in this example, and table 2 shows the corresponding initial control parameters.
TABLE 1 LCL-SAPF System parameters
TABLE 2 LCL-SAPF initial control parameters
It should be noted that the LCL-SAPF current strategy of sampling grid current and inverter side current contains 2 active damping effects, wherein the boundary frequency of the inverter side current active damping is only 1/6 of the sampling frequency, which is much smaller than the general upper design limit of the LCL initial resonance frequency. The existing control parameter design method cannot guarantee high time-response of a system to line impedance at any LCL initial resonance frequency, and generally requires that the LCL initial resonance frequency is lower than 1/6 sampling frequency, but the system cost and energy loss of the LCL-SAPF are obviously increased; meanwhile, aiming at the condition that the initial resonant frequency of the LCL exceeds 1/6 sampling frequency, the existing design method is easy to cause operation faults such as system oscillation instability, tripping protection and the like when the line impedance of the access point fluctuates.
On the basis of the above, the LCL-SAPF stability control method based on unified stability constraint is provided, and is applicable to various LCL-SAPF current strategies, and the system stability operation can be realized when a new energy power station is largely connected to cause line impedance change, so that the system has excellent fluctuation universality and harmonic compensation performance. As shown in fig. 1, the method includes:
step 1, evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on a virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as a segmentation basis of an LCL initial resonance frequency range;
step 2, aiming at the condition that the LCL initial resonance frequency is located in different frequency bands, utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each condition;
and step 3, carrying out line impedance universality control parameter correction design according to the gain curve or curved surface which is realized by the unified stability constraint.
In step 1, the virtual admittance model is equivalent to a feedback loop or a feedforward loop which generates active damping effect in a forward channel of the system, does not comprise a current outer loop for harmonic suppression, and can evaluate the maximum active damping boundary frequency by drawing amplitude-frequency curves of a conductance part and a susceptance part in the virtual admittance under different line impedancesf adbmax Positive and negative damping characteristics before and after the boundary;
the expression of the virtual admittance model is as follows:
wherein,K pwm for the pulse width modulation gain,T s in order to sample the period of time,ωangular frequency for characterizing frequency domain information;L 1 for the LCL inverter-side inductance,L 2 for the LCL network side inductance,C f for the LCL filter capacitor,L line is the line impedance;G uff (ω) For an access point grid voltage feedforward controller,G ifb (ω) A current feedback controller for characterizing active damping.
The conductance and susceptance portions of the virtual admittance are expressed as
Wherein,G ad (ω) In the form of a conductive portion,B ad (ω) Is a susceptance portion.
Maximum active damping boundary frequencyf adbmax Is the maximum frequency value of the intersection of the amplitude-frequency curve of the conductance part in the virtual admittance and the zero-coordinate transverse axis, and is the full frequency band only before the boundary frequencyG ad (ω)>0 (i.e. positive damping), partial frequency band after boundary frequencyG ad (ω)<0 (i.e., negative damping) is considered to be effective;
the LCL initial resonant frequency range is classified by using the maximum active damping boundary frequencyf adbmax Initial resonant frequency of LCLf r_ini The range of possible values of (1) is divided into (0,f adbmax ) Or%f adbmax ,f s 2) two cases, whereinf s And/2 is the Nyquist frequency, generally regarded asf r_ini The maximum value that may be chosen.
In step 2, the expression of the unified stability constraint is:
wherein,representation ofL line Forward channel transfer function of system when=0L(z) At-180 degree crossing frequencyf cros Gain at->Representing 0 to less than or equal toL line <L line_b Time of dayL(z) At the LCL actual resonant frequencyf r_act The minimum gain that occurs at this point,L line_b to make a match withL(z) Does not satisfy the first constraint of the forward inner ring root trackL line Maximum value.
Furthermore, the expression unifying the stability constraints is expressed inf r_ini ∈(0,f adbmax ) In this case it can be further simplified as:
in step 2, forward channel transfer functionL(z) The expression of (2) is:
wherein,zfor an operator in a discrete system that characterizes frequency information,ω r is the natural resonant angular frequency of the LCL filter, composed ofL 1 、L 2 、C f AndL line is determined uniquely by the value of (a),G ih (z) A current feedback controller for characterizing harmonic suppression;
when sampling the current on the inversion sideN(z) The expression of (2) is:
when sampling the filter capacitance currentN(z) The expression of (2) is:
in step 2, the first constraint of the forward inner loop root track is applied tof r_ini ∈(0,f adbmax ) Andf r_ini ∈(f adbmax ,f s two cases, the expression of which is
Wherein,to be at a certain levelL line The actual active damping boundary frequency of the system is taken;K ifb_max is thatK ifb Is determined by the closed loop root trajectory of the active damping loop including the feed-forward of the access point grid voltage.
In addition, the forward minimum phase characteristic second constraint is expressed as
The second constraint of the forward minimum phase characteristic is expressed as that when the first constraint of the forward inner loop root track is not satisfied
。
As shown in fig. 11, step 3 includes:
step 3.1, based on the system parameters and current strategy adopted by LCL-SAPF, determining the maximum active damping boundary frequency according to the step 1f adbmax And according to the LCL initial resonant frequencyf r_ini Is designed to take the value of (1) and determine the frequency range in which it is locatedf r_ini ∈(0，f adbmax ) Or (b)f r_ini ∈(f adbmax ，f s /2)；
Step 3.2, neglecting other control units of non-proportional gain in each current controller, and drawing the control units inL line Corresponding to different values within the range of possible fluctuationsL(z) Frequency characteristic curve to approximate determinationL line_b Taking a value;
step 3.3 based onf r_ini Frequency range and to which it is subjectedL line_b Taking a value, and realizing a gain curve or a curved surface with uniform stability constraint by using a list method;
step 3.4, determining based on the gain curve or curved surfaceG ifb (z) Proportional gain of (2)K ifb And (3) withG ih (z) Proportional gain of (2)K ih Respective uniform stable value ranges, and selecting within the value rangesK ifb And (3) withK ih Is a value of (2);
step 3.5 based on the selectionK ifb And (3) withK ih Is combined withL line At the maximum valueL(z) Judging the crossing frequency of the frequency characteristic curve of (2)f cros Whether the highest harmonic compensation frequency of LCL-SAPF can be covered; if not, properly reduceG uff (ω) Representing control parameters of the bandwidth and repeating step 3.2;
and 3.6, considering the control units of the current controllers for harmonic suppression, and optimally designing the control parameters of the harmonic suppression units by utilizing closed-loop root locus diagram, nyquist diagram and Bode diagram tools, so that the control parameters of a final system can meet the normal requirement of a stability margin.
In step 3.1, the current strategy comprises: the current strategy of sampling the grid current and the inversion side current, the current strategy of sampling the load current and the inversion side current and the current strategy of sampling the load current and the filter capacitor current are adopted, and access point grid voltage feedforward is introduced by default. This embodiment takes as an example an LCL-SAPF current strategy that samples grid current and inverter side current.
Step 3.3 comprises: when (when)f r_ini ∈(0,f adbmax ) When drawingAnd->Only along withG ifb (z) Proportional gainK ifb A varying two-dimensional gain curve; when (when)f r_ini ∈(f adbmax ,f s Drawing +.>And->Along with itK ifb And (3) withL line A varying three-dimensional gain curve.
Based on the two sets of LCL-SAPF system parameters of Table 1, and adopting the steps, a worker can obtain analysis results of each step of the stability control method, and the analysis results comprise:
by way of example, fig. 3 and 4 illustrate differentL line Conductivity part in virtual admittance under working conditionG ad (ω) And susceptance portionB ad (ω) Is a frequency curve of (a). As can be seen from fig. 3 and 4, whenL line When=0, the actual active damping boundary frequency of the system is onlyf s And/6, equivalently, the feed-forward of the access point grid voltage does not generate damping effect. In contrast, whenL line When not equal to 0, can approachf s 3, at the same timeB ad (ω) To achieve the aim off s /6,f s A significant decrease in the range of/2) resulting in an LCL actual resonant frequencyf r_act At the position ofL line Less time may be exceeded, thereby creating a pair of open loop unstable poles. In summary, based on the system parameters and current strategy of the present embodiment, the active damping boundary frequency will followL line Fluctuation and change, maximumValue off adbmax Is thatf s 3, the LCL initial resonant frequency range can be divided intof r_ini ∈(0,f s 3) andf r_ini ∈(f s /3,f s and/2) two cases.
Fig. 5 and 6 show differentL line Under working conditionsf r_ini ∈(0,f s 3) andf r_ini ∈(f s /3,f s and/2) the corresponding inversion side current feedback loop closed-loop root track. As can be seen from FIG. 5, whenL line When not equal to 0, there isK ifb So that the system contains only open loop stable poles. At this time, since the actual active damping boundary frequency of the system is close tof s 3 to makeIs satisfied andK ifb boundary values of (2)K ifb_max Will followL line Increasing and increasing. In contrast, as can be seen from FIG. 6, whenL line When=50μh, due tof r_ini ∈(f s /3,f s 2) andL line smaller, resulting inAnd the open loop unstable pole exists in the system all the time; when (when)L line Further increase to 200. Mu.H,/o>At this time there isK ifb So that the system contains only open loop stable poles, after whichK ifb Boundary values of (2)K ifb_max Along with itL line Increasing and increasing. To sum up, inf r_ini ∈(0,f s 3) andf r_ini ∈(f s /3,f s in both cases, the system will not have an open loop unstable pole if and only if the first constraint of the forward inner radicle trajectory is satisfied.
Fig. 7 and 8 show different embodimentsL line Working conditions ofLower part(s)f r_ini ∈(0,f s 3) andf r_ini ∈(f s /3,f s and/2) corresponding forward open loop frequency characteristics. As can be seen from FIG. 7, inf r_ini ∈(0,f s In the case of/3), when the first constraint of the forward inner root locus is satisfied,along with itL line Increase and decrease->Then followL line Increasing and increasing. In contrast, as can be seen from FIG. 8, inf r_ini ∈(f s /3,f s In the case of/2), when the first constraint of the forward inner root locus is satisfied,along with itL line Increase and decrease->Then followL line Increase to go beyondL line_b And then decrease and then increase. Thus, forf r_ini ∈(0,f s /3) orf r_ini ∈(f s /3,f s 2) in both cases, after correctionK ifb And (3) withK ih Can meet the unified stability constraint, no matterL line How to fluctuate, even when a large amount of new energy is connected to cause a weak network working condition, the LCL-SAPF always has excellent fluctuation universality and harmonic compensation performance.
FIG. 9 shows a view directed tof r_ini ∈(0,f s In the case of the/3) of the above-mentioned materials,L line different when=0K ifb Take the value ofAnd->Is a gain curve of (a). As can be seen from the view of figure 9,when (when)K ifb Above 1.5 ohm, i.eK ifb After exceeding the unified stable value range, the method comprises the step of ++>Will be greater than->Thereby leading to the absence ofK ih And the unified stability constraint is satisfied.
FIG. 10 shows a schematic view of a targetf r_ini ∈(f s /3,f s In the case of/2), differentK ifb AndL line take the value ofAnd->Is a gain curve of (a). As can be seen from the view of figure 10,K ifb stable value range of (1) is dependent onL line Increase and decrease, and->And->Respectively followK ifb Increase and decrease and increase, so smaller should be chosenK ifb To ensure thatL line Always under wave motionK ih And the unified stability constraint is satisfied.
FIG. 11 is a flow chart showing a circuit impedance universality control parameter correction design, and the correction results obtained by combining the two LCL-SAPF system parameters in the table 1 are shown in the table 3.
TABLE 3 correction of LCL-SAPF control parameters
Example 2:
based on embodiment 1, embodiment 2 of the present application provides another LCL-SAPF stability-causing control method based on a unified stability constraint, including:
step 1, evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on a virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as a segmentation basis of an LCL initial resonance frequency range;
step 2, aiming at the condition that the LCL initial resonance frequency is located in different frequency bands, utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each condition;
step 3, carrying out line impedance universality control parameter correction design according to the gain curve or curved surface which is realized by the unified stability constraint;
and 4, verifying the correctness of the universality control parameters of the line Lu Zukang.
Specifically, step 4 takes a 30kVA three-phase two-level LCL-SAPF prototype as an example for verification, and the system parameters are consistent with Table 1.
FIG. 12 showsf r_ini ∈(0,f s 3) andL line when the temperature is increased from 0 to approximately 1mH, the LCL-SAPF experimental result corresponding to the corrected control parameter is adopted. From top to bottom in the figure, respectively the access point grid voltagesu s Grid currenti s And SAPF output currenti out . It can be seen that in both casesL line Under the condition that the LCL-SAPF always keeps excellent harmonic compensation effect, the power grid currenti s Up to 4.9%, which is already universal to line impedance fluctuations.
FIG. 13 showsf r_ini ∈(0,f s 3) andL line when=0, control parametersK ifb And increasing the corrected numerical value to the LCL-SAPF experimental result which does not meet the unified stability constraint. It can be seen that when the control parameters do not meet the unified stability constraint, the control parameters cannot ensure the stable operation of the LCL-SAPF under the impedance of each line, so that the waveform of the current injected into the power grid is obviously distorted, the THD is increased to 11.2%, and the harmonic water specified by GB/T24337-2009 is far exceededFlat.
FIG. 14 showsf r_ini ∈(f s /3,f s 2) andL line when the temperature is increased from 0 to approximately 1mH, the LCL-SAPF experimental result corresponding to the corrected control parameter is adopted. As can be seen, LCL-SAPF is inL line Always keep stable operation under fluctuation, and the current of the power gridi s Up to 4.7%, which is also universally applicable to line impedance fluctuations.
FIG. 15 showsf r_ini ∈(f s /3,f s 2) andL line and when the temperature is increased to approximately 300 mu H from 0, adopting an LCL-SAPF experimental result corresponding to the control parameter before correction. It can be seen that the output current of LCL-SAPF is atL line Oscillations and diverges under small fluctuations, thereby causing tripping of the system, which is obviously poor in line impedance fluctuation adaptability before correction of control parameters.
Therefore, after the LCL-SAPF is improved by adopting the stability-inducing control method, the system can realize stability-inducing operation when the line impedance is changed, and has excellent fluctuation universality and harmonic compensation performance all the time, so that the correctness of the stability-inducing control method is fully proved.
In this embodiment, the same or similar parts as those in embodiment 1 may be referred to each other, and will not be described in detail in this application.
Example 3:
based on embodiment 1, embodiment 3 of the present application provides an LCL-SAPF stability control system based on a unified stability constraint and adapted for multiple current strategies, comprising:
the evaluation module is used for evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on the virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as the segmentation basis of the LCL initial resonance frequency range;
the induction module is used for aiming at the situation that the LCL initial resonant frequency is located in different frequency bands, and utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each situation;
and the correction module is used for carrying out line impedance universality control parameter correction design according to the gain curve or curved surface which is realized by the unified stability constraint.
Specifically, the system provided in this embodiment is a system corresponding to the method provided in embodiment 1, so that the portions in this embodiment that are the same as or similar to those in embodiment 1 may be referred to each other, and will not be described in detail in this application.
Claims (6)
1. The LCL-SAPF stabilization control method based on the unified stabilization constraint is characterized by comprising the following steps:
step 1, evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on a virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as a segmentation basis of an LCL initial resonance frequency range; the virtual admittance model is equivalent to a feedback or feedforward loop which generates active damping effect in a forward channel of the system; in step 1, the maximum active damping boundary frequency is estimated by drawing amplitude-frequency curves of the conductance part and the susceptance part in the virtual admittance under different line impedancesf adbmax Positive and negative damping characteristics before and after the boundary; maximum active damping boundary frequencyf adbmax Is the maximum frequency value of the intersection of the amplitude-frequency curve of the conductance part in the virtual admittance and the zero-coordinate transverse axis, and the maximum active damping boundary frequencyf adbmax Full band before boundary frequencyG ad (ω)>0. The frequency band is partially located after the boundary frequencyG ad (ω)<And is considered valid at 0; wherein,G ad (ω) Representing the conductance fraction in the virtual admittance; the LCL initial resonant frequency range is classified by using the maximum active damping boundary frequencyf adbmax Initial resonant frequency of LCLf r_ini The value range of (2) is divided into (0),f adbmax ) Or%f adbmax , f s 2) two cases, whereinf s 2 is the Nyquist frequency;
step 2, aiming at the condition that the LCL initial resonance frequency is located in different frequency bands, utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each condition;
step 3, carrying out line impedance universality control parameter correction design according to the gain curve or curved surface which is realized by the unified stability constraint;
the step 3 comprises the following steps:
step 3.1, determining based on the system parameters and current strategy adopted by LCL-SAPFf r_ini A frequency range in which the frequency is located;
step 3.2, determiningL line_b Taking a value;L line_b to make forward channel transfer functionL(z) Line impedance corresponding to first constraint of forward inner loop root track is not satisfiedL line A maximum value;
step 3.3, a gain curve or a curved surface with an embodied unified stability constraint;
step 3.4, determining the proportional gain and the unified stable value range of the current feedback controller, and selecting the value of the proportional gain;
step 3.5, judging the crossing frequencyf cros Whether the highest harmonic compensation frequency of LCL-SAPF can be covered; if the voltage of the power grid of the access point cannot be met, reducing the feedforward controller of the power grid voltage of the access pointG uff (ω) Representing control parameters of the bandwidth and repeating step 3.2;
and 3.6, optimally designing the control parameters of each harmonic suppression unit so that the control parameters of a final system can meet the normal requirement of a stability margin.
2. The LCL-SAPF stability control method according to claim 1, wherein in step 2, the forward inner root locus first constraint is applied tof r_ini ∈(0, f adbmax ) Andf r_ini ∈(f adbmax , f s and/2) two cases.
3. The LCL-SAPF stability control method based on uniform stability constraints of claim 2, wherein in step 3.1, the current strategy comprises: the current strategy of sampling the grid current and the inversion side current, the current strategy of sampling the load current and the inversion side current and the current strategy of sampling the load current and the filter capacitor current are adopted, and the default current strategy is introduced into the access point grid voltage feedforward.
4. An LCL-SAPF stability control system based on a unified stability constraint and adapted for use with a multi-current strategy, for performing the LCL-SAPF stability control method based on a unified stability constraint of any one of claims 1 to 3, comprising:
the evaluation module is used for evaluating the maximum active damping boundary frequency and positive and negative damping characteristics before and after the boundary based on the virtual admittance model, and taking the maximum active damping boundary frequency and the positive and negative damping characteristics before and after the boundary as the segmentation basis of the LCL initial resonance frequency range; the virtual admittance model is equivalent to a feedback or feedforward loop which generates active damping effect in a forward channel of the system;
the induction module is used for aiming at the situation that the LCL initial resonant frequency is located in different frequency bands, and utilizing a first constraint of a forward inner loop root track, a second constraint of a forward minimum phase characteristic and forward open loop frequency characteristics under different line impedances to obtain unified stability constraint under each situation;
and the correction module is used for carrying out line impedance universality control parameter correction design according to the gain curve or curved surface which is realized by the unified stability constraint.
5. An electronic device comprising a memory and a processor; the memory stores an executable program; the processor is configured to run the program, wherein the program when run performs the LCL-SAPF stability-causing control method according to any one of claims 1 to 3 based on the unified stability constraint.
6. A computer readable storage medium, wherein the computer readable storage medium includes a stored executable program, and when the executable program runs, the computer readable storage medium is controlled to execute the LCL-SAPF stability-causing control method based on the unified stability constraint according to any one of claims 1 to 3.
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| CN113629984A (en) * | 2021-07-27 | 2021-11-09 | 浙江大学 | Three-phase LCL type SAPF parameter design method based on double-loop current control strategy |
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| CN115632401A (en) * | 2022-12-21 | 2023-01-20 | 浙江大学 | SAPF parameter design method considering load and power grid impedance influence |
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