CN104569696A - Island detection method based on dq conversion and used for voltage per unit value positive feedback - Google Patents

Island detection method based on dq conversion and used for voltage per unit value positive feedback Download PDF

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Publication number
CN104569696A
CN104569696A CN201510050208.9A CN201510050208A CN104569696A CN 104569696 A CN104569696 A CN 104569696A CN 201510050208 A CN201510050208 A CN 201510050208A CN 104569696 A CN104569696 A CN 104569696A
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voltage
perunit value
positive feedback
detection method
current
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CN201510050208.9A
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Inventor
闫朝阳
王楠楠
王子晗
张青山
郑倩男
杨振华
刘安平
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Large Chao Hua Electronic Science And Technology Co Ltd Of Qinhuangdao Swallow
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Large Chao Hua Electronic Science And Technology Co Ltd Of Qinhuangdao Swallow
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Abstract

The invention discloses an island detection method based on dq conversion and used for voltage per unit value positive feedback. The island detection method includes that according to the commonly-known island detection method based on voltage positive feedback, current reference value is constantly increased or decreased through a squared equal relationship between an active per unit value in which reference current is output to an inverter and voltage of a common coupling point to increase or decrease voltage of PCC until exceeding a threshold value to detect an island. By the island detection method, blind-zone-free island detection can be realized, so that detection range is expanded greatly; no harmonic wave is injected into a power grid, so that reliability of the power grid is guaranteed; a feedback system is omitted, so that a series of problems caused by selecting of the feedback system are avoided.

Description

Based on the island detection method of the voltage perunit value positive feedback of dq conversion
Technical field
The present invention relates to the method for distributed generation system islanding detect, the active detection method particularly in the detection of this locality, belongs to power electronics power electronics combining inverter control field.
Background technology
Distributed generation system, the capacity of typically referring to is less than 10MW, for electric energy emergency backup, supplements network system, local or the electricity generation system generated electricity from far-off regions.Distributed power generation power supply mainly contains: miniature gas turbine, fuel cell, photovoltaic cell, wind-power electricity generation, tide, underground heat etc., and these systems most have the little feature of pollution.Wherein combining inverter is the core of whole system, determines the quality of electric energy.When grid cut-off or maintenance, the isolating switch between electrical network and its confession electric loading can be disconnected, and distributed generation system does not detect the malfunction of electrical network, inverter works always, also continue to local RLC load supplying, then distributed generation system and local RLC load just constitute the isolated island of a self-energizing.
Summary of the invention
The object of the invention is to the check frequency problem solving islanding detect existence, and electrical network harmonic can not be thought, ensure that the operational reliability of other consumers upper of electrical network.Relative to traditional voltage positive feedback islanding detect method, because it does not exist feedback factor, improve detection speed.
For solving the problems of the technologies described above, the technical solution used in the present invention is:
The technical solution adopted in the present invention implements the mistake/low-voltage protection link, three-phase list synchronizing software phaselocked loop, three-phase voltage perunit value positive feedback algorithm, current feed-forward uneoupled control four part that comprise islanding detect.
Island detection method based on the voltage perunit value positive feedback of dq conversion is, according to the known island detection method based on voltage positive feedback, by to the real component perunit value of inverter output reference electric current and the perunit value square equal relation of point of common coupling voltage, continuous increase or reduction current reference value, raise or reduce the voltage of PCC, until exceed threshold values, isolated island detected.
Specifically comprise the following steps:
Step one, in distributed grid-connected inverter, by DG system PCC point voltage u a, u b, u cundertaken phase-locked by software phase-lock loop, obtain angular frequency and the positive sequence phase angle theta of electrical network.
Step 2, to PCC point voltage u a, u b, u ccarry out dq conversion, by judging the amplitude u of the d axle component of voltage dpccwhether within the threshold values of setting, if so, carry out step 3, if not, carry out step 7.
The amplitude u of step 3, calculating d shaft voltage component dpccperunit value u dpcc-p.u..
Step 4, calculate given electric current perunit value i * d-p.u.equal the amplitude u of d shaft voltage component dpccperunit value u dpcc-p.u.square.
Step 5, calculates given current i * dfor load current value i d * 'with given electric current perunit value i * d-p.u.product.
Step 6, by the control to given electric current and feedback current, changes the amplitude of PCC point voltage, if it exceeds threshold range, then carries out step 7, otherwise returns step 3.
Step 7, detects isolated island, carries out pulse blocking.
As preferably, the threshold voltage scope described in step 2 is u dmin=10V, u dmax=50V.Given electric current perunit value computing method described in step 4, by the Varying Coefficients Linear relation with voltage perunit value, is converted into the quadratic relationship with voltage perunit value.The product that given electric current described in step 5 equals rated current and perunit value adds the periodic perturbation amount Δ I of electric current.The d axle component u of the Current Control described in step 6 and PCC point voltage dthe positive feedback formed, when combining inverter output current is changed, PCC point voltage also can respective change, until reach the scope of islanding detect.
In synchronous rotating frame, three-phase grid-connected inverter exports (u gq=0) and the meritorious and idle of partial load be shown below:
P = 3 2 u gd · i d Q = - 3 2 u gd · i q - - - ( 1 )
P load = 3 u aRMs 2 / R Q load = 3 ( 1 ω a L - ω a C ) u a 2 - - - ( 2 )
According to above-mentioned two formulas, a voltage positive feedback can be set up at the control section of inverter.Its principle of work is as follows: when detection computations goes out PCC voltage d axle component u dduring increase, due to positive feedback, inverter exports d shaft current to be increased, and inverter exports meritorious P also to be increased, if there is isolated island, PCC voltage magnitude will be made to increase, when PCC voltage magnitude be increased to exceed normal range time, island effect is just detected; In like manner, when voltage magnitude reduces, will to changing inversely, until island protect.
Beneficial effect of the present invention is:
By the island detection method to the voltage perunit value positive feedback converted based on dq, both islanding detect non-blind area can be realized, substantially increase sensing range, and not to electrical network harmonic, ensure that the reliability of electrical network, can not feedback factor be there is again, avoid and choose due to feedback factor the series of problems brought.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is further detailed explanation.
Fig. 1 mentioned by the present invention based on dq conversion voltage magnitude and meritorious positive feedback graph of a relation.
The load of Fig. 2 mentioned by the present invention and electric current, the voltage perunit value curve map of inverter output.
The Control system architecture figure of the three-phase voltage perunit value positive feedback method of Fig. 3 mentioned by the present invention.
The application of Fig. 4 mentioned by the present invention detects isolated island based on the voltage perunit value positive feedback method that dq converts and rear inverter output current oscillogram occurs.
The application of Fig. 5 mentioned by the present invention detects isolated island based on the voltage perunit value positive feedback method that dq converts and rear PCC voltage oscillogram occurs.
Fig. 6 is the voltage perunit value positive feedback method interrupt routine process flow diagram based on dq conversion that the present invention proposes.
Fig. 7 is the voltage perunit value positive feedback method experimental waveform based on dq conversion that the present invention proposes.
Embodiment
Fig. 1 be based on dq conversion voltage magnitude and meritorious positive feedback graph of a relation.As can be seen from Figure, active-power P is proportional to d axle real component i * d, therefore, d axle component i * dchange can cause the change of PCC voltage magnitude.When detection computations goes out PCC voltage d axle component u dduring increase, due to positive feedback, inverter exports d shaft current to be increased, and inverter exports meritorious P also to be increased, if there is isolated island, PCC voltage magnitude will be made to increase, when PCC voltage magnitude be increased to exceed normal range time, island effect is just detected; In like manner, when voltage magnitude reduces, will to changing inversely, until island protect.
Fig. 2 is electric current, the voltage perunit value curve map that load and inverter export.D axle active current and PCC voltage magnitude linear.As id > 1.1p.u. or id < 0.88p.u., PCC voltage magnitude can exceed specified scope.The mode of perunit value can be adopted to represent electric current, magnitude of voltage, curve plotting figure.In figure, the straight-line equation of zero crossing is: i (p.u.)=ku (p.u.), and curvilinear equation is: i (p.u.)=u 2(p.u.).
Islanding detect algorithm is:
i * d-p.u.＝k 1×u dpcc-p.u.(5)
I * d-p.u.for the perunit value of d axle reference current; u dpcc-p.u.for the perunit value of PCC voltage d axle component; k 1for feedback factor.
i * d-p.u.＝u 2 dpcc-p.u.(6)
i＝i×i+ΔI (7)
In formula, i * d-p.u.for the perunit value of d axle reference current; u dpcc-p.u.for the perunit value of PCC voltage d axle component; Δ I is periodic perturbation amount.
Fig. 3 is for being three-phase voltage perunit value positive feedback method (i * d-p.u.=u 2 dpcc-p.u.) Control system architecture figure.After electric network fault, as k>1, load active power is greater than output power, and PCC voltage can reduce, and given value of current is also 1 this moment, supposes to drop to A point, and within the scope of blind area, after voltage sample, given value of current is u 2(p.u.).After quadratic power, the change of current reference is obvious compared to straight line i (p.u.)=ku (p.u.) very large, constantly reduces current reference value, improves the speed of islanding detect; In like manner, as k<1, load active power is less than output power straight line, and PCC voltage can increase, by i (p.u.)=u 2(p.u.) constantly increase current reference value, raise the voltage of PCC, until exceed threshold values, isolated island detected.Can find out that obviously increasing reference current exports the change of following PCC voltage after isolated island.As k=1, load active power mates with system output power, i.e. i (p.u.)=ku (p.u.), and the method just enters blind area, and B point is blind area point, cannot isolated island be detected, so be necessary to add small disturbance.
Fig. 4 is that application is based on inverter output current oscillogram after the voltage perunit value positive feedback method detection isolated island generation of dq conversion.Electrical network is in 0.13s suspension.Change with reference current in the disturbance quantity of this setting, be set to ± 2%i * d(its value is with u dpcc-p.u.change and constantly change perturbation direction), the disturbance cycle is 0.1s, each disturbance 0.02s.
Fig. 5 is that application is based on PCC voltage oscillogram after the voltage perunit value positive feedback method detection isolated island generation of dq conversion.When load in worst case, namely during R=44 Ω, in 0.13s suspension, just in time avoid initial disturbance amount, as shown in Figure 6, in 0.22s under-voltage protection, isolated island detected, detection time is 0.09s; PCC voltage reduces to 0 at about 0.3s.
The voltage perunit value positive feedback method interrupt routine process flow diagram that Fig. 6 converts based on dq.By the feedback of the voltage magnitude of PCC, joined in given electric current, change the output of reference current, thus the voltage of PCC is also changed thereupon, until voltage transfinites, realize island protect.Arranging grid-connected voltage in experiment is 30V, and grid-connected current is 1A, and partial load is resistive worst condition, R=30 Ω.In order to the trend of change in voltage in voltage positive feedback can be embodied, be convenient to observe, improve in the voltage range of this island protect, be chosen for 10V<ud<50V, draw process flow diagram with this.
Fig. 7 is the voltage perunit value positive feedback method experimental waveform based on dq conversion.Can obtain after electrical network disconnects, after about 5 grid cycle, isolated island detected, inverter quits work.
Be only the specific embodiment of this patent above, but this patent is not limited thereto, for the person of ordinary skill of the art, under the premise without departing from the principles of the invention, the distortion made should be considered as belonging to scope.

Claims (5)

1., based on an island detection method for the voltage perunit value positive feedback of dq conversion, it is characterized in that comprising the following steps:
Step one, in distributed grid-connected inverter, by DG system PCC point voltage u a, u b, u cundertaken phase-locked by software phase-lock loop, obtain angular frequency and the positive sequence phase angle theta of electrical network;
Step 2, to PCC point voltage u a, u b, u ccarry out dq conversion, by judging the amplitude u of the d axle component of voltage dpccwhether within the threshold values of setting, if so, carry out step 3, if not, carry out step 7;
The amplitude u of step 3, calculating d shaft voltage component dpccperunit value u dpcc-p.u.;
Step 4, calculate given electric current perunit value i * d-p.u.equal the amplitude u of d shaft voltage component dpccperunit value u dpcc-p.u.square;
Step 5, calculates given current i * dfor load current value i d * 'with given electric current perunit value i * d-p.u.product;
Step 6, by the control to given electric current and feedback current, changes the amplitude of PCC point voltage, if it exceeds threshold range, then carries out step 7, otherwise returns step 3;
Step 7, detects isolated island, carries out pulse blocking.
2. the island detection method of the voltage perunit value positive feedback based on dq conversion according to claim 1, is characterized in that: the threshold voltage scope described in step 2 is u dmin=10V, u dmax=50V.
3. the island detection method of the voltage perunit value positive feedback based on dq conversion according to claim 1, it is characterized in that: the given electric current perunit value computing method described in step 4, by the Varying Coefficients Linear relation with voltage perunit value, is converted into the quadratic relationship with voltage perunit value.
4. the island detection method of voltage perunit value positive feedback based on dq conversion according to claim 1, is characterized in that: the product that the given electric current described in step 5 equals rated current and perunit value adds the periodic perturbation amount Δ I of electric current.
5. the island detection method of the voltage perunit value positive feedback based on dq conversion according to claim 1, is characterized in that: the d axle component u of the Current Control described in step 6 and PCC point voltage dthe positive feedback formed, when combining inverter output current is changed, PCC point voltage also can respective change, until reach the scope of islanding detect.
CN201510050208.9A 2015-01-30 2015-01-30 Island detection method based on dq conversion and used for voltage per unit value positive feedback Pending CN104569696A (en)

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CN104950202A (en) * 2015-06-16 2015-09-30 珠海许继电气有限公司 Island detection method and system based on reactive power-frequency positive feedback
CN105467237A (en) * 2015-11-25 2016-04-06 东方日立(成都)电控设备有限公司 Positive feedback island detection method based on active current disturbance
CN105606921A (en) * 2015-11-26 2016-05-25 国家电网公司 Negative sequence voltage positive feedback-based islanding detection system and method
CN105629114A (en) * 2016-03-03 2016-06-01 西安科技大学 Islanding detection method based on voltage harmonic fault component
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Cited By (9)

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Publication number Priority date Publication date Assignee Title
CN104950202A (en) * 2015-06-16 2015-09-30 珠海许继电气有限公司 Island detection method and system based on reactive power-frequency positive feedback
CN105467237A (en) * 2015-11-25 2016-04-06 东方日立(成都)电控设备有限公司 Positive feedback island detection method based on active current disturbance
CN105606921A (en) * 2015-11-26 2016-05-25 国家电网公司 Negative sequence voltage positive feedback-based islanding detection system and method
CN105629114A (en) * 2016-03-03 2016-06-01 西安科技大学 Islanding detection method based on voltage harmonic fault component
CN106019008A (en) * 2016-05-19 2016-10-12 西安科技大学 Island detection method based on voltage harmonic dq component
CN106019068A (en) * 2016-06-20 2016-10-12 北京交通大学 Network voltage interruption detection and control method for multi-unit train network side converter
CN106019068B (en) * 2016-06-20 2018-08-31 北京交通大学 A kind of net pressure interruption detection and control method of EMU net side current transformer
CN108306521A (en) * 2018-02-08 2018-07-20 澄瑞电力科技（上海）有限公司 A kind of high voltage shore power power supply major loop and its compound suppressing method of inverse probability
CN110289637A (en) * 2019-07-16 2019-09-27 中腾微网（北京）科技有限公司 A kind of joint island detection method that region multi-inverter is grid-connected

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