CN102998559A - Island detection method and device and electric system - Google Patents

Abstract

An embodiment of the invention provides an island detection method and device and an electric system. The island detection method includes detecting voltage frequency in a circuit formed by an inverter, virtual reactive load and power grid load, wherein the virtual reactive load performs energy exchange and does not consume energy; and determining that the inverter, the virtual reactive load and the power grid load form an island if the detected voltage frequency surpasses the set range. According to the island detection method and device and the electric system, grid-connected current quality cannot be affected and accordingly normal operation of the electric system is ensured.

Description

Island detection method, device and electric system

Technical field

The present invention relates to electric and electronic technical field, relate in particular to a kind of island detection method, device and electric system.

Background technology

Under the electrical network normal operation, by main power supply system and the common peripherad load supplying of distributed power source, in the situation that main power supply system fault or maintenance after associated switchgear disconnects, are independently powered to the load by distributed power source.After the main distribution system disconnected, distributed power source formed a little island network with load, is called isolated island.Isolated island is the part of electrical network, still keeps a kind of state that moves when other parts with electrical network separate.Isolated island can cause consumer to damage owing to abnormal voltage or frequency offer load, and the series of problems such as distribution system misoperation also may cause personnel to get an electric shock, and therefore need to detect isolated island.

Existing island detection method, by inverter to load harmonic electric current, when inverter is connected with electrical network with load, the frequency of inverter output end can not change, when inverter and load and electrical network disconnection, the frequency of inverter output end can be offset, thereby can detect the generation of isolated island.Yet this method can impact the grid-connected current quality, affects the normal operation of electric system.

Summary of the invention

The embodiment of the invention provides a kind of island detection method, inverter and electrical network.Avoid the grid-connected current quality is impacted to carry, guarantee the normal operation of electric system.

First aspect, the embodiment of the invention provide a kind of island detection method, comprising:

Electric voltage frequency in the circuit that inverter, virtual reactive load and electrical network load are consisted of detects, and described virtual reactive load carries out energy exchange and consumed energy not;

If the described electric voltage frequency that detects exceeds setting range, determine that then described inverter, described virtual reactive load and described electrical network load form isolated island.

In a kind of embodiment of first aspect, the lagging reactive power that described virtual reactive load absorbs increases along with the increase of the described electric voltage frequency that detects; Perhaps, the capacitive reactive power of described virtual reactive load absorption increases along with the reducing of described electric voltage frequency that detects.

In conjunction with first aspect and the first embodiment thereof, in the second embodiment of first aspect, if the described electric voltage frequency that detects is the ratings of mains frequency, then the reactive power of described virtual reactive load absorption is 0, and the reactive power of sending is 0.

In conjunction with first aspect and the first embodiment and the second embodiment, in the third embodiment of first aspect, before electric voltage frequency in the described circuit that inverter, virtual reactive load and electrical network load are consisted of detects, also comprise: produce described virtual reactive load by described inverter.

In first aspect and the first embodiment, the second embodiment and the third embodiment, in the 4th kind of embodiment of first aspect, the electric current that described virtual reactive load absorbs is: iq=id * (f-f _N) * k; Wherein, id is the active current that described inverter sends, and f is detected described electric voltage frequency, f _NBe the ratings of mains frequency, k is scale-up factor, and iq is the electric current that described virtual reactive load absorbs.

Second aspect, the embodiment of the invention provide a kind of isolated island detecting device, comprising:

Detection module, the electric voltage frequency in the circuit that is used for inverter, virtual reactive load and electrical network load are consisted of detects, and described virtual reactive load carries out energy exchange and consumed energy not;

Determination module exceeds setting range if be used for the described electric voltage frequency of described detection module detection, determines that then described inverter, described virtual reactive load and described electrical network load form isolated island.

In a kind of embodiment of second aspect, the lagging reactive power that described virtual reactive load absorbs increases along with the increase of the described electric voltage frequency that detects; Perhaps, the capacitive reactive power of described virtual reactive load absorption increases along with the reducing of described electric voltage frequency that detects.

In conjunction with second aspect and the first embodiment thereof, in the second embodiment of second aspect, if the described electric voltage frequency that described detection module detects is the ratings of mains frequency, then the reactive power of described virtual reactive load absorption is 0, and the reactive power of sending is 0.

In conjunction with second aspect and the first embodiment and the second embodiment, in the third embodiment of second aspect, described virtual reactive load is produced by described inverter.

In second aspect and the first embodiment, the second embodiment and the third embodiment, in the 4th kind of embodiment of second aspect, the electric current that described virtual reactive load absorbs is: iq=id * (f-f _N) * k; Wherein, id is the active current that described inverter sends, and f is detected described electric voltage frequency, f _NBe the ratings of mains frequency, k is scale-up factor, and iq is the electric current that described virtual reactive load absorbs.

The third aspect, the embodiment of the invention also provide a kind of electric system, comprising: electrical network, at least one inverter, electrical network load, at least one virtual reactive load, electrical network load and the isolated island detecting device that provides such as the embodiment of the invention.

In a kind of embodiment of the third aspect, described isolated island detecting device and described inverter integrate.

The island detection method that the embodiment of the invention provides, device and electric system, in electrical network, produce virtual reactive load, detect by the electric voltage frequency in the circuit that inverter, virtual reactive load and electrical network load are consisted of, realize exceeding setting range when the electric voltage frequency that detects, determine that then inverter, virtual reactive load and electrical network load form isolated island.Because when virtual reactive load does not disconnect at the circuit of electrical network and inverter, virtual reactive load and electrical network load composition, virtual reactive load is absorbing reactive power neither, does not also send reactive power, therefore, can not affect the grid-connected current mass formation, thus the normal operation of assurance electric system.

Description of drawings

In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art, the below will do one to the accompanying drawing of required use in embodiment or the description of the Prior Art and introduce simply, apparently, accompanying drawing in the following describes is some embodiments of the present invention, for those of ordinary skills, under the prerequisite of not paying creative work, can also obtain according to these accompanying drawings other accompanying drawing.

Fig. 1 is the process flow diagram of an embodiment of island detection method provided by the invention;

The inverter that Fig. 2 provides for the embodiment of the invention breaks away from the model schematic diagram of electrical network islet operation;

Fig. 3 is the structural representation of an embodiment of isolated island detecting device provided by the invention;

Fig. 4 is the structural representation of an embodiment of electric system provided by the invention.

Embodiment

For the purpose, technical scheme and the advantage that make the embodiment of the invention clearer, below in conjunction with the accompanying drawing in the embodiment of the invention, technical scheme in the embodiment of the invention is clearly and completely described, obviously, described embodiment is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills belong to the scope of protection of the invention not making the every other embodiment that obtains under the creative work prerequisite.

Fig. 1 is the process flow diagram of an embodiment of island detection method provided by the invention, and as shown in Figure 1, the method comprises:

Electric voltage frequency in S101, the circuit that inverter, virtual reactive load and electrical network load are consisted of detects, and virtual reactive load carries out energy exchange and consumed energy not.

If the electric voltage frequency that S102 detects exceeds setting range, determine that then inverter, virtual reactive load and electrical network load form isolated island.

Above-mentioned steps can be carried out by the pick-up unit that is arranged in the electrical network, perhaps, can also be carried out by the inverter in the electrical network.

Wherein, the electrical network load can be the load parts in the electrical network, for example: RLC(resistance, inductance, capacity; Resistance, inductance, electric capacity) load etc.Virtual reactive load can be arranged on the module that can absorb and send reactive power in the electrical network; Perhaps, virtual reactive load can also be produced by the inverter in the electrical network.

Virtual reactive load can be only to carry out energy exchange and not catabiotic a kind of control module.During the electric system normal operation, electrical network is connected with inverter, virtual reactive load and electrical network load.Implement under the scene at this, the electric voltage frequency of the circuit that inverter, virtual reactive load and electrical network load form is in steady state (SS), this electric voltage frequency is generally the ratings of mains frequency, therefore, the electric voltage frequency that detects is in the scope of setting usually, and this setting range is the normal range of operation of mains frequency.Under this implements scene and since virtual reactive load neither absorbing reactive power do not send reactive power yet, that is, the reactive power that virtual reactive load absorbs is 0, and the reactive power of sending is 0.Therefore, can not affect the grid-connected current quality, thereby guarantee the normal operation of electric system.

Electric system break down or the situation of overhauling under, electrical network and inverter, virtual reactive load and electrical network load disconnect.Implement under the scene at this, the electric voltage frequency of the circuit that inverter, virtual reactive load and electrical network load form plays pendulum, and the electric voltage frequency that detects departs from the scope of setting usually, namely departs from the normal range of operation of mains frequency.Therefore, when the electric voltage frequency that detects the circuit that inverter, virtual reactive load and electrical network load form exceeds setting range, determine that then inverter, virtual reactive load and electrical network load form isolated island.And implement under the scene at this, the lagging reactive power that virtual reactive load absorbs can increase along with the increase of the electric voltage frequency that detects; Perhaps, the capacitive reactive power of virtual reactive load absorption can increase along with the reducing of electric voltage frequency that detects.

Optionally, the embodiment of the invention provides a kind of embodiments possible of virtual reactive load, and electric current that this virtual reactive load absorbs can be iq=id * (f-f _N) * k;

Wherein, id is the active current that inverter sends, and f is detected electric voltage frequency, f _NBe the ratings of mains frequency, k is scale-up factor, and iq is the electric current that virtual reactive load absorbs.

Concrete, when electrical network was connected with inverter, virtual reactive load and electrical network load, the electric voltage frequency f that detects can be identical with the mains frequency ratings, therefore, and f-f _N=0, this moment reactive load neither absorb idle do not send yet idle; When electrical network and inverter, virtual reactive load and electrical network load disconnection, when inverter, virtual reactive load and electrical network load form isolated island, the electric voltage frequency f that detects can increase or reduce, when f increases, load absorbs lagging reactive power to be increased, when f reduced, load absorbs capacitive reactive power to be increased.

The inverter that Fig. 2 embodiment of the invention provides breaks away from the model schematic diagram of electrical network islet operation, as shown in Figure 2, to comprise an inverter in the system, the electrical network load comprises that a resistance (R), an inductance (L) and an electric capacity (C) describe for example, produce virtual reactive load by inverter, and carry out isolated island and detect.

The LC load resonant frequency is 50Hz, and the active power reactive power is mated fully.In order to make the inverter islet operation, then have:

$P=\frac{{\mathrm{Ug}}^2}{R}---\left(1\right)$

Q=0

Wherein, P is the active power of inverter output, and Q is the reactive power of inverter output.

Inverter produces reactive current disturbance, i.e. virtual reactive load:

Δiq=id×(f-50)×k （2）

Wherein, id is active current, and f is the electric voltage frequency of the circuit that forms of the inverter that detects of inverter, virtual reactive load and electrical network load, and k is scale-up factor.

So also the voltage phasor of site is:

$\stackrel{\·}{U}g=(\mathrm{id}+j\×\mathrm{iq})\×(R//\mathrm{j\ωL}//\frac{1}{\mathrm{j\ωc}})$

$=\sqrt{{\mathrm{id}}^2+{\mathrm{iq}}^2}\∠a\tan \frac{\mathrm{iq}}{\mathrm{id}}\×\frac{\mathrm{R\ωL}}{\sqrt{{\left(\mathrm{\ωL}\right)}^2+{({\mathrm{R\ω}}^2\mathrm{LC}-R)}^2}}\∠-a\tan \frac{{\mathrm{R\ω}}^2\mathrm{LC}-R}{\mathrm{\ωL}}---\left(3\right)$

$=\sqrt{{\mathrm{id}}^2+{\mathrm{iq}}^2}\×\frac{\mathrm{R\ωL}}{\sqrt{{\left(\mathrm{\ωL}\right)}^2+{({\mathrm{R\ω}}^2\mathrm{LC}-R)}^2}}\∠(a\tan \frac{\mathrm{iq}}{\mathrm{id}}-a\tan \frac{{\mathrm{R\ω}}^2\mathrm{LC}-R}{\mathrm{\ωL}})$

Wherein, ω is the voltage angle speed of the circuit of inverter, virtual reactive load and electrical network load composition:

ω=2πf

The phase deviation of point voltage of then being incorporated into the power networks is:

$\mathrm{\Δ\θ}=a\tan \frac{\mathrm{iq}}{\mathrm{id}}-a\tan \frac{{\mathrm{R\ω}}^2\mathrm{LC}-R}{\mathrm{\ωL}}---\left(4\right)$

Because except the reactive current disturbance quantity, inverter is not exported idle, therefore:

iq=Δiq=id×(f-50)×k （5）

In addition, the resonance frequency of LC is 50Hz, therefore:

${\mathrm{\ω}}_0=\frac{1}{\sqrt{\mathrm{LC}}}=2{\mathrm{\πf}}_N=2\mathrm{\π}\×50---\left(6\right)$

The quality factor of load are:

$Q_f=R\sqrt{C/L}=R/\left({\mathrm{\ω}}_{0}L\right)---\left(7\right)$

In conjunction with (4), (5), (6) and (7), the phase deviation of the point voltage that can obtain being incorporated into the power networks is:

$\mathrm{\Δ\θ}=a\tan [(f-50)\×k]-a\tan [Q_f\×(\frac{2\mathrm{\πf}}{{\mathrm{\ω}}_0}-\frac{{\mathrm{\ω}}_0}{2\mathrm{\πf}})]$

$=a\tan [(f-50)\×k]-a\tan [Q_f\×(\frac{f}{50}-\frac{50}{f})]$

Order:

α ₁(f)=(f-50)×k

${\mathrm{\α}}_2\left(f\right)=Q_f\×(\frac{f}{50}-\frac{50}{f})$

So:

α ₁(50)=α ₂(50)=0

α ₁(f)′=k

${\mathrm{\α}}_2{\left(f\right)}^{\′}=Q_f(\frac{1}{50}+\frac{50}{f^2})$

If the minimum frequency that allows is f _MinThen:

${\mathrm{\α}}_2{\left(f\right)}^{\′}=Q_f(\frac{1}{50}+\frac{50}{f^2})\≤Q_f(\frac{1}{50}+\frac{50}{{f_{\min }}^2})$

Order:

$k>Q_f(\frac{1}{50}+\frac{50}{{f_{\min }}^2})$

So since atan (x) (∞ ,+be monotonically increasing function in ∞), therefore:

As f〉Δ θ during 50Hz〉0, thus frequency f continues to increase;

Δ θ＜0 when f＜50Hz, thus frequency f continues to reduce;

Therefore, system plays pendulum, and final frequency f is offset out allowed band, thereby realizes that the non-blind area isolated island detects.

The island detection method that the present embodiment provides, in electrical network, produce virtual reactive load, detect by the electric voltage frequency in the circuit that inverter, virtual reactive load and electrical network load are consisted of, realize exceeding setting range when the electric voltage frequency that detects, determine that then inverter, virtual reactive load and electrical network load form isolated island.Because when virtual reactive load does not disconnect at the circuit of electrical network and inverter, virtual reactive load and electrical network load composition, virtual reactive load is absorbing reactive power neither, does not also send reactive power, therefore, can not affect the grid-connected current mass formation, thus the normal operation of assurance electric system.Electric voltage frequency by time-dependent system that inverter, virtual reactive load and electrical network load are consisted of detects, and can realize that the non-blind area isolated island detects.

Further, comprise that in electric system each inverter can be separate under the enforcement scene of a plurality of inverters, produce respectively virtual reactive load.In the embodiment of the invention, idle perturbation direction is definite by the electric voltage frequency that detects, and the lagging reactive power that virtual reactive load absorbs increases along with the increase of the electric voltage frequency that detects; Perhaps, the capacitive reactive power of virtual reactive load absorption increases along with the reducing of electric voltage frequency that detects.Therefore, the idle perturbation direction of each inverter is synchronous, has avoided the idle disturbance of each inverter to cancel each other.

Fig. 3 is the structural representation of an embodiment of isolated island detecting device provided by the invention, and as shown in Figure 3, this isolated island detecting device comprises: detection module 31 and determination module 32;

Detection module 31, the electric voltage frequency in the circuit that is used for inverter, virtual reactive load and electrical network load are consisted of detects, and virtual reactive load carries out energy exchange and consumed energy not;

Determination module 32 exceeds setting range if be used for the electric voltage frequency of detection module detection, determines that then inverter, virtual reactive load and electrical network load form isolated island.

Need to prove, the isolated island detecting device that the embodiment of the invention provides can be for being arranged on separately the pick-up unit in the electrical network, and perhaps, its function can also be realized by the inverter in the electrical network.

Optionally, the lagging reactive power of virtual reactive load absorption can increase along with the increase of the electric voltage frequency that detects; Perhaps, the capacitive reactive power of virtual reactive load absorption can increase along with the reducing of electric voltage frequency that detects.

Optionally, if the electric voltage frequency that detection module 31 detects is the ratings of mains frequency, then the reactive power of virtual reactive load absorption can be 0, and the reactive power of sending can be 0.

Optionally, virtual reactive load can be produced by inverter.

Optionally, the virtual reactive load electric current that absorbs can be iq=id * (f-f _N) * k;

Wherein, id is the active current that inverter sends, and f is detected electric voltage frequency, f _NBe the ratings of mains frequency, k is scale-up factor, and iq is the electric current that virtual reactive load absorbs.

The isolated island detecting device that the embodiment of the invention provides, the actuating equipment of the island detection method that provides for the embodiment of the invention, its detailed process of carrying out island detection method can referring to the associated description in the embodiment of the method, not repeat them here.

The isolated island detecting device that the present embodiment provides, in electrical network, produce virtual reactive load, detect by the electric voltage frequency in the circuit that inverter, virtual reactive load and electrical network load are consisted of, realize exceeding setting range when the electric voltage frequency that detects, determine that then inverter, virtual reactive load and electrical network load form isolated island.Because when virtual reactive load does not disconnect at the circuit of electrical network and inverter, virtual reactive load and electrical network load composition, virtual reactive load is absorbing reactive power neither, does not also send reactive power, therefore, can not affect the grid-connected current mass formation, thus the normal operation of assurance electric system.

The present invention also provides a kind of electric system, comprising: electrical network, at least one inverter, electrical network load, at least one virtual reactive load, electrical network load and isolated island detecting device.

Wherein, isolated island detecting device can be for being arranged on separately the pick-up unit in the electrical network, and perhaps, its function can also realize by the inverter in the electrical network, that is, isolated island detecting device can integrate with inverter.

Fig. 4 is the structural representation of an embodiment of electric system provided by the invention, as shown in Figure 4, a kind of typical structure of electric system is provided among this embodiment, has comprised two inverters: inverter 1 and inversion 2, the electrical network load comprises: a resistance, an inductance and an electric capacity; Inverter 1 and inverter 2 can produce respectively a virtual reactive load.The function of isolated island detecting device can be realized by inverter 1 and inverter 2.

Concrete, electric voltage frequency in the circuit that the virtual reactive load that inverter 1 can produce inverter 1, inverter 1 and electrical network load consist of detects, if the electric voltage frequency that detects exceeds setting range, can determine that then virtual reactive load and electrical network load that inverter 1, inverter 1 produce form isolated island.Similarly, electric voltage frequency in the circuit that the virtual reactive load that inverter 2 can produce inverter 2, inverter 2 and electrical network load consist of detects, if the electric voltage frequency that detects exceeds setting range, can determine that then virtual reactive load and electrical network load that inverter 2, inverter 2 produce form isolated island.

In the present embodiment, comprise 2 inverters in the electric system, these two inverters can separately produce respectively virtual reactive load.Idle perturbation direction is definite by the electric voltage frequency that inverter detects, and the lagging reactive power that virtual reactive load absorbs increases along with the increase of the electric voltage frequency that detects; Perhaps, the capacitive reactive power of virtual reactive load absorption increases along with the reducing of electric voltage frequency that detects.Therefore, these 2 idle perturbation direction of inverter are synchronous, avoided the idle disturbance of 2 inverters to cancel each other.

Need to prove, the present embodiment only comprises that 2 inverters describe as example in the electric system, but not with this as the restriction to the embodiment of the invention.For the enforcement scene that comprises 2 above inverters in the electric system, the idle perturbation direction of each inverter is synchronous, has avoided the idle disturbance of each inverter to cancel each other.

The electric system that the present embodiment provides, in electrical network, produce virtual reactive load, detect by the electric voltage frequency in the circuit that inverter, virtual reactive load and electrical network load are consisted of, realize exceeding setting range when the electric voltage frequency that detects, determine that then inverter, virtual reactive load and electrical network load form isolated island.Because when virtual reactive load does not disconnect at the circuit of electrical network and inverter, virtual reactive load and electrical network load composition, virtual reactive load is absorbing reactive power neither, does not also send reactive power, therefore, can not affect the grid-connected current mass formation, thus the normal operation of assurance electric system.

The those skilled in the art can be well understood to, be the convenience described and succinct, only the division with above-mentioned each functional module is illustrated, in the practical application, can as required the above-mentioned functions distribution be finished by different functional modules, the inner structure that is about to device is divided into different functional modules, to finish all or part of function described above.The system of foregoing description, the specific works process of device and unit can with reference to the corresponding process among the preceding method embodiment, not repeat them here.

In several embodiment that the application provides, should be understood that, disclosed system, apparatus and method can realize by another way.For example, device embodiment described above only is schematic, for example, the division of described module or unit, only be that a kind of logic function is divided, during actual the realization other dividing mode can be arranged, for example a plurality of unit or assembly can in conjunction with or can be integrated into another system, or some features can ignore, or do not carry out.Another point, the shown or coupling each other discussed or direct-coupling or communication connection can be by some interfaces, indirect coupling or the communication connection of device or unit can be electrically, machinery or other form.

Described unit as separating component explanation can or can not be physically to separate also, and the parts that show as the unit can be or can not be physical locations also, namely can be positioned at a place, perhaps also can be distributed on a plurality of network element.Can select according to the actual needs wherein some or all of unit to realize the purpose of the present embodiment scheme.

In addition, each functional unit in each embodiment of the application can be integrated in the processing unit, also can be that the independent physics of unit exists, and also can be integrated in the unit two or more unit.Above-mentioned integrated unit both can adopt the form of hardware to realize, also can adopt the form of SFU software functional unit to realize.

If described integrated unit is realized with the form of SFU software functional unit and during as independently production marketing or use, can be stored in the computer read/write memory medium.Based on such understanding, part or all or part of of this technical scheme that the application's technical scheme contributes to prior art in essence in other words can embody with the form of software product, this computer software product is stored in the storage medium, comprise that some instructions are with so that a computer equipment (can be personal computer, server, the perhaps network equipment etc.) or processor (processor) carry out all or part of step of the described method of each embodiment of the application.And aforesaid storage medium comprises: the various media that can be program code stored such as USB flash disk, portable hard drive, ROM (read-only memory) (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), magnetic disc or CD.

The above, above embodiment only in order to the application's technical scheme to be described, is not intended to limit; Although with reference to previous embodiment the application is had been described in detail, those of ordinary skill in the art is to be understood that: it still can be made amendment to the technical scheme that aforementioned each embodiment puts down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution break away from the spirit and scope of each embodiment technical scheme of the application.

Claims (13)

1. an island detection method is characterized in that, comprising:

Electric voltage frequency in the circuit that inverter, virtual reactive load and electrical network load are consisted of detects, and described virtual reactive load carries out energy exchange and consumed energy not;

If the described electric voltage frequency that detects exceeds setting range, determine that then described inverter, described virtual reactive load and described electrical network load form isolated island.

2. method according to claim 1 is characterized in that, the lagging reactive power that described virtual reactive load absorbs increases along with the increase of the described electric voltage frequency that detects; Perhaps, the capacitive reactive power of described virtual reactive load absorption increases along with the reducing of described electric voltage frequency that detects.

3. method according to claim 1 and 2 is characterized in that, if the described electric voltage frequency that detects is the ratings of mains frequency, then the reactive power of described virtual reactive load absorption is 0, and the reactive power of sending is 0.

4. each described method is characterized in that according to claim 1-3, before the electric voltage frequency in the described circuit that inverter, virtual reactive load and electrical network load are consisted of detects, also comprises:

Produce described virtual reactive load by described inverter.

5. method according to claim 4 is characterized in that, the electric current that described virtual reactive load absorbs is: iq=id * (f-f _N) * k;

Wherein, id is the active current that described inverter sends, and f is detected described electric voltage frequency, f _NBe the ratings of mains frequency, k is scale-up factor, and iq is the electric current that described virtual reactive load absorbs.

6. an isolated island detecting device is characterized in that, comprising:

Detection module, the electric voltage frequency in the circuit that is used for inverter, virtual reactive load and electrical network load are consisted of detects, and described virtual reactive load carries out energy exchange and consumed energy not;

Determination module exceeds setting range if be used for the described electric voltage frequency of described detection module detection, determines that then described inverter, described virtual reactive load and described electrical network load form isolated island.

7. device according to claim 6 is characterized in that, the lagging reactive power that described virtual reactive load absorbs increases along with the increase of the described electric voltage frequency that detects; Perhaps, the capacitive reactive power of described virtual reactive load absorption increases along with the reducing of described electric voltage frequency that detects.

8. according to claim 6 or 7 described devices, it is characterized in that, if the described electric voltage frequency that described detection module detects is the ratings of mains frequency, then the reactive power that absorbs of described virtual reactive load is 0, and the reactive power of sending is 0.

9. each described device is characterized in that according to claim 6-8, and described virtual reactive load is produced by described inverter.

10. device according to claim 9 is characterized in that, the electric current that described virtual reactive load absorbs is: iq=id * (f-f _N) * k;

Wherein, id is the active current that described inverter sends, and f is detected described electric voltage frequency, f _NBe the ratings of mains frequency, k is scale-up factor, and iq is the electric current that described virtual reactive load absorbs.

11. each described device is characterized in that according to claim 6-10, described device is inverter.

12. an electric system is characterized in that, comprising: electrical network, at least one inverter, electrical network load, at least one virtual reactive load, electrical network load and such as each described isolated island detecting device of claim 6-11.

13. electric system according to claim 12 is characterized in that, described isolated island detecting device and described inverter integrate.

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