CN103825300B - A kind of line voltage phase-lock technique passed through for photovoltaic combining inverter no-voltage - Google Patents

Abstract

A kind of line voltage phase-lock technique passed through for photovoltaic combining inverter no-voltage.The invention discloses a kind of photovoltaic combining inverter no-voltage traversing control method.The method comprises the line voltage phase-lock technique of photovoltaic combining inverter in no-voltage crossing process, Active Current Control of Varying and reactive current control method.Described phase-lock technique can for Current Control provides phase place in no-voltage crossing process.The active current that the present invention can make inverter carry to electrical network carries out automatic amplitude limit in grid voltage sags process, and after line voltage recovers fast quick-recovery, possess the degree reduced according to grid voltage amplitude sends ability from reactive current to electrical network simultaneously.

Description

A kind of line voltage phase-lock technique passed through for photovoltaic combining inverter no-voltage

Technical field

The invention belongs to three-phase grid-connected inverter control technology field.

Background technology

When power system accident or disturbance cause line voltage significantly to fall, the unexpected off-grid of photovoltaic plant can worsen the running status of whole electrical network further, the power shortage caused during this period may cause adjacent power station tripping operation, thus causes more large-area power failure.For this reason, there has been proposed photovoltaic plant and must possess the requirement that no-voltage passes through function, it refers to when grid voltage sags even directly drops into zero because of system short-circuit, photovoltaic generating system still can ensure that off-grid does not run continuously, and provide certain reactive power to return to normal level to support faulty grids, thus pass through this region of no-voltage.

Along with the continuous increase of photovoltaic plant capacity, no-voltage passes through the problem becoming current photovoltaic plant and need solve, no-voltage ride-through capability is also considered to one of ultimate challenge in photovoltaic DC-to-AC converter control technology, is directly connected to the large-scale application of photovoltaic generation.Its difficult point is mainly reflected in three aspects: first, photovoltaic DC-to-AC converter can be analyzed to active current and reactive current component to the electric current that electrical network sends, wherein active current and line voltage same-phase, and reactive current component lag or lead line voltage 90 degree.For effectively sending meritorious or reactive power to electrical network, must carry out phase-locked to line voltage.If adopt common phase-lock mode, such as catch the zero crossing of line voltage or directly calculate the phase place etc. of line voltage with the component under two-phase rest frame, when line voltage is normal, electric network voltage phase can be followed the tracks of, but when grid voltage sags to zero, just cannot obtain for electric network voltage phase, cause inverter out of control and off-grid.Second, period is passed through in no-voltage, due to the reduction of line voltage, the power be input on electrical network also reduces suddenly, the power outputted to from DC capacitor battle array electrical network is greater than from the photovoltaic pond plate power be transported in DC capacitor battle array, thus DC capacitor voltage can be raised, no-voltage pass through before power-balance be broken, need to set up new power-balance in no-voltage crossing process, this power-balance has come by the active current controlled in output current, for this reason, in no-voltage crossing process, reasonably need carry out the adjustment of active current.3rd, effectively can improve line voltage owing to sending reactive current to electrical network, therefore when line voltage reduces, inverter needs as much as possible to send reactive current to electrical network.

Traditional three-phase voltage phase-lock technique, often through three-phase to two-phase coordinate transform, obtains two orthogonal phase voltages, then calculates phase place or obtains phase place by closed loop phase lock ring.The shortcoming of this kind of traditional locks phase method is: 1), and when line voltage occurs that imbalance is fallen, the voltage signal under two phase coordinate systems is no longer orthogonal, directly calculates phase place and Current Control can be made also uneven; 2), when grid voltage sags to zero, phase place cannot be calculated or obtain phase place by closed loop phase lock ring.

Summary of the invention

For solving above technical problem, the invention provides a kind of photovoltaic combining inverter no-voltage traversing control method, photovoltaic combining inverter is line voltage self adaptation phase-lock technique in no-voltage crossing process.

Technical solution of the present invention is as follows:

A kind of line voltage phase-lock technique passed through for photovoltaic combining inverter no-voltage, it is characterized in that: comprise two closed loop band pass filters, each band pass filter has a closed loop coefficient, this coefficient fall degree of depth different according to line voltage adjusts automatically, and when line voltage reduces, closed loop coefficient reduces, be equivalent to filtering bandwidth reduce, filtering output attenuatoin is slack-off, when actual electric network voltage attenuation to zero time, filtering export and a period of time can be maintained; When line voltage recovers, closed loop coefficient increases, and be equivalent to filtering bandwidth and become large, filtering exports and increases rapidly, follows the tracks of upper electric network voltage phase very soon.

Improve as one, the transfer function expression formula that described band pass filter exports for input is:

$\frac{e_{\mathrm{\α}1}}{e_{\mathrm{\α}}}=\frac{e_{\mathrm{\β}2}}{e_{\mathrm{\β}}}=\frac{\mathrm{\αws}}{s^2\mathrm{\αws}+w^2},\frac{e_{\mathrm{\β}1}}{e_{\mathrm{\α}}}=\frac{e_{\mathrm{\α}2}}{e_{\mathrm{\β}}}=\frac{{\mathrm{\αw}}^2}{s^2+\mathrm{\αws}+w^2}---\left(1\right)$

Wherein w is the centre frequency of band pass filter, gets the angular frequency of line voltage here; Factor alpha reflects the bandwidth of this band pass filter, and α is larger, and bandwidth is larger, and α is less, and bandwidth is less, and the bandwidth of this band pass filter by regulating the value of α and self adaptation dynamic conditioning, can be got here wherein E _gfor the mean value E using moving average filter to obtain the effective value of three-phase power grid voltage _g, and for specified line voltage.Line voltage is when rated value, and α is larger, i.e. α=1; When grid voltage sags, α diminishes, and filtering bandwidth diminishes, and filtering output attenuatoin obtains very slow; When line voltage recovers suddenly, α becomes large, and filtering exports rises very fast, can catch up with actual line voltage very soon.

Improve as one, include following steps:

(1) by three-phase power grid voltage e _a, e _b, e _ce is obtained to the conversion of two-phase rest frame through three-phase static coordinate system _α, e _β.

(2) to voltage signal e under two-phase static coordinate _α, e _βcarry out bandpass filtering;

(3) positive sequence component is calculated, the positive sequence component of α axle with the positive sequence component of β axle calculating formula is:

$e_{\mathrm{\α}}^P=\frac{e_{\mathrm{\α}1}+e_{\mathrm{\α}2}}{2},e_{\mathrm{\β}}^P=\frac{e_{\mathrm{\β}1}+e_{\mathrm{\β}2}}{2}$

(4) the phase angle cosine value cos θ of electrical network positive sequence voltage is calculated, and sine value sin θ:

$\cos \mathrm{\θ}=\frac{e_{\mathrm{\α}}^P}{\sqrt{e_{\mathrm{\α}}^P+e_{\mathrm{\β}}^P}},\sin \mathrm{\θ}=\frac{e_{\mathrm{\β}}^P\left(n\right)}{\sqrt{e_{\mathrm{\α}}^P+e_{\mathrm{\β}}^P}}---\left(3\right)$

(5) cosine value and sine value is utilized just can to complete the rotation transformation of closed-loop current control needs.

Improve as one, whether the ratio of the mean value and line voltage rated value that it is characterized in that the three-phase power grid voltage effective value using moving average filter to obtain is less than 0.9 as judging the foundation whether line voltage falls; When detecting that line voltage does not fall, the PI Output rusults of direct current pressure ring is given as active current, when detecting that line voltage falls, to the PI output violent change of direct current pressure ring, amplitude limit value is that rated current is multiplied by Voltage Drop coefficient, then it is given that the PI output after amplitude limit is assigned to active current; When detecting that line voltage recovers, the PI of direct current pressure ring exports to be increased again automatically gradually, makes that active current is given returns to the value before falling.

Improve as one, given according to the mean value calculation reactive current of the three-phase power grid voltage effective value using moving average filter to obtain, under normal circumstances, line voltage is greater than 0.9 times of rated voltage, reactive current is given is set to zero, namely keeps inverter output current and line voltage with frequency homophase; When line voltage is between the rated voltage of 0.2 times and 0.9 times of rated voltage, line voltage lower transmission reactive current is more, and reactive current increases linearly with the reduction of line voltage; When line voltage is lower than 0.2 times of rated voltage, send the maximum reactive current of bearing of inverter to electrical network.

The adaptive phase locked loop that the present invention proposes can make up these two shortcomings of traditional locks phase method.1), no matter whether line voltage balances, it always obtains the fundametal compoment of A phase voltage in positive sequence voltage, and obtain the orthogonal signalling of delayed A phase fundametal compoment simultaneously, equal by this group amplitude, the signal that phase place mutual deviation is 90 degree, as the basis of given value of current, can remain that given value of current is balance; 2), during grid voltage sags to 0%, adaptive phase locked loop still can pass through in no-voltage the fundametal compoment that period remains output voltage by self-adjusting straps is wide.

Accompanying drawing explanation

Fig. 1 three-phase photovoltaic grid connected inverter system.

Fig. 2 no-voltage traversing control method theory diagram.

The specific implementation block diagram of Fig. 3 adaptive phase locked loop.

The program flow diagram of Fig. 4 active power regulation method.

The program flow diagram of Fig. 5 method for controlling reactive power.

Current Control design sketch when Fig. 6 electrical network ABC three-phase voltage drops to 0% simultaneously.

Current Control design sketch during Fig. 7 electrical network AB line Voltage Drop to 20%.

Embodiment

The present invention's self adaptation phase-lock technique used as shown in Figure 3.Input signal e in figure _α, e _βfor voltage signal under two-phase static coordinate, it is by three-phase power grid voltage e _a, e _b, e _cconvert to two-phase rest frame through three-phase static coordinate system.

First step in Fig. 3 is to voltage signal e under two-phase static coordinate _α, e _βcarry out bandpass filtering.Two closed loop band pass filter outputs for the transfer function expression formula inputted are:

$\frac{e_{\mathrm{\α}1}}{e_{\mathrm{\α}}}=\frac{e_{\mathrm{\β}2}}{e_{\mathrm{\β}}}=\frac{\mathrm{\αws}}{s^2\mathrm{\αws}+w^2},\frac{e_{\mathrm{\β}1}}{e_{\mathrm{\α}}}=\frac{e_{\mathrm{\α}2}}{e_{\mathrm{\β}}}=\frac{{\mathrm{\αw}}^2}{s^2+\mathrm{\αws}+w^2}---\left(1\right)$

Wherein w is the centre frequency of band pass filter, gets the angular frequency of line voltage here; Factor alpha reflects the bandwidth of this band pass filter, and α is larger, and bandwidth is larger, and α is less, and bandwidth is less, and the bandwidth of this band pass filter is can by regulating the value of α and self adaptation dynamic conditioning.Here get wherein E _gfor the mean value E using moving average filter to obtain the effective value of three-phase power grid voltage _g, and E _gNfor specified line voltage.Line voltage is when rated value, and α is larger, i.e. α=1.When grid voltage sags, α diminishes, and filtering bandwidth diminishes, and filtering output attenuatoin obtains very slow; When line voltage recovers suddenly, α becomes large, and filtering exports rises very fast, can catch up with actual line voltage very soon.As can be seen from transfer function, when filtering output reaches stable state, the output e of first closed loop _{α 1}with line voltage e _αsame-phase, another of first closed loop exports e _{β 1}delayed line voltage e _α90 degree, phase place, the output e of second closed loop _{β 2}with line voltage e _βsame-phase, another of second closed loop exports e _{α 2}delayed line voltage e _β90 degree, phase place.The basic role of these two band pass filters has: 1), the harmonic wave of filtering line voltage and only get the first-harmonic of line voltage; 2) utilize the feature that filtering output attenuatoin is slower, for grid voltage sags to zero time phase-locked required signal is provided; 3) component exporting phase shift 90 degree is in order to next step calculates positive sequence component.

Another step in Fig. 3 calculates positive sequence component.The object calculating positive sequence component is the situation making phase-lock technique be adapted to imbalance of three-phase voltage, such as during electrical network generation unbalanced fault, the α axle component of line voltage and the amplitude of beta-axis component are different, with the phase place that it calculates be fluctuation, be unfavorable for controlling, be therefore necessary to calculate positive sequence component.According to the positive-negative sequence separation theorem under two-phase rest frame, known, the positive sequence component of α axle with the positive sequence component of β axle calculating formula is::

$e_{\mathrm{\α}}^P=\frac{e_{\mathrm{\α}1}+e_{\mathrm{\α}2}}{2},e_{\mathrm{\β}}^P=\frac{e_{\mathrm{\β}1}+e_{\mathrm{\β}2}}{2}---\left(2\right)$

Positive sequence component can calculate the phase place of line voltage positive sequence thus, and its phase place is more stable.

Last step in Fig. 3 is the phase angle cosine value cos θ calculating electrical network positive sequence voltage, and sine value sin θ:

$\cos \mathrm{\θ}=\frac{e_{\mathrm{\α}}^P}{\sqrt{e_{\mathrm{\α}}^P+e_{\mathrm{\β}}^P}},\sin \mathrm{\θ}=\frac{e_{\mathrm{\β}}^P\left(n\right)}{\sqrt{e_{\mathrm{\α}}^P+e_{\mathrm{\β}}^P}}---\left(3\right)$

Have this cosine value and sine value just can complete the rotation transformation of closed-loop current control needs, namely line voltage is phase-locked completes.

2, active power regulation method

Photovoltaic grid-connected inverting system, as shown in Figure 1, when not considering the device loss such as IGBT switch and reactor, should meet following power balance equation:

$P_e-P_g=\frac{d\left(\frac{1}{2}{\mathrm{Cu}}_{\mathrm{dc}}^2\right)}{\mathrm{dt}}---\left(4\right)$

Wherein P _efor photovoltaic battery panel power output, P _gfor the grid-connected power P of photovoltaic DC-to-AC converter _g, for the energy on DC capacitor.The P when stable state _e=P _g, when photovoltaic pond plate is in stable electric generation state, DC bus-bar voltage is also stablized.When line voltage falls, grid-connected power output P _gto reduce, instant of failure photovoltaic battery panel exports constant, and the input of whole electricity generation system, the power-balance relation of output will be broken, and produces imbalance power Δ P=P _e-P _g, imbalance power Δ P will cause DC bus-bar voltage u _dcrise.Due to the output characteristic of photovoltaic battery panel, DC voltage rises, and the output current of photovoltaic cell group can be caused to decline.If the active current now to electrical network conveying is stable, so as DC bus-bar voltage u _dcwhen being elevated to a certain degree, photovoltaic pond plate is transported to power on DC capacitor, and less to just in time equaling output AC power, now direct voltage no longer increases, and power-balance re-establishes.Therefore, the key of no-voltage crossing process power-balance is the control of active current.

As can be seen from Fig. 2 (e), due under normal voltage, the output of maximal power tracing (MPPT) is given as direct voltage, this given variation per second 1 time, each variation step-length 1 is to 2V, and therefore in no-voltage crossing process, this is given is substantially constant.The given of active current is by the proportional integral of direct current pressure ring (PI) Output rusults, suddenly fall at voltage and be, direct voltage rises, but direct voltage is given constant, therefore the PI of direct current pressure ring exports and can become suddenly large, now, amplitude limit must be carried out, otherwise the given too senior general of active current makes inverter overcurrent and off-grid, and fall period due to no-voltage and require that inverter provides reactive power to recover in order to support line voltage, the electric current mainly idle component exported, therefore can reduce active current set-point thus reserve current margins in order to export reactive current thus control inverter not overcurrent.

Active current regulates as shown in Figure 4, and its main process is as follows:

With Voltage Drop coefficient whether be less than 0.9 as judging the foundation whether line voltage falls.When detecting that line voltage does not fall, the PI Output rusults of direct current pressure ring is given as active current, when detecting that line voltage falls, to the PI output violent change of direct current pressure ring, amplitude limit value is that rated current is multiplied by Voltage Drop coefficient, then it is given that the PI output after amplitude limit is assigned to active current.When detecting that line voltage recovers, the PI of direct current pressure ring exports to be increased again automatically gradually, makes that active current is given returns to the value before falling.

Method for controlling reactive power

During grid voltage sags, photovoltaic plant not only needs to keep and net state, and preferably dynamically can send reactive power to support line voltage.Method for controlling reactive power flow process as shown in Figure 5.

According to the formula of line voltage mean effective value calculating reactive current set-point be wherein:

$\left\{\begin{array}{cc}{i}_q^{*}=0& (E_g>0.9*E_{g^N})\\ i_q^{*}=1.5*(0.9-\frac{E_g}{E_{g^N}})*I_N& (0.2*E_{g^N}<E_g<0.9*E_{g^N})\\ i_q^{*}=1.05*I_N& (E_g<0.2*E_{g^N})\end{array}\right.$

I in formula _nfor photovoltaic DC-to-AC converter exports rated current.Here suppose that inverter overload capacity is 5%.Under normal circumstances, line voltage is greater than 0.9 times of rated voltage, i.e. E _g>0.9*E _gN, reactive current is given is set to zero, namely keeps inverter output current and line voltage with frequency homophase.When line voltage is between the rated voltage of 0.2 times and 0.9 times of rated voltage, line voltage lower transmission reactive current is more.When line voltage is lower than 0.2 times of rated voltage, send the reactive current of 1.05 times of rated current to electrical network, if overload capacity is better, idlely can send out more.

Active power regulation and reactive power regulating effect

Control algolithm of the present invention is applied on the photovoltaic combining inverter of rated voltage 270V, rated current 1070A, rated power 500kw, and the electrical network symmetry obtained and unbalanced fault Current Control effect are as shown in figure 5 and figure 7., uppermost passage is alternating voltage in figure from top to bottom, and second passage is direct voltage, and third and fourth passage is AB biphase current.

Composition graphs 6, illustrates that the effect of this algorithm has: 1) grid voltage sags is during zero, and electric current is still sinusoidal wave, and the electric network voltage phase demonstrated now exports still to be stablized; 2) in the one-period that line voltage has just fallen, current phase changes, active current before falling is switched to reactive current, and the size of reactive current is about the rated current of 1.05 times, and inverter maximum possible is that electrical network have sent reactive current to the greatest extent; 3) when line voltage recovers, reactive current diminishes, and active current starts to increase, and less than just returning to the value before falling in the time of 1 second, resume speed is satisfactory; 4) in grid voltage sags process, direct voltage first increases to certain value and settles out, and after line voltage recovers, direct voltage gets back to again the value before falling, and the power-balance demonstrated in photovoltaic inverting system is keep all the time.

Composition graphs 7, it can also be seen that algorithm runs when asymmetric falling occurs electrical network with still can keeping current balance type, maintains the stable of whole system.

1, circuit topology

The hardware objects that the present invention is based on is three-phase grid-connected inverting system, and as shown in Figure 1, in figure, Far Left is photovoltaic (PV) cell panel to its circuit topology, it is connected with the DC capacitor of inverter, on DC capacitor, direct current voltage sensor is housed, for detecting direct voltage u _dc.Three-phase inverter often has a brachium pontis mutually, and the bridge up and down of each brachium pontis is made up of IGBT and antiparallel diode.The mid point of each brachium pontis connects the ABC three-phase of AC reactor respectively, every through LC filter circuit, is connected to electrical network.Often mutually current sensor is housed, detects inverter ABC three-phase output current i respectively _a, i _b, i _c.Every phase is also equipped with voltage sensor, detects three-phase power grid voltage e respectively _a, e _b, e _c.In figure, nethermost control module adopts conventional SVPWM modulation algorithm to calculate the driving duty ratio ρ of device for power switching _a, ρ _b, ρ _c, modulate three-phase voltage u in order to driving power switching device _a, u _b, u _c.

2, no-voltage passes through the specific implementation step of control

The control method specific implementation step that the no-voltage of indication of the present invention is passed through can illustrate by composition graphs 2 as follows.

The first step: calculate line voltage mean effective value, as Fig. 2 (a).Moving average filter is first used to obtain the effective value E of three-phase power grid voltage _a, E _b, E _c.In order to ensure the real-time to network voltage detection, in program, 100us calls a moving average filter.The line voltage cycle is 20ms, and therefore the sampling number of moving average is 200.Then the mean value E of line voltage effective value is calculated _g,

Second step: line voltage is phase-locked, as Fig. 2 (b) and Fig. 3.First, electrical network three-phase voltage is first transformed into two-phase rest frame from three-phase static coordinate system, transformed representation is: $\left[\begin{array}{c}{e}_{\mathrm{\&alpha;}}\\ e_{\mathrm{\&beta;}}\end{array}\right]\begin{array}{c}=\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]*\left[\begin{array}{c}{e}_a\\ e_b\\ e_c\end{array}\right];\end{array}$ Then, according to the E that the first step calculates _g, press determine closed-loop control coefficient; Again according to Fig. 3, calculate the phase angle cosine value cos θ of electrical network positive sequence voltage by formula (2) and formula (3), sine value sin θ.

3rd step: rotation transformation, as Fig. 2 (c) and (d).The line voltage of two-phase rest frame is transformed into dq rotating coordinate system, and transformed representation is: $\left[\begin{array}{c}{e}_d\\ e_q\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\&theta;}& \sin \mathrm{\&theta;}\\ \sin \mathrm{\&theta;}& -\cos \end{array}\right]*\left[\begin{array}{c}{e}_{\mathrm{\&alpha;}}\\ e_{\mathrm{\&beta;}}\end{array}\right];$ Meanwhile, inverter output current is first transformed into two-phase rest frame from three-phase static coordinate system, and transformed representation is:

$\left[\begin{array}{c}{i}_{\mathrm{\&alpha;}}\\ i_{\mathrm{\&beta;}}\end{array}\right]\begin{array}{c}=\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]*\left[\begin{array}{c}{i}_a\\ i_b\\ i_c\end{array}\right],\end{array}$ Carry out the conversion that two-phase static coordinate is tied to dq rotating coordinate system again, transformed representation is: $\left[\begin{array}{c}{i}_d\\ i_q\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\&theta;}& \sin \mathrm{\&theta;}\\ \sin \mathrm{\&theta;}& -\cos \end{array}\right]*\left[\begin{array}{c}{i}_{\mathrm{\&alpha;}}\\ i_{\mathrm{\&beta;}}\end{array}\right].$

4th step: the given calculating of active current, as shown in Fig. 2 (e) He Fig. 4.First, realize MPPT maximum power point tracking in Fig. 2 (e) and control (MPPT), control algolithm adopts common disturbance observation method, and judge that the condition at maximum power point place disturbs the power that moves a step about voltage no longer to increase, the output of MPPT is given as direct voltage .Secondly, given to direct voltage u is fed back with direct voltage _dcdifference, carry out PI control.Again, according to Voltage Drop coefficient whether be less than 0.9 judgement line voltage whether to fall, when detecting that line voltage does not fall, the PI Output rusults of direct current pressure ring is given as active current, when detecting that line voltage falls, the PI of direct current pressure ring exports and is multiplied by Voltage Drop coefficient, then it is given to be assigned to active current.

5th step: the given calculating of reactive current, as shown in Figure 5.The given size of reactive current calculates by formula (5).

6th step: the closed-loop control of active current and reactive current, as Fig. 2 (e).The active current obtained the 4th step is given the active current obtained with the 3rd step feeds back i _ddifference carry out PI control.The voltage feed-forward control d axle component e that PI Output rusults and the 3rd step obtain _d, decoupling zero item wLi _qaddition obtains the d axle modulation voltage u under dq rotating coordinate system _d.Meanwhile, given to the reactive current of the 5th step calculating the reactive current calculated with the 3rd step feeds back i _qdifference also carry out PI control, the voltage feed-forward control item q axle component e that PI Output rusults and the 3rd step obtain _q, decoupling zero item-wLi _daddition obtains the q axle modulation voltage u under dq rotating coordinate system _q.U _d, u _qthe conversion being tied to two-phase rest frame through dq rotational coordinates obtains the modulation voltage u under two-phase rest frame _α, u _β, the driving duty ratio ρ of device for power switching is calculated finally by common SVPWM modulation algorithm _a, ρ _b, ρ _c.

Claims (3)

1. the line voltage phase-lock technique passed through for photovoltaic combining inverter no-voltage, it is characterized in that: comprise two closed loop band pass filters, each band pass filter has a closed loop coefficient, this coefficient fall degree of depth different according to line voltage adjusts automatically, and when line voltage reduces, closed loop coefficient reduces, be equivalent to filtering bandwidth reduce, filtering output attenuatoin is slack-off, when actual electric network voltage attenuation to zero time, filtering export and a period of time can be maintained; When line voltage recovers, closed loop coefficient increases, and be equivalent to filtering bandwidth and become large, filtering exports and increases rapidly, follows the tracks of upper electric network voltage phase very soon; The transfer function expression formula that described band pass filter exports for input is:

Wherein e _αfor α shaft voltage under two-phase rest frame, e _βfor β shaft voltage under two-phase rest frame; e _{α 1}for e _αexport and e through first band pass filter _αsynchronous voltage, e _{α 2}for e _βthrough second band pass filter lag output e _βthe voltage that phase place is 90 degree; e _{β 1}for e _αthrough first band pass filter lag output e _αthe voltage that phase place is 90 degree, e _{β 2}for e _βexport and e through second band pass filter _βsynchronous voltage; Wherein w is the centre frequency of band pass filter, gets the angular frequency of line voltage here; Factor alpha reflects the bandwidth of this band pass filter, and α is larger, and bandwidth is larger, and α is less, and bandwidth is less, and the bandwidth of this band pass filter by regulating the value of α and self adaptation dynamic conditioning, can be got here wherein Eg is the mean value Eg using moving average filter to obtain the effective value of three-phase power grid voltage, and EgN is specified line voltage, and line voltage is when rated value, and α is larger, i.e. α=1; When grid voltage sags, α diminishes, and filtering bandwidth diminishes, and filtering output attenuatoin obtains very slow; When line voltage recovers suddenly, α becomes large, and filtering exports rises very fast, can catch up with actual line voltage very soon;

Also include following steps:

(1) three-phase power grid voltage ea, eb, ec are obtained e α, e β through three-phase static coordinate system to the conversion of two-phase rest frame;

(2) to voltage signal e α under two-phase static coordinate, e β carries out bandpass filtering;

(3) positive sequence component is calculated, the positive sequence component of α axle with the positive sequence component of β axle calculating formula is:

(4) the phase angle cosine value cos θ of electrical network positive sequence voltage is calculated, and sine value sin θ:

(5) cosine value and sine value is utilized just can to complete the rotation transformation of closed-loop current control needs.

2. the described line voltage phase-lock technique passed through for photovoltaic combining inverter no-voltage according to claim 1, whether the ratio of the mean value and line voltage rated value that it is characterized in that the three-phase power grid voltage effective value using moving average filter to obtain is less than 0.9 as judging the foundation whether line voltage falls; When detecting that line voltage does not fall, the PI Output rusults of direct current pressure ring is given as active current, when detecting that line voltage falls, to the PI output violent change of direct current pressure ring, amplitude limit value is that rated current is multiplied by Voltage Drop coefficient, then it is given that the PI output after amplitude limit is assigned to active current; When detecting that line voltage recovers, the PI of direct current pressure ring exports to be increased again automatically gradually, makes that active current is given returns to the value before falling.

3. the described line voltage phase-lock technique passed through for photovoltaic combining inverter no-voltage according to claim 2, it is characterized in that according to the mean value calculation reactive current of the three-phase power grid voltage effective value using moving average filter to obtain given, under normal circumstances, line voltage is greater than 0.9 times of rated voltage, reactive current is given is set to zero, namely keeps inverter output current and line voltage with frequency homophase; When line voltage is between the rated voltage of 0.2 times and 0.9 times of rated voltage, line voltage lower transmission reactive current is more, and reactive current increases linearly with the reduction of line voltage; When line voltage is lower than 0.2 times of rated voltage, send the maximum reactive current of bearing of inverter to electrical network.