CN112701691A - Wind power plant harmonic suppression method based on embedded active filtering algorithm - Google Patents
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Abstract
The invention discloses a wind power plant harmonic suppression method based on an embedded active filter algorithm, which belongs to the field of electric energy quality of an electric power system. According to the invention, an embedded active filtering algorithm is formed by applying Clark conversion and park conversion and combining a high-pass filter and a low-pass filter, so that harmonic waves at the near-end grid-side inverter and the far-end grid-connected point of the wind power plant can be inhibited simultaneously, and the power quality is improved.
Description
Technical Field
The invention belongs to the field of electric energy quality of an electric power system, relates to a wind power plant harmonic suppression method of the electric power system, and particularly relates to a wind power plant harmonic suppression method based on an embedded active filter algorithm.
Background
How to suppress harmonic waves of a wind power plant of a power system in a low-cost, high-efficiency and self-adaptive manner and improve the electric energy quality of the wind power plant have important significance for future renewable energy systems. The traditional passive filter and the active filter are high in cost, occupy installation space, are difficult to popularize especially for an offshore wind farm, and lack good adaptability. In addition, the scholars propose active-passive hybrid filters, which suppress harmonics by integrating the active-passive filters and optimizing their control strategies. In recent years, active filters based on embedded control are receiving common attention from both academia and industry due to their advantages of low cost, wide bandwidth and high flexibility, but current research is mainly focused on theoretical exploration based on transfer function, and detailed research is lacking for specific control structures of embedded active filters.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides the wind power plant harmonic suppression method based on the embedded active filtering algorithm, which can reduce the harmonic content of the wind power plant at low cost and high efficiency and improve the electric energy quality of a power system.
In order to achieve the purpose, the invention provides a wind power plant harmonic suppression method based on an embedded active filter algorithm, which comprises the following steps:
s1: detecting a real-time current signal at an inverter at the near-end grid side of a wind power plant and a real-time current signal at a far-end grid-connected point of the wind power plant;
s2: obtaining harmonic compensation current needed by an inverter at the near-end power grid side and a grid-connected point at the far-end by using an embedded active filtering algorithm which is formed by Clark conversion, park conversion and combination of a high-pass filter and a low-pass filter;
s3: phase compensation between the inverter at the near-end power grid side and the far-end grid-connected point is considered;
s4: and outputting the required harmonic compensation current by the grid-side inverter based on the harmonic compensation current required by the near-end grid-side inverter and the far-end grid-connected point and the phase compensation between the near-end grid-side inverter and the far-end grid-connected point.
In some alternative embodiments, step S2 includes:
s2.1: processing input real-time current signals at a near-end grid-side inverter and real-time current signals at a far-end grid-connected point by using Clark conversion and park conversion;
s2.2: processing a current signal at a near-end power grid side inverter and a current signal at a far-end grid-connected point after Clark conversion and park conversion by using a high-pass filter and a low-pass filter;
s2.3: and harmonic compensation currents needed at the inverter at the near-end power grid side and the far-end grid-connected point are obtained by applying inverse park transformation.
In some alternative embodiments, step S2.1 comprises:
respectively processing a real-time current signal at a near-end power grid side inverter and a real-time current signal at a far-end grid-connected point by applying Clark conversion;
processing a real-time current signal at a near-end power grid side inverter and an alpha-beta coordinate axis current signal of a real-time current signal at a far-end grid-connected point after Clark conversion by using park conversion respectively;
wherein d is obtained by converting the current signal at the inverter at the near-end power grid side by parkh-qhH in the h current signals of the coordinate axis is 1; d is converted by park for current signals at a far-end grid-connected pointh-qhH in the h-order current signal of the coordinate axis is m, wherein m is more than 1, and h and m represent harmonic order.
In some alternative embodiments, step S2.2 comprises:
for a current signal at an inverter at the near-end power grid side, after park conversion, an original fundamental frequency current signal is changed into a direct current signal, an original harmonic signal is changed into an alternating current signal, a high-pass filter is adopted to filter the direct current signal, and the alternating current signal is reserved;
and for the current signal at the far-end grid-connected point, after park conversion, the original m-th harmonic signal is changed into a direct current signal, and the direct current signal is reserved by adopting a low-pass filter.
In some alternative embodiments, step S2.3 comprises:
applying park inverse transformation to the current signal at the inverter at the near-end power grid side after being processed by the high-pass filter to obtain harmonic compensation current required by the inverter at the near-end power grid side;
applying park inverse transformation to the current signal at the far-end grid-connected point processed by the low-pass filter to obtain harmonic compensation current required by the far-end grid-connected point;
wherein, for the current signal at the inverter at the near-end grid side, d after inverse park transformationh-qhH in the h current signals of the coordinate axis is 1; d after inverse park transformation for current signals at a far-end grid-connected pointh-qhH in the h-order current signal of the coordinate axis is m, wherein m is more than 1, and h and m represent harmonic order.
In some alternative embodiments, step S3 includes:
s3.1: establishing a circuit model between a near-end power grid side inverter and a far-end grid-connected point;
s3.2: and calculating phase compensation between the inverter at the near-end power grid side and the far-end grid-connected point.
In some alternative embodiments, step S3.1 comprises:
the circuit model of the power transmission cable adopts an equivalent pi model, and the series impedance Z and the parallel admittance Y are
Wherein Z isLIs a series impedance per unit length, YLIs a parallel admittance per unit length, and ZLAnd YLBoth frequency dependent parameters taking into account proximity effects and skin effects;
the circuit model of the transformer adopts a harmonic impedance model and reactance XtRelated to the leakage reactance of the fundamental frequency, Xt(h)＝2πhfLσWherein L isσH is the harmonic frequency, and f is the frequency of the fundamental current;
parallel resistor RuAnd a series resistance RsAre all independent of frequency, and
wherein, XtIs reactance, SnTan λ is an empirical formula for the nominal power of the transformer;
by
Obtaining a circuit mathematical model between a near-end grid-side inverter and a far-end grid-connected point, wherein p is the total number of nodes, [ I (h)]，[Y(h)]，[Z(h)]And [ V (h)]Respectively, a current matrix, an admittance matrix, an impedance matrix and a voltage matrix at the h-th harmonic.
In some alternative embodiments, step S3.2 comprises:
from Delta thetah＝∠Zm,n(h) Calculating phase compensation between a near-end grid-side inverter and a far-end grid-connected point, wherein h represents harmonic times, and delta thetahFor phase compensation between near-end grid-side inverter and far-end grid-connected point, Zm,nThe impedance between the near-end grid-side inverter and the far-end grid-connected point is taken from an impedance matrix in h harmonic waves.
In some alternative embodiments, step S4 includes:
by
Determining a harmonic compensation current required by the grid-side inverter output, wherein iac，ibc，iccCompensating currents, i, for the desired three-phase harmonics, respectivelyαo，iβoCurrent carrier signals, i, being respectively the axis of the alpha-beta coordinateα ～，iβ ～Common harmonic compensation signals, i, for the alpha-beta coordinate axes, respectivelyαmt ～，iβmt ～，iαnt ～，iβnt ～Specific harmonic compensation signals of order m and order n, respectively, of the alpha-beta axis with phase compensation taken into accountmAnd Δ θnThe phase compensation of the m-order harmonic wave and the n-order harmonic wave is respectively carried out, so that the current harmonic wave of the wind power plant is restrained, and the electric energy quality is improved.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. the embedded active filtering algorithm formed by combining the Clark transformation and the park transformation and combining the high-pass filter and the low-pass filter can comprehensively inhibit all times of harmonic waves and can also inhibit specific times of harmonic waves, extra hardware equipment is not introduced, and the harmonic wave inhibition cost is reduced; 2. meanwhile, the compensation current required by the inverter at the near-end power grid side and the compensation current required by the grid-connected point at the far end are considered, so that the power quality of the wind power plant can be comprehensively improved; 3. the phase compensation between the near-end compensation point and the far-end grid-connected point is considered, so that the harmonic suppression effect is more obvious.
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FIG. 1 is a schematic flow chart of a wind power plant harmonic suppression method based on an embedded active filter algorithm according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an electrical system with a wind farm of 10 2.5MW wind generators connected to an external power grid according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an embedded active filtering algorithm provided by an embodiment of the present invention;
FIG. 4 is a schematic diagram of an equivalent circuit model of the power system of FIG. 2 according to an embodiment of the present invention;
FIG. 5 illustrates the original current harmonics at the near-end low-voltage bus and at the far-end grid-connected node without any embedded active filtering algorithm, according to an embodiment of the present invention;
fig. 6 shows current harmonic quantities at a near-end low-voltage bus and a far-end grid-connected point when an embedded active filtering algorithm with only common harmonic compensation is added according to an embodiment of the present invention;
FIG. 7 is a graph of current harmonics at the near-end low-voltage bus when an embedded active filtering algorithm is provided that incorporates both general harmonic compensation and specific harmonic compensation in accordance with an embodiment of the present invention;
fig. 8 shows the current harmonic amount at the far-end grid-connected point when the embedded active filtering algorithm for general harmonic compensation and specific harmonic compensation is added simultaneously according to the embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention aims to solve the technical problem that the harmonic waves of a wind power plant of a power system are difficult to suppress with low cost and high efficiency in the existing method, and the scheme adopted by the invention is as follows: the method comprises the steps of firstly detecting real-time currents at a near-end grid-side inverter and a far-end grid-connected point of a wind power plant, then obtaining harmonic compensation current by using an embedded active filtering algorithm which is formed by Clark conversion and park conversion and combining a high-pass filter and a low-pass filter, then considering phase compensation between the near-end grid-side inverter and the far-end grid-connected point, and finally outputting the required harmonic compensation current by the grid-side inverter to suppress wind power plant harmonics.
Fig. 1 is a schematic flow chart of a wind farm harmonic suppression method based on an embedded active filtering algorithm according to an embodiment of the present invention, which includes the following steps:
s1: detecting real-time current at an inverter at the near-end grid side of a wind power plant and real-time current at a grid-connected point at the far end of the wind power plant;
in the embodiment of the present invention, step S1 may be implemented as follows:
fig. 2 is a schematic diagram of an electric power system in which a wind farm including 10 2.5MW wind power generators according to an embodiment of the present invention is connected to an external power grid, wherein current measuring devices are installed at a near-end grid-side inverter and a far-end grid-connected point of the wind farm, real-time current signals at the near-end grid-side inverter and the far-end grid-connected point of the wind farm are detected, and the measured real-time current signals are input to an embedded active filtering algorithm.
Through step S1, the measured real-time current signal at the grid-side inverter near the wind farm and the real-time current signal at the grid-tie point far away may be input into the embedded active filtering algorithm.
S2: obtaining harmonic compensation current needed by an inverter at the near-end power grid side and a grid-connected point at the far-end by using an embedded active filtering algorithm which is formed by Clark conversion, park conversion and combination of a high-pass filter and a low-pass filter;
in the embodiment of the present invention, step S2 may be implemented as follows:
fig. 3 is a schematic diagram of an embedded active filtering algorithm provided by an embodiment of the present invention. Firstly, the input real-time current signals at the near-end grid-side inverter and the input real-time current signals at the far-end grid-connected point are processed by applying Clark conversion and park conversion.
Firstly, Clark transformation is applied to process real-time current signals at a near-end grid-side inverter and real-time current signals at a far-end grid-connected point, namely
Wherein ia，ib，icIs a three-phase current signal at an inverter at the near-end power grid side or a three-phase current signal at a far-end grid-connected point iα，iβIs a Clark transformed alpha-beta coordinate axis current signal, Tabc-αβIs clark transform matrix, w is 2/3, representing constant amplitude transform; then processing the alpha-beta coordinate axis current signal after Clark transformation by using park transformation, namely
Wherein iα，iβIs a current signal of alpha-beta coordinate axis after Clark transformation, idh，iqhIs d after park transformationh-qhH current signals of coordinate axes, thetahProvided by a phase-locked loop, representing dh-qhPhase of the coordinate axes, Tαβ-dqhIs a park transformation matrix. For the current signal at the inverter at the near-end power grid side, h in park transformation is 1, namely after park transformation, the original fundamental frequency current signal is changed into a direct current signal, and the original harmonic signal is changed into an alternating current signal; for the current signal at the far-end grid-connected point, h in park transformation is m (m is more than 1), namely after park transformation, the original m-th harmonic signal is changed into a direct current signal.
Next, the current signals after clark transformation and park transformation are processed using a high pass filter and a low pass filter. For current signal at near-end grid-side inverterAfter park conversion, the original fundamental frequency current signal is changed into a direct current signal, and the original harmonic signal is changed into an alternating current signal, so that the direct current signal (namely the original fundamental frequency current signal) is filtered by adopting a high-pass filter, the alternating current signal (namely the original harmonic signal) is reserved, and the transfer function G of the high-pass filterH(s)Is composed of
Wherein s ═ j ω, G0HRepresenting the gain of the high-pass filter, ωcHRepresents the high pass filter cut-off angular frequency; for the current signal at the far-end grid-connected point, after park conversion, the original m-th harmonic signal is changed into a direct current signal, so that the direct current signal (namely the original m-th harmonic signal) is reserved by adopting a low-pass filter, and the transfer function G of the low-pass filterL(s)Is composed of
Wherein s ═ j ω, G0LRepresenting the gain of the low-pass filter, ωcLRepresenting the low pass filter cut-off angular frequency.
Then, harmonic compensation currents needed at the inverter at the near-end power grid side and the far-end grid-connected point are obtained by applying inverse park transformation, and the inverse park transformation is
Wherein idh，iqhIs dh-qhH current signals of coordinate axes iα，iβIs a current signal of alpha-beta coordinate axis, thetahProvided by a phase-locked loop, representing dh-qhPhase of the coordinate axes, Tαβ-dqhIs a park transformation matrix. For a current signal at a near-end grid side inverter, h in inverse park transformation is 1; for the current signal at the far-end grid-connected point, h in inverse park transformation is m (m is more than 1).
Through the step S2, the harmonic compensation current required at the near-end grid-side inverter and the far-end grid-connected point calculated by the embedded active filtering algorithm can be obtained.
S3: phase compensation between the inverter at the near-end power grid side and the far-end grid-connected point is considered;
in the embodiment of the present invention, step S3 may be implemented as follows:
FIG. 4 is a schematic diagram of an equivalent circuit model of the power system in FIG. 2 according to an embodiment of the present invention, in which the circuit model of the power transmission cable adopts an equivalent pi model, and the series impedance Z and the parallel admittance Y are
Wherein Z isLIs a series impedance per unit length, YLIs a parallel admittance per unit length, and ZLAnd YLAre frequency dependent parameters that take into account proximity effects and skin effects. The circuit model of the transformer adopts a harmonic impedance model and reactance XtRelated to leakage reactance of fundamental frequency, i.e. Xt(h)＝2πhfLσWherein L isσH is the harmonic frequency, f is 50 Hz, and the frequency of the fundamental current is shown as the leakage reactance; parallel resistor RuAnd a series resistance RsAre all independent of frequency, i.e.
Wherein, XtIs reactance, SnTan λ is an empirical formula for the nominal power of the transformer. Therefore, the circuit mathematical model between the near-end grid-side inverter and the far-end grid-connected point is
Wherein p is the total number of nodes, [ I (h)]，[Y(h)]，[Z(h)]And [ V (h)]A current matrix, an admittance matrix, an impedance matrix and a voltage matrix at the h harmonic, respectively. Thus, the phase compensation between the near-end grid-side inverter and the far-end grid-connected point is Δ θh＝∠Zm,n(h) Where h denotes the harmonic order, Δ θhFor phase compensation between near-end grid-side inverter and far-end grid-connected point, Zm,nThe impedance between the near-end grid-side inverter and the far-end grid-connected point is taken from an impedance matrix in h harmonic waves.
Through step S3, a phase shift between the near-end grid-side inverter and the far-end grid-connected point can be obtained.
S4: and outputting the required harmonic compensation current by the grid-side inverter based on the harmonic compensation current required by the near-end grid-side inverter and the far-end grid-connected point and the phase compensation between the near-end grid-side inverter and the far-end grid-connected point.
In the embodiment of the present invention, step S4 may be implemented as follows:
according to the Clark inverse transformation, the harmonic compensation current required by the output of the inverter on the power grid side is
Wherein iac，ibc，iccCompensating currents, i, for the desired three-phase harmonics, respectivelyαo，iβoCurrent carrier signals, i, being respectively the axis of the alpha-beta coordinateα ～，iβ ～Common harmonic compensation signals, i, for the alpha-beta coordinate axes, respectivelyαmt ～，iβmt ～，iαnt ～，iβntSpecific harmonic compensation signals m and n, respectively, for the alpha-beta coordinate axis with phase compensation taken into account, where delta thetamAnd Δ θnPhase compensation for the m and n harmonics, respectively.
The common harmonic compensation signal is a harmonic compensation current obtained by combining Clark conversion, park conversion and a high-pass filter, and the specific harmonic compensation signal is a harmonic compensation current obtained by combining Clark conversion, park conversion and a low-pass filter, and is obtained by adding phase compensation.
Through step S4, a harmonic compensation current that takes into account the phase offset between the near-end compensation point and the far-end grid-connected point can be obtained.
The technical solution of the present invention is further described in detail by using an embodiment in a power system with 10 wind farms with 2.5MW wind generators connected to an external power grid as shown in fig. 2 and with reference to the accompanying drawings.
Firstly, no embedded active filtering algorithm is added to the power system shown in fig. 2, in which the wind farm including 10 2.5MW wind power generators is connected to the external power grid, so as to obtain the original current harmonic quantities at the near-end low-voltage bus (i.e. at the near-end grid-side inverter) and the far-end grid-connected point, as shown in fig. 5.
Then, only an embedded active filtering algorithm for general harmonic compensation is added to the power system shown in fig. 2, in which the wind farm including 10 2.5MW wind power generators is connected to the external power grid, to obtain current harmonic quantities at the near-end low-voltage bus and the far-end grid-connected point, as shown in fig. 6.
Finally, an embedded active filtering algorithm for general harmonic compensation and specific harmonic compensation is added to the power system shown in fig. 2, in which the wind farm with 10 2.5MW wind power generators is connected to the external power grid, to obtain the current harmonic quantity at the near-end low-voltage bus (as shown in fig. 7) and the current harmonic quantity at the far-end grid-connected point (as shown in fig. 8).
As can be seen from comparison of fig. 5, 6, 7 and 8, the proposed embedded active filtering algorithm effectively reduces the current harmonics at the near-end low-voltage bus and the far-end grid-connection point.
The embodiment demonstrates that the power quality of the power system can be effectively improved through the proposed wind power plant harmonic suppression method based on the embedded active filtering algorithm.
It should be noted that, according to the implementation requirement, each step/component described in the present application can be divided into more steps/components, and two or more steps/components or partial operations of the steps/components can be combined into new steps/components to achieve the purpose of the present invention.
Although the invention makes more use of terms like power system, wind farm, embedded active filtering, harmonic currents, clarke variations, park transformation, high pass filter, low pass filter, etc., the possibility of using other terms is not excluded. These terms are used merely to more conveniently describe and explain the nature of the present invention; they are to be construed as being without limitation to any additional limitations that may be imposed by the spirit of the present invention.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A wind power plant harmonic suppression method based on an embedded active filter algorithm is characterized by comprising the following steps:
s1: detecting a real-time current signal at an inverter at the near-end grid side of a wind power plant and a real-time current signal at a far-end grid-connected point of the wind power plant;
s2: obtaining harmonic compensation current needed by an inverter at the near-end power grid side and a grid-connected point at the far-end by using an embedded active filtering algorithm which is formed by Clark conversion, park conversion and combination of a high-pass filter and a low-pass filter;
s3: phase compensation between the inverter at the near-end power grid side and the far-end grid-connected point is considered;
s4: and outputting the required harmonic compensation current by the grid-side inverter based on the harmonic compensation current required by the near-end grid-side inverter and the far-end grid-connected point and the phase compensation between the near-end grid-side inverter and the far-end grid-connected point.
2. Wind farm harmonic suppression method according to claim 1, characterized in that step S2 comprises:
s2.1: processing input real-time current signals at a near-end grid-side inverter and real-time current signals at a far-end grid-connected point by using Clark conversion and park conversion;
s2.2: processing a current signal at a near-end power grid side inverter and a current signal at a far-end grid-connected point after Clark conversion and park conversion by using a high-pass filter and a low-pass filter;
s2.3: and harmonic compensation currents needed at the inverter at the near-end power grid side and the far-end grid-connected point are obtained by applying inverse park transformation.
3. Wind farm harmonic suppression method according to claim 2, characterized in that step S2.1 comprises:
respectively processing a real-time current signal at a near-end power grid side inverter and a real-time current signal at a far-end grid-connected point by applying Clark conversion;
processing a real-time current signal at a near-end power grid side inverter and an alpha-beta coordinate axis current signal of a real-time current signal at a far-end grid-connected point after Clark conversion by using park conversion respectively;
wherein d is obtained by converting the current signal at the inverter at the near-end power grid side by parkh-qhH in the h current signals of the coordinate axis is 1; d is converted by park for current signals at a far-end grid-connected pointh-qhH in the h-order current signal of the coordinate axis is m, wherein m is more than 1, and h and m represent harmonic order.
4. A wind farm harmonic suppression method according to claim 3, characterised in that step S2.2 comprises:
for a current signal at an inverter at the near-end power grid side, after park conversion, an original fundamental frequency current signal is changed into a direct current signal, an original harmonic signal is changed into an alternating current signal, a high-pass filter is adopted to filter the direct current signal, and the alternating current signal is reserved;
and for the current signal at the far-end grid-connected point, after park conversion, the original m-th harmonic signal is changed into a direct current signal, and the direct current signal is reserved by adopting a low-pass filter.
5. Wind farm harmonic suppression method according to claim 4, characterized in that step S2.3 comprises:
applying park inverse transformation to the current signal at the inverter at the near-end power grid side after being processed by the high-pass filter to obtain harmonic compensation current required by the inverter at the near-end power grid side;
applying park inverse transformation to the current signal at the far-end grid-connected point processed by the low-pass filter to obtain harmonic compensation current required by the far-end grid-connected point;
wherein, for the current signal at the inverter at the near-end grid side, d after inverse park transformationh-qhH in the h current signals of the coordinate axis is 1; for remote grid connection pointCurrent signal, d after inverse parker transformationh-qhH in the h-order current signal of the coordinate axis is m, wherein m is more than 1, and h and m represent harmonic order.
6. Wind farm harmonic suppression method according to claim 5, characterized in that step S3 comprises:
s3.1: establishing a circuit model between a near-end power grid side inverter and a far-end grid-connected point;
s3.2: and calculating phase compensation between the inverter at the near-end power grid side and the far-end grid-connected point.
7. Wind farm harmonic suppression method according to claim 6, characterized in that step S3.1 comprises:
the circuit model of the power transmission cable adopts an equivalent pi model, and the series impedance Z and the parallel admittance Y are
Wherein Z isLIs a series impedance per unit length, YLIs a parallel admittance per unit length, and ZLAnd YLBoth frequency dependent parameters taking into account proximity effects and skin effects;
the circuit model of the transformer adopts a harmonic impedance model and reactance XtRelated to the leakage reactance of the fundamental frequency, Xt(h)＝2πhfLσWherein L isσH is the harmonic frequency, and f is the frequency of the fundamental current;
parallel resistor RuAnd a series resistance RsAre all independent of frequency, and
wherein, XtIs reactance, SnTan λ is an empirical formula for the nominal power of the transformer;
by
Obtaining a near-end grid-side inverterMathematical model of the circuit between local and remote point of connection, where p is the total number of nodes, [ I (h)]，[Y(h)]，[Z(h)]And [ V (h)]Respectively, a current matrix, an admittance matrix, an impedance matrix and a voltage matrix at the h-th harmonic.
8. Wind farm harmonic suppression method according to claim 7, characterized in that step S3.2 comprises:
from Delta thetah＝∠Zm,n(h) Calculating phase compensation between a near-end grid-side inverter and a far-end grid-connected point, wherein h represents harmonic times, and delta thetahFor phase compensation between near-end grid-side inverter and far-end grid-connected point, Zm,nThe impedance between the near-end grid-side inverter and the far-end grid-connected point is taken from an impedance matrix in h harmonic waves.
9. The wind farm harmonic suppression method according to claim 8, wherein step S4 includes:
by
Determining a harmonic compensation current required by the grid-side inverter output, wherein iac，ibc，iccCompensating currents, i, for the desired three-phase harmonics, respectivelyαo，iβoCurrent carrier signals, i, being respectively the axis of the alpha-beta coordinateα ～，iβCommon harmonic compensation signal, i, for the alpha-beta coordinate axes, respectivelyαmt ～，iβmt ～，iαnt ～，iβnt ～Specific harmonic compensation signals of order m and order n, respectively, of the alpha-beta axis with phase compensation taken into accountmAnd Δ θnThe phase compensation of the m-order harmonic wave and the n-order harmonic wave is respectively carried out, so that the current harmonic wave of the wind power plant is restrained, and the electric energy quality is improved.
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