CN105552956A - Safety running control method for grid-connected current transformer under power grid fault - Google Patents

Abstract

The invention provides a safety running control method for a grid-connected current transformer under a power grid fault. The method comprises the following steps of s1, determining a parameter limitation value for safety running of the grid-connected current transformer, wherein the parameter limitation value comprises an active power fluctuation margin limitation value and a phase current limitation value; s2, setting an active power reference value and a reactive power reference value containing a positive-sequence component and a negative-sequence component under a rotating coordinate system, allocating the positive-sequence components and the negative-sequence components of active power and reactive power according to the parameter limitation value, and outputting the active power reference value and the reactive power reference value after allocating; and s3, calculating an output current reference value of the grid-connected current transformer according to the allocated active power reference value and the reactive power reference value containing the positive-sequence component and the negative-sequence component under the rotating coordinate system, and controlling the grid-connected current transformer to output current according to the current reference value. Through the above method, factors such as phase current and power fluctuation are comprehensively considered, the reference current is accurately output and controlled, the safety running of the grid-connected current transformer under the power grid fault can be effectively ensured, the normal working and the service lifetime of the grid-connected current transformer are guaranteed, and an effective support can be formed for a power grid.

Description

Grid-connected converter safety operating control method under electric network fault

Technical field

The present invention relates to a kind of control method of grid equipment, particularly relate to grid-connected converter safety operating control method under a kind of electric network fault.

Background technology

Along with the extensive application of generation of electricity by new energy technology, combining inverter, as one of its hardcore, is the interface connecting electrical network and generation of electricity by new energy; Because electrical network scale is more and more huger, during electric network fault, a large amount of grid-connected converter off-grid can bring very important impact to electrical network.

In order to realize the safe operation of grid-connected converter under grid fault conditions, conventional control method can under the prerequisite meeting different positive-negative sequence voltage compensation targets, restriction output current of converter, meet the safe operating conditions that current transformer exports not overcurrent, but do not consider the restriction of active power fluctuation, thus cause impacting grid-connected converter.

Therefore, need to propose a kind of new control method, effectively can ensure grid-connected converter safe operation under electric network fault condition, guarantee normal work and the useful life of grid-connected converter, and effective support can be formed to electrical network.

Summary of the invention

In view of this, the object of this invention is to provide grid-connected converter safety operating control method under a kind of electric network fault, effectively can ensure grid-connected converter safe operation under electric network fault condition, guarantee normal work and the useful life of grid-connected converter, and effective support can be formed to electrical network.

Grid-connected converter safety operating control method under a kind of electric network fault provided by the invention, comprises the steps:

S1. determine the parameter limits value of grid-connected converter safe operation, comprising: active power fluctuation amplitude limits value and phase current limits value;

S2. under rotating coordinate system, setting active power reference value and the reactive power reference qref comprising positive sequence component and negative sequence component, and positive sequence component and the negative sequence component of active power and reactive power is distributed according to parameter limits value, export the reference value of the active power reference value after distributing and reactive power;

S3., under rotating coordinate system, calculate the output current reference value of grid-connected converter according to the active power reference value after distribution and the reactive power reference qref including positive sequence component and negative sequence component, and control grid-connected converter according to current reference value output current.

Further, in step S1, according to following steps determination active power fluctuation amplitude limits value and phase current limits value:

S11. according to the power device lowest high-current value I in grid-connected converter _limit1with passive filter lowest high-current value I _limit2determine the maximum current limit value I of grid-connected converter _limit, and have I _limit<min{I _limit1, I _limit2, wherein, power device lowest high-current value I _limit1with passive filter lowest high-current value I _limit2determine according to the specifications and models of power device and passive filter respectively;

S12. the active power limits value △ p of grid-connected converter is determined _limit, wherein, active power limits value △ p _limitdetermine that meritorious power fluctuation limit value is △ p by DC bus-bar voltage maximum _limit1, by the lowest high-current value I of the triple-frequency harmonics of grid-connected phase current _{3rdma x} determine that meritorious power fluctuation limit value is △ p _limit2, and Δ p _limit<min{ Δ p _limit1, Δ p _limit2.

Further, in step S2, distribute positive sequence component and the negative sequence component of active power and reactive power according to following steps:

S21. set the positive sequence component of reactive power and negative sequence component and active power by the operating condition of grid-connected converter, wherein, the active power of setting is P _ref, the positive sequence component of the reactive power of setting is Q _pref, negative sequence component is Q _nref;

S22. the three-phase current I in electrical network is obtained _a, I _a, I _c, and determine maximum phase current value I _max1;

If I _max1>I _limit, then grid-connected converter power output positive sequence reactive power Q _pref1with negative phase-sequence reactive power Q _nref1be respectively: $Q_{pref1}=\frac{I_{max1}}{I_{\lim it}}{Q}_{pref},Q_{nref1}=\frac{I_{max1}}{I_{\lim it}}{Q}_{nref};$

The positive sequence component P of the active power that grid-connected converter exports _pref1with negative sequence component P _nref1be respectively:

P _pref1＝0,P _nref1＝0

If I _max1≤ I _limit, then the positive sequence reactive power Q of grid-connected converter output _pref1with negative phase-sequence reactive power Q _nref1be respectively: Q _pref1=Q _pref, Q _nref1=Q _nref;

The positive sequence component P of the active power that grid-connected converter exports _pref1with negative sequence component P _nref1be respectively: P _pref1=k _poptip _ref, P _nref1=(1-k _popti) P _ref, wherein, k _poptifor active power distribution coefficient;

S23. the active power fluctuation amplitude △ p in electrical network is obtained ₁:

If △ is p ₁> △ p _limit, then the positive sequence reactive power Q of grid-connected converter output _pref2with negative phase-sequence reactive power Q _nref2be respectively:

$Q_{pref2}=\frac{{\mathrm{\&Delta;p}}_{\lim it}}{{\mathrm{\&Delta;p}}_1}{Q}_{pref1},Q_{nref2}=\frac{{\mathrm{\&Delta;p}}_{\lim it}}{{\mathrm{\&Delta;p}}_1}{Q}_{nref1}$

If △ is p ₁≤ △ p _limit, then the positive sequence reactive power Q of grid-connected converter output _pref2with negative phase-sequence reactive power Q _nref2be respectively:

Q _pref2＝Q _pref1,Q _nref2＝Q _nref1。

Further, in step S22, three-phase current I _a, I _a, I _cand I _max1obtain according to following formulae discovery:

$I_a=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}}}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})-\frac{2}{3}\mathrm{\&pi;})}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})+\frac{2}{3}\mathrm{\&pi;})}$

I _max1＝max{I _a,I _b,I _c}

Wherein, v _dp, v _qp, v _dn, v _qnbe respectively the positive sequence d axle component of line voltage under rotatable coordinate axis system, positive sequence q axle component, negative phase-sequence d axle component, negative phase-sequence q axle component; i _dp, i _qp, i _dn, i _qnbe respectively the positive sequence d axle component of power network current under rotatable coordinate axis system, positive sequence q axle component, negative phase-sequence d axle component, negative phase-sequence q axle component, and obtained by following formulae discovery:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{dn}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$

$i_{qn}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$

, wherein, i _dp, i _qp, i _dn, i _qnfor Q _pref, Q _nref, P _pref=0, P _nrefobtain under the condition of=0.

Further, in step S22, active power fluctuation amplitude △ p ₁obtain according to following formula:

${\mathrm{\&Delta;p}}_1=\frac{3}{2}\sqrt{{(v_{qn}{i}_{dp}-v_{dn}{i}_{qp}-v_{qp}{i}_{dn}+v_{dp}{i}_{qn})}^2+{(v_{dp}{i}_{dn}+v_{qp}{i}_{qn}+v_{dn}{i}_{dp}+v_{qn}{i}_{qp})}^2};$

Wherein,

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{dn}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref});$ Wherein, i _dp, i _qp,

$i_{qn}=\frac{2}{3}\left(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref}\right)$

I _dn, i _qnfor Q _pref, Q _nref, P _pref=0, P _nrefobtain under the condition of=0.

Further, in step S22, active power distribution coefficient k _poptiobtain in accordance with the following steps:

S221. active power distribution coefficient is defined: P _p=k _pp _ref, P _n=(1-k _p) P _ref, P _pfor the positive sequence component of active power, P _nfor the negative sequence component of active power;

S222. by k _p, P _ref, Q _pref2, Q _nref2substitution following formula obtains:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dn}=\frac{2}{3}\left(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qn}=\frac{2}{3}\left(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

$I_a=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}}}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})-\frac{2}{3}\mathrm{\&pi;})}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})+\frac{2}{3}\mathrm{\&pi;})}$

I _max＝max{I _a,I _b,I _c}

; K is set up according to above-mentioned two formula _pand I _maxfunctional relation, and draw function curve diagram according to this functional relation;

S223. by k _p, P _ref, Q _pref2, Q _nref2substitution following formula obtains:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dn}=\frac{2}{3}\left(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qn}=\frac{2}{3}\left(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

$\mathrm{\&Delta;}p=\frac{3}{2}\sqrt{{(v_{qn}{i}_{dp}-v_{dn}{i}_{qp}-v_{qp}{i}_{dn}+v_{dp}{i}_{qn})}^2+{(v_{dp}{i}_{dn}+v_{qp}{i}_{qn}+v_{dn}{i}_{dp}+v_{qn}{i}_{qp})}^2};$

K is set up according to above-mentioned two formula _pwith the functional relation of △ p, and draw function curve diagram according to this functional relation;

S224. according to I _max<I _limitconstraints at k _pand I _maxfunction curve on find out satisfactory interval, and be designated as [k _p1, k _p2]; And the point finding out △ p minimum in this interval is designated as (k _popti, △ p _min);

If [k _p1, k _p2] interval in be empty set or △ p _min> △ p _limit,according to the derate step-length of adjustment △ p, repeat step S221 to step 224, until [k _p1, k _p2] be not empty set, and △ p _min≤ △ p _limit.

Further, according to the Q determined in step S2 _pref2, Q _nref2, P _pref1, P _nref1, by following formulae discovery current reference value:

$i_{dpref}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref1}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qpref}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref2}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dnref}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref1}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qnref}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref1}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

Wherein, i _dpref, i _qpref, i _dnref, i _qnreffor positive sequence d axle component, positive sequence q axle component, negative phase-sequence d axle component, the negative phase-sequence q axle component of reference current, by reference to current value, control is carried out to grid-connected converter and make grid-connected converter safe operation under electric network fault.

Further, active power fluctuation limits value is △ p _limit1be △ p with active power fluctuation limits value _limit2by following formulae discovery: Δ p _limit1=< V _dc> 2 ω C _dc(V _max-< V _dc>), ${\mathrm{\&Delta;p}}_{\lim it2}=\frac{4I_{3rdmax}\&CenterDot;<V_{dc}>2{\mathrm{\&omega;C}}_{dc}{X}_L}{m};$ Wherein, V _maxfor the DC bus-bar voltage maximum of setting, <V _dc> is DC bus-bar voltage mean value, C _dcfor dc-link capacitance capacity, I _3rdmaxfor the maximum of triple-frequency harmonics in grid-connected phase current, X _lfor electrical network induction reactance value, m is inverter modulation degree, and ω is line voltage angular frequency.

Beneficial effect of the present invention: grid-connected converter safety operating control method under electric network fault of the present invention, consider the factor of phase current and power fluctuation, accurate output controls reference current, effectively can ensure grid-connected converter safe operation under electric network fault condition, guarantee normal work and the useful life of grid-connected converter, and effective support can be formed to electrical network.

Accompanying drawing explanation

Below in conjunction with drawings and Examples, the invention will be further described:

Fig. 1 is flow chart of the present invention.

Fig. 2 is the system block diagram of three-phase grid-connected converter of the present invention.

Fig. 3 is k of the present invention _pand I _maxfunction curve diagram.

Fig. 4 is k of the present invention _pwith the function curve diagram of △ p.

Embodiment

Fig. 1 is flow chart of the present invention, and Fig. 2 is the system block diagram of three-phase grid-connected converter of the present invention, and Fig. 3 is k of the present invention _pand I _maxfunction curve diagram, Fig. 4 is k of the present invention _pwith the function curve diagram of △ p as shown in the figure, grid-connected converter safety operating control method under a kind of electric network fault provided by the invention, comprises the steps:

S1. determine the parameter limits value of grid-connected converter safe operation, comprising: active power fluctuation amplitude limits value and phase current limits value;

S2. under rotating coordinate system, setting active power reference value and the reactive power reference qref comprising positive sequence component and negative sequence component, and positive sequence component and the negative sequence component of active power and reactive power is distributed according to parameter limits value, export the reference value of the active power reference value after distributing and reactive power;

S3. under rotating coordinate system, the output current reference value of grid-connected converter is calculated according to the active power reference value after distribution and the reactive power reference qref including positive sequence component and negative sequence component, and control grid-connected converter according to current reference value output current, pass through said method, consider the factor of phase current and power fluctuation, accurate output controls reference current, effectively can ensure grid-connected converter safe operation under electric network fault condition, guarantee normal work and the useful life of grid-connected converter, and effective support can be formed to electrical network.

In the present embodiment, in step S1, according to following steps determination active power fluctuation amplitude limits value and phase current limits value:

S11. according to the power device lowest high-current value I in grid-connected converter _limit1with passive filter lowest high-current value I _limit2determine the maximum current limit value I of grid-connected converter _limit, and have I _limit<min{I _limit1, I _limit2, wherein, power device lowest high-current value I _limit1with passive filter lowest high-current value I _limit2determine according to the specifications and models of power device and passive filter respectively;

S12. the active power limits value △ p of grid-connected converter is determined _limit, wherein, active power limits value △ p _limitdetermine that meritorious power fluctuation limit value is △ p by DC bus-bar voltage maximum _limit1, by the lowest high-current value I of the triple-frequency harmonics of grid-connected phase current _3rdmadetermine that meritorious power fluctuation limit value is △ p _limit2, and Δ p _limit<min{ Δ p _limit1, Δ p _limit2, wherein: active power fluctuation limits value is △ p _limit1be △ p with active power fluctuation limits value _limit2by following formulae discovery: Δ p _limit1=< V _dc> 2 ω C _dc(V _max-< V _dc>), ${\mathrm{\&Delta;p}}_{\lim it2}=\frac{4I_{3rdmax}\&CenterDot;<V_{dc}>2{\mathrm{\&omega;C}}_{dc}{X}_L}{m};$ Wherein, V _maxfor the DC bus-bar voltage maximum of setting, <V _dc> is DC bus-bar voltage mean value, C _dcfor dc-link capacitance capacity, I _3rdmaxfor the maximum of triple-frequency harmonics in grid-connected phase current, X _lfor electrical network induction reactance value, m is inverter modulation degree, and ω is line voltage angular frequency.

In the present embodiment, in step S2, distribute positive sequence component and the negative sequence component of active power and reactive power according to following steps:

S21. set the positive sequence component of reactive power and negative sequence component and active power by the operating condition of grid-connected converter, wherein, the active power of setting is P _ref, the positive sequence component of the reactive power of setting is Q _pref, negative sequence component is Q _nref;

S22. the three-phase current I in electrical network is obtained _a, I _a, I _c, and determine maximum phase current value I _max1;

If I _max1>I _limit, then grid-connected converter power output positive sequence reactive power Q _pref1with negative phase-sequence reactive power Q _nref1be respectively: $Q_{pref1}=\frac{I_{max1}}{I_{\lim it}}{Q}_{pref},Q_{nref1}=\frac{I_{max1}}{I_{\lim it}}{Q}_{nref};$

The positive sequence component P of the active power that grid-connected converter exports _pref1with negative sequence component P _nref1be respectively:

P _pref1＝0,P _nref1＝0

If I _max1≤ I _limit, then the positive sequence reactive power Q of grid-connected converter output _pref1with negative phase-sequence reactive power Q _nref1be respectively: Q _pref1=Q _pref, Q _nref1=Q _nref;

The positive sequence component P of the active power that grid-connected converter exports _pref1with negative sequence component P _nref1be respectively: P _pref1=k _poptip _ref, P _nref1=(1-k _popti) P _ref, wherein, k _poptifor active power distribution coefficient;

S23. the active power fluctuation amplitude △ p in electrical network is obtained ₁:

If △ is p ₁> △ p _limit, then the positive sequence reactive power Q of grid-connected converter output _pref2with negative phase-sequence reactive power Q _nref2be respectively:

$Q_{pref2}=\frac{{\mathrm{\&Delta;p}}_{\lim it}}{{\mathrm{\&Delta;p}}_1}{Q}_{pref1},Q_{nref2}=\frac{{\mathrm{\&Delta;p}}_{\lim it}}{{\mathrm{\&Delta;p}}_1}{Q}_{nref1}$

If △ is p ₁≤ △ p _limit, then the positive sequence reactive power Q of grid-connected converter output _pref2with negative phase-sequence reactive power Q _nref2be respectively:

Q _pref2＝Q _pref1,Q _nref2＝Q _nref1。

In the present embodiment, in step S22, three-phase current I _a, I _a, I _cand I _max1obtain according to following formulae discovery:

$I_a=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}}}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})-\frac{2}{3}\mathrm{\&pi;})}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})+\frac{2}{3}\mathrm{\&pi;})}$

I _max1＝max{I _a,I _b,I _c}

, wherein, v _dp, v _qp, v _dn, v _qnbe respectively the positive sequence d axle component of line voltage under rotatable coordinate axis system, positive sequence q axle component, negative phase-sequence d axle component, negative phase-sequence q axle component; i _dp, i _qp, i _dn, i _qnbe respectively the positive sequence d axle component of power network current under rotatable coordinate axis system, positive sequence q axle component, negative phase-sequence d axle component, negative phase-sequence q axle component, and obtained by following formulae discovery:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{dn}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$

$i_{qn}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$

, wherein, i _dp, i _qp, i _dn, i _qnfor Q _pref, Q _nref, P _pref=0, P _nrefobtain under the condition of=0.

In the present embodiment, in step S22, active power fluctuation amplitude △ p ₁obtain according to following formula:

${\mathrm{\&Delta;p}}_1=\frac{3}{2}\sqrt{{(v_{qn}{i}_{dp}-v_{dn}{i}_{qp}-v_{qp}{i}_{dn}+v_{dp}{i}_{qn})}^2+{(v_{dp}{i}_{dn}+v_{qp}{i}_{qn}+v_{dn}{i}_{dp}+v_{qn}{i}_{qp})}^2};$

Wherein,

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{dn}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref});$ Wherein, i _dp, i _qp,

$i_{qn}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$

I _dn, i _qnfor Q _pref, Q _nref, P _pref=0, P _nrefobtain under the condition of=0.

In the present embodiment, in step S22, active power distribution coefficient k _poptiobtain in accordance with the following steps:

S221. active power distribution coefficient is defined: P _p=k _pp _ref, P _n=(1-k _p) P _ref, P _pfor the positive sequence component of active power, P _nfor the negative sequence component of active power;

S222. by k _p, P _ref, Q _pref2, Q _nref2substitution following formula obtains:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dn}=\frac{2}{3}\left(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qn}=\frac{2}{3}\left(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

$I_a=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}}}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})-\frac{2}{3}\mathrm{\&pi;})}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})+\frac{2}{3}\mathrm{\&pi;})}$

I _max＝max{I _a,I _b,I _c}

; K is set up according to above-mentioned two formula _pand I _maxfunctional relation, and draw function curve diagram according to this functional relation, as shown in Figure 3;

S223. by k _p, P _ref, Q _pref2, Q _nref2substitution following formula obtains:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dn}=\frac{2}{3}\left(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qn}=\frac{2}{3}\left(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

$\mathrm{\&Delta;}p=\frac{3}{2}\sqrt{{(v_{qn}{i}_{dp}-v_{dn}{i}_{qp}-v_{qp}{i}_{dn}+v_{dp}{i}_{qn})}^2+{(v_{dp}{i}_{dn}+v_{qp}{i}_{qn}+v_{dn}{i}_{dp}+v_{qn}{i}_{qp})}^2}$ ；

K is set up according to above-mentioned two formula _pwith the functional relation of △ p, and draw function curve diagram according to this functional relation, as shown in Figure 4;

S224. according to I _max<I _limitconstraints at k _pand I _maxfunction curve on find out satisfactory interval, and be designated as [k _p1, k _p2]; And the point finding out △ p minimum in this interval is designated as (k _popti, △ p _min);

If [k _p1, k _p2] interval in be empty set or △ p _min> △ p _limit,according to the derate step-length of adjustment △ p, repeat step S221 to step 224, until [k _p1, k _p2] be not empty set, and △ p _min≤ △ p _limit.

In the present embodiment, according to the Q determined in step S2 _pref2, Q _nref2, P _pref1, P _nref1, by following formulae discovery current reference value:

$i_{dpref}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref1}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qpref}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref2}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dnref}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref1}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qnref}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref1}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

Wherein, i _dpref, i _qpref, i _dnref, i _qnreffor positive sequence d axle component, positive sequence q axle component, negative phase-sequence d axle component, the negative phase-sequence q axle component of reference current, by reference to current value, control is carried out to grid-connected converter and make grid-connected converter safe operation under electric network fault.

What finally illustrate is, above embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although with reference to preferred embodiment to invention has been detailed description, those of ordinary skill in the art is to be understood that, can modify to technical scheme of the present invention or equivalent replacement, and not departing from aim and the scope of technical solution of the present invention, it all should be encompassed in the middle of right of the present invention.

Claims (8)

1. a grid-connected converter safety operating control method under electric network fault, is characterized in that: comprise the steps:

S1. determine the parameter limits value of grid-connected converter safe operation, comprising: active power fluctuation amplitude limits value and phase current limits value;

S2. under rotating coordinate system, setting active power reference value and the reactive power reference qref comprising positive sequence component and negative sequence component, and positive sequence component and the negative sequence component of active power and reactive power is distributed according to parameter limits value, export the reference value of the active power reference value after distributing and reactive power;

S3., under rotating coordinate system, calculate the output current reference value of grid-connected converter according to the active power reference value after distribution and the reactive power reference qref including positive sequence component and negative sequence component, and control grid-connected converter according to current reference value output current.

2. grid-connected converter safety operating control method under electric network fault according to claim 1, is characterized in that: in step S1, according to following steps determination active power fluctuation amplitude limits value and phase current limits value:

S11. according to the power device lowest high-current value I in grid-connected converter _limit1with passive filter lowest high-current value I _limit2determine the maximum current limit value I of grid-connected converter _limit, and have I _limit<min{I _limit1, I _limit2, wherein, power device lowest high-current value I _limit1with passive filter lowest high-current value I _limit2determine according to the specifications and models of power device and passive filter respectively;

S12. the active power limits value △ p of grid-connected converter is determined _limit, wherein, active power limits value △ p _limitdetermine that meritorious power fluctuation limit value is △ p by DC bus-bar voltage maximum _limit1, determine that meritorious power fluctuation limit value is △ p by the lowest high-current value I3rdmax of the triple-frequency harmonics of grid-connected phase current _limit2, and △ p _limit<min{ △ p _limit1, △ p _limit2.

3. grid-connected converter safety operating control method under electric network fault according to claim 2, is characterized in that: in step S2, distributes positive sequence component and the negative sequence component of active power and reactive power according to following steps:

S21. set the positive sequence component of reactive power and negative sequence component and active power by the operating condition of grid-connected converter, wherein, the active power of setting is P _ref, the positive sequence component of the reactive power of setting is Q _pref, negative sequence component is Q _nref;

S22. the three-phase current I in electrical network is obtained _a, I _a, I _c, and determine maximum phase current value I _max1;

If I _max1>I _limit, then grid-connected converter power output positive sequence reactive power Q _pref1with negative phase-sequence reactive power Q _nref1be respectively: $Q_{pref1}=\frac{I_{max1}}{I_{\lim it}}{Q}_{pref},Q_{nref1}=\frac{I_{max1}}{I_{\lim it}}{Q}_{nref};$

The positive sequence component P of the active power that grid-connected converter exports _pref1with negative sequence component P _nref1be respectively:

P _pref1＝0,P _nref1＝0

If I _max1≤ I _limit, then the positive sequence reactive power Q of grid-connected converter output _pref1with negative phase-sequence reactive power Q _nref1be respectively: Q _pref1=Q _pref, Q _nref1=Q _nref;

The positive sequence component P of the active power that grid-connected converter exports _pref1with negative sequence component P _nref1be respectively:

P _pref1=k _poptip _ref, P _nref1=(1-k _popti) P _ref, wherein, k _poptifor active power distribution coefficient;

S23. the active power fluctuation amplitude △ p in electrical network is obtained ₁:

If △ is p ₁> △ p _limit, then the positive sequence reactive power Q of grid-connected converter output _pref2with negative phase-sequence reactive power Q _nref2be respectively:

$Q_{pref2}=\frac{{\mathrm{\&Delta;p}}_{\lim it}}{{\mathrm{\&Delta;p}}_1}{Q}_{pref1},Q_{nref2}=\frac{{\mathrm{\&Delta;p}}_{\lim it}}{{\mathrm{\&Delta;p}}_1}{Q}_{nref1}$

If △ is p ₁≤ △ p _limit, then the positive sequence reactive power Q of grid-connected converter output _pref2with negative phase-sequence reactive power Q _nref2be respectively:

Q _pref2＝Q _pref1,Q _nref2＝Q _nref1。

4. grid-connected converter safety operating control method under electric network fault according to claim 3, is characterized in that: in step S22, three-phase current I _a, I _a, I _cand I _max1obtain according to following formulae discovery:

$I_a=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}}}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})-\frac{2}{3}\mathrm{\&pi;})}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})+\frac{2}{3}\mathrm{\&pi;})}$

I _max1=max{I _a, I _b, I _c, wherein, v _dp, v _qp, v _dn, v _qnbe respectively the positive sequence d axle component of line voltage under rotatable coordinate axis system, positive sequence q axle component, negative phase-sequence d axle component, negative phase-sequence q axle component; i _dp, i _qp, i _dn, i _qnbe respectively the positive sequence d axle component of power network current under rotatable coordinate axis system, positive sequence q axle component, negative phase-sequence d axle component, negative phase-sequence q

Axle component, and obtained by following formulae discovery:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{dn}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$

$i_{qn}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$ , wherein, i _dp, i _qp, i _dn, i _qnfor Q _pref, Q _nref, P _pref=0, P _nrefobtain under the condition of=0.

5. grid-connected converter safety operating control method under electric network fault according to claim 4, is characterized in that: in step S22, active power fluctuation amplitude △ p ₁obtain according to following formula:

${\mathrm{\&Delta;p}}_1=\frac{3}{2}\sqrt{{(v_{qn}{i}_{dp}-v_{dn}{i}_{qp}-v_{qp}{i}_{dn}+v_{dp}{i}_{qn})}^2+{(v_{dp}{i}_{dn}+v_{qp}{i}_{qn}+v_{dn}{i}_{dp}+v_{qn}{i}_{qp})}^2};$

Wherein,

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref})$

$i_{dn}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{pref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{pref});$ Wherein, i _dp, i _qp,

$i_{qn}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref})$

I _dn, i _qnfor Q _pref, Q _nref, P _pref=0, P _nrefobtain under the condition of=0.

6. grid-connected converter safety operating control method under electric network fault according to claim 5, is characterized in that: in step S22, active power distribution coefficient k _poptiobtain in accordance with the following steps:

S221. active power distribution coefficient is defined: P _p=k _pp _ref, P _n=(1-k _p) P _ref, P _pfor the positive sequence component of active power, P _nfor the negative sequence component of active power;

S222. by k _p, P _ref, Q _pref2, Q _nref2substitution following formula obtains:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dn}=\frac{2}{3}\left(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qn}=\frac{2}{3}\left(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

$I_a=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}}}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})-\frac{2}{3}\mathrm{\&pi;})}$

$I_b=\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{qp}\right)}^2+{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2+2\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}cos\left(arccos\right(\frac{i_{dp}{i}_{dn}+i_{qp}{i}_{qn}}{\sqrt{{\left(i_{dp}\right)}^2+{\left(i_{dp}\right)}^2}\sqrt{{\left(i_{dn}\right)}^2+{\left(i_{qn}\right)}^2}})-\frac{2}{3}\mathrm{\&pi;})}$

I _max=max{I _a, I _b, I _c; K is set up according to above-mentioned two formula _pand I _maxfunctional relation, and draw function curve diagram according to this functional relation;

S223. by k _p, P _ref, Q _pref2, Q _nref2substitution following formula obtains:

$i_{dp}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qp}=\frac{2}{3}(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{k}_p{P}_{ref}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{dn}=\frac{2}{3}\left(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qn}=\frac{2}{3}\left(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}\right(1-k_p)P_{ref}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

$\mathrm{\&Delta;}p=\frac{3}{2}\sqrt{{(v_{qn}{i}_{dp}-v_{dn}{i}_{qp}-v_{qp}{i}_{dn}+v_{dp}{i}_{qn})}^2+{(v_{dp}{i}_{dn}+v_{qp}{i}_{qn}+v_{dn}{i}_{dp}+v_{qn}{i}_{qp})}^2}$ ；

K is set up according to above-mentioned two formula _pwith the functional relation of △ p, and draw function curve diagram according to this functional relation;

S224. according to I _max<I _limitconstraints at k _pand I _maxfunction curve on find out satisfactory interval, and be designated as [k _p1, k _p2]; And the point finding out △ p minimum in this interval is designated as (k _popti, △ pmin);

If [k _p1, k _p2] interval in be empty set or △ p _min> △ p _limit,according to the derate step-length of adjustment △ p, repeat step S221 to step 224, until [k _p1, k _p2] be not empty set, and △ p _min≤ △ p _limit.

7. grid-connected converter safety operating control method under electric network fault according to claim 6, is characterized in that: according to the Q determined in step S2 _pref2, Q _nref2, P _pref1, P _nref1, by following formulae discovery current reference value:

$i_{dpref}=\frac{2}{3}(\frac{v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref1}+\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2})$

$i_{qpref}=\frac{2}{3}\left(\frac{v_{qp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{P}_{pref2}+\frac{-v_{dp}}{{\left(v_{dp}\right)}^2+{\left(v_{qp}\right)}^2}{Q}_{pref2}\right)$

$i_{dnref}=\frac{2}{3}(\frac{v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref1}+\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2});$

$i_{qnref}=\frac{2}{3}(\frac{v_{qn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{P}_{nref1}+\frac{-v_{dn}}{{\left(v_{dn}\right)}^2+{\left(v_{qn}\right)}^2}{Q}_{nref2})$

Wherein, i _dpref, i _qpref, i _dnref, i _qnreffor positive sequence d axle component, positive sequence q axle component, negative phase-sequence d axle component, the negative phase-sequence q axle component of reference current, by reference to current value, control is carried out to grid-connected converter and make grid-connected converter safe operation under electric network fault.

8. grid-connected converter safety operating control method under electric network fault according to claim 2, is characterized in that: active power fluctuation limits value is △ p _limit1be △ p with active power fluctuation limits value _limit2by following formulae discovery: △ p _limit1=<V _dc>2 ω C _dc(V _max-<V _dc>) ${\mathrm{\&Delta;p}}_{\lim it2}=\frac{4I_{3rdmax}\&CenterDot;<V_{dc}>2{\mathrm{\&omega;C}}_{dc}{X}_L}{m};$ Wherein, V _maxfor the DC bus-bar voltage maximum of setting, <V _dc> is DC bus-bar voltage mean value, C _dcfor dc-link capacitance capacity, I _3rdmaxfor the maximum of triple-frequency harmonics in grid-connected phase current, X _lfor electrical network induction reactance value, m is inverter modulation degree, and ω is line voltage angular frequency.