CN103954863A - Three-phase grid-connected inverter anti-islanding detection method - Google Patents

Abstract

The invention discloses a three-phase grid-connected inverter anti-islanding detection method. By setting a relation characteristic curve between the frequency of reactive current and the frequency of power grid side voltage, reactive current disturbance is superposed on a current inner ring set value to obtain a new inner ring reactive current set value, and the advantages that influences on the electric energy quality are small, the island detection time is short, the disturbance direction is self-adaptive, and the slope of the disturbance equation is self-adaptive are achieved. According to specific configuration, the corresponding disturbance quantity is calculated by a disturbance rule calculating module, then, the corresponding disturbance quantity is superposed on the reactive current inner ring set value, and therefore island detection of a three-phase grid-connected inverter based on a power grid side feedback current and power grid side voltage frequency characteristic curve can be achieved, and the grid-connected inverter meets the national standard grid connection requirement of inverters.

Description

A kind of detection method of three-phase grid-connected inverter isolated island effect prevention

Technical field

The invention belongs to inverter technology field, more specifically say, relate to a kind of detection method of three-phase grid-connected inverter isolated island effect prevention.

Background technology

When island effect refers to grid-connected inverters operation, due to the intentional or unintentional main electric network power-fail keeping in repair or equipment failure causes, invertor operation makes the part circuit in grid power blackout region still maintain electriferous state and powers to the load continuation of power supply interrupted district, forms by the independently-powered isolated island of distributed power source.If inverter can not be shut down in time still to continue to power to the load and can be produced following serious consequence in this case:

(1), the circuit that is connected with inversion system after occurring of isolated island is still charged, and maintainer is caused to danger, reduces the security of electrical network;

(2), common point voltage magnitude and frequency be not subject to power grid control, if voltage magnitude and frequency exceed the scope of permission, may cause damage to user's equipment;

(3) if, when mains supply recovers, the phase place of line voltage and common point voltage is asynchronous, during combined floodgate, can cause line short, causes the collapse of electrical network when serious.

Therefore, no matter be from security, or the consideration of reliability aspect, combining inverter all should possess the ability that prevents that isolated island from producing.In view of these reasons, country has formulated corresponding standard, requires grid-connected distributed generation system to have isolated island effect prevention defencive function, must detect in time isolated island, and combining inverter and public electric wire net are disconnected.Isolated island effect prevention guard method based on inverter side is divided into passive type and active, and passive type method judges by detecting the information of voltage (as voltage magnitude, frequency, electric current and voltage phase differential) of inverter ac output end whether isolated island occurs conventionally.But when inverter output power and load consumption power match; the information of voltage of the rear grid side of isolated island generation changes very little, cannot reach passive protection threshold value, and passive type isolated island detects and loses protective effect; therefore in order to detect reliably isolated island, whether occur, must adopt active method.Active method is by injecting disturbance to electrical network wittingly, by detecting the variable change such as voltage magnitude, frequency of grid-connected inverters point, judges whether isolated island occurs.Conventional active isolated island effect prevention detection method has: Active frequency drift method (AFD), active phase-shifting method (SMS), Harmonic Injection Method (HJ), power disturbance method etc.There is following main problem at present existing active isolated island effect prevention detection method: 1) most active isolated island effect prevention detection method (as active frequency shift method, variation method, Harmonic Injection Method) needs constantly to electrical network, to inject undesired signal, has affected the inverter quality of power supply; 2) disturbance adding mostly is fixedly disturbance, can not automatically regulate disturbance size according to the variable quantity of aim parameter; 3) some active anti-isolated island methods can be because of the inconsistent generation dilution effect of perturbation direction when multi-inverter parallel, and disturbance is cancelled out each other and caused isolated island to detect inefficacy; 4) some active isolated island effect prevention detection methods have good detection effect in single-phase inverter, but and the anti-isolated island that is not suitable for three-phase inverter detect.

Summary of the invention

The object of the invention is to overcome the deficiencies in the prior art, a kind of detection method of three-phase grid-connected inverter isolated island effect prevention is provided, by encircle the reactive current disturbance that superposes on set-point in reactive current, the isolated island effect prevention of realizing three-phase grid-connected inverter detects, and has that quality of power supply impact is little, isolated island detection time is fast, perturbation direction self-adaptation, the adaptive advantage of perturbation equation slope.

For achieving the above object, the isolated island effect prevention detection method of a kind of three-phase grid-connected inverter of the present invention, is characterized in that, comprises the following steps:

(1), gather voltage, current signal and the DC voltage signal of grid side; The outside AD sampling A/D chip of high precision by combining inverter middle controller gathers the voltage signal of voltage, current signal and the DC side of grid side, and the grid side voltage of collection, current signal and DC voltage signal are transferred in digital signal processor DSP;

(2), digital signal processor DSP by the voltage receiving, current signal for control algolithm computing;

(2.1), by electrical network three-phase voltage V _a, V _band V _cby two synchronous coordinate system decoupling zero phaselocked loops (DDSRF-PLL) module, carry out clark, park conversion and obtain grid side magnitude of voltage V under synchronous rotating frame _d, V _q, and the frequency f of grid side voltage and phase angle theta; Simultaneously by clark, _park conversion, by the grid side current i gathering _a, i _band i _cfrom abc three phase static coordinate system transformation to dq synchronous rotating frame, obtain grid side feedback current value i _qand i _d;

By the grid side magnitude of voltage V calculating _d, V _q, and the power given command signal P of three-phase grid-connected inverter ^*and Q ^*be input to power outer shroud control module, calculate respectively ring set-point in reactive current with

The frequency f of the grid side voltage calculating is sent to disturbance rule computing module, by disturbance rule computing module, calculates reactive current disturbance quantity i' _q, and the phase angle theta of grid side voltage is sent to dq synchronous rotating frame, for the coordinate transform of next control cycle;

(2.2) the grid side electric voltage frequency f, obtaining according to DDSRF-PLL module judges whether island effect occurs;

If a) frequency f of grid side voltage, not within the scope of the normal frequency of the grid-connected standard regulation of three-phase grid-connected inverter, is judged as island effect and occurs, stop the operation of three-phase grid-connected inverter;

B) if within the scope of the normal frequency that the frequency f of grid side voltage is stipulated in the grid-connected standard of three-phase grid-connected inverter, the reactive current disturbance quantity i' disturbance rule computing module being calculated _qring set-point in the reactive current that is added to the interior ring of the reactive current set-point that upper conduct is new, enters step (2.3);

(2.3), set-point will be encircled in reactive current value of feedback i with the grid side electric current obtaining _ddiffer from, and encircle set-point and grid side feedback current value i in new reactive current _qdo to be input to interior circular current control module after difference, by obtaining command voltage V after anti-park conversion simultaneously _α, V _β;

(2.4), by the command voltage V obtaining in step (2.3) _α, V _βwith DC voltage-stabilizing capacitive side voltage V _dcjointly be sent to SVPWM space vector PWM modulation module, produce 6 road pulse-width modulation PWM signals and control opening and turn-offing of power switch pipe in inversion unit; After finishing, current control cycle returns to step (1).

Further, the present invention also provides a kind of disturbance rule computing module to calculate reactive current disturbance quantity i' _qmethod be:

After island effect occurs, meritorious, the reactive power of load are provided by inverter completely, and inverter output power can be expressed from the next:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}\frac{U_p^2}{R}\\ U_p^2(\frac{1}{\mathrm{\ωL}}-\mathrm{\ωC})\end{array}\right]---\left(1\right)$

By above formula, can be released:

$\mathrm{\ω}=\frac{1}{\sqrt{\mathrm{LC}}}(1-\frac{Q}{{2\mathrm{PQ}}_f})---\left(2\right)$

Wherein: U _peffective value for grid side voltage; R, L, C are respectively equivalent resistance, the inductance of load, the value of electric capacity; ω is the angular frequency of grid side voltage; According to the definition of loaded quality factor under synchronous rotating frame, inverter output power is expressed as follows:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}{V}_{\mathrm{\α}}{i}_{\mathrm{\α}}+V_{\mathrm{\β}}{i}_{\mathrm{\β}}\\ V_{\mathrm{\β}}{i}_{\mathrm{\α}}+V_{\mathrm{\α}}{i}_{\mathrm{\β}}\end{array}\right]=\left[\begin{array}{c}\frac{3}{2}(V_d{i}_d+V_q{i}_q)\\ \frac{3}{2}(V_d{i}_q+V_q{i}_d)\end{array}\right]---\left(3\right)$

When the three-phase voltage of electrical network is desirable when sinusoidal wave, so in dq synchronous rotating frame, grid side voltage V _q=0, under synchronous rotating frame, inverter output power is expressed as:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}\frac{3}{2}{V}_d{i}_d\\ \frac{3}{2}{V}_d{i}_q\end{array}\right]---\left(4\right)$

Formula (4) substitution formula (2) can be obtained wherein f is grid side electric voltage frequency, f ₀resonance frequency for load; According to the relation property curve between reactive current and frequency, obtain calculating reactive current disturbance quantity i' _qdisturbance curvilinear equation:

$i_q^{\′}=-(\frac{{2i}_d{Q}_f}{f_0}+i_{\mathrm{ref}})(f-f_0)---\left(5\right)$

Wherein, i _reffor the disturbance factor adding, then provide disturbance factor i according to different frequency ranges _refdifferent values:

$\left\{\begin{array}{cc}{i}_{\mathrm{ref}}=C& \left|\mathrm{\&Delta;f}\right|<0.1\mathrm{Hz};\\ i_{\mathrm{ref}}=C+k(f-f_0)& \left|\mathrm{\&Delta;f}\right|>0.1\mathrm{Hz};\end{array}\right.---\left(6\right)$

Wherein, C is greater than 0 constant; for positive feedback coefficient.

Wherein, described grid side voltage V _q=0 o'clock, grid side electric voltage frequency f and phase angle theta and the synchronized of phaselocked loop locking.

Goal of the invention of the present invention is achieved in that

The detection method of three-phase grid-connected inverter isolated island effect prevention of the present invention, by setting the relation property curve between reactive current and the frequency of grid side voltage, the reactive current that superposes on current inner loop set-point disturbance is as new interior ring reactive current set-point, has that quality of power supply impact is little, isolated island detection time is fast, perturbation direction self-adaptation, the adaptive performance of perturbation equation slope.In concrete configuration, disturbance rule computing module calculates corresponding disturbance quantity, in the reactive current that is added to again, encircle on set-point, thereby realized the isolated island of three-phase grid-connected inverter based on grid side feedback current and grid side voltage frequency characteristics curve, detect, guaranteed that like this combining inverter meets the grid-connected requirement of inverter national standard.

Meanwhile, the detection method of three-phase grid-connected inverter isolated island effect prevention of the present invention also has following beneficial effect:

(1), three-phase grid-connected inverter does not need to continue while normally moving to inject undesired signal to electrical network, so affects minimum on the inverter output quality of power supply;

(2) phaselocked loop, based on dq synchronous rotating frame has advantages of real-time acquisition electrical network three-phase voltage frequency, has strengthened the real-time that isolated island detects;

(3), the disturbance curvilinear equation that calculates reactive current disturbance quantity can add the reactive current disturbance of different directions according to different frequency shift (FS) directions, perturbation direction no longer immobilizes; According to different frequency ranges, adopt different disturbance curvilinear equations, thereby can increase along with the degree of depth of frequency departure normal value and dynamic change reduces isolated island detection time at the slope of the not normal rear disturbance curvilinear equation of frequency;

(4), the detection method of three-phase grid-connected inverter isolated island effect prevention of the present invention do not need to increase extra hardware, has advantage cheaply.

Accompanying drawing explanation

Fig. 1 is a kind of embodiment Organization Chart of the detection method of three-phase grid-connected inverter isolated island effect prevention of the present invention.

Fig. 2 is the inner structure block diagram of inverter shown in Fig. 1.

Fig. 3 is the computation rule principle analysis figure of disturbance curve.

Fig. 4 is the spectrogram of grid side feedback current while not adding island detection method under inverter unit state.

Fig. 5 is the spectrogram of grid side electric voltage frequency while not adding island detection method under inverter unit state.

Fig. 6 is the spectrogram of grid side feedback current while adding island detection method under inverter unit state.

Fig. 7 is the spectrogram of grid side electric voltage frequency while adding island detection method under inverter unit state.

Fig. 8 is the frequency analysis figure of output current while not adding the inverter of island detection method to be normally incorporated into the power networks under unit state.

Fig. 9 is the frequency analysis figure of output current while adding the inverter of island detection method to be normally incorporated into the power networks under unit state.

Figure 10 is the spectrogram of two inverter parallels grid side feedback current while not adding island detection method.

Figure 11 is the spectrogram of two inverter parallels grid side electric voltage frequency while not adding island detection method.

Figure 12 is the spectrogram of two inverter parallels grid side feedback current while adding island detection method.

Figure 13 is the spectrogram of two inverter parallels grid side electric voltage frequency while adding island detection method.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described, so that those skilled in the art understands the present invention better.Requiring particular attention is that, in the following description, when perhaps the detailed description of known function and design can desalinate main contents of the present invention, these are described in here and will be left in the basket.

Embodiment

Fig. 1 is a kind of embodiment Organization Chart of the detection method of three-phase grid-connected inverter isolated island effect prevention of the present invention.

In the present embodiment, as shown in Figure 1, by two grid-connected inverters that model is identical, the active power of inverter output is P, and the reactive power of inverter output is Q, and the active power that electrical network provides is Δ P, the reactive power that electrical network provides is Δ Q, and the active power of load consumption is P _l, the reactive power of load consumption is Q _l, Δ P=P _l-P, Δ Q=Q _l-Q;

Fig. 2 is the inner structure block diagram of inverter shown in Fig. 1.

In the present embodiment, as shown in Figure 2, a kind of isolated island effect prevention detection method of three-phase grid-connected inverter, comprises the following steps:

(1), gather grid side voltage, current signal and DC voltage signal; The outside AD sampling A/D chip of high precision by combining inverter middle controller gathers the voltage signal of voltage, current signal and the DC side of grid side, and the grid side voltage of collection, current signal and DC voltage signal are transferred in digital signal processor DSP;

In the present embodiment, adopting model is that the outside AD module of AD7606 high precision gathers grid side voltage, current signal and DC voltage signal, then the high performance float-point type DSP that is TMS320F28335 by model processes signals such as the line voltage gathering, electric currents;

(2), digital signal processor DSP by the voltage receiving, current signal for control algolithm computing;

(2.1), by electrical network three-phase voltage V _a, V _band V _cby two synchronous coordinate system decoupling zero phaselocked loops (DDSRF-PLL) module, carry out clark, park conversion and obtain grid side magnitude of voltage V under synchronous rotating frame _d, V _q, and the frequency f of grid side voltage and phase angle theta; By clark, park, convert, by the grid side current i gathering simultaneously _a, i _band i _cfrom abc three phase static coordinate system transformation to dq synchronous rotating frame, obtain grid side feedback current value i _qand i _d;

By the grid side magnitude of voltage V calculating _d, V _q, and the power given command signal P of three-phase grid-connected inverter ^*and Q ^*be input to power outer shroud control module, calculate respectively ring set-point in reactive current with

The frequency f of the grid side voltage calculating is sent to disturbance rule computing module, by disturbance rule computing module, calculates reactive current disturbance quantity i' _q, and the phase angle theta of grid side voltage is sent to dq synchronous rotating frame, for the coordinate transform of next control cycle; Wherein, disturbance rule computing module calculates reactive current disturbance quantity i' _qmethod be:

After island effect occurs, meritorious, the reactive power of load are provided by inverter completely, i.e. P _l=P, Q _l=Q, inverter output power can be expressed from the next:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}\frac{U_p^2}{R}\\ U_p^2(\frac{1}{\mathrm{\&omega;L}}-\mathrm{\&omega;C})\end{array}\right]---\left(1\right)$

By above formula, can be released:

$\mathrm{\&omega;}=\frac{1}{\sqrt{\mathrm{LC}}}(1-\frac{Q}{{2\mathrm{PQ}}_f})---\left(2\right)$

Wherein: U _peffective value for grid side voltage; R, L, C are respectively equivalent resistance, the inductance of load, the value of electric capacity; ω is the angular frequency of grid side voltage; According to the definition of loaded quality factor under synchronous rotating frame, inverter output power is expressed as follows:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}{V}_{\mathrm{\&alpha;}}{i}_{\mathrm{\&alpha;}}+V_{\mathrm{\&beta;}}{i}_{\mathrm{\&beta;}}\\ V_{\mathrm{\&beta;}}{i}_{\mathrm{\&alpha;}}+V_{\mathrm{\&alpha;}}{i}_{\mathrm{\&beta;}}\end{array}\right]=\left[\begin{array}{c}\frac{3}{2}(V_d{i}_d+V_q{i}_q)\\ \frac{3}{2}(V_d{i}_q+V_q{i}_d)\end{array}\right]---\left(3\right)$

When the three-phase voltage of electrical network is desirable when sinusoidal wave, so in dq synchronous rotating frame, grid side voltage V _q=0, under synchronous rotating frame, inverter output power is expressed as:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}\frac{3}{2}{V}_d{i}_d\\ \frac{3}{2}{V}_d{i}_q\end{array}\right]---\left(4\right)$

Formula (4) substitution formula (2) can be obtained wherein f is grid side electric voltage frequency, f ₀resonance frequency for load; In the present embodiment, the resonance frequency of load is got f ₀=50Hz, when setting inverter active power of output 100kW, calculates grid side feedback current i _d≈ 214.4A, sets loaded quality factor Q _f=2.5;

According to the relation property curve between reactive current and frequency, obtain calculating reactive current disturbance quantity i' _qdisturbance curvilinear equation:

$i_q^{\&prime;}=-(\frac{{2i}_d{Q}_f}{f_0}+i_{\mathrm{ref}})(f-f_0)---\left(5\right)$

Wherein, i _reffor the disturbance factor adding, then provide disturbance factor i according to different frequency ranges _refdifferent values:

$\left\{\begin{array}{cc}{i}_{\mathrm{ref}}=C& \left|\mathrm{\&Delta;f}\right|<0.1\mathrm{Hz};\\ i_{\mathrm{ref}}=C+k(f-f_0)& \left|\mathrm{\&Delta;f}\right|>0.1\mathrm{Hz};\end{array}\right.---\left(6\right)$

Wherein, C is greater than 0 constant; for positive feedback coefficient;

(2.2) the grid side electric voltage frequency f, obtaining according to DDSRF-PLL module judges whether island effect occurs;

If a) frequency f of grid side voltage, not within the scope of the normal frequency of the grid-connected standard regulation of three-phase grid-connected inverter, is judged as island effect and occurs, stop the operation of three-phase grid-connected inverter;

B) if within the scope of the normal frequency that the frequency f of grid side voltage is stipulated in the grid-connected standard of three-phase grid-connected inverter, the reactive current disturbance quantity i' disturbance rule computing module being calculated _qring set-point in the reactive current that is added to the interior ring of the reactive current set-point that upper conduct is new, enters step (2.3);

In the present embodiment, the normal frequency scope of the grid-connected standard of three-phase grid-connected inverter regulation be ± 0.5Hz, and the upper frequency limit that island detection method provided by the invention is protected is 50.5Hz, and lower-frequency limit is 49.5Hz; When grid side electric voltage frequency being detected and exceed the normal frequency scope of regulation, judge that island effect occurs, and now will stop the operation of three-phase grid-connected inverter;

(2.3), set-point will be encircled in reactive current value of feedback i with the grid side electric current obtaining _ddiffer from, and encircle set-point and grid side feedback current value i in new reactive current _qdo to be input to interior circular current control module after difference, by obtaining command voltage V after anti-park conversion simultaneously _α, V _β;

(2.4), by the command voltage V obtaining in step (2.3) _α, V _βwith DC voltage-stabilizing capacitive side voltage V _dcjointly be sent to SVPWM space vector PWM modulation module, produce 6 road pulse-width modulation PWM signals and control opening and turn-offing of power switch pipe in inversion unit; After finishing, current control cycle returns to step (1).

Fig. 3 is the computation rule principle analysis figure of disturbance curve.

In the present embodiment, as shown in Figure 3, reactive current disturbance quantity i' _qthe family curve of disturbance curvilinear equation as shown in the curve 1 in Fig. 3, in order to break the balance between load reactive current and grid side electric voltage frequency, add given curve 2 between curve 1 and curve 3.After occurring, isolated island supposes that now system frequency is because disturbance runs to A point by stable point P saltus step, A is the normal frequency scope of the grid-connected standard regulation of three-phase grid-connected inverter, if now there is no adding of disturbance, grid side electric voltage frequency f is finally because the effect of system control unit can be got back to stable load resonant frequency f so ₀the point P place of=50Hz, isolated island continuous service, if according to the given grid side feedback current of curve 1 i _q, i.e. ordinate i corresponding to B point _qvalue, grid side electric voltage frequency f can keep being stabilized in A point, however A point is not tuning-points, can not trigger island protect, so we must break the balance of load, the reactive current disturbance quantity i' adding _qmake system works in unsure state, until trigger island protect, if now carry out given grid side feedback current i according to the linear relationship of curve 2 _qvalue, when grid side electric voltage frequency f be A order value time, shown in curve 2, we add the grid side feedback current i of C point ordinate _qvalue, so corresponding to reactive current disturbance quantity i' _qthe family curve 1 of disturbance curvilinear equation, the grid side feedback current i now adding _qcan allow grid side electric voltage frequency f be stabilized in the frequency that D point is corresponding, we pass grid side electric voltage frequency f to D point from A point, and grid side electric voltage frequency f is to the direction operation reducing.Effect due to positive feedback; now will continuously add disturbance; grid side electric voltage frequency f corresponding to D point can be pushed to less point again, until the protection of trigger rate in like manner can allow frequency surpass the upper limit of protection when grid side electric voltage frequency f increases.

Fig. 4 is the spectrogram of grid side feedback current while not adding island detection method under inverter unit state.

Fig. 5 is the spectrogram of grid side electric voltage frequency while not adding island detection method under inverter unit state.

Fig. 6 is the spectrogram of grid side feedback current while adding island detection method under inverter unit state.

Fig. 7 is the spectrogram of grid side electric voltage frequency while adding island detection method under inverter unit state.

In the present embodiment, during unit emulation, the active power of output of inverter is set to P=100kW, reactive power Q=0var; It is 2.5 that load arranges RLC shunt load quality factor, and the power of load consumption (meritorious, idle) mates with inverter; The frequency protection threshold values of electrical network is 50 ± 0.5Hz, and it is the power-off of 0.2s place at simulation time that electrical network is set.

Under inverter unit state, take and add and do not add island detection method provided by the invention as example, observe inverter grid side electric voltage frequency f and feedback current i _qspectral change.As shown in Figure 4, the feedback current i of the rear grid side of electrical network tripping operation after not adding detection method provided by the invention _qalmost do not change, remain on 0A left and right, as shown in Figure 5, the grid side electric voltage frequency simultaneously detecting changes very little and remains in normal range after 0.2s electric network power-fail, but reaches far away 50.5 upper frequency limit protection threshold value; Add after island detection method provided by the invention, as shown in Figure 6, the feedback current i of grid side after electrical network tripping operation _qstart negative sense gradually and increase, after 0.2s isolated island occurs, its value is more and more less, and isolated island algorithm plays a role, the grid side electric voltage frequency f simultaneously detecting, and as shown in Figure 7, grid side electric voltage frequency f is with feedback current i _qvariation and significant change, and overfrequency upscale protection threshold value.Therefore, from Fig. 4,5,6,7 contrasts, can find out the obvious detection effect adding island detection method provided by the invention, when about 0.4s, frequency surpasses protection upper limit 50.5Hz, detects the about 0.2s of generation used time of isolated island.

Fig. 8 is the frequency analysis figure of output current while not adding the inverter of island detection method to be normally incorporated into the power networks under unit state.

Fig. 9 is the frequency analysis figure of output current while adding the inverter of island detection method to be normally incorporated into the power networks under unit state.

In the present embodiment, when when not adding island detection method provided by the invention, inverter normally moves, output current is through row frequency analysis, each harmonic distributes as shown in Figure 8, use MATLAB software analysis to show that the total harmonic wave of inverter output current is now 2.32%, meet 5% the requirement of being less than of grid-connected regulation; While adding island detection method provided by the invention, as shown in Figure 9, the total harmonic wave THD=2.34% of output current when inverter normally moves, can see algorithm the adding almost the output quality of power supply without impact of island detection method when inverter normally moves.

Figure 10 is the spectrogram of two inverter parallels grid side feedback current while not adding island detection method.

Figure 11 is the spectrogram of two inverter parallels grid side electric voltage frequency while not adding island detection method.

Figure 12 is the spectrogram of two inverter parallels grid side feedback current while adding island detection method.

Figure 13 is the spectrogram of two inverter parallels grid side electric voltage frequency while adding island detection method.

In the present embodiment, while take two inverter parallels, carry out emulation as example, it is consistent when load arranges same single inverter emulation, the output general power that two inverters are set is constant, half of power when each inverter output power is single inverter emulation, the active power of output is 50kW separately, and reactive power is 0var, electrical network is set and when 0.2s, trips.

Two inverters, when all not adding island detection method provided by the invention, are observed the feedback current i of grid side _qwith grid side electric voltage frequency f, respectively as shown in Figure 9 and Figure 10, the feedback current i of grid side after electrical network tripping operation _qalmost do not change, remain on 0A left and right, the grid side electric voltage frequency now detecting changes very little and remains in normal range after 0.2s electric network power-fail, but reaches far away the lower-frequency limit protection threshold value of 49.5Hz; In two inverters, all add after island detection method provided by the invention the feedback current i of observation grid side _qwith grid side electric voltage frequency f, as shown in Figure 11 and Figure 12, electrical network tripping operation is the feedback current i of grid side afterwards respectively _qstart forward gradually and increase, and the grid side electric voltage frequency f now detecting is with feedback current i _qvariation and significant change, and final overfrequency downscale protection threshold value.Can see that the rear frequency of electrical network 0.2s tripping operation does not offset downward a little when adding island detection method provided by the invention, added after island detection method provided by the invention, inverter is adaptive has added reverse disturbance to allow grid side electric voltage frequency continue to carry out to the direction reducing, and detects the generation of isolated island about 0.305s place.

Although above the illustrative embodiment of the present invention is described; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various variations appended claim limit and definite the spirit and scope of the present invention in, these variations are apparent, all utilize innovation and creation that the present invention conceives all at the row of protection.

Claims (3)

1. an isolated island effect prevention detection method for three-phase grid-connected inverter, is characterized in that, comprises the following steps:

(1), gather voltage, current signal and the DC voltage signal of grid side; The outside AD sampling A/D chip of high precision by combining inverter middle controller gathers voltage, the current signal of voltage, current signal and the DC side of grid side, and the grid side voltage of collection, current signal and DC voltage signal are transferred in digital signal processor DSP;

(2), digital signal processor DSP by the voltage receiving, current signal for control algolithm computing;

(2.1), by electrical network three-phase voltage V _a, V _band V _cby two synchronous coordinate system decoupling zero phaselocked loops (DDSRF-PLL) module, carry out clark, park conversion and obtain grid side magnitude of voltage V under synchronous rotating frame _d, V _q, and the frequency f of grid side voltage and phase angle theta; By clark, park, convert, by the grid side current i gathering simultaneously _a, i _band i _cfrom abc three phase static coordinate system transformation to dq synchronous rotating frame, obtain grid side feedback current value i _qand i _d;

By the grid side magnitude of voltage V calculating _d, V _q, and the power given command signal P of three-phase grid-connected inverter ^*and Q ^*be input to power outer shroud control module, calculate respectively ring set-point in reactive current with

The frequency f of the grid side voltage calculating is sent to disturbance rule computing module, by disturbance rule computing module, calculates reactive current disturbance quantity i' _q, and the phase angle theta of grid side voltage is sent to dq synchronous rotating frame, for the coordinate transform of next control cycle;

(2.2) the grid side electric voltage frequency f, obtaining according to DDSRF-PLL module judges whether island effect occurs;

If a) frequency f of grid side voltage, not within the scope of the normal frequency of the grid-connected standard regulation of three-phase grid-connected inverter, is judged as island effect and occurs, stop the operation of three-phase grid-connected inverter;

B) if within the scope of the normal frequency that the frequency f of grid side voltage is stipulated in the grid-connected standard of three-phase grid-connected inverter, the reactive current disturbance quantity i' disturbance rule computing module being calculated _qring set-point in the reactive current that is added to the interior ring of the reactive current set-point that upper conduct is new, enters step (2.3);

(2.3), set-point will be encircled in reactive current value of feedback i with the grid side electric current obtaining _ddiffer from, and encircle set-point and grid side feedback current value i in new reactive current _qdo to be input to interior circular current control module after difference, by obtaining command voltage V after anti-park conversion simultaneously _α, V _β;

(2.4), by the command voltage V obtaining in step (2.3) _α, V _βwith DC voltage-stabilizing capacitive side voltage V _dcjointly be sent to SVPWM space vector PWM modulation module, produce 6 road pulse-width modulation PWM signals and control opening and turn-offing of power switch pipe in inversion unit; After finishing, current control cycle returns to step (1).

2. the island effect detection method that three-phase grid-connected inverter according to claim 1 is put, is characterized in that, described disturbance rule computing module calculates reactive current disturbance quantity i' _qmethod be:

After island effect occurs, meritorious, the reactive power of load are provided by inverter completely, and inverter output power can be expressed from the next:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}\frac{U_p^2}{R}\\ U_p^2(\frac{1}{\mathrm{\&omega;L}}-\mathrm{\&omega;C})\end{array}\right]---\left(1\right)$

By above formula, can be released:

$\mathrm{\&omega;}=\frac{1}{\sqrt{\mathrm{LC}}}(1-\frac{Q}{{2\mathrm{PQ}}_f})---\left(2\right)$

Wherein: U _peffective value for grid side voltage; R, L, C are respectively equivalent resistance, the inductance of load, the value of electric capacity; ω is the angular frequency of grid side voltage; According to the definition of loaded quality factor under synchronous rotating frame, inverter output power is expressed as follows:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}{V}_{\mathrm{\&alpha;}}{i}_{\mathrm{\&alpha;}}+V_{\mathrm{\&beta;}}{i}_{\mathrm{\&beta;}}\\ V_{\mathrm{\&beta;}}{i}_{\mathrm{\&alpha;}}+V_{\mathrm{\&alpha;}}{i}_{\mathrm{\&beta;}}\end{array}\right]=\left[\begin{array}{c}\frac{3}{2}(V_d{i}_d+V_q{i}_q)\\ \frac{3}{2}(V_d{i}_q+V_q{i}_d)\end{array}\right]---\left(3\right)$

When the three-phase voltage of electrical network is desirable when sinusoidal wave, so in dq synchronous rotating frame, grid side voltage V _q=0, under synchronous rotating frame, inverter output power is expressed as:

$\left[\begin{array}{c}P\\ Q\end{array}\right]=\left[\begin{array}{c}\frac{3}{2}{V}_d{i}_d\\ \frac{3}{2}{V}_d{i}_q\end{array}\right]---\left(4\right)$

Formula (4) substitution formula (2) can be obtained wherein f is grid side electric voltage frequency, f ₀resonance frequency for load; According to the relation property curve between reactive current and frequency, obtain calculating reactive current disturbance quantity i' _qdisturbance curvilinear equation:

$i_q^{\&prime;}=-(\frac{{2i}_d{Q}_f}{f_0}+i_{\mathrm{ref}})(f-f_0)---\left(5\right)$

Wherein, i _reffor the disturbance factor adding, then provide disturbance factor i according to different frequency ranges _refdifferent values:

$\left\{\begin{array}{cc}{i}_{\mathrm{ref}}=C& \left|\mathrm{\&Delta;f}\right|<0.1\mathrm{Hz};\\ i_{\mathrm{ref}}=C+k(f-f_0)& \left|\mathrm{\&Delta;f}\right|>0.1\mathrm{Hz};\end{array}\right.---\left(6\right)$

Wherein, C is greater than 0 constant; for positive feedback coefficient.

3. the isolated island effect prevention detection method of three-phase grid-connected inverter according to claim 1 and 2, is characterized in that, described grid side voltage V _q=0 o'clock, grid side electric voltage frequency f and phase angle theta and the synchronized of phaselocked loop locking.