CN110401206B - Grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance - Google Patents
Grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance 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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
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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
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Abstract
The invention provides a grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance, which comprises the following steps: the method comprises the steps of introducing non-cross feedback virtual impedance and an infinite impulse response filter into a grid-connected converter containing current loop control, calculating an optimal non-cross feedback virtual impedance value, and controlling an instruction i through a current loop according to the optimal non-cross feedback virtual impedance value2 *And an output current i2The closed-loop control of (3) inhibits the low-frequency oscillation of the grid-connected converter. The method can effectively inhibit the low-frequency oscillation of the grid-connected converter, and improves the dynamic response characteristic of the system while inhibiting the oscillation.
Description
Technical Field
The invention relates to the field of a grid-connected converter of a new energy system based on current loop control, in particular to a grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance.
Background
In recent years, many low-frequency oscillation phenomena related to new energy grid connection occur around the world, the safe and stable operation of a power grid is seriously threatened, and adverse effects are caused on the further popularization and application of new energy. The research on the low-frequency oscillation mechanism by taking the new energy grid-connected converter as a research object has a plurality of achievements, and from the control angle, the key control factor for inducing the low-frequency oscillation of the grid-connected converter is a current loop.
The traditional means for suppressing the low-frequency oscillation of the Power system is to add a Power System Stabilizer (PSS) or improve the interconnection structure of the interconnected Power grid, but the low-frequency oscillation becomes more complex as the Power electronics of the Power system becomes more and more obvious. Although the grid-connected converter active damping method in the prior art can well inhibit higher harmonic resonance, the low-frequency oscillation inhibition effect from several hertz to tens of hertz is still not good for a new energy grid-connected system.
Therefore, a method for effectively suppressing the low-frequency oscillation of the grid-connected converter is needed.
Disclosure of Invention
The invention provides a grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance, which aims to overcome the defects in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme.
The invention provides a grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance, wherein the grid-connected converter comprises a current loop controller, and the method comprises the following steps:
the method comprises the steps of introducing non-cross feedback virtual impedance and an infinite impulse response filter into a grid-connected converter containing current loop control, calculating an optimal non-cross feedback virtual impedance value, and controlling an instruction i through a current loop according to the optimal non-cross feedback virtual impedance value2 *And an output current i2The closed-loop control of (3) inhibits the low-frequency oscillation of the grid-connected converter.
Preferably, the calculating the optimal non-cross feedback virtual impedance value includes using the non-cross feedback virtual impedance value corresponding to the maximum phase margin of the open-loop transfer function of the control system as the optimal non-cross feedback virtual impedance value for low-frequency oscillation suppression, which is defined as mBCalculated according to the following formula (1):
where m is the non-cross feedback virtual impedance, ωc0To adopt an optimal non-cross feedback virtual impedance mBCorresponding cut-off frequency, Go(j ω) represents the frequency domain open loop transfer function,
d/dm is a differential operator, and is a phase margin function corresponding to the non-cross feedback virtual impedance m.
Preferably, the control object of the grid-connected converter is a transfer function from the converter side output current to the bridge arm voltage of the converter side output current, and the input end of the current loop controller is a control command i2 *And output currenti2The output end of the difference value of (1) is connected with the positive end of the comparison point and is used for carrying out difference comparison with the output end of the infinite impulse response filter; the non-cross feedback virtual impedance input end is output current i2The output end of the filter is connected with the infinite impulse response filter; the input end of the infinite impulse response filter is connected with the output end of the non-crossed feedback virtual impedance, and the output end of the infinite impulse response filter is connected with the negative end of the comparison point; the input end of the control object is the output difference value of the infinite impulse response filter and the current loop controller, and the output end is the output current i2。
Preferably, the optimal value of the coefficient of the infinite impulse response filter is a filter coefficient a corresponding to the phase margin under the optimal non-cross feedback virtual impedance value, and a >0, and the complex frequency domain s expression of the infinite impulse response filter is as shown in the following formula (2):
where a is the variable coefficient of the filter, TsIs the sampling period.
Preferably, when the grid-connected converter is controlled in a dq coordinate system, the output current i of d and q axes2d、i2qAre respectively the output current i2The current loop command values i of d and q axes obtained by performing abc/dq conversion are used as input signals of d and q axis infinite impulse response filters, respectively2d*、i2q*And d, q axis output current i2d、i2qThe difference values of the input signals of the current loop controller are d and q axes respectively, and the output end of the infinite impulse response filter is connected with the input end of the non-crossed feedback virtual impedance;
d. q-axis cross decoupling factor omega0L2Used for d and q axis control cross decoupling of current loop, one omega0L2The input end is d-axis output current i2dOutput end and q-axis feedforward net voltage uqComparing and making difference; another omega0L2The input end is q-axis output current i2qOutput end and d-axis feedforward net pressure udComparison of difference, ω0Outputting angular frequency for the converter in a steady state;
the d and q axes feedforward net pressure ud、uqFor grid-connected converter and power grid common connection point voltage upccObtained by performing abc/dq conversion, or ac-side filter capacitor voltage uabcPerforming abc/dq transformation;
the d and q axes output voltage reference value udref、uqrefRespectively d and q axes control output value, feedforward network pressure udCross decoupling factor omega between d-axis and q-axis by difference from output of current loop controller0L2Is summed with the d-axis non-crossed feedback virtual impedance output to udref(ii) a Feed forward net pressure uqCross decoupling factor omega between q axis and d axis by difference from output of current loop controller0L2Is subtracted from the q-axis non-cross feedback virtual impedance output by uqref。
Preferably, when the grid-connected converter is controlled in a two-phase stationary alpha and beta coordinate system, the alpha and beta axes output current i2α、i2βAre respectively the output current i2The input signals of the alpha and beta axis infinite impulse response filters obtained by performing abc/alpha and beta conversion, and the alpha and beta axis current loop command values i2α *、i2β *And alpha and beta axis output current i2α、i2βThe difference values of the two are respectively input signals of an alpha-axis current loop controller and a beta-axis current loop controller, and the output end of the infinite impulse response filter is connected with the input end of the non-crossed feedback virtual impedance;
the alpha and beta axis feedforward net pressure uα、uβFor grid-connected converter and power grid common connection point voltage upccObtained by performing abc/α β conversion, or the AC-side filter capacitor voltage uabcPerforming abc/alpha beta transformation;
the alpha and beta axes output voltage reference value uαref、uβrefRespectively alpha and beta axis control output values, respectively feedforward network pressure uα、uβDifferencing with the output of the current loop controller, and then respectively non-intersecting the obtained difference with the alpha and beta axesThe fork feeds back the action and the output of the virtual impedance.
Preferably, the non-cross feedback virtual impedance is one or a combination of a positive virtual resistor, a virtual inductor or a virtual capacitor.
Preferably, the output current is a sampled current on the grid-connected converter side.
Preferably, the grid-connected converter is a three-phase DC/AC grid-connected converter, and the level of the three-phase DC/AC grid-connected converter is not limited.
Preferably, the inner loop of the control system of the three-phase DC/AC grid-connected converter is controlled by a current loop.
The technical scheme provided by the grid-connected converter low-frequency oscillation suppression method based on the non-cross feedback virtual impedance can be seen that the grid-connected converter low-frequency oscillation suppression method based on the non-cross feedback virtual impedance provided by the invention adopts the non-cross feedback virtual impedance to act on a current loop of a control system, namely, the proportion coefficient of the current loop is increased and the proportion coefficient of a phase-locked loop is reduced, the impedance characteristic of the converter is effectively improved, and the low-frequency oscillation of the grid-connected converter can be effectively suppressed, but the introduction of the non-cross feedback virtual impedance is equivalent to the superposition of a resistor on a filter inductor, so that the adverse effect is brought to the dynamic response characteristic of the system, the dynamic response characteristic of the grid-connected converter can be effectively improved by adopting the compensation of the non-cross feedback virtual impedance feedback loop infinite impulse response filter, under the values of the optimal, the dynamic performance of the original system is not influenced basically.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a topological diagram of a grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance according to an embodiment of the invention;
FIG. 2 is a topological diagram of the grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance controlled in a dq coordinate system;
FIG. 3 is a topological diagram of the control of a grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance in an alpha beta coordinate system;
FIG. 4 is a three-phase grid-connected converter topology structure diagram applying a grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance;
FIG. 5 is a schematic diagram of a dual-loop control principle of an inner loop of an alternating current of an outer loop of a direct current voltage under a dq coordinate system;
FIG. 6 is a schematic diagram illustrating a control principle of a virtual synchronous motor in a dq coordinate system;
FIG. 7 is a waveform diagram of a low-frequency oscillation suppression experiment when a two-level grid-connected converter adopts double-loop control of a DC voltage outer loop AC current inner loop under a dq coordinate system;
FIG. 8 is an experimental waveform diagram of a DC voltage step when a two-level grid-connected converter adopts double-loop control of a DC voltage outer loop and an AC current inner loop under a dq coordinate system;
fig. 9 is an experimental waveform diagram of a sudden change of a direct-current load when the two-level grid-connected converter adopts double-loop control of a direct-current voltage outer loop alternating-current inner loop under a dq coordinate system.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
To facilitate understanding of the embodiments of the present invention, the following description will be further explained by taking specific embodiments as examples with reference to the accompanying drawings.
A grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance is disclosed, wherein the grid-connected converter comprises a current loop controller, and the method comprises the following steps:
the method comprises the steps of introducing non-cross feedback virtual impedance and an infinite impulse response filter into a grid-connected converter containing current loop control, calculating an optimal non-cross feedback virtual impedance value, and controlling an instruction i through a current loop according to the optimal non-cross feedback virtual impedance value2 *And an output current i2The closed-loop control of (3) inhibits the low-frequency oscillation of the grid-connected converter. In the embodiment, the non-cross feedback virtual impedance is in a coordinate system of different axes and does not participate in cross control among the different axes, an input signal of the non-cross feedback virtual impedance is derived from non-cross feedback current, and an output value is fed back to pulse width output of a corresponding axis; when controllingWhen the axis is dq coordinate axis, the non-cross feedback virtual impedance does not affect the cross decoupling control of the grid-connected converter.
Calculating the optimal non-cross feedback virtual impedance value comprises taking the non-cross feedback virtual impedance value corresponding to the maximum phase margin of the open-loop transfer function of the control system as the optimal non-cross feedback virtual impedance value for low-frequency oscillation suppression, and defining the optimal non-cross feedback virtual impedance value as mBCalculated according to the following formula (1):
where m is the non-cross feedback virtual impedance, ωc0To adopt an optimal non-cross feedback virtual impedance mBCorresponding cut-off frequency, Go(j ω) represents the frequency domain open loop transfer function,
d/dm is a differential operator, and is a phase margin function corresponding to the non-cross feedback virtual impedance m.
Fig. 1 is a schematic diagram of a method for suppressing low-frequency oscillation of a grid-connected converter based on non-cross feedback virtual impedance according to an embodiment of the present invention, and referring to fig. 1, a control object G of the grid-connected converterpA current loop controller H for transfer function of current from converter side output current to bridge arm voltageiThe input end of is a control instruction i2 *And an output current i2The output terminal of which is connected to the positive terminal of the comparison point for connection to the infinite impulse response filter HfThe output ends of the two-way valve are subjected to difference comparison; the input end of the non-cross feedback virtual impedance m is the output current i2Output terminal and said infinite impulse response filter HfConnecting; infinite impulse response filter HfThe input end of the comparator is connected with the output end of the non-cross feedback virtual impedance m, and the output end of the comparator is connected with the negative end of the comparison point; control object GpThe input terminal of (A) is an infinite impulse response filter HfAnd current loop controller HiIs output with an output current i2。
Infinite impulse response filteringH devicefThe optimal value of the coefficient is the optimal non-cross feedback virtual impedance value mBThe lower phase margin corresponds to the filter coefficient a, and>0, the complex frequency domain s expression of the infinite impulse response filter is shown as the following formula (2):
where a is the variable coefficient of the filter, TsIs the sampling period.
FIG. 2 is a schematic diagram of the implementation of the method for suppressing low-frequency oscillation of the grid-connected converter based on non-cross feedback virtual impedance in the dq coordinate system control, and referring to FIG. 2, when the grid-connected converter is controlled in the dq coordinate system, the output currents i of d and q axes are2d、i2qAre respectively the output current i2Obtained by performing abc/dq conversion as d-and q-axis infinite impulse response filters HfInput signal of (1), d, q-axis current loop command value i2d*、i2q*And d, q axis output current i2d、i2qCurrent loop controller H with d and q axis difference valuesiInput signal of, an infinite impulse response filter HfThe output end of the non-cross feedback virtual impedance m is connected with the input end of the non-cross feedback virtual impedance m;
d. q-axis cross decoupling factor omega0L2Used for d and q axis control cross decoupling of current loop, one omega0L2The input end is d-axis output current i2dOutput end and q-axis feedforward net voltage uqComparing and making difference; another omega0L2The input end is q-axis output current i2qOutput end and d-axis feedforward net pressure udComparison of difference, ω0Outputting angular frequency for the converter in a steady state;
d. q-axis feedforward net pressure ud、uqFor grid-connected converter and power grid common connection point voltage upccObtained by performing abc/dq conversion, or ac-side filter capacitor voltage uabcThe abc/dq transformation is performed.
A current loop controller H under the control of dq coordinate systemiIs a proportional-integral controller, and is,the expression is shown in the following formula (3):
wherein k ispiIs a proportionality coefficient, kiiIs an integral coefficient.
d. q-axis output voltage reference udref、uqrefRespectively d and q axes control output value, feedforward network pressure udAnd current loop controller HiThe difference value of the difference between the output of the two-way valve is a cross decoupling factor omega between the d axis and the q axis0L2Is summed with the d-axis non-crossed feedback virtual impedance moutput to udref(ii) a Feed forward net pressure uqAnd current loop controller HiThe difference value of the difference between the output of the two-way valve is a cross decoupling factor omega between the q axis and the d axis0L2Is subtracted from the q-axis non-cross feedback virtual impedance moutput by uqref。
The non-cross feedback virtual impedance m of the present embodiment does not participate in the cross control of the d and q axes of the control system, and outputs feedback signals controlled by the d and q axes respectively.
Fig. 3 is a schematic diagram of implementation of a non-cross feedback virtual impedance-based method for suppressing low-frequency oscillation of a grid-connected converter in an α β coordinate system, and referring to fig. 3, when the grid-connected converter is controlled in a two-phase stationary α β coordinate system, α and β axis output currents i are output2α、i2βAre respectively the output current i2The infinite impulse response filter H is obtained by performing abc/alpha-beta conversion and has alpha and beta axes respectivelyfInput signal of, alpha, beta axis current loop command values i2α*、i2β*And alpha and beta axis output current i2α、i2βAre respectively alpha-axis and beta-axis current loop controllers HiInput signal of, an infinite impulse response filter HfThe output end of the non-cross feedback virtual impedance m is connected with the input end of the non-cross feedback virtual impedance m;
alpha, beta axis feedforward net pressure uα、uβFor grid-connected converter and power grid common connection point voltage upccObtained by performing abc/alpha beta conversion, or by AC side filteringWave capacitor voltage uabcAnd performing abc/alpha-beta transformation.
Under the control of an alpha beta coordinate system, the current loop controller HiFor a proportional resonant controller, the expression is shown in the following equation (4):
wherein k ispIs a proportionality coefficient, krIs the resonance coefficient.
Reference value u of output voltage of alpha and beta axisαref、uβrefRespectively alpha and beta axis control output values, respectively feedforward network pressure uα、uβAnd current loop controller HiThe obtained difference is compared with the alpha axis and the beta axis to do and output the non-crossed feedback virtual impedance m respectively.
The non-cross feedback virtual impedance m does not participate in the cross control of the alpha axis and the beta axis of the control system, and the output of the non-cross feedback virtual impedance m is respectively a feedback signal controlled by the alpha axis and the beta axis.
The non-cross feedback virtual impedance m is one or a combination of a plurality of positive virtual resistors, virtual inductors or virtual capacitors. The output current is sampling current at the side of the grid-connected converter.
The embodiment also provides a grid-connected converter topology structure diagram applying a low-frequency oscillation suppression method based on non-cross feedback virtual impedance, as shown in fig. 4, the adopted grid-connected converter is a three-phase DC/AC grid-connected converter, and the level of the three-phase DC/AC grid-connected converter is not limited. The embodiment also provides a schematic diagram of a dq coordinate system control system applying a low-frequency oscillation suppression method based on non-cross feedback virtual impedance, as shown in fig. 5 and 6, an inner ring of a control system of a three-phase DC/AC grid-connected converter is controlled by a current ring, an outer ring is not limited, and fig. 5 is a schematic diagram of a double-ring control principle method of an inner ring of an alternating current of a direct-current voltage outer ring under a dq coordinate system; fig. 6 is a schematic diagram of a control principle of a virtual synchronous motor in a dq coordinate system.
According to the low-frequency oscillation mechanism of the grid-connected converter, the method can effectively inhibit the low-frequency oscillation problem caused by current loop control, and basically does not influence the dynamic and steady-state performance of the original control system.
FIG. 7 is a waveform diagram of a low-frequency oscillation suppression experiment when a two-level grid-connected converter adopts double-loop control of a DC voltage outer loop and an AC current inner loop under a dq coordinate system, and in FIG. 7, t0The non-cross feedback virtual impedance m introduced by the time grid-connected converter is 12, grid-connected current low-frequency oscillation is suppressed, direct-current voltage does not have obvious oscillation after a control system is stabilized, and grid-connected current amplitude smoothness is high, referring to fig. 7, it can be seen that oscillation can be effectively suppressed by adopting the method of the embodiment, and system stability is improved.
By adopting the optimal non-cross feedback virtual impedance and the optimal infinite impulse response filter coefficient, fig. 8 and 9 are respectively experimental wave diagrams of direct-current voltage step and direct-current load sudden change when the two-level grid-connected converter adopts double-loop control of a direct-current voltage outer loop alternating-current inner loop under a dq coordinate system. Fig. 8(a) shows a step experiment waveform of the grid-connected converter when the virtual impedance and the infinite impulse response filter are not introduced into the grid-connected converter, and it can be seen that the adjustment time of the converter is 110ms, and in fig. 8(b), the infinite impulse response filter under the values of the optimal virtual impedance and the optimal filter coefficient is introduced, and the adjustment time of the grid-connected converter is also about 110 ms; in fig. 9, an infinite impulse response filter under the values of the optimal virtual impedance and the optimal filter coefficient is introduced when the direct-current load suddenly changes, and the adjustment time of the grid-connected converter is approximately equal to the adjustment time when the virtual impedance and the infinite impulse response filter are not introduced. Referring to fig. 8 and 9, it can be seen that by adopting the low-frequency oscillation suppression strategy of the present invention, the adjustment time of the grid-connected converter is substantially the same as that of the original control system, and the dynamic and steady-state performance of the original system is not substantially affected.
Claims (9)
1. A grid-connected converter low-frequency oscillation suppression method based on non-cross feedback virtual impedance is disclosed, wherein the grid-connected converter comprises a current loop controller, and the method is characterized by comprising the following steps:
the optimal non-cross feedback virtual impedance value is calculated by introducing non-cross feedback virtual impedance and an infinite impulse response filter into a grid-connected converter containing current loop control, and the optimal non-cross feedback virtual impedance value is calculated according to the maximumThe optimal non-cross feedback virtual impedance value controls an instruction i through a current loop2 *And an output current i2The closed-loop control of the grid-connected converter is used for inhibiting the low-frequency oscillation of the grid-connected converter;
the calculation of the optimal non-cross feedback virtual impedance value comprises the step of taking the non-cross feedback virtual impedance value corresponding to the maximum phase margin of the open-loop transfer function of the control system as the optimal non-cross feedback virtual impedance value for low-frequency oscillation suppression, and the optimal non-cross feedback virtual impedance value is defined as mBCalculated according to the following formula (1):
where m is the non-cross feedback virtual impedance, ωc0To adopt an optimal non-cross feedback virtual impedance mBCorresponding cut-off frequency, Go(j ω) represents the frequency domain open loop transfer function,
d/dm is a differential operator, and is a phase margin function corresponding to the non-cross feedback virtual impedance m.
2. The method according to claim 1, wherein the control object of the grid-connected converter is a transfer function of the converter side output current to the bridge arm voltage thereof, and the input end of the current loop controller is a control command i2 *And an output current i2The output end of the difference value of (1) is connected with the positive end of the comparison point and is used for carrying out difference comparison with the output end of the infinite impulse response filter; the non-cross feedback virtual impedance input end is output current i2The output end of the filter is connected with the infinite impulse response filter; the input end of the infinite impulse response filter is connected with the output end of the non-crossed feedback virtual impedance, and the output end of the infinite impulse response filter is connected with the negative end of the comparison point; the input end of the control object is the output difference value of the infinite impulse response filter and the current loop controller, and the output end is the output current i2。
3. The method of claim 1, wherein the optimal value of the coefficient of the infinite impulse response filter is a filter coefficient a corresponding to the phase margin under the optimal non-cross feedback virtual impedance value, and a >0, and the complex frequency domain s expression of the infinite impulse response filter is as shown in the following formula (2):
where a is the variable coefficient of the filter, TsIs the sampling period.
4. The method according to claim 1, wherein when the grid-connected converter is controlled in dq coordinate system, the output current i of d and q axes2d、i2qAre respectively the output current i2The current loop command values i of d and q axes obtained by performing abc/dq conversion are used as input signals of d and q axis infinite impulse response filters, respectively2d*、i2q*And d, q axis output current i2d、i2qThe difference values of the input signals of the current loop controller are d and q axes respectively, and the output end of the infinite impulse response filter is connected with the input end of the non-crossed feedback virtual impedance;
d. q-axis cross decoupling factor omega0L2Used for d and q axis control cross decoupling of current loop, one omega0L2The input end is d-axis output current i2dOutput end and q-axis feedforward net voltage uqComparing and making difference; another omega0L2The input end is q-axis output current i2qOutput end and d-axis feedforward net pressure udComparison of difference, ω0Outputting angular frequency for the converter in a steady state;
the d and q axes feedforward net pressure ud、uqFor grid-connected converter and power grid common connection point voltage upccObtained by performing abc/dq conversion, or ac-side filter capacitor voltage uabcPerforming abc/dq transformation;
the d and q axes output voltage reference value udref、uqrefRespectively d and q axes control output value, feedforward network pressure udCross decoupling factor omega between d-axis and q-axis by difference from output of current loop controller0L2Is summed with the d-axis non-crossed feedback virtual impedance output to udref(ii) a Feed forward net pressure uqCross decoupling factor omega between q axis and d axis by difference from output of current loop controller0L2Is subtracted from the q-axis non-cross feedback virtual impedance output by uqref。
5. The method according to claim 1, wherein when the grid-connected converter is controlled in a two-phase stationary α β coordinate system, α and β axis output currents i2α、i2βAre respectively the output current i2The input signals of the alpha and beta axis infinite impulse response filters obtained by performing abc/alpha and beta conversion, and the alpha and beta axis current loop command values i2α *、i2β *And alpha and beta axis output current i2α、i2βThe difference values of the two are respectively input signals of an alpha-axis current loop controller and a beta-axis current loop controller, and the output end of the infinite impulse response filter is connected with the input end of the non-crossed feedback virtual impedance;
the alpha and beta axis feedforward net pressure uα、uβFor grid-connected converter and power grid common connection point voltage upccObtained by performing abc/α β conversion, or the AC-side filter capacitor voltage uabcPerforming abc/alpha beta transformation;
the alpha and beta axes output voltage reference value uαref、uβrefRespectively alpha and beta axis control output values, respectively feedforward network pressure uα、uβAnd the difference value is compared with the output of the current loop controller, and then the obtained difference value is respectively compared with the alpha axis and the beta axis to do and output the non-crossed feedback virtual impedance.
6. The method according to any one of claims 1-5, wherein the non-cross feedback virtual impedance is one or a combination of a positive virtual resistor, a virtual inductor, or a virtual capacitor.
7. The method according to any one of claims 1 to 5, wherein the output current is a sampled current on the grid-connected converter side.
8. The method according to any one of claims 1 to 5, wherein the grid-connected converter is a three-phase DC/AC grid-connected converter, and the level of the three-phase DC/AC grid-connected converter is not limited.
9. The method according to claim 8, wherein the control system inner loop of the three-phase DC/AC grid-connected converter is current loop control.
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