CN106961121B - Seamless switching control system and strategy based on current indirect control and sagging control - Google Patents

Seamless switching control system and strategy based on current indirect control and sagging control Download PDF

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CN106961121B
CN106961121B CN201710284236.6A CN201710284236A CN106961121B CN 106961121 B CN106961121 B CN 106961121B CN 201710284236 A CN201710284236 A CN 201710284236A CN 106961121 B CN106961121 B CN 106961121B
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grid
control
inverter
voltage
switch
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CN106961121A (en
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刘进军
孟鑫
刘增
武腾
王施珂
刘宝谨
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Xi an Jiaotong University
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388Islanding, i.e. disconnection of local power supply from the network

Abstract

The invention discloses a kind of seamless switching control system and strategy based on current indirect control and sagging 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, it further include simultaneously unique phase-locked loop module and phase angle selecting module and sagging control module, inverter when turning isolated operation that may be implemented to be incorporated into the power networks is switched to the voltage source based on sagging control by current source control automatically and controls, and improves the load voltage quality in the grid-connected conversion process to island mode.

Description

Seamless switching control system and strategy based on current indirect control and sagging control
Technical field
The invention belongs to gird-connected inverters to 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 technique
With the increasingly intensification of environment and energy crisis, generation of electricity by new energy has obtained more and more concerns and application, and Gird-connected inverter is essential interface equipment of the grid-connected power generation system to power grid conveying electric energy, the performance of gird-connected inverter Important influence will be generated to the stability of electricity generation system and power grid.
When power grid is normal, gird-connected inverter should be able to be incorporated into the power networks, and jointly be load supplying with power grid, when power grid occurs When failure, distributed generation unit should be disconnected with power grid immediately, and be individually for load supplying, form isolated operation.In electricity After network recovery, it is incorporated into the power networks again.Therefore, gird-connected inverter should have grid-connected and island operating capacity, and can realize Seamless switching between both of which guarantees that the power supply quality of local important load is unaffected.According to the difference of control mode, Gird-connected inverter can be divided into current-control type and two kinds of voltage-controlled type.Seamless switching control strategy universal at present can be divided into Following three classes: 1. mixed-voltage Controlled in Current Mode and Based;2. voltage mode controls;3. current indirect control.In mixed-voltage electric current In scheme control, inverter control is current source when grid-connected, and inverter control is voltage source when isolated island, therefore there are two sets of controls System, when grid-connected and isolated 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 are influenced by isolated island detection rapidity.In voltage mode control, no matter in grid-connected or isolated island Mode, inverter are all made of sagging control, are run with voltage source, but due to the presence of power ring in sagging control, no matter The dynamic response characteristic of isolated island or grid-connect mode, system is slow.In current indirect control, inverter control when being incorporated into the power networks Current source is made, when isolated island occurs, haves no need to change control structure, inverter automatically switches to voltage source, therefore loads electricity The available raising of quality is pressed, but when being incorporated into the power networks, injection power network current peak value is adjusted in electric current outer ring, dynamic is rung It answers poor.Therefore it has been proposed that the shortcomings that a kind of improvements current indirect control overcomes its poor dynamic, but when using the control When method processed, micro-grid system in isolated operation using it is single main mostly from structure, once main inverter breaks down, entire microgrid System can not work, and system reliability is lower.
Summary of the invention
It is an object of the invention to overcome the entire microgrid system of main inverter failure in above-mentioned improvement current indirect control The problem of system can not work, provides a kind of seamless switching control system and strategy based on current indirect control and sagging control, It can be realized seamless switching of the inverter between grid-connect mode and island mode, improve the load voltage matter in handoff procedure Amount, and in island mode, micro-grid system can mostly be run from structure with mostly main, improve the reliability of system.
In order to achieve the above object, a kind of to include based on current indirect control and the seamless switching control system of sagging control The output end of three-phase inverter, three-phase inverter connects LC filter, the capacitor C of LC filterfIt is parallel with load, LC filter Downstream passes through line impedance LgConnect grid-connected switch Si, grid-connected switch SiDownstream passes through electric network protection switch SuConnect power grid.
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 sagging control are as follows:
When power grid is normal, grid-connected switch SiWith electric network protection switch SuIt is closed, 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 instruction value, the active and nothing for keeping main inverter output given Function power;
When the grid collapses, electric network protection switch SuIt disconnects immediately, micro-grid system is separated with bulk power grid, micro-grid system Flow of power between bulk power grid is reduced to 0, therefore grid-connected inductance L is flowed through in main invertergElectric current can deviate instruction value. In D axis, PI controller GIGOutput can keep increasing or decreasing, reach the upper limit value V of limiterdmaxOr lower limit value Vdmax, Similarly PI controller exports the lower limit value V for reaching limiter in Q axisqminOr upper limit value Vdmax, when the output of D axis limiter reaches After its amplitude limit value, by data select switch S2It is selected as the voltage instruction value E that sagging control reactive power ring generatesdroop, synchronous It is unified data after control signal makes the output of the D axis limiter in each main inverter control module reach upper limit value Select switch S2By VIGdoutIt is switched to Edroop, that is, complete the switching of island mode.
In island mode, inverter is based on sagging control, is run with voltage source mode, using how main mostly from structure In micro-grid system, more main inverters, which are all made of, to be run based on sagging control with voltage source mode, is made between more 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 network voltage System, after the two realizes that voltage magnitude is synchronous with phase, grid-connected switch SiClosure, inverter are incorporated into the power networks again, complete simultaneously Net mode.
Compared with prior art, the present invention uses 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 further including unique phase-locked loop module and phase angle selecting module and sagging control Molding block, inverter when turning isolated operation that may be implemented to be incorporated into the power networks are switched to by current source control based on sagging control automatically Voltage source control, improves the load voltage quality in the grid-connected conversion process to island mode.
Method of the invention is realized simultaneously by being switched to isolated operation by being incorporated into the power networks and being switched to the process being incorporated into the power networks again When net mode based on the current source inverter of current indirect control to island mode when the voltage-source type based on sagging control it is inverse Become the automatic switchover of device, microgrid system when improving the grid-connected load voltage quality turned during isolated island, and improving isolated operation The reliability of system.Realize the power-sharing without rapid communication line between isolated operation Shi Duotai main inverter.Due in orphan There are more main inverters when island is run provides voltage magnitude and frequency support for micro-grid system, even if certain main inverter occurs Failure will not influence the normal operation of micro-grid system.So the reliability of micro-grid system can be improved in the control method.
Detailed description of the invention
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;
Fig. 5 sagging control block diagram when being isolated 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 wave in entire micro-grid system operational process Shape, (b) be 0.4s grid collapses when, the waveform of threephase load voltage, (c) be 1.2s power system restoration, threephase load voltage Waveform, (d) for during whole service, grid voltage amplitude EgAnd control variable EdroopAnd VIGdoutWaveform;
Fig. 8 is before isolated 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.
Specific embodiment
The present invention will be further described with reference to the accompanying drawing.
A kind of seamless switching control system based on current indirect control and sagging control includes three-phase inverter, three contraries The output end for becoming device connects LC filter, the capacitor C of LC filterfIt is parallel with load, LC filter downstream passes through line impedance Lg Connect grid-connected switch Si, grid-connected switch SiDownstream passes through electric network protection switch SuPower grid 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 sagging control is, when power grid just Chang Shi, grid-connected switch SiWith electric network protection switch SuIt is closed, 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 SuIt disconnects immediately, isolated island is determined by isolated island detection algorithm Afterwards, grid-connected switch SiIt disconnects, distributed generation unit is in isolated operation, completes island mode;
After power system restoration, electric network protection switch SuAutomatic closure, carries out the presynchronization control of load voltage and network voltage System, after the two realizes that voltage magnitude is synchronous with phase, grid-connected switch SiClosure, inverter are incorporated into the power networks again, complete simultaneously Net mode.
Distributed generation unit includes four kinds of operating statuses: grid-connect mode altogether, and grid-connect mode turns the converted of island mode Journey, island mode, island mode turn the conversion process of grid-connect mode.
1, grid-connect mode
When power grid is normal, grid-connected switch and electric network protection switch are closed, and inverter is based on current indirect control, control For current source.Control structure shown in Fig. 2 is made of capacitive current inner ring, capacitance voltage ring and grid-connected current outer ring, simultaneously When net mode, three control rings play a role jointly, control switch S1, S4, S5It disconnects, data selector S2With VIGdoutIt is connected It connects, data selector S3With θgridIt is connected.Distributed generation system control injects active and idle function to power grid for current source Rate, and the active and reactive power injected is by current reference value igrefdAnd igrefqIt determines.Power network current adjuster G at this timeIGIt adjusts Power network current is saved, makes its trace command value, therefore the limiter after adjuster cannot limit its output.
2, grid-connect mode is converted to island mode
Under grid-connect mode, the active and reactive power that distributed generation unit is injected to power grid is respectively formula (1), (2).
For easy analysis, it is assumed that when grid-connected, the active and reactive power that distributed generation unit is injected to power grid is Positive value.It is analyzed first with separate unit distributed generation unit shown in Fig. 1.When the grid collapses, electric network protection switch Su It disconnects immediately, flows through grid-connected inductance LgElectric current to be reduced rapidly be 0.Grid-connected current igD axis component igd0, q axis is kept to by positive value Component igqIncreased by negative value is 0.In D axis, PI controller GIGOutput can keep increasing, reach the upper limit value of limiter Vdmax, in Q axis, PI controller GIGOutput can keep reducing, reach the lower limit value V of limiterqmin.Limiter upper lower limit value Selection it is extremely important, can be described in detail later.After the output of D axis limiter reaches its upper limit value, data are selected Select switch S2It is selected as the voltage instruction value E that sagging control reactive power ring generatesdroop, since there are more masters are inverse in micro-grid system Become device, therefore in order to enable each main inverter is switched to sagging control simultaneously, needs to increase a synchronous control signal, when each It is unified data select switch S after the output of D axis limiter in platform main inverter control module reaches upper limit value2By VIGdoutIt is switched to Edroop.Because of amplitude given value E in sagging control block diagram shown in Fig. 5 (b)0Equal to Vdmax(amplitude given value E0D axis limiter lower limit value V may also be equal todmin, active power when depending on being incorporated into the power networks flows to, if sent out by distribution Electric unit flows to power grid, i.e. Pg> 0, then E0Equal to Vdmax;If flowing to distributed generation unit, i.e. P by power gridg< 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 is so that the angle values θ that sagging control generatesdroopThe θ generated with PLL modulegridTogether Step, by judging automatically for Fig. 4 phase angle selecting module, 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. 43It is selected as θdroop.At this point, being completed by the switching of current indirect control to sagging control.
When grid-connect mode, power network current adjuster GIGShould be able to normal control power network current, therefore limiter cannot limit Make its output, D axis limiter upper limit value VdmaxGrid voltage magnitudes should be greater than, while it cannot be much larger than network voltage width again Degree, otherwise load voltage amplitude will be far from rated value.Therefore, D axis limiter upper limit value VdmaxIt is selected as grid voltage magnitudes most Big value.According to ieee standard IEEE Std.1547-2003, network voltage maximum value is 1.1p.u., so VdmaxIt can be by formula (3) it indicates, wherein VnIt is specified phase voltage.
D axis limiter lower limit value V can similarly be obtaineddminIt is selected as grid voltage magnitudes minimum value, as shown in formula (4).
In order to make load voltage amplitude in the normal range, the upper limit value V of Q axis limiterqmaxD axis clipping should be much smaller than Device upper limit Vdmax, the 10% of specified grid voltage magnitudes is set it to herein.The lower limit value of Q axis limiter should be with upper limit value It is symmetrical about 0, therefore VqminIt is set as-the 10% of specified grid voltage magnitudes.
When microgrid structure is as shown in Figure 6, there are more main inverters and from inverter, main inverter grid-connected current at this time (electric current of the grid-connected current between distributed generation unit and PCC point) is in electric network protection switch SuIt is not 0 after disconnection, but by It is separated in micro-grid system with bulk power grid, the flow of power between micro-grid system and bulk power grid is reduced to 0, therefore flows in main inverter Cross grid-connected inductance LgElectric current can deviate instruction value.In D axis, PI controller GIGOutput can keep increasing or decreasing, reach The upper limit value V of limiterdmaxOr lower limit value Vdmax, similarly PI controller exports the lower limit value V for reaching limiter in Q axisqminOn or Limit value Vdmax, after the output of D axis limiter reaches its amplitude limit value, by data select switch S2It is selected as the sagging idle function of control The voltage instruction value E that rate ring generatesdroopIf D axis limiter is still not up to its amplitude limit value after one section of setting time T, together Sample is by data select switch S2It is selected as the voltage instruction value E that sagging control reactive power ring generatesdroop, synchronous control signal makes respectively Platform main inverter control module is simultaneously data select switch S2By VIGdoutIt is switched to Edroop, that is, complete the switching of island mode.
3, island mode
In island mode, inverter is based on sagging control, is run with voltage source mode.Using how main mostly from structure In micro-grid system, more main inverters can use this control strategy, in isolated island based on sagging control with voltage source mode The power-sharing without connection between more main inverters is realized in operation.Mostly microgrid system can be improved from the microgrid of structure in more masters System reliability.
4, island mode is converted to grid-connect mode
After power system restoration is normal, electric network protection switch SuAutomatic closure, in grid-connected switch SiBefore closure, head is needed First carry out the presynchronization control of load voltage and network voltage.
PLL module automatically tracks electric network voltage phase, closure switch S after power system restoration4, so that θdroopWith θgridIt is synchronous, After synchronously completing, phase angle selecting module is automatically by S3With θgridIt is connected.Closure switch S later5And S1, so that EdroopAnd VIGdout With grid voltage amplitude EgIt is synchronous.Later by data selector S2With VIGdoutIt is connected, disconnects switch S5And S1
It is led specifically, the present invention has built gird-connected inverter model conduct as shown in Figure 1 in simulation software PSCAD more Mostly 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) indicates that A phase load voltage waveform in entire micro-grid system operational process, Fig. 7 (b) indicate 0.4s When grid collapses, the waveform of threephase load voltage, Fig. 7 (c) expression 1.2s power system restoration, the waveform of threephase load voltage, During Fig. 7 (d) indicates whole service, grid voltage amplitude EgAnd control variable EdroopAnd VIGdoutWaveform.Emulation starts When, power grid operates normally, and distributed generation unit injects active and reactive power to power grid, and at the 0.4s moment, event occurs for power grid Barrier, electric network protection switch SuIt disconnects immediately, according to analysis above, the output of D axis limiter reaches upper limit value and Q axis limiter exports Reach lower limit value, therefore it can be seen that load is electric when turning isolated operation by being incorporated into the power networks after 0.4s in simulation waveform Fig. 7 (a) Pressure amplitude value will increase to a certain degree, but still be within the scope of operation standard, can be clearly seen that grid-connected turn of orphan by Fig. 7 (b) When island is run, load three-phase voltage increases to a certain degree.When 1.2s moment power system restoration, electric network protection switch is automatic to be closed, By after the presynchronization of load voltage and grid voltage amplitude and phase, being closed grid-connected switch, micro-grid system grid-connected fortune again Row.By Fig. 7 (a) and Fig. 7 (c) it can be seen that load voltage restores to rated value when isolated island turns to be incorporated into the power networks.By Fig. 7 (b) and figure 7 (c) can be seen that no matter turned during being incorporated into the power networks by grid-connected isolated operation or the isolated island of turning, and load voltage quality can obtain To guarantee.During Fig. 7 (d) indicates whole service, grid voltage amplitude EgAnd control variable EdroopAnd VIGdoutWaveform. By Fig. 7 (d) it can be seen that near 0.42s, VIGdoutValue and EdroopValue it is approximately equal, therefore by current indirect control under Vertical control can smoothly switch;Near 1.4s, VIGdout,EdroopValue all and EgValue it is approximately equal, therefore by it is sagging control to Current indirect control can smoothly switch.Fig. 8 gives the process that Phase synchronization and amplitude synchronize during presynchronization.
A kind of seamless handover method based on current indirect control and sagging control is provided in the present invention.For access control The feasibility of method, author built simulation model in simulation software PSCAD, simulation results show the control method can be with Realize that micro-grid system is incorporated into the power networks the seamless switching between isolated operation, the available guarantor of load voltage in handoff procedure Card, and there are more main inverters to provide voltage support for system in isolated operation, in micro-grid system, improves microgrid system The reliability of system.This method is correct, reliable, provides good reference value for engineer application.

Claims (2)

1. a kind of seamless switching control system based on current indirect control and sagging control, which is characterized in that including three contraries Become device, the output end of three-phase inverter connects LC filter, the capacitor C of LC filterfIt is parallel with load, LC filter downstream is logical Cross line impedance LgConnect grid-connected switch Si, grid-connected switch SiDownstream passes through electric network protection switch SuConnect power grid;
The inverter includes two main inverters and two from inverter, and two main inverters and two transport from inverter parallel Row;
When power grid is normal, grid-connected switch SiWith electric network protection switch SuIt is closed, grid-connected inductance is flowed through in grid-connected inverters operation LgElectric current igx(x=a, b, c) is grid-connected current, completes grid-connect mode;
When the grid collapses, electric network protection switch SuIt disconnects immediately, after determining that isolated island occurs by isolated island detection algorithm, and Net switch SiIt disconnects, distributed generation unit is in isolated operation, completes island mode;
After power system restoration, electric network protection switch SuAutomatic closure carries out the presynchronization control of load voltage and network voltage, when After load voltage realizes that voltage magnitude is synchronous with phase with network voltage, grid-connected switch SiClosure, inverter grid-connected fortune again Row completes grid-connect mode;
When grid collapses, electric network protection switch SuIt disconnects immediately, flows through grid-connected inductance LgElectric current to be reduced rapidly be 0, it is grid-connected Electric current igD axis component igd0, q axis component i is kept to by positive valuegqIncreased by negative value is 0, in d axis, PI controller GIGOutput It can keep increasing, reach the upper limit value V of limiterdmax, in q axis, PI controller GIGOutput can keep reducing, reach clipping The lower limit value V of deviceqmin, after the output of d axis limiter reaches its upper limit value, by data select switch S2It is selected as sagging control The voltage instruction value E that reactive power ring generatesdroop, when the output of the d axis limiter in each main inverter control module reaches To after upper limit value, synchronous control signal is unified data select switch S2By VIGdoutIt is switched to Edroop, that is, complete island mode Switching.
2. a kind of control of seamless switching control system based on current indirect control and sagging control according to claim 1 System strategy, which is characterized in that in island mode, main inverter is based on sagging control, is run with voltage source mode, using more Main more main inverters, which are all made of, to be run based on sagging control with voltage source mode mostly from the micro-grid system of structure, makes more Without the power-sharing of connection between main inverter.
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