CN106961121A - Seamless switching control system and strategy based on current indirect control and droop control - Google Patents
Seamless switching control system and strategy based on current indirect control and droop control Download PDFInfo
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- CN106961121A CN106961121A CN201710284236.6A CN201710284236A CN106961121A CN 106961121 A CN106961121 A CN 106961121A CN 201710284236 A CN201710284236 A CN 201710284236A CN 106961121 A CN106961121 A CN 106961121A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- Power Engineering (AREA)
- Supply And Distribution Of Alternating Current (AREA)
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Abstract
The invention discloses a kind of seamless switching control system and strategy based on current indirect control and droop control, using unique control structure, using capacitive current inner ring, the three close-loop control structure of capacitance voltage ring and grid-connected current ring, also include the phase-locked loop module and phase angle selecting module and droop control module of uniqueness simultaneously, can realize that inverter when turning islet operation that is incorporated into the power networks is automatic switches to the voltage source based on droop control to control by current source control, improves the load voltage quality in the grid-connected transfer process to island mode.
Description
Technical field
The invention belongs to combining inverter control research field, and in particular to one kind is based on current indirect control and sagging control
The seamless switching control system and strategy of system.
Background technology
With the increasingly intensification of environment and energy crisis, generation of electricity by new energy has obtained increasing concern and application, and
Combining inverter is the essential interface equipment that grid-connected power generation system conveys electric energy to power network, the performance of combining inverter
Important influence will be produced to electricity generation system and the stability of power network.
When power network is normal, combining inverter should be able to be incorporated into the power networks, and be load supplying jointly with power network, when power network occurs
During failure, distributed generation unit should disconnect with power network immediately, and be individually for load supplying, form islet operation.In electricity
After network recovery, it is incorporated into the power networks again.Therefore, combining inverter should possess grid-connected and island operating capacity, and can realize
Seamless switching between both of which, it is ensured that the power supply quality of local important load is unaffected.According to the difference of control mode,
Combining inverter can be divided into two kinds of current-control type and voltage-controlled type.Seamless switching control strategy universal at present can be divided into
Three class below：1. mixed-voltage Controlled in Current Mode and Based；2. voltage mode is controlled；3. current indirect control.In mixed-voltage electric current
In Schema control, inverter control is current source when grid-connected, and inverter control is voltage source during isolated island, therefore there are two sets of controls
System, when grid-connected and islet operation changes, due to the presence of isolated island detection time, load voltage can be out of control in the presence of one section
Time, load voltage quality is influenceed by isolated island detection rapidity.In voltage mode control, no matter in grid-connected or isolated island
Pattern, inverter uses droop control, is run with voltage source, but be due to the presence of power ring in droop control, no matter
Isolated island or grid-connect mode, the dynamic response characteristic of system are slow.In current indirect control, inverter control when being incorporated into the power networks
Current source is made, when isolated island occurs, it is not necessary to change control structure, inverter automatically switches to voltage source, therefore load electricity
Pressure quality can be improved, but when being incorporated into the power networks, injection power network current peak value is adjusted electric current outer shroud, and dynamic is rung
Should be poor.Therefore it has been proposed that a kind of improve the shortcoming that current indirect control overcomes its poor dynamic, but when using the control
During method processed, micro-grid system in islet operation using it is much single more main from structure, once main inverter breaks down, whole microgrid
System can not work, and system reliability is relatively low.
The content of the invention
It is an object of the invention to overcome the whole microgrid system of main inverter failure in above-mentioned improvement current indirect control
The problem of can not working unite there is provided a kind of seamless switching control system and strategy based on current indirect control and droop control,
Seamless switching of the inverter between grid-connect mode and island mode can be realized, the load voltage matter in handoff procedure is improved
Amount, and in island mode, micro-grid system can improve the reliability of system with how main many from structure operation.
In order to achieve the above object, a kind of seamless switching control system based on current indirect control and droop control includes
Three-phase inverter, the output end connection LC wave filters of three-phase inverter, the electric capacity C of LC wave filtersfIt is parallel with load, LC wave filters
Downstream passes through line impedance LgConnect grid-connected switch Si, grid-connected switch SiDownstream switchs S by electric network protectionuConnect power network.
The inverter includes two main inverters and two from inverter, two main inverters and two from inverter simultaneously
Through transport row.
A kind of control strategy of the seamless switching control system based on current indirect control and droop control is：
When power network is normal, grid-connected switch SiS is switched with electric network protectionuClose, micro-grid system is incorporated into the power networks, main inversion
Grid-connected inductance L is flowed through in devicegElectric current igx(x=a, b, c) follows its command value, the active and nothing for making main inverter output given
Work(power；
When the grid collapses, electric network protection switch SuDisconnect immediately, micro-grid system is separated with bulk power grid, micro-grid system
Flow of power between bulk power grid is reduced to flow through grid-connected inductance L in 0, therefore main invertergElectric current can deviate command value.
In D axles, PI controllers GIGOutput can keep increasing or decreasing, reach the higher limit V of limiterdmaxOr lower limit Vdmax,
Similarly the output of PI controllers reaches the lower limit V of limiter in Q axlesqminOr higher limit Vdmax, when the output of D axle limiters reaches
After its amplitude limit value, by data select switch S2Elect the voltage instruction value E of droop control reactive power ring generation asdroop, it is synchronous
Control signal makes after the output of the D axle limiters in each main inverter control module reaches higher limit, unified data
Selecting switch S2By VIGdoutSwitch to Edroop, that is, complete the switching of island mode.
In island mode, inverter is based on droop control, is run with voltage source mode, using how main many from structure
In micro-grid system, many main inverters are used to be run based on droop control with voltage source mode, is made between many main inverters
Power-sharing without connection.
After power system restoration, electric network protection switch SuAutomatic closure, carries out the presynchronization control of load voltage and line voltage
System, after the two realizes the synchronization of voltage magnitude and phase, grid-connected switch SiClosure, inverter is incorporated into the power networks again, completes simultaneously
Net pattern.
Compared with prior art, the present invention is using unique control structure, using capacitive current inner ring, capacitance voltage ring with
And the three close-loop control structure of grid-connected current ring, while also including phase-locked loop module and phase angle selecting module and the sagging control of uniqueness
Molding block, it is possible to achieve inverter when turning islet operation that is incorporated into the power networks is automatic to be switched to based on droop control by current source control
Voltage source is controlled, and improves the load voltage quality in the grid-connected transfer process to island mode.
The method of the present invention switches to the process being incorporated into the power networks again by switching to islet operation by being incorporated into the power networks, and realizes simultaneously
The current source inverter based on current indirect control is inverse to the voltage-source type based on droop control during island mode during net pattern
Become the automatic switchover of device, improve the grid-connected load voltage quality turned during isolated island, and microgrid system when improving islet operation
The reliability of system.Realize the power-sharing without rapid communication line between many main inverters during islet operation.Due in orphan
There are many main inverters and provide voltage magnitude and frequency support for micro-grid system in island, even if certain main inverter occurs when running
Failure does not interfere with the normal operation of micro-grid system yet.So the control method can improve the reliability of micro-grid system.
Brief description of the drawings
Fig. 1 is main circuit diagram of the invention；
Fig. 2 is main control block diagram of the present invention；
Fig. 3 is the phaselocked loop of the invention with frequency limiter；
Fig. 4 is phase angle selecting module of the invention；
Sagging control block diagram when Fig. 5 is islet operation of the present invention；
Fig. 6 is the circuit diagram of micro-grid system of the present invention；
Fig. 7 is simulation waveform of the invention；Wherein, (a) is A phase load voltage waves in whole micro-grid system running
Shape, when (b) is 0.4s grid collapses, the waveform of threephase load voltage, (c) is 1.2s power system restorations, threephase load voltage
Waveform, (d) be whole service during, grid voltage amplitude EgAnd control variable EdroopAnd VIGdoutWaveform；
Fig. 8 is before islet operation turns to be incorporated into the power networks, during load voltage and grid voltage amplitude and phase presynchronization
Simulation waveform；(a) it is phase angle presynchronization process waveform, (b) is amplitude presynchronization process waveform.
Embodiment
The present invention will be further described below in conjunction with the accompanying drawings.
A kind of seamless switching control system based on current indirect control and droop control includes three-phase inverter, three contraries
Become the output end connection LC wave filters of device, the electric capacity C of LC wave filtersfLoad is parallel with, LC wave filters downstream passes through line impedance Lg
Connect grid-connected switch Si, grid-connected switch SiDownstream switchs S by electric network protectionuPower network is connected, inverter includes two main inverters
With two from inverter, two main inverters and two are from inverter parallel.
A kind of control strategy of the seamless switching control system based on current indirect control and droop control is, when power network just
Chang Shi, grid-connected switch SiS is switched with electric network protectionuClose, grid-connected inductance L is flowed through in grid-connected inverters operationgElectric current igx(x
=a, b, c) it is grid-connected current, complete grid-connect mode；
When the grid collapses, electric network protection switch SuDisconnect immediately, isolated island is determined by isolated island detection algorithm
Afterwards, grid-connected switch SiDisconnect, distributed generation unit is in islet operation, complete island mode；
After power system restoration, electric network protection switch SuAutomatic closure, carries out the presynchronization control of load voltage and line voltage
System, after the two realizes the synchronization of voltage magnitude and phase, grid-connected switch SiClosure, inverter is incorporated into the power networks again, completes simultaneously
Net pattern.
Distributed generation unit includes four kinds of running statuses altogether：Grid-connect mode, grid-connect mode turns the converted of island mode
Journey, island mode, island mode turns the transfer process of grid-connect mode.
1st, grid-connect mode
When power network is normal, grid-connected switch and electric network protection switch is closed, and inverter is based on current indirect control, control
For current source.Control structure shown in Fig. 2 is made up of capacitive current inner ring, capacitance voltage ring and grid-connected current outer shroud, simultaneously
During net pattern, three control rings play a role jointly, controlling switch S1, S4, S5Disconnect, data selector S2With VIGdoutIt is connected
Connect, data selector S3With θgridIt is connected.Distributed generation system control injects active and idle work(for current source to power network
Rate, and the active and reactive power injected is by current reference value igrefdAnd igrefqDetermine.Now power network current adjuster GIGAdjust
Power network current is saved, makes its trace command value, therefore the limiter after adjuster can not limit its output.
2nd, grid-connect mode is changed to island mode
Under grid-connect mode, the active and reactive power that distributed generation unit injects to power network is respectively formula (1), (2).
For easy analysis, it is assumed that when grid-connected, the active and reactive power that distributed generation unit injects to power network is
On the occasion of.Analyzed first with separate unit distributed generation unit shown in Fig. 1.When the grid collapses, electric network protection switch Su
Disconnect immediately, flow through grid-connected inductance LgElectric current be reduced to 0 rapidly.Grid-connected current igD axle components igdBy on the occasion of being kept to 0, q axles
Component igqIt is 0 by negative value increase.In D axles, PI controllers GIGOutput can keep increase, reach the higher limit of limiter
Vdmax, in Q axles, PI controllers GIGOutput can keep reduce, reach the lower limit V of limiterqmin.Limiter upper lower limit value
Selection it is extremely important, after can be described in detail.After the output of D axle limiters reaches its higher limit, data are selected
Select switch S2Elect the voltage instruction value E of droop control reactive power ring generation asdroop, it is inverse due to there are many masters in micro-grid system
Become device, therefore in order that obtain each main inverter switches to droop control, it is necessary to increase a synchronous control signal, when each simultaneously
The output of D axle limiters in platform main inverter control module is reached after higher limit, unified data select switch S2By
VIGdoutSwitch to Edroop.Because amplitude set-point E in the droop control block diagram shown in Fig. 5 (b)0Equal to Vdmax(amplitude set-point
E0D axle limiter lower limits V may also be equal todmin, flowed to depending on active power when being incorporated into the power networks, if by distribution hair
Electric unit flows to power network, i.e. Pg>0, then E0Equal to Vdmax；If flowing to distributed generation unit, i.e. P by power networkg<0, then E0
Equal to Vdmin.And due to the sagging coefficient k in Fig. 5 (b)qVery little, so by VIGdoutTo EdroopConversion be smooth.So
Logic switch S in Fig. 5 (a) afterwards4Closure causes the angle values θ that droop control is produceddroopThe θ produced with PLL modulesgridTogether
Step, by the automatic decision of Fig. 4 phase angle selecting modules, when the difference of the two is less than some threshold value, it is believed that the two is synchronized,
Data selector S in Fig. 43Elect θ asdroop.Now, completed by the switching of current indirect control to droop control.
During grid-connect mode, power network current adjuster GIGPower network current should be able to be normally controlled, therefore limiter can not be limited
Make its output, D axle limiter higher limits VdmaxGrid voltage magnitudes should be more than, while it can not be much larger than line voltage width again
Degree, otherwise load voltage amplitude will be far from rated value.Therefore, D axles limiter higher limit VdmaxSelect as grid voltage magnitudes most
Big value.According to ieee standard IEEE Std.1547-2003, line voltage maximum is 1.1p.u., so VdmaxCan be by formula
(3) represent, wherein VnIt is specified phase voltage.
D axle limiter lower limits V can similarly be obtaineddminSelect as grid voltage magnitudes minimum value, as shown in formula (4).
In order that load voltage amplitude is in normal range (NR), the higher limit V of Q axle limitersqmaxD axle amplitude limits should be much smaller than
Device upper limit Vdmax, the 10% of specified grid voltage magnitudes is set it to herein.The lower limit of Q axle limiters should be with higher limit
It is symmetrical on 0, therefore VqminIt is set as-the 10% of specified grid voltage magnitudes.
When microgrid structure is as shown in Figure 6, there are many main inverters and from inverter, now main inverter grid-connected current
(grid-connected current is the electric current between distributed generation unit and PCC points) switchs S in electric network protectionuIt is not 0 after disconnection, but by
Separated in micro-grid system with bulk power grid, the flow of power between micro-grid system and bulk power grid is reduced to flow in 0, therefore main inverter
Cross grid-connected inductance LgElectric current can deviate command value.In D axles, PI controllers GIGOutput can keep increasing or decreasing, reach
The higher limit V of limiterdmaxOr lower limit Vdmax, similarly the output of PI controllers reaches the lower limit V of limiter in Q axlesqminOr on
Limit value Vdmax, after the output of D axle limiters reaches its amplitude limit value, by data select switch S2Elect the idle work(of droop control as
The voltage instruction value E of rate ring generationdroopIf D axles limiter is still not up to its amplitude limit value after one section of setting time T, together
Sample is by data select switch S2Elect the voltage instruction value E of droop control reactive power ring generation asdroop, synchronous control signal makes respectively
Platform main inverter control module is simultaneously data select switch S2By VIGdoutSwitch to Edroop, that is, complete the switching of island mode.
3rd, island mode
In island mode, inverter is based on droop control, is run with voltage source mode.Using how main many from structure
In micro-grid system, many main inverters can use this control strategy, in isolated island based on droop control with voltage source mode
Operation, realizes the power-sharing without connection between many main inverters.Many masters are more can to improve microgrid system from the microgrid of structure
System reliability.
4th, island mode is changed to grid-connect mode
After power system restoration is normal, electric network protection switch SuAutomatic closure, in grid-connected switch Si, it is necessary to first before closure
First carry out the presynchronization control of load voltage and line voltage.
PLL modules are from motion tracking electric network voltage phase, closure switch S after power system restoration4So that θdroopWith θgridIt is synchronous,
After synchronously completing, phase angle selecting module is automatic by S3With θgridIt is connected.Closure switch S afterwards5And S1So that EdroopAnd VIGdout
With grid voltage amplitude EgIt is synchronous.Afterwards by data selector S2With VIGdoutIt is connected, disconnects switch S5And S1。
Specifically, the present invention has built combining inverter model as shown in Figure 1 as more main in simulation software PSCAD
More from the main inverter in structure micro-grid system, 2 main inverters, 2 parallel runnings from inverter are realized.Simulation result
As shown in fig. 7, wherein Fig. 7 (a) represents A phase load voltage waveforms in whole micro-grid system running, Fig. 7 (b) represents 0.4s
During grid collapses, the waveform of threephase load voltage, Fig. 7 (c) expression 1.2s power system restorations, the waveform of threephase load voltage,
During Fig. 7 (d) expression whole services, grid voltage amplitude EgAnd control variable EdroopAnd VIGdoutWaveform.Emulation starts
When, power network is normally run, and distributed generation unit injects active and reactive power to power network, and at the 0.4s moment, event occurs for power network
Barrier, electric network protection switch SuDisconnect immediately, according to analyzing above, the output of D axles limiter reaches higher limit and Q axles limiter is exported
Lower limit is reached, therefore it can be seen that when turning islet operation by being incorporated into the power networks after 0.4s, load is electric in simulation waveform Fig. 7 (a)
Pressure amplitude value can increase to a certain degree, but still be within the scope of operation standard, and grid-connected turn of orphan is can be clearly seen that by Fig. 7 (b)
When island is run, load three-phase voltage increases to a certain degree.When 1.2s moment power system restorations, electric network protection switch is automatic to be closed,
After presynchronization by load voltage and grid voltage amplitude and phase, grid-connected switch is closed, micro-grid system grid-connected fortune again
OK.By Fig. 7 (a) and Fig. 7 (c) it can be seen that when isolated island turns to be incorporated into the power networks, load voltage recovers to rated value.By Fig. 7 (b) and figure
7 (c) can be seen that no matter turned by grid-connected islet operation or the isolated island of turning during being incorporated into the power networks, and load voltage quality can be obtained
To guarantee.During Fig. 7 (d) expression whole services, grid voltage amplitude EgAnd control variable EdroopAnd VIGdoutWaveform.
It is can see by Fig. 7 (d) near 0.42s, VIGdoutValue and EdroopValue approximately equal, therefore by current indirect control under
Vertical control can take over seamlessly；Near 1.4s, VIGdout,EdroopValue all and EgValue approximately equal, therefore by droop control to
Current indirect control can take over seamlessly.Fig. 8 gives Phase synchronization and the synchronous process of amplitude during presynchronization.
A kind of seamless handover method based on current indirect control and droop control is provided in the present invention.For access control
The feasibility of method, author built simulation model in simulation software PSCAD, and the simulation results show control method can be with
The seamless switching that micro-grid system is incorporated into the power networks between islet operation is realized, load voltage can be protected in handoff procedure
Card, and in islet operation, there are many main inverters in micro-grid system and provide voltage support for system, improve microgrid system
The reliability of system.This method is correct, reliable, and good reference value is provided for engineer applied.
Claims (4)
1. a kind of seamless switching control system based on current indirect control and droop control, it is characterised in that including three contraries
Become device, the output end connection LC wave filters of three-phase inverter, the electric capacity C of LC wave filtersfLoad is parallel with, LC wave filters downstream leads to
Cross line impedance LgConnect grid-connected switch Si, grid-connected switch SiDownstream switchs S by electric network protectionuConnect power network；
The inverter includes two main inverters and two from inverter, and two main inverters and two transport from inverter parallel
OK.
2. a kind of control plan of seamless switching control system based on current indirect control and droop control described in claim 1
Slightly, it is characterised in that when power network is normal, grid-connected switch SiS is switched with electric network protectionuClose, grid-connected inverters operation, stream
Cross grid-connected inductance LgElectric current igx(x=a, b, c) is grid-connected current, completes grid-connect mode；
When the grid collapses, electric network protection switch SuDisconnect immediately, after determining that isolated island occurs by isolated island detection algorithm, and
Net switch SiDisconnect, distributed generation unit is in islet operation, complete island mode；
After power system restoration, electric network protection switch SuAutomatic closure, carries out the presynchronization control of load voltage and line voltage, when
The two is realized after the synchronization of voltage magnitude and phase, grid-connected switch SiClosure, inverter is incorporated into the power networks again, completes grid-connected mould
Formula.
3. a kind of control of seamless switching control system based on current indirect control and droop control according to claim 2
System strategy, it is characterised in that during grid collapses, electric network protection switch SuDisconnect immediately, flow through grid-connected inductance LgElectric current it is fast
Speed is reduced to 0, grid-connected current igD axle components igdBy on the occasion of being kept to 0, q axle components igqIt is 0 by negative value increase, in D axles, PI
Controller GIGOutput can keep increase, reach the higher limit V of limiterdmax, in Q axles, PI controllers GIGOutput can protect
Keep reducing small, reach the lower limit V of limiterqmin, after the output of D axle limiters reaches its higher limit, data selection is opened
Close S2Elect the voltage instruction value E of droop control reactive power ring generation asdroop, when the D axles in each main inverter control module
The output of limiter reaches after higher limit that synchronous control signal is unified data select switch S2By VIGdoutSwitch to
Edroop, that is, complete the switching of island mode.
4. a kind of control of seamless switching control system based on current indirect control and droop control according to claim 2
System strategy, it is characterised in that in island mode, main inverter is based on droop control, is run with voltage source mode, using many
Main many from the micro-grid system of structure, many main inverters are used to be run based on droop control with voltage source mode, makes many
Power-sharing without connection between main inverter.
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| CN112260315A (en) * | 2020-10-16 | 2021-01-22 | 成都英格利科技有限公司 | Seamless switching control system and strategy based on improved droop control |
| CN112909999A (en) * | 2021-01-29 | 2021-06-04 | 四川大学 | Phase-locked loop-free high-power-quality seamless switching system and control method thereof |
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| CN112260315A (en) * | 2020-10-16 | 2021-01-22 | 成都英格利科技有限公司 | Seamless switching control system and strategy based on improved droop control |
| EP4020746A1 (en) * | 2020-12-23 | 2022-06-29 | Toyota Jidosha Kabushiki Kaisha | Electric power system and server |
| US11710983B2 (en) | 2020-12-23 | 2023-07-25 | Toyota Jidosha Kabushiki Kaisha | Electric power system and server |
| CN112909999A (en) * | 2021-01-29 | 2021-06-04 | 四川大学 | Phase-locked loop-free high-power-quality seamless switching system and control method thereof |
| CN112909999B (en) * | 2021-01-29 | 2023-02-21 | 四川大学 | Phase-locked loop-free high-power-quality seamless switching system and control method thereof |
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