CN101123349B - Islanding effect detection method and device based on active frequency offset - Google Patents
Islanding effect detection method and device based on active frequency offset Download PDFInfo
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Abstract
基于主动频率偏移的孤岛效应检测方法及其装置，涉及分布式新能源并网供电的测控方法及装置，尤其涉及一种基于主动频率偏移的孤岛效应检测方法及其装置。主要是以25个周波为一个大循环，在前15个周波中斩波率cf＝0，同时检测频率的变化趋势，对于频率的变化趋势属于频率有上升趋势的情形，在后10个周波中向电网频率中加入斩波率为cf的频率扰动，斩波率cf的初始值cfmax为正值，对于频率的变化趋势属于频率有下降趋势的情形，同样在后10个周波中向电网频率中加入斩波率为cf的频率扰动，斩波率cf的初始值cfmin为负值。本发明不仅提高了检测出孤岛运行的概率，同时缩短检测时间，降低注入电网电流谐波。
The islanding effect detection method and device based on active frequency offset relate to a measurement and control method and device for distributed new energy grid-connected power supply, in particular to an islanding effect detection method and device based on active frequency offset. Mainly take 25 cycles as a large cycle. In the first 15 cycles, the chopping rate cf=0, and at the same time detect the changing trend of the frequency. The changing trend of the frequency belongs to the situation that the frequency has an upward trend. In the last 10 cycles Add the frequency disturbance of the chopping rate cf to the grid frequency, the initial value cf max of the chopping rate cf is a positive value, the trend of the frequency change belongs to the situation that the frequency has a downward trend, and also increases to the grid frequency in the last 10 cycles Add the frequency perturbation of the chopping rate cf in , and the initial value cf min of the chopping rate cf is a negative value. The invention not only improves the probability of detecting isolated island operation, but also shortens the detection time and reduces the current harmonics injected into the grid.
Description
Technical field
The present invention relates to investigating method and device that distributed new is incorporated into the power networks and powers, relate in particular to a kind of island effect detection method and device thereof based on intentional frequency offset.
Background technology
More and more being paid close attention to the distributed generation system that new forms of energy are formed, is representative with wind-force, solar grid-connected generating especially wherein.This be because: (1) power demand grows with each passing day, and non-renewable energy resources such as coal, oil are day by day exhausted, and it is extremely urgent to seek alternative energy source; (2) environmental pollution that brings of centralized, the large-scale fuel of tradition generating has had a strong impact on social production and life, and green novel energy source helps to alleviate ambient pressure; (3) because new forms of energy such as wind-force, photovoltaic generation have region characteristics such as distribution is wide, density is low, the low capacity of the formula of gathering materials on the spot, how distributed generating electricity by way of merging two or more grid systems have more advantage than independent generating.This distributed power source that emerged in large numbers has in recent years produced tangible economic benefits, application prospect light for the mode of distribution user power supply simultaneously with the big electrical network of tradition.
Because the electric energy instability of the initial generation of new forms of energy, the at present employing is converted into stable direct current by power electronic technology more, obtains the also net mode of synchronous AC again via inverter.Compare with traditional supply power mode, reverse transmission of electric energy has appearred in this type of distributed grid-connected system, and the fail safe of the quality of power supply and electrical network becomes very important and distinct issues.Wherein, topmost topic is exactly the detection of isolated island phenomenon and prevents.
Consideration disperses the existence of electricity generation system with building not in the design of current power system, if certain bar line failure in the distribution can rely on nearest protective relaying device to remove.In case there is the distributed generation system that is incorporated into the power networks in this distribution, distributed power source can continue in particular cases to form independently small power generation system to powering with the distribution of big electrical network disconnection at some.This phenomenon just is called " island effect ".Islet operation brings very big harm can for electrical network, user, personal safety: (1) because circuit breaker should still not continue power supply by charged circuit after disconnecting, the lineman touches circuit unwittingly probably and causes personal injury originally; (2) do not have the support of big electrical network, the quality of power supply of distributed power source can not get guaranteeing, directly damages user's equipment; When (3) reclosing widely-used caused overlapping, voltage, the inconsistent not asynchronous switch-on that causes of phase place caused bigger accident, hindered electrical network to power again.
Fig. 1 is the electrical network block diagram roughly that comprises distributed power generation.Originally the bus 1 that only inserts load after the switch S 3 is introduced traditional electrical network via be incorporated into the power networks transformer and two switches that are incorporated into the power networks with distributed generation system, carries reverse power.Be example to break down between switch S 3 and the bus 2, relaying protection tripping switch S 3, then distributed power source and load form islet operation, very likely equipment in this mini-system and personal safety are caused very big harm.Therefore, in the shortest time, detect islet operation, send the be incorporated into the power networks trip signal of the switch S 1 or the switch S 2 that is incorporated into the power networks of tripping, keep the safe operation of system.
At first introduce grid-connected inverting system, for the introducing of the anti-isolated island scheme of aftermentioned provides good hardware foundation and platform.
Fig. 2 is the distributed generation system work of the being incorporated into the power networks block diagram that comprises island detection and control system.Whole system roughly is made up of five parts.Block diagram 1 has been represented by power supply energy, DC stabilization control system, the output of stable DC voltage, inverter, the transformer Power Conversion major loop that switch constitutes that is incorporated into the power networks; The local load of block diagram 2 representatives; Block diagram 3 representatives utility network to be accessed; Block diagram 4 representative tripping operation control relays; The anti-islet operation of block diagram 5 representatives detects and control module, is whole system control core; The pwm signal that control system is sent in block diagram 6 representative is converted to and can drives in the block diagram 1 switching device in the inverter bridge and turn-off driver module with Continuity signal;
In this article, with the application special case of photovoltaic generation, be convenient to explanation as anti-isolated island algorithm.Block diagram 1 has been represented dc inverter that photovoltaic is sent out to exchanging, and in parallelly with the electrical network in the block diagram 3 provides electric energy to the load rlc circuit.Block diagram 5 has comprised various control circuits, and anti-islet operation device also is a wherein important part.
Block diagram 5 is whole system cores, comprising: Hall element 53, in order to the magnitude of voltage at real-time collection common node place; AD modular converter 52, being converted in order to the analog signal that Hall element 53 is collected can be for the digital signal of digit chip DSP processing; DSP control module 51, it is the core in the core, receive on the one hand in real time from AD modular converter 52 be converted to about common node place voltage digital signal, on the other hand, acquired signal is handled, finally sent the suitable control signal pwm signal of switching device shutoff and conducting in switch drive module 6 is sent in order to control inverter simultaneously to relay.
Conventional voltage, frequency parameter are measured the application in the passive detection method of isolated island
Fig. 5 is the reduced graph of whole system, and the RLC parallel circuits of representing local load is by common node a, is connected with photovoltaic generating system after the inversion via transformer, connects circuit breaker and electrical network parallel running greatly simultaneously.During the whole system operate as normal, big electrical network can be regarded as capacity infinity, the stable ideal voltage source of voltage.The voltage clamp at common node a place is on the line voltage normal value, and the power of photovoltaic array output is carried to electrical network with current forms.Local load RLC parallel circuits can obtain sufficient electric energy from photovoltaic generating system and big electrical network, that is:
P
load＝P
inv+ΔP(1)
Q
load＝Q
inv+ΔQ(2)
P in the formula
Load, Q
LoadNeeded meritorious, reactive power when representing load normally to move; P
Inv, Q
InvRepresent meritorious, the reactive power of photovoltaic generating system by inverter output; Δ P, Δ Q represent electrical network to load RLC parallel circuits " replenish " required electric energy (Δ P, Δ Q can just can bear, promptly the grid power actual flow to can with homophase shown in Figure 5 or anti-phase).Simultaneously, the voltage at RLC parallel circuits two ends and frequency thereof and load meritorious idle have following shown in relation:
V in the formula
aRepresent the magnitude of voltage at common node a place, ω represents the angular frequency of node a place voltage.Simultaneous formula (1) (2) (3) (4) can get:
Find out from formula (5) (6), (disconnect) the electric energy P ' that load obtains when causing wherein having circuit breaker to disconnect owing to fault as the switch among Fig. 52 as if electrical network
Load, Q '
LoadProvide by photovoltaic generating system fully, shown in (7) (8):
V ' in the formula
a, ω ' represents this moment a point voltage and frequency thereof respectively.In most cases, photovoltaic generating system power output P
Inv, Q
InvOrganize the demand P of power demand with the normal worker of load
Load, Q
LoadDiffer greatly (being so-called not matching), cause the voltage V of common node place
a, frequencies omega fluctuation occurs until V '
a, ω ' to be to reach P '
Load=P
Inv, Q '
Load=Q
InvBecause the operation of photovoltaic generating system is controlled at (electric current and the line voltage of input electrical network are synchronous), i.e. Q ' on the unity power factor
Load=Q
Inv=0.Push away by (8):
arg{R
-1+(jωL)
-1+jωC}
-1＝0(9)
Be that RLC parallel circuits operating frequency drifts to the load resonance frequency
No matter be V '
aStill drifting to the ω ' of load resonance frequency, the variation of this tangible voltage and frequency all can use/and the passive means of under voltage (OVR/UVR) and mistake/under-frequency (OFR/UFR) detects.
Inspired by the most basic above-mentioned principle, the cardinal principle of anti-islet operation detects common node a place's voltage or frequency exactly whether in normal scope.Though traditional passive means of this direct detection voltage, frequency has high speed, can not exert an influence to electrical network, but along with the development of technology, the capacity of grid-connected photovoltaic power generation system constantly enlarges, the situation of meeting complete failure when inverter power output and loading demand coupling very likely occurring.Simultaneously, because the input and the excision of load, voltage, frequency jitter might appear in electrical network itself, and this variation might cause the situation of mistrip.Therefore, the active method of anti-islet operation has been subjected to more concern.
Traditional intentional frequency offset method (AFD)
The intentional frequency offset method, i.e. AFD method (Active Frequency Drift Method) is by changing the power frequency that injects electrical network, make when islet operation, the frequency of line voltage can constantly rise or descend, and departs from the resonance frequency of formula (9), until exceeding allowed band.
1, AFD method brief introduction
Fig. 6 a, Fig. 6 b have shown the current i of the line voltage sine wave of 50Hz for the injection electrical network of reference
PVWaveform.T
VutilIt is the cycle of line voltage; T
IPVIt is the cycle of the positive string section of output current.Zero output time t
zWith the half period of line voltage
Ratio be called copped wave rate cf (chopping fraction).Grid-connected current is synchronous with it when the line voltage zero crossing, but the cf of copped wave rate subsequently makes output current shift to an earlier date (or hysteresis) voltage.Do not break down at whole big electrical network, when promptly not having the circuit breaker tripping, the voltage of the end that is connected to the grid under the clamping action of big electrical network all the time with synchronized.Slightly distort though inject the electric current of electrical network, each when the line voltage zero crossing restoring current and line voltage synchronous, the aberration rate of controlling output current simultaneously can not exert an influence to line voltage in allowed band.In case generation islet operation, voltage are determined jointly by output current and load impedance, shift to an earlier date or lag behind arriving zero point.So repeatedly, distribution side electric voltage frequency constantly rises or descends, and is detected the operation of excision photovoltaic generating system at last by OFR/UFR.
According to Fourier analysis, this injection power network current high order harmonic component can be ignored, and thinks V
aBe i
PVThe first-harmonic function.Zero output makes to be imported in the electric current of electrical network, and fundametal compoment is for i
PVPhase shift, i.e. an i are arranged
PVFundametal compoment compare i
PVShift to an earlier date t
z/ 2.Therefore, during system generation islet operation, with i
PVThe V that fundametal compoment is synchronous
aCan be in advance
If V
aWith i
PVSynchronously, then system frequency satisfies certainly:
arg{R
-1+(jωL)
-1+jωC}
-1＝0.5ωt
z＝0.5πcf(10)
Promptly when (10) formula is satisfied in system load, V
aWith i
PVJust do not had phase difference, system frequency remains unchanged, and enters to detect the blind area.
2, AFD method shortcoming
When generating electricity by way of merging two or more grid systems inversion system generation islet operation, it is little more a lot of than the detection blind area (Non-Detection Zone) of basic voltage, frequency detecting method that the AFD theoretical method detects the blind area.But the detection blind area of this method still needs further to dwindle to satisfy the harsh day by day condition of electrical network.
Traditional AFD detection method can reduce and detect the blind area by the value (, mentioning in this method that " increasing the cf value " all refers to the absolute value of cf because cf can just can bear) that increases cf.But copped wave rate cf value is excessive, and the current distortion that injects electrical network can have a strong impact on the quality of power supply; And copped wave rate cf value is too small, compares the superiority that just can not highlight method with conventional voltage frequency detecting method.Therefore reasonably selecting the value size of copped wave rate cf is the key of this method.
When using the AFD method, if (10) formula is not satisfied in system load, system frequency always can be displaced to beyond the normal range of operation in theory, and this misoperation situation is detected.But detecting island effect is free regulation, the use of high speed reclosing especially at present, if anti-isolated island speed is slow excessively, before reclosing closes once more, still do not disconnect the inversion system that generates electricity by way of merging two or more grid systems, very likely electrical network is produced concuss, cause the accident.This situation occurs in the AFD method probably.Being perception with local load is example, and voltage-phase has the trend of leading current, and after islet operation took place, if do not apply AFD, the frequency of voltage can constantly rise.But in case after using the AFD method, copped wave rate cf gets changeless negative value, has offset the electric voltage frequency variation tendency that this load characteristic causes, slowed down electric voltage frequency and floated, can incur loss through delay the trip time on the contrary.Vice versa.
Above-mentioned shortcoming shows that the AFD method provides good thinking for island detection, but still needs further to improve.
Summary of the invention
At the passive means of conventional voltage, frequency detecting in the source-detect the bigger defective in blind area during load matched, the invention provides a kind of island effect detection method and device thereof based on intentional frequency offset, the present invention has not only improved the probability that detects islet operation, shorten detection time simultaneously, reduce and inject the power network current harmonic wave.
The present invention adopts following technical scheme:
Step 1: with 25 cycles is a systemic circulation, copped wave rate cf=0 in preceding 15 cycles, detect the variation tendency of frequency simultaneously, variation tendency for frequency belongs to frequency situation on the rise, adding the copped wave rate in back 10 cycles in mains frequency is the frequency disturbance of cf, the initial value cf of copped wave rate cf
MaxFor on the occasion of, belong to the situation that frequency has downward trend for the variation tendency of frequency, same to add the copped wave rate in back 10 cycles in mains frequency be the frequency disturbance of cf, the initial value cf of copped wave rate cf
MinBe negative value,
The detection method of said frequencies variation tendency is: in preceding 15 cycles in each systemic circulation, the phase lock circuitry of use grid-connected inverting system detects the frequency values of cycle, if the original frequency of voltage cycle is power frequency 50Hz, the size of more detected first cycle frequency values and original frequency value, if first cycle frequency values is greater than the original frequency value, then be recorded as ascendant trend 1 time, otherwise, then be recorded as 1 downward trend, after this, the size of a more detected current cycle frequency values and a preceding cycle frequency values, if current cycle frequency values is greater than a preceding cycle frequency values, then be recorded as ascendant trend 1 time, otherwise, then be recorded as 1 downward trend, at last, how much are the ascendant trend in more above-mentioned 15 cycles and the number of times of downward trend, if the number of times of ascendant trend is greater than the number of times of downward trend, the variation tendency that then is judged to this systemic circulation belongs to electric voltage frequency situation on the rise, otherwise the variation tendency that then is judged to this systemic circulation belongs to the situation that electric voltage frequency has downward trend;
Step 2: the line voltage frequency is monitored, this method for monitoring is: the line voltage frequency values f when obtaining the line voltage zero passage by phase lock circuitry, the situation of line voltage frequency values f 〉=50.5Hz when line voltage frequency values f≤49.5Hz during with zero passage or zero passage is as line voltage frequency anomaly phenomenon, if line voltage frequency anomaly phenomenon occurs at 5 continuous cycles, then be judged to be and island effect occurs, send trip signal.
The present invention includes control module 51, the voltage digital input signal of control module 51 is gathered the magnitude of voltage at common node place in real time by Hall element 53, by AD modular converter 52 analog signal that Hall element 53 collects is converted into voltage digital signal again, control module 51 sends the switch command that is incorporated into the power networks according to its result calculated, it is characterized in that control module 51 comprises line voltage, frequency computation part module 511 and anti-islet operation Detection ﹠ Controling module 512, line voltage, frequency computation part module 511 is handled in order to the voltage digital signal to the common node place that collects, to obtain common node place voltage magnitude, the information of electric voltage frequency, line voltage, anti-islet operation Detection ﹠ Controling module 512 comprises frequency monitoring module 5123, frequency change trend detection module 5121 and copped wave rate apply module 5122, electric voltage frequency message transmission to the frequency change trend detection module 5121 and copped wave rate that said frequencies computing module 511 is handled resulting common node place, back with voltage signal applies module 5122, and described frequency change trend detection module 5121 is used for determining by frequency detecting the frequency change trend of preceding 15 cycles of 25 cycle systemic circulations; When described copped wave rate applied frequency change trend that module 5122 makes according to frequency change trend detection module 5121 and belongs to ascendant trend, adding the copped wave rate in back 10 cycles in mains frequency was the frequency disturbance of cf and the initial value cf of copped wave rate cf
MaxFor on the occasion of, otherwise adding the copped wave rate in back 10 cycles in mains frequency is the frequency disturbance of cf and the initial value cf of copped wave rate cf
MinBe negative value; Described frequency monitoring module 5123 is used to monitor electrical network, during the situation of the line voltage frequency values f 〉=50.5Hz when line voltage frequency values f≤49.5Hz when zero passage appears in 5 continuous cycles or zero passage, be judged to be and island effect occurs, send trip signal.
Compared with prior art, the present invention has following advantage:
This programme is on traditional intentional frequency offset method basis, adopted first detection of grid electric voltage frequency variation tendency, apply improving one's methods of rational copped wave rate again, not only significantly reduced the detection blind area, also accelerated detection speed, maximum possible reduces the current harmonics that injects electrical network, reduces the influence that active method produces electrical network.
(1) island effect detection method of the present invention is by changing the injection current frequency, when taking place, islet operation can change the frequency of load both end voltage effectively, even under the situation of source-load matched, also can force electric voltage frequency skew normal range (NR), detect the misoperation situation, send trip signal, avoided traditional under the situation of source-load matched and passed through to detect the shortcoming that method that whether electric voltage frequency range detection island effect take place lost efficacy because of electric voltage frequency does not change.
(2) island effect detection method of the present invention is by first detection of grid electric voltage frequency variation tendency, apply improving one's methods of rational copped wave rate again, overcome traditional active frequency rate of change method and caused the shortcoming that prolongs detection time because of being present in contradiction between load characteristic and the copped wave rate cf character, intentional frequency offset method after the improvement of the present invention can detect islet operation and cut-off switch as early as possible before reclosing overlaps, guarantee system's security of operation.
(3) the intentional frequency offset method exists the interference to electrical network inevitably, island effect detection method of the present invention combines international standard, under the prerequisite that tallies with the national condition, exhaust the big copped wave rate cf value of possibility, reduce and detect the blind area, accelerate detection speed, reduced the harmonic wave that electrical network is injected simultaneously, reduced influence electrical network.
Description of drawings
Figure 1 shows that distributed grid-connected system block diagram;
Fig. 2 is the distributed grid-connected system block diagram that comprises novel island detection of the present invention and control system;
Fig. 3 is DSP control module 51 inner detailed structure view among Fig. 2;
Fig. 4 be among Fig. 3 anti-islet operation in detection module 512 inner detailed structure view;
Fig. 5 is the reduced graph of system shown in Figure 2;
Fig. 6 a is that to be illustrated in the line voltage frequency be to the injection current i of electrical network institute when adopting the intentional frequency offset method to apply positive copped wave rate under the 50Hz situation
PVWaveform.
It is to the injection current i of electrical network institute when adopting the intentional frequency offset method to apply negative copped wave rate under the 50Hz situation that Fig. 6 b is illustrated in the line voltage frequency
PVWaveform.
The flow chart of Fig. 7 island detection of the present invention and control method;
Figure 8 shows that the copped wave rate applies 5122 module detail flowcharts among Fig. 7;
Fig. 9 is Fig. 7 medium frequency monitor module 5123 detail flowcharts;
Figure 10 shows that the graph of relation between copped wave rate cf value and the harmonic content THD.
Embodiment
Step 1: with 25 cycles is a systemic circulation, copped wave rate cf=0 in preceding 15 cycles, detect the variation tendency of frequency simultaneously, variation tendency for frequency belongs to frequency situation on the rise, adding the copped wave rate in back 10 cycles in mains frequency is the frequency disturbance of cf, the initial value cf of copped wave rate cf
MaxFor on the occasion of, belong to the situation that frequency has downward trend for the variation tendency of frequency, same to add the copped wave rate in back 10 cycles in mains frequency be the frequency disturbance of cf, the initial value cf of copped wave rate cf
MinBe negative value,
The detection method of said frequencies variation tendency is: in preceding 15 cycles in each systemic circulation, the phase lock circuitry of use grid-connected inverting system detects the frequency values of cycle, if the original frequency of voltage cycle is power frequency 50Hz, the size of more detected first cycle frequency values and original frequency value, if first cycle frequency values is greater than the original frequency value, then be recorded as ascendant trend 1 time, otherwise, then be recorded as 1 downward trend, after this, the size of a more detected current cycle frequency values and a preceding cycle frequency values, if current cycle frequency values is greater than a preceding cycle frequency values, then be recorded as ascendant trend 1 time, otherwise, then be recorded as 1 downward trend, at last, how much are the ascendant trend in more above-mentioned 15 cycles and the number of times of downward trend, if the number of times of ascendant trend is greater than the number of times of downward trend, the variation tendency that then is judged to this systemic circulation belongs to electric voltage frequency situation on the rise, otherwise the variation tendency that then is judged to this systemic circulation belongs to the situation that electric voltage frequency has downward trend;
Step 2: the line voltage frequency is monitored, this method for monitoring is: the line voltage frequency values f when obtaining the line voltage zero passage by phase lock circuitry, the situation of line voltage frequency values f 〉=50.5Hz when line voltage frequency values f≤49.5Hz during with zero passage or zero passage is as line voltage frequency anomaly phenomenon, if line voltage frequency anomaly phenomenon occurs at 5 continuous cycles, then be judged to be and island effect occurs, send trip signal.
The implementation method of frequency disturbance is:
Step 1: the use phase lock circuitry detects the phase signal θ=ω t of line voltage,
Step 2: when line voltage is in positive half cycle (during 0≤θ≤π), by electric network voltage phase signal θ calculate the phase theta that applied corresponding grid-connected current after the copped wave rate cf '=(1+cf) * θ, if θ '＜π, the phase place of grid-connected current signal is θ ' synchronously; If θ ' 〉=π, the phase place of grid-connected current signal is 0 synchronously,
Step 3: when detection of grid voltage is in negative half period (π≤θ≤2 π), by electric network voltage phase signal θ calculate the phase theta that applied corresponding grid-connected current after the copped wave rate cf '=(1+cf) * (θ-π), if θ '＜π, the phase place of grid-connected current signal is 2 π-θ ' synchronously, if θ ' 〉=π, the phase place of grid-connected current signal is 0 synchronously.
Comprise control module 51, the voltage digital input signal of control module 51 is gathered the magnitude of voltage at common node place in real time by Hall element 53, by AD modular converter 52 analog signal that Hall element 53 collects is converted into voltage digital signal again, control module 51 sends the switch command that is incorporated into the power networks according to its result calculated, it is characterized in that control module 51 comprises line voltage, frequency computation part module 511 and anti-islet operation Detection ﹠ Controling module 512, line voltage, frequency computation part module 511 is handled in order to the voltage digital signal to the common node place that collects, to obtain common node place voltage magnitude, the information of electric voltage frequency, line voltage, anti-islet operation Detection ﹠ Controling module 512 comprises frequency monitoring module 5123, frequency change trend detection module 5121 and copped wave rate apply module 5122, electric voltage frequency message transmission to the frequency change trend detection module 5121 and copped wave rate that said frequencies computing module 511 is handled resulting common node place, back with voltage signal applies module 5122, and described frequency change trend detection module 5121 is used for determining by frequency detecting the frequency change trend of preceding 15 cycles of 25 cycle systemic circulations; When described copped wave rate applied frequency change trend that module 5122 makes according to frequency change trend detection module 5121 and belongs to ascendant trend, adding the copped wave rate in back 10 cycles in mains frequency was the frequency disturbance of cf and the initial value cf of copped wave rate cf
MaxFor on the occasion of, otherwise adding the copped wave rate in back 10 cycles in mains frequency is the frequency disturbance of cf and the initial value cf of copped wave rate cf
MinBe negative value; Described frequency monitoring module 5123 is used to monitor electrical network, during the situation of the line voltage frequency values f 〉=50.5Hz when line voltage frequency values f≤49.5Hz when zero passage appears in 5 continuous cycles or zero passage, be judged to be and island effect occurs, send trip signal.Control module 51 can adopt digital signal processing chip DSP to realize, line voltage in the control module 51, frequency computation part module 511 are handled in order to the voltage digital signal to the common node place that collects, to obtain the information of common node place voltage magnitude, electric voltage frequency; Anti-islet operation Detection ﹠ Controling module 512 in the control module 51 comprises that frequency monitoring module 5123, frequency change trend detection module 5121 and copped wave rate apply module 5122, described frequency monitoring module 5123 is in order to the frequency at monitoring common node place, judge whether in normal range (NR), during the situation of the line voltage frequency values f 〉=50.5Hz when line voltage frequency values f≤49.5Hz when zero passage appears in 5 continuous cycles or zero passage, be judged to be and island effect occurs, send trip signal; Described frequency change trend detection module 5121 is used for determining by frequency detecting the frequency change trend of preceding 15 cycles of 25 cycle systemic circulations; Described copped wave rate applies frequency change trend that module 5122 makes according to frequency change trend detection module 5121 and judges and apply corresponding copped wave rate: when belonging to ascendant trend, adding the copped wave rate in back 10 cycles in mains frequency is the frequency disturbance of cf and the initial value cf of copped wave rate cf
MaxFor on the occasion of, otherwise adding the copped wave rate in back 10 cycles in mains frequency is the frequency disturbance of cf and the initial value cf of copped wave rate cf
MinBe negative value.
With reference to the accompanying drawings, the present invention is made explanation in more detail:
1.1. island detection scheme
1.1.1. detect frequency change trend to determine copped wave rate value
When system moves among the present invention program, at first sample by the voltage at 53 pairs of common node places of Hall element module, the analog signal that sampling obtains is carried out digital translation through AD modular converter 52, the DSP control module receives through the voltage signal after the conversion, and this digital signal handled, as shown in Figure 2.Wherein, the centre point of island detection is: for overcoming AFD method deficiency, the variation tendency of this detection method elder generation determination frequency determines to strengthen the copped wave rate cf sign of same trend, the injection power network current THD maximum that is allowed by relevant national standard is chosen the strongest copped wave rate cf value again, periodically applies copped wave rate cf.
Idiographic flow such as Fig. 7～shown in Figure 9, be described as follows.
1, frequency detecting
Frequency detecting mainly is to monitor that the be incorporated into the power networks frequency of voltage of inverter exists and rises or downward trend.Frequency detecting is a cycle period with 25 cycles (when electrical network normally moved, a cycle maintained 0.02s substantially) of line voltage.Preceding 15 cycles are electric voltage frequency variation tendency detection period, and back 10 cycles are that copped wave rate cf applies the phase.In preceding 15 cycles (electric voltage frequency variation tendency detection period), anti-isolated island system detection of grid electric voltage frequency has and rises or downward trend, stops to detect in back 10 cycles (copped wave rate cf applies the phase).
Detect in the cycle (electric voltage frequency variation tendency detection period) at preceding 15, anti-isolated island scheme can not change the waveform of inverter output current, and assurance electric current and the detected line voltage in load both sides are exported synchronously with same phase.Simultaneously, the electric voltage frequency variation tendency is determined in the meantime.Since the 16th cycle, stop detection to frequency change.By judging that preceding 15 cycle electric voltage frequencies rise or downward trend, anti-isolated island system applies suitable copped wave rate cf value to electric current in back 10 cycles (copped wave rate cf applies the phase), make and the trend of under the situation that islet operation takes place, strengthening frequency change detect islet operation with the fastest speed.
It is as described below that concrete frequency change trend detects step:
Step 1: counter min and max, in order to accumulative total mains frequency the rise and fall times in these 15 cycles.The number of times that on behalf of the last cycle of line voltage frequency, max rise, the number of times that the last cycle of min accumulative total line voltage frequency descends.No matter line voltage is in normal operating condition, or inverter is in islet operation, and electric voltage frequency always has fluctuation.Just can give expression in this section system frequency variation tendency roughly in the time with these two counters.
Step 2: when electric voltage frequency variation tendency detection period begins (the 1st cycle beginning), min and max counter reset are zero.Preset a frequency register PreF, write down the frequency (, then being made as power frequency 50Hz) of a last voltage cycle if program just begins.
Step 3: when a cycle finished, the phase lock circuitry of use grid-connected inverting system detected the frequency values of this cycle, compares with the frequency PreF of a last cycle.If frequency increases or is constant, give tacit consent to that it is on the rise, the max counter adds 1; In like manner, if frequency reduces, represent that it has downward trend, the min counter adds 1.The electric voltage frequency value of this cycle is replaced original value among the PreF, for the frequency ratio of following one-period writes down numerical value.
Step 4: in preceding 15 cycles, repeating step 3.
Step 5: in the 16th to 25 cycle, stop frequency being risen or the detection of decline, keep aforementioned min that obtains and max Counter Value constant.But the electric voltage frequency of PreF upgrades and can not stop.
After 15 cycles (electric voltage frequency variation tendency detection period) finish, just stop in back 10 cycles (copped wave rate cf applies the phase) numerical value of max and min is upgraded.At this moment, max and min counter are compared.If max＞=min, in 15 cycles, the situation that electric voltage frequency rises is in the great majority, and can think that electric voltage frequency has the trend of rising; Otherwise if max＜min can think that electric voltage frequency has a declining tendency.
This a part of flow process as shown in Figure 7.
From the flow chart of Fig. 7 as can be seen, shown in the frame of broken lines 5121 functions of modules, the working condition in preceding 15 cycles (electric voltage frequency variation tendency detection period) is corresponding with above-mentioned detection step.It is pointed out that block diagram 5122 represented be applying of the copped wave rate that hereinafter will set forth, be operated in back 10 cycles (copped wave rate cf applies the phase), here draw in the lump, it is clearer and more definite that whole flow process is got up.Simultaneously, frequency surveillance system function in the block diagram 5123 mainly in order to observe the scope of the operate as normal whether electric voltage frequency exceed constantly, if find operation exception, will be thought islet operation to have occurred, send trip signal, combining inverter is broken from electrical network.This function also can elaborate hereinafter.The assignment that block diagram 51211 and 511 is represented variable PreF respectively with utilize digital phase-locking mutually treatment technology obtain mains frequency, these two functions each line voltage cycle in whole frequency detecting circulation large period all will carry out.
2, copped wave rate cf applies
Applying of copped wave rate cf is exactly the application of AFD method in essence.In order to overcome the defective that traditional AFD method applies fixing cf always, this programme only applies the suitable copped wave rate of adding in the phase at back 10 cycle copped wave rate cf.During the electrical network operate as normal, floating about electric voltage frequency also might produce.But size regardless of max and min in preceding 15 cycles, how positive and negative the copped wave rate cf that grid-connected current applies in back 10 cycles is, can big influence not arranged, this interim ground but not continue the average harmonic wave that the distortion that grid-connected current produces has significantly reduced electrical network is injected to line voltage.If islet operation has taken place, combining inverter institute bringing onto load character (perception or capacitive) can cause that electric voltage frequency rises or descends, and this trend can clearly be detected by max, min counter.If max＞=min, electric voltage frequency has the trend of rising, can be defaulted as islet operation institute bringing onto load and be perception, and grid-connected current is applied positive copped wave rate cf value (cf
Max), the electric current that injects electrical network in each cycle arrives zero point in advance shown in Fig. 6 a, strengthen the frequency growth trend, accelerates island detection speed.If max＜min, electric voltage frequency has a declining tendency, and can think that islet operation institute bringing onto load is capacitive, and grid-connected current is applied negative copped wave rate cf value (cf
Min), the electric current that injects electrical network in each cycle is shown in Fig. 6 b, and lagging behind arrives zero point, strengthens the frequency sluggish trend, accelerates the speed that frequency shift (FS) goes out normal range (NR).
The detection of frequency change trend has determined to apply the sign of copped wave rate cf, and cf
MaxWith cf
MinThe definite of occurrence needs to rely on grid-connected current resultant distortion rate (THD) to limit.Though the big more detection of copped wave rate cf absolute value blind area is more little, the intensity that increases copped wave rate cf simply can cause the aberration rate of injecting power network current to rise rapidly, and the harmonic pollution that causes to electrical network can not be ignored.IEEE Std 929-2000 regulation, the THD that injects power network current can not this means that the value of copped wave rate cf has certain restriction greater than 5%.
Figure 10 has demonstrated the relation between copped wave rate cf value and the THD.In the prime grid-connected inverter circuit of this programme, the physical presence that is incorporated into the power networks current ripples is even copped wave rate cf=0 also can inject the harmonic wave of THD about 2% to electrical network.Cf
MaxGet 4.9%, corresponding THD4.97%; Cf
MinGet-4.81%, corresponding THD4.9%.Different circuit conditions, suitable copped wave rate cf value be difference slightly also, general cf
MaxGet 4.5%, cf
MinGet about-4.5% all feasible.Certainly, also can obtain the relation curve between the similar Figure 10 copped wave of different grid-connected inverter circuits rate cf and the THD by experiment, determine to be no more than cf under 5% the prerequisite at THD
MaxWith cf
MinSelection.
It is as described below that concrete copped wave rate cf applies step:
Step 1: the value that compares max and min.If max＞=min gets cf=cf
Max=4.9%; If max＜min gets cf=cf
Min=-4.81.
Step 2: when detection of grid voltage is in positive half cycle, use phase lock circuitry to detect phase signal θ=ω t (0≤θ≤π) wherein of line voltage.
Step 3: by electric network voltage phase signal θ calculate the phase theta that applied corresponding grid-connected current after the copped wave rate cf '=(1+cf) * θ.If θ '＜π, output i=sin (θ ') is as the grid-connected current synchronizing signal; If θ ' 〉=π, output 0.
Step 4: when detection of grid voltage is in negative half period, use phase lock circuitry to detect the phase signal θ=ω t (wherein π≤θ≤2 π) of line voltage.
Step 5: by electric network voltage phase signal θ calculate the phase theta that applied corresponding grid-connected current after the copped wave rate cf '=(1+cf) * (θ-π).If θ '＜π, output i=-sin (θ ') is as the grid-connected current synchronizing signal; If θ ' 〉=π, output 0.
The flow chart that copped wave rate cf applies step as shown in Figure 8.
2, frequency surveillance system
Above-mentioned anti-islet operation control is by periodically applying interference to electrical network, make after islet operation takes place electric voltage frequency with the fastest velocity shifts to normal range (NR).As shown in Figure 7, whole be in the systemic circulation with 25 cycles, all there is frequency surveillance system (block diagram 5123 among Fig. 7) in each cycle, whether the frequency of the main detection of grid voltage of this function in normal range value.
The IEEE Std 929-2000 regulation technical indicator that inversion system need reach of generating electricity by way of merging two or more grid systems is comprising the requirement of power grid quality, to the detection time of abnormal running, the detection time of island effect etc.But this international standard at be the 60Hz system, in order to adapt to the China Power system, according to State Grid's standard " quality of power supply power system frequency permissible variation ", this paper has improved to detect and has required: when continuous 5 cycles of system voltage frequency drift about out 49.5～50.5Hz scope, control system is sent trip signal, disconnect circuit breaker between inverter and the electrical network, inverter stops to mains supply.Because the raising of reclosing service behaviour at present, shorten its reclosing time greatly, detects island detection in traditional 2 seconds and can not meet the demands.Therefore, this method control algolithm detects this abnormal running state in 0.5 second after island effect takes place, why Here it is chooses 25 cycles as the reason in systemic circulation cycle, and existing sufficiently long time determination frequency variation tendency (15 cycles) also has the abundant time to apply cf
MaxWith cf
Min(10 cycles).
The frequency monitoring step is as follows:
Step 1: set a counter FrequencyCounter, initial value is zero.This counter is used for writing down the undesired periodicity of keeping of line voltage frequency.
Step 2: whether detection of grid voltage zero passage.If detect zero passage (i.e. rising, trailing edge), then obtain line voltage frequency values f by phase lock circuitry.
Step 3: if f≤49.5Hz or f 〉=50.5Hz then represent the line voltage frequency anomaly, the FrequencyCounter counter adds 1; If electric voltage frequency f returns to normal condition, then FrequencyCounter counter O reset.
Step 4: if FrequencyCounter does not satisfy 10, repeating step 2,3.In case FrequencyCounter expires 10, thinks that promptly continuous 5 cycles of electrical network are improper, and islet operation has taken place, and sends trip signal, as shown in Figure 1.This be since FrequencyCounter in the equal technology of rising, trailing edge of SineWave, so FrequencyCounter reaches 10 but not 5 start tripping operation.
The flow chart of frequency surveillance system step is as shown in Figure 9:
2. realization example
After powering on, device at first obtains the locking phase of the phase information of line voltage with the decision grid-connected current by Phase Lock Technique (PLL), obtain the amplitude of grid-connected current simultaneously according to prime maximal power tracing (MPPT) function, determine to realize being incorporated into the power networks synchronously with electrical network behind the suitable output current by phase place and amplitude.During inversion system normal operation in parallel with electrical network, island detection method is very little to the influence of electrical network as can be seen from oscillogram, even cf occurring in the non-vanishing cycle, detection obtains injecting the harmonic wave of electrical network also in tolerance band, if when system worked long hours, the harmonic wave that on average injects electrical network can be littler.When system runs to 5 seconds, deliberately disconnect being connected of electrical network and inversion system, make islet operation.At this moment, some loads have also been connected on the inverter.Because island detection method constantly changes the frequency of output current, cause also departing from normal value gradually by the electric voltage frequency at the load two ends of its decision, usually in 0.2 second, just can detect this abnormal conditions, checkout gear in time sends the inverter silence signal, disconnect being connected between inverter and the load, prevented islet operation effectively.
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