CN103217595B - A kind of detection method of one-phase island of three-phase grid-connected inverter, equipment and system - Google Patents
A kind of detection method of one-phase island of three-phase grid-connected inverter, equipment and system Download PDFInfo
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- CN103217595B CN103217595B CN201310052676.0A CN201310052676A CN103217595B CN 103217595 B CN103217595 B CN 103217595B CN 201310052676 A CN201310052676 A CN 201310052676A CN 103217595 B CN103217595 B CN 103217595B
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Abstract
The embodiment of the invention discloses a kind of detection method of one-phase island of three-phase grid-connected inverter, equipment and system.By the embodiment of the present invention, injecting reactive current on the output current of inverter.Before calculating injecting reactive current, the phase differential in three-phase voltage between every two phase voltages
after calculating injecting reactive current again, the phase differential in three-phase voltage between every two phase voltages
judge
with
phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.Method provided by the invention can judge whether isolated island occurs accurately and efficiently by phase difference value, and what inject the output current of inverter due to the present invention is reactive current, the harmonic content of such output waveform is very little, only has minimum idle change during grid-connected inverters work.Compared with the perturbation motion method based on frequency or active power of the prior art, the reactive current that the present invention injects can not affect generated energy.
Description
Technical field
The present invention relates to technical field of power systems, more particularly, relate to a kind of detection method of one-phase island of three-phase grid-connected inverter, equipment and system.
Background technology
At present, in short supply along with world energy sources, the application of wind-power electricity generation and photovoltaic generation is more and more extensive.No matter be wind-power electricity generation and photovoltaic generation, all need feeding electric energy blower fan and photovoltaic module produced to AC network.The electric energy produced due to blower fan and photovoltaic module is direct current, when therefore feeding back to AC network, needs application combining inverter to be fed to AC network after alternating current by DC inversion.
See Fig. 1, this figure is the operating diagram of a kind of three-phase grid-connected inverter of the prior art.
AC network side comprises electrical network 1(A, B and C three-phase) and grid side K switch K1; C phase mounts single-phase load 3(and is equivalent to RLC load, comprise resistance R, inductance L and electric capacity C); Single-phase load 3 is local load.
Three-phase grid-connected inverter side comprises inverter 7, inverter side K switch K2 and circuit control device 6;
DC side comprises filter capacitor and cell panel BAT, and cell panel BAT represents the electric energy that wind-power electricity generation or photovoltaic generation send.
The principle of work of inverter 7 is, is to be fed to AC network side after alternating current by the DC inverter that DC side produces.
When inverter 7 is to electrical network 1 feed, KK1 and KK2 is all closed, and inverter 7 is fed to electrical network 1 after the DC inverter on right side is become alternating current.Single-phase load 3 is powered, if inverter C phase output power and single-phase load 3 consumed power equal and opposite in direction, now AC network side not powering load jointly by inverter 7 and electrical network 1.
When single-phase load 3 works, inverter 7 powering load common with electrical network 1, KK1 closes, and KK2 closes.
But in the actual grid-connected course of work of inverter 7, electrical network 1 may be stopped power supply to load suddenly.Because load consuming power mates with inverter output power, inverter 7 fails to detect in time the change of electric network state, thus makes inverter 7 and load form independently system, i.e. an isolated island.To impact maintenance and power system restoration like this.
Islanding detect is exactly the phenomenon that can detect that the single-phase of electrical network or two-phase have a power failure in time, and disconnects inverter side K switch K2 in time, avoids the formation of isolated island, thus reduces the harm to electrical network and maintainer.
Introduce the method for three kinds of islanding detect of the prior art below.
The first:
The electric parameter changes such as the electric current and voltage of passive detection point of common coupling, are realized by the overvoltage/undervoltage of detection of grid voltage, excessively under-frequency.
But, when load equivalent is RLC load, occur after isolated island, inverter the line voltage adopted and frequency determined by load.Voltage and frequency are when inverter active power of output and reactive power mate completely, and the resonance frequency of load is 50Hz.If do not apply disturbance, do not change before and after voltage and frequency and electrical network disconnect, like this can not triggered under-voltage, cross underfrequency protection, inspection does not measure whether define isolated island.
Therefore, when detecting isolated island and whether occurring, there is the blind area detected in above prior art.
The second:
Initiatively disturbance is carried out to electric parameters such as the electric current and voltages that inverter exports, detect response condition, determined whether that isolated island occurs.
Such as, disturbance is carried out to the frequency of the output current of inverter.After disconnecting electrical network, the frequency of electrical network is determined by load.By changing the frequency of inverter output current, the voltage swing in load and frequency are added on loaded impedance by inverter output current and determine.Change the frequency of output current, also just change the frequency of line voltage sampling, by over frequency protection or the underfrequency protection realization of line voltage.
But the method mainly carries out islanding detect for when three phase network generation three-phase isolated island or single-phase electrical network single-phase inverter generation isolated island, a phase or two-phase are broken to three phase network three-phase inverter and inapplicable.Because the frequency measurement of electrical network is generally measure mutually for a certain.If after generation isolated island, disconnection be non-frequency measurement phase, even if add the disturbance of electric parameter, make frequency shift (FS) be the protection point of under-frequency, inverter also can not be protected.
The third:
If electrical network has a power failure, then depart from electrical network in time, in order to avoid form isolated island by communication or interlocking notice inverter.
But such a process increases equipment investment, cost is too high, and communication likely exists false triggering.
In sum, the method that the three-phase grid-connected inverter provided in prior art detects isolated island all accurately and timely can not detect generation that is single-phase or two-phase isolated island, thus disconnects the connection of inverter and load, thus the harm avoiding isolated island to bring.
Summary of the invention
In view of this, the embodiment of the present invention provides a kind of detection method of one-phase island of three-phase grid-connected inverter, equipment and system, accurately and timely can detect the generation of isolated island, thus the harm avoiding isolated island to bring.
The embodiment of the present invention provides a kind of detection method of one-phase island of three-phase grid-connected inverter, comprising:
Phase differential between every two-phase of calculating three-phase power grid voltage
Injecting reactive current on the output current of inverter;
Phase differential between every two-phase of the three-phase power grid voltage after calculating injecting reactive current
Obtain the phase differential after injecting reactive current
with the phase differential before injecting reactive current
phase difference value
Judge described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
The embodiment of the present invention provides a kind of checkout equipment of one-phase island of three-phase grid-connected inverter, comprising: first-phase potential difference computing unit, reactive current injection unit, second-phase potential difference computing unit, phase difference value acquiring unit and isolated island judging unit;
Described first-phase potential difference computing unit, for calculate three-phase power grid voltage every two-phase between phase differential
Described reactive current injection unit, for injecting reactive current on the output current of inverter;
Described second-phase potential difference computing unit, for calculate the three-phase power grid voltage after injecting reactive current every two-phase between phase differential
Described phase difference value acquiring unit, for the phase differential after obtaining injecting reactive current
with the phase differential before injecting reactive current
phase difference value
Described isolated island judging unit, for judging described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
The embodiment of the present invention provides a kind of detection system of one-phase island of three-phase grid-connected inverter, comprising: inverter, circuit control device and electrical network;
Described circuit control device, for calculate the three-phase power grid voltage of electrical network every two-phase between phase differential
injecting reactive current on the output current of inverter; Phase differential between every two-phase of the three-phase power grid voltage of the electrical network after calculating injecting reactive current
obtain the phase differential after injecting reactive current
with the phase differential before injecting reactive current
phase difference value
judge described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
Compared with the existing technology, in the embodiment of the present invention, injecting reactive current on the output current of inverter.Before calculating injecting reactive current, the phase differential in three-phase voltage between every two phase voltages
after calculating injecting reactive current again, the phase differential in three-phase voltage between every two phase voltages
judge
with
phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.Method provided by the invention can judge whether isolated island occurs accurately and efficiently by phase difference value, and what inject the output current of inverter due to the present invention is reactive current, the harmonic content of such output waveform is very little, only has minimum idle change during grid-connected inverters work.Compared with the perturbation motion method based on frequency or active power of the prior art, the reactive current that the present invention injects can not affect generated energy.
Accompanying drawing explanation
In order to be illustrated more clearly in the technical scheme of the embodiment of the present invention, be briefly described to the accompanying drawing used required in embodiment or description of the prior art below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawing can also be obtained according to these accompanying drawings.
Fig. 1 is the operating diagram of a kind of three-phase grid-connected inverter of the prior art;
Detection method embodiment one process flow diagram of the one-phase island of the three-phase grid-connected inverter that Fig. 2 provides for the embodiment of the present invention;
Fig. 3 is detection method embodiment two process flow diagram of the one-phase island of three-phase grid-connected inverter provided by the invention;
Fig. 4 is the full-scale investigation oscillogram of the method that Fig. 3 is corresponding;
Fig. 5 is that method that Fig. 3 is corresponding is to the full-scale investigation oscillogram of disconnected BC phase time;
Fig. 6 is checkout equipment embodiment one schematic diagram of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that the embodiment of the present invention provides;
Fig. 7 is checkout equipment embodiment two schematic diagram of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that the embodiment of the present invention provides;
Fig. 8 is checkout equipment embodiment three schematic diagram of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that embodiment provides;
Detection system embodiment one schematic diagram of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that Fig. 9 is to provide.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on the embodiment in the present invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to the scope of protection of the invention.
Embodiments provide a kind of detection method of one-phase island of three-phase grid-connected inverter, equipment and system; the generation of one-phase island or two-phase isolated island can be judged timely and accurately when three-phase grid-connected inverter works; thus send isolated island warning; make the timely detachment system of inverter, play a protective role.
For the ease of fully understanding embodiment of the present invention technical scheme, below in conjunction with the accompanying drawing in the embodiment of the present invention, clear, complete description is carried out to the technical scheme in the embodiment of the present invention.
First, the detection method of the one-phase island of the three-phase grid-connected inverter that the embodiment of the present invention provides is illustrated as follows.The method comprises: the phase differential between every two-phase of calculating three-phase power grid voltage
injecting reactive current on the output current of inverter; Phase differential between every two-phase of the three-phase power grid voltage after calculating injecting reactive current
obtain the phase differential after injecting reactive current
with the phase differential before injecting reactive current
phase difference value
judge described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
It should be noted that, the operative scenario of the inverter in embodiments of the invention is Figure 1 shows that example is described.RLC load is equivalent at C phase load.For the electric voltage frequency of electrical network for 50Hz is introduced, i.e. the resonance frequency of load is 50Hz.The method that the embodiment of the present invention is carried goes for one-phase island and detects and two-phase islanding detect.Such as, after C phase disconnects, inverter and load form isolated island.Or such as, after B phase and C phase all disconnect, inverter and load form isolated island.Below in conjunction with specific embodiment, concrete introduction is carried out to these two kinds of islanding detect.
Embodiment of the method one:
See Fig. 2, this figure is detection method embodiment one process flow diagram of the one-phase island of the three-phase grid-connected inverter that the embodiment of the present invention provides.
S201: the phase differential between every two-phase of calculating three-phase power grid voltage
It should be noted that, before injecting reactive current, if do not have isolated island to produce, then the phase differential between the every two-phase of three-phase power grid voltage is determined by line voltage, namely phase differential be 120 degree (between A and B phase, between B and C phase, between A and C phase).
S202: injecting reactive current on the output current of inverter;
Why to injecting reactive current on the output current of inverter in the embodiment of the present invention, be because:
If not injecting reactive current on the output current of inverter, when there is isolated island, likely on certain point of load, resonance frequency is 50Hz, namely identical with the frequency of line voltage, phase place.Like this, the phase place that isolated island phase occurs, when without external interference, can maintain normal operation, can't trigger island protect, make inverter detachment system.
The method that the present embodiment provides has superposed reactive current on the output current of inverter, and such load voltage can change along with the phase place change of the output current of inverter.The phase place of the voltage of fault phase is determined by load.Total output current after the output current that load voltage equals inverter has superposed reactive current is multiplied by the impedance of load.Now the sampled point of the line voltage of this fault phase is exactly the load voltage after isolated island occurs (because this fault phase is disconnected, it doesn't matter for the voltage of this fault phase and line voltage), and the phase place of load voltage there occurs change owing to being filled with reactive current, thus detect that the phase differential of the phase place of fault phase and the phase place of other healthy phases there occurs change.
It should be noted that, make loaded work piece at resonance frequency 50Hz, can realize by regulating L and C in RLC equivalent load.
S203: the phase differential between every two-phase of the three-phase power grid voltage after calculating injecting reactive current
At this moment, the phase place of the voltage of healthy phases is still decided by line voltage, and the phase place of the voltage of fault phase is decided by the voltage in load, therefore, the phase differential between every two-phase of the voltage phase difference now in three-phase between every two-phase and before not breaking down there occurs change.
S204: obtain the phase differential after injecting reactive current
with the phase differential before injecting reactive current
phase difference value
namely
or
S205: judge described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
It should be noted that, a threshold value of described setting phase threshold and predetermined set, when phase difference value is less than or equal to this setting phase threshold, does not think and there occurs isolated island, only have when phase difference value is greater than this setting phase threshold, just think and there occurs isolated island.Because electrical network itself also exists certain fluctuation, when normally working, also phase differential may be there is.
The method that the present embodiment provides, injecting reactive current on the output current of inverter.Before calculating injecting reactive current, the phase differential in three-phase voltage between every two phase voltages
after calculating injecting reactive current again, the phase differential in three-phase voltage between every two phase voltages
judge
with
phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.Method provided by the invention can judge whether isolated island occurs very accurately and effectively by phase difference value, and what inject the output current of inverter due to the present invention is reactive current, the harmonic content of such output waveform is very little, only has minimum idle change during grid-connected inverters work.Compared with the perturbation motion method based on frequency or active power of the prior art, the reactive current that the present invention injects can not affect generated energy.
It should be noted that, the reactive current that the output current of inverter injects is related with the output current of inverter, and physical relationship can be preferably: described reactive current be the k of the output current of described inverter doubly, k be less than 1 decimal.
Generally arranging k is the less decimal being less than 1, such as, be 0.02.It should be noted that, it is too large that k can not be arranged, because the power factor command of general grid type inverter is 1, injects the requirement that very little reactive current does not affect power factor.0.02 is empirical value, can fluctuate up and down about 0.02.
Embodiment of the method two:
See Fig. 3, this figure is detection method embodiment two process flow diagram of the one-phase island of three-phase grid-connected inverter provided by the invention.
Be photovoltaic DC-to-AC converter below with inverter for example is introduced.
This inverter power is 20kW, for fully loaded output.Certainly, inverter also can not be fully loaded with output, and fully loaded output is only one of them operating mode.Such as, inverter exports only has 10kW, and the load consumption of a certain phase is just in time 3.333kW, now, consumes and equals to export, load matched.
Connect single-phase RLC equivalent load between inverter and electrical network, it should be noted that, load may not be RLC, but according to circuit working principle, can be equivalent to RLC load.Hookup signal as shown in Figure 1.
R consumed power is herein 6.666kW, regulates the value of L and C, makes the resonance frequency of load at 50Hz.
Isolated island test is carried out to disconnect C phase electrical network.
S301: circuit control device gathers the zero crossing of three-phase power grid voltage, obtains the phase place of each phase in three-phase power grid voltage A, B and C three-phase; Calculate the phase differential between the every two-phase of A, B and C
S302: send drive control signal to inverter by circuit control device, changes the output current of inverter, makes the output current of inverter become superposing of the reactive current of the original output current of inverter and injection.
S303: circuit control device gathers the zero crossing of the three-phase power grid voltage after injecting reactive current, obtains the phase place of each phase in three-phase power grid voltage A, B and C three-phase; Calculate the phase differential between the every two-phase of A, B and C
S304-S305 and S204-S205 is identical, does not repeat them here.
Due to C phase electric network power-fail, therefore, before injecting reactive current, the phase differential of three-phase power grid voltage is 120 degree (A phase is 120 degree with the phase differential of B phase, and B phase is 120 degree with the phase differential of C phase, and A phase is 120 degree with the phase place of C phase).But after the injecting reactive current of the schedule time, because A phase continues by mains supply with B phase, therefore, the voltage-phase of A phase and B phase does not change, and the voltage-phase of C phase and the voltage-phase of load consistent.Like this, the voltage phase difference between B phase and C phase will change, and the voltage phase difference between C phase and A phase also will change.
Therefore, when C phase and inverter form isolated island, the method utilizing the present embodiment to provide can detect that the phase differential between BC and CA there occurs change, reports to the police, opened by inverter in time from system break isolated island.Thus the harm that can effectively avoid isolated island to bring.Such as, switch upper end is charged, easily gets an electric shock when maintenance personal overhauls.
See Fig. 4, this figure is the full-scale investigation oscillogram of the method that Fig. 3 is corresponding.
Wherein, 4 passages are the electric current that electrical network exports, and the current vanishes moment is the moment that isolated island occurs.2 passages are the output voltage of inverter.2 passages become 0 and represent island protect inverter is shut down.
By the contrast of time shaft, the actuation time that can calculate one-phase island protection is 2.46s, meets the demands.The actuation time of General Requirements island protect is within 5s.When it should be noted that the European countries such as Germany require one-phase island occurs, combining inverter is stopped power supply in 5s, if standard-required time shorten, then can pass through to regulate k to increase, or reduce the realization of setting phase threshold.
As can be seen from this experiment, the method that the embodiment of the present invention provides can detect the generation of one-phase island effectively in time, carries out the disengaging protection of inverter within effective time.
See Fig. 5, this figure is the full-scale investigation oscillogram of method provided by the invention to disconnected BC phase time.
Also be make the resonance frequency of load be 50Hz in the present embodiment, namely identical with the frequency of line voltage.Injecting reactive current on the output current of inverter.Phase differential before and after test injecting reactive current between every two phase voltages.
Be understandable that, after the B phase of electrical network and C phase all disconnect, the phase differential between AB, BC and CA all there occurs change before and after injecting reactive current.
In Fig. 5,4 passages are the electric current that electrical network exports, and the current vanishes moment is the moment that isolated island occurs.1,2 passages are the output voltage of inverter.1,2 passages become 0 and represent island protect inverter is shut down.
By the contrast of time shaft, the time that can calculate two-phase island protect is 2.53s, meets the demands.The actuation time of General Requirements island protect is within 5s.
As can be seen from this experiment, the method that the embodiment of the present invention provides can detect the generation of two-phase isolated island effectively in time, carries out the disengaging protection of inverter within effective time.
It should be noted that, in the above method in the embodiment of the present invention, on the output current of inverter, injecting reactive current injects once in predetermined time interval, such as, inject a reactive current every 500ms, each injection cannot also can set time of electric current, such as, inject 20ms.I.e. 500ms one-period, injects the reactive current of 20ms in one-period.
The embodiment of the present invention additionally provides the checkout equipment of the single-phase of a kind of three-phase grid-connected inverter or two-phase isolated island, is described in detail below in conjunction with accompanying drawing.
Apparatus embodiments one:
See Fig. 6, this figure is checkout equipment embodiment one schematic diagram of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that the embodiment of the present invention provides.
The checkout equipment of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that the present embodiment provides, comprising: first-phase potential difference computing unit 100, reactive current injection unit 200, second-phase potential difference computing unit 300, phase difference value acquiring unit 400 and isolated island judging unit 500;
Described first-phase potential difference computing unit 100, for calculate three-phase power grid voltage every two-phase between phase differential
It should be noted that, before injecting reactive current, if do not have isolated island to produce, then the phase differential between the every two-phase of three-phase power grid voltage is determined by line voltage, namely phase differential be 120 degree (between A and B phase, between B and C phase, between A and C phase).
Described reactive current injection unit 200, for injecting reactive current on the output current of inverter;
Why to injecting reactive current on the output current of inverter in the embodiment of the present invention, be because:
If not injecting reactive current on the output current of inverter, when there is isolated island, likely on certain point of load, resonance frequency remains 50Hz, namely identical with the frequency of line voltage.Like this, the phase place that isolated island phase occurs, when without external interference, can maintain normal operation, can't trigger island protect, make inverter detachment system.
The equipment that the present embodiment provides has superposed reactive current on the output current of inverter, and such load voltage can change along with the phase place change of the output current of inverter.Now the sampled point of the line voltage of this fault phase is exactly the load voltage after isolated island occurs (because this fault phase is disconnected, it doesn't matter for the voltage of this fault phase and line voltage), and the phase place of load voltage there occurs change owing to being filled with reactive current, thus detect that the phase differential of the phase place of fault phase and the phase place of other healthy phases there occurs change.
It should be noted that, make loaded work piece at resonance frequency 50Hz, can realize by regulating L and C in equivalent RLC load.
Described second-phase potential difference computing unit 300, for calculate the three-phase power grid voltage after injecting reactive current every two-phase between phase differential
At this moment, the phase place of the voltage of healthy phases is still decided by line voltage, and the phase place of the voltage of fault phase is decided by the voltage in load, therefore, the phase differential between every two-phase of the voltage phase difference now in three-phase between every two-phase and before not breaking down there occurs change.
Described phase difference value acquiring unit 400, for the phase differential after obtaining injecting reactive current
with the phase differential before injecting reactive current
phase difference value
Described isolated island judging unit 500, for judging described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
It should be noted that, a threshold value of described setting phase threshold and predetermined set, when phase difference value is less than or equal to this setting phase threshold, does not think and there occurs isolated island, only have when phase difference value is greater than this setting phase threshold, just think and there occurs isolated island.Because electrical network itself also exists certain fluctuation, when normally working, also phase differential may be there is.
The equipment that the present embodiment provides, injecting reactive current on the output current of inverter.Before calculating injecting reactive current, the phase differential in three-phase voltage between every two phase voltages
after calculating injecting reactive current again, the phase differential in three-phase voltage between every two phase voltages
judge
with
phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.Equipment provided by the invention can judge whether isolated island occurs very accurately and effectively by phase difference value, and what inject the output current of inverter due to the present invention is reactive current, the harmonic content of such output waveform is very little, only has minimum idle change during grid-connected inverters work.Compared with the perturbation motion method based on frequency or active power of the prior art, the reactive current that the present invention injects can not affect generated energy.
It should be noted that, the reactive current that the output current of inverter injects is related with the output current of inverter, and physical relationship can be preferably: described reactive current be the k of the output current of described inverter doubly, k be less than 1 decimal.
Generally arranging k is the less decimal being less than 1, such as, be 0.02.
Apparatus embodiments two:
See Fig. 7, this figure is checkout equipment embodiment two schematic diagram of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that the embodiment of the present invention provides.
The implementation introducing first-phase potential difference computing unit and second-phase potential difference computing unit in detail with the difference of apparatus embodiments one in the present embodiment.
First-phase potential difference computing unit 100 in the present embodiment comprises phase acquisition first subelement 101, first-phase potential difference computation subunit 102;
Described phase acquisition first subelement 101, for gathering the zero crossing of injecting reactive current three-phase line voltage, obtains the phase place of each phase in three-phase power grid voltage A, B and C three-phase;
Described first-phase potential difference computation subunit 102, for the phase place of each phase by described phase acquisition first subelement acquisition, calculates the phase differential between the every two-phase of A, B and C
Described second-phase potential difference computing unit 300 comprises phase acquisition second subelement 301, second-phase potential difference computation subunit 302;
Described phase acquisition second subelement 301, for gathering the zero crossing of three-phase power grid voltage after injecting reactive current, obtains the phase place of each phase in three-phase power grid voltage A, B and C three-phase;
Described second-phase potential difference computation subunit 302, for the phase place of each phase by described phase acquisition second subelement acquisition, calculates the phase differential between the every two-phase of A, B and C
Such as, when C phase voltage disconnects, application the present embodiment test isolated island.Due to C phase electric network power-fail, therefore, before injecting reactive current, the phase differential of three-phase power grid voltage is 120 degree (A phase is 120 degree with the phase differential of B phase, and B phase is 120 degree with the phase differential of C phase, and A phase is 120 degree with the phase place of C phase).But after the injecting reactive current of the schedule time, because A phase continues by mains supply with B phase, therefore, the voltage-phase of A phase and B phase does not change, and the voltage-phase of C phase and the voltage-phase of load consistent.Like this, the voltage phase difference between B phase and C phase will change, and the voltage phase difference between C phase and A phase also will change.
Apparatus embodiments three:
See Fig. 8, this figure is checkout equipment embodiment three schematic diagram of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that the embodiment of the present invention provides.
The implementation of reactive current injection unit 200 is mainly introduced in the present embodiment.
Reactive current injection unit 200 in the present embodiment comprises drive control signal and sends subelement 201, for sending drive control signal to inverter, change the output current of inverter, make the output current of inverter become superposing of the reactive current of the original output current of inverter and injection.
It should be noted that, the power section of inverter is mainly realized by power tube.Drive control signal sends subelement 201 and produces pwm pulse signal, the on off state of the power tube in this pwm pulse signal control inverter, thus makes inverter be the alternating current needed by DC inverter.Wherein, the frequency of alternating current and amplitude can realize regulating by changing pwm pulse signal.
Therefore, on the output current of inverter, injecting reactive current in fact just can be realized by the pwm pulse signal changing control inverter, that is, the output current of inverter is made to become superposing of the reactive current of the original output current of inverter and injection by sending drive control signal to inverter.
The embodiment of the present invention additionally provides the detection system of the single-phase of a kind of three-phase grid-connected inverter or two-phase isolated island, is described in detail below in conjunction with accompanying drawing.
See Fig. 9, this figure is detection system embodiment one schematic diagram of the single-phase of three-phase grid-connected inverter provided by the invention or two-phase isolated island.
The detection system of the single-phase or two-phase isolated island of the three-phase grid-connected inverter that the embodiment of the present invention provides, comprising: inverter 800, circuit control device 900 and electrical network 1000;
Described circuit control device 900, for calculate the three-phase power grid voltage of electrical network 1000 every two-phase between phase differential
injecting reactive current on the output current of inverter 800; Phase differential between every two-phase of the three-phase power grid voltage of the electrical network 1000 after calculating injecting reactive current
obtain the phase differential after injecting reactive current
with the phase differential before injecting reactive current
phase difference value
judge described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
Be understandable that, in three-phase grid-connected inverting system, inverter 800, for after by the DC inverter of wind-power electricity generation or photovoltaic generation being alternating current, is fed to electrical network 1000.Wherein the effect of circuit control device 900 is the power tubes in control inverter 800, and circuit control device 900 is by send to inverter 800 PWM drive singal direct current that control inverter 800 exports needs.
The system that the present embodiment provides, circuit control device 900 injecting reactive current on the output current of inverter 800.Before circuit control device 900 calculates injecting reactive current, the phase differential in three-phase voltage between every two phase voltages
after calculating injecting reactive current again, the phase differential in three-phase voltage between every two phase voltages
judge
with
phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.System provided by the invention can judge whether isolated island occurs very accurately and effectively by phase difference value, and what inject the output current of inverter 800 due to the present invention is reactive current, the harmonic content of such output waveform is very little, only has minimum idle change during inverter 800 grid-connected work.Compared with the perturbation motion method based on frequency or active power of the prior art, the reactive current that the present invention injects can not affect generated energy.
It should be noted that, described circuit control device is to injecting reactive current on the output current of inverter, be specially: send drive control signal by circuit control device to inverter, change the output current of inverter, make the output current of inverter become superposing of the reactive current of the original output current of inverter and injection.
It should be noted that, the reactive current that the output current of inverter injects is related with the output current of inverter, and physical relationship can be preferably: described reactive current be the k of the output current of described inverter doubly, k be less than 1 decimal.
Generally arranging k is the less decimal being less than 1, such as, be 0.02.
It should be noted that, the technical scheme in above embodiment, go in the various systems shown in Fig. 1, be not only grid-connected photovoltaic system, can also be used in other three-phase grid-connected inverting systems, such as, wind power-generating grid-connected inversion system, or accumulator system etc.
Device embodiment described above is only schematic, the wherein said unit illustrated as separating component or can may not be and physically separates, parts as unit display can be or may not be physical location, namely can be positioned at a place, or also can be distributed in multiple network element.Some or all of module wherein can be selected according to the actual needs to realize the object of the present embodiment scheme.Those of ordinary skill in the art, when not paying creative work, are namely appreciated that and implement.
To the above-mentioned explanation of the disclosed embodiments, professional and technical personnel in the field are realized or uses the present invention.To be apparent for those skilled in the art to the multiple amendment of these embodiments, General Principle as defined herein when not departing from the spirit or scope of the embodiment of the present invention, can realize in other embodiments.Therefore, the embodiment of the present invention can not be restricted to these embodiments shown in this article, but will meet the widest scope consistent with principle disclosed herein and features of novelty.
Claims (10)
1. a detection method for the single-phase or two-phase isolated island of three-phase grid-connected inverter, is characterized in that, comprising:
Phase differential between every two-phase of calculating three-phase power grid voltage
Injecting reactive current on the output current of inverter;
Phase differential between every two-phase of the three-phase power grid voltage after calculating injecting reactive current
Obtain the phase differential after injecting reactive current
with the phase differential before injecting reactive current
phase difference value
Judge described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
2. the detection method of the single-phase or two-phase isolated island of three-phase grid-connected inverter according to claim 1, is characterized in that, described reactive current be the k of the output current of described inverter doubly, k be less than 1 decimal.
3. the detection method of the single-phase or two-phase isolated island of three-phase grid-connected inverter according to claim 1 and 2, it is characterized in that, described to injecting reactive current on the output current of inverter, be specially: send drive control signal by circuit control device to inverter, change the output current of inverter, make the output current of inverter become superposing of the reactive current of the original output current of inverter and injection.
4. the detection method of the single-phase or two-phase isolated island of three-phase grid-connected inverter according to claim 1, is characterized in that, the phase differential between every two-phase of described calculating three-phase power grid voltage
and the phase differential between the every two-phase calculating the three-phase power grid voltage after injecting reactive current
be specially:
Circuit control device gathers the zero crossing of three-phase power grid voltage, obtains the phase place of each phase in three-phase power grid voltage A, B and C three-phase;
Calculate the phase differential between the every two-phase of A, B and C.
5. a checkout equipment for the single-phase or two-phase isolated island of three-phase grid-connected inverter, is characterized in that, comprising: first-phase potential difference computing unit, reactive current injection unit, second-phase potential difference computing unit, phase difference value acquiring unit and isolated island judging unit;
Described first-phase potential difference computing unit, for calculate three-phase power grid voltage every two-phase between phase differential
Described reactive current injection unit, for injecting reactive current on the output current of inverter;
Described second-phase potential difference computing unit, for calculate the three-phase power grid voltage after injecting reactive current every two-phase between phase differential
Described phase difference value acquiring unit, for the phase differential after obtaining injecting reactive current
with the phase differential before injecting reactive current
phase difference value
Described isolated island judging unit, for judging described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
6. the checkout equipment of the single-phase or two-phase isolated island of three-phase grid-connected inverter according to claim 5, is characterized in that, described first-phase potential difference computing unit comprises phase acquisition first subelement, first-phase potential difference computation subunit;
Described phase acquisition first subelement, for gathering the zero crossing of injecting reactive current three-phase line voltage, obtains the phase place of each phase in three-phase power grid voltage A, B and C three-phase;
Described first-phase potential difference computation subunit, for the phase place of each phase by described phase acquisition first subelement acquisition, calculates the phase differential between the every two-phase of A, B and C
7. the checkout equipment of the single-phase or two-phase isolated island of three-phase grid-connected inverter according to claim 5, is characterized in that,
Described second-phase potential difference computing unit comprises phase acquisition second subelement, second-phase potential difference computation subunit;
Described phase acquisition second subelement, for gathering the zero crossing of three-phase power grid voltage after injecting reactive current, obtains the phase place of each phase in three-phase power grid voltage A, B and C three-phase;
Described second-phase potential difference computation subunit, for the phase place of each phase by described phase acquisition second subelement acquisition, calculates the phase differential between the every two-phase of A, B and C
8. the checkout equipment of the single-phase or two-phase isolated island of three-phase grid-connected inverter according to claim 5, it is characterized in that, described reactive current injection unit comprises drive control signal and sends subelement, for sending drive control signal to inverter, change the output current of inverter, make the output current of inverter become superposing of the reactive current of the original output current of inverter and injection.
9. a detection system for the single-phase or two-phase isolated island of three-phase grid-connected inverter, is characterized in that, comprising: inverter, circuit control device and electrical network;
Described circuit control device, for calculate the three-phase power grid voltage of electrical network every two-phase between phase differential
injecting reactive current on the output current of inverter; Phase differential between every two-phase of the three-phase power grid voltage of the electrical network after calculating injecting reactive current
obtain the phase differential after injecting reactive current
with the phase differential before injecting reactive current
phase difference value
judge described phase difference value
when being greater than setting phase threshold, then judge isolated island occurs.
10. the detection system of the single-phase or two-phase isolated island of three-phase grid-connected inverter according to claim 9, it is characterized in that, described circuit control device is to injecting reactive current on the output current of inverter, be specially: send drive control signal by circuit control device to inverter, change the output current of inverter, make the output current of inverter become superposing of the reactive current of the original output current of inverter and injection.
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| CN103713211B (en) * | 2013-11-29 | 2016-07-06 | 江苏兆伏新能源有限公司 | The single-phase, two-phase island detection method of a kind of three-phase grid-connected inverter and device |
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