CN103207335B - Island detection method based on phase-frequency positive feedback - Google Patents
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Abstract
The invention provides an island detection method based on phase-frequency positive feedback and relates to the technical field of grid-connected inverter control. The island detection method includes: acquiring voltage signals of inverter grid-connected points through an analog to digital (AD) converter, utilizing a phase-locking ring to perform phase locking, and obtaining power grid frequency f and a voltage phase theta; calculating a power grid frequency average value F through cumulative number N of the power grid frequency f; obtaining an offset angle d theta through calculation according to the power grid frequency average value F, compensating the phase, obtaining a compensated output phase phi, measuring frequency f' of an inverter grid-connected point according to the output phase phi, and judging whether an inverter is in an island operation state. Compared with a traditional algorithm, the island detection method cannot be influenced by current, power and load impedance, has no non-detection zone and no artificial disturbance of frequency, the phase and the like, and does not lead harmonic wave toward a power grid. The island detection method is simple, rapid, reliable and accurate and improves island detection speed.
Description
Technical field
The present invention relates to combining inverter control technology field, refer more particularly to a kind of island detection method based on phase-frequency positive feedback.
Background technology
Along with energy shortage and environmental problem are day by day serious, the utilization of the regenerative resource such as sun power, wind energy becomes the study hotspot of countries in the world.The function of distributed electrical source inventer is that the electric energy that the device such as blower fan, photovoltaic panel produces is converted to the alternating current meeting national networking standard.During grid-connected inverters work, in electric system, island phenomenon may be produced.When so-called island phenomenon refers to bulk power grid dead electricity, inverter is still to bulk power grid electric energy transmitting, fail to detect the power down mode of bulk power grid and depart from it, distributed power source and local load form the electric power system that a self-supporting voltage and frequency are not controlled by bulk power grid.Island phenomenon if load capacity is greater than the capacity of distributed power source, then may cause removal of load or the electricity generation system such as photovoltaic, blower fan in microgrid to burn after producing; If bulk power grid is in interruption maintenance state, the circuit be connected with inverter is still charged, probably causes personal injury to maintainer.At present, domestic and international linked groups and mechanism clear stipulaties distributed grid-connected system must possess islanding detect ability.As can be seen here, islanding detect is related to personnel's personal safety, the safety of electric system, reliable power supply, is the indispensable link of grid-connected system.
Existing islanding detect mainly contains passive detection and active detecting method.Passive detection refers to and detects the isoparametric situation of change of inverter output voltage, frequency, phase place and harmonic wave to carry out islanding detect.The method is mainly through the change in voltage upper and lower bound of setting voltage monitoring point, and the frequency change upper and lower bound of frequency monitoring point, carries out out-of-limit inspection to judge whether inverter is in island operation state to the voltage of reality, frequency.But there is very large dead band in passive detection.When local load mates with the output power of inverter, electrical network is hardly to inverter and local transfers loads power.Whether grid power blackout to be, on the output voltage of inverter and frequency change impact very little, now, passive detection lost efficacy.
Active detecting method refers to by control inverter, and its output power is changed according to certain rules, and current waveform distorts at certain position, and frequency or phase place are with disturbance.Because electrical network is enough powerful, the parameters of electrical network can not follow the disturbance of inverter and disturbance, and isolated island detecting device also would not detect these disturbances.Once generation island phenomenon, the output disturbance of inverter will be accumulated rapidly and surmount the limit value of setting, thus detects isolated island.These method work dead bands are little, and detection speed is fast, and precision is high, but algorithm is complicated, require high, and bring harmonic problem to electrical network to chip travelling speed.
Therefore, for above deficiency, the invention provides a kind of based on phase place. the island detection method of frequency positive feedback.
Summary of the invention
(1) technical matters solved
For the deficiencies in the prior art, the present invention proposes a kind of based on phase place. the island detection method of frequency positive feedback, simply, fast and accurately can detect island phenomenon, and avoid check frequency, not bring artificial temporary disturbance and harmonic pollution to electrical network.
(2) technical scheme
For achieving the above object, the invention provides one based on phase place. the island detection method of frequency positive feedback, it comprises the following steps:
S1, gathered the voltage signal of grid-connected inverters point by AD converter, utilize phaselocked loop to carry out phase-locked, obtain mains frequency f and voltage-phase θ;
S2, by the mains frequency f cumulative number N described in S1, calculate mains frequency mean value F;
S3, calculate offset angle d θ according to the mains frequency mean value F described in S2, described voltage-phase θ is compensated, the output phase place after being compensated
S4, according to the output phase place in S3
measure grid-connected inverters point frequency f ', judge whether inverter is in island operation state.
Phaselocked loop wherein described in Sl is the phaselocked loop based on Second Order Generalized Integrator; In S3, offset angle d θ computing formula is:
dθ=k·(F-50)+d
Wherein, k and d is the scale-up factor and constant coefficient that simulate according to the phase-frequency characteristic curve linear of Second Order Generalized Integrator respectively;
Inverter after compensation exports phase place
computing formula be:
Wherein, θ
ibe the voltage-phase in i-th S1, d θ is linear compensation angle phaselocked loop being exported to phase place, and F is the mains frequency mean value calculated in S2, F
minthe lower-frequency limit of linear compensation, F
maxbe the upper frequency limit of linear compensation, d is the fixed compensation angle after frequency out-of-limit.
The wherein frequency f of grid-connected inverters point in S4 ' computing formula be:
Wherein Δ β is the phase-frequency response curved line relation formula of phaselocked loop, and τ is the Engineering Error of invertor operation, and d θ is offset angle, and PI is the PI control function in phaselocked loop, f
initial set valuethe setpoint frequency of inverter when bringing into operation, θ
ithat the phaselocked loop calculated after i-th AD converter sampling exports phase place,
be the output phase place of inverter after the i-th-1 time AD converter sampling, Δ t is the interval time of double sampling.
As the one optimization to this programme, after S3, also comprise step: each AD converter sampling, all performs a step S1 to S3, after performing i time, using the average frequency value F described in S2 as reference frequency, with the voltage-phase θ calculated for i-th time in S1
ias initial phase, Second Order Generalized Integrator is utilized to obtain fixed phase Φ.
The process wherein constructing fixed phase Φ is:
Average frequency value F, i-th AD converter are sampled the voltage-phase θ calculated
ithe fixed phase Φ sampled when calculating with the secondary AD converter of the i-th+j
i+jpass is:
Φ
i+j=θ
i+2π·F·Δt·j
Wherein i is that S1 to S3 repeats number of times, and j represents and obtains initial phase θ
ithe number of times that rear AD converter sampling performs.
Phase place is exported after last computing reference phase place Φ and compensation
phase differential
judge whether inverter is in island operation state according to phase differential.
(3) beneficial effect
The present invention is by providing a kind of based on phase place. and the island detection method of frequency positive feedback adopts the means of linear fit to carry out phase compensation, calculates simple.Compared with passive detection method, detected parameters is and amplitude, frequency, the phase information of the voltage of site, does not comprise the information such as power, electric current, there is not load power and mate the dead-time problem caused with inverter output power.Compared with active detecting method, this method does not add the disturbances such as any phase place, waveform.On the contrary, this method with the mobility of frequency, carries out Contrary compensation to it for the phase place of Second Order Generalized Integrator, correct for the unreasonable movement that inverter exports phase place, reduces the inverter harmonic wave that cause poor with grid phase.
Accompanying drawing explanation
A kind of embodiment circuit diagram when Fig. 1 is bidirectional energy-storage inverter islanding detect;
Fig. 2 a is for the present invention is based on phase place. a kind of algorithm flow chart of the island detection method of frequency positive feedback;
Fig. 2 b is for the present invention is based on phase place. the another kind of algorithm flow chart of the island detection method of frequency positive feedback;
Fig. 3 a is the phase-frequency characteristic curve of Second Order Generalized Integrator;
Fig. 3 b is the phase angle compensation curve obtained the phase-frequency characteristic curve linear matching of Second Order Generalized Integrator;
Fig. 3 c is phaselocked loop phase-frequency characteristic curve after phase angle compensation;
Fig. 4 is the comparison chart of line voltage and output voltage before and after isolated island occurs;
The frequency measurement of grid-connected point voltage when Fig. 5 is isolated island generation;
When Fig. 6 is isolated island generation and site exports the phase differential of phase place and fixed phase.；
Wherein Reference numeral 41 is line voltage, and mark 42 is output voltage.
Embodiment
Under regard to one proposed by the invention based on phase place. the island detection method of frequency positive feedback, describes in detail in conjunction with the accompanying drawings and embodiments.
The present invention is applicable to the digital control type inversion system with grid-connected function.Described in method of the present invention based on phase place. the island detection method of frequency positive feedback mainly revises the phase-frequency characteristic of Second Order Generalized Integrator, phaselocked loop is exported and carries out phase compensation, phaselocked loop generation positive feedback when being operated in island state to make inverter, Engineering Error is infinitely amplified, frequency shift (FS) until meet determine that isolated island occurs.
Below for bidirectional energy-storage inverter, other such as grid-connected photovoltaic systems still can use the present invention, at this not as limitation of the present invention.
If Fig. 2 a is for the present invention is based on phase place. a kind of algorithm flow chart of the island detection method of frequency positive feedback;
Sl, gathered the voltage signal of grid-connected inverters point by AD converter, utilize the phaselocked loop based on Second Order Generalized Integrator to carry out phase-locked, obtain mains frequency f and voltage-phase θ.
As shown in Figure l, be circuit diagram during bidirectional energy-storage inverter islanding detect, system adopts the inverter of conventional Industrial Frequency Transformer structure.
Inverter major parameter is as follows:
Rated power: 6kW
Line voltage: 230V
Mains frequency: 50Hz
Transformer voltage ratio: 1: 8
Cell voltage: 48V
AD sample frequency: 12kHz
Mains frequency is within the scope of 48 ~ 52Hz, and during grid-connected inverters work, the phaselocked loop after phase compensation exports phase place and electrical network does not almost have phase differential.The upper and lower bound of the present embodiment medium frequency protection is set as 50.5Hz and 49.5Hz respectively.Voltage detecting circuit amplifies grid-connected point voltage, and in DSP sheet, AD converter is sampled to voltage signal;
Obtain mains frequency f through the phaselocked loop based on Second Order Generalized Integrator, grid phase θ is obtained to mains frequency f integration.
Computation process is: the voltage waveform measured constructs two-way orthogonal signal by Second Order Generalized Integrator ' υ ' and qv', wherein υ ' is synchronous sinusoidal signal with voltage waveform, and qv' is the cosine signal with voltage waveform phase 90 °.The pass of the idle component q under dq rotating coordinate system and orthogonal signal υ ', qv ', voltage-phase θ is:
q=υ‘·cosθ+qυ’·sinθ
Do the input quantity of pi regulator with q, calculate frequency compensation value df, mains frequency is
f=df+f
0
Wherein, original frequency f
0=50Hz;
Voltage-phase θ can be obtained by frequency f integration:
θ
i+1=θ
i+2πf·Δt
Wherein, θ
i+1be the phase place of voltage during the i-th+1 time measurement, θ
ibe the phase place of voltage during i-th measurement, f is mains frequency, and Δ t is that twice measurement interlude is poor.
Because pi regulator has negative feedback, phaselocked loop realizes phase-locked function, and obtains mains frequency f and voltage-phase θ.
S2, by the mains frequency f cumulative number N described in S1, calculate mains frequency mean value F.
Often to sample 240 points, calculate an average frequency F:
The process of calculated rate mean value is as follows:
S3, calculate offset angle d θ according to the mains frequency mean value F described in S2, phase place is compensated, the output phase place after being compensated
According to the phase-frequency characteristic curve formulae discovery phase compensation angle d θ of average frequency and second-order integrator.Computing formula is:
dθ=k·(F-50)+d
Wherein, k and d is the scale-up factor and constant coefficient that simulate according to the phase-frequency characteristic curve linear of Second Order Generalized Integrator respectively.
It should be noted that: the method obtaining the phase-frequency characteristic curve of second-order integrator carries out transform to Second Order Generalized Integrator, then draw Bode diagram.In actual applications, DSP also can be adopted to export different frequency, the method for comparison phase differential.No matter which kind of method, all needs to carry out matching to this phase-frequency characteristic curve.Due within the scope of 48 ~ 52Hz, this curve linear degree is better, and the present invention adopts the method for linear fit, and such as quadratic polynomial fitting precision is higher for other.
As shown in Fig. 3 a ~ 3c, after carrying out phase compensation for Second Order Generalized Integrator, the phase offset of phaselocked loop maintains near 0 ° or with frequency exists very little positive correlation.Inverter exports phase place
Wherein, θ
ibe the voltage-phase in i-th step S1, d θ is linear compensation angle phaselocked loop being exported to phase place, and F is the mains frequency mean value calculated, F
minthe lower-frequency limit of linear compensation, F
maxbe the upper frequency limit of linear compensation, d is the fixed compensation angle after frequency out-of-limit.
S4, according to the output phase place in S3
measure the frequency f of grid-connected inverters point ', judge whether inverter is in island operation state.
The frequency f of grid-connected inverters point ' computing formula be:
Wherein Δ β is the phase-frequency response curved line relation formula of phaselocked loop, and τ is the Engineering Error of invertor operation, and d θ is offset angle, and PI is the PI control function in phaselocked loop, f
initial set valuethe setpoint frequency of inverter when bringing into operation, θ
ithat the phaselocked loop calculated after i-th AD converter sampling exports phase place,
be the output phase place of inverter after the i-th-1 time AD converter sampling, Δ t is the interval time of double sampling.
As shown in Figure 4, inverter line impedance is very large, and now grid-connected current is zero.Before isolated island occurs, because electrical network is to the clamping action of frequency.The output frequency of inverter is all identical with electrical network with phase place, and does not comprise any artificial disturbance, only there is Engineering Error, calculates truncation error etc.After isolated island occurs, inverter loses power network signal, and initial phase error enters phaselocked loop as phase differential, and as detected, the phaselocked loop of oneself exports phase place and is ahead of output voltage phase place, this phase differential, as phaselocked loop PI input value, makes phase-locked loop frequency reduce.Because Engineering Error still exists, direction does not change, and such error is constantly accumulated, and forms phase place. frequency positive feedback.
For ensureing positive feedback Accelerating running, can phase place be revised. the slope of frequency curve fitting formula, makes phase place and frequency positive correlation.
As shown in Figure 5, frequency f ' out-of-limit inspection is one of condition judging that isolated island occurs.
If Fig. 2 b is for the present invention is based on phase place. shown in the another kind of algorithm flow chart of the island detection method of frequency positive feedback:
As above-mentioned based on phase place. the improvement of the island detection method of frequency positive feedback, present invention also offers a kind of detection method, also step is comprised: each AD converter sampling after the step S3 of said method, all perform a step S1 to S3, after performing i time, using the average frequency value F described in S2 as reference frequency, with the voltage-phase θ calculated for i-th time in S1
ias initial phase, Second Order Generalized Integrator is utilized to obtain fixed phase Φ.
The process wherein constructing fixed phase Φ is:
Average frequency value F, i-th AD converter are sampled the voltage-phase θ calculated
ithe fixed phase Φ sampled when calculating with the secondary AD converter of the i-th+j
i+jpass is:
Φ
i+j=θ
i+2π·F·Δt·j
Wherein i is that Sl to S3 repeats number of times, and j represents in claim 4 and obtains initial phase θ
ithe number of times that rear AD converter sampling performs.
Phase place is exported after last computing reference phase place Φ and compensation
phase differential
judge whether inverter is in island operation state according to phase differential.
As shown in Figure 6, fixed phase exports phase place as initial phase using the phaselocked loop of certain time point, carries out integration to mains frequency.The difference that fixed phase exports phase place with reality is out-of-limit, then illustrate and enter island operation state.
It should be noted that at this: the structure of fixed phase is applicable to the highly stable environment of mains frequency.Fixed phase is benchmark according to the phase place put sometime and frequency, and phase calculation is carried out in each sampling instant afterwards.When chronic time, fixed phase and actual output phase error can be large.At this moment need to use current phase place and frequency to re-construct fixed phase, and by phase differential zero before.When Engineering Error is very little, frequency shift (FS) is very slow, and phase offset is larger.
Implementation result:
Once after isolated island generation, the Engineering Error of inverter is accumulated rapidly, and frequency reduces rapidly or increases.According to the size of Engineering Error and the difference of setting limit value, above detection method can detect island operation state within the scope of 0.02s ~ 1s.Compared with prior art, by the impact of electric current, power, loaded impedance, there is not check frequency, there is not the disturbances such as artificial frequency, phase place in the island detection method that the present invention proposes hardly, also do not introduce harmonic wave to electrical network.This detection method is simple, rapidly, reliable, accurately, particularly phase difference detection is more responsive, improves the speed of islanding detect.
Above embodiment is only for illustration of the present invention; and be not limitation of the present invention; the those of ordinary skill of relevant technical field; without departing from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all equivalent technical schemes also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.
Claims (5)
1. based on an island detection method for phase-frequency positive feedback, it is characterized in that, comprise the following steps:
S1, gathered the voltage signal of grid-connected inverters point by AD converter, utilize phaselocked loop to carry out phase-locked, obtain mains frequency f and voltage-phase θ;
S2, by the mains frequency f cumulative number N described in S1, calculate mains frequency mean value F;
S3, calculate offset angle d θ according to the mains frequency mean value F described in S2, described voltage-phase θ is compensated, the output phase place after being compensated
S4, according in S3 compensate after output phase place
measure the frequency f of grid-connected inverters point ', judge whether inverter is in island operation state;
The frequency f of the point of grid-connected inverters described in S4 ' computing formula be:
Wherein Δ β is the phase-frequency response curved line relation formula of phaselocked loop, and τ is the Engineering Error of invertor operation, and d θ is offset angle, and PI is the PI control function in phaselocked loop, f
initial set valuethe setpoint frequency of inverter when bringing into operation, θ
ithe voltage-phase calculated after i-th AD converter sampling,
be the output phase place after the voltage-phase calculated after the i-th-1 time AD converter sampling compensates, Δ t is the interval time of double sampling.
2. a kind of island detection method based on phase-frequency positive feedback as claimed in claim 1, it is characterized in that, the phaselocked loop described in S1 is the phaselocked loop based on Second Order Generalized Integrator; The d of offset angle described in S3 θ computing formula is:
dθ＝k·(F-50)+d
Wherein, k is the scale-up factor simulated according to the phase-frequency characteristic curve linear of Second Order Generalized Integrator, and d is the fixed compensation angle after frequency out-of-limit;
Output phase place after the voltage-phase calculated after i-th AD converter sampling compensates
computing formula be:
Wherein, θ
ibe the voltage-phase in i-th S1, F is the mains frequency mean value calculated in step S2, F
minthe lower-frequency limit of linear compensation, F
maxit is the upper frequency limit of linear compensation.
3. a kind of island detection method based on phase-frequency positive feedback as claimed in claim 1, it is characterized in that, also step is comprised: each AD converter sampling after S3, all perform a step S1 to S3, after performing i time, using the mains frequency mean value F described in S2 as reference frequency, with the voltage-phase θ calculated for i-th time in S1
ias initial phase, Second Order Generalized Integrator is utilized to obtain fixed phase Φ.
4. a kind of island detection method based on phase-frequency positive feedback as claimed in claim 3, is characterized in that, the process of structure fixed phase Φ is:
Mains frequency mean value F, i-th AD converter are sampled the voltage-phase θ calculated
ithe fixed phase Φ sampled when calculating with the secondary AD converter of the i-th+j
i+jpass is:
Φ
i+j＝θ
i+2π·F·Δt·j
Wherein i is that S1 to S3 repeats number of times, and j represents and obtains initial phase θ
ithe number of times that rear AD converter sampling performs.
5. a kind of island detection method based on phase-frequency positive feedback as described in claim 3 or 4, is characterized in that: computing reference phase place Φ and the output phase place after compensating
phase differential
judge whether inverter is in island operation state according to phase differential.
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| CN105529950B (en) * | 2016-02-17 | 2018-02-06 | 广东工业大学 | A kind of single-phase grid-connected inverter control method based on Second Order Generalized Integrator |
| CN106451534A (en) * | 2016-09-13 | 2017-02-22 | 南昌大学 | Photovoltaic grid-connected island detection algorithm based on abrupt phase change and active phase shifting |
| CN107918082B (en) * | 2016-10-10 | 2021-01-15 | 中国电力科学研究院 | Island detection method for parallel operation of inverters |
| CN108110785B (en) | 2016-11-24 | 2021-04-20 | 华为技术有限公司 | Inverter anti-islanding control system |
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